2017 ISAKOS Biennial Congress ePoster #1708
Correlation Between Knee Size and TT-TG Only in Patients with Patellofemoral Instability
Peter W. Ferlic, MD, Innsbruck AUSTRIA
Florian Dirisamer, MD, Linz AUSTRIA
Peter Balcarek, PhD, Pforzheim GERMANY
Johannes M. Giesinger, PhD, Amsterdam NETHERLANDS
Rainer G. Biedermann, MD, Priv. Doz., Innsbruck AUSTRIA
Michael C. Liebensteiner, MD, PhD, Innsbruck, Tyrol AUSTRIA
Wolfgang Hackl, MD, Innsbruck AUSTRIA
Medical University Innsbruck, Innsbruck, AUSTRIA
FDA Status Not Applicable
Summary
Individual knee joint size should be considered in patients with patellofemoral instability, rather than using absolute cut-off values of TT-TG for directing surgical treatment with medial transfer of the tibial tuberosity, as a significant correlation between TT-TG and joint size was found in patients with patellofemoral instability.
ePosters will be available shortly before Congress
Abstract
Background
Pathologically increased tibial tuberosity-trochlear groove distance (TT-TG), is one established risk factor for patellofemoral instability (PFI). A TT-TG greater than 20 mm is used as cut-off value for directing surgical treatment with medial transfer of the tibial tuberosity. This absolute value, however, does not respect differences in individual knee joint size.
Hypothesis/Purpose:
The hypothesis of this study was that TT-TG and joint size correlate in 1) patients with PFI and 2) in a control group of patients without a history of patella dislocation.
Methods
This study comprised a retrospective analysis of knee CT scans, including 36 cases with patellofemoral instability (PFI) and 30 cases who did not suffer from PFI (controls).
Besides TT-TG, five measures of knee joint size were evaluated in axial CT slices: medio-lateral femur width, antero-posterior lateral condylar height, medio-lateral width of the tibia, width of the patella and the proximal-distal joint size (TT-TE). Furthermore, the length of the femur, the tibia and the total leg length were measured in the CT scanogram. Correlation analysis of TT-TG and the other parameters was done by calculating the Spearman correlation coefficient.
Results
In the group of patients with PFI lateral condylar height (r = 0.389), tibia width (r = 0.41) and patella width (r = 0.4) showed significant correlations (p < 0.02) with TT-TG. The correlation coefficient between TT-TG and femur, tibia and leg length did not reach the level of significance. The control group showed no significant correlation between TT-TG and knee joint size or between TT-TG and measures of lower limb length.
Conclusion
TT-TG correlates with several parameters of knee joint size in patients with patellofemoral instability. No such associations were found in knees without PFI. Therefore, the previously suggested application of indices determining TT-TG as a ratio of joint size could be helpful when establishing the indication for medial transfer of the tibial tuberosity.