The biomechanics of the Medial Patellofemoral Ligament

Abstract

Injury of the Medial Patellofemoral Ligament (MPFL) occurs during patellofemoral joint (PFJ) dislocation. Reconstruction of this ligament is a common treatment for this patient population. This thesis is composed of a series of cadaveric experiments examining the MPFL.

The MPFL was found to originate from the midpoint between the medial epicondyle and adductor tubercle. Its length change pattern was close to isometric through knee flexion range. Transection of the MPFL resulted in significant increases in lateral patellar translation, tilt and increased lateral PFJ contact pressures in early knee flexion (all: P<0.05). Anatomical reconstruction of the ligament restored patellar motion and joint contact pressures (P>0.05). Femoral tunnels positioned too proximal resulted in increased medial contact pressures and patellar motion in deeper knee flexion, whilst distal tunnels caused increased medial contact pressures near extension (P<0.05). Anterior-posterior femoral positioning or varying position of the patellar attachment was not found to have a significant effect on ligament length change patterns (P>0.05). The radiographic femoral MPFL attachment point, assuming the anterior-posterior medial femoral condyle diameter to be 100%, was; 40% from the posterior, 50% from the distal and 60% from the anterior femoral border.

Reduction in medial quadriceps muscle tension was similar to the effect of MPFL transection causing a significant increase of lateral patellar tracking and lateral PFJ contact pressures (all: P<0.05). Progressive tibial tuberosity (TT) lateralisation caused increased lateral patellar tracking, lateral PFJ contact pressures and reduced patellar stability (P<0.05). TT medialisation did not cause corresponding excessive increases in mean medial contact pressures (P>0.05). With tibial tuberosity-trochlear groove (TT-TG) distances of up to 15mm PFJ mechanics were satisfactorily restored with anatomical MPFL reconstruction (P>0.05). However in cases with TT-TG distances greater than 15mm, MPFL reconstruction alone was not sufficient to restore PFJ contact mechanics and patellar kinematics (P<0.05).