A Biomechanical Comparison of Patellar Fixation Techniques in Medial Patellofemoral Ligament Reconstruction.

BACKGROUND

Graft loosening/rupture or iatrogenic patellar fractures after medial patellofemoral ligament reconstruction (MPFLR) can result in continued anterior knee pain and recurrent patellar instability that may necessitate revision surgery. Interference screw fixation at the patellar-graft interface has been associated with higher rates of iatrogenic patellar fractures than suture anchor fixation.

PURPOSE: To biomechanically compare interference screw versus suture anchor fixation of a semitendinosus graft to the patella.

STUDY

DESIGN

Controlled laboratory study.

METHODS

Eight pairs of human cadaveric patellae (16 total specimens) were harvested along with their corresponding semitendinosus autografts. Matched pair specimens were assigned to 2 groups: 8 specimens underwent graft fixation to the patella using 2 parallel 3-mm BioComposite SutureTak suture anchors, and 8 specimens underwent graft fixation to the patella using 2 parallel 3.9-mm BioComposite Swivelock interference screws. Constructs underwent biomechanical testing to compare displacement after cycling, stiffness, ultimate load to failure, and mode of failure.

RESULTS

There was no significant difference in mean displacement after cycling between the interference screw (5.44 ± 1.22 mm) and suture anchor groups (6 ± 1.64 mm) (P = .47). The interference screw had a significantly lower mean ultimate failure load (153.4 ± 81.5 N) than the suture anchor group (281.56 ± 81.5 N) (P = .008). There was no significant difference in mean stiffness between the suture anchor (48.22 ± 20.75 N/mm) and interference screw groups (52.18 ± 13.24 N/mm) (P = .67).

CONCLUSION

Suture anchor fixation (3 mm) of a semitendinosus graft to the patella failed at significantly higher ultimate tensile loads than interference screw fixation (3.9 mm). There was no difference in displacement or stiffness after cyclic loading. This information should be helpful to surgeons seeking to avoid drilling tunnels in the patella.

CLINICAL RELEVANCE: Suture anchor fixation at the patella-graft interface in MPFLR provides a biomechanically stronger construct with less patella violation compared with interference screws. This may make it the preferred option for MPFL graft fixation on the patella.