Adding Tibial Tuberosity Medialization to Medial Patellofemoral Ligament Reconstruction Reduces Lateral Patellar Maltracking During Multidirectional Motion in a Computational Simulation Model

Abstract

Purpose: To determine whether adding tibial tuberosity medialization to medial patellofemoral ligament (MPFL) reconstruction reduces lateral patellar maltracking during a dynamic multidirectional activity and to investigate when medial patellofemoral contact pressures are elevated during daily activities, such as squatting.

Methods: Seven computational models representing knees with patellar instability, including lateral patellar maltracking, were evaluated following simulated MPFL reconstruction (bisect offset index > .75). Tibial tuberosity medialization was added to MPFL reconstruction for each model. Patellar tracking during multidirectional motion was evaluated by simulating pivot landing. Analysis of pivoting focused on early flexion (5° to 40°). Patellofemoral contact pressures during daily function were evaluated by simulating knee squatting. Data were analyzed with paired comparisons between MPFL reconstruction with and without tuberosity medialization.

Results: The patella dislocated during pivoting for 2 models with an isolated MPFL reconstruction and for 1 model including tibial tuberosity medialization. Adding tibial tuberosity medialization to MPFL reconstruction significantly decreased bisect offset index by ∼0.1 from 5° to 40° (P < .03). For knee squatting, medializing the tibial tuberosity significantly increased maximum medial contract pressure by ∼0.5 MPa from 30° to 85° (P < .05) but did not significantly influence maximum lateral pressure.

Conclusions: In this study of simulated multidirectional motion, MPFL reconstruction did not sufficiently constrain the patella for some knees. Adding tibial tuberosity medialization to MPFL reconstruction in these models reduced lateral patellar maltracking during multidirectional motion but increased pressure applied to medial cartilage during squatting.

Clinical relevance: After establishing the influence of tibial tuberosity medialization on patellar maltracking for an idealized population, as was done in the current study, future simulation studies can be performed to better determine the anatomical characteristics of patients for whom tibial tuberosity medialization is needed to reduce the risk of postoperative patellar maltracking.

Fig 1

(A) Computational model for multibody dynamic simulation of a pivot landing. Knee squatting was represented with a smaller peak quadriceps force (500 N) and gravitational force at the hip (200 N) and no external tibial torque. (B) Representation of the patellofemoral contact pressure distribution. (C) Parameters used to characterize patellar tracking.

Fig 2

Average (±SD) bisect offset index. An asterisk (∗) at a position of knee flexion indicates a significant difference due to adding tibial tuberosity medialization to medial patellofemoral ligament reconstruction.

Fig 3

Average (±SD) patellar tilt. An asterisk (∗) at a position of knee flexion indicates a significant difference due to adding tibial tuberosity medialization to medial patellofemoral ligament reconstruction.

Fig 4

Average (±SD) graft tension. An asterisk (∗) at a position of knee flexion indicates a significant difference due to adding tibial tuberosity medialization to medial patellofemoral ligament reconstruction.

Fig 5

Average (±SD) lateral force ratio. An asterisk (∗) at a position of knee flexion indicates a significant difference due to adding tibial tuberosity medialization to medial patellofemoral ligament reconstruction.

Fig 6

Average (±SD) maximum contact pressure for cartilage on the lateral and medial facet of the patella. An asterisk (∗) at a position of knee flexion indicates a significant difference due to adding tibial tuberosity medialization to medial patellofemoral ligament reconstruction.