To investigate muscle volume changes in all body regions after total hip arthroplasty (THA) with dual-energy X-ray absorptiometry (DEXA), and determine the positive effects of THA for systemic muscle atrophy in patients with hip osteoarthritis (HOA).
In total, 116 patients with a mean age of 65.8 (45-84) years who had undergone THA for unilateral HOA were included in this study. DEXA scans were performed serially at 2 weeks, 3, 6, 12, 18, and 24 months after THA. The normalized height squared muscle volume (NMV) and the change ratio of NMV (ΔNMV) were calculated independently for operated lower extremity (LE), non-operated LE, both upper extremities (UEs), and trunk. Skeletal mass index, which is a sum of NMV of both LEs and UEs, was evaluated at 2 weeks and 24 months after THA to identify systemic muscle atrophy equivalent to the diagnostic criteria of sarcopenia.
ΔNMVs in non-operated LE, both UEs, and trunk increased gradually up to 6, 12, and 24 months after THA, although that in operated LE did not increase during a 24-month period. The ΔNMVs in operated LE, non-operated LE, both UEs, and trunk at 24 months after THA were +0.6%, +7.1%, +4.0%, and +4.0%, respectively (P = 0.993, P < 0.001, P < 0.001, P = 0.012). The proportion of systemic muscle atrophy significantly decreased from 2 weeks (38%) to 24 months (23%) after THA (P = 0.022).
THA can potentially have secondary positive effects for systemic muscle atrophy exception of operated LE.

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