Basic Science
Mechanical Influence of Pubic Nonunion on the Stress Distribution After Curved Periacetabular Osteotomy: Patient-Specific Three-Dimensional Finite Element Analysis

https://doi.org/10.1016/j.arth.2022.02.071Get rights and content

Highlights

  • Mechanical influence of pubic nonunion on the stress distribution after CPO based on patient-specific 3-dimensional finite element models.

  • Increased mechanical stress concentration at the ischial ramus in the pubic nonunion models.

  • Importance of achieving complete union of the pubic ramus to obtain the optimal mechanical ischial ramus stress distribution after CPO.

Abstract

Background

Pubic nonunion after curved periacetabular osteotomy (CPO) reportedly occurs in 1%-17% of patients and causes pubic pain in 21%. Furthermore, pubic nonunion is associated with a risk of ischial ramus stress fracture, but the mechanical influence of pubic nonunion has not been fully clarified.

Methods

Patient-specific finite element (FE) analysis was performed using Mechanical Finder software. Three FE models (pre-CPO, union, and nonunion models) were constructed from preoperative and postoperative computed tomographic data. The contact area (mm2) and contact pressure (MPa) in the hip joint as well as the equivalent stress (MPa) at the ischial ramus were evaluated among the 3 FE models.

Results

Patient-specific FE models were generated using 18 consecutive hips treated with CPO. The mean contact pressure in the hip joint was not significantly different between the union and nonunion models (0.50 ± 0.10 vs 0.50 ± 0.09 MPa, P = .88). However, the mean equivalent stress at the ischial ramus in the nonunion models was 1.7 times higher than that in the union models (1.13 ± 0.77 vs 0.64 ± 0.45 MPa, P < .01).

Conclusion

FE analysis revealed that pubic nonunion did not affect the mechanical distribution in the hip joint itself but increased the mean equivalent stress at the ischial ramus. This finding suggests the importance of achieving pubic union after CPO to avoid the risk of ischial ramus stress fracture.

Section snippets

Materials and Methods

This study was approved by our Institutional Review Board (approval no. 2018M057).

From January to December 2016, CPO was performed in 28 hips of 27 patients for the treatment of symptomatic dysplasia at our hospital. All surgical procedures were performed by 2 surgeons. We excluded 7 hips because postoperative radiographs or postoperative CT scans after CPO were incomplete. We also excluded 3 hips because the osteotomy sites in the pubic ramus exhibited nonunion after CPO.

Preoperative and

Results

This study included 18 consecutive hips (17 patients: 1 male, 16 females) with union of all the osteotomy sites (pubic ramus, ischial ramus, and ilium) on postoperative CT scans after CPO (Fig. 1). Table 1 presents the patients’ demographic data. Patients’ mean age at the time of surgery was 35.5 (range 23.8-44.3) years, and their mean body mass index was 23.4 (range 21.0-25.8) kg/m2. Follow-up postoperative CT scanning was performed at 13.7 (range 10.1-24.6) months.

The mean contact area in the

Discussion

The primary finding of this study was that pubic nonunion did not influence mechanical joint stress distribution in the hip joint. Additional findings of the study included increases in mechanical stress concentration at the ischial ramus.

Computational FE analysis is considered to be useful for the evaluation of mechanical stress distribution and direction in the hip joint as well as in the upper extremities [[9], [10], [11], [12],18]. The accuracy of FE analysis has been proven based on

Conclusion

FE analysis revealed that pubic nonunion did not affect the mechanical distribution in the hip joint itself but increased the mean equivalent stress at the ischial ramus. This finding suggests the importance of achieving pubic union after CPO to avoid the risk of ischial ramus stress fracture.

Acknowledgments

We thank Edanz (https://jp.edanz.com/ac) for editing a draft of this manuscript.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

References (25)

  • J.C. Clohisy et al.

    Periacetabular. osteotomy: a systematic literature review

    Clin Orthop Relat Res

    (2009)
  • N. Espinosa et al.

    Extraarticular fractures. after periacetabular osteotomy

    Clin Orthop Relat Res

    (2008)
  • Cited by (0)

    No author associated with this paper has disclosed any potential or pertinent conflicts which may be perceived to have impending conflict with this work. For full disclosure statements refer to https://doi.org/10.1016/j.arth.2022.02.071.

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