Rectus-sparing approach to the periacetabular osteotomy in adolescents preserves hip flexion strength

Abstract

Purpose The classic periacetabular osteotomy (PAO) approach can result in hip flexor weakness in adolescents. The rectus-sparing approach (PAO-RS) preserves the origin of the rectus femoris tendon which may prevent hip flexor weakness and improve functional outcome. Methods This is a prospective analysis of adolescents treated with a PAO or PAO-RS. The PAO group included 24 hips/21 patients (18 female, meanage 16 years (sd 4)); the PAO-RS group included ten hips (eight female, mean age 16 years (sd 1)). Preoperatively, the PAO group had decreased hip flexion strength compared with the PAO-RS group (83 Nm/kg versus 102 Nm/kg). A subset of PAO patients (n = 13 hips/12 patients, nine female, mean age 15 years (sd 3)) were matched for preoperative flexion strength to the PAO-RS group. Radiographic parameters, modified Harris hip score (mHHS), isokinetic hip strength and instrumented motion analysis preoperatively, six months and one-year postoperatively were compared. Results There were no differences in preoperative deformity, postoperative correction or degree of correction between groups. Hip flexor strength decreased significantly at six months in the PAO group compared with the PAO-RS group (-35 Nm/kg versus -7 Nm/kg; p = 0.012), as did hip flexion pull-off power (1.33 W/kg PAO versus 1.76 W/kg PAO-RS; p = 0.010). Hip flexion strength improved from six months to one year in the PAO group, with no significant differences in strength at one year between groups (80 Nm/kg versus 90 Nm/kg). There were no differences between groups in mHHS any time point; both groups improved significantly postoperatively. Conclusion Preserving the rectus femoris may lead to improved short-term hip flexor strength and pull-off power. Further assessment at long-term follow-up is needed to determine if this strength leads to improved functional outcomes. Level of Evidence II