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

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 (mm) 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.