Function of the hand and fingers is important for the performance of most daily activities, with manual dexterity being an important indicator for detection and measurement of disability (Duruöz, 2014). Understanding of the underlying mechanics of hand function has been dramatically improved with implementation of biomechanical models, with important information such as passive joint stiffness and muscle force contributions derived from biomechanical models that would otherwise not be possible to derive from experimental results alone (Kamper et al., 2002). However, the hand and fingers present unique challenges in biomechanical modeling in comparison to other limbs, due to their relatively small masses and inertial components (Binder-Markey and Murray, 2017).

One specific component of the hand that presents unique challenges to modeling is the extensor hood aponeurosis that governs the extension of the fingers. This is due to the extensor hood forming a sheath-like surface of tendinous structures and soft tissues comprised of heterogenous materials (Qian et al., 2014). Previous modeling approaches have been implemented, such as modeling the extensor hood as a tendinous rhombus (Valero-Cuevas et al., 1998;​ Winslow, 1732). However, this approach is limited as it must assume the extensor hood is comprised of homogenous materials (Lee et al., 2008;​ Qian et al., 2014).

This thesis examines and attempts to validate two different approaches to modeling of the extensor hood aponeurosis:​ the first approach uses an existing rigid body dynamics model, and the second a newly developed integrated model that combines finite element modeling with rigid body dynamics to simulate the heterogenous nature of the extensor hood. Two models were used in this study. The first model is a previously developed dynamic model of the hand, index finger, and thumb that has been validated using cadaveric data for isometric fingertip force production (Barry et al., 2018). The second model used in this study is a modified version of a finite element model of the index finger extensor hood and phalanges (Ellis et al., 2011), that implements the heterogenous nature of the extensor hood using material stiffnesses derived from cadaveric dissections (Qian et al., 2014). This study attempted to validate each model using experimental data, with isometric fingertip forces and experimentally acquired material strains used for validation of the dynamic model and finite element models respectively. Lastly, this study compares the isometric fingertip forces developed using the integrated finite element and rigid body dynamic model to the original dynamic model and experimental data to evaluate the performance of the integrated model.

Validation of the dynamic finger model demonstrated a similar pattern of predicted force magnitudes to experimental data within 0.53N, but the orientations did not match the experimental data within one standard deviation. The validation of the finite element model demonstrated similar longitudinal strains to the experimental data, with longitudinal strains at the central and terminal slips lying within one standard deviation of the experimental data;​ however, lateral strains were underpredicted. Evaluation of the integrated model similarly did not match the experimental results, apart from the force magnitude produced using the first palmar interosseous muscle, which replicated the experimental data within one standard deviation. Discrepancies between the dynamic model results and experimental data may be due to unwanted joint motion during simulation, whilst the discrepancy with the finite element model may arise due to the material model assumptions used. To improve the results from these models, a sensitivity study of joint motion constraint and acquisition of more accurate materials data are necessary.