Biomechanical effects of ankle sprain orthoses

Abstract

When treating grade III ankle sprains, patients are often instructed to immobilize the affected ligaments in order to allow reparative healing. However, signs of functional instability are apparent after long periods of immobilization. Several studies have compared the efficacy of controlled range of motion walker boots and braces against traditional casts in reducing muscle activity. Nevertheless, the integrity of the affected ligaments during conservative and functional treatments of ankle sprains is a subject that is not yet fully understood. The main objective of this thesis is to use musculoskeletal dynamic simulations to study the effectiveness of functional articulated ankle foot orthoses in providing muscle stimulation, while simultaneously protecting the affected ligaments and accelerate recovery. Ligaments are passive structures that connect articulating bones and keep joints assembled. Mechanically they are much like muscles but with no active contractile element. To validate the simulated ligament forces, a comparison of EMG muscle activity is made against simulated muscle activity. Special attention is given to the tibialis anterior (TA), the extensor digitorum longus (EDL), and the peroneus longus (PL). Three walking conditions are introduced: regular walking (no ankle boot orthosis), walking with a rigid boot, and walking with an articulated boot. The experiments show that there is a significant difference between collected and simulated muscle activity of the PL. On the other hand, there is no overall significant difference between all walking conditions when comparing EMG activity and simulated activity of the TA and EDL muscles. Additionally, there is little change in ATFL ligament force loads between rigid and articulated orthoses. The research performed in this study indicates that the use of articulated ankle foot orthoses does in fact stimulate important muscle activity necessary for proper motor control while in turn maintaining the ATFL forces at a minimal. This conveys evidence that functional treatment should be preferred over conservative immobilization.