A noncontact sensor for measurement of distal residual-limb position during walking.

Abstract--A simple noncontact device was implemented for measuring the position of the distal residual limb relative to the prosthetic socket during ambulation. The device was a small and lightweight photoelectric sensor positioned within a frame mounted immediately beneath the socket. Calibration tests showed that the sensor had a displacement range of 60.0 mm. The root-mean-square error for all sources of error considered (different reflective surfaces, peak-to-peak signal noise, drift, nonlinearity, different surface tilt angles, surface curvature, and wetness [simulating sweating]) was Key words: ambulation, displacement, interface, liner, pistoning, position, prosthetics, rehabilitation, sensor, socket, transtibial amputee. INTRODUCTION Measurement of the position of the residual limb in the prosthetic socket during walking is potentially useful in both prosthetics research and clinical practice. The amount of slip, or pistoning, between a limb and socket with different suspension systems for different activities could be quantitatively evaluated. Comfortable prosthetic fitting has been correlated with decreased vertical tibial translation [1]. In a clinical setting, when excessive pistoning is deemed detrimental to the patient, a prosthetist could use the measurement to quantify the degree of pistoning and work to minimize the motion. A number of studies have used traditional imaging methods to assess the positions of bony structures within the residual limb relative to the socket wall. Radiological methods include roentgenology [2-3], cineradiography [1,4-5], fluoroscopy [6], and roentgen stereophotogrammetric analysis [7]. These studies have shown that for transtibial amputee subjects, the vertical motion between the bones and the socket ranged to approximately 40 mm between the midstance and swing phases. Ultrasonic methods have also been used, in which ultrasound transducers are attached to the socket wall and their subsequent video recordings are analyzed [8-9]. While the bone-to-socket displacement data collected with these techniques provide interesting insight, the methods are not generally available to many researchers or prosthetists because of the cost of the equipment and the lack of portability. In addition, data collection and analysis can be complex and time-consuming. If radiological methods are to be used and the analysis is to occur frequently, then radiation exposure to the patient may be a concern. In this research, we implemented an easy-to-use nonradiological means to measure the position of the distal residual-limb surface relative to the distal socket during ambulation. Such a device has the potential to provide insight into the dependence of limb position and vertical motion on a range of componentry, treatments, or other features of clinical relevance. It could be used to characterize the pistoning induced by different suspension systems or different limb fluid control treatments for different activities. Clinically, the device could be a useful tool for measuring the amount of pistoning that feels optimal to a patient, information that would be useful during refitting. …