BACKGROUND: Previous studies on different periacetabular osteotomy approaches for correction of hip dysplasia disagree on the time course of normalisation of muscle function postoperatively, some stating that especially hip flexor function is not fully normalised after 12 months.

PURPOSE: The purpose of this study was to evaluate hip function during walking before, and 6 and 12 months after minimally invasive periacetabular osteotomy.

METHODS: Using conventional 3D inverse dynamics followed by static optimisation, we calculated hip net joint moment and angular impulse, as well as individual muscle forces and hip joint contact force, during walking for 32 patients with hip dysplasia and 32 matched controls.

RESULTS: None of the extensor and abductor measures were significantly different between controls and patients tested preoperatively, nor between any of the 3 time points patients were tested. For all of the flexor measures, patients' preoperative values were lower than controls', but had increased to values above the controls 6 months postoperatively.

CONCLUSION: Hip muscle function during walking seemed normalised after 6 months after minimally invasive periacetabular osteotomy, while joint contact force did not fully normalise until 12 months postoperatively, perhaps because the hip joint structures need a longer time to heal than the muscles and a potential pain alleviating strategy was still in effect.

TRIAL REGISTRY: Movement pattern in patients with hip dysplasia https://clinicaltrials.gov/ct2/show/NCT01344421 , NCT01344421.