Femorotibial rotation is linearly associated with tibial tubercle-trochlear groove distance: A cadaveric study

ObjectivesA tibial tubercle-trochlear groove (TT-TG) distance of 20 millimeters (mm) is typically used when determining whether tibial tubercle medialization is performed for surgical treatment of patellar instability. Without knowledge of the variability of an individual's TT-TG distance influenced by through-the-knee femorotibial rotation, the use of a specific TT-TG distance during pre-operative planning for patellar instability may lead to incorrect decisions on the use of tibial tubercle medializtion. We hypothesized that knee joint IE rotation is related to the TT-TG distance.MethodsEight independent human cadaveric knee specimens (age: 32 ± 6 years; 4 males, 4 females) were utilized. A robotic manipulator (ZX165U, Kawasaki Robotics, Wixom, MI, USA) instrumented with a universal force/moment sensor was used to determine knee joint IE rotation under applied moments of ±5 newton-meters (Nm) at full extension. Two independent reviewers selected the trochlear groove and tibial tuberosity points on computerized tomography (CT) images of each specimen to define TT-TG. To determine the influence of knee joint IE rotation on TT-TG distance, three-dimensional (3D) models generated from CT scans were registered to tibiofemoral kinematics. Linear regression was performed to determine the relationship between knee joint IE rotation and TT-TG distance. The regression coefficient and standard error of measurement (α = 0.05), and coefficient of determination (r2) were reported.ResultsAt 0° of rotation, the mean TT-TG distance was 14.2 ± 5.0 mm. Knee joint IE rotation averaged 23.0 ± 4.2°. For every degree of knee joint IE rotation, TT-TG distance changed by 0.52 mm.ConclusionTT-TG distance was linearly dependent on knee joint IE rotation changing by 0.52 mm for every degree of knee joint IE rotation. Thus, an offset of IE rotation of 10° would lead to a change in TT-TG distance of 5.2 mm, enough to alter surgical decision-making for/or against tibial tubercle medialization.Level of Evidence: IVThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.