Kinematic evaluation of isolated and combined medial patellofemoral and patellotibial ligament reconstruction to address lateral patellar instability

OBJECTIVES: The roles of the medial patellofemoral and patellotibial ligaments in patellofemoral kinematics have been previously reported. However, the effect of isolated and combined surgical reconstruction of these ligaments to restore native patellofemoral kinematics is not well understood. The purpose of this study was to determine the isolated and combined effects of medial patellofemoral and patellotibial ligament deficiency and reconstruction on patellofemoral kinematics. METHODS: Sixteen matched-paired female, fresh-frozen, cadaveric knee specimens with a mean age of 53.5 years (range, 26-65) were used. Specimens were tested in five conditions; 1) intact, 2) MPFL or MPTL cut, 3) MPFL and MPTL combined cut, 4) MPFL or MPTL reconstruction, and 5) MPFL and MPTL combined reconstruction. Dynamic testing was performed by taking the knees through range of motion from 0° to 90° of knee flexion at 60 mm/min using a dynamic tensile testing machine by applying a force through the quadricep tendon. Following dynamic testing, knees were tested statically using a lateral load of 45 N applied to the patella at 0°, 30°, 60°, and 90° of flexion. In both dynamic and static loading tests, a motion capture system detected patellar position for each testing state to distinguish changes in patellar kinematics. Linear mixed effects modeling was performed to compare testing states. RESULTS: Isolated MPFL deficiency created the greatest lateral translation of the patella at all knee flexion angles (p<0.001). MPTL deficiency alone did not create significant patella instability (p=0.68 or greater), but further increased instability when the MPFL was deficient (p<0.001). Isolated MPFL and combined MPFL and MPTL reconstruction decreased lateral patella translation (p<0.001). Native patella tracking was best recreated with combined ligament reconstruction while MPFL reconstruction alone over constrained the patella in extension and under constrained in flexion. CONCLUSIONS: The MPFL plays the greatest role in medial patellar stability, but the MPTL appears to have a large influence on patella tracking. The MPTL may be most important in preventing patellofemoral osteoarthritis following patella dislocation. Further investigation is needed to evaluate patellofemoral contact pressure following medial patellar ligament reconstruction.