Modeling of the muscle/tendon excursions and moment arms in the thumb using the commercial software anybody

doi:10.1016/j.jbiomech.2008.11.008

Journal of Biomechanics

Volume 42, Issue 3, 9 February 2009, Pages 383-388

https://doi.org/10.1016/j.jbiomech.2008.11.008 Get rights and content

Abstract

A biomechanical model of a thumb would be useful for exploring the mechanical loadings in the musculoskeletal system, which cannot be measured in vivo. The purpose of the current study is to develop a practical kinematic thumb model using the commercial software Anybody (Anybody Technology, Aalborg, Denmark), which includes real CT-scans of the bony sections and realistic tendon/muscle attachments on the bones. The thumb model consists of a trapezium, a metacarpal bone, a proximal and a distal phalanx. These four bony sections are linked via three joints, i.e., IP (interphalangeal), MP (metacarpophalangeal) and CMC (carpometacarpal) joints. Nine muscles were included in the proposed model. The theoretically calculated moment arms of the tendons are compared with the corresponding experimental data by Smutz et al. [1998. Mechanical advantage of the thumb muscles. J. Biomech. 31(6), 565–570]. The predicted muscle moment arms of the majority of the muscle/tendon units agree well with the experimental data in the entire range of motion. Close to the end of the motion range, the predicted moment arms of several muscles (i.e., ADPt and ADPo (transverse and oblique heads of the adductor pollicis, respectively) muscles for CMC abduction/adduction and ADPt and FPB (flexor pollicis brevis) muscle for MP extension/flexion) deviate from the experimental data. The predicted moment potentials for all muscles are consistent with the experimental data. The findings thus suggest that, in a biomechanical model of the thumb, the mechanical functions of muscle–tendon units with small physiological cross-sectional areas (PCSAs) can be well represented using single strings, while those with large PCSAs (flat-wide attachments, e.g., ADPt and ADPo) can be represented by the averaged excursions of two strings. Our results show that the tendons with large PCSAs can be well represented biomechanically using the proposed approach in the major range of motion.

Introduction

Biomechanical models of the hand can also be used to analyze the biomechanical consequences of surgical interventions, such as tendon (Xu, 2003) and ligament (Oka et al., 2003) repair and pulley reconstruction (Guelmi et al., 1997). Holzbaur et al. (2005) simulated the musculoskeletal surgery and analyzed neuromuscular control using a biomechanical model of upper extremity, which includes 15 degrees of freedom. A biomechanical model will be very useful in pre-surgical planning when tendon transfer procedure is considered (Cooney et al., 1984).

The kinematics of the musculoskeletal system of the thumb has been studied experimentally by Smutz et al. (1998). They measured the moment arms of four extrinsic muscles and four intrinsic muscles of the thumb as a function of the IP (interphalangeal), MP (metacarpophalangeal) and CMC (carpometacarpal) joint motions using six cadaver specimens. Although there are several biomechanical models of the thumb (e.g., Srinivasan and Landsmeer, 1982, Valero-Cuevas et al., 2003, Harley et al., 2004), most of them were mathematical models developed for specific cases and none of the previous studies have calibrated the model predictions on the muscle excursions with the experimental measurements for the entire range of motions. The goal of this study is to develop a generic, biomechanical model of the thumb and to calibrate the model predictions of the muscle/tendon kinematics with the experimental data by Smutz et al. (1998). The model will be developed using the commercial software AnyBody (version 2.0, AnyBody Technology, Aalborg, Denmark), such that it will become a tool for practical problems.

Section snippets

Methods

The thumb is modeled as a linkage system consisting of a trapezium, a metacarpal bone, a proximal and a distal phalanx (Fig. 1a). The trapezium bone is considered to be fixed. The dimensional scale of the bony sections is consistent with the normative model (An et al., 1979). These four bony sections are linked via three joints: IP, MP and CMC joints. The IP joint is modeled as a hinge with one DOF (degree-of-freedom), while the MP and CMC joints are modeled as universal joints with two DOFs.

Results

The predicted moment arms of the muscles EPL and FPL corresponding to the IP extension/flexion are generally within or close to the regions of the 95% confidence intervals of the experimental data by Smutz et al. (1998) (Fig. 2).

The moment arms of the muscles/tendons with respect to the MP joint motions predicted using the current model are compared with those measured experimentally by Smutz et al. (1998) (Fig. 3). The left column of the figure (Fig. 3a–g) shows the muscle/tendon moment arms

Discussion and conclusion

A comparison of the theoretical predictions with the experimental data indicated that the model predictions agree generally well with the experimental data in the middle of the motion ranges, while close to the end of the motion range the predicted muscle moment arms of the ADPt, ADPo and FPB muscles (e.g., Fig. 3, Fig. 4) deviate from the experimental data. The adductor pollicis muscles, especially ADPt, have a large PCSA and are attached to the metacarpal bone and proximal phalanx in a

Conflict of interest statement

I understand that all authors of this manuscript have no conflict of interest.

Disclaimer

The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health.

Acknowledgments

We would like to thank Dr. Thomas McDowell (NIOSH/HELD) and Ms. Xiaoming Liang (NIOSH/DRDS) for their suggestions on the statistical analysis of the experimental data.

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Short communicationModeling of the muscle/tendon excursions and moment arms in the thumb using the commercial software anybody

Abstract

Introduction

Section snippets

Methods

Results

Discussion and conclusion

Conflict of interest statement

Disclaimer

Acknowledgments

J. Biomech.

J. Hand Surg. (Am.)

J. Hand Surg. (Am.)

J. Hand Surg. (Br.)

J. Hand Surg. (Am.)

J. Hand Surg. (Am.)

Short communication
Modeling of the muscle/tendon excursions and moment arms in the thumb using the commercial software anybody