Smart Memory Cast

Abstract

In up to 39% of reduced distal radius fractures, re-displacement of the fracture occurs in the cast. In most cases, the cast becomes too loose as soft tissue swelling decreases over time and the cast no longer provides sufficient support to keep the fracture reduced. This issue could be addressed by introducing a smart memory cast, a cast that would employ soft polymer foam to relieve stress concentration while providing the required support stiffness to maintain the reduction throughout the whole cast treatment period. Soft polymer foams are characterised by a plateau phase in which the pressure does not increase as the material is compressed. The concept is tested by placing a soft polyurethane foam between an artificial arm that mimics soft tissue swelling and a synthetic cast. The pressure in the smart memory cast is measured by thin film pressure sensors. The average pressure in the smart memory cast was 15.4 mmHg and was reduced by 47.8% compared to the average pressure measured, 29.5 mmHg, in a traditional cast. The pressure in the smart memory cast remained under 25.0 mmHg which was set as a threshold value that could lead to a compartment syndrome. In contrast with the traditional cast where the pressure kept increasing above the threshold value as the artificial arm kept swelling, in the smart memory cast the pressure plateaued. The results from this study show that by introducing a filler material with non-linear elastic properties in a synthetic cast, the pressure concentration is reduced compared to a traditional cast and the pressure plateaus as soft tissue swelling increases.