The influence of tibial tubercle transfer on patellofemoral contact: A cadaveric study

The effects of tibial tubercle transfer, lateral retinacular release and proximal realignment on patellofemoral contact pressure and the patellofemoral contact area, as well as the medial-lateral shift, were studied on 8 fresh above the knee amputation specimens. Lateral retinacular release did not significantly alter the patellofemoral contact pressure, or the patellofemoral contact area. Proximal realignment increased the patellofemoral contact pressure by 34% and the patellofemoral contact area by 18%. Anterior and medial transfers of the tibial tubercle collectively affected the contact pressure and the contact area of the patellofemoral joint. The values of medial-lateral shift were inconsistent and unpredictable. Medial transfer and anterior transfer of the tibial tubercle exhibited a 'see-saw' phenomenon on the reduction of the contact pressure and the contact area of the patellofemoral joint. With zero medial displacement, a 20 mm anterior displacement is optimal in reducing the contact pressure by 12% and the contact area by 25%. With 5-10 mm medial displacement, a 15 mm anterior displacement is optimal in reducing the contact pressure by 9-12% and the contact area by 25%. With 15 mm medial displacement, anterior displacement of 10 mm reduces the contact pressure by 9% and the contact area by 20%. Clinical relevance: Lateral retinacular release and proximal realignment are only indicated in selected patients. The goals of surgery in patellofemoral disorders are to correct the abnormal Q angle by medial transfer, and to reduce the patellofemoral contact pressure by anterior transfer of the tibial tubercle. In knees with patellofemoral arthrosis with no evidence of malalignment, a 20 mm anterior transfer without medial displacement of the tibial tubercle is recommended. In knees with moderate patellofemoral malalignment and moderately increased Q angle, a 5 to 10 mm medial transfer to reduce the Q angle to 10°or less plus a 15 mm anterior transfer is suggested. In knees with severe patellofemoral malalignment and markedly increased Q angle 15 mm medial transfer is required to optimize the Q angle, but only 10 mm anterior transfer is suggested.