3D-PLANNED PERIACETABULAR OSTEOTOMY FOR HIP DYSPLASIA: PERSONALIZED CUTS IMPROVE FEMORAL HEAD COVERAGE, WHILE MINIMIZING FRAGMENT MOVEMENT AND MAXIMIZING BONE OVERLAP

Periacetabular osteotomy (PAO) for hip dysplasia aims to reposition the acetabulum using four surgical cuts, to increase femoral head coverage (FHC). We developed a novel 3D planner to measure CT-based acetabular morphology and simulate PAO cuts, fragment position, and FHC. We evaluated how adjusting location, and orientation impacts FHC and bone contact. We simulated 274 feasible PAOs on four dysplastic hips. Posterior column and ischial cuts were standardised, whilst iliac and pubic cut combinations varied. The slope of the iliac cut was either neutral (aligned to pelvis), exit point 5mm above the entry point (+5), or 5mm below (−5). The slope of the pubic cut was either 90°, 50°, or 70° (medial-to-lateral). Iliac and pubic cuts were simulated 0, 5 and 15mm - distal and medial – to a classic cut. Outcome measures were achieved LCEA, Tönnis, FHC and % bone overlap at the pubic cut. Targets were LCEA >30°, Tonnis angle <10°, and FHC >70% and minimum bone overlap ≥10%. All feasible PAOs resulted in improvement from pre-operative metrics. Personalised cutting planes provided greater benefit than standard planes with less fragment translation/rotation. Superior iliac cuts (+ 5 and +15mm) superior resulted in a greater LCEA and lower Tönnis compared to the classic cut (p<0.05). Medial pubic cuts resulted in greater pubic displacement and lower % overlap (p < 0.01). However, changing location of the pubic cut, and slope of the iliac and pubic cuts did not significantly affect LCEA and Tönnis in all hips (p<0.05). Cut combinations optimising metrics were associated with a lower % pubic cut overlap. 3D-planning enables personalised PAO for hip dysplasia. Iliac cut height had the greatest impact on restoring normal morphology; medializing the pubic cut increased pubic displacement without necessarily improving potential femoral head coverage.