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Biomechanical Evaluation of the Depth of Resection During Femoral Neck Osteoplasty for Anterior Impingement Following Slipped Capital Femoral Epiphysis

Dale, Kevin M., MD*; Burns, Geoffrey T., MS; Li, Ying, MD*

Journal of Pediatric Orthopaedics: July 2019 - Volume 39 - Issue 6 - p 275–281
doi: 10.1097/BPO.0000000000000956
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Background: Femoroacetabular impingement as a result of slipped capital femoral epiphysis (SCFE) has been treated traditionally with a proximal femoral osteotomy, but open and arthroscopic femoral osteoplasty is becoming increasingly popular. Cam lesions result from excess bone primarily at the anterolateral femoral head-neck junction. SCFEs result from posterior and inferior slippage of the femoral epiphysis, causing the metaphysis to move anteriorly. This study’s purpose was to compare fourth-generation sawbones standard femurs with SCFE femurs to determine whether bone resection from the anterior metaphysis results in similar biomechanical properties.

Methods: A custom fourth-generation composite SCFE sawbone was created with a 30-degree slip angle. Control group consisted of fourth-generation composite standard nondeformed medium femurs. The femoral neck at the head-neck junction was divided into 4 quadrants. All resections were done in the anterolateral quadrant. Twenty SCFE sawbones and 20 standard sawbones were divided into 4 subgroups based on resection depths of 0%, 10%, 30%, and 50% of the metaphysis at the head-neck junction. After resection, all proximal femurs were loaded to failure in an Instron testing machine to determine the ultimate load to failure, stiffness, and energy to failure.

Results: The standard femurs were significantly stronger than the SCFE femurs (P<0.001) and the strength of the femurs decreased significantly as the resection amount increased (P<0.001). Similarly, the standard femurs withstood significantly more energy before failing than the SCFE femurs (P<0.001) and the energy to failure decreased significantly with varying resection amounts (P<0.001).

Conclusions: SCFE femurs demonstrate a significant reduction in strength and energy to failure after osteoplasty compared with nondeformed femurs in a sawbone model. Strength and energy to failure are inversely proportional to the depth of bone resection.

Clinical Relevance: Aggressive femoral neck osteoplasty for treatment of a SCFE deformity may lead to increased risk of fracture. Further studies are necessary to determine the safe depth of resection in a clinical setting.

*Department of Orthopaedic Surgery, C.S. Mott Children’s Hospital

Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, MI

K.M.D.: study design, grant approval, biomechanical testing, and drafting final work. G.T.B.: study design, grant approval, biomechanical testing, statistics, and editing work. Y.L.: study design, grant approval, biomechanical testing, and editing work.

Supported by a grant from the University of Michigan, Department of Orthopaedic Surgery Research Advisory Committee.

The authors declare no conflicts of interest.

Reprints: Kevin M. Dale, MD, Department of Orthopaedic Surgery, C.S. Mott Children’s Hospital, University of Michigan, 1540 E. Hospital Drive, SPC 4241, Ann Arbor, MI 48109-4241. E-mail: kevin.m.dale@vanderbilt.edu.

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