Biomechanical comparison of patellar fixation techniques in medial patellofemoral ligament reconstruction.

BACKGROUND

Multiple techniques for reconstruction of the medial patellofemoral ligament (MPFL) have been described; however, little is known about the biomechanical properties of these techniques. Fixation of the graft to the patella has not been studied in a human cadaveric model.

HYPOTHESIS/PURPOSE: The purpose of this study was to compare the ultimate failure load and stiffness of 2 different MPFL patellar fixation techniques: suture anchor fixation and interference screw fixation. The null hypothesis was that the suture anchor group would show no difference in the ultimate failure load and stiffness compared with the interference screw group.

STUDY DESIGN

Controlled laboratory study.

METHODS

Reconstruction of the MPFL with semitendinosus autografts was performed in 8 pairs of fresh-frozen cadaveric knees (16 knees total; mean age, 55.8±7.7 years). The specimens were randomly assigned to 2 groups of 8 specimens each based on the method used to fix the graft to the medial patella: suture anchor or interference screw fixation. Each reconstruction technique was performed on 1 knee from the same cadaveric specimen. Suture anchor reconstruction was completed with 2 parallel 3.0-mm biocomposite suture anchors. Interference screw fixation was accomplished with two 4.75-mm biocomposite interference screws docked in parallel tunnels. The reconstructions were cyclically loaded for 10 cycles to 30 N and then tested to failure at a constant displacement rate of 6 mm/s with a line of pull parallel to the anchors or interference screws. Ultimate failure load (N), stiffness (N/mm), and mode of failure were recorded for each specimen.

RESULTS

The suture anchor group had a significantly lower mean failure load (201.54±63.14 N) than the interference screw group (299.25±99.87 N) (P=.007). The suture anchor group also had significantly lower mean stiffness (20.60±6.78 N/mm) compared with the interference screw group (34.66±10.74 N/mm) (P=.007). The most common mode of failure in the suture anchor group was failure at the graft-suture interface. In the interference screw group, the most common mode of failure was the tendon graft pulling out of the tunnel.

CONCLUSION

Interference screw fixation to the medial patella was found to be significantly stronger than suture anchor fixation when comparing the ultimate failure load and stiffness.

CLINICAL RELEVANCE

This study compares the biomechanical properties of 2 commonly used methods for patellar graft fixation in MPFL reconstruction surgery. It supports the use of interference screw fixation based on the ultimate load and stiffness, although suture anchor fixation may be sufficient when compared with the native MPFL based on previously published data.