Dynamic balance control in transfemoral amputees: Individual contribution of the prosthesis side

1. Summary/conclusions This study explores the use of a new developed method to assess the individual contribution of both legs to postural control. The results imply that the contribution of the prosthetic leg in balance control is not a mere reflection of the weight distribution. 2. Introduction A major goal in the rehabilitation of lower limb amputees is to regain effective postural control. Particularly in transfemoral amputees this requires complex adaptation strategies in both the prosthesis side and the non-amputated side [1] and [2]. This study explores the use of a new developed method [3] to assess the Dynamic Balance Control (DBC). Unlike previous methods using weight distribution as a measure of balance, this method determines the individual contribution of both legs to postural control during perturbations. 3. Statement of clinical significance Assessments of the DBC may indicate the necessity for (and efficacy of) balance training and guide the prescription of prosthetic components. 4. Methods Four unilateral transfemoral amputees were included. Subjects stood on a force platform mounted on a motion platform and were instructed to stand still. The experiment consisted of one static and three perturbation trials of 90 s each. During the static trial the platform did not move. During the (dynamic) perturbation trials, balance responses were elicited by continuous random sagital platform movements consisting of a multiple sine signal (ranging from 0.06 to 2.37 Hz). Weight distribution during the static (SW) and the dynamic perturbation trial (DW) were calculated by dividing the average vertical force below the prosthesis foot by the sum of forces below both feet. The Dynamic Balance control (DBC) represents the ratio between the stabilizing mechanism of the prosthetic leg to the stabilizing mechanism of the non-amputated leg. The stabilizing mechanism is calculated from the corrective ankle torque (assessed with inverse dynamics) in response to sway (assessed by the movement of CoM) and averaged over all the perturbation frequencies. 5. Results All patients showed a clear asymmetric weight bearing in favor of the non-amputated leg (see Fig. 1). However the DBC ratio showed that the contribution of both legs to balance control was even more asymmetric