Pre‐operative psoas muscle mass and post‐operative gait speed following total hip arthroplasty for osteoarthritis

Muscle volumes of the gluteus medius, gluteus maximus, and tensor faciae latae assessed by a computed tomography (CT) scan were greater in men than women and not different between the left and the right side after total hip arthroplasty (THA). Body mass index, sex, age, and ambulatory status affected functional outcome after THA. However, the effects of psoas muscle mass and muscle quality on functional outcomes after THA are unknown. The purpose of this study was to investigate the association between pre-operative psoas muscle mass, muscle quality assessed by a pelvic CT scan, and post-operative gait speed following THA. A retrospective cohort study was conducted on 135 consecutive hip osteoarthritis patients who received unilateral THA (right/left: 83/52). We measured psoas muscle area (PMA) and psoas muscle attenuation (PMT in Hounsfield Units) by pre-operative (median 32 days) pelvic CT to assess the hip joint at the level of the fourth lumbar vertebra using Slice-O-Matic software (v.5.0; Tomovision, Magog, Quebec, Canada). Post-operative gait speed was measured by a 10m walk test at discharge. Body mass index, PMA, skeletal muscle index (SMI) calculated by PMA/body height (cm/m), and PMT were larger in men, and post-operative gait speed was faster (Table 1). PMA, SMI, and PMT were larger in the contralateral nonoperated (NOP) side (Table 2). A significant association was found between post-operative gait speed, PMA, SMI, PMT on the NOP side, and age (Table 3). A stepwise multiple linear regression analysis of post-operative gait speed adjusted by age, sex, post-operative length of stay, SMI, and PMT on the NOP side revealed that age, postoperative length of stay, and SMI were independently associated with postoperative gait speed (gait speed=0.070×SMI on the NOP LETTER TO THE EDITOR