How Do Socket Size Adjustments during Ambulation Affect Residual Limb Fluid Volume? Case Study Results

Using magnetic panels to enlarge a transtibial prosthetic socket

A novel method is described to connect a prosthetic liner to the panels of an adjustable socket to facilitate limb fluid volume stabilization in prosthesis users. Magnets are placed in the socket panels, and iron powder is embedded in the user's prosthetic liner. When the magnet is in close proximity to the liner, a firm connection is formed. The system's capability to execute panel pull on transtibial prosthesis users was tested. The backs of the panels were supported by a bracket mounted to the external surface of the socket that allowed the radial position of the panels to be adjusted. Bench testing demonstrated an optimized strength-to-weight ratio using 1.27-cm thick annular-shaped magnets supported by 0.32-cm thick backplates. Testing on four people with transtibial amputation showed that the maximum socket increase achieved using magnetic panel pull ranged from 5.3% to 13.8% of the initial (panels flush) socket volume. The results indicate that magnetic panel pull induces a meaningful increase in socket volume during sitting. The clinical relevance is a novel strategy that may help stabilize prosthesis users' limb fluid volume over the day.

Residual limb volume fluctuations in transfemoral amputees

This study constitutes the first attempt to systematically quantify residual limb volume fluctuations in transfemoral amputees. The study was carried out on 24 amputees to investigate variations due to prosthesis doffing, physical activity, and testing time. A proper experimental set-up was designed, including a 3D optical scanner to improve precision and acceptability by amputees. The first test session aimed at measuring residual limb volume at 7 time-points, with 10 min intervals, after prosthesis doffing. This allowed for evaluating the time required for volume stabilization after prosthesis removal, for each amputee. In subsequent sessions, 16 residual limb scans in a day for each amputee were captured to evaluate volume fluctuations due to prosthesis removal and physical activity, in two times per day (morning and afternoon). These measurements were repeated in three different days, a week apart from each other, for a total of 48 scans for each amputee. Volume fluctuations over time after prosthesis doffing showed a two-term decay exponential trend (R2 = 0.97), with the highest variation in the initial 10 min and an average stabilization time of 30 min. A statistically significant increase in residual limb volume following both prosthesis removal and physical activity was verified. No differences were observed between measures collected in the morning and in the afternoon.Clinical Trials.gov ID: NCT04709367.

Socket size adjustments in people with transtibial amputation: Effects on residual limb fluid volume and limb-socket distance

BACKGROUND

Small intermittent adjustments of socket size using adjustable sockets may be a means for people with transtibial amputation to better maintain residual limb fluid volume and limb position while using a prosthesis.

METHODS

Socket size, limb fluid volume, and distance from the limb to the socket, termed "sensed distance," were recorded while participants with transtibial amputation walked on a treadmill wearing a motor-driven, cabled-panel, adjustable socket. Researchers made frequent socket size adjustments using a mobile phone app to identify participants' acceptable socket size range. Limb fluid volume and sensed distance were then monitored as incremental adjustments were made to the socket.

FINDINGS

Prosthesis users in this study (n = 10) accepted socket sizes between -5% and +5% of their neutral socket volume. There was a rapid increase in limb fluid volume and sensed distance upon socket enlargement, and a rapid decrease upon reduction. Subsequently, there were gradual changes in fluid volume and sensed distance. While visually monitoring limb fluid volume data in real time, researchers were able to adjust socket size to maintain consistent limb fluid volume within a -0.7% to +0.9% volume change for 24 min.

INTERPRETATION

Participant residual limbs compensated to socket size adjustment. Using socket-mounted sensors to monitor limb-socket mechanics, an automatic adjustable socket that maintains limb fluid volume may be possible and may improve socket fit in instances where fit deteriorates during use.