Muscular Asymmetries in Anatomical Donors with Lower‐Limb Amputations

Abstract

Individuals with lower-limb amputations experience asymmetrical musculoskeletal loading associated with increased gait asymmetry, fall risk, and overuse injuries. Many biomechanical modeling systems rely on cadaveric data for a gold standard, so it is important to confirm asymmetries in donors with lower-limb amputation reflect those of living individuals for an accurate standard. Previously, we examined skeletal asymmetries in these donors using a threshold of 10% for clinical significance, which is considered symmetrical in healthy controls. We found less bone mineral density and bone mineral content, and wider knee joint space on each donor's most compromised limb compared to their most intact limb. Amputation can also result in muscle atrophy, leading to changes in muscle mass, architecture, and fiber phenotype. This study investigated these between-limb muscular differences in donors with lower-limb amputations to determine if donor findings reflect findings in living individuals. We hypothesized each donor's most compromised limb would show less muscle mass, lower pennation angle and physiological cross-sectional area (PCSA), and fewer and smaller type 1 fibers compared to their most intact limb. Two male unembalmed donors 61 and 67 years of age with lower-limb amputations secondary to diabetes were obtained through the University of North Texas Health Science Center (UNTHSC) Willed Body Program. Four muscles were dissected from each limb: gluteus maximus, sartorius, rectus femoris, and biceps femoris long head. Muscle mass and fiber lengths were collected using a hanging scale and calipers, then muscles were photographed to collect pennation angle in ImageJ software. PCSA was calculated using the following formula: [(muscle mass x cos(pennation angle)] / [fiber length (cm) x muscle density (1.067 g/cm-3)]. The density of human skeletal muscle was taken from the literature. Histological (H&E) staining of muscle tissue was used to determine fiber density and cross-sectional area. Immunohistochemical (IHC) staining was used to identify the percentage of fibers containing the fast type II isoform of myosin heavy chain. Biceps femoris PCSA was 18.1-68.6% larger on each donor's most compromised limb compared to their most intact limb. Differences were largely driven by pennation angle, as opposed to muscle mass or fiber lengths. H&E staining also showed smaller cross-sectional biceps femoris muscle fibers on the most compromised side compared to the most intact side. IHC analyses of fiber phenotype in these muscles are ongoing. More donors should be included to assess the generalizability of our findings. Knowledge of muscle adaptations following amputation in donors can confirm accurate biomechanical modeling and inform rehabilitation techniques to reduce muscle atrophy. The authors would like to thank the donors and their families, as well as the UNTHSC Willed Body Program.