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.