Abstract
Introduction
The medial patellofemoral ligament (MPFL) is the main stabilizer of the patella and therefore mostly reconstructed in the surgical correction of patellofemoral dislocation. Various biomechanical and clinical studies have been conducted on MPFL reconstruction, while the patellofemoral contact pressure (PFCP) which is indicated as one of the predictors of retropatellar osteoarthritis was neglected. Therefore, the aim of this study was to investigate how different MPFL reconstruction approaches affect PFCP.
Material & Methods
After radiographic examination and preparation six human cadaveric knee joints (52.1 ± 8.4yrs) were placed in a 6-DOF knee simulator. Three flexion-extension cycles (0–90°) were applied, while the extensor muscles (175N) and an axial joint load (200N) were simulated. PFCP was measured in knee flexion of 0°, 30° and 90° using a calibrated pressure measurement system (K-Scan, Tekscan Inc., USA). The following MPFL conditions were examined: native (Pnat), anatomical reconstruction (Pa), proximal and distal patellar single-bundle reconstruction (Pp, Pd), proximal and ventral femoral reconstruction (Fp, Fv). The cohesive gracillis graft of each knee was used for MPFL reconstruction. Further, the effect of three different graft pre-tensioning levels (2N, 10N, 20N) on the PFCP were compared. Nonparametric statistical analysis was performed using SPSS (IBM Inc., USA).
Results
In 0° knee flexion median PFCP of the native state (Pnat=0.46MPa) was significantly higher (p=0.04) compared to the ventral femoral fixation state (Fv=0.24MPa). No significant differences were observed in 30° knee flexion. In 90° knee flexion PCFP of both femoral reconstructions (Fp=1.26MPa, Fv=1.12MPa) were significantly higher (p<0.04) compared to the native state (Pnat =0.43MPa). Graft pre-tensioning had no significant impact (p>0.27) on the PFCP in 0°, 30° and 90° knee flexion for all pre-tensioning levels.
Discussion
We investigated the PFCP of different MPFL reconstructions and compared them during continuous joint motion from 0° to 90° knee flexion. While a non-anatomical graft fixation on the femoral side leads to an excessive increase of PFCP (293%), a non-anatomical positioning on the patellar side only showed minor impact on the PFCP. An anatomical MPFL reconstruction showed comparable PFCP to the native joint. In contrast to the literature, we did not find a significant influence of graft pre-tensioning from 2N up to 20N on the PFCP. With respect to all study findings we would recommend to use the anatomical footprints for MPFL reconstruction and a moderate graft pre-tensioning of 2N.
