EP1.88 Low Nonunion Rates with a Lateralized Fitted-Wedge Superior Pubic Ramus Osteotomy During Bernese Periacetabular Osteotomy

Abstract

Despite favorable clinical outcomes, one of the most common complications during Bernese periacetabular osteotomy (PAO) is nonunion of the superior pubic ramus (SPR). Non-union of this osteotomy occurs more often in comparison to the other osteotomy sites, and SPR nonunion may predispose patients to inferior pubic ramus (IPR) stress fractures and, in some cases, reoperation. Identified risk factors for SPR nonunion include: (1) increasing severity of dysplasia, (2) increased age and body mass index at the time of surgery, and (3) a more medial location of the SPR osteotomy site. Modifications in intraoperative techniques have therefore been proposed to mitigate the risk of SPR nonunion following PAO. During the SPR osteotomy utilizing the fitted-wedge osteotomy, two cuts are made with a Midas Rex burr, leaving the inferior portion of the ramus intact. The first cut is typically parallel to the ilioschial line and divides the anterosuperior and posterior cortices. The second cut is a variable distance (range=3-12 mm) from the first cut and dependent on the intended medialization of the acetabular fragment. The second cut goes through the anterosuperior cortex, but not through the posterior cortex. A narrow straight osteotome is then used to osteotomize the inferior portion of the ramus. The pituitary rongeur is then used to remove the inferior portion of the ramus and create a greenstick fracture of the posterior cortex which is hinged medially. The overall complication rate for this cohort of 137 hips utilizing the modified SPR osteotomy was 8.03%. Specific complications included 2 cases of SPR non-unions (1.5%) and 2 cases of surgically addressed heterotopic ossification (1.5%). Infections occurred in 4 patients (2.9%) and venous thromboembolism was observed in 1 patient (0.7%). Two postoperative fractures (1.5%) were identified, both of which were inferior pubic ramus fractures in the setting of SPR non-union. There were no fixation failures (0%) or peripheral nerve injuries (0%). The fitted wedge technique allows for a more cancellous osteotomy in the lateral ramus that allows for improved bone healing quality, increased acetabular medialization, and decreased ramus deformity postoperatively while providing very low rates of common PAO complications.