patella fracture imaging

8/13/2019 Patella Fracture Imaging

1/8

Patella Fracture Imaging

Author: Christine Lamoureux, MD; Chief Editor: Felix S Chew, MD, MBA, MEd more...

Updated: Jul 11, 2013

Overview

Several primary types of patellar fractureshave been identified, each with separate diagnostic, imaging, and

management considerations. The primary types include transverse, vertical, marginal, and osteochondral fractures.Transverse patellar fractures, displaced and nondisplaced, are seen in the images below.

[1]

Radiograph of a displaced transverse fracture of the patella.


Today

News

Reference

Education

Log OutMy Account

R Kurniawan Md

Discussion

a Fracture Imaging http://emedicine.medscape.com/article/394270-

1/12/2014


2/8

Radiograph of a nondisplaced transverse fracture of the patella.


Radiographically recognized morbidity

Many of the complications of a patellar fracture can be recognized radiographically.

Orthopedic hardware failure may result in malalignment of fractured patellar fragments; in these cases, further

surgery may be necessary. Other complications related to hardware placement include sepsis, malunion or

nonunion, and femoropatellar degenerative arthritis.

A distance of 3 mm or more between fractured patellar fragments should be noted in the radiology report. This

degree of separation may lead to an increased incidence of malunion and posttraumatic degenerative arthritis.

Recognizing an osteochondral fracture is important, because displacement of a fragment that contains cartilage,

subchondral bone, and trabecular bone may occur, resulting in a loose body.

In long-term follow-up studies, degenerative arthritis of the patella has been reported to be more common in knees

that were injured previously than in noninjured knees. The arthritis may be due to surface irregularities that involvethe fracture fragments, as well as damage to the articular cartilage, resulting in increased contact stresses.

Preferred examination

In most patients, radiography is the most useful imaging modality for the examination of patella fractures, followed by

computed tomography (CT) scanning, bone scanning, and magnetic resonance imaging (MRI).[2, 3, 4, 5]

CT scanning is useful when a suspected fracture is not visible on radiographs. The expeditious use of CT scanning

can prevent a delay in treatment and help to identify the position of fracture fragments and the localization of intra-

articular loose bodies.

Bone scans are useful when a fracture is suspected yet the radiographic findings are normal. If the bone scan results

are also normal, a fracture can be excluded. However, if the findings are positive, the age of the fracture cannot beaccurately determined, because bone scanning results can be positive in the setting of fractures for as long as 24

months.

MRI also can help to detect abnormalities that are not identified on plain radiographs. Unlike bone scanning, MRI

can be performed without delay and does not use radiation; it may also be less expensive. This modality can show

bone-marrow and soft-tissue injury in great detail.

Radiography

Radiographic examination for the detection of patellar fractures optimally includes anteroposterior (AP), lateral, and

tangential or Merchant views.


1/12/2014


3/8

AP radiographs may obscure the findings of patellar fractures. Lateral views can be useful in evaluating the

trabecular arrangement of the patella, as well as comminution and separation of fracture fragments. Tangential views

are especially helpful in assessing vertical fractures, as well as in distinguishing a fracture from a partitioned patella.

Transverse fractures are characterized by a lucent fracture line that courses medially to laterally across the middle or

distal third of the patella (as seen in the first 2 images below). Transverse fracture fragments may be displaced (as

seen in the third and fourth images below).





1/12/2014


4/8


Vertical fractures demonstrate a fracture line that courses superiorly to inferiorly, and these fractures can also be

displaced. Comminuted fractures demonstrate a stellate pattern of fracture. Osteochondral sleeve fractures are

characterized by a small avulsion fragment from the inferior pole of the patella, which is best demonstrated on the

lateral view; these findings are usually accompanied by the presence of an effusion and a high-riding patella.

Degree of confidence

Other imaging modalities (eg, MRI) are more useful than radiographs in fully characterizing the cartilaginous injury

associated with an osteochondral patellar fracture and can define radiographically occult fractures. Because a sleeve

fracture is in the coronal plane of the patella, this injury may be difficult to diagnose based on plain radiographs.

False positives/negatives

The differentiation of an acute fracture from a partitioned patella may be difficult on radiographs. Usually, the features

of bipartite patella include a wide radiolucent line that courses across the superolateral margin of the patella, as well

as smooth, well-corticated, opposing margins. These features are well depicted in the tangential projection. Because

a bipartite patella is often bilateral, views of the opposite knee can be helpful for comparison. A sleeve fracture

occurs in the coronal plane of the patella and may be difficult to diagnose on plain radiographs.

Computed Tomography

In patellar fractures, CT scanning is primarily performed for occult or osteochondral injuries. The patient is placed in

the supine position with his or her feet externally rotated 15 and pressed against a perpendicular footrest. CT-scan

sections are obtained with the knee at rest, with the knee extended and quadriceps contracted, and with the knee in

15 of flexion with a relaxed quadriceps.

The position of the fracture fragments can be determined by identifying the fracture line. The reconstructed images in

the sagittal, coronal, and axial planes can aid in localization of the fragments.


CT scanning is limited in the evaluation of soft-tissue injury, but MRI may be performed to further evaluate this

condition. CT scanning may be more useful than MRI in the identification of loose bodies.

Magnetic Resonance Imaging

MRI is useful in the diagnosis of patellar injuries when making the clinical diagnosis is difficult, as in patients with

sleeve fractures. On MRIs, the appearance of the normal patella includes signal intensities that are consistent with

those of bone marrow and cortex. Articular cartilage has a lower signal intensity than do marrow spin-echo images

that are obtained with a short repetition time and echo time spin-echo. The signal intensity slightly increases on

images obtained with a longer repetition time and echo time.[3, 4]

MRI is advantageous in the assessment of imaging signs related to patellar fracture, including bone bruises,

soft-tissue injury, and loose bone fragments. The anatomy of the patellofemoral joint can be assessed in severalplanes. For example, axial imaging is useful for evaluating patellofemoral joint alignment, retinacular attachments,

and overlying patellar cartilage. Sagittal images are useful for evaluating the quadriceps muscles and tendons, and

the patellar tendon can be imaged in all 3 planes.

Traumatic dislocation of the patella (seen in the image below) may result in patellar fracture, medial retinaculum

damage, lateral femoral condyle contusion, and effusion. These injuries can be evaluated with T1-weighted ,

T2-weighted fast spin-echo (FSE), or short-tau inversion recovery (STIR) images in all 3 planes.


1/12/2014


5/8

Magnetic resonance image following a patellar dislocation.

Avulsions of the medial retinaculum are best imaged with fat-saturated, T2-weighted FSE MRI for detection of bone

fragments, edema, and hemorrhage. Edema and hemorrhage appear as areas of increased signal intensity on

T2-weighted images; fat-saturated, T2-weighted FSE images; and STIR images. Increased signal intensity in the

patella after dislocation can be seen on T2-weighted images.

A dorsal defect of the patella, which is a benign defect of the posterior patella covered by articular cartilage, canmimic osteochondral pathology. MRI is useful in characterizing this lesion, which has intermediate or low signal

intensity on T1-weighted MRIs, sometimes with central regions of increased signal intensity, and is usually a

centimeter in diameter, well defined, and located in the superolateral part of the patella.

Fractures of the inferior pole of the patella may be associated with tears of the patellar tendon. Patellar tendon tears

are characterized by increased signal intensity on T2-weighted; fat-saturated, T2-weighted FSE; and STIR images.

The tendon may be retracted or thickened.

Patellar fractures may also be associated with damage to the quadriceps tendon and/or extensor musculature.

Coronal or sagittal images are helpful in illustrating the longitudinal extent of the muscular injury, whereas axial views

are helpful in defining the anatomic relationships among the involved muscle groups. Axial T1-weighted imaging is

appropriate for evaluation of muscular atrophy. Increased signal intensity in the quadriceps tendon on images

obtained with any sequence is highly associated with the presence of a muscular tear.

Sinding-Larsen-Johansson syndrome, which is defined as osteochondrosis of the distal pole of the patella at the

tendinous insertion, is of uncertain etiology but is related to chronic traction injury. This condition may mimic a stress

fracture of the patella, an osteochondral sleeve fracture, or an un-united ossification center. The injury is

characterized by a focal area of decreased signal on T1-weighted images and increased signal intensity on

gradient-echo or fat-saturated, T2-weighted FSE images.

Occult stress or insufficiency fractures are characterized by the presence of a linear band of low signal intensity on

images obtained with all sequences; surrounding edema is also depicted. Occult fractures are seen in the images

below.

Magnetic resonance image of an occult patellar fracture.


1/12/2014


6/8



Patellar fractures may also be detected in the healed phase on MRI, as seen in the images below.

Magnetic resonance image of a healed patellar fracture.

Magnetic resonance image of a healed patellar fracture.

Ultrasonography

The effectiveness of ultrasonography in the setting of patellar fractures is limited. Because of the close association of

the articular cartilage posterior to the patella with the femur, an adequate scanning angle that is unimpeded by the

overlying bone is not attainable. Therefore, ultrasonography is rarely used in clinical practice.

Secondary signs may be present in an acute patellar fracture, and sonograms may demonstrate these well. For

example, ultrasonography can be useful in defining an effusion within the suprapatellar bursa, a well-defined fluid-filled space that is superior to the patella and posterior to the quadriceps tendon. The normal, moderate echogenicity

of the patellar ligament and quadriceps tendon may be interrupted by focal areas of echogenicity, or they may be

discontinuous in a partial tear.

Nuclear Imaging

Bone scanning is useful for evaluating a stress fracture of the patella, especially when an injury is superimposed on

a bipartite patella. Early after an injury to the patella, increased radionucleotide uptake can be present. This finding is

indicative of hyperemia and edema. In the acute phase (first 3-4 wk), uptake in the patella is more diffuse. In the

subacute phase (2-3 mo), radionucleotide uptake becomes more intense and localized; subsequently, in the healing

phase, the uptake gradually decreases. Within 2 years, the results of 90% of bone scan studies return to normal.


1/12/2014


7/8


A normal patellar bone scan that is obtained 1 week after trauma excludes an occult patellar fracture. Consider the

use of other imaging modalities (eg, CT scanning, MRI) for suspected injuries, because the resolution and evaluation

of soft tissues is limited with bone scanning.

Contributor Information and DisclosuresAuthor

Christine Lamoureux, MD Diagnostic Radiologist, Christine A. Lamoureux, MD, PC

Christine Lamoureux, MD is a member of the following medical societies:American College of Radiologyand

Radiological Society of North America

Disclosure: Nothing to disclose.

Specialty Editor Board

David S Levey, MD PA, San Antonio, Texas

David S Levey, MD is a member of the following medical societies:American Roentgen Ray Society, Radiological

Society of North America, and Texas Medical Association


Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, Hutt

Valley District Health Board, New Zealand


Theodore E Keats, MD Professor, Departments of Radiology and Orthopedics, University of Virginia School of

Medicine


Robert M Krasny, MD Resolution Imaging Medical Corporation

Robert M Krasny, MD is a member of the following medical societies:American Roentgen Ray Societyand

Radiological Society of North America


1/12/2014


8/8

Medscape Reference 2011 WebMD, LLC


Chief Editor

Felix S Chew, MD, MBA, MEd Professor, Department of Radiology, Vice Chairman for Academic Innovation,

Section Head of Musculoskeletal Radiology, University of Washington School of Medicine

Felix S Chew, MD, MBA, MEd is a member of the following medical societies:American Roentgen Ray Society,

Association of University Radiologists, and Radiological Society of North America


Additional Contributors

We wish to thank Dr. Ray F Kilcoyne, MD, for his previous contributions to this article.

References

Moretti B, Speciale D, Garofalo R, Moretti L, Patella S, Patella V. Spontaneous bilateral fracture of patella.

Geriatr Gerontol Int. Mar 2008;8(1):55-8. [Medline].

1.

Lee J, Sagel S, Stanley R, Heiken J, eds. Computed Tomography With MRI Correlation. 3rd

ed.

Philadelphia, Pa: Lippincott-Raven; 1998:1402-6.

2.

Dupuis CS, Westra SJ, Makris J, et al. Injuries and conditions of the extensor mechanism of the pediatric

knee. Radiographics. May-Jun 2009;29(3):877-86. [Medline].

3.

von Engelhardt LV, Raddatz M, Bouillon B, et al. How reliable is MRI in diagnosing cartilaginous lesions in

patients with first and recurrent lateral patellar dislocations?. BMC Musculoskelet Disord. Jul 5 2010;11:149.

[Medline]. [Full Text].

4.

Smith TO, Davies L, Toms AP, et al. The reliability and validity of radiological assessment for patellar

instability. A systematic review and meta-analysis. Skeletal Radiol. May 23 2010;[Medline].

5.


patella fracture imaging

Documents