Biomechanical tensile strength analysis for medial patellofemoral ligament reconstruction

Abstract

Background

Medial patellofemoral ligament (MPFL) reconstruction is a surgery for acute and chronic dislocating patella. Several surgical techniques have been described. No biomechanical study has compared suture anchors, interference screws, and suspensory cortical fixation for MPFL reconstruction using human gracilis allograft.

Methods

Twelve human cadaver knees were used for the analysis of five MPFL reconstruction techniques on the femur (F) and patella (P): suspensory cortical (SC), interference screw (IS) and suture anchor (SA) fixation (SC-F/SC-P, SC-F/IS-P, SC-F/SA-P, IS-F/SC-P, IS-F/IS-P). Each method was examined six times, each using a new human gracilis allograft. The force necessary for 50% patellar displacement and 100% patellar displacement were recorded for each method. Additionally, we examined the peak force to fixation failure for all methods. Patella dislocation or loss of fixation was considered failure.

Results

SC-F/SC-P, IS-F/SC-P, and SC-F/IS-P required force to failure greater than that of the native MPFL. The SC-F/IS-P required the largest force to failure. The SC-F/SA-P fixation technique required significantly less force to failure (P < 0.05) than the native MPFL and significantly less force to failure (P < 0.05) than all four other fixation techniques. All methods of fixation employing an interference screw failed secondary to graft pullout at the interference screw-bone interface. Methods employing suture anchors and two suspensory cortical fixations failed at the graft-suture anastomosis.

Conclusion

SC-F/SC-P, IS-F/SC-P, and SC-F/IS-P fixations were found to be stronger than the native MPFL, with the strongest being SC-F/IS-P.

Introduction

Lateral dislocation of the patella is an injury appreciated in both athletes and non-athletes, and is often associated with disruption of the medial patellofemoral ligament (MPFL) [1], [5]. The MPFL is critical for patellofemoral stability, provides 50–60% of passive medial resistance, and helps maintain the patella within the trochlear groove [5], [6], [7].

Medial patellofemoral ligament ruptures usually occur at the femoral origin during lateral dislocation of the patella [5]. Traumatic acute patellar dislocation is often associated with sports and physical activities, typically occurring in terminal extension with an axial-valgus stress on the knee during rotation [4]. The patella may dislocate as the femur rotates internally and the tibia rotates externally with the foot fixed on the ground [4]. Disruption of the MPFL is reportedly involved in > 90% of such injuries [8].

Findings after an MPFL disruption may include the following: tenderness over the MPFL, specifically at the femoral origin; positive J sign, indicating patella maltracking; positive tilt test with increased lateral retinacular tightness; and positive apprehension test, inducing an uncomfortable sensation of dislocation [1], [2], [3], [5], [9]. Patients with recurrent dislocation or subluxation may report either diffuse knee pain when using stairs or intermittent feelings of knee instability [9]. Painful symptoms of chronic instability commonly result from non-operative management of MPFL injuries [9]. Additionally, an estimated 15–45% rate of re-dislocation may be seen in patients treated non-operatively following primary patellar dislocation [10]. Thus, surgical reconstruction is indicated for persistent or recurring instability, dislocation, and knee pain [5]. The need for MPFL reconstruction has become more apparent with increasing knowledge of its role in maintaining patellar stability [10]. The use of soft tissue restraints to restore lateral patellar stability was initially described by Galeazzi [11].

Multiple surgical techniques have been outlined to address patellar instability, including: Q-angle correction with osteotomy, trochleoplasty, lateral release, MPFL repair, MPFL reconstruction, and medial plication [1], [5], [12]. Multiple techniques and approaches have also been described in the literature for MPFL reconstruction [1], [5]. Reconstructions using the gracilis, semitendinosus, adductor magnus, quadriceps tendon, and synthetic tissue have all been described, as have numerous methods of fixation [13], [14], [15], [16], [17], [18], [19].

Several studies have been performed to assess the strongest biomechanical reconstruction of the MPFL [13], [19], [20], [21]. However, none of these studies assessed suspensory cortical fixation and one demonstrated a fixation method greater than the strength of the native MPFL [20]. Additionally, no biomechanical study, to date, has examined the fixation strength of MPFL reconstruction using human gracilis allografts [19].

The purpose of the present study was to examine the fixation strength of MPFL reconstruction using human gracilis allograft and current fixation methods. It was hypothesized that the use of suspensory cortical fixation would demonstrate a method of fixation stronger than that of the native MPFL.