Purpose:

Digital flexion contracture is a common complication of rehabilitation therapy with dynamic splints following flexor tendon injury. Multiple modifications have been described to improve the dynamic splint, but post-rehabilitation flexion contracture has not been addressed completely. In accordance with most rehabilitation protocols, the most recognized dynamic splint design includes elastic bands that are directly linked to the fingers to provide passive flexion following active extension of the fingers against the elastic band traction (straight pull configuration). Due to the normal characteristics of the elastic band combined with the standard splint design, extreme resistance is encountered at maximum digital extension, therefore full active extension is not consistently achieved. We hypothesize that the extreme forces preventing full digital extension are responsible for the increased incidence of flexion contracture seen at the completion of rehabilitation following flexor tendon injury repair. The purpose of this study is to test, compare, and describe the advantages obtained by the incorporation of a simple modification to one of the most recognized dynamic splint designs for flexor tendon rehabilitation.

Methods and Materials:

The proposed modification to the current linear design includes the addition of a block pulley system between the elastic bands and the fingers (Pulley configuration). By adding a pulley, the magnitude of force and the load differential change, therefore reducing the workload necessary to achieve full digital extension. This modification was tested by developing a mechanical model that simulates active extension and passive flexion of the fingers. Load and displacement data were obtained from four different elastic bands. Graphics were generated and data was analyzed using the two-way analysis of variance.

Results:

Throughout the entire flexion and extension cycle, the magnitude of force was lower in the pulley configuration for the same length of displacement, when compared to its counterpart linear configuration. Furthermore, the overall force differential was smaller, demonstrating a more constant load throughout the length of digital excursion.

Conclusions:

The inclusion of the block-pulley in the splint design not only decreases the magnitude of force needed to actively extend the fingers, but also creates a more constant load that is applied to the digits throughout the entire range of motion. This decrease in force seen at maximal digital extension should decrease the tendency to not achieve maximal digital extension during flexor tendon rehabilitation, thus resulting in a lower incidence of flexion contractures at the completion of the rehabilitation period with a dynamic splint. Although this initial biomechanical data supports the addition of this modification to dynamic splints, further clinical studies will be needed to determine the clinical impact this modification will have on the rate of flexion contractures.