Oskar C. Aszmann

The Extraction of Neural Information from the Surface EMG for the Control of Upper-Limb Prostheses: Emerging Avenues and Challenges

Despite not recording directly from neural cells, the surface electromyogram (EMG) signal contains information on the neural drive to muscles, i.e, the spike trains of motor neurons. Using this property, myoelectric control consists of the recording of EMG signals for extracting control signals to command external devices, such as hand prostheses. In commercial control systems, the intensity of muscle activity is extracted from the EMG and used for single degrees of freedom activation (direct control). Over the past 60 years, academic research has progressed to more sophisticated approaches but, surprisingly, none of these academic achievements has been implemented in commercial systems so far. We provide an overview of both commercial and academic myoelectric control systems and we analyze their performance with respect to the characteristics of the ideal myocontroller. Classic and relatively novel academic methods are described, including techniques for simultaneous and proportional control of multiple degrees of freedom and the use of individual motor neuron spike trains for direct control. The conclusion is that the gap between industry and academia is due to the relatively small functional improvement in daily situations that academic systems offer, despite the promising laboratory results, at the expense of a substantial reduction in robustness. None of the systems so far proposed in the literature fulfills all the important criteria needed for widespread acceptance by the patients, i.e. intuitive, closed-loop, adaptive, and robust real-time (<;200 ms delay) control, minimal number of recording electrodes with low sensitivity to repositioning, minimal training, limited complexity and low consumption. Nonetheless, in recent years, important efforts have been invested in matching these criteria, with relevant steps forwards.

Anatomical course of the lateral femoral cutaneous nerve and its susceptibility to compression and injury

&NA; The anatomy of the lateral femoral cutaneous nerve was investigated through dissection of 52 human anatomic specimens. The variability of its course and location as it exits the pelvis is described and related to soft‐tissue and bony landmarks. Five different types are identified: type A, posterior to the anterior superior iliac spine, across the iliac crest (4 percent); type B, anterior to the anterior superior iliac spine and superficial to the origin of the sartorius muscle but within the substance of the inguinal ligament (27 percent); type C, medial to the anterior superior iliac spine, ensheathed in the tendinous origin of the sartorius muscle (23 percent); type D, medial to the origin of the sartorius muscle located in an interval between the tendon of the sartorius muscle and thick fascia of the iliopsoas muscle deep to the inguinal ligament (26 percent); and type E, most medial and embedded in loose connective tissue, deep to the inguinal ligament, overlying the thin fascia of the iliopsoas muscle, and contributing the femoral branch of the genitofemoral nerve (20 percent). The results of this study suggest that the lateral femoral cutaneous nerve is most susceptible to mechanical trauma when the nerve is type A, B, or C. (Plast. Reconstr. Surg. 100: 600, 1997.)

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.

Osteopontin Is an Activator of Human Adipose Tissue Macrophages and Directly Affects Adipocyte Function

Osteopontin (OPN) is highly up-regulated in adipose tissue in human and murine obesity and has been recently shown to be functionally involved in the pathogenesis of obesity-induced adipose tissue inflammation and associated insulin resistance in mice. OPN is a protein with multiple functions and acts as a chemokine and an inflammatory cytokine through a variety of different receptors (CD44, integrins). It is expressed in many cell types including adipose tissue macrophages (ATM). However, the target cells of OPN action in obese adipose tissue are still elusive. Here, we investigated expression of OPN receptors and the impact of OPN on ATM, adipocytes, and other cells of human adipose tissue. We found broad expression of OPN receptors in different adipose tissue cell types including adipocytes. OPN stimulated inflammatory signaling pathways and secretion of cytokines in model macrophages as well as isolated human ATM. Moreover, OPN impaired differentiation and insulin sensitivity of primary adipocytes as determined by peroxisomal proliferator-activated receptor-γ and adiponectin gene expression and insulin-stimulated glucose uptake. Furthermore, OPN induced inflammatory signaling in human adipocytes. In conclusion, OPN activates ATM and interferes with adipocyte function. Thus these data underline the potential of OPN as a therapeutic target for obesity-induced complications.

Prosthetic Myoelectric Control Strategies: A Clinical Perspective

Control algorithms for upper limb myoelectric prostheses have been in development since the mid-1940s. Despite advances in computing power and in the performance of these algorithms, clinically available prostheses are still based on the earliest control strategies. The aim of this review paper is to detail the development, advantages and disadvantages of prosthetic control systems and to highlight areas that are current barriers for the transition from laboratory to clinical practice. Current surgical strategies and future research directions to achieve multifunctional control will also be discussed. The findings from this review suggest that regression algorithms may offer an alternative feed-forward approach to direct and pattern recognition control, while virtual rehabilitation environments and tactile feedback could improve the overall prosthetic control.

The anatomic basis of the internal mammary artery perforator flap: a cadaver study *

INTRODUCTION The perforating branches of the internal mammary artery have recently been described as recipient vessel for free-tissue transfer breast reconstruction. However, reports on perforator flaps based on these vessels are rare. The aim of this study was to investigate the vascular basis of the internal mammary artery perforator (IMAP) flap and to describe the location and size of the individual flaps. MATERIAL AND METHODS The IMAPs of 10 fresh female cadavers were injected with methylene blue solution. The location and size of the labelled skin area were observed. Finally, the arterial perforators were dissected, and the length, diameter and the distance of the lateral sternal border to the perforation point were recorded. RESULTS The IMAPs supplied the skin of the ventromedial thorax and breast from the clavicle to the skin of the cranial abdominal wall in a sequential order. The mean size of all injected skin areas was 84+/-54 cm(2) (13 x 7 cm). The biggest detected skin dimensions were 16 x 9 cm on average for IMAP 2 (area 138+/-41 cm(2)). The mean external diameter of the IMAP was 1.3+/-0.5 mm (range: 0.4-2.9 mm). The mean dissectible length was 8.3+/-3.6 cm (range: 3-17 cm). The largest diameter was found for IMAP 2 with a mean of 1.6+/-0.5 mm (range: 0.9-2.3 mm). CONCLUSIONS In the present study, a reliable anatomy of the IMAP flap could be demonstrated. Based on these results, different clinical applications exist for the individual IMAP flaps. The flaps based on IMAP 1 or 2 may be rotated cranially for tracheostoma or anterior neck reconstruction. The flaps based on IMAP 4 supplying the skin of the inframammary fold could be used for reconstruction of the contralateral thoracic wall or breast. The harvest site of IMAP 1 and 2 can be closed directly if the width of the flap is less than 6 cm. The IMAP 4 harvest site could be closed via a reduction mammaplasty technique, thus minimising donor-site morbidity.

Bionic reconstruction to restore hand function after brachial plexus injury: a case series of three patients

BACKGROUND Brachial plexus injuries can permanently impair hand function, yet present surgical reconstruction provides only poor results. Here, we present for the first time bionic reconstruction; a combined technique of selective nerve and muscle transfers, elective amputation, and prosthetic rehabilitation to regain hand function. METHODS Between April 2011, and May 2014, three patients with global brachial plexus injury including lower root avulsions underwent bionic reconstruction. Treatment occurred in two stages; first, to identify and create useful electromyographic signals for prosthetic control, and second, to amputate the hand and replace it with a mechatronic prosthesis. Before amputation, the patients had a specifically tailored rehabilitation programme to enhance electromyographic signals and cognitive control of the prosthesis. Final prosthetic fitting was applied as early as 6 weeks after amputation. FINDINGS Bionic reconstruction successfully enabled prosthetic hand use in all three patients. After 3 months, mean Action Research Arm Test score increased from 5·3 (SD 4·73) to 30·7 (14·0). Mean Southampton Hand Assessment Procedure score improved from 9·3 (SD 1·5) to 65·3 (SD 19·4). Mean Disabilities of Arm, Shoulder and Hand score improved from 46·5 (SD 18·7) to 11·7 (SD 8·42). INTERPRETATION For patients with global brachial plexus injury with lower root avulsions, who have no alternative treatment, bionic reconstruction offers a means to restore hand function. FUNDING Austrian Council for Research and Technology Development, Austrian Federal Ministry of Science, Research & Economy, and European Research Council Advanced Grant DEMOVE.

Evidence in support of collateral sprouting after sensory nerve resection.

The extent and time course of sensory recovery has been investigated in 13 patients who had resection of a cutaneous nerve. Seven patients were studied within 8 weeks of denervation; 6 others were studied more than 6 months after denervation. Touch sensation was evaluated using a computer-assisted measuring device that recorded the pressure thresholds for static and moving touch, and static and moving two-point discrimination within a continual range from 0.1 to 100 gm per square millimeter. Recovery of sensation within the autonomous zone of the resected nerve could be documented as early as 3 weeks after denervation. After 6 months, two-point discrimination had recovered in the previously denervated areas. Thresholds for all test modalities were found to be elevated within the sensory distribution of adjacent nerves, which suggests that these areas have been the donor source for reinnervation of the chronically denervated territory. Anesthetic block of these adjacent donor nerves resulted in loss of the recovered sensation.

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).

Bridging critical nerve defects through an acellular homograft seeded with autologous schwann cells obtained from a regeneration neuroma of the proximal stump.

Over the last decade, several models have investigated the usefulness of different biologic and/or synthetic matrices as alternatives to conventional nerve grafts. Still, axonal regeneration did not occur over longer (> 3 cm) distances. One problem may be that a growth-promoting environment not only includes physical cues but also a rich spectrum of different growth factors only provided by reactive Schwann cells. In the current study, we investigated whether a hybrid graft consisting of first-generation autologous Schwann cells seeded onto an acellular auto- or homograft can aid regeneration across a critical nerve defect in a rat model. In this paradigm, Schwann cells were not expanded in vitro but harvested from the proximal stump neuroma at the time of reconstruction and seeded into either an acellular homo- or autograft. Regeneration was then quantitated with functional muscle testing, regular histology, histomorphometry, and retrograde tracing techniques 12 weeks after reconstruction. Results showed successful regeneration over the entire distance regardless of whether Schwann cells were transplanted onto auto- or homologous acellular matrix. Schwann cells did populate both grafts; however, only sensory axons persisted through the entire distance. The functional outcome was dismal with no motor and poor sensory recovery. Control group C with homologous matrix only without Schwann cells showed no signs of directed axonal regeneration. Control group D with autologous reverse graft showed excellent recovery, as was expected. The present experiment sought to create a hybrid graft where the proximal stump neuroma is used as a biological resource for autologous Schwann cells that are seeded unto an acellular matrix, thus providing both physical and chemical support to regenerating axons. The results are encouraging in that successful regeneration was observed over the entire distance; however, only sensory axons had enough regenerative potential to also make end-organ contact. For motor axons, further refinements in conduit preparation have to be done.