Offloading Patellofemoral Contact Pressures: A Biomechanical Comparison Between Tibial Tubercle Osteotomy and a...

A novel retropatellar tendon implant (LIFT) that is fixed deep to the patellar tendon proximal to the tibial tubercle may provide patellofemoral offloading benefits.

The purpose of this study was to analyze the patellofemoral contact pressures from 0° to 60° of knee flexion in 3 states: (1) intact knee, (2) knee with the implantation of a retropatellar tendon implant, and (3) knee with a 45° anteromedialization tibial tubercle osteotomy (TTO). It was hypothesized that the implant would significantly reduce the contact pressure between the patella and trochlea compared with the intact state and produce a similar offloading effect as an anteromedializing TTO.

Controlled laboratory study.

Trochlear pressure sensors were placed in 7 cadaveric knees (6 donors). Patellofemoral contact area, contact pressure, peak force, and center of force were measured using a model for native quadriceps force on the patella. On each specimen, measurements were taken in an intact state, after implantation of a novel retropatellar tendon implant, and after a 45° anteromedializing TTO. Force data were collected from 0° to 60° of flexion in 15° increments and normalized to each specimen's intact state.

Compared with the intact and implant groups, the TTO reduced the contact area at 30°, 45°, and 60° of flexion. TTO reduced contact pressure compared with intact from 15° to 60° of flexion, and reduced contact pressure at 15° when compared with the implant. The implant reduced the contact pressure compared with the intact state at 30° and 45° of flexion. For peak force, TTO reduced the force seen in 15° to 60° of flexion compared with the intact condition, while outperforming the implant at 15° of flexion. The implant reduced the peak force compared with the intact condition at 30° of flexion. Center of force analysis revealed that the implant medialized the center of force at 45° and 60° of flexion.

The main finding from our biomechanical cadaveric study was that the novel retropatellar tendon implant did not reduce patellofemoral contact area, contact pressure, and peak force as much as a 45° anteromedializing TTO. The implant does reduce peak and contact pressures in early degrees of knee flexion compared with native states.

An implant that allows for offloading patellofemoral contact pressures without the morbidity, complication profile, or postoperative rehabilitation associated with a TTO may aid in the treatment of patellofemoral chondral lesions and retropatellar knee pain.