Understanding recurrent groin pain following periacetabular osteotomy: assessment of psoas tendon mechanics using discrete element analysis.

Recurrent groin pain following periacetabular osteotomy (PAO) is a challenging problem. The purpose of our study was to evaluate the position and dynamics of the psoas tendon as a potential cause for recurrent groin pain following PAO. A total of 386 PAO procedures, performed between January 2013 and January 2020, were identified from a single surgeon series. Thirteen patients (18 hips) had a psoas tendinopathy, as confirmed with relief of symptoms following a diagnostic injection into the psoas tendon. All patients underwent computed tomography (CT) scans pre- and post-operatively. The data from CT scan was used to manually segment bony structures and create 3D models using Mimics software (Materialise NV). A validated discrete element analysis model using rigid body springs was used to predict psoas tendon movement during hip circumduction and walking. The distance of the iliopsoas tendon to any bony abnormality was calculated. All computational analyses were performed using MATLAB software. Thirteen hips (13/18) showed bony malformations (spurs, hypertrophic callus or delayed union and malunion) secondary to callus at the superior pubic ramus. The mean minimal distance of the iliopsoas tendon to osteotomy site was found to be 13.73 mm (σ = 3.09) for spurs, 10.99 mm (σ = 2.85) for hypertrophic callus and 11.91 mm (σ = 2.55) for canyon type. In normal bony healing, the mean minimal distance was 18.55 mm (σ = 4.11). Using a validated computational modelling technique, this study has demonstrated three different types of malformation around the superior pubic osteotomy site, which are associated with psoas impingement. In all of the cases, the minimal distance of the iliopsoas tendon to the osteotomy site was reduced by 59-74%, as compared with the normal anatomy.