Targeted reinnervation in the transfemoral amputee: a preliminary study of surgical technique.

BACKGROUND: Lower limb amputation is a common and growing problem in the United States. Current prosthetic technology is insufficient for transfemoral amputees to safely control their prostheses for demanding exercise such as stair climbing. Using a technique called targeted reinnervation, intuitive control of prosthetic devices has been achieved for upper limb amputees. To bring this technique to transfemoral amputees, a comprehensive understanding of the location of motor and sensory nerves is required. METHODS: Five lower limbs were dissected and the locations of motor points for 13 muscles of the thigh were documented, as was the location of the posterior femoral cutaneous nerve of the thigh. A transfemoral amputation was performed on one limb to demonstrate the targeted reinnervation procedure. The tibial and common peroneal divisions of the sciatic nerve were coapted to the motor points of the semimembranosus and biceps femoris, respectively. The posterior femoral cutaneous nerve was coapted in end-to-side fashion to the tibial nerve. RESULTS: The average number of motor points per muscle were as follows: sartorius, 4.75; rectus femoris, 3.25; vastus lateralis, 4.5; vastus intermedius, 4.5; vastus medialis, 4; adductor brevis, 2.3; adductor longus, 3; adductor magnus, 2.7; gracilis, 3; semitendinosus, 1.5; semimembranosus, 2.5; biceps femoris long head, 2.75; and biceps femoris short head, 1. CONCLUSION: The results of this study indicate that targeted reinnervation is technically feasible in a transfemoral amputee.

Pattern recognition control of multifunction myoelectric prostheses by patients with congenital transradial limb defects: a preliminary study.

BACKGROUND: Electromyography (EMG) pattern recognition offers the potential for improved control of multifunction myoelectric prostheses. However, it is unclear whether this technology can be successfully used by congenital amputees. OBJECTIVE: The purpose of this investigation was to assess the ability of congenital transradial amputees to control a virtual multifunction prosthesis using EMG pattern recognition and compare their performance to that of acquired amputees from a previous study. STUDY DESIGN: Preliminary cross-sectional study. METHODS: Four congenital transradial amputees trained and tested a linear discriminant analysis (LDA) classifier with four wrist movements, five hand movements, and a no-movement class. Subjects then tested the classifier in real time using a virtual arm. RESULTS: Performance metrics for the residual limb were poorer than those with the intact limb (classification accuracy: 52.1% ± 15.0% vs. 93.2% ± 15.8%; motion-completion rate: 49.0%± 23.0% vs. 84.0% ± 9.4%; motion-completion time: 2.05 ± 0.75 s vs. 1.13 ± 0.05 s, respectively). On average, performance with the residual limb by congenital amputees was reduced compared to that reported for acquired transradial amputees. However, one subject performed similarly to acquired amputees. CONCLUSIONS: Pattern recognition control may be a viable option for some congenital amputees. Further study is warranted to determine success factors.

Use of two-axis joystick for control of externally powered shoulder disarticulation prostheses.

We explored a new method for simple and accurate control of shoulder movement for externally powered shoulder disarticulation prostheses with a two-axis joystick. We tested 10 subjects with intact shoulders and arms to determine the average amount of shoulder motion and force available to control an electronic input device. We then applied this information to two different input strategies to examine their effectiveness: (1) a traditional rocker potentiometer and a pair of force-sensing resistors and (2) a two-axis joystick. Three nondisabled subjects and two subjects with shoulder disarticulation amputations attempted to control an experimental externally powered shoulder using both control strategies. Two powered arms were tested, one with powered flexion/extension and humeral rotation and one with powered flexion/extension and adduction/abduction. Overwhelmingly, the subjects preferred the joystick control, because it was more intuitively linked with their shoulder movement. Additionally, two motions (one in each axis) could be controlled simultaneously. This pilot study provides valuable insight into an effective means of controlling high-level, externally powered prostheses with a two-axis joystick.

Neural interfaces for control of upper limb prostheses: the state of the art and future possibilities.

Current treatment of upper limb amputation restores some degree of functional ability, but this ability falls far below the standard set by the natural arm. Although acceptance rates can be high when patients are highly motivated and receive proper training and care, current prostheses often fail to meet the daily needs of amputees and frequently are abandoned. Recent advancements in science and technology have led to promising methods of accessing neural information for communication or control. Researchers have explored invasive and noninvasive methods of connecting with muscles, nerves, or the brain to provide increased functionality for patients experiencing disease or injury, including amputation. These techniques offer hope of more natural and intuitive prosthesis control, and therefore increased quality of life for amputees. In this review, we discuss the current state of the art of neural interfaces, particularly those that may find application within the prosthetics field.

Quantifying pattern recognition-based myoelectric control of multifunctional transradial prostheses.

We evaluated real-time myoelectric pattern recognition control of a virtual arm by transradial amputees. Five unilateral patients performed 10 wrist and hand movements using their amputated and intact arms. In order to demonstrate the value of information from intrinsic hand muscles, this data was included in EMG recordings from the intact arm. With both arms, motions were selected in approximately 0.2 s on average, and completed in less than 1.25 s. Approximately 99% of wrist movements were completed using either arm; however, the completion rate of hand movements was significantly lower for the amputated arm (53.9% +/- 14.2%) than for the intact arm ( 69.4% +/- 13.1%). For the amputated arm, average classification accuracy for only 6 movements-including a single hand grasp-was 93.1% +/- 4.1%, compared to 84.4% +/- 7.2% for all 10 movements. Use of 6 optimally-placed electrodes only reduced this accuracy to 91.5% +/- 4.9%. These results suggest that muscles in the residual forearm produce sufficient myoelectric information for real-time wrist control, but not for performing multiple hand grasps. The outcomes of this study could aid the development of a practical multifunctional myoelectric prosthesis for transradial amputees, and suggest that increased EMG information-such as made available through targeted muscle reinnervation-could improve control of these prostheses.

Examination of force discrimination in human upper limb amputees with reinnervated limb sensation following peripheral nerve transfer.

Artificial limbs allow amputees to manipulate objects, but the loss of a limb severs the sensory link between a subject and objects they touch. A novel surgical technique we term targeted reinnervation (TR) allows severed cutaneous nerves to reinnervate skin on a different portion of the body. This technique provides a physiologically appropriate portal to the sensory pathways of the missing limb through the reinnervated skin. This study quantified the ability of three amputee subjects who had undergone TR surgery on the chest (two subjects) and upper arm (one subject) to discriminate changes in graded force on their reinnervated skin over a range of 1-4 N using a stochastic staircase approach. These values were compared to those from sites on their intact contralateral skin and index fingers, and from the chests and index fingers of a control population (n = 10) . Weber's ratio (WR) was used to examine the subjects' abilities to discriminate between a baseline force and subsequent forces of different magnitudes. WRs of 0.22, 0.25, and 0.12 were measured on the reinnervated skin of the three TR subjects, whereas WRs of 0.25, 0.23, and 0.12 were measured on their contralateral skin. TR subjects did not have substantially different WRs on their reinnervated versus their contralateral normal side and did not appear to exhibit a trend towards impaired sensation. No significant difference was found between the WR of the chest and index finger of the control subjects, which ranged between 0.09 and 0.21. WR of reinnervated skin for TR subjects were within the 95% confidence interval of the control group. These data suggest that subjects with targeted reinnervation have unimpaired ability to discriminate gradations in force.

Sensory capacity of reinnervated skin after redirection of amputated upper limb nerves to the chest.

Targeted reinnervation is a new neural-machine interface that has been developed to help improve the function of new-generation prosthetic limbs. Targeted reinnervation is a surgical procedure that takes the nerves that once innervated a severed limb and redirects them to proximal muscle and skin sites. The sensory afferents of the redirected nerves reinnervate the skin overlying the transfer site. This creates a sensory expression of the missing limb in the amputee's reinnervated skin. When these individuals are touched on this reinnervated skin they feel as though they are being touched on their missing limb. Targeted reinnervation takes nerves that once served the hand, a skin region of high functional importance, and redirects them to less functionally relevant skin areas adjacent to the amputation site. In an effort to better understand the sensory capacity of the reinnervated target skin following this procedure, we examined grating orientation thresholds and point localization thresholds on two amputees who had undergone the targeted reinnervation surgery. Grating orientation thresholds and point localization thresholds were also measured on the contralateral normal skin of the targeted reinnervation amputees and on analogous sites in able-bodied controls. Grating orientation thresholds for the reinnervated skin of the targeted reinnervation amputees were found to be similar to normal ranges for both the amputees' contralateral skin and also for the control population. Point localization thresholds for these amputees were found to be lower for their reinnervated skin than for their contralateral skin. Reinnervated point localization thresholds values were also lower in comparison to homologous chest sites on the control population. Mechanisms appear to be in place to maximize re-established touch input in targeted reinnervation amputees. It seems that sound sensory function is provided to the denervated skin of the residual limb when connected to afferent pathways once serving highly functionally relevant regions of the brain. This suggests that tactile interface devices could be used to give a physiologically appropriate sense of touch to a prosthetic limb, which would likely help with better functional utilization of the prosthetic device and possibly help to more effectively integrate the device with the user's self-image.

Vibrotactile detection thresholds for chest skin of amputees following targeted reinnervation surgery.

Recent advances in the design of prosthetic arms have helped upper limb amputees achieve greater levels of function. However, control of upper limb prostheses is limited by the lack of sensory feedback to the user. Targeted reinnervation, a novel surgical technique for amputees, offers the potential for returning this lost sensation. During targeted reinnervation surgery, truncated nerves are directed to reinnervate new muscle and skin sites. Contractions of reinnervated muscles generate electrical signals that are used to control prosthetic arms. In addition, stimulation of reinnervated skin is perceived on the missing limb. Vibration detection thresholds were measured at four frequencies on the reinnervated chest skin of three shoulder-level amputees following targeted reinnervation surgery. Thresholds were also measured on the contralateral chest and arm skin of these amputees, as well as on the chest and arm skin of a control population. Vibrations applied to reinnervated skin were perceived at various locations on the missing arm and hand. Thresholds for the reinnervated chest skin were generally within the range of values measured on the chests of the control population. For the two unilateral amputees, these thresholds were similar to measures on their contralateral chests, but greater than measures on their contralateral hands. Targeted reinnervation appears to result in near-normal vibration-detection ability with respect to the target tissue, suggesting the functional reinnervation of mechanoreceptors by the reinnervating afferents. The functional limb sensation following targeted reinnervation could be used to provide prosthesis users with a sense of touch.

Expert opinions on success factors for upper-limb prostheses.

The goal of this study was to gather the opinions of prosthetics experts on the most important factors for the successful use of upper-limb (UL) prostheses, compare them with those of prosthesis users, and ultimately direct research efforts in this field. UL prosthetics experts were asked to compare the importance of the comfort, function, and cosmesis of a prosthetic device for a transhumeral amputee. Categories were subdivided into weight, socket-interface comfort, power, agility, color, and shape. The majority of those who responded viewed comfort as the most important factor for a unilateral amputee and considered socket-interface comfort to be more important than weight. Function was considered to be the most important factor for a bilateral amputee, with agility considered more important than power. Cosmesis was consistently reported as being less important than comfort and function, and shape was considered more important than color.