Myoelectric prosthesis hand grasp control following targeted muscle reinnervation in individuals with transradial amputation

Abstract

Background: Despite the growing availability of multifunctional prosthetic hands, users' control and overall functional abilities with these hands remain limited. The combination of pattern recognition control and targeted muscle reinnervation (TMR) surgery, an innovative technique where amputated nerves are transferred to reinnervate new muscle targets in the residual limb, has been used to improve prosthesis control of individuals with more proximal upper limb amputations (i.e., shoulder disarticulation and transhumeral amputation).

Objective: The goal of this study was to determine if prosthesis hand grasp control improves following transradial TMR surgery.

Methods: Eight participants were trained to use a multi-articulating hand prosthesis under myoelectric pattern recognition control. All participated in home usage trials pre- and post-TMR surgery. Upper limb outcome measures were collected following each home trial.

Results: Three outcome measures (Southampton Hand Assessment Procedure, Jebsen-Taylor Hand Function Test, and Box and Blocks Test) improved 9-12 months post-TMR surgery compared with pre-surgery measures. The Assessment of Capacity for Myoelectric Control and Activities Measure for Upper Limb Amputees outcome measures had no difference pre- and post-surgery. An offline electromyography analysis showed a decrease in grip classification error post-TMR surgery compared to pre-TMR surgery. Additionally, a majority of subjects noted qualitative improvements in their residual limb and phantom limb sensations post-TMR.

Conclusions: The potential for TMR surgery to result in more repeatable muscle contractions, possibly due to the reduction in pain levels and/or changes to phantom limb sensations, may increase functional use of many of the clinically available dexterous prosthetic hands.

Fig 1. Participant flow diagram of enrollment, allocation, follow-up, and analysis.

Fig 2. Home usage from two representative participants during the 8-week Pre-TMR (top) and 8-week Post-TMR-1 (bottom) home trials.

Each graph indicates the number of hours the device was turned on (bar, with scale on left-hand axis) and the number of calibrations (dot, with scale on right-hand axis) performed for each day of the home trial. Days of no use were logged as 0 hours on the plots.

Fig 3. Changes in post-home trial outcome measures for 7 subjects from the Pre-TMR 8-week trial to the Post-TMR 8-week trial (Post-TMR-1, orange) and from the Pre-TMR 8-week trial the final Post-TMR 3 month trial (Post-TMR-2, red).

The SHAP, Box & Blocks, and Jebsen-Taylor showed the largest improvements Post-TMR-2 compared to Pre-TMR.

Fig 4

32-channel EMG data collection setup (top) and results (bottom) for 6 subjects. Offline classification error rates are plotted for the system with increasing number of grips configured (left) and thumb and finger movements (right). Colors represent data collected Pre-TMR (grey) and Post-TMR (orange) optimized for a system using only 4 channels and all 32 channels. Standard deviations for the 4 channels are shown with error bars and for the 32 channel data with shaded bands.

Fig 5. Reinnervated forearm skin of the two subjects who underwent targeted sensory reinnervation.

For both individuals, sensations referred from their missing hand were felt in their residual forearm. Referred sensations were localized to either the palmar side (red), the dorsal side (blue), or both (purple).