Abstract 55: Osseointegrated Neural Interface (ONI): Rethinking a Conventional Surgical Treatment for Amputation Neuromas in the Digital Age.
Aaron M. DingleJoseph NoveloJared P. NessJacqueline S. IsraelBrett NemkeYan LuSarah BrodnikJane A. PissanelloLisa Krugner‐HigbyMark D. MarkelDavid C. GoodspeedJustin C. WilliamsSamuel O. Poore
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PURPOSE: Modern prosthetic limbs have reaped the benefits of the Digital Age, with improvements in materials, degrees of freedom and computational power. What has lagged behind these advances, is the ability of the recipient to control these devices. Neural interfaces are devices that aim to bridge the gap between the biological tissues and the robotic prosthetic. In most cases, the neural interface is placed on the skin, actuated by myoelectric signals highly susceptible to motion artifact and muscle signal crosstalk, ultimately preventing widespread clinical application. In 1943 Edwin Boldrey first published the transposition of nerve in bone to treat amputation neuromas. This method is still in use today, under the fundamental principal that placing the nerve in bone protects the neuroma from the mechanical and electrical stimuli that causes neuropathic pain. By re-directing transected nerves into the medullary cavity of long bones, the terminal end of the nerve is protected from external stimuli, whilst also providing direct access to the highly vascular stem cell niece. This already established surgical model presents the perfect in vivo bioreactor for the potential interfacing of transected nerves and electronic prosthetic devices. The research objectives of this pilot study were to create an animal model -termed the Osseointegrated Neural Interface (ONI), utilizing histology to demonstrate the stability and health of the nerve and surrounding tissues and electrophysiology to demonstrate nerve conductivity. METHODS: Transfemoral amputation was performed in New Zealand white rabbits. Briefly, the sciatic nerve was isolated and severed above the point of bifurcation. The femur was amputated at the midpoint and the nerve passed through a corticotomy. The terminal end of the nerve was sutured into a PDMS nerve sleeve, representing a mock electrode, which was pressed back into the opening of the medullary cavity forming a tight seal. The muscle and skin were closed over the femur. Animals were explored at 5 weeks via histology and electrophysiology. RESULTS: Gross examination of the ONI limb demonstrates that the nerve is stable at 5 weeks. Healthy nerve morphology can be identified by Schwann cells (S100+) along the length of the transected nerve. Cross sections of proximal portions of the nerve demonstrate the ONI nerve contains smaller myelinated axons when compared to the contralateral healthy sciatic nerve. Electrophysiology demonstrates that the nerve is alive within the bone, as demonstrated by compound action potentials. The transected nerve demonstrated action potentials equivalent to half that of the contralateral healthy nerve, which correlates with the smaller diameter of the myelinated axons in the ONI nerve. CONCLUSION: Terminal ends of amputated nerves are functional following being re-directed into the medullary cavity of the femur at 5 weeks. This result provides proof of principle for the ONI model and its ability to house functional prosthetic interfaces. Work is currently underway to test various electrodes in this model.Keywords:
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We report a case of a 55-year-old female with extreme right fourth toe pain of unknown origin that was resistant to conservative care. Resection confirmed invasion of the neuroma into the fourth digit with hypertrophy and herniation of the proper digital nerve. The patient experienced an uneventful recovery with some minor neurogenic symptoms experienced at six months postoperatively that resolved with off-loading padding and heat massage. Complete pain relief was reported at her 12-month review. Isolated neuroma within a toe results in digital pain that may respond to excision.
Digital nerve
Neuroma
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Acoustic neuroma
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Digital nerve
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Current standard management of a cut digital nerve is end-to-end microsurgical nerve coaptation where possible. A recent systematic review of adult digital nerve injuries that were either repaired or left unrepaired showed that the evidence for good nerve recovery or improved function following nerve repair is poor. In the 30 studies included, only 24% of repaired nerves regained sensory recovery close to or equivalent to estimated pre-injury levels. Neuroma rates were the same in those nerves repaired (4.6%) and those not repaired (5%). Questions under debate include proper assessment methods of outcomes, decision making for repair or no repair to different fingers or the thumb, levels of injury, age, and hand dominance. This review summarizes the major evidence available and debates the surgical dogma that surrounds this injury.
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Digital nerve
Nerve repair
Nerve Injury
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Background: Hand and digit amputations represent a relatively common injury affecting an active patient population. Neuroma formation following amputation at the level of the digital nerve can cause significant disability and lead to revision surgery. One method for managing digital nerves in primary and revision partial hand amputations is to perform interdigital end-to-end nerve coaptations to prevent neuroma formation. Methods: All patients with an amputation at the level of the common or proper digital nerves that had appropriate follow-up at our institution from 2010 to 2020 were included. Common or proper digital nerves were managed with either traction neurectomy or digital end-to-end neurorrhaphy. The primary outcome was the development of a neuroma. Secondary outcomes included revision surgery, complications, and visual analog pain scores. Results: A total of 289 nerves in 54 patients underwent hand or digital amputation in the study period. Thirteen hands with 78 nerves (27%) underwent direct end-to-end coaptation with a postoperative neuroma incidence of 12.8% compared with 22.7% in the 211 nerves that did not have a coaptation performed. Significantly fewer patients reported persistent pain if an end-to-end coaptation was performed (0% vs. 11.8%, P < .01). The prevalence of depression and workers compensation status was significantly higher in in patients with symptomatic neuromas than in patients without symptomatic neuromas ( P < .01). Conclusions: Digital nerve end-to-end neurorrhaphy is a method for neuroma prevention in partial hand amputations that results in decreased residual hand pain without increase complications. Depression and worker’s compensations status were significantly associated with symptomatic neuroma formation.
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Hypertrophy of the sciatic nerve after lower-limb amputation in patients with sarcomas has been previously reported by magnetic resonance imaging; however, sonographic evaluation of the sciatic nerve after lower-limb amputation due to nonmalignant causes has not been done before. Therefore, the aim of this study was to perform imaging of the sciatic nerve in lower-limb amputees and to find out whether sonographic findings were related to clinical characteristics. Twenty-three males with lower-limb amputations due to traumatic injuries were enrolled. Sonographic evaluations were performed using a linear array probe (Aloka UST-5524-7.5 MHZ). Sciatic nerve diameters were measured bilaterally at the same level, and the values of the normal limbs were taken as controls. Sciatic nerve width and thickness values were found to be greater on the amputated sides than the normal sides (P = 0.001). The thickness values were greater in above-knee amputees than below-knee amputees (P = 0.05). Subjects with a neuroma also had thicker sciatic nerves (P = 0.04). The diameters were found not to change between subjects with different liners (P > 0.05), but they were correlated with time after amputation (r = 0.6, P = 0.006; r = 0.4, P = 0.05, respectively). Our results clearly show that the sciatic nerves were wider and thicker on the amputated sides. Amputation level, duration, and the presence of a neuroma seem to affect the eventual diameters of the nerves.
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Trigger digit release is a common surgical procedure with a low complication rate. One of the potential complications is digital nerve injury. Though uncommon, digital nerve injury can be significantly symptomatic to the patient. We report a case of radial digital nerve neuroma formation following trigger release of the middle finger, which is considered to be safe, in terms of risk of digital nerve injury. We discuss our management of the complication, possible pitfalls which may have resulted in the complication in our case and offer possible means of overcoming these pitfalls.
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A delay in the formation of the terminal neuroma following sciatic nerve section in rats was obtained by means of free nerve grafts sutured to the proximal stump of the sectioned sciatic nerve branches. The automutilating behaviour in these animals was statistically compared with that which follows single sciatic section and sciatic section plus end-to-end suture. The results showed that in animals with grafted nerve stumps, autotomy begins significantly later than in those with single sciatic section. However, when the self-mutilation started, it followed the same increasing evolution in both groups. These results suggest that autotomy after a nerve section is behaviour related to the aparition and nature of the terminal neuroma.
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