A Comparison of High-Profile and Low-Profile Dynamic Mobilization Splint Designs
Despite claims that the high-profile dynamic mobilization splint design requires less frequent adjustments than the low-profile design, the authors are not aware of biomechanical evidence supporting such claims. The purpose of this study was to reexamine this claim and quantitatively analyze each design as well as the differences between designs with respect to the actual deviation from a 90° angle of applied force for 60°, 30°, 20°, and 10° gains in proximal interphalangeal joint (PIP) extension. Additionally, for 10°, 20°, and 30°gains in PIP extension, the authors determined the corrective and shear forces as a function of the deviation from a 90° angle of applied force for each design, as well as the difference between the designs. Results show that in all instances examined, the actual difference between the designs is quite small. Implications of such findings are discussed along with newly identified relationships of potential utility to the hand therapist.
Dynamic mobilization splinting is a common intervention employed by hand therapists to manage finger, hand, and wrist dysfunctions including contracture, tendon laceration, joint arthroplasty, systemic disease, replantation, neurologic disease, and burn. Ultimately, the dynamic mobilization splint allows for the prolonged application of therapeutic force believed to increase compliance of stiff structures, lengthen shortened soft tissues, increase range of motion (ROM), provide resistance for weak contractile tissues, prevent imbalances of forces and associated substitution patterns, prevent tendon adhesions, decrease edema, and restore functional use of limited joints.
Hand therapists considering a dynamic mobilization splint may choose between low-profile and high-profile designs. Despite a recent increase in the number of clinical trials addressing dynamic mobilization splints. there remains little to guide the hand therapist in evidence-based clinical choices between high-profile and low-profile designs. Consequently, these decisions are necessarily based on a multitude of mechanical and nonmechanical factors, including material composition, weight, pressure distribution, cosmesis, bulkiness, effect on function, constancy of mobilization force, and adjustment schedules. The two designs are similar with respect to the material composition and weight, and it has been suggested that properly fabricated high-profile and low-profile dynamic mobilization splints are comparable with respect to pressure distribution. Although the outrigger component serves to provide a mechanical advantage for the mobilization force, in both designs it is unattractive, bulky, impinges on functional use of the hand, and is more apparent in the high-profile design. The most significant differences between the high-profile and low-profile designs are believed to be the constancy of the mobilization force offered by the low-profile design and less frequent adjustments required of the high-profile design. Despite claims supporting the advantage of the high-profile over the low-profile with respect to adjustment schedule, we are not aware of biomechanical evidence supporting such claims. Furthermore, examination of the existing information reveals a reliance on assumptions that warrant further examination.
The purpose of this study, therefore, was to logically reexamine and mathematically analyze this commonly held belief that high-profile and low-profile dynamic mobilization splint designs are fundamentally different. First, we precisely quantified the actual deviation from a 90° angle of applied force for each design, as well as the difference between the designs, over a 60° gain in ROM. Second, based on the assumption that adjustments would likely occur before ROM increased beyond 30°, we determined the actual deviation from a 90° angle of applied force for each design, as well as the difference between the designs, over gains of 10°, 20°, and 30°. Finally, we determined the corrective and shear forces as a function of the deviation from a 90° angle of applied force for each design, as well as the difference between the designs, over gains of 10°, 20°, and 30°.
Austin, G. P., Slamet, M., Cameron, D., & Austin, N. M. (2004). A comparison of high-profile and low-profile dynamic mobilization splint designs. Journal of Hand Therapy, 17(3), 335-343. Doi: 10.1197/j.jht.2004.04.003
Journal of Hand Therapy