Original Article
Mechanical Strength of the Proximal Femur After Arthroscopic Osteochondroplasty for Femoroacetabular Impingement: Finite Element Analysis and 3-Dimensional Image Analysis

https://doi.org/10.1016/j.arthro.2018.03.036Get rights and content

Purpose

To examine the influence of femoral neck resection on the mechanical strength of the proximal femur in actual surgery.

Methods

Eighteen subjects who received arthroscopic cam resection for cam-type femoroacetabular impingement (FAI) were included. Finite element analyses (FEAs) were performed to calculate changes in simulative fracture load between pre- and postoperative femur models. The finite element femur models were constructed from computed tomographic images; thus, the models represented the shape of the original femur, including the bone resection site. Three-dimensional image analysis of the bone resection site was performed to identify morphometric factors that affect strength in the postoperative femur model. Four oblique sagittal planes running perpendicular to the femoral neck axis were used as reference planes to measure the bone resection site.

Results

At the transcervical reference plane, both the bone resection depth and the cross-sectional area at the resection site correlated strongly with postoperative changes in the simulated fracture load (R2 = 0.6, P = .0001). However, only resection depth was significantly correlated with the simulated fracture load at the reference plane for the head-neck junction. The resected bone volume did not correlate with the postoperative changes in the simulated fracture load.

Conclusions

The results of our FEA suggest that the bone resection depth measured at the head-neck junction and transcervical reference plane correlates with fracture risk after osteochondroplasty. By contrast, bone resection at more proximal areas did not have a significant effect on the postoperative femur model strength in our FEA. The total volume of resected bone was also not significantly correlated with postoperative changes in femur model strength.

Clinical Relevance

This biomechanical study using FEA suggest that there is a risk of femoral neck fracture after arthroscopic cam resection, particularly when the resected lesion is located distally.

Section snippets

Subjects and Data Collection

Forty-one consecutive patients who received hip arthroscopy between April 2014 and August 2016 were assessed for eligibility. Twenty-three patients with cam-type FAI remained after exclusion of 12 patients received hip arthroscopy for osteoarthritis and 6 patients with borderline developmental dysplasia of the hip (DDH) without cam deformity. A diagnosis of cam-type FAI was based on the patient's history, physical diagnostic tests (Patrick test and the anterior impingement test),13 and

Results

The characteristics of the study subjects are summarized in Table 1. The average preoperative radiographic alpha angle (61.5° ± 7.6°) was reduced significantly (to 40.6° ± 5.3°) at first postoperative week (P < .001). With respect to patient-reported outcomes, the average preoperative NAHS (64.6 ± 19.3) improved significantly (P = .0005) at the 6-month follow-up (88.1 ± 9.3). The number of subjects with a poor NAHS score (<70 points) fell from 8 (44.4%) to 1 (6.0%).

FE analyses conducted under

Discussion

To investigate the effect of the location of bone resection on the mechanical strength of proximal femur, we combined 2 different approaches: FEA and 3-dimensional image analysis using pre- and postoperative CT image data. The results of our study suggest that bone resection at the distal side of the femoral neck would be more likely to affect the femoral neck strength than bone resection at the proximal side of the femoral neck. The volume of resected bone was not significantly correlated to

Conclusions

The results of our FEA suggest that the bone resection depth measured at the head-neck junction and the transcervical reference plane correlates with fracture risk after osteochondroplasty. By contrast, bone resection at more proximal areas did not have a significant effect on the postoperative femur model strength in our FEA. The total volume of resected bone was also not significantly correlated with postoperative changes in femur model strength.

References (36)

  • A. Trompeter et al.

    Hip arthroscopy for femoroacetabular impingement: Results of 118 consecutive cases in a district general hospital

    Hip Int

    (2013)
  • V.Y. Ng et al.

    Efficacy of surgery for femoroacetabular impingement: A systematic review

    Am J Sports Med

    (2010)
  • J. Gillespie et al.

    Clinical outcome scores for arthroscopic femoral osteochondroplasty in femoroacetabular impingement: A quantitative systematic review

    Scott Med J

    (2015)
  • M.T. Milone et al.

    Novel CT-based three-dimensional software improves the characterization of cam morphology hip

    Clin Orthop Relat Res

    (2013)
  • J.R. Ross et al.

    Residual deformity is the most common reason for revision hip arthroscopy: A three-dimensional CT study

    Clin Orthop Relat Res

    (2015)
  • O.R. Ayeni et al.

    Femoral neck fracture after arthroscopic management of femoroacetabular impingement. A case report

    J Bone Joint Surg Am

    (2011)
  • P.O. Zingg et al.

    Femoral neck fractures after arthroscopic femoral neck osteochondroplasty for femoroacetabular impingement

    Knee Surg Sports Traumatol Arthrosc

    (2014)
  • R.M. Mardones et al.

    Surgical treatment of femoroacetabular impingement: Evaluation of the effect of the size of the resection. Surgical technique

    J Bone Joint Surg Am

    (2006)
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    The authors report that they have no conflicts of interest in the authorship and publication of this article. Full ICMJE author disclosure forms are available for this article online, as supplementary material.

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