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Biomechanical Comparison of All-Suture Anchors Versus Interference Screws for Femoral Fixation in Pediatric MPFL
Amin M Alayleh1, Austin Stoner1, Ian Hollyer1
1Department of Orthopaedic Surgery, Stanford University School of Medicine, San Francisco, California, USA.
Background:
Pediatric patellofemoral instability is common, and medial patellofemoral ligament (MPFL) reconstruction is a highly effective treatment option. Femoral graft fixation methods include suture anchors (SAs) and interference screws (ISs), although comparative biomechanical studies in pediatric bone are lacking.
Purpose:
To compare the biomechanical properties of SA versus IS femoral graft fixation in pediatric MPFL reconstruction.
Study Design:
Controlled laboratory study.
Methods:
Ten fresh-frozen pediatric knees underwent femoral MPFL graft fixation using SA and IS (mean age, 9.5 years; range, 8-10 years). Posterior tibialis tendon allograft was used in both groups. For the IS group, 8-mm tunnels were drilled and 8 × 25-mm biocomposite IS was used for graft fixation. For the SA group, a 1.8-mm knotless all-suture SA was placed and secured to the graft. Specimens were loaded onto an Instron 5944 and subjected to cyclic preconditioning, followed by an ultimate failure load at 6 mm/s. The load displacement curve was then used to calculate stiffness (N/mm). Data were analyzed using repeated-measures analysis of variance to account for multiple measurements on the same specimens.
Results:
IS graft fixation demonstrated significantly higher ultimate failure load than SA (246.4 ± 79.7 N vs 90.4 ± 20.6 N, P < .001). Similarly, stiffness was significantly greater for IS compared to SA (17.8 ± 4.1 N/mm vs 13.4 ± 2.2 N/mm, P = .009). All but 1 IS reconstruction failed by graft pullout from the femoral tunnel, whereas all 10 SA reconstructions failed by anchor pullout.
Conclusion:
IS offers significantly higher ultimate failure load and stiffness values compared to SA femoral MPFL graft fixation in human pediatric knees. Mean ultimate failure load values for femoral MPFL fixation in pediatric bone may be lower than in adult bone, based on comparative adult studies. These results provide initial biomechanical data comparing 2 commonly used femoral fixation methods in skeletally immature patients.
Clinical Relevance:
This study characterized the biomechanical strength of SA and IS femoral MPFL fixation in pediatric bone, revealing differences in ultimate failure load and stiffness between constructs and compared to adult bone. While SA may pose less risk for growth alteration from physeal injury in younger patients, greater "time-zero" MPFL fixation strength with IS may allow for accelerated rehabilitation and earlier return to sport, which is a key patient and family satisfaction variable. In some circumstances, SA fixation may be preferred due to physeal proximity, and postoperative therapy regimens may be modified to account for lower fixation strength. These findings can help surgeons optimize implant selection, tailor rehabilitation protocols, and minimize the risk of graft failure in skeletally immature patients.
