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Biomechanical Comparison of Patellar Fixation Techniques in Medial Patellofemoral Ligament Reconstruction: A
Bryan Khoo1, Henry B G Baird2, Jude Alawa3
1Pediatric Orthopaedic Surgery, Stanford University, Stanford, California, USA.
Background:
The biomechanical properties of different medial patellofemoral ligament (MPFL) reconstruction (MPFLR) techniques have been described in adult cadaveric models. However, little is known about the biomechanical properties of these techniques in pediatric specimens.
Purpose:
To (1) evaluate the biomechanical fixation strength of pediatric patellae in the context of MPFLR and (2) compare the performance of suture-anchor (SA) and bone-tunnel (BT) patellar fixation.
Study Design:
Controlled laboratory study.
Methods:
Ten pediatric cadaveric patellae from 6 donors (3 male and 3 female, mean 9.8 + 0.75 years, range 9-11 years) were utilized. For the all-SA group, two 1.8-mm all-SA, each loaded with sutures, were placed on the medial side of the patella at the articular cartilage margin. For the BTs, two 2-mm tunnels were drilled from the medial side of the patella to the anterior patellar surface. No. 2 braided suture was then passed through the tunnels. Both constructs were loaded into a servomechanical testing apparatus, and a suture was tied to the top frame such that pullout would be in the same plane as the fixation construct, oriented to approximate the plane of the native MPFL insertion.
Results:
BT constructs demonstrated a mean ultimate failure load of 169.8 ± 88.6 N, significantly higher than the 55.3 ± 20.1 N observed for SA constructs (P = .002). No significant difference in stiffness was found between BT (6 ± 1.9 N/mm) and SA (6.4 ± 1.7 N/mm; P = .647). The mechanisms of failure were anchor pullout for all SAs and suture cheese-wiring for all BTs.
Conclusion:
In this pediatric cadaveric model, BT fixation demonstrated higher ultimate failure loads than the SA fixation, while construct stiffness was similar between techniques.
Clinical Relevance:
To our knowledge, this is the first biomechanical study of MPFL patellar fixation reconstruction techniques performed in pediatric specimens. To reduce the risk of patellar graft fixation failure, the relatively low load-to-failure of all-SA fixation demonstrated in this study may be considered when treating pediatric patients with lower bone density. Moreover, biomechanically superior small-diameter oblique BTs with low fracture risk may be considered to maximize time-zero fixation strength compared with SAs in the pediatric population. However, these results are limited by evaluating only a single all-SA design and a testing methodology that focused on time-zero fixation strength, without cyclic loading or in vivo healing.