Surgical Anatomy and Exercises Using the Chicken Thigh Sciatic Nerve for Microsurgery Training.

Introduction Vessel repair in a chicken thigh is commonly used in microsurgery training model. The sciatic nerve is closely associated with the vessels and has been used for training nerve coaptation, which has different technical considerations from vessel anastomosis. We describe in detail the relevant surgical anatomy and training exercises that can be used with this model. Methods With 32 fresh store-bought chicken thighs, 16 were used to analyze the gross and histological features of the sciatic nerve, and 16 were intended to create and perform training models. Results The average visible length of the nerve in the thigh was 51 mm (standard deviation [SD] 2.57 mm). The average diameter of the nerve was 2 mm (SD 0.33 mm) and was largest at its proximal end (3.21 mm, SD 0.27 mm). The nerve consistently branched into two along the chicken thigh, with more branching subsequently. This simulation model is appropriate not only for the classical end-to-end epineural suture, but also for advanced exercises, in terms of longitudinal fasciculus dissection, mismatched size nerve transfer, injured nerve preparation, and vein conduit technique. Dyeing of nerve fascicles enhanced the visibility of nerve surface quality. Conclusion The sciatic nerve in the chicken thigh is a suitable and accessible model for microsurgery training. The branching and fascicular patterns of the nerve lends itself well to both novice training and advanced simulation. We have incorporated this model into our training curricula.

STEER: 3D Printed Guide for Nerve Regrowth Control and Neural Interface in Non-Human Primate Model.

OBJECTIVE: Peripheral neural interface (PNI) with a stable integration of synthetic elements with neural tissue is key for successfulneuro-prosthetic applications. An inevitable phenomenon of reactive fibrosis is a primary hurdle for long term functionality of PNIs. This proof-of-concept study aimed to fabricate and test a novel, stable PNI that harnesses fibro-axonal outgrowth at the nerve end and includes fibrosis in the design. METHODS: Two non-human primates were implanted with Substrate-guided, Tissue-Electrode Encapsulation and Integration (STEER) PNIs. The implant included a 3D printed guide that strove to steer the regrowing nerve towards encapsulation of the electrodes into a fibro-axonal tissue. After four months from implantation, we performed electrophysiological measurements to test STEER's functionality and examined the macro and micro- morphology of the outgrowth tissue. RESULTS: We observed a highly structured fibro-axonal composite within the STEER PNI. A conduction of intracranially generated action potentials was successfully recorded across the neural interface. Immunohistology demonstrated uniquely configured laminae of myelinated axons encasing the implant. CONCLUSION: STEER PNI reconfigured the structure of the fibro-axonal tissue and facilitated long-term functionality and stability of the neural interface. SIGNIFICANCE: The results point to the feasibility of our concept for creating a stable PNI with long-term electrophysiologic functionality by using simple design and materials.

Guidelines for management of crush injuries of the hand.

Crush injuries of the hand involve damage to multiple structures within the hand, loss of tissue, devascularisation and possibly amputation of digits. They are complex and difficult to classify. Each injury has a unique pattern and requires a unique plan of management. There are no set procedures that can be described, however fundamental principles can be laid down to guide surgical management. Optimum management requires a planned and decisive approach. The surgeon or the team must be well versed with techniques necessary for management of all the structures within the hand, microsurgery and free tissue transfer. The essential components of management are, accurate assessment of the injury and creating a reconstructive plan by structures. The essential components for primary surgery are precise and complete debridement, skeletal stabiliation, vascular repair and if vessels are exposed, soft tissue cover. Secondary surgery should include procedures to enhance the function of the hand or to improve the aesthetics of the hand. These include bone grafting, fusion, tendon and nerve reconstruction, flap de-bulking and toe to hand transfers. The following article is a concise synthesis of the fundamental principles which a hand surgeon must understand while undertaking these challenging procedures.

Maintaining Effective Microsurgery Training with Reduced Utilisation of Live Rats.

Background: Microvascular surgery is now an integral part of many surgical disciplines, and the success of these procedures relies on the technical skills of the surgeon. Although numerous training models and simulations have been developed, the living rat model is favoured for its high fidelity to clinical microsurgery. However, there are serious ethical concerns over the use of live models for training. The aim of this study was to demonstrate if effective skill acquisition was possible with a reduction in the number of live rats. Methods: Two course structures were designed, that were implemented. Total training hours remained the same in both the courses, but the number of rats used was reduced from conventional five rats per participant to four in group A and to three in group B while increasing the training time spent on synthetic and ex-vivo models. We assessed the effectiveness of the courses by comparing the patency rates, the time taken per anastomosis and efficiency of the utilisation rate of rats. Results: There were 30 participants in Group A and 28 participants in group B. We observed that group B was able to perform anastomosis in a significantly shorter time and with patency rates similar to group A in spite of a lesser number of rats used in the training. Conclusions: we were able to conclusively demonstrate that it was possible to reduce live rat usage in microsurgical training without compromising on the quality of training.

Vascular Anatomy of the Hand in Relation to Flaps.

The vascular supply of the hand and wrist is derived from the radial and ulnar arteries. This forms a complex network of vessels on the palmar and dorsal surfaces of the hand. Anastomoses and branching patterns of vessels at the level of the carpals, metacarpals, and phalanges form the basis of old and new flap designs. This article provides an overview on the vascular anatomy of the hand and forearm with emphasis on the blood supply to various flaps.

Managing Mutilating Hand Injuries.

Mutilating injuries include a wide and heterogeneous spectrum of clinical presentations, each being unique in terms of pattern of tissue damage, patient characteristics, and functional requirements. Understanding the principles of reconstruction of bone and soft tissues, a wide repertoire of surgical techniques, and the ability to plan the reconstructive journey leading to a functional hand are crucial. Management of these injuries involves several on-the-spot decisions by the surgeon. This article aims to equip the surgeon with the key principles and the bits of knowledge that are essential for effective planning and execution when dealing with such injuries.

Fibro-Neuronal Guidance on Common, 3D-Printed Textured Substrates.

Ability to direct neuronal growth not only carries great potential for treating neural conditions-for example, bridging traumatically shattered connections-but would also be an exquisite tool for bionic applications that require a physical interface between neurons and electronics. A testing platform is needed to better understand axonal guidance in the context of a specific in vivo application. Versatility of 3D printing technology allows tailoring to researcher needs, both in vitro and in vivo. In this paper, we establish a fibro-neuronal co-culture inspired by our neural interface research and demonstrate axon alignment on a textured substrate fabricated with a common, versatile 3D-printing set-up.

MnSOD is implicated in accelerated wound healing upon Negative Pressure Wound Therapy (NPWT): A case in point for MnSOD mimetics as adjuvants for wound management.

Negative Pressure Wound Therapy (NPWT), a widely used modality in the management of surgical and trauma wounds, offers clear benefits over conventional wound healing strategies. Despite the wide-ranging effects ascribed to NPWT, the precise molecular mechanisms underlying the accelerated healing supported by NPWT remains poorly understood. Notably, cellular redox status-a product of the balance between cellular reactive oxygen species (ROS) production and anti-oxidant defense systems-plays an important role in wound healing and dysregulation of redox homeostasis has a profound effect on wound healing. Here we investigated potential links between the use of NPWT and the regulation of antioxidant mechanisms. Using patient samples and a rodent model of acute injury, we observed a significant accumulation of MnSOD protein as well as higher enzymatic activity in tissues upon NPWT. As a proof of concept and to outline the important role of SOD activity in wound healing, we replaced NPWT by the topical application of a MnSOD mimetic, Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP5+, MnE, BMX-010, AEOl10113) in the rodent model. We observed that MnE is a potent wound healing enhancer as it appears to facilitate the formation of new tissue within the wound bed and consequently advances wound closure by two days, compared to the non-treated animals. Taken together, these results show for the first time a link between NPWT and regulation of antioxidant mechanism through the maintenance of MnSOD activity. Additionally this discovery outlined the potential role of MnSOD mimetics as topical agents enhancing wound healing.

Surmounting the Learning Curve of Core Suture Placement with Tendon Repair Simulator.

BACKGROUND: Attaining competency in placement of core suture with adequate distance from juncture is a key skill for learners of tendon repair. Currently, this is most commonly practiced on animal models in wet laboratory environment. To improve accessibility and availability, we developed a tendon repair trainer that aims to guide learners in obtaining this key competency. METHODS: A customized tendon dock was designed and manufactured with additive method that permits insertion of 6mm silicon tendon rods to simulate flexor tendon repair along a digit. Four residents, divided into two groups, were instructed to repair two sets of tendon rods (60 rods per resident) with Kessler suture loop placed at 10 mm from juncture (Group A: rods marked at 10 mm, Group B: unmarked rods). The main criterion for passing was a loop placed within 1 mm of the target distance (10 mm). At a second session, both groups repaired unmarked tendons, and these were marked based on similar criterion. RESULTS: At the first session, 100% of those who repaired marked rods (Group A) passed while 25% of unmarked rods (Group B) attained a pass. At the second session, where both groups repaired unmarked rods, residents from group A achieved a pass rate of 95% while group B achieved 33.3% pass. CONCLUSIONS: Learners who had previously repaired marked rods were able to retain their experience when repairing unmarked rods. This suggest that the proposed model may be a helpful adjunct to sharpen learners' skills prior to practicing tendon repairs in more costly animal or cadaveric models.

Computer Aided Assessment in Microsurgical Training.

BACKGROUND: Acquiring competence in microsurgical suturing is a basic requirement for any trainee aspiring to perform clinical microsurgery. New methods and simulation platform continue to evolve, but the assessment of the quality of microsurgical suturing is largely subjective. We present the concept of computer aided assessment of standardised microsurgical task, using a novel training platform. The platform comprises of a simulator (hardware) that provides the trainee standardised microsurgical tasks, which are then evaluated using a customised software. METHODS: A cohort of trainees attending a five day microsurgery training course was selected. The trainees performed three standardised exercises on the platform, on the first third and the fifth day of the course. All the exercises were subjected to computer aided assessment. RESULTS: Trainees demonstrated a learning curve over the five day period through the evaluation system, with initial increase in performance followed by a plateau. Eighty four percent of the trainees were able to achieve acceptable scores. Sixteen percent of the trainees were unable to perform a suturing of acceptable quality at the end of the training (fifth day). CONCLUSIONS: The mean scores correlated with the level of difficulty of the exercise. We conclude that computer aided assessment can provide an objective view of the quality of suturing as well as skill maintenance in for trainees.

An Anechoic Space at the Carpal Tunnel Inlet is a Consistent Ultrasonographic Entity which Accommodates Tendon Displacement during Finger Flexion.

BACKGROUND: We consistently observed the presence of anechoic spaces on standard ultrasonographic imaging of the carpal tunnel inlet in normal subjects. These spaces change in size during finger flexion and have not been characterized in a large sample of normal individuals. Ultrasonographic quantification of these spaces may indicate the available space in the region of the carpal tunnel, which allows the normal motion of tendons and the median nerve. METHODS: Transverse ultrasonographic images of the carpal tunnel inlet from 33 asymptomatic volunteers were obtained at Position A (fingers in extension) and B (fingers in flexion). Cross-sectional area (CSA), perimeter and position of anechoic space relative to median nerve were recorded. RESULTS: Analysis showed a 75.4% prevalence rate of a single anechoic space. Two discrete patterns were observed. 89.1% had a decrease in CSA and perimeter of anechoic space from Position A to B while 10.9% exhibited an increase. Mean position of the anechoic space is ulnar (7.49 ± 3.57 mm) and dorsal (2.18 ± 1.28 mm) to the median nerve. CONCLUSIONS: A consistent anechoic space at the carpal tunnel inlet is seen in 75.4% of normal hands and can be quantified (cross sectional area 11.75 ± 7.36 mm(2)). It allows for the accommodation of flexor tendons during finger flexion.

Factors associated with failure of free gracilis flap in reconstruction of acute traumatic leg defects.

BACKGROUND: Possible factors associated with failure of free gracilis flaps were studied. MATERIALS AND METHODS: All gracilis free flaps used to reconstruct acute traumatic leg defects in a 5 year period were collected. This included open fractures of the tibia and/or fibula in which a gracilis free flap was used for reconstruction. Pre-op factors included age, ethnicity, gender, presence of diabetes, ischaemic heart disease, peripheral vascular disease, or coagulation disorders; days from trauma to flap surgery, Gustilo class, presence of a concurrent ipsilateral femur fracture, and use of CT angiogram to determine adequacy of blood supply. Intra-op factors included type of arterial anastomosis (end to side or end to end), presence of arterial transection, initial arterial anastomotic failure, initial venous anastomotic failure, use of systemic vasoconstrictors by anaesthetists for correction of hypotension, and use of modulators of the coagulation mechanism (dextran/heparin). Post-op factors included post-op day when flap was removed and use of modulators of the coagulation mechanism. RESULTS: Patients with a concurrent ipsilateral femur fracture had a 9.67 (95% CI of OR = 1.32-70.96) times increased risk of flap failure compared to patients without an associated femur fracture. CONCLUSION: The finding of increased risk of free gracilis flap failure for coverage of leg defects in patients with ipsilateral femur fractures has implications on flap selection and pre-operative counselling. In such a situation, a non-microvascular option could be safer if it is available as an alternative.

Self-organization of "fibro-axonal" composite tissue around unmodified metallic micro-electrodes can form a functioning interface with a peripheral nerve: A new direction for creating long-term neural interfaces.

INTRODUCTION: A long-term peripheral neural interface is an area of intense research. The use of electrode interfaces is limited by the biological response to the electrode material. METHODS: We created an electrode construct to harbor the rat sciatic nerve with interposition of autogenous adipose tissue between the nerve and the electrode. The construct was implanted for 10 weeks. RESULTS: Immunohistochemistry showed a unique laminar pattern of axonal growth layered between fibro-collagenous tissue, forming a physical interface with the tungsten micro-electrode. Action potentials transmitted across the intrerface showed mean conduction velocities varying between 6.99 ± 2.46 and 20.14 ± 4 m/s. CONCLUSIONS: We have demonstrated the feasibility of a novel peripheral nerve interface through modulation of normal biologic phenomena. It has potential applications as a chronic implantable neural interface.

Biphasic motion of the median nerve in the normal Asian population.

BACKGROUND: The biomechanical interaction between the median nerve and the flexor tendons is an important consideration in Carpal tunnel syndrome (CTS). We aim to quantify the displacement and compressive deformation pattern of the median nerve in various stages of finger flexion in the normal population at the inlet of the carpal tunnel. METHODS: Transverse ultrasounds images were taken at the carpal tunnel inlet during full-extension, mid-flexion and full flexion. The displacement, distance, Feret's diameter, and perimeter of the median nerve were calculated and compared between each position. RESULTS: Biphasic median nerve motion was observed, with a displacement of 2.84 ± 3.49 mm in the ulnar direction from full-extension to mid-flexion (Phase I) and a further 0.93 ± 3.04 mm from mid-flexion to full flexion (Phase II). Of 49 hands, 37 (75.5%) exhibited ulnar displacement in Phase I while 12 (24.5%) exhibited radial displacement. Feret's diameter (5.95 ± 1.08 mm) and perimeter (13.28 ± 2.09) of the median nerve were greatest in the mid-flexed position. CONCLUSION: In a healthy Asian population, the median nerve has a biphasic motion during finger flexion, with maximal deformation in the mid-flexed position.

Use of a definitive cement spacer for simultaneous bony and soft tissue reconstruction of mid- and hindfoot diabetic neuroarthropathy:a case report.

The prevalence of diabetes mellitus has been increasing, and ≤25.8 million people, or 8.3% of the US population, have diabetes. Diabetic Charcot arthropathy and foot ulcers are serious complications of diabetes mellitus. They have been associated with greater risks of lower extremity amputation and mortality. Studies have shown that the amputation risk relative to patients with Charcot arthropathy alone is 7 times greater for patients with a foot ulcer, and 12 times greater for patients with Charcot arthropathy and a foot ulcer. Surgical reconstruction of Charcot arthropathy of the foot is often difficult, because of bone loss, deformities, vasculopathy, and the presence of active infection with or without soft tissue loss. It will be even more challenging if >1 region of the foot has been affected, such as the mid- and hindfoot. In such situations, an amputation would usually be the surgical option. We present a case of limb-threatening Charcot deformity with instability complicated by osteomyelitis, bone loss, and a large soft tissue defect. We used a limb salvage strategy with hindfoot fusion combined with an antibiotic-impregnated cement spacer for reconstruction of the midfoot, which was performed simultaneously with a local adipofascial flap for soft tissue coverage, resulting in a plantigrade, painless, and functional foot.

Predominant patterns of median nerve displacement and deformation during individual finger motion in early carpal tunnel syndrome.

Idiopathic carpal tunnel syndrome (CTS) is a common neuropathy, yet the pathologic changes do not explain the fleeting dynamic symptoms. Dynamic nerve-tendon interaction may be a contributing factor. Based on dynamic ultrasonographic examination of the carpal tunnel, we quantified nerve-tendon movement in thumb, index finger and middle finger flexion in normal subjects and those with mild-idiopathic CTS. Predominant motion patterns were identified. The nerve consistently moves volar-ulnarly. In thumb and index finger flexion, the associated tendons move similarly, whereas the tendon moves dorsoradially in middle finger flexion. Nerve displacement and deformation increased from thumb to index finger to middle finger flexion. Predomination motion patterns may be applied in computational simulations to prescribe specific motions to the tendons and to observe resultant nerve pressures. By identification of the greatest pressure-inducing motions, CTS treatment may be better developed. Symptomatic subjects displayed reduced nerve movement and deformation relative to controls, elucidating the physiologic changes that occur during mild CTS.

Correlation between muscular and nerve signals responsible for hand grasping in non-human primates.

Neuroprosthetic devices that interface with the nervous system to restore functional motor activity offer a viable alternative to nerve regeneration, especially in proximal nerve injuries like brachial plexus injuries where muscle atrophy may set in before nerve re-innervation occurs. Prior studies have used control signals from muscle or cortical activity. However, nerve signals are preferred in many cases since they permit more natural and precise control when compared to muscle activity, and can be accessed with much lower risk than cortical activity. Identification of nerve signals that control the appropriate muscles is essential for the development of such a `bionic link'. Here we examine the correlation between muscle and nerve signals responsible for hand grasping in the M. fascicularis. Simultaneous recordings were performed using a 4-channel thin-film longitudinal intra-fascicular electrode (tf-LIFE) and 9 bipolar endomysial muscle electrodes while the animal performed grasping movements. We were able to identify a high degree of correlation (r > 0.6) between nerve signals from the median nerve and movement-dependent muscle activity from the flexor muscles of the forearm, with a delay that corresponded to 25 m/s nerve conduction velocity. The phase of the flexion could be identified using a wavelet approximation of the ENG. This result confirms this approach for a future neuroprosthetic device for the treatment of peripheral nerve injuries.