Preservation technique of the piriformis tendon is superior to reattachment technique in terms of contiguity and muscle atrophy: using magnetic resonance imaging

Purpose: The preservation technique of the piriformis tendon during the posterolateral approach in total hip arthroplasty (THA) is reportedly superior to the reattachment technique in terms of dislocation. However, the long-term effects of preservation of the piriformis tendon during THA remain unknown. In this study, we evaluated the contiguity of the piriformis/conjoined tendon and atrophy of the piriformis/internal obturator muscle during a long-term postoperative follow-up using magnetic resonance imaging (MRI). Methods: We retrospectively evaluated 48 patients with available MRI. The 48 patients were classified into a P group (n = 29), in which the piriformis tendon was preserved, and an R group (n = 19), in which the piriformis was reattached after sectioning. The mean follow-up duration was 45.9 months. The contiguity of the piriformis/conjoined tendon and atrophy of the piriformis/internal obturator muscle were evaluated in all patients. Results: The piriformis tendon remained attached to the greater trochanter in all P-group patients and 68.4% of R-group patients. The mean piriformis muscle atrophy ratios were 15.9% ± 21.1% in the P group and 41.6% ± 19.1% in the R group (p < 0.001). The conjoined tendon repair remained intact in 72.4% of P-group patients and 36.8% of R-group patients (p < 0.05). The mean internal obturator muscle atrophy ratio was 31.4% ± 26.2% in the P group and 50.4% ± 19.1% in the R group (p < 0.05). No postoperative pulmonary embolism, wound infection, deep infection, or hip dislocation occurred. Conclusions: In our study, we suggest that the preservation technique of the piriformis tendon is superior to the reattachment technique in terms of contiguity and muscle atrophy.