Psoas muscle atrophy following unilateral hip arthroplasty.

BACKGROUND: Studies have demonstrated the presence of muscle atrophy around the hip in patients with hip osteoarthritis. Few studies have examined the psoas muscle or assessed it at a paraspinal level in patients post-total hip arthroplasty. The aim of this study was to determine if there is significant psoas muscle atrophy as indicated by muscle cross-sectional area and high degree of fat infiltration post-unilateral hip arthroplasty. METHODS: Retrospective analysis of 341 patients with unilateral hip implant and subsequent lumbar spine MRI over a 8-year period was performed. Fat infiltration and cross-sectional area of the psoas muscle at L3/4 level were measured by two musculoskeletal fellows (1 year experience in musculoskeletal radiology), and comparison made between the implant and non-operative sides was made. Fat infiltration was measured using the modified Goutallier grading. The degree of hip osteoarthritis in the non-operative side was measured using the Kellgren-Lawrence grading. The data was analysed using paired t test, ANOVA, unpaired t test, Pearson correlation and Jonckheere-Terpstra test. RESULTS: The cross-sectional area of the psoas muscle on the implant side was significantly less than the non-operative side. There was significance between the cross-sectional area difference and the fat grade of the implant side. CONCLUSION: Our results demonstrate psoas atrophy on the implant side compared to the non-operative side in post-unilateral implant patients. Post-operative hip implant rehabilitation may benefit from more focused psoas strengthening exercises to improve functional outcome.