Binder-Markey BI, Dewald JPA, Murray WM. The Biomechanical Basis of the Claw Finger Deformity: A Computational Simulation Study.
J Hand Surg Am 2019;
44:751-761. [PMID:
31248678 PMCID:
PMC6718315 DOI:
10.1016/j.jhsa.2019.05.007]
[Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2018] [Revised: 03/12/2019] [Accepted: 05/03/2019] [Indexed: 02/02/2023]
Abstract
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.
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