A Coronally Clutching Ankle to Improve Amputee Balance on Coronally Uneven and Unpredictable Terrain

Abstract

To improve the balance of individuals with lower limb amputation on coronally uneven terrain, a coronally clutching ankle (CCA) was developed to actively adapt through ±15 deg of free coronal foot rotation during the first ∼60 ms of initial contact. Three individuals with lower limb amputations were fit with the CCA and walked across an instrumented walkway with a middle step that was either flush, 15 deg inverted, or 15 deg everted. An opaque latex membrane was placed over the middle step, making the coronally uneven terrain unpredictable. Compared to participants' clinically prescribed prosthesis, the CCA exhibited significantly more coronal angular adaption during early stance. The CCA also improved participants' center of mass (COM) path regulation during the recovery step (reduced variation in mediolateral position) and reduced the use of the hip and stepping recovery strategies, suggesting it improved participants' balance and enabled a quicker recovery from the disturbance. However, use of the CCA did not significantly affect participants' ability to regulate their coronal angular momentum during the disturbance, suggesting that the CCA did not improve all elements of dynamic balance. Reducing the distance between the CCA's pivot axis and the base of the prosthetic foot might resolve this issue. These findings suggest that actively adapting the coronal plane angle of a prosthetic ankle can improve certain elements of balance for individuals with lower limb amputation who walk on coronally uneven and unpredictable terrain.