Biomechanical Analysis of Tibial Tuberosity Medialization and Medial Patellofemoral Ligament Reconstruction

Abstract

Biomechanical studies are commonly performed to evaluate the influence of medial patellofemoral ligament (MPFL) reconstruction and tibial tuberosity medialization on patellar tracking and patellofemoral contact pressures. The most common method is in vitro simulation of knee function, but computational simulation of knee function and computational reconstruction of in vivo motion can also be utilized. The current review of the biomechanical literature indicates that MPFL reconstruction and tibial tuberosity medialization reduce lateral patellar tracking. Decreased lateral patellofemoral contact pressures have also been noted. For MPFL reconstruction, the most commonly noted biomechanical concerns are graft overtensioning and nonanatomic attachment on the femur leading to overconstraint of the patella and elevated medial contact pressures. For tuberosity medialization, the influence of altered tibiofemoral kinematics on postoperative function is unknown. Future biomechanical studies should emphasize inclusion of anatomic features and tracking patterns related to patellar instability, with comparison between the surgical approaches for continued development of treatment guidelines.

Figure 1

A schematic diagram of in vitro simulation of knee function. Cables applying the forces representing the quadriceps and hamstrings muscles were secured into the tendons and run over pulleys. Patellofemoral and tibiofemoral motion was characterized based on the motion of magnetic tracking sensors secured to the bones. A pressure sensor measured the patellofemoral contact pressure distribution. The tibial tuberosity was osteotomized from the tibia to allow representation of tibial tuberosity medialization. (Adapted with permission from Elias et al. Clin Biomech 2011; 26:841–6).

Figure 2

Representation of patellar tracking at multiple flexion angles for one knee evaluated with computational reconstruction of in vivo function based on dynamic CT imaging. The patient was analyzed pre-operatively and following surgical patellar stabilization with the combination of tibial tuberosity medialization and MPFL reconstruction. (Reprinted with permission from Elias et al., Knee Surg Sports Traumatol Arthrosc. 2014; 22:2350–6.)

Figure 3

Computational simulation of knee extension based on a multibody dynamic model of the knee. Patellar tracking is shown as a knee extends from a flexed position (A) to full extension (B) in the pre-operative condition, and for the knee extended with an MPFL graft wrapping around the femoral condyle, with a solid used to represent the graft from the femoral attachment to the wrapping point (C). The calculated patellofemoral contact pressure distribution is also shown for one knee with an MPFL graft, with pressure concentrated on the lateral facet of the patella (D). (Modified with permission from Elias et al., Orthop J Sports Med 2016;4:2325967116665080)