Optimising spherical periacetabular osteotomy: a strategy to minimise leg shortening.

Abstract

Spherical periacetabular osteotomy (SPO) preserves pelvic structures but can cause leg shortening due to the upward and outward shift of the centre of rotation. Modified preoperative planning aims to medially shift the acetabular fragment's highest point to reduce leg shortening. This study investigated the fixation state of the rotated bone fragment in SPO, its relationship with leg length, and strategies to prevent leg shortening. Between February 2019 and August 2023, 57 joints in 52 patients undergoing SPO were examined. The postoperative acetabular movement was classified as "contact" or "non-contact" based on whether the proximal osteotomy surfaces of the rotated and host bone made direct contact on postoperative computed tomography scans. Radiographic assessments included leg length, centre-edge (CE) angle, and acetabular roof obliquity (ARO), measured on standardised anteroposterior pelvic radiographs before and after surgery. Average correction angles were 24° for CE and 23° for ARO, with an average leg length change of -1.3 mm (range -14.5-9.7 mm). Contact-type fixation minimised leg shortening, with an average change of 0.3 mm (range -4.7-9.7 mm), and demonstrated better ARO correction. In contrast, non-contact fixation resulted in greater leg shortening, with an average change of -6.1 mm (range -14.5-4.9 mm). Contact-type fixation effectively reduced leg shortening and stabilizsed bone fragments. Conversely, non-contact types allowed greater correction angles but led to increased leg shortening due to instability. Enhanced fixation methods are recommended for non-contact cases to maintain stability.