Objectives: The purpose of this study was to evaluate the ultimate failure load and stiffness of 2 non anatomic patellar fixation techniques for MPFL reconstruction: (i) quadriceps fixation (QT), (ii) single tunnel (ST) patella fixation with gracilis autograft. These surgical techniques employ a single point of patella fixation in an attempt to recreate the native MPFL anatomy.
A total of 16 fresh-frozen cadaveric knees (8 matched pairs; 5 male, 3 female; mean age 66.22,SD 8.0 years) were used. The specimens were randomized into two groups (8 specimens each). Each group corresponded to different patella fixation technique: QT group vs ST group.
For the biomechanical testing, the patella was stabilized with a custom device that would not injure neither the patella, nor the reconstructed MPFL.
Prior to application of tensile load, the MPFL reconstructions were subjected to cyclic loading for 10 cycles to 30 N to reduce the phenomenon of tissue hysteresis and then tested to failure at a constant displacement rate of 15 mm/min with a traction line parallel to the quadriceps fibers and the tunnel sutures using a materials-testing machine (MTS 810 Universal Testing System). Failure mode, ultimate failure load and stiffness were recorded for each cadaveric specimen.
There was no significant difference in mean ultimate failure load among groups (p=0.41). The ST group failed at a mean ultimate load of 190.113 N (SD 42.289 N) and the QT group failed at 201.014 (SD 51.625N).
The ST group had a mean stiffness of 21.711 N/mm (SD 3.457). This was not significantly higher than the mean stiffness value achieved for QT group 19.218N/mm (SD 8.263) (p<0.05). In the QT group all the reconstructions failed due to tendon rupture at the patella attachment. The most common reason for failure in the ST group occurred in the graft-suture connection.
This cadaver study showed no statistically significant difference in biomechanical performance of the evaluated patella fixation techniques, in terms of maximum load to failure and stiffness. Both techniques are reliable in terms of biomechanical properties and could offer additional surgical solutions.