Summary

MPFL injury frequently accompanies acute patellar dislocation, with MPFL reconstruction being a common treatment; however, the biomechanical effects of lateral release during reconstruction, which reduces patellofemoral contact but increases lateral patellar displacement, suggest that this additional procedure should be cautiously considered due to potential risks of exacerbating instability.

Abstract

Background

Medial patellofemoral ligament (MPFL) injury occurs in the majority of the cases of acute patellar dislocation, as the ligament resists lateral patellar dislocation. Although MPFL reconstruction is a well-established treatment, the role of a concomitant lateral release, a surgical procedure where the lateral retinaculum is incised to relieve pressure, remains unclear. Even if the lateral retinaculum plays a role in both medial and lateral patellofemoral joint stability in MPFL intact knees, studies have shown controversial clinical outcomes following its release during MPFL reconstruction surgery. Therefore, understanding the specific biomechanical effects of lateral release on an already reconstructed MPFL is critical.

Aim

The study uses a finite element (FE) model of the patellofemoral joint to simulate the effects of a lateral release in addition to MPFL reconstruction.
The aim was to determine whether performing lateral release during MPFL reconstruction would disrupt patellofemoral biomechanics, leading to lateral patellar instability.

Methods

The study employed an FE model of the patellofemoral joint, validated in prior studies, to simulate conditions following MPFL reconstruction with and without lateral release. The simulations examined key metrics such as contact pressure (CP), contact area (CA), and lateral patellar displacement at varying degrees of knee flexion. Four conditions were modeled: a healthy knee, patellar instability due to MPFL injury, MPFL reconstruction, and MPFL reconstruction with lateral release.

Results

The results revealed that lateral release led to significant biomechanical changes compared to MPFL reconstruction alone. Specifically, the addition of lateral release resulted in a 39% decrease in CP and a 44% decrease in CA, coupled with a 20% increase in lateral patellar displacement at 90° of knee flexion compared to a knee with intact MPFL. The decrease in CP and CA following lateral release suggests reduced patellofemoral joint contact, which could explain why lateral release is recommended in cases of lateral patellar compression syndrome. However, the increased lateral patellar displacement suggests that lateral release may exacerbate patellar instability, particularly at higher degrees of knee flexion.

Discussion

Lateral release reduces the load on the patella and could relieve pain in cases of compression, but it also increases the risk of lateral patellar instability following MPFL reconstruction. This finding supports the hypothesis that lateral release should be used cautiously during MPFL reconstruction, particularly in patients with patellar instability. Surgeons must carefully assess the biomechanical effects of lateral release on the patellofemoral joint to avoid exacerbating instability.