Theodore A. Kung

Regenerative peripheral nerve interface viability and signal transduction with an implanted electrode

Background: The regenerative peripheral nerve interface is an internal interface for signal transduction with external electronics of prosthetic limbs; it consists of an electrode and a unit of free muscle that is neurotized by a transected residual peripheral nerve. Adding a conductive polymer coating on electrodes improves electrode conductivity. This study examines regenerative peripheral nerve interface tissue viability and signal fidelity in the presence of an implanted electrode coated or uncoated with a conductive polymer. Methods: In a rat model, the extensor digitorum longus muscle was moved as a nonvascularized free tissue transfer and neurotized by the divided peroneal nerve. Either a stainless steel pad electrode (n = 8) or a pad electrode coated with poly(3,4-ethylenedioxythiophene) conductive polymer (PEDOT) (n = 8) was implanted on the muscle transfer and secured with an encircling acellular extracellular matrix. The contralateral muscle served as the control. Results: The free muscle transfers were successfully revascularized and over time reinnervated as evidenced by serial insertional needle electromyography. Compound muscle action potentials were successfully transduced through the regenerative peripheral nerve interface. The conductive polymer coating on the implanted electrode resulted in increased recorded signal amplitude that was observed throughout the course of the study. Histologic examination confirmed axonal sprouting, elongation, and synaptogenesis within regenerative peripheral nerve interface regardless of electrode type. Conclusions: The regenerative peripheral nerve interface remains viable over seven months in the presence of an implanted electrode. Electrodes with and without conductive polymer reliably transduced signals from the regenerative peripheral nerve interface. Electrodes with a conductive polymer coating resulted in recording more of the regenerative peripheral nerve interface signal.

Migraine surgery: a plastic surgery solution for refractory migraine headache.

Migraine headache can be a debilitating condition that confers a substantial burden to the affected individual and to society. Despite significant advancements in the medical management of this challenging disorder, clinical data have revealed a proportion of patients who do not adequately respond to pharmacologic intervention and remain symptomatic. Recent insights into the pathogenesis of migraine headache argue against a central vasogenic cause and substantiate a peripheral mechanism involving compressed craniofacial nerves that contribute to the generation of migraine headache. Botulinum toxin injection is a relatively new treatment approach with demonstrated efficacy and supports a peripheral mechanism. Patients who fail optimal medical management and experience amelioration of headache pain after injection at specific anatomical locations can be considered for subsequent surgery to decompress the entrapped peripheral nerves. Migraine surgery is an exciting prospect for appropriately selected patients suffering from migraine headache and will continue to be a burgeoning field that is replete with investigative opportunities.

Innovations in prosthetic interfaces for the upper extremity.

Summary: Advancements in modern robotic technology have led to the development of highly sophisticated upper extremity prosthetic limbs. High-fidelity volitional control of these devices is dependent on the critical interface between the patient and the mechanical prosthesis. Recent innovations in prosthetic interfaces have focused on several control strategies. Targeted muscle reinnervation is currently the most immediately applicable prosthetic control strategy and is particularly indicated in proximal upper extremity amputations. Investigation into various brain interfaces has allowed acquisition of neuroelectric signals directly or indirectly from the central nervous system for prosthetic control. Peripheral nerve interfaces permit signal transduction from both motor and sensory nerves with a higher degree of selectivity. This article reviews the current developments in each of these interface systems and discusses the potential of these approaches to facilitate motor control and sensory feedback in upper extremity neuroprosthetic devices.

Motor Unit Changes Seen With Skeletal Muscle Sarcopenia in Oldest Old Rats

Sarcopenia leads to many changes in skeletal muscle that contribute to atrophy, force deficits, and subsequent frailty. The purpose of this study was to characterize motor unit remodeling related to sarcopenia seen in extreme old age. Whole extensor digitorum longus muscle and motor unit contractile properties were measured in 19 adult (11-13 months) and 12 oldest old (36-37 months) Brown-Norway rats. Compared with adults, oldest old rats had significantly fewer motor units per muscle, smaller muscle cross-sectional area, and lower muscle specific force. However, mean motor unit force generation was similar between the two groups due to an increase in innervation ratio by the oldest old rats. These findings suggest that even in extreme old age both fast- and slow-twitch motor units maintain the ability to undergo motor unit remodeling that offsets some effects of sarcopenia.

Clinical factors associated with replantation after traumatic major upper extremity amputation.

Background: Little knowledge exists concerning replantation following traumatic major upper extremity amputation. This study characterizes the injury patterns and outcomes of patients suffering major upper extremity amputation and ascertains clinical factors associated with the decision to attempt replantation. Methods: A retrospective cohort study was conducted on patients treated at a Level I trauma center between June of 2000 and August of 2011. Patients who experienced traumatic upper extremity amputation at or proximal to the radiocarpal joint were included in the study. The subset of patients subsequently undergoing replantation was identified. Medical records were reviewed and bivariate analysis was performed to identify factors associated with attempted replantation and replant survival. Results: Sixty-two patients were treated for traumatic upper extremity amputation and 20 patients underwent replantation. Injury factors associated with attempted replantation included a sharp/penetrating injury (p = 0.004), distal level of amputation (p = 0.017), Injury Severity Score less than 16 (p = 0.020), absence of avulsion (p = 0.002), absence of significant contamination (p ⩽ 0.001), and lack of multilevel involvement (p = 0.007). Replantation exhibited a complete replant survival rate of 70 percent. An Injury Severity Score of 16 or more was associated with replant failure (p = 0.004). Patients who underwent replantation demonstrated increased rates of secondary surgical revisions (p ⩽ 0.001) and complications (p = 0.023) and had a greater length of hospital stay (p = 0.024). Conclusions: Several injury characteristics are associated with the decision to attempt replantation of the major upper extremity. A high global injury severity (Injury Severity Score ≥ 16) is associated with replantation failure when attempted. Patients who undergo replantation demonstrate higher resource use, warranting further cost-analysis and outcomes investigation. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, III.

Current Concepts in the Surgical Management of Lymphedema

Learning Objectives: After studying this article, the participant should be able to: 1. Discuss the key points in diagnosing lymphedema. 2. Understand the imaging modalities that facilitate diagnosis and surgical planning. 3. Appreciate the indications for both physiologic and ablative procedures. 4. Recognize the potential role of lymphaticovenular anastomosis and vascularized lymph node transfer in the treatment of patients with lymphedema. Summary: Lymphedema is an incurable disease caused by insufficient lymphatic drainage leading to abnormal accumulation of interstitial fluid within the soft tissues. Although this condition may result from a primary structural defect of the lymphatic system, most cases in developed countries are secondary to iatrogenic causes. The diagnosis of lymphedema can be made readily by performing a clinical history and physical examination and may be confirmed by imaging studies such as lymphoscintigraphy, magnetic resonance lymphangiography, or indocyanine green lymphangiography. Nonsurgical treatment continues to be the mainstay of lymphedema management. However, advances in microsurgical techniques have revolutionized surgical options for treating lymphedema, and emerging evidence suggests that reconstructive methods may be performed to restore lymphatic flow. Procedures such as lymphaticovenular anastomosis and vascularized lymph node transfer can potentially offer a more permanent solution to chronic lymphedema, and initial studies have demonstrated promising results.

Treatment of peroneal nerve injuries with simultaneous tendon transfer and nerve exploration

BackgroundCommon peroneal nerve palsy leading to foot drop is difficult to manage and has historically been treated with extended bracing with expectant waiting for return of nerve function. Peroneal nerve exploration has traditionally been avoided except in cases of known traumatic or iatrogenic injury, with tendon transfers being performed in a delayed fashion after exhausting conservative treatment. We present a new strategy for management of foot drop with nerve exploration and concomitant tendon transfer.MethodWe retrospectively reviewed a series of 12 patients with peroneal nerve palsies that were treated with tendon transfer from 2005 to 2011. Of these patients, seven were treated with simultaneous peroneal nerve exploration and repair at the time of tendon transfer.ResultsPatients with both nerve repair and tendon transfer had superior functional results with active dorsiflexion in all patients, compared to dorsiflexion in 40% of patients treated with tendon transfers alone. Additionally, 57% of patients treated with nerve repair and tendon transfer were able to achieve enough function to return to running, compared to 20% in patients with tendon transfer alone. No patient had full return of native motor function resulting in excessive dorsiflexion strength.ConclusionThe results of our limited case series for this rare condition indicate that simultaneous nerve repair and tendon transfer showed no detrimental results and may provide improved function over tendon transfer alone.

Development of a Regenerative Peripheral Nerve Interface for Control of a Neuroprosthetic Limb.

Background. The purpose of this experiment was to develop a peripheral nerve interface using cultured myoblasts within a scaffold to provide a biologically stable interface while providing signal amplification for neuroprosthetic control and preventing neuroma formation. Methods. A Regenerative Peripheral Nerve Interface (RPNI) composed of a scaffold and cultured myoblasts was implanted on the end of a divided peroneal nerve in rats (n = 25). The scaffold material consisted of either silicone mesh, acellular muscle, or acellular muscle with chemically polymerized poly(3,4-ethylenedioxythiophene) conductive polymer. Average implantation time was 93 days. Electrophysiological tests were performed at endpoint to determine RPNI viability and ability to transduce neural signals. Tissue samples were examined using both light microscopy and immunohistochemistry. Results. All implanted RPNIs, regardless of scaffold type, remained viable and displayed robust vascularity. Electromyographic activity and stimulated compound muscle action potentials were successfully recorded from all RPNIs. Physiologic efferent motor action potentials were detected from RPNIs in response to sensory foot stimulation. Histology and transmission electron microscopy revealed mature muscle fibers, axonal regeneration without neuroma formation, neovascularization, and synaptogenesis. Desmin staining confirmed the preservation and maturation of myoblasts within the RPNIs. Conclusions. RPNI demonstrates significant myoblast maturation, innervation, and vascularization without neuroma formation.

Endoscopic Strip Craniectomy for Craniosynostosis: Do We Really Understand the Indications, Outcomes, and Risks?

AbstractEndoscopic strip craniectomy with postoperative helmet therapy has been introduced as a means to correct various forms of craniosynostosis. Although some authors have deemed the procedure safe and effective, many questions remain regarding this promising yet developing approach. The authors discuss 4 cases where patients were inadequately treated with endoscopic strip craniectomy resulting in a recommendation of complete secondary open cranial vault reconstruction. In addition, the authors present the findings from an informal survey of craniofacial colleagues to highlight an important discrepancy between published and anecdotal reports of complications. Finally, the authors highlight the need for further investigation into the proper indications and clinical outcomes of endoscopic strip craniectomy to better understand the role of this technique in the treatment of craniosynostosis.

An individualized approach to severe elbow burn contractures.

Summary: Contracture of the antecubital fossa is a common occurrence following thermal burn injury to the upper extremity. Scarring of the superficial tissues can be treated with a variety of surgical methods to provide release and coverage. However, complex scarring of the elbow, which involves the deeper structures, requires a patient-specific technique for which each scarred, shortened, or contracted component is purposefully addressed during the operation. In addition, severe elbow contractures may be complicated by other conditions, such as peripheral neuropathy and heterotopic ossification. This article will discuss the evaluation of the patient with a severe elbow burn contracture and emphasize the importance of an individualized and comprehensive surgical approach. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, V.