A Musculoskeletal Model of the Hand and Wrist Capable of Simulating Functional Tasks.

OBJECTIVE: The purpose of this work was to develop an open-source musculoskeletal model of the hand and wrist and to evaluate its performance during simulations of functional tasks. METHODS: The current model was developed by adapting and expanding upon existing models. An optimal control theory framework that combines forward-dynamics simulations with a simulated-annealing optimization was used to simulate maximum grip and pinch force. Active and passive hand opening were simulated to evaluate coordinated kinematic hand movements. RESULTS: The model's maximum grip force production matched experimental measures of grip force, force distribution amongst the digits, and displayed sensitivity to wrist flexion. Simulated lateral pinch strength replicated in vivo palmar pinch strength data. Additionally, predicted activations for 7 of 8 muscles fell within variability of EMG data during palmar pinch. The active and passive hand opening simulations predicted reasonable activations and demonstrated passive motion mimicking tenodesis, respectively. CONCLUSION: This work advances simulation capabilities of hand and wrist models and provides a foundation for future work to build upon. SIGNIFICANCE: This is the first open-source musculoskeletal model of the hand and wrist to be implemented during both functional kinetic and kinematic tasks. We provide a novel simulation framework to predict maximal grip and pinch force which can be used to evaluate how potential surgical and rehabilitation interventions influence these functional outcomes while requiring minimal experimental data.

Intramuscular connective tissue differences in spastic and control muscle: a mechanical and histological study.

Cerebral palsy (CP) of the spastic type is a neurological disorder characterized by a velocity-dependent increase in tonic stretch reflexes with exaggerated tendon jerks. Secondary to the spasticity, muscle adaptation is presumed to contribute to limitations in the passive range of joint motion. However, the mechanisms underlying these limitations are unknown. Using biopsies, we compared mechanical as well as histological properties of flexor carpi ulnaris muscle (FCU) from CP patients (n = 29) and healthy controls (n = 10). The sarcomere slack length (mean 2.5 µm, SEM 0.05) and slope of the normalized sarcomere length-tension characteristics of spastic fascicle segments and single myofibre segments were not different from those of control muscle. Fibre type distribution also showed no significant differences. Fibre size was significantly smaller (1933 µm2, SEM 190) in spastic muscle than in controls (2572 µm2, SEM 322). However, our statistical analyses indicate that the latter difference is likely to be explained by age, rather than by the affliction. Quantities of endomysial and perimysial networks within biopsies of control and spastic muscle were unchanged with one exception: a significant thickening of the tertiary perimysium (3-fold), i.e. the connective tissue reinforcement of neurovascular tissues penetrating the muscle. Note that this thickening in tertiary perimysium was shown in the majority of CP patients, however a small number of patients (n = 4 out of 23) did not have this feature. These results are taken as indications that enhanced myofascial loads on FCU is one among several factors contributing in a major way to the aetiology of limitation of movement at the wrist in CP and the characteristic wrist position of such patients.

Flexor carpi ulnaris tenotomy alone does not eliminate its contribution to wrist torque.

BACKGROUND: Flexor carpi ulnaris muscle tenotomy and transfer to the extensor side of the wrist are common procedures used to improve wrist position and dexterity in patients with cerebral palsy. Our aim was to determine whether this muscle still influences wrist torque even after tenotomy of its distal tendon. METHODS: Intra-operatively, we determined in vivo maximal wrist torque in hemiplegic cerebral palsy patients (n=15, mean age 17 years) in three conditions: 1) with the arm and the muscle intact; 2) after tenotomy of the flexor carpi ulnaris just proximal to the pisiform bone, with complete release from its insertion; and 3) after careful dissection of the belly of the muscle from its fascial surroundings up until approximately halfway its length. FINDINGS: After tenotomy of the flexor carpi ulnaris muscle, the maximal wrist torque decreased 18% whereas dissection of the muscle resulted in an additional decrease of 18%. INTERPRETATION: We conclude that despite the tenotomy of its distal tendon, the flexor carpi ulnaris still contributes to the flexion torque at the wrist through myofascial force transmission. Quantification of this phenomenon will help in the study of the effects of fascial dissection on the functional results of tendon transfer surgery.

Long-term results of lateral band translocation for the correction of swan neck deformity in cerebral palsy.

PURPOSE: The aim of this study was to evaluate the long-term effect of lateral band translocation for correcting swan neck deformity in patients with cerebral palsy at a minimum follow-up of 5 years. METHODS: Swan neck deformities of 62 fingers were corrected using a modified lateral band translocation. At 1-year and 5-year follow-up, any recurrence of hyperextension was recorded through nonconstrained evaluation. Active extension of the proximal interphalangeal joint beyond 0 degree was considered a recurrence. RESULTS: Correction was successful for 84% of the operated fingers at 1-year follow-up. After 5 years, the success rate had decreased to 60%. Furthermore, no relationship was found between any of the concomitant surgical procedures and the number of patients with recurrences. CONCLUSIONS: The long-term result of lateral band translocation is disappointing in our series, and it should not be advocated as a procedure with long-lasting success in patients with cerebral palsy.