The Effect of Simulated Total Distal Interphalangeal Joint Stiffness on Grip Strength
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Purpose: Production of a functional grip pattern requires the concerted action of numerous structures within the hand. This study quantifies the effect of total distal interphalangeal joint (DIPJ) stiffness to grip strength. Methods: Fifty (25 men, 25 women, 100 hands) individuals with a mean age of 38 years (range: 17-69 years) were recruited. Exclusion criteria included history of previous upper limb injury, neuropathies, or systemic disease. Custom thermoplastic orthoses were used to splint participants' DIPJ in full extension simulating stiffness. Grip strength before and after splinting was measured using a calibrated Jamar dynamometer. Data were analyzed using paired and independent sample t tests and 2 × 2 repeated-measures analysis of variance with hand dominance and configuration (splinted or unsplinted) as within-subject factors. Results: Restriction of DIPJ flexion led to a 20% decrease in grip strength (P < .001). There was no significant difference in this decrease between dominant and non-dominant hands. Univariate analysis did not demonstrate any interaction between hand dominance and testing configuration. Post hoc analysis revealed no statistical difference in baseline grip strength between the dominant and non-dominant hands. Furthermore, men had significantly stronger grip strength than women in all configurations (P < .001). Conclusions: Flexion at the DIPJ contributes significantly to grip strength, and stiffness at this joint greatly limits functional capabilities of the hand. This necessitates the need for targeted rehabilitation in DIPJ injuries to minimize adverse effects on grip strength.