The Radiological Work Up Of Patients With Patellar Femoral Pathology: Should The TT-TG Distance Be Measured On MRI And What Is Its

Relationship To The TT-PCL Distance?

C Anley1, G Morris1, A Saithna1, S James2, M Snow1

1 Arthroscopy Division, The Royal Orthopaedic Hospital, Birmingham, UK2 Radiology Department, The Royal Orthopaedic Hospital, Birmingham, UK

Disclosures

The authors have no financial conflicts related to this poster to disclose

TT-TG Measurement

Tibial tubercle-Trochlear groove (TT-TG) traditionally radiographic measure to determine lateralisation of TT

TT-TG > 20mm on CT surgical intervention

Varies with knee flexion and difficult in trochlea dysplasia

Dejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc. 1994;2(1):19-26

TT-PCL Measurement

TT-PCL is the mediolateraldistance between the midpoint of the insertion of the patellar tendon and the medial border of the posterior cruciate ligamentMeasured parallel to the dorsal tibia condylar lineNormal: 24 mm

dTCL: Dorsal tibia condylar linePCL: Posterior cruciate ligament;TT-PCL: Tibial tubercle-Posterior Cruciate Ligament distance

Seitlinger G, Scheurecker G, Hogler R, Labey L, Innocenti B, Hofmann S. Tibial tubercle-posterior cruciate ligament distance: a new measurement to define the position of the tibial tubercle in patients with patella dislocation.

Am J Sports Med. 2012;40(5):1119-1125

TT-PCL

Objective

Radiographic study to:1. Review whether TT-TG on CT and MRI are

interchangeable 2. Establish if there is a correlation between TT

lateralisation as indicated by TT-TG and TT-PCL

Methods141 scans (108F 33M) with patellar pathology and both MRI and CT scan, were identified on the hospital PACS system. Ave age: 28.5 yrs (10-59, SD ±11.13 yrs)

TT-TG, TT-PCL and Knee Joint Rotation were measured independently by two fellowship trained orthopaedic surgeons according to the methods used by Seitlinger et al and Shoettle

Thirty measurements where repeated on a separate occasion to allow for an assessment of the intraraterreliability

Results: TT-PCL

Mean TT-PCL: 20.32mm (10.11-32.01, SD: ± 3.45mm)

Excellent (> 0.75) inter- and intraobserveragreement

14% (20/141) TT-PCL > 24 mm of which55% (11/20) had TT-TG >20mm on CT

31% (44/141) TT-TG > 20mm on CT of which25% (11/44) had TT-PCL >24mm

Results: TT-TG CT vs MRIInterobserver and intraobserver agreement was considered excellent (> 0.75) for both MRI and CT (0.98 and 0.97)

ICC for each rater comparing the two imaging modalities was only fair (0.54 and 0.48)

Measurements are not interchangeable between the two modalities

CT MRI

Mean 17.72mm 13.56mm

Mean difference: 4.16mm

Range 6.97-31.33mm 2-30.04mm

SD ±5.15 ±6.07

P value p<0.001

Results

Based on the TT-TG and TT-PCL measurements, 4 groups of patients can be established.

When comparing knee joint rotation (KJR) between groups, we noted that an increased TT-TG may result from either true lateralisation of the TT, an increased knee joint rotation or a combination of both.

Results: TG and PCL

TG <20mmPCL<24mm

TG<20mmPCL>24mm

TG>20mmPCL<24mm

TG>20mmPCL>24mm

Number (%) 88 (62.4%) 9 (6.4%) 33 (23.4%) 11 (7.8%)

Mean TGMean PCL

15.0418.92

15.0625.92

23.2220.82

25.4225.88

SD TGSD PCL

±3.12±2.66

±3.55±2.42

±2.77±2.27

±3.99±1.75

CT KJA 6.8 6.7 12.5 10.3

P < 0.05

Conclusion

Commonly accepted values for the TT-TG distance cannot be used interchangeably between CT and MRI and a TT-TG >20mm measured on MRI should not be used as an indication for surgery

Conclusion

The TT-PCL measurement is a measure of true lateralisation of the tibial tubercle while the TT-TG is an amalgamated measure of true lateralisation and KJR.

The clinical relevance of these different groups requires further investigation and may explain the poor results in some patients following tibialtubercle transfers.

ReferencesDejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports TraumatolArthrosc. 1994;2(1):19-26

Seitlinger G, Scheurecker G, Hogler R, Labey L, Innocenti B, Hofmann S. Tibial tubercle-posterior cruciate ligament distance: a new measurement to define the position of the tibial tubercle in patients with patella dislocation. Am J Sports Med. 2012;40(5):1119-1125

Schoettle PB, Zanetti M, Seifert B, Pfirrmann CW, Fucentese SF, Romero J. The tibial tuberosity–trochlear groove distance: a comparative study between CT and MRI scanning. Knee. 2006;13:26-31.