Regressions for estimating muscle parameters in the thoracic and lumbar trunk for use in musculoskeletal modeling

Abstract

Musculoskeletal modeling requires information on muscle parameters such as cross-sectional area (CSA) and moment arms. A variety of previous studies have reported muscle parameters in the trunk based on in vivo imaging, but there remain gaps in the available data as well as limitations in the generalizability of such data. Specifically, available trunk muscle CSA data is very limited for older adults, lacking entirely in the thoracic region. In addition, previous studies have made measurements in groups of healthy volunteers or hospital patients who may not be representative of the population in general. Finally, such studies have not reported data for the major muscles connecting the upper limb to the thoracic trunk. In this study, muscle morphology measurements were made for major muscles present in the trunk between vertebral levels T6 and L5 using quantitative computed tomography scans from a community-based sample of 100 men and women aged 36-87. We present regression equations to predict trunk muscle CSA and position relative to the vertebral body in the transverse plane from sex, age, height and weight at vertebral levels T6 to L5. Regressions were also developed for predicting anatomical CSA and muscle moment arms, which were estimated using literature data on muscle line of action. This work thus provides a resource for estimating muscle parameters in the general population for musculoskeletal modeling of the thoraco-lumbar trunk.

Fig. 1

Measurement of muscle position in transverse plane scans. Position was calculated as the difference between centroid locations of muscle and vertebral body in the ML direction (ML-d) and in the AP direction (AP-d), shown here for (a) the left serratus anterior muscle at the T7 vertebral level, and (b) the left rectus abdominis muscle at the L3 vertebral level. Asterisks (*) denote examples of a muscle (latissimus dorsi) that extends outside the QCT image field of view, and thus was not measured.

Fig. 2

Mean values of measured (a) muscle CSAs in the transverse plane, (b) position in the medial-lateral direction (ML-d), and (c) position in the anterior-posterior direction (AP-d), for vertebral levels T6 through L5. Note that for AP-d, positive indicates anterior to, and negative indicates posterior to, the center of the vertebral body. Values for shaded levels (T6, T12, L1) were estimated by interpolation or extrapolation.

Fig. 3

Mean values of estimated (a) muscle ACSAs, (b) moment arm in the medial-lateral direction (MA-X), and (c) moment arm in the anterior-posterior direction (MA-Y), for vertebral levels T6 through L5. Note that for MA-Y, positive indicates anterior to, and negative indicates posterior to, the center of the vertebral body. Values for shaded levels (T6, T12, L1) were estimated by interpolation or extrapolation.