Biomechanical tensile strength analysis for medial patellofemoral ligament reconstruction
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.
Section snippets
Cadaver preparation
Six matched pairs of fresh, frozen cadaver knees with an average age of 60 ± 2.2 years were used. Each knee was thawed at four degrees Celsius over a span of 48 h prior to joint preparation. The experiment was performed over a period of 24 h. Therefore, each knee was thawed for a maximum of 72 h.
The knees were prepared in a similar manner as that described by Mountney et al. [13] The skin and subcutaneous tissue were removed 10 cm proximal to the proximal pole of the patella and inferior to the tibial
Results
The results demonstrating 50% and 100% displacement of the patella from the trochlea, and peak force at failure of the fixation are summarized in Figure 11, Figure 12, Figure 13, respectively. These forces are presented in comparison with the native MPFL strength, which was previously found to be 208 N [13], [22], [23].
All methods of MPFL reconstruction, when compared against each other and the native strength of the MPFL (208 N), demonstrated significantly different strengths when examined for
Discussion
Three different methods of MPFL reconstruction (SC-F/SC-P, IS-F/SC-P and SC-F/IS-P), each employing suspensory cortical fixation, were demonstrated to be stronger than the native MPFL. Of these three fixation methods, SC-F/IS-P required the highest average force to failure. Furthermore, the weakest form of fixation, which was significantly weaker than the native MPFL, was SC-F/SA-P.
This is not the first study to demonstrate a method of MPFL reconstruction stronger than the native MPFL [21].
Limitations
A limitation of this study was that not all current techniques of MPFL reconstruction were examined. Some recent techniques have been developed in the hope of decreasing the complications of postoperative patella fracture [36]. Patellar fracture has been reported in the literature as a postoperative complication and is likely the result of the bone tunnels drilled in the patella [37], [38]. However, patellar fractures have occurred following an MPFL reconstruction when bone tunnels were not
Conclusion
Suspensory cortical fixation is an acceptable option for use in MPFL reconstructions. Biomechanically, suspensory cortical fixation femur and interference screw patella provides the strongest form of MPFL reconstruction. Furthermore, it was demonstrated that human gracilis allograft could withstand forces greater than the native MPFL.
Presentations
Society of Military Orthopaedic Surgeons
“Biomechanical Tensile Strength Analysis of Current Techniques for Medial Patellofemoral Ligament Reconstruction” (podium presentation). December 15–19, 2014.
Arthroscopy Association of North America (AANA)
“Biomechanical Tensile Strength Analysis of Current Techniques for Medial Patellofemoral Ligament Reconstruction” (podium presentation). May 3–5, 2014.
Southern Orthopedic Association (SOA)
“Biomechanical Tensile Strength Analysis of Current Techniques for
Acknowledgments
This study was in part supported by Arthrex Inc., Naples, Florida, Study Number 301 “Fixation of Strength in MPFL Reconstruction”.
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2024, Arthroscopy, Sports Medicine, and RehabilitationInterference Screws Are Biomechanically Superior to Suture Anchors for Medial Patellofemoral Ligament Reconstruction: A Systematic Review and Meta-Analysis
2022, Arthroscopy, Sports Medicine, and RehabilitationCitation Excerpt :Six studies, including a total of 108 cadaveric specimens, met inclusion criteria for MPFL patellar fixation and 3 studies, including a total of 50 cadaveric specimens, met inclusion criteria for MPFL femoral fixation. These studies are summarized in Table 1.4,11-18 Two of the 6 studies reporting on patellar fixation used bovine extensors of the foot.12,13
Medial Patellofemoral Ligament Reconstruction and Lateral Retinacular Lengthening from a Lateral Approach
2021, Arthroscopy TechniquesCitation Excerpt :Interference screw graft fixation, when used for MPFL reconstruction, can cause overtensioning, undertensioning, graft damage, screw migration, and screw prominence. With an adjustable loop cortical button system, we have the advantage of minimizing or eliminating these potential interference screw-related complications, without sacrificing the adequate strength necessary to reconstruct the MPFL.18 This system is further advantaged with the lateral incision because it allows the button to be secured on the lateral femur under direct visualization and negate the risks of deployment on the iliotibial band or incomplete passage through the distal femur.
Medial Patellofemoral Ligament Reconstruction and Lateral Retinacular Lengthening in the Skeletally Immature Patient
2020, Arthroscopy TechniquesCitation Excerpt :The only modification from what would be done for a skeletally mature patient is the trajectory of the femoral tunnel. Thus, an anatomic reconstruction with suspensory cortical fixation is performed, which has been shown to have superior biomechanical strength and can allow for early and aggressive rehabilitation.20 It is our observation that if attention is paid to anatomic and radiographic landmarks during the case, a safe femoral tunnel can be drilled completely across the epiphysis that does not violate the physis, intercondylar notch, or articular cartilage and provides an anatomic placement of the graft.