baker 6

Causation Review – Popliteal Cysts/Baker’s Cyst of the knee.

Prepared by Peter Larking

Senior Research Advisor

Research

Governance, Policy and Research

ACC

March 2011

Important Note

This review summarises information on popliteal cysts of the knee with a view to clarifying the existing evidence on causation. It is not intended to replace clinical judgement, or be used as a clinical protocol. A reasonable attempt has been made to find and review papers relevant to the focus of this report but it is not exhaustive. The content does not necessarily represent the official view of ACC or represent ACC policy.

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Contents

Causation Review – Popliteal Cysts/Baker’s Cyst of the knee ..................................................4

Summary ..................................................................................................................................4

Introduction.................................................................................................................................. 6

Methodology ................................................................................................................................. 6

Discussion..................................................................................................................................... 8

1. Prevalence.................................................................................................................................. 8

2. Prevalence of symptomatic cysts and significance of large popliteal cysts.............................. 12

3. Association with age................................................................................................................ 13

4. Gender..................................................................................................................................... 13

5. Association of popliteal cysts with meniscal pathology, effusion, osteoarthritis and ACL tears................................................................................................................................................. 13

• General studies .................................................................................................................. 13

• Meniscal pathology............................................................................................................ 14

• Effusion.............................................................................................................................. 15

• Osteoarthritis ..................................................................................................................... 15

• ACL tears ........................................................................................................................... 16

6. Association with trauma.......................................................................................................... 16

7. Association with knee pain and other symptoms.................................................................... 17

8. Association of popliteal cysts with other pathologies.............................................................. 18

Causation .................................................................................................................................... 18

Suggestions for reviewing claims to ACC where personal injury is said to be a substantial causative factor............................................................................................................................ 19

Summaries of papers reviewed…………………………………………………………………….20

Acknowledgements ..................................................................................................................... 26

References ................................................................................................................................... 27

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Causation Review – Popliteal Cysts/Baker’s Cyst of the knee

Summary

At the suggestion of the Clinical Advisory Panel, Elective Services, ACC, a report has been prepared on the etiology of popliteal cysts to assist with the determination of causation with respect to compensability.

Popliteal cysts or Baker’s cysts are found in the posteromedial aspect of the knee and are the most frequently encountered cystic mass around the knee. The majority extend between the deep fascia and the medial head of the gastrocnemius muscle and represent a fluid distension of a bursa between the gastrocnemius and semimembranosus tendons through a communication in the knee joint2. It is claimed that the two requirements for cyst formation are the anatomical communication and a chronic effusion3.

The main findings of the review follow. All the evidence statements rely largely on case series studies or lower grade cohort studies. Evidence is therefore at best only moderate for most statements.

1. The determination of prevalence of popliteal cysts is dependent on methodology; As determined by MRI a prevalence of around 0 to 7% may be expected in middle aged subjects with no internal knee derangements or disease, around 20% in the asymptomatic knee of those with internal derangements in the contralateral knee, range from 5 to 30% in those with suspected internal derangements of the knee and reach a ratio of nearly one in two in older subjects with advanced osteoarthritis (OA).

2. There is some evidence that prevalence increases with age. In some case series studies, over 50% of popliteal cysts found were in those over 50 years of age.

3. The effect of gender on prevalence does not seem to be an important consideration.

4. The presence of a popliteal cysts is strongly associated with internal derangements of the knee:

• Strong associations of popliteal cysts with medial meniscal tears are typically and consistently reported. In many populations (case series studies), of those with popliteal cysts, 70 to 90% had medial meniscal tears.

• There is good evidence that prevalence of popliteal cysts is significantly associated with the presence and size of effusion; typically around 70% of cases with popliteal cysts had joint effusion.

• There is good evidence that popliteal cysts have a high rate of occurrence in subjects with OA and some evidence that prevalence is associated with severity of OA: in older subjects with advanced OA prevalence of popliteal cysts may approach 50%.

5. There is good evidence that the great majority of popliteal cysts as detected by MRI or

ultrasonography are symptomless.

6. The mechanism of cyst formation as proposed by Lindgren1 supports the view that degeneration of the knee joint capsule contributes to the formation of a popliteal cysts as

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shown by the increased prevalence with age of a communication between the joint and the bursa.

7. There is an absence of good data to show that prevalence of popliteal cysts are associated directly with traumatic events but it seems highly likely that trauma resulting in internal derangement, effusion or osteoarthritis will result in an increased incidence of popliteal cysts as a consequence of the acquired pathology.

A number of criteria are given which may assist with the determination of compensability of individual cases.

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Causation Review – Popliteal Cysts/Baker’s Cyst of the knee

Introduction

At the suggestion of the Clinical Advisory Panel, Elective Services, ACC, a report has been prepared on the etiology of popliteal cysts to assist with the determination of causation with respect to compensability.

Popliteal cysts or Baker’s cyst are found in the posteromedial aspect of the knee and are the most frequently encountered cystic mass around the knee. As reported by Labropoulos4 the majority extend between the deep fascia and the medial head of the gastrocnemius muscle. Popliteal cysts are typically formed by an intercommunication between the posterior joint capsule and the bursa which is lined with synovial cells5. It is claimed that the two requirements for cyst formation are the anatomical communication and a chronic effusion3. Some authors have emphasized the importance of the intercommunication as the means by which the popliteal cysts can become symptomatic and responsive to intraarticular disease6.

Debris, hemorrhage, loose bodies and synovial proliferation can be present in the cyst7. Diseases that cause chronic joint effusions such as inflammatory arthritis, crystal deposition diseases, OA and internal derangements of the knee are associated with popliteal cysts7.

Popliteal cysts in children less than 16 of age are believed to have a different etiology to that in adults and occur without intraarticular disorders and without communication between the bursa and the joint cavity8. In most cases they are treated successfully by conservative means. Because of this their occurrence in children is not further considered here. Similarly popliteal cysts in patient’s with rheumatoid arthritis has not been included although it should be noted that prevalence of popliteal cysts with this condition may exceed 50%9.

Methodology

As the review is concerned with causation, the focus of the literature search was directed to etiological factors that may be relevant, including pathophysiology and prevalence with age. Because there is much literature, mostly case series in design, not all papers have been reviewed. Case reports on less than 10 subjects were excluded. While this approach is less than ideal it is practical. Key papers and topics that may have been missed can be added if drawn to our attention. An emphasis has been placed on reviewing cohort and case/control studies when they were available. Ovid Medline, EMBASE, TRIP, Cochrane and other evidenced based healthcare databases were searched for papers relevant to the topic. Papers were graded according to the Sign methodology (Appendix 1).

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Evidence Statements

All the evidence statements below rely largely on patient case series studies or lower grade cohort studies. Evidence is therefore at best only moderate for most statements.

1. The determination of prevalence of popliteal cysts is dependent on methodology; As determined by MRI a prevalence of around 0 to 7% may be expected in middle aged subjects with no internal knee derangements or disease, around 20% in the asymptomatic knee of those with internal derangements in the contralateral knee, range from 5 to 30% in those with suspected internal derangements of the knee and reach a ratio of nearly one in two in older subjects with advanced OA.

2. There is some evidence that prevalence increases with age. In some case series studies, over 50% of popliteal cysts found, were in those over 50 years of age.

3. The effect of gender on prevalence does not seem to be an important consideration.

4. The presence of a popliteal cyst is strongly associated with internal derangements of the knee:

• Strong associations of popliteal cysts with medial meniscal tears are typically and consistently reported. In many populations (case series studies), of those with popliteal cysts, 70 to 90% had medial meniscal tears

• There is good evidence that prevalence of popliteal cysts is significantly associated with the presence and size of effusion; typically around 70% of cases with popliteal cysts had joint effusion

• There is good evidence that popliteal cysts have a high rate of occurrence in subjects with OA and some evidence that prevalence is associated with severity of OA: in older subjects with advanced OA prevalence of popliteal cysts may approach 50%.

5. There is good evidence that the great majority of popliteal cysts as detected by MRI

or ultrasonography are symptomless.

6. The mechanism of cyst formation as proposed by Lindgren1 supports the view that degeneration of the knee joint capsule contributes to the formation of a popliteal cysts as shown by the increased prevalence with age of a communication between the joint and the bursa.

7. There is an absence of good data to show that prevalence of popliteal cysts are associated directly with traumatic events but it seems highly likely that trauma resulting in internal derangement, effusion or osteoarthritis will result in an increased incidence of popliteal cysts as a consequence of the acquired pathology.

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Discussion

The findings below are dependent on case series; no studies based on general populations were found. The findings are -

1. Prevalence

Many studies were based on patients attending clinics for investigation of suspected internal derangements3 6 10-14, for osteoarthritis2 15-18 and for symptoms of DVT (along with controls and those with internal derangements)4. Sometimes a control group of patients was included and these were classified as healthy volunteers4, not having knee pain13 or no or low grades of OA2 16. Two cohort studies were reviewed19 20 but in each case subjects with predetermined characteristics were randomly recruited so the true prevalence of popliteal cysts in the general population cannot be determined from the data. The findings relating to prevalence are (Table 1):

• In control groups (healthy volunteers4 21, no knee pain13, no OA2 or low grades of OA16) prevalence ranged from 0 – 7% (mean ages ranged from 45 - 61)

• In patients referred for internal derangements of the knee prevalence in the asymptomatic knee was 18.6% (mean age 43) 14

• In subjects recruited from a Veterans population and of mean age 67 prevalence was 28% in those with no knee pain but OA present, 33% in those with pain and OA and 9.1% in those with without knee pain or OA20

• Prevalence in patient populations with suspected internal derangements range from 4.7%22 (mean age 46) to 38%11 (mean age 39)

• In patients with OA prevalence ranged from 22%18 to 47%17 this latter figure being seen in subjects of median age 60 and with OA at multiple sites.

It would seem then that a prevalence of less than 7% may be expected in middle aged subjects1 with no internal knee derangements or disease, will be around 20% in asymptomatic knees of those with internal derangements in the contralateral knee, range from 5 to 38% in those presenting with internal derangement of the knee and reach a ratio of nearly one in two in older subjects with advanced OA.

It is widely agreed that the prevalence of popliteal cysts is related to the diagnostic test employed11. High quality MRI is very sensitive and will find the cysts in as many as 38% of patients referred with suspected nonacute knee internal derangements11. Many of these cysts are small, asymptomatic and not usually of clinical relevance. MRI is protocol dependent as well

1 A study ( 23. Stehling C et al) investigating prevalence of knee lesions with past physical activity has reported that in a random selection of 236, 45 – 55 year olds without knee pain and normal BMI, that by 3T MRI, popliteal cysts were found in 31 images, a percentage prevalence of 13% (the present author’s calculation) . This would therefore suggest that by this technology presence of popliteal cysts in asymptomatic subjects is very common. The data though has not been further used here as there are inconsistencies in relation to the popliteal cyst data which inquires have not resolved.

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though; it has been suggested that the low results of Fielding’s study10 (5%) may be due to an inappropriate imaging protocol12 although others using MRI have found low prevalence levels in their populations22. Ultrasonography appears to be also highly regarded for its diagnostic utility16.

Conclusion

The quality of evidence on prevalence is largely dependent on case series data and there is a lack of large community studies. It would seem however that popliteal cysts are very common in populations with internal derangements of the knee or with osteoarthritis.

Most of the popliteal cysts found by the various diagnostic methods are asymptomatic and some authors have speculated that if the structure is not giving rise to local symptoms that it should not be called popliteal cyst at all24.

Table 1. Prevalence of popliteal cysts. Summary of papers reviewed. Author and study design

Population Number of subjects and mean age

% Prevalence popliteal cysts

Notes

MRI methodology

Hayes19

MRI

Random selection

Selected from a random

community cohort but

selected according to preset

patient characteristics. Not

a true random selection of

community –living subjects

117 women

Mean age, 46

Woman were in one

of 4 categories

depending on the

presence of OA and

pain.

34% overall A small popliteal cyst

was found in 29% of

knees; in another 5%

they were moderate to

large.

Tschirch14

MRI

Case series

Patients with clinically

suspected meniscal tears in

the contralateral knee.

Study investigated the

asymptomatic knee

102 asymptomatic

knees

Mean age 43

39.6% female

18.6% 8% of popliteal cysts

were greater than

30mm in diam

Marti-Bonmati11

MRI

Case series

Suspected internal

derangements of the knee

382 patients

Mean age 38.8

38% female

38% 3.1% of total

population had massive

cysts

Hill 20

MRI

Cross-sectional

Subjects with and without

knee pain recruited from

Veteran’s Affairs and

Community sources

458 subjects

Mean age 67,

33% female, Subjects

In those with knee

pain and OA 33%

In those with OA but

without knee pain

In those without knee

pain about one –third

of cysts were of

moderate to large in

size but the clinical

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Author and study design



Notes

were drafted into one

of three groups.

28%

In those without knee

pain or OA 9.1%

relevance of these

larger cysts was not

investigated.

Kornaat17

MRI

Cohort

Subjects with OA at

multiple joint sites

205 subjects with

multiple joint OA

80% female

Median age 60

47% Popliteal cysts of grade

2 or 3 (moderate to

severe extension) were

not associated with

pain.

Sansone22

MRI

Case series

Patients referred for

internal derangement of the

knee.

1001 patients, 33%

female, mean age 36.

4.7%

Fielding10

Case series

MRI

Patients mostly referred for


knee

1103 patients, mean

age 36.3,

approximately equal

nos. of male and

female.

5%

Tarhan21

Case series

MRI and US

Patients with OA and

controls

58 patients with

symptomatic knee

OA (mean age 57.4,

83% female) and 16

volunteer control

subjects (mean age

59, 75% female).

Cases 35% by MRI

Controls 6.9%

Miller12

Case series

MRI

Patients referred to

Orthopaedic Clinic mainly

for internal derangement of

the knee

384 patients, mean

age 47, gender split

not described

19%

Ultrasonography

Labropoulos 4

Ultrasonography

Cases/controls

Healthy volunteers

Painful knees (Suspected


knee, inflammatory

conditions or previous

trauma)

Suspected DVT

50 subjects, 50%

female, mean age 45

100 subjects, 46%

female, mean age 54

162 subjects, 52%

4%

(prevalence based on

legs not cases)

19.8%

9.5%

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Notes

female, mean age 51

de Miguel Mendieta15

Ultrasonography

Cases/controls from Case

series

Attendees at a

Rheumatology Clinic

81 patients with knee

pain associated with

OA, 20 without knee

pain;

Knee pain group =

mean age 66, 93%

female.

No knee pain group =

mean age 62, 70%

female.

In those with knee

pain 37%

In those without 15%

Naredo18

Ultrasonography

Case series

Patients attending clinic

with primary OA

50 consecutive

patients, 90 knees

symptomatic, 10

knees asymptomatic

Mean age 64.3, 88%

female

In those with knee

pain 22%,

Without knee pain

0%.

Rupp13

Ultrasonography

Case control (unmatched)

100 cases scheduled for

arthroscopy;

100 hospital patients with

no knee complaints

100 cases with knee

pain, mean age 41,

35% female,

100 without, mean

age 50, 45% female

In cases - 20%

Controls – 0%

5% were small < 30

mm

50% medium 30 – 50

mm

45% large >50mm

Chatzopoulos2

Ultrasonography

Case series

Patients with chronic OA

Controls with no OA –

otherwise not described

196 patients with

chronic OA, 75%

female, mean age 69

54 controls, gender

and age not given

Chronic OA 37%

Controls 2%

Fam16

Prospective case – control

series

Ultrasonograpy

Patients , Primary OA >= 2

Controls, inpatients with

OA <=1

50 patients, mean age

64.6, 84% female

25 controls, mean age

61.3, 48% female

Patients, 42%

Controls 0%

Liao25

Case control

Ultrasonography

All referred for

ultrasonography of the

knee

1,120 patients of

whom 145 had

popliteal cyst.

Mean age of those

with cysts was 59.6,

age range 21 – 94;

12.9% 8% were ruptured

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Notes

55% female

Other methods

Johnson6

Case series

Arthroscopy



knee.

187 patients, 195

knees

Mean age 40, 32%

female

37% of knees had a

popliteal bursa

Wolfe3

Case series

Arthrography



knee (mainly).

Group 1, 247 knees,

mean age 27, 15%

female

Group 2, 202 knees,

mean age 40, 52%

female

Group 1, 23% (of

knees)

Group 2, 32%

Pulich26

Case series

Arthrography

Patients whose chief

complaint did not relate to

the popliteal space, usually

meniscal tears

940 subjects 24.9% 23.5% were

symptomatic

2. Prevalence and significance of large cysts

The prevalence of clinically relevant, popliteal cysts including large cysts is not well described in the case series data reviewed. Tschirch14 found that of the popliteal cysts found in asymptomatic knees (of those with suspected internal derangements in the contralateral knee), 8% were greater than 30mm; Other studies reporting on prevalence of larger cysts in their studies included Marti-Bonmati11 who found 3.1% (cf. to a total of 38%) and Hill20 6.5% (cf. 20.8%)in older asymptomatic veterans. Rupp13 who reported a prevalence of 20% of cysts in those being investigated for knee pain found that 95% had medium or large sized cysts.

Vasilevska27 concluded that size of the popliteal cyst was strongly correlated with degenerative changes of the cartilage and the degree of medial meniscus degeneration whereas Hayes19 found no significant statistical association of size with OA.

In one series of 940 arthrograms, 76% of cysts were asymptomatic and of these 21% had a palpable mass26.

Liao25 reported that 8% of his series had ruptured cysts.

Conclusion

It is concluded that often case series will find that of those with popliteal cysts a variable proportion, often much less than one third, will have larger cysts but even these are not always symptomatic14. Some case series do have a much higher prevalence of large cysts13.

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3. Association with age

It is widely believed that the prevalence of popliteal cysts increases with age and that it is significantly higher in those over 50 years of age by which time they are relatively common. There is some evidence for this belief. Statistically significant effects of age on prevalence were observed in the case series studies of Labropoulos 4 and Johnson6. Labropoulos4 found that incidence was significantly higher in those with DVT or knee symptoms over 50 years of age (p<0.001). Some authors noted that the mean age of those with cysts was higher than those without3 10 11; Sansone22 for example found that those with cysts were of mean age 46 years compared to 36 in those without and Fielding10 reported that the mean age of their total case series was 35.4; the mean age of those with popliteal cysts was 51.6 and more than 50% of cysts were found in those over 50 years of age. Age trends are not always observed though2.

Lindgren(1978) found that the frequency of communication of the gastrocnemio-semimembranosus bursa and the joint increased with age; over half of those over 50 had such a communication1

Prevalence of meniscal lesions and OA is strongly related to age28 and it would seem reasonable to assume that the increase with age is at least in part due to the increase in intra-articular pathology with age4.

Conclusion

It is concluded that there is reasonable evidence for an increase in prevalence of popliteal cysts with age but the evidence is not strong and results are dependent on the case series populations studied.

4. Gender

There is a tendency in many of the studies reviewed (Table 1), for females to have a lower prevalence of cysts compared to males. Sansone for example found in his series 63% were in men22. This gender difference is only thought by some to reflect the lower incidence of intra-articular lesions in woman3. The higher prevalence in men is not always observed though 2 12 25 and the prevalence of an intercommunication between the joint space and bursa has been reported as being independent of gender29.

Conclusion

It is difficult to draw any conclusions on gender given the absence of studies in the general population, the preponderance of men with internal derangements of the knee and the preponderance of women presenting with OA in many of the populations studied. Gender does not appear to be an important factor though.

5. Association of popliteal cysts with meniscal pathology, effusion, osteoarthritis and ACL tears

• General studies

It is commonly stated that popliteal cysts are almost always associated with other pathologies of the knee such as internal derangements and OA and the evidence found in the studies reviewed

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here would support this view. Miller in his case series12 determined by MRI the prevalence of popliteal cysts in a general orthopaedic population of 384 subjects (mean age 47), and their association with effusion, internal derangement, and degenerative arthropathy. Overall prevalence of popliteal cysts was 19%; 99% were associated with other pathology and 80.5 % with meniscal tears. There were significant associations (P < .01) for effusion, meniscal tears, and degenerative arthropathy, independent of one another. The probability of having a popliteal cyst for the whole series given the presence of any one variable was 0.08-0.10; any two variables, 0.19-0.21; and all three variables, 0.38. They found only one case in the series which occurred in the complete absence of internal derangement, effusion or degenerative joint disease.

Sansone22 in his case series found that popliteal cysts were associated in 94% of cases with one, or more disorders detected by MRI; the commonest lesions were meniscal (83%), frequently involving the posterior horn of the medial meniscus, chondral (43%), and anterior cruciate ligament tears (32%).

Conclusion

Case series data therefore suggest strong associations of intra-articular pathology with prevlance of popliteal cysts.

• Meniscal pathology

Strong associations with medial meniscal tears are typically and consistently reported. For example Rupp in a controlled study of hospital patients13 found that of those with popliteal cysts, 70% had medial meniscal tears compared to a prevalence of 19% in those without tears, a difference that was highly significant. Wolfe3 found in patients at an airforce medical centre (mean age 27), that of those with popliteal cysts, 86% had damage to one or both menisci; in their general hospital population (mean age 40) of those with popliteal cysts 94% had damage to one or both menisci.

• Fielding10 reported that 71% of those with popliteal cysts had medial meniscal tears; and lateral tears were seen in 38%

• Sansone30 found that 90% of his cases with poplitieal cysts had medial meniscal tears and 16.6% lateral

• Ahn31 found 68% of those with larger popliteal cysts had medial meniscus tears and 29% lateral tears.

Studies that related prevalence of popliteal cysts to type of meniscal tear were not found apart from the case series study by Marti-Bonmati who found prevalence to be statistically related to the presence of meniscal degeneration and to meniscal tearing11. Further analysis of tear type was not made. In subjects with primary OA the presence of popliteal cysts was significantly associated with medial meniscus protrusion18.

Though cysts have a high association with tears at the posterior horn of the medial meniscus they are also associated with lateral tears and some consider that the incidence of association is simply a reflection of the ratio of medial to lateral tears reported in the literature3.

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Conclusion

It is concluded that meniscal tears and degeneration occur with high frequency in those who have popliteal cysts.

• Effusion

Wolfe3 believed that while there was a strong association between prevalence of popliteal cyst and medial meniscal tears of the posterior horn this association is commonly observed because it is one of the commonest joint derangments seen; they considered that it was the presence of an effusion producing abnormality that was important.

There is good evidence that prevalence of popliteal cysts is significantly associated with the presence and size of effusion11 12 20. 77% of cases with popliteal cysts had joint effusion in Millar’s series12, 91.7% in Liao’s25 and 70% of Marti-Bonmati’s11. Hill20 found that in those with moderate to larger effusion, 43.2% had cysts compared to 22.7% in those with an effusion which was small or absent. There was also a weak but statistically significant relationship between size of effusion and size of cyst. A case series study of those with primary OA of grade 2 or more found that effusion was present in 86% of knees with cysts compared to 36% without cysts (p<0.02)16.

While Miller showed that effusion was strongly associated with the presence of popliteal cysts he also concluded from his data that cysts could occur where there were normal physiological amounts of fluid in the presence of a meniscal tear and/or degenerative arthropathy. Vasilevska27 in their series in patients with medial compartment OA found no relationship between the size of popliteal cysts and effusion.

Suggestions to account for the development of popliteal cysts in the absence of increased joint effusion have been that fluid accumulation occurred within the cyst from previous resolved joint effusions11 and that altered biomechanics due to presence of internal derangements are sufficient to squeeze even normal amounts of fluid into the bursa. This last suggestion is supported by studies which have shown that intra-articular pressure is higher in patients with meniscal abnormalities compared to that in healthy individuals12.

Some authors suggest that the development of popliteal cysts cannot be explained by the accumulation of intraarticular fluid accumulation alone; other factors are important as well such as the patency status of the interconnection between the bursa and the joint, and the intrinsic features of the joint capsule2.

Conclusion

It is concluded that effusion is an important feature associated with the development of popliteal cysts but it is probably not the sole factor.

• Osteoarthritis (OA)

Chatzopoulos2 has determined the prevalence by ultrasonography of popliteal cysts in knees with chronic osteoarthritic pain, reporting a case series study on 196 patients (mean age 69, 75% female) and 54 non-osteoarthritic controls, (age and gender mix not given). Popliteal cysts were detected in 37% of OA patients compared to 2% in non OA patients. Abnormal and intense tracer accumulation in early-phase bone scintigraphy (detects the severity of inflammation in soft-tissue) was significantly more frequent in osteoarthritic knees with

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popliteal cysts than in those without. Similarly Fam16 has determined the prevalence and significance of popliteal cysts in primary OA of the knee in a prospective case-control series. They found that cysts were present in 42% of patients with OA; 38% had bilateral cysts. In the controls no cysts were detected. The majority of cysts were small and symptomless. The occurrence of popliteal cysts correlated with the radiological grade of OA and were detected in 47% of knees with grade 3 or 4 OA compared to 18% with grade 2 p<0.03). They concluded that OA may be a more common cause of popliteal cysts than generally recognized. The results of some other studies were;

• Ahn31 found in his case series on of those with a popliteal cysts, knee pain and an associated intra-articular lesion, that 39% also had degenerative cartilage damage

• Liao25 reported that 50.6% of those with popliteal cysts had OA • In a cohort study of patients with OA at multiple joint sites, 47% of patients had a

popliteal cyst17 • Rupp also found a statistically significant association between prevalence of popliteal

cysts and presence of OA13; in patients with popliteal cysts grade 3 and 4 cartilage lesions were predominant (70%) whereas in those without cysts only 6% had grade 3 or 4 lesions

• In a case control study based on case series patients 35% of those with OA had popliteal cysts compared to 6.9% of controls21

• Qualitative associations with OA have also been reported15 19 20.

Conclusion

It is concluded that there is good evidence that popliteal cysts have a high rate of occurrence in subjects with OA and some evidence that prevalence is associated with severity of OA.

• ACL tears

Some authors found no statistical association between tears to the ACL and prevalence of popliteal cysts11 12. Feilding though10 found a 13% association with complete tear of the ACL and Sansone22 in their study of 1001 adults referred for MRI for intra-articular disorders (mean age 36, 33% women) found an association in 32% of cases.

Conclusion

It is concluded that an association of popliteal cysts with ACL tears is found but it does not reach the magnitude of the associations with meniscal tears, effusion, and OA. Moreover given the close association of chronic ACL tears to other pathologies of the knee it is possible that the ACL tear association with popliteal cyst prevalence is a reflection of the onset or development of that pathology.

6. Association with trauma

Many studies did not address a history of trauma as a contributing factor 3 4 12 14 17 20 22 27 30. Cysts certainly occur in the absence of a history of acute trauma, as in a number of studies patients presenting after acute trauma were excluded. And excluding trauma cases does not seem to

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exclude the finding of high rates of prevalence in populations with various pathologies such as internal knee derangements or OA, eg 20%13, 38%11, 37%15, 22%18, 34%19, 35%21 and 37%2.

Pulich26 reported that 61% of those with popliteal cysts had a history of trauma. Johnson6 found that 64% of his case series of patients presenting for suspected internal derangements of the knee who had a bursal communication had a history of trauma compared to 66% of those without a bursal communication. They concluded that there was no significance to the presence of a history of trauma and prevalence of cysts.

Only one study investigated the prevalence of popliteal cysts in younger subjects (247 knees, mean age 26, 85% male) most of whom presented with suspected internal derangement of the knee3. This study is of some relevance since at this age significant degenerative pathology would not be expected to be at an advanced state: cysts were found in 23% of knees.

A study that investigated the relationship of severe focal knee lesions to past physical activity has reported that whereas prevalence of cartilage, meniscus and ligament lesions, bone marrow edema and joint effusion were significantly related to past activity level, popliteal cysts were not23.

Conclusion

It is concluded that there is no good evidence to show that popliteal cysts form as a result of trauma itself, however it seems reasonable, in the absence of good evidence to assume that trauma resulting in internal derangements of the knee will then result in formation of popliteal cysts in an unknown proportion of the population.

7. Association with knee pain and other symptoms

Popliteal cysts are often asymptomatic5. The presence of popliteal cysts as detected by MRI in asymptomatic knees in subjects of mean age 42 was 18.6%14. Pulich found in his case series that of the popliteal cysts observed in 24% of patients, 75% were asymptomatic.

Patients with symptoms typically present with internal or mechanical derangements, swelling, a palpable mass, pain, tenderness or signs and symptoms of thrombophlebitis. Large popliteal cysts may cause compression of adjacent structures, lead to mechanical problems in knee flexion and limited mobility and may cause ischaemia and deep vein thrombosis5. There is conflicting evidence that prevalence is related to knee pain. In a cohort study of patients with OA at multiple joint sites 47% of patients had a popliteal cyst; the presence of a popliteal cyst was not however related to clinical symptoms and severe (Grade 2 or 3) cysts were not significantly related to pain or stiffness17. Labrapoulos4 though, found a much higher incidence of popliteal cysts in those with knee symptoms compared to those without pain (19.8% v. 4%) as did de Miguel Mendieta(37% v. 15%) 15, Naredo18 (22% v. 0%) and Hill20 (33% v.20.8%). Not all of these differences were statistically significant.

Conclusion

It is concluded that popliteal cysts may occur frequently in populations with asymptomatic knees but there is a tendency for cyst prevalence to be higher in knees that are symptomatic. The evidence for this statement is of low quality and findings probably depend on the population studied.

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8. Association of popliteal cysts with other pathologies

Because small studies and case reports were not included in this review the relation of pathologies other than that reported above has not been researched. According to Labropoulos4 who summarised the literature on this topic, other pathologies associated with popliteal cysts include total knee replacement, rheumatoid arthritis, and infections including tuberculosis coccidiomycosis, sarcoidosis’ candidiasis and brucellosis. Labropoulos reviewing other’s work concluded like Wolfe3 that any pathology that can cause a knee effusion can cause popliteal cysts.

Causation

Theories regarding formation of popliteal cysts centre on the relative weakness of he posterior joint capsule5 and increased intra-articular pressure due to joint effusion or altered biomechanics (meniscal tears or degenerative joint disease) which causes the extravasation of joint fluid into the gastrocnemius-semimembranosus bursa32. The increased pressure leads to the gradual formation of an enlarging popliteal cyst32. The flow of fluid may be valvular or free. Lindgren24 found in subjects with symptomatic and palpable popliteal cysts that a valve mechanism was present in 61% of cases.

Lindgren1 concluded from his studies on cadavers that degeneration of the knee joint capsule increased with age and its elasticity diminished; these conditions then facilitated the tearing of the posterior part of the capsule on extension of the joint1. He considered that with increasing age, less and less strain was required for such a tear to occur. Fluid in the joint associated with other pathologies, which also increase with age, played a role in causing a rise in pressure in the dorsal part of the joint on flexion. A communication between the joint and the bursa then resulted from either a tear in a degenerated joint capsule or through a rupture of the thin membranes in a previously formed slit.

Wolfe3 considered that there was overwhelming evidence that popliteal cysts were usually secondary to intra-articular pathological processes and Rupp13 concluded that the popliteal cyst was a secondary phenomenon and treatment should address the underlying intra-articular lesions.

Conclusions

The mechanism of cyst formation as proposed by Lindgren supports the view that degeneration of the knee joint is largely causative in the formation of a popliteal cyst as shown by the increased prevalence of a communication between the joint and the bursa with age. There is little evidence to suggest that trauma to the knee is it itself a risk factor but it seems highly likely that trauma resulting in internal derangement or osteoarthritis of traumatic origin will result in an increased incidence of popliteal cysts.

From an evidential point of view the above statements may be said to be reasonable in the light of the available evidence but they are by no means definitive. From ACC’s perspective such mechanisms suggest that both degeneration and trauma can be the cause the formation of a popliteal cyst. Trauma is likely to be causative in many younger subjects.

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Suggestions for reviewing claims to ACC where personal injury is said to be a substantial causative factor

It is suggested that trauma may be accepted as a causative factor of a popliteal cysts33 when –

• There is a clear history of a trauma event likely to be causative

• There was no history of knee pathology prior to the injury

• The traumatic event resulted in the development of internal pathology to the knee consistent with the injury and which is consonant with the formation of a popliteal cyst. Such pathology would include effusion and medial meniscal tears likely to be of traumatic origin.

• The patient has not been symptom free from the date of injury (evidence of derangement)

• The symptoms are unilateral only, in the injured knee

• The popliteal cyst developed within a reasonable period from the date of injury

• When the subject is older the presence of significant pre-existing meniscal degeneration, OA and rheumatoid arthritis should be excluded. There should be no signs of advanced joint disease in the contralateral knee. A weight bearing x-ray may be desirable.

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Summaries of papers reviewed

General papers

1. Tschirch14 has shown by MRI in a case series of 102 asymptomatic knees (mean age 43, 40% female) that the prevalence of popliteal cyst was 18.6% (26 cysts in 19 knees). Sign level 3.

2. Labropoulos 4 has investigated the aetiology of popliteal cysts by prospectively studying 426 legs in 312 individuals with ultrasonography. Participants included healthy volunteers (n=50, 50% female, mean age 54), patients with a painful knee (n= 100, 46% female, mean age 45), and a group of patients with signs and symptoms of deep vein thrombosis (DVT) (n=164, 52% female, mean age 51). They found that the prevalence of popliteal cyst increased with age and was significantly higher in those aged over 50 years and with knee or DVT symptoms (P < 0.001). Compared with controls (incidence 4.0 per cent), cysts were more common in patients with DVT symptoms (9.5 per cent; P = 0.141) and those with painful knees (19.8 per cent; P < 0.001). All cysts were located in the posteromedial aspect of the popliteal fossa. They concluded that popliteal cysts are relatively common in patients over 50 years old with a painful knee or with signs and symptoms of DVT. A cross-sectional study but largely based on case series. Sign level 3.

3. Marti-Bonmati11 has evaluated the prevalence of popliteal cysts in a prospective case

series of 382 consecutive patients by MRI (38% female, mean age 39) . No patient had rheumatoid arthritis, infection or trauma. Of the 382 patients, 145 had Popliteal cysts (38.0%). Cyst content was minimum in 99, moderate in 34 and massive in 12. Joint effusion was observed in 269 patients (70.4%), being minimal in 140 patients, moderate in 119 and massive in ten. Meniscal lesions were observed in 195 patients (51%), while 58 patients (15%) had a cruciate ligament lesion. Popliteal cyst had a statistically significant direct relationship with the presence and quantity of synovial fluid (P=0.002) and with the presence and type of meniscal lesion (degeneration or tear) (P=0.01) but not with cruciate ligaments or cartilage lesions. Patients with popliteal cysts were older than those without which was of statistical significance (mean age 41.8 v. 36.9; Chi Sq = 0.003). It was concluded that the presence and volume of popliteal cysts in MR studies of the knee are related to the quantity of synovial fluid, and to the presence and severity of meniscal lesions. Prospective case series. Sign level 3.

4. Sansone30 described 30 cases of popliteal cyst (37% female, mean age 56) as seen at

arthropscopy and by sonography. In all cases there was an associated intra-articular pathology. 90% of cases were related to a medial meniscal tear on the posterior horn and the tear had horizontal components. In 10% (3) of cases the medial meniscus was normal; 2 of the 3 cases had chondral lesions, the third serious rheumatoid synovitis. 66% had chondral lesions. In all cases a connection between the joint space and the cyst was found. A case series – Sign level = 3.

5. Sansone22 has studied the epidemiological features of popliteal cysts in 1001 adults

referred for MRI of intra-articular disorders (mean age 36, 33% women). Popliteal cysts were seen in 4.7% of this group of whom 37% were women. The mean age of those with

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cysts was higher than the whole group, 46 v. 36 (P<.001). The cysts had the highest prevalence in those 50 – 60 and increased gradually with age. A communication with the joint was invariably found. The cysts were associated with one, or more, disorders detected by MRI in 94% of cases. The commonest lesions were meniscal (83%), frequently involving the posterior horn of the medial meniscus, chondral (43%), and anterior cruciate ligament tears (32%). 42% had chondral injury graded 3 or 4. Case series, Sign level = 3.

6. Johnson6 has sought to establish by arthroscopy the incidence of popliteal cysts in 187

consecutive knee surgery patients (199 knees, mean age 40, 32% female). A cyst was defined as such only if it had a communication with the knee joint via the posterior medial compartment. 37% of knees had a popliteal bursa so identified (mean age 43.4, 33% female, age range 13.0 – 75 years) There was a significant correlation with age (p<.05) for right knees only. A history of trauma was identified in 66% of the those without bursal communication and in 64% of those with cysts and respectively, posterior pain, 15% v. 21%; joint effusion in 37% v. 32%; meniscal tear in 66% v. 71% and OA 80% v. 82%. None of these differences were significant. Case series, Sign level = 3.

7. Wolfe3 has analysed by arthrography two case series: Group 1; 247 knees, Mean age 27,

15% female; and Group 2; 202 knees, mean age 40, 52% female. They found that in Group 1 the prevalence of cysts was 23%; 24% in males and 19% in females. 86% of those with cysts had damage to one or both menisci. The lateral meniscus was damaged in 12.5% of patients. In group 2, prevalence was 32%; 36% in males and 27.6% in females. 94% had damaged menisci. The lateral meniscus was involved in 14% of patients. The average age of those with cysts was always greater than those without, 32 v. 26 in group one and 46 v. 37 in group 2. Incidence of cysts increased with age – from 25.7% in those 21 – 30 to 53.5% in those 51 – 90. They considered that there was overwhelming evidence that popliteal cysts were usually secondary to intra-articular pathological processes. Case series – Sign level = 3.

8. Fielding10 has reviewed MRIs from a case series to find the incidence of popliteal cyst and

its associated injuries in 1103 patients referred for evaluation of internal derangement; (approximately even numbers of male and female, mean age 36.3). The incidence of popliteal cyst was 5%. Mean age of those with cysts was 51.6 and those without 35.4. 50% of cysts occurred in those greater than 50. 71% of those with cysts had a meniscal tear at the posterior horn of the medial meniscus. Lateral tears were found in 38%; 27% had tears in both menisci. 13% had a tear to the ACL, 71% had supratellar joint effusions and 21% signs of OA. They concluded that the reported higher incidence found with arthrography is thought to be due to arthrographic distension of normal, collapsed bursae. Case series, Sign level 3.

9. Miller12 has determined by MRI the prevalence of popliteal cyst in a general orthopaedic population and its association with effusion, internal derangement, and degenerative arthropathy in 384 subjects, mean age 47, age range 14 – 88. Prevalence was 19%. 62.3% of those with cysts were female. Mean age of those with cysts was 53 compared to those without cysts of 46 years. The epicentre of 44% cysts were located at the level of the knee joint and 52% slightly superior to it. 99% of cysts

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were associated with other pathology, 80.5% being with meniscal tears. No association was found between popliteal cyst and anterior cruciate ligament tear or medial collateral ligament injury. There were significant associations (P < .01) for effusion, meniscal tear, and degenerative arthropathy, independent of one another. Probability of having popliteal cyst given the presence of any one variable was 0.08-0.10; any two variables, 0.19-0.21; and all three variables, 0.38. Case series – Sign level = 3.

10. Rupp13 has studied by ultrasonography the prevalence of popliteal cysts and the

associated intraarticular lesions via a prospective case-control study based on case series subjects. They studied 100 patients scheduled for arthroscopic surgery of the knee, all with knee pain (mean age 41, 35% women) and 100 patients without any knee complaints as a control group (mean age 50, 45% women) from subjects hospitalised for other spine, joint or foot surgery. The prevalence of popliteal cysts was 20% in the study group and 0% in the control group. Patients with a popliteal cyst had a significantly higher prevalence of medial meniscal tears (70% versus 19%) (P<.001) and of chondral lesions (85% versus 28%) (P<.001). Tears of the lateral meniscus were more evenly distributed (20% versus 36%) (p = ns). They concluded that the popliteal cyst is a secondary phenomenon and that treatment should address the underlying intraarticular lesions. Case-control Sign level 3.

11. Lindgren1 29 has described the anatomy and histology of the gastrocnemio-

semimembranosus bursa after reviewing 544 patients attending for clinical arthrography and 248 knee joints from 154 autopsy cases (Age range 10 – 100). A communication between the joint and the bursa was found with greater frequency in the older subjects, frequency increasing from age group 10 - 19 to 40 – 50 from where it appears to plateau at around 50 to 60% of subjects: a communication was present in over half of those over 50 years, none in those under 10. There was no gender difference in the frequency of a communicating bursa; the frequency did not differ between those with and without other knee abnormalities as established by radiography; the duration of symptoms had no influence on the frequency of joints with and without communication. The wall of the bursa and the wall of the joint capsule had a similar histological appearance. They concluded that the results supported the hypothesis that the popliteal cyst is formed via rupture of the joint capsule giving a communication with the normal gastrocnemio-semimembranosus bursa. Case series – sign level 3.

12. Pulich26 has investigated asymptomatic popliteal cysts in 940 patients of whom 234 had popliteal cysts; 179 were asymptomatic. No age or gender data was given. Prevalence was 24.9%; 76.5% were asymptomatic. Of those with asymptomatic cysts; 68.2% had a history of a related traumatic event and 59.8% had meniscal tears; 70.4% had no joint effusion. The author suggests that the term popliteal cyst refer only to a clinically evident entity. Case series, Sign level 3.

Association with OA, effusion and knee pain

1. Hayes19 studied 117 randomly selected women (mean age, 46 years; range, 32-56 years) selected from a community-based arthritis study (n = 1053) with 30 women in each of

22

four categories: (a) no pain and no OA of the knee, (b) no pain and OA of the knee, (c) pain and no OA of the knee, and (d) pain and OA of the knee; a small popliteal cyst was found in 29% of knees; in 5% they were moderate to large. The prevalence of popliteal cyst did not significantly correlate with radiographically determined incidence of OA though a qualitative trend was observed. Sign level 2-.

2. Hill 20 has evaluated the association of effusions, popliteal cysts, and synovial thickening with knee symptoms in older persons in a cross-sectional analysis of subjects selected from a veteran’s cohort. The knee pain/XROA group had knee symptoms and radiographic OA (259 male, 122 female (33%)); No knee pain/XROA (radiographic OA) group (17 male, 8 female) had no knee symptoms and radiographic OA; and No knee pain/no XROA group (29 male, 23 female) had no knee symptoms and a normal radiograph. Mean age 67. Popliteal cysts were seen in 20.8% of those without knee pain and 33% of those with knee pain. The cysts were more common in those with OA than in those without. Prevalence was also related to size of effusion (p<.001). After adjusting for the severity of radiographic OA, there was no difference in the prevalence of popliteal cysts between those with and without knee pain. It was concluded that knee pain is not related to the presence of popliteal cysts. A cross-sectional analysis of a selection from a cohort. Sign level 2-.

3. de Miguel Mendieta15 investigated the prevalence of clinical and sonographic factors

associated with painful episodes in patients with knee OA. Patients were selected from attendees at a Rheumatoid Clinic; Group A: 81 patients with knee pain during physical activity >or=30 mm in visual analogue scale (VAS) for pain for at least 48 h prior to inclusion (96.3% female, mean age 66.8); Group B: 20 patients without knee pain from at least 1 month prior to inclusion (70% female, mean age 62.1). The prevalence of popliteal cyst was 37% v 15% (P=0.06). Sign level 3.

4. Naredo18 has compared ultrasonographic findings with clinical and radiographic assessment of knee OA. Fifty consecutive patients with primary knee OA attending rheumatology clinic, mean age 64.3, 88% female, 10 unilateral OA, 40 bilateral were examined clinically and with ultrasonography. 22.2% of knees with symptoms (90 knees) had a popliteal cyst, none without symptoms had cysts (p = NS). The presence of popliteal cyst was significantly associated with medial meniscus protrusion (p<.005), and effusion (P,.005) but not with pain. Sign level 3.

5. Kornaat17 has prospectively evaluated the association between clinical features and

structural abnormalities found at magnetic resonance (MR) imaging in patients with osteoarthritis (OA) of the knee in a cross-sectional analysis of a cohort. The study examined by MRI 205 subjects (80% female) of median age 60 years; all patients in had symptomatic OA at multiple joint sites. 35% had radiographically diagnosed OA in the knee. 47% of patients had a popliteal cyst. The presence of a popliteal cyst was not related to clinical symptoms; Grade 2 or 3 cysts were not significantly related to pain (p=.16) or to stiffness p = .14. Cross-sectional analysis of cohort. Sign level 2-.

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6. Vasilevska27 has evaluated the relationship between size of popliteal cyst and medial compartment knee osteoarthritis in a retrospective review of a case series. 66 patients with popliteal cyst and medial compartment knee osteoarthritis were investigated. 31 had a large popliteal cyst (65% female, mean age 54) and 35 had a small popliteal cyst (only detectable by MRI) (66% female, mean age 59). In the group with the large popliteal cysts, 84% had medial compartment cartilage loss and 58% of these had associated 3rd degree meniscal degeneration; 16% cases had only medial meniscus involvement. There was a statistically significant relationship between meniscal degeneration and distension of the cyst (p<.01) in this group. In the second group, 48% of cases had cartilage loss, and of these 82% had 3rd degree meniscal degeneration. In 52% of cases meniscus degeneration was only present. They concluded that the size of the popliteal cyst was strongly correlated with degenerative changes of the cartilage and with the degree of meniscus degeneration in the medial compartment of the knee joint. Sign level 3.

7. Chatzopoulos2 has determined the ultrasonographic prevalence of popliteal cysts in knees with chronic osteoarthritic pain in a case series study on 196 patients with chronic OA, (mean age 69, 75% female) and 54 non-osteoarthritic controls, (age and gender mix not given). Popliteal cysts were detected in 37% of OA patient compared to 2% in non OA patients. 9% of patients had bilateral cysts. There was no significant difference in prevalence between men and woman nor was an age affect observed although this may have been due to the population studied. Abnormal and intense tracer accumulation in early-phase bone scintigraphy (detects the severity of inflammation in soft-tissue) were significantly more frequent in osteoarthritic knees with popliteal cysts (97 and 56%, respectively), than in those without (89 and 40%, respectively, P<0.05 for both). A case series; Sign level 3.

8. Fam16 has determined the prevalence and significance of popliteal cysts in primary osteoarthritis (OA) of the knee in a prospective case-control series by ultrasonography in 50 patients with primary OA (grade 2 or more) , mean age 64.6, 84% female; and 25 controls, mean age 61.3, 48% female with radiographic OA = 0 or1. They found that cysts were found in 42% of patients; (38%) had bilateral cysts, and in 0% of controls. The majority of cysts were small and symptomless. The occurrence of cysts correlated with the presence of knee effusion (effusion was present in 86% of knees with cysts compared to 36% without cysts (P<.02)) and the radiological grade of OA (P<.002). Cysts were detected in 47% of knees with grade 3 or 4 OA compared to 18% with grade 2 (p<.03). They concluded that OA may be a more common cause of popliteal cysts than generally recognized. Prospective case series, Sign level = 3.

9. Ahn31 has examined the functional and magnetic resonance imaging (MRI) outcomes of popliteal cysts with combined intra-articular pathologies that were treated arthroscopically. There were 31 subjects with popliteal cysts combined with pain and an intra-articular lesion or with larger popliteal cysts unresponsive to aspirations; 55% female, mean age 47.7. The connecting valvular mechanism was found in all cases. 68% were associated with medial meniscal tears, 29% lateral meniscal tears, 39% degenerative cartilage damage and 6% synovitis. Case series, Sign level 3.

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10. Liao25 has investigated the pathology associated with popliteal cyst (BC) in patients

attending a rheumatology clinic using a case series design. Of 1,120 patients who underwent ultrasound studies, 145 had popliteal cyst; mean age 59.6, 54% female. Prevalence 12.9%. The associated diseases were as follows: 50.6% osteoarthritis of the knee, 20.6% rheumatoid arthritis, 13.9% gout, 7.8% seronegative spondyloarthropathy and 7.2% pyrophosphate arthropathy. Effusion was present in 91.7% of knees with popliteal cysts and synovitis present in 69.9%. Case series, Sign level 3.

11. Tarhan21 has reported the prevalence of the abnormalities detected by magnetic resonance imaging (MRI) and ultrasonography in a group of 58 patients with symptomatic knee OA (mean age 57.4, 83% female) and 16 volunteer control subjects (mean age 59, 75% female). All knees with OA had cartilage abnormalities on US examinations and normal cartilage was detected in less than 3% of these knees by MRI. Joint effusion was present in 24.1% of the controls; 6.9% had synovial thickening and 6.9% popliteal cysts as shown by MRI. In the cases, synovial thickening was present in 50%, effusion in 85% and popliteal cysts in 35% as determined by MRI. This study confirmed that there was a significant correlation between the MRI and US techniques for evaluating the cartilage and soft tissue changes in the patients with knee OA. Case series, Sign level 3.

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Appendix One, Level of evidence in the SIGN system

SIGN criteria for classifying studies. Score Design 1++ High quality meta-analyses, systematic review of RCTs, or RCTs with a very low risk of bias 1+ Well conducted meta-analyses, systematic reviews of RCTs, or RCTs with a low risk of bias 1- Meta-analyses, systematic reviews of RCTs or RCTs with a high risk of bias 2++ High quality systematic reviews of case-control or cohort studies. High quality case-control or

cohort studies with a very low risk of confounding, bias or chance and a high probability that the relationship is causal

2+ Well conducted case control or cohort studies with a low risk of confounding, bias or chance and a moderate probability that the relationship is causal

2- Case control or cohort studies with a high risk of confounding, bias or chance and a significant risk that the relationship is not causal.

3 Non-analytic studies

4 Expert opinion

Acknowledgements The timely and helpful assistance of the ACC librarians, Helen Brodie and Beth Tillier is gratefully acknowledged.

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References

1. Lindgren P, Willen R. Gastrocnemio-semimembranosus bursa and its relation to the knee joint. Part 1 Anatomy and histology. Acta Radiologica Diagnosis 1977;18(5):497-512.

2. Chatzopoulos D, Moralidis E, Markou P, Makris V, Arsos G. Baker's cysts in knees with chronic osteoarthritic pain: a clinical, ultrasonographic, radiographic and scintigraphic evaluation. Rheumatology International 2008;29(2):141-6.

3. Wolfe RD, Colloff B. Popliteal cysts. An arthrographic study and review of the literature. Journal of Bone & Joint Surgery - American Volume 1972;54(5):1057-63.

4. Labropoulos N, Shifrin DA, Paxinos O. New insights into the development of popliteal cysts. British Journal of Surgery 2004;91(10):1313-8.

5. Beaman FD, Peterson JJ. MR imaging of cysts, ganglia, and bursae about the knee. Magnetic Resonance Imaging Clinics of North America 2007;15(1):39-52.

6. Johnson LL, van Dyk GE, Johnson CA, Bays BM, Gully SM. The popliteal bursa (Baker's cyst): an arthroscopic perspective and the epidemiology. Arthroscopy 1997;13(1):66-72.

7. Morrison JL, Kaplan PA. Water on the knee: cysts, bursae, and recesses. Magnetic Resonance Imaging Clinics of North America 2000;8(2):349-70.

8. Lodewyk W, Jansen EJ, H P. Long-term follow up of conservatively treated popiteal cysts in children. J Pediatric Orthopaedics Part B 2000;9:62-64.

9. Moore CP, Sarti DA, Louie JS. Ultrasonographic demonstration of popliteal cysts in rheumatoid arthritis. A noninvasive technique. Arthritis & Rheumatism 1975;18(6):577-80.

10. Fielding JR, Franklin PD, Kustan J. Popliteal cysts: a reassessment using magnetic resonance imaging. Skeletal Radiology 1991;20(6):433-5.

11. Marti-Bonmati L, Molla E, Dosda R, Casillas C, Ferrer P. MR imaging of Baker cysts --prevalence and relation to internal derangements of the knee. Magma 2000;10(3):205-10.

12. Miller TT, Staron RB, Koenigsberg T, Levin TL, Feldman F. MR imaging of Baker cysts: association with internal derangement, effusion, and degenerative arthropathy. Radiology 1996;201(1):247-50.

13. Rupp S, Seil R, Jochum P, Kohn D. Popliteal cysts in adults. Prevalence, associated intraarticular lesions, and results after arthroscopic treatment. American Journal of Sports Medicine 2002;30(1):112-5.

14. Tschirch FTC, Schmid MR, Pfirrmann CWA, Romero J, Hodler J, Zanetti M. Prevalence and size of meniscal cysts, ganglionic cysts, synovial cysts of the popliteal space, fluid-filled bursae, and other fluid collections in asymptomatic knees on MR imaging. AJR American Journal of Roentgenology 2003;180(5):1431-6.

15. de Miguel Mendieta E, Cobo Ibanez T, Uson Jaeger J, Bonilla Hernan G, Martin Mola E. Clinical and ultrasonographic findings related to knee pain in osteoarthritis. Osteoarthritis & Cartilage 2006;14(6):540-4.

16. Fam AG, Wilson SR, Holmberg S. Ultrasound evaluation of popliteal cysts on osteoarthritis of the knee. Journal of Rheumatology 1982;9(3):428-34.

17. Kornaat PR, Bloem JL, Ceulemans RYT, Riyazi N, Rosendaal FR, Nelissen RG, et al. Osteoarthritis of the knee: association between clinical features and MR imaging findings. Radiology 2006;239(3):811-7.

27

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18. Naredo E, Cabero F, Palop MJ, Collado P, Cruz A, Crespo M. Ultrasonographic findings in knee osteoarthritis: a comparative study with clinical and radiographic assessment. Osteoarthritis & Cartilage 2005;13(7):568-74.

19. Hayes CW, Jamadar DA, Welch GW, Jannausch ML, Lachance LL, Capul DC, et al. Osteoarthritis of the knee: Comparison of MR imaging findings with radiographic severity measurements and pain in middle-aged women. Radiology 237(3)(pp 998-1007), 2005 .

20. Hill CL, Gale DG, Chaisson CE, Skinner K, Kazis L, Gale ME, et al. Knee effusions, popliteal cysts, and synovial thickening: association with knee pain in osteoarthritis. Journal of Rheumatology 2001;28(6):1330-7.

21. Tarhan S, Unlu Z. Magnetic resonance imaging and ultrasonographic evaluation of the patients with knee osteoarthritis: a comparative study. Clinical Rheumatology 2003;22(3):181-8.

22. Sansone V, de Ponti A, Paluello GM, del Maschio A. Popliteal cysts and associated disorders of the knee. Critical review with MR imaging. International Orthopaedics 1995;19(5):275-9.

23. Stehling C, Lane NE, Nevitt MC, Lynch J, McCulloch CE, Link TM. Subjects with higher physical activity levels have more severe focal knee lesions diagnosed with 3T MRI: Analysis of a non-symptomatic cohort of the osteoarthritis initiative. Osteoarthritis and Cartilage 18 (6) (pp 776-786), 2010 .

24. Lindgren PG, Rauschning W. Radiographic investigation of popliteal cysts. Acta Radiologica: Diagnosis 1980;21(5):657-62.

25. Liao S-T, Chiou C-S, Chang C-C. Pathology associated to the Baker's cysts: a musculoskeletal ultrasound study. Clinical Rheumatology;29(9):1043-7.

26. Pulich JJ. Asymptomatic popliteal cysts. Journal of the American Osteopathic Association 1975;75(3):319-23.

27. Vasilevska V, Szeimies U, Staebler A. MRI diagnosis of Baker cyst and significance of associated medial compartment knee osteoarthritis. Radiology and Oncology 42(2)(pp 51-58), 2008.

28. Larking P. Causation Review - Meniscal Tears. Classification Of Mensical Tears Of The Knee And The Evidence That Certain Tears Are Degenerative In Origin; Including The Relationship Of Meniscal Tears To Knee Osteoarthritis. ACC Evidence Report 2010.

29. Lindgren P. Gastrocnemio-semimembranosus bursa and its relation to the knee joint. 4. Clinical considerations. Acta Radiologica Diagnosis 1978;19(4):609-22.

30. Sansone V, De Ponti A. Arthroscopic treatment of popliteal cyst and associated intra-articular knee disorders in adults. Arthroscopy 1999;15(4):368-72.

31. Ahn JH, Lee SH, Yoo JC, Chang MJ, Park YS. Arthroscopic treatment of popliteal cysts: clinical and magnetic resonance imaging results. Arthroscopy;26(10):1340-7.

32. Marra MD, Crema MD, Chung M, Roemer FW, Hunter DJ, Zaim S, et al. MRI features of cystic lesions around the knee. Knee 2008;15(6):423-38.

33. Lantz B, Singer KM. Meniscal cysts. Clinics in Sports Medicine 1990;9(3):707-25.

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