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Relative Motion Flexion Splinting for Flexor Tendon Repairs: Proof of Concept
Bryan Chung, MD, PhD1; Vishal Thanik, MD2; David T.W. Chiu, MD3
1Plastic Surgery/ Hand Program, University of Toronto, Toronto, ON, Canada; 2Institute of Reconstructive Plastic Surgery, New York University Medical Center, New York, NY; 3Plastic Surgery, NYU Langone Medical Center, New York, NY

Purpose: Early active motion protocols after flexor tendon repair have resulted in a better range of motion and decrease in flexion contractures, but still involve long periods of immobilization with interspersed sessions of motion, and activities of daily living are usually significantly impaired. The principle of relative motion in extensor tendon repairs has allowed patients to regain a higher degree of hand function, while protecting the repair. The purpose of this study was to determine if the principle of relative motion could be a feasible method to protect a flexor tendon repair.

Methods: Four fresh frozen cadaver arms were used in this study. The flexor digitorum profundus (FDP) tendons of the middle fingers were dissected in the palm (zone 3) distally, while the muscles of the FDP and extensor digitorum communis were dissected proximally in the forearm. Each arm was mounted on a testing apparatus with the wrist in 30 degrees of extension, and the MCP joints blocked to 70-80 degrees. A minimum of 11N was used to cyclically load the FDP and EDC tendons to maximum allowable flexion and extension for 25 cycles. Measurements of elongation of the tendons were obtained through the use of differential variable reluctance transducers (Lord Microstrain, Williston, VT). Following intact tendon testing, a tenotomy was made in the FDP tendon of the middle finger in zone 3 and immediately repaired with a single 6-0 nylon suture. Measurement of elongation was repeated with and without the relative motion splint. The tendon was visualized to determine if visible gapping was present after cycling.

Results: In all hands, elongation was restricted to less than 1.3mm in repaired tendon in the relative motion flexion splint compared to elongation >2mm in the non-splinted condition. Average elongation was 0.86mm (SD=0.45) Visual examination of the tendons demonstrated no gapping with the use of the relative motion splint in any of the hands (Fig 1). All repairs had suture breakage and repair rupture without the relative motion splint (Fig 2).

Conclusion: Relative motion splinting decreases elongation and eliminates tendon gapping and tendon rupture after flexion/extension cycling in a cadaver model. It provides proof-of-concept that relative motion splinting may be a viable protective mechanism for flexor tendon repairs, allowing for development of protocols that allow earlier tendon mobilization and less restricted hand function during the post-operative and rehabilitation phase.

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