Bridging the gap between cadaveric and in vivo experiments: A biomechanical model evaluating thumb-tip endpoint forces

Abstract

The thumb is required for a majority of tasks of daily living. Biomechanical modeling is a valuable tool, with the potential to help us bridge the gap between our understanding of the mechanical actions of individual thumb muscles, derived from anatomical cadaveric experiments, and our understanding of how force is produced by the coordination of all of the thumb muscles, derived from studies involving human subjects. However, current biomechanical models do not replicate muscle force production at the thumb-tip. We hypothesized that accurate representations of the axes of rotation of the thumb joints were necessary to simulate the magnitude of endpoint forces produced by human subjects. We augmented a musculoskeletal model with axes of rotation derived from experimental measurements (Holzbaur et al., 2005) by defining muscle–tendon paths and maximum isometric force-generating capacity for the five intrinsic muscles. We then evaluated if this augmented model replicated a broad range of experimental data from the literature and identified which parameters most influenced model performance. The simulated endpoint forces generated by the combined action of all thumb muscles in our model yielded comparable forces in magnitude to those produced by nonimpaired subjects. A series of 8 sets of Monte Carlo simulations demonstrated that the difference in the axes of rotation of the thumb joints between studies best explains the improved performance of our model relative to previous work. In addition, we demonstrate that the endpoint forces produced by individual muscles cannot be replicated with existing experimental data describing muscle moment arms.

Connecting the wrist to the hand: A simulation study exploring changes in thumb-tip endpoint force following wrist surgery

“…Such experiments can also simultaneously address issues associated with external validation of our models. For example, the nonimpaired thumb model (excluding the wrist) was validated by replicating cadaveric and in vivo data (see Wohlman and Murray 2013). The endpoint forces simulated with the SE4CF and PRC models have not been evaluated against similar data, despite being based on experimental data (Blankenhorn et al 2007; Nichols et al 2015; Nichols et al 2016; Nichols et al 2017).…”

“…The dynamic musculoskeletal models of the nonimpaired, SE4CF, and PRC conditions were developed by adapting previously published models of the nonimpaired wrist (Saul et al 2015) and thumb (Wohlman and Murray 2013). Condition-specific bone geometry, joint kinematics, and muscle moment arms at the wrist for each model were based on experimental data, as described below.…”

“…These actuators included the five primary wrist muscles, four extrinsic thumb muscles, and five intrinsic thumb muscles (see Table 2 for muscle names and abbreviations). The nonimpaired muscle lines of action and muscle force-generating parameters have been previously described (Wohlman and Murray 2013; Saul et al 2015). …”

“…Instead, these studies have elucidated the biomechanics of force production at the index finger (Valero-Cuevas et al 1998; Wu et al 2008; Lee and Kamper 2009), the thumb (Valero-Cuevas et al. 2003; Goehler and Murray 2010; Wohlman and Murray 2013), and the end-points of multiple digits to produce coordinated grip forces (Esteki and Mansour 1997; Sancho-Bru et al 2003) in isolation from the proximal upper limb.…”

“…To test this hypothesis, we leverage available biomechanical data characterizing the wrist surgeries (Blankenhorn et al. 2007; Nichols et al 2015; Nichols et al 2016; Nichols et al 2017) and computational advances in biomechanical simulation of force development at the thumb (Valero-Cuevas et al 2003; Goehler and Murray 2010; Wohlman and Murray 2013) to develop dynamic musculoskeletal simulations of lateral pinch force that integrate the wrist and thumb. We then utilize these simulations to specifically examine how having a nonimpaired versus a surgically-altered wrist influences joint torques, muscle force transmission, and muscle control strategies during lateral pinch.…”