A malpositioned femoral tunnel or overtensioned graft during MPFL reconstruction resulted in increased medial contact pressures and patellar tilting. This may lead to adverse outcomes such as early degenerative joint changes or pain if occurring in a clinical population.

Medial patellofemoral ligament (MPFL) disruption may alter patellofemoral joint (PFJ) kinematics and contact mechanics, potentially causing pain and joint degeneration. In this controlled laboratory study, we investigated the hypothesis that MPFL transection would change patellar tracking and PFJ contact pressures and increase the distance between the attachment points of the MPFL. Eight fresh frozen dissected cadaveric knees were mounted in a rig with the quadriceps and ITB loaded to 205 N. An optical tracking system measured joint kinematics, and pressure sensitive film between the patella and trochlea measured PFJ contact pressures. Length patterns of the distance between the femoral and patellar attachments of the MPFL were measured using a suture led to a linear displacement transducer. Measurements were repeated with the MPFL intact and following MPFL transection. A significant increase in the distance between the patellar and femoral MPFL attachment points was noted following transection (p < 0.05). MPFL transection resulted in significantly increased lateral translation and lateral tilt of the patella in early flexion (p < 0.05). Peak and mean medial PFJ contact pressures were significantly reduced and peak lateral contact pressures significantly elevated in early knee flexion following MPFL transection (p < 0.05). MPFL transection resulted in significant alterations to PFJ tracking and contact pressures, which may affect articular cartilage health. The medial patellofemoral ligament (MPFL) is the most important patellofemoral joint (PFJ) stabilizer from 0 to 30˚of knee flexion, contributing 50-60% of the passive resistance to patellar lateral translation.1-4 Patellar dislocation as a consequence of trochlear dysplasia and patella alta were previously highlighted in the literature.5-7 Given its anatomic position, lateral patellar dislocation will almost always damage the MPFL. 8Rupture of the MPFL occurs in 95-100% and injury in 100% of patients suffering patellar dislocation.9-11 PFJ dislocation is linked to the development of abnormal contact stress and joint degeneration. 12,13 This, alongside reports of recurrent instability rates >50% with non-operative management, 14 have perhaps contributed to the recent increase in primary management with operative MPFL repair. 15,16 Given the high levels of patient dissatisfaction following patellar dislocation, the associated incidence of MPFL rupture, and the link to joint degeneration, we hypothesized that MPFL transection would allow the patella to track more laterally than normal, and that this would lead to elevated articular contact pressure on the lateral facet of the PFJ. MATERIALS AND METHODS Specimen PreparationFive male and three female right-sided, fresh-frozen cadaveric knees of mean age 73.5 years (range: 46-88) were obtained from a tissue bank, following approval from a local Research Ethics Committee. Each specimen was cut to 20 cm of femur and 15 cm of tibia, with no deformity apparent on visual inspection. Specimens were stored at À2...

Lateral patellofemoral joint contact pressures increased with progressive lateralization of the TT; medialization of the TT reduced these effects, restoring patellar stability, and did not cause excessive peak pressures. These data provide a rationale for medial TT transfer surgery in patients with elevated TT-TG distances.

This provides guidance to surgeons as to the threshold at which MPFL reconstruction may satisfactorily restore patellofemoral mechanics, beyond which more invasive surgery such as TT transfer may be indicated.