Validity of cadaveric data for muscle physiological cross-sectional area ratios: a comparative study of cadaveric and in-vivo data in human thigh muscles.

Muscle physiological cross-sectional area (PCSA) is calculated from muscle volume, fibre length and fibre pennation angle, and is a measure of force/stress. Muscle force analyses in the human body usually yield combined forces of groups of synergistic muscles rather than individual muscle forces, because of the constraints of statically determinate models. As stresses acting in a group of muscles are uniform, the ratio of the physiological cross-sectional areas of a group of muscles can be used to divide the combined force into its component parts. This paper investigates the validity of the common practice of using cadaveric physiological cross-sectional area to divide in-vivo group muscle forces into component parts. Muscle volumes were determined in vivo using a combination of radiographic techniques for a small number of active young males, and 'in-vivo' physiological cross-sectional areas were calculated using cadaveric data for fibre length and pennation angle. As would be expected, in absolute terms, the 'in-vivo' values were much larger than those of cadavers. Comparison of the percentage contribution of each muscle to the total value of its group showed little difference between the cadaveric and 'in-vivo' data. We conclude that it is reasonable to use cadaveric data when only relative physiological cross-sectional areas are required, more so in the quadriceps than in the hamstrings. Considering data from active young subjects and cadavers, we have shown the ratios of the physiological cross-sectional area of the individual muscles of the quadriceps (and to a lesser extent the hamstrings) to be comparable. This validates the practice of using cadaveric data for relative physiological cross-sectional area in statically determinate force analysis in the human body. 9n-vivo' ratios are also presented for future use.