Wrist kinematic coupling and performance during functional tasks: effects of constrained motion.

PURPOSE: To quantify the coupled motion of the wrist during selected functional tasks and to determine the effects of constraining this coupled motion using a radial-ulnar deviation blocking splint on performance of these tasks. METHODS: Ten healthy, right-handed men performed 15 trials during selected functional tasks with and without a splint, blocking radial and ulnar deviation. The following tasks were performed: dart throwing, hammering, basketball free-throw, overhand baseball and football throwing, clubbing, and pouring. Kinematic coupling parameters (coupling, kinematic path length, flexion-extension range of motion, radial-ulnar deviation range of motion, flexion-extension offset, and radial-ulnar deviation offset) and performance were determined for each functional task. A generalized estimation equation model was used to determine whether each kinematic coupling parameter was significantly different across tasks. A repeated-measures generalized estimation equation model was used to test for differences in performance and kinematic coupling parameters between the free and splinted conditions. RESULTS: Wrist motion exhibited linear coupling between flexion-extension and radial-ulnar deviation, demonstrated by R(2) values from 0.70 to 0.99. Average wrist coupling and kinematic path lengths were significantly different among tasks. Coupling means and kinematic path lengths were different between free and splinted conditions across all tasks other than pouring. Performance was different between wrist conditions for dart throwing, hammering, basketball shooting, and pouring. CONCLUSIONS: Wrist kinematic coupling parameters are task specific in healthy individuals. Functional performance is decreased when wrist coupling is constrained by an external splint. CLINICAL RELEVANCE: Surgical procedures that restrict wrist coupling may have a detrimental effect on functional performance as defined in the study. Patients may benefit from surgical reconstructive procedures and wrist rehabilitation protocols designed to restore kinematic coupling.

Surface replacement arthroplasty of the proximal interphalangeal joint using a volar approach: case series.

PURPOSE: To evaluate the outcomes (range of motion, function, and pain relief) of the volar approach to proximal interphalangeal (PIP) joint surface replacement arthroplasty (SRA) in active, high-demand patients. METHODS: A single surgeon performed PIP SRA in 6 joints using a volar approach. Patients with posttraumatic arthritis or osteoarthritis of the PIP joint were included. Range of motion, postoperative key pinch and grip strength, and Disabilities of the Arm, Shoulder, and Hand questionnaire data were collected. Complications, component integration, and use of cement were noted. Average follow-up was 35 months (range, 12-66 mo). RESULTS: Total arc of motion averaged 33° before surgery and improved significantly in all patients, for an average postoperative arc of motion of 60°. Grip strength averaged 30 kg in the affected hand and 35 kg in the contralateral hand after surgery. Postoperative key pinch strength averaged 6 and 7 kg in ipsilateral and contralateral hands, respectively. The average Disabilities of the Arm, Shoulder, and Hand score after surgery was 14. No coronal plane deformity or postural deformity was observed. Good component integration and stability were observed in all 5 cemented joints. The only noncemented joint demonstrated progressive subsidence of both components. CONCLUSIONS: The volar approach to PIP SRA can result in excellent range of motion, function, and pain relief with minimal complications in active patients with osteoarthritis or posttraumatic arthritis. The volar approach offers the advantages of maintaining the integrity of the extensor mechanism and allowing early postoperative motion. This case series demonstrates compelling data for a prospective, randomized study comparing dorsal and volar approaches to PIP SRA in patients with osteoarthritis and posttraumatic arthritis. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.