Biomechanics of Medial Patellofemoral Ligament (MPFL) Reconstruction for Patellar Instability

Abstract & Commentary

Synopsis: Patellar tracking was restored to normal by reconstructing the MPFL with a gracilis graft in a cadaveric model.

Source: Sandmeier RH, et al. The effect of reconstruction of the medial patellofemoral ligament on patellar tracking. Am J Sports Med 2000;28:345-349.

This article evaluates the biomechanical effects of reconstruction of the medial patellofemoral ligament (MPFL) with a free gracilis tendon graft. Six cadaveric knees were evaluated with (a) intact medial restraints, (b) following sectioning of the medial restraints, and (c) following reconstruction of the MPFL. Patellar tracking was measured with a position-sensing system with and without lateral forces applied to the patella. With no lateral force applied to the patella, patellar tracking was unaffected by the presence or absence of the medial restraints or by reconstruction of the medial patellofemoral ligament. With a lateral force applied to the patella (as occurs in vivo) patellar tracking was changed significantly by the loss of the medial restraints. Normal patellar tracking was substantially restored by reconstruction of the medial patellofemoral ligament.

Comment by Mark Miller, MD

Although many sports medicine physicians have probably never heard of the MPFL, this article provides an opportunity to review recent literature regarding this important structure. The MPFL was described in detail and was found to be the major medial soft tissue restraint to lateral patellar displacement by Conlan et al in 1993.1 In a follow-up study at Duke University, 15 of 16 patients with acute patellar dislocations were found to have a torn MPFL upon surgical exploration. Surgical repair in these 15 patients resulted in no episodes of recurrent dislocation.2 Sallay et al also described the MRI findings of MPFL injury. The concept has been extended by one of the current authors (Burks3) and others for reconstruction of this ligament in cases of recurrent dislocation. In my own clinical experience, I have been impressed with the remarkable improvement in patellar tracking (viewed arthroscopically from a far proximal medial portal) following acute MPFL repair. I have also been interested in extending the indications to patients with recurrent dislocations, and we have performed MPFL imbrications in select patients with good initial success.

The present study demonstrates that reconstruction of this ligament (in this case, with a free gracilis tendon graft) can substantially restore normal patellar tracking. This has important implications for patients with recurrent patellar dislocations, and may change the way that we address this difficult problem. Long-term clinical follow-up studies may help us to be more successful in restoring normal patellar tracking in patients with recurrent patellar instability.

References

1. Conlan T, et al. Evaluation of the medial soft-tissue restraints of the extensor mechanism of the knee.J Bone Joint Surg Am 1993;75:682-693.

2. Sallay PI, et al. Acute dislocation of the patella. A correlative pathoanatomic study. Am J Sports Med 1996; 24:52-60.

3. Burks RT, Luker MG. Medial patellofemoral ligament reconstruction. Tech Orthopaedics 1997; 12:185-191.