Abstract
PurposeThe correlation between tibial tuberosity-trochlear groove distance (TT-TG) and joint size, taking into account several different parameters of knee joint size as well as lower limb dimensions, is evaluated in order to assess whether TT-TG indices should be used in instead of absolute TT-TG values.MethodsThis study comprised a retrospective analysis of knee CT scans, including 36 cases with patellofemoral instability (PFI) and 30 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.ResultsIn the PFI group lateral condylar height (r = 0.370), tibia width (r = 0.406) and patella width (r = 0.366) showed significant moderate correlations (p < 0.03) with TT-TG. Furthermore, we found a significant correlation between TT-TG and tibia length (r = 0.371) and total leg length (r = 381). The control group showed no significant correlation between TT-TG and knee joint size or between TT-TG and measures of lower limb length.ConclusionsTibial tuberosity-trochlear groove distance correlates with several parameters of knee joint size and leg length in patients with patellofemoral instability. Application of indices determining TT-TG as a ratio of joint size could be helpful in establishing the indication for medial transfer of the tibial tuberosity in patients with PFI.Level of evidenceLevel III
Highlights
Patellofemoral instability (PFI) linked to pathological tibial tuberosity-trochlear groove distance (TT-TG) can be surgically addressed by medial transfer of the tibial tuberosity
We found a significant correlation between TTTG and tibia length (r = 0.371) and total leg length (r = 381)
The control group showed no significant correlation between tibial tubercle (TT)-TG and knee joint size or between TT-TG and measures of lower limb length
Summary
Patellofemoral instability (PFI) linked to pathological tibial tuberosity-trochlear groove distance (TT-TG) can be surgically addressed by medial transfer of the tibial tuberosity. Recent literature has introduced various indices evaluating TT-TG as a ratio of joint size: the TT-TG/TT-TE ratio expresses TT-TG in relation to the proximal-distal joint size [2] and the TT-TG/femur width ratio in relationship to the medio-lateral width of the distal femur [3, 4]. Camp et al studied a patellar instability ratio in order to individualize the TT-TG distance. They reported that TT-TG divided by trochlea width and patella width more effectively predict recurrent instability than the TT-TG distance alone [5]
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