Hip dysplasia in patients undergoing total hip arthroplasty in a major centre in New Zealand

aim: The aim of this study was to determine the absolute number of total hip arthroplasties (THA) performed in a single centre for patients whose pre-operative radiographs demonstrated evidence of hip dysplasia. methods: We retrospectively analysed 317 consecutive primary THA cases at Dunedin Hospital. Pre-operative radiographs were reviewed using standardised measurements: lateral centre-edge angle (LCEA), Tönnis angle (TA), acetabular quotient (AQ) and crossover sign. results: Overall, 21% had dysplastic TA (>10 degrees), increasing to 30% in those <60 years. Severe under-coverage (LCEA <20 degrees) was present in 8% overall and 17% of patients <60, while mild under-coverage (LCEA 20–25 degrees) occurred in 15%. A pathological AQ (<250) was found in 29% of all patients, rising to 38% in those <65 years. Among evaluable radiographs, 18% showed a positive crossover sign, indicating acetabular retroversion. conclusion: Developmental dysplasia of the hip was present in up to one-third of THA patients, over 10 times the rate recorded in the New Zealand Joint Registry. These findings highlight the likelihood of underdiagnosed dysplasia in patients undergoing THA for osteoarthritis. Recognition of subtle dysplastic features, coupled with refined registry coding and potential adjustments to screening policy, may improve early detection and preventative strategies aimed at delaying or avoiding joint replacement.