Effects of post-fracture non-weight-bearing immobilization on muscle atrophy, intramuscular and intermuscular adipose tissues in the thigh and calf.

Abstract

Disuse and/or a non-weight-bearing condition changes muscle composition, with decreased skeletal muscle tissue and increased fat within (intramuscular adipose tissue, IntraMAT) and between (intermuscular adipose tissue, InterMAT) given muscles. Excessive adipose tissue contributes to dysfunctional and metabolically impaired muscle. How these adipose tissues change during orthopedic treatment (e.g., cast immobilization, daily use of crutches) is not well documented. This study aimed to quantify changes in IntraMAT, InterMAT, and thigh and calf muscle tissue during orthopedic treatment. We studied 8 patients with fifth metatarsal bone or fibular fractures. The ankle joint involved underwent plaster casting for approximately 4 weeks, with crutches used during that time. Axial T1-weighted MRI at the mid-thigh and a 30% proximal site at the calf were obtained to measure IntraMAT and InterMAT cross-sectional areas (CSAs) and skeletal muscle tissue CSA before treatment and 4 weeks afterward. Thigh and calf muscle tissue CSAs were significantly decreased from before to after treatment: thigh, 85.8 ± 7.6 to 77.1 ± 7.3 cm²; calf, 53.3 ± 5.5 to 48.9 ± 5.0 cm² (p < 0.05). None of the IntraMAT or InterMAT changes was statistically significant. There was a relation between the percentage change of thigh IntraMAT CSA and muscle tissue CSA (r_s = -0.86, p < 0.01). The 4 weeks of treatment primarily induced skeletal muscle atrophy with less of an effect on IntraMAT or InterMAT. There is a risk of increasing IntraMAT relatively by decreasing skeletal muscle tissue size during orthopedic treatment.