The Biomechanical Basis of the Claw Finger Deformity: A Computational Simulation Study.

PURPOSE: Claw finger deformity occurs during attempted finger extension in patients whose intrinsic finger muscles are weakened or paralyzed by neural impairments. The deformity is generally not acutely present after intrinsic muscle palsy. The delayed onset, with severity progressing over time, suggests soft tissue changes that affect the passive biomechanics of the hand exacerbate and advance the deformity. Clinical interventions may be more effective if such secondary biomechanical changes are effectively addressed. Using a computational model, we simulated these altered soft tissue biomechanical properties to quantify their effects on coordinated finger extension. METHODS: To evaluate the effects of maladaptive changes in soft tissue biomechanical properties on the development and progression of the claw finger deformity after intrinsic muscle palsy, we completed 45 biomechanical simulations of cyclic index finger flexion and extension, varying the muscle excitation level, clinically relevant biomechanical factors, and wrist position. We evaluated to what extent (1) increased joint laxity, (2) decreased mechanical advantage of the extensors about the proximal interphalangeal joint, and (3) shortening of the flexor muscles contributed to the development of claw finger deformity in an intrinsic-minus hand model. RESULTS: Of the mechanisms studied, shortening (or contracture) of the extrinsic finger flexors was the factor most associated with the development of claw finger deformity in simulation. CONCLUSIONS: These simulations suggest that adaptive shortening of the extrinsic finger flexors is required for the development of claw finger deformity. Increased joint laxity and decreased extensor mechanical advantage only contributed to the severity of the deformity in simulations when shortening of the flexor muscles was present. CLINICAL RELEVANCE: In both the acute and chronic stages of intrinsic finger paralysis, maintaining extrinsic finger flexor length should be an area of focus in rehabilitation to prevent formation of the claw finger deformity and achieve optimal outcomes after surgical interventions.

Using the extensor carpi ulnaris as the motor tendon in reconstruction of ulnar nerve palsy / 中华显微外科杂志

Objective To investigate the efficacy of using the extensor carpi ulnaris as the motor tendon in correcting claw hand deformity and improving hand function.Methods A total of 12 patients with ulnar nerve palsy and claw finger deformity were included into this study from October, 2009 to September, 2011.Results All ceses had an average followed-up of 15.5 months, ranging from 12 months to 24 months.According to the Total Active Movement (TAM) score, there were 4 cases receiving excellent results, 6 cases receiving good results and 2 cases receiving fair results.The claw finger deformity was corrected and intrinsic hand function improved significantly.The average increase in grip strength was 41％ at the 12 months post operation, compared with the preoperative data (P ＜ 0.05).The mean DASH score decreased from 53.6 ± 11.4 preoperatively to 20.4 ± 6.8 postoperatively (P ＜ 0.05).Conclusion The technique of using the extensor carpi ulnaris as the motor tendon is effective in correcting claw fingers, increasing the grip strength and improving overall hand function.This surgical procedure is also beneficial for patients accompanied by the median nerve injury.