Bidirectional bionic limbs: a perspective bridging technology and physiology.

Precise control of bionic limbs relies on robust decoding of motor commands from nerves or muscles signals and sensory feedback from artificial limbs to the nervous system by interfacing the afferent nerve pathways. Implantable devices for bidirectional communication with bionic limbs have been developed in parallel with research on physiological alterations caused by an amputation. In this perspective article, we question whether increasing our effort on bridging these technologies with a deeper understanding of amputation pathophysiology and human motor control may help to overcome pressing stalls in the next generation of bionic limbs.

Long-term implant of intramuscular sensors and nerve transfers for wireless control of robotic arms in above-elbow amputees.

Targeted muscle reinnervation (TMR) amplifies the electrical activity of nerves at the stump of amputees by redirecting them in remnant muscles above the amputation. The electrical activity of the reinnervated muscles can be used to extract natural control signals. Nonetheless, current control systems, mainly based on noninvasive muscle recordings, fail to provide accurate and reliable control over time. This is one of the major reasons for prosthetic abandonment. This prospective interventional study includes three unilateral above-elbow amputees and reports the long-term (2.5 years) implant of wireless myoelectric sensors in the reinnervation sites after TMR and their use for control of robotic arms in daily life. It therefore demonstrates the clinical viability of chronically implanted myoelectric interfaces that amplify nerve activity through TMR. The patients showed substantial functional improvements using the implanted system compared with control based on surface electrodes. The combination of TMR and chronically implanted sensors may drastically improve robotic limb replacement in above-elbow amputees.

Relieving phantom limb pain with multimodal sensory-motor training.

OBJECTIVE: The causes for the disabling condition of phantom limb pain (PLP), affecting 85% of amputees, are so far unknown, with few effective treatments available. Sensory feedback based strategies to normalize the motor commands to control the phantom limb offer important targets for new effective treatments as the correlation between phantom limb motor control and sensory feedback from the motor intention has been identified as a possible mechanism for PLP development. APPROACH: Ten upper-limb amputees, suffering from chronic PLP, underwent 16 days of intensive training on phantom-limb movement control. Visual and tactile feedback, driven by muscular activity at the stump, was provided with the aim of reducing PLP intensity. MAIN RESULTS: A 32.1% reduction of PLP intensity was obtained at the follow-up (6 weeks after the end of the training, with an initial 21.6% reduction immediately at the end of the training) reaching clinical effectiveness for chronic pain reduction. Multimodal sensory-motor training on phantom-limb movements with visual and tactile feedback is a new method for PLP reduction. SIGNIFICANCE: The study results revealed a substantial reduction in phantom limb pain intensity, obtained with a new training protocol focused on improving phantom limb motor output using visual and tactile feedback from the stump muscular activity executed to move the phantom limb.

Nerve grafts bridging the thenar branch of the median nerve to the ulnar nerve to enhance nerve recovery: a report of three cases.

We report a nerve graft procedure bridging the thenar branch of the median nerve to the ulnar nerve in three patients with ulnar nerve transection and defect at the mid-forearm. Ulnar nerve function was evaluated with electroneurography and quantitative sensory-motor testing before and after surgery, and at a 6-year follow-up. After surgery all patients showed electroneurographic evidence of median nerve innervation of the intrinsic muscles normally innervated by the ulnar nerve. The average strength was Grade 4 in the intrinsic muscles originally supplied by the ulnar nerve at the final follow-up. Our results indicate that the thenar branch of the median nerve may support ulnar nerve regeneration and so help prevent intrinsic muscles from irreversible atrophy, but our report is preliminary. This procedure should be validated by future clinical data, especially those with complete ulnar nerve transection at or above the elbow. LEVEL OF EVIDENCE: IV.

[Exoprosthetic Replacement of the Upper Extremity]. / Exoprothetischer Ersatz bei Amputationen der oberen Extremität.

During the last years, the prosthetic replacement in upper limb amputees has undergone different developments. The use of new nerve surgical concepts improved the control strategies tremendously, especially for high-level amputees. Technological innovation in the field of pattern recognition enables the control of multifunctional myoelectric hand prostheses in a natural and intuitive manner. However, the different levels of amputation pose different challenges for the therapeutic team which concern not only the prosthetic attachment; also the expected functional outcome of prosthetic limb replacement differs greatly between the individual levels of amputation. Therefore, especially in partial hand amputations the indication for prosthetic fitting has to be evaluated critically, as these patients may benefit more from biologic reconstructive concepts. The value of the upper extremity, in particular of the hand, is undisputable and, as such represents the driving force for the technological and surgical developments within the exoprosthetic replacement. This article discusses the possibilities and limitations of exoprosthetic limb replacement on the different amputation levels and explores new developments.

[Prosthetic reconstruction of the upper extremity]. / Prothetische Rekonstruktion der oberen Extremität.

BACKGROUND: Prosthetic replacement after amputation or loss of function of the upper extremity has gained therapeutic value over the last years. The control of upper arm prostheses has been refined by the use of selective nerve transfers, and the indication for prosthetic replacement has been expanded. OBJECTIVES: Overview regarding surgical, therapeutic and prosthetic options in upper extremity amputations or their loss of function. METHODS: Selective literature research including the authors' own experience in everyday clinical practice, as well as a review of medical records. RESULTS: Selective nerve transfers of the amputated nerves of the brachial plexus to the remaining stump muscles can create up to six myosignals for intuitive and simultaneous control of the different prosthetic joints. This way, an efficient and harmonious control of the prosthetic device is possible without the need to change between the different control levels. The prosthetic replacement, with consequent elective amputation, represents a new approach in the functional reconstruction of the upper extremity, especially in patients with a functionless hand after massive soft tissue or nerve damage.

Hand Transplantation Versus Hand Prosthetics: Pros and Cons.

Composite tissue transplantation and new developments in the field of prosthetics have opened new frontiers in the restoration of function among upper limb amputees. It is now possible to restore hand function in affected patients; however, the indications, advantages, and limitations for either hand transplantation or prosthetic fitting must be carefully considered depending on the level and extent of the limb loss. Hand transplantation allows comprehensive hand function to be restored, yet composite tissue transplantation comes with disadvantages, making this method a controversial topic in the hand surgical community. Alternatively, prosthetic limb replacement represents the standard of care for upper limb amputees, but results in the known limitations of function, sensation, and usage. The indication for hand transplantation or prosthetic fitting strongly depends on the level of amputation, as well as on the extent (unilateral/bilateral) of the amputation. In this review, we discuss the advantages and disadvantages of hand transplantation and prosthetic replacement for upper limb amputees in general, as well as in regard to the different levels of amputation.

Prosthetic reconstruction to restore function in transcarpal amputees.

Mutilated hands at the distal level may pose a challenge for reconstruction. Biological treatment options may require multiple surgical interventions and a long rehabilitation course with little hope of good functional outcome. Standard hand prostheses are also not an ideal solution, as they are too long and cumbersome for partial hand injuries. This paper outlines the functional outcomes of prosthetic reconstruction with devices customized for the transcarpal amputation levels. The functional outcome was evaluated with the Action Research Arm Test (ARAT), Southampton Hand Assessment Procedure (SHAP), and the Disabilities of the Arm, Shoulder and Hand questionnaire (DASH). Functional evaluation was performed at least 12 months after final fitting. Psychological assessment was performed with the Short Form-36. The three patients achieved a mean ARAT score of 35.67 ± 0.58. The average SHAP score was 74 ± 7.81. The average DASH score was found to be 16.11 ± 12.03. The reconstructed hand achieved a score of 75.27 ± 8.16% in SHAP and 62.57 ± 1.02% in ARAT in relation to the healthy hand. All patients exhibited average physical and mental component summary scales in the Short Form-36. The majority of transcarpal amputations are seen in manual laborers due to work-related trauma. Returning to work is the main goal in such young and otherwise-healthy patients. As shown with this study, prosthetic fitting results in quick and reliable functional reconstruction. Therefore, this treatment should be considered as an option during the initial decision-making process of reconstructing difficult traumatic injuries of the hand.

Experimental nerve transfer model in the rat forelimb.

BACKGROUND: Nerve transfers are a powerful tool in extremity reconstruction, but the neurophysiological effects have not been adequately investigated. As 81 % of nerve injuries and most nerve transfers occur in the upper extremity with its own neurophysiological properties, the standard rat hindlimb model may not be optimal in this paradigm. Here we present an experimental rat forelimb model to investigate nerve transfers. METHODS: In ten male Sprague-Dawley rats, the ulnar nerve was transferred to the motor branch of long head of the biceps. Sham surgery was performed in five animals (exposure/closure). After 12 weeks of regeneration, muscle force and Bertelli test were performed and evaluated. RESULTS: The nerve transfer successfully reinnervated the long head of the biceps in all animals, as indicated by muscle force and behavioral outcome. No aberrant reinnervation occurred from the original motor source. Muscle force was 2,68 N ± 0.35 for the nerve transfer group and 2,85 N ± 0.39 for the sham group, which was not statically different (p = 0.436). The procedure led to minor functional deficits due to the loss of ulnar nerve function; this, however, could not be quantified with any of the presented measures. CONCLUSION: The above-described rat model demonstrated a constant anatomy, suitable for nerve transfers that are accessible to standard neuromuscular analyses and behavioral testing. This model allows the study of both neurophysiologic properties and cognitive motor function after nerve transfers in the upper extremity.

[Prosthetic reconstruction in high amputations of the upper extremity]. / Prothetische Rekonstruktion hoher Amputationen der oberen Extremität.

BACKGROUND: Conventional upper arm prostheses are controlled via two surface electrodes that measure motor activity of two separately innervated muscle groups. The various prosthetic joints are chosen by co-contractions and controlled linearly by these two muscles. A harmonious and natural course of movements is not possible in this way. OBJECTIVES: Overview regarding surgical, therapeutical and prosthetic options in high amputations of the upper extremity. METHODS: Selective literature research including the authors' own experience in everyday clinical practice as well as a review of medical records. RESULTS: Selective nerve transfers of the amputated nerves of the brachial plexus to the remaining stump muscles can create up to six myosignals for intuitive and simultaneous control of the different prosthetic joints. In this way, an efficient and harmonious control of the prosthetic device is possible without the need to change between the different control levels. At the same time, possible neuromas are treated and painless wear of the prosthesis is achieved. Due to the resulting extended use of the prosthetic device, the demands regarding stump quality are increased. Thus, both surgically and by the means of the orthopedic technician a stable stump-socket connection should be achieved to enable optimal prosthetic function.

Prospective study on complications following a lower body lift after massive weight loss.

BACKGROUND: Lower body lift procedures are in high demand following the increase of massive weight loss patients. As surgical complication rates in this patient group are generally high, patients need to be prepared for risk factors and complications in lower body lift surgery. The aim of this study was to identify the complications and possible risk factors of a lower body lift as concrete data for this procedure are limited. METHODS: A prospective study on 50 consecutive patients who underwent a lower body lift procedure was performed. Measures included co-morbidities and complications. Risk factors assessed included patient age, gender, highest lifetime body mass index (BMI) (BMI max), current BMI, excess weight loss (EWL), type of weight loss and nicotine consumption. RESULTS: There were 50 patients (44 females, six males) with a mean age of 41±10.8 years and a mean EWL of 86.4±15.6%. Mean BMI max was 49.5±10.5 kg m(-2), current BMI was 27.8±4.0 kg m(-2). A total of 35 (70%) patients developed at least one complication. Five patients (10%) suffered a major complication that necessitated surgical revision. Wound dehiscence occurred in 30 patients (60%), followed by seroma in 17 patients (34%). A surgical complication was directly related to BMI max (p=0.02) and age of the patient at the time of surgery (p=0.03). CONCLUSIONS: The overall complication rate following a lower body lift was 70%, which is comparable with that known for high-risk patient groups. The most important risk factors are BMI max and age of the patient (Clinical trial registration number (ISRCTN): NCT01551862).

[Treatment of painful neuromas via end-to-side neurorraphy]. / Die Behandlung chronisch schmerzhafter Neurome mittels End-zu-Seit Neurorraphie.

INTRODUCTION: Management of the painful neuroma has been subject to controversy since the earliest descriptions of this disabling problem. Today, treatment is limited to resection of the neuroma and implantation of the nerve in a muscle at a location where it is safe from irritation and trauma. This however is not attainable in many cases and it is our clinical experience, that nerves without a target remain a source of constant discomfort and pain. Recently we reported of the feasibility of neuroma prevention through end-to-side neurorraphy into adjacent sensory and/or motor nerves to provide a target for axons deprived of their endorgan. Here we report of our first clinical experience with this method in sixteen patients with longstanding upper and lower extremity neuromas. PATIENTS AND METHODS: 16 patients were included in this study. All had neuromas of different sensory nerves of both the upper and lower extremity. 11 were of iatrogenic origin, 5 were caused by different traumas. 8 had previous attempts to surgically treat the neuroma. Finally, all were treated by end-to-side neurorraphy into adjacent nerves. Postoperatively quantitative sensorymotor testing was performed to evaluate possible changes of nerve function of the recipient nerves. Pain was evaluated by visual analogue score and changes in pain medication. RESULTS: In no patient a sensory or motor deficit or painful sensations were induced in the target area of the recipient nerve. Some had dysaesthesias for about 6 months, which finally subsided. All but 1 patient improved in their symptoms at a follow-up of more than 2 years. CONCLUSION: Previous experimental work and present clinical results suggest that axons of a severed peripheral nerve that are provided with a pathway and target through an end-to-side coaptation will either be pruned or establish some type of end-organ contact so that a neuroma can be prevented without inducing sensory or motor dysfunctions in the recipient nerve.

[Selective nerve transfers to improve the control of myoelectrical arm prostheses]. / Selektive Nerventransfers zur verbesserten Steuerung myoelektrischer Armprothesen.

To date, the movement of myoelectrical arm prostheses proceeds via two transcutaneous electrodes that are controlled by two separately innervated muscle groups. The various control levels are chosen by co-contractions of these muscles and the respective level is linearly controlled by the same muscles. A harmonious course of movement as in the corresponding natural pattern of motion is not possible in this way. An appreciable improvement would be given by the control of the individual movement levels by signals that correspond neuronally with the natural pattern of motion. Just recently, prostheses with six control levels have been realised technically. The objective is to separate the major arm nerves, such as the musculocutaneous nerve, radial nerve, median nerve and ulnar nerve, from the proximal arm nerve plexus and to transfer them to the residual nerve branches of muscles near the stem in order to create meaningful neuromuscular units that can serve as impulse sources for myoelectrical prosthesis. As target muscles, above all, one can consider the major/minor pectoral muscles or, respectively, the latissimus muscle. According to the activity of the donor nerves, these muscles would contract and control the prosthesis via transcutaneous electrode. In this way, a harmonious control corresponding intuitively to the natural pattern of movement would be possible without the necessity for the patient to continuously switch between the various control levels. Prerequisites for this are intact proximal muscle groups and a more or less intact arm nerve plexus with the possibility to isolate donor nerves according to the topographic-anatomic situation. For this reason, a preoperative MRI examination, a high resolution sonographic study and balancing NLG and EMG of the residual nerve plexus are necessary. For the preoperative planning phase as well as for the postoperative follow-up, a detailed procedure has been established, in cooperation with the innovation department of the Otto Bock company, to create the most meaningful switch levels, to optimise electrode placement as well as to clarify prosthesis incorporation. Finally, a complex rehabilitation programme is necessary for the patient to achieve an optimal result.

[Is a differentiated treatment depending on the degree of severity justified in cubital tunnel syndrome?]. / Ist eine unterschiedliche Behandlung bei verschiedenen Schweregraden des Sulcus nervi ulnaris-Syndroms sinnvoll?

BACKGROUND: Cubital tunnel syndrome is the second most common chronic nerve entrapment of the upper extremity, yet both diagnosis and staging of the severity of the progression of the disease rely mostly on the keen observation and interpretation of clinical signs and symptoms. To be valid, a staging system must correlate well with the known pathophysiological mechanisms of chronic nerve compression, have objective parameters available to quantify differing degrees of sensory and motor dysfunction, and finally must allow different therapeutic consequences. PATIENTS AND METHODS: In this study we have prospectively evaluated 44 patients who presented with the clinical diagnosis of cubital tunnel syndrome. Quantitative Sensory Testing was performed using a computer-assisted testing system (Sensory-Management Services L. L. C., Baltimore). Classic two-point discrimination, one point pressure threshold, pinch and grip strength were measured. Progression of disease was staged according to the gradual loss of sensory and motor function. After an average of 15 months postoperatively, ulnar nerve function was re-evaluated using the same parameters and outcome measured with the modified Bishop rating scale. RESULTS: The results of this study indicate that 100 % of patients in the moderate group had a good and excellent outcome, whereas only 74 % of the severe group were rated as good and excellent with 17 % moderate and 9 % poor outcome.

[Significance of electroneurographic parameters in the diagnosis of chronic neuropathy of the ulnar nerve at the elbow]. / Die Wertigkeit elektroneurographischer Messparameter in der Diagnostik der chronischen Ulnarisneuropathie am Ellenbogen.

PURPOSE: Ulnar neuropathy at the elbow (UNE) is the second most common compressive neuropathy of the upper limb. Besides clinical evaluation, electrodiagnostic studies are usually applied to confirm the diagnosis. However, there are certain limitations to the diagnosis of UNE by electrodiagnostic studies. In a prospectively performed study we compared the diagnostic value of the electrodiagnostic parameters to the symptoms and the clinical parameters for different degrees of sensory and motor dysfunctions. METHODS AND MATERIALS: Between 2001 and 2003, 38 patients (mean age 53.9 +/- 8.8 years, 19 men and 19 women) were treated at our institution for UNE. For 34 (89%) patients complete electrodiagnostic studies were performed and for 25 patients there was also an electrodiagnostic evaluation of the asymptomatic contralateral arm. According to the symptoms and clinical parameters (grip and pinch grip, two-point discrimination), the patients were assigned to three stages (mild, moderate, and severe). Electrophysiological measurements for each stage were compared with one another. The diagnostic value for each electrophysiological parameter was evaluated in comparison to the normal limits of the "Deutsche Gesellschaft für Neurologie (DGN)" and the "American Association of Electrodiagnostic Medicine (AAEM)". RESULTS: In the 34 symptomatic arms the mean values for motor nerve conduction were: conduction velocity (MNCV) = 41.2 +/- 11.6 m/s; velocity change above-to-below-elbow segment = 12.8 +/- 7.7 m/s; CMAP = 9224 +/- 5514 microV; dL = 3.24 +/- 0.82 mg. For the moderate stages of nerve compression (n = 11) the mean values are: MNCV = 42.5 +/- 12.7; velocity change MNCV = 13.2 +/- 6.8; CMAP = 11 890 +/- 4750; dL = 2.97 +/- 0.57; for severe nerve compression (n = 23): MNCV = 40.6 +/- 11.0; change MNCV = 12.7 +/- 8.3; CMAP = 7948 +/- 5358; dL = 3.37 +/- 0.8. The difference for each parameter between the symptomatic and asymptomatic contralateral arm was statistically significant (p < 0.05) as it was for the difference of the parameters of the group with severe nerve compression in comparison to the asymptomatic arm. In the comparison of the moderate stage group with the asymptomatic arm there was only a significant difference for MNCV and there was no significant difference between the moderate and the severe group. In our study the calculated sensitivities for the electrodiagnostic studies were 76% for all symptomatic arms, 64% for the moderate group, and 83% for the severe nerve compression group. In all patients the MNCV was the most sensitive parameter. CONCLUSION: Electrodiagnostic studies were only able to reveal 3/4 of all patients with an affection of the ulnar nerve and only 2/3 of the patients with a moderate stage of ulnar nerve compression. Although important for the further therapy, a differentiation between a moderate and severe degree of nerve compression was not possible.

The anatomy of the pectoral nerves and their significance in brachial plexus reconstruction.

Twenty-nine brachial plexuses from 13 embalmed and 5 fresh cadavers were examined under x3.5 loupe magnification to collect systematic and topographic anatomical data regarding the lateral and medial pectoral nerves. Additionally, nerve biopsy specimens were harvested in 5 fresh cadavers to obtain histomorphometric data. In all dissections the pectoral nerves exited at the trunk level as 3 distinct nerves. The superior pectoral nerve (from the anterior division of the superior trunk) commences just distal to the suprascapular nerve and courses laterally to innervate the lateral clavicular portion of the pectoralis major muscle (PM) with 2 to 4 branches. The middle pectoral nerve (from the anterior division of the middle trunk) courses distally and enters the infraclavicular fossa with 2 constant branches. The superficial branch terminates in the medial clavicular and upper sternal parts of the PM. The deep branch always forms a plexus with the medial pectoral or inferior pectoral nerve (from the anterior division of the inferior trunk), which courses at a right angle around the the lateral thoracic artery. From this plexus several branches terminate in the Pm. The branch to the lower aspect of the PM pierces the pectoralis minor muscle in two thirds of cases, whereas it passes its inferior border to reach the lower aspects of the PM with an average length of 15 cm in one third of cases. Knowledge of the detailed anatomy of the pectoral nerves, as outlined in this study, clarifies the obscure anatomic relationship of the lateral and medial pectoral nerves and allows easy intraoperative location of the medial pectoral nerve at the exit of the lateral thoracic artery. The length of the inferior pectoral nerve, the number of motor axons, and the anatomical proximity of this nerve make it an expendable but powerful source of reinnervation to the musculocutaneous nerve in upper brachial plexus injuries.

Results of decompression of peripheral nerves in diabetics: a prospective, blinded study.

Diabetic neuropathy traditionally is considered progressive and irreversible and will result in lower extremity ulceration and amputation in a segment of the diabetic population, despite the best efforts to control serum glucose levels. Restoration of sensation to the diabetic may prevent these complications of neuropathy. The present study was designed to evaluate whether decompression of a peripheral nerve at a known site of anatomic narrowing can restore sensibility to that nerve in the diabetic. Twenty diabetic patients ( 14 type I, 6 type II, with a mean duration of diabetes of 14.8 years) had surgical decompression of a median nerve at the wrist and an ulnar nerve at the elbow, or a decompression of the posterior tibial nerve at the ankle (total of 31 nerves). A therapist, in a manner blind to the operative site, evaluated two-point discrimination in the pulp of the appropriate digit. The postoperative sensibility was compared with that of the nontreated, contralateral extremity. At a mean of 23.3 months, 69 percent of the lower-extremity nerves and 88 percent of the upper-extremity nerves (79 percent overall) had improvement in sensibility. In comparison, 32 percent of the control (not decompressed) contralateral nerves had measurable progression of neuropathy. The hypothesis that decompression of a peripheral nerve in the diabetic will improve sensibility was confirmed at the p < 0.001 level.

Cutaneous innervation of the medial ankle: an anatomic study of the saphenous, sural, and tibial nerves and their clinical significance.

The distribution and variability of the nerves innervating the skin overlying the medial ankle were determined in 22 human anatomic specimens using x3.5 loupe magnification for dissection. Five different types could be identified: (1) Type A received contributions from the saphenous (SP), sural (SR), and the tibial (TB) nerves (54%); (2) Type B received contributions from the SR and SP nerves (14%); (3) Type C received contributions from the TB and SP nerves (9%); (4) Type D was singularly innervated by the SP (14%); and (5) Type E received contributions only from the TB nerve (9%). In two specimens, an unusual connection between the SP and the medial plantar nerves was found. Based on these findings, an incision line for tarsal tunnel release is suggested to avoid injury to the small cutaneous branches of the SP, SR, and TB nerves.