Early Controlled Passive Motion Improves Early Fracture Alignment and Structural Properties in a Closed Extra-Articular Metacarpal Fracture in a Rabbit Model

PurposeTo investigate if early controlled passive mobilization was likely to cause harm with regard to affecting the quality and rate of early fracture healing in a closed, potentially unstable, diaphyseal fracture in a rabbit model.MethodsThis was a preclinical, block-randomized, single-blind efficacy trial examining 3 time periods (baseline [day 5], day 14, day 28) and 2 treatment conditions (immobilization, passive motion). Fifty mature, female, New Zealand white rabbits were preconditioned to a non–weight-bearing brace before creating a closed third metacarpal fracture. Fractures were reduced under fluoroscopy and placed in a custom-molded fracture brace. On day 5, rabbits randomly allocated to the early passive motion protocol received twice-daily 15-minute sessions of passive digital motion combined with gentle pinch stabilization of the fracture. Outcome evaluations included lateral x-rays, peripheral quantitative computerized tomography imaging, and 4-point bending to structural failure.ResultsCompared with the immobilized fractures, the early controlled passive motion fractures showed significantly better gains in initial stiffness, maximum stiffness, failure load, and energy absorbed per unit area, as well as showing a significant reduction in dorsal fracture angulation. The total callus area was not significantly different between the 2 groups.ConclusionsDuring the initial 28 days after the fracture, in this simulated hand, closed, potentially unstable, extra-articular fracture, the early controlled passive motion protocol used in this study led to a clinical and statistical significant reduction in fracture dorsal angulation and improvement in the fracture’s ability to resist and bear 4-point bending loads without increasing the total callus area. Therefore, early controlled passive mobilization after a closed, potentially unstable, diaphyseal hand fracture warrants further clinical consideration.