Compression induced damage on in-situ severed and intact nerves

Nerve cuff electrode pressure estimation via electrical impedance measurement

OBJECTIVE

Implantable neuromodulation devices that have cuff electrodes are known to exert mechanical pressure on the target nerves. The amount of pressure exerted by cuff enclosures is one of the key determinants of physiological safety of these devices since excess pressures can cause neural damage. Because direct measurements of pressure on a nerve are challenging, the current cuff design approaches rely heavily on theoretical models or numerical computations for pressure predictions. An experimental approach to test these devices for pressure can complement existing theoretical models and can also serve as a quality control step to screen cuff electrode designs before implantation.

APPROACH

We hypothesize that the pressure exerted on a nerve by a cuff can be estimated by measuring the resulting changes to the nerve's electrical impedance.

MAIN RESULTS

We investigated ten 1 cm-long explanted rat sciatic nerves: five that were used within an hour after surgery, and five after 50 h of storage in physiological saline. For each experiment we applied variable pressure on the nerve ex vivo and measured the resulting changes in its impedance. We found a strong correlation between the external pressure on the nerve and its impedance and generated a pressure-impedance calibration curve. At the upper limit of physiologically safe pressure, the nerve impedance increased by ~2 kΩ, whereas, a rise of ~3 kΩ corresponded to pressure value that onsets irreversible nerve damage.

SIGNIFICANCE

As a proof-of-concept, we used this protocol to generate a pressure-impedance calibration curve for a monkey tibial nerve and estimated pressure exerted by a commercial silicone cuff electrode on the explanted nerve. This single-point measurement was in an agreement with an independent estimate of the pressure measured using a mechanical pull test within 3 mmHg.

Neurologic complications of shoulder joint replacement

BACKGROUND

Little attention has been given to neurologic complications after shoulder joint replacement (SJR). Previously thought to occur infrequently, it is likely that many are not clinically recognized, and they can result in postoperative morbidity and impair the patient's recovery. The purpose of this study was to document the prevalence of nerve complications after SJR, to identify the nerves involved, and to define patient outcomes.

METHODS

This was a retrospective review of 211 SJRs in 202 patients during a 5-year period were included, with 89 male and 122 female patients at an average age of 70 years. All patients underwent a comprehensive analysis of any postoperative nerve complication, including onset, duration, investigation, treatment, and symptom resolution.

RESULTS

Of the 211 SJR procedures, 44 were identified as having sustained a nerve complication (20.9%), with 36 female (81.8%) and 8 male patients (18.2%). Reverse SJR was associated with the highest number of nerve complications. The median nerve (25 patients) and musculocutaneous nerve (8 patients) were most commonly involved. Most nerve complications were transient and resolved within 6 months. Permanent sequelae and injuries that required secondary surgical intervention were rare.

CONCLUSION

The occurrence of nerve complications after SJR is common, but almost all will fully recover. Most are transient neurapraxias involving the lateral cord of the brachial plexus. Women are more likely to be affected, as are patients who have undergone prior surgery to the affected shoulder. Most are likely to be the result of excessive traction or direct injury to the nerves during glenoid exposure.

Biomimetic Microelectronics for Regenerative Neuronal Cuff Implants

Smart biomimetics, a unique class of devices combining the mechanical adaptivity of soft actuators with the imperceptibility of microelectronics, is introduced. Due to their inherent ability to self-assemble, biomimetic microelectronics can firmly yet gently attach to an inorganic or biological tissue enabling enclosure of, for example, nervous fibers, or guide the growth of neuronal cells during regeneration.

Perioperative upper extremity peripheral nerve traction injuries

Peripheral nerve traction injuries may occur after surgical care and can involve any of the upper extremity large peripheral nerves. In this review, injuries after shoulder or elbow surgical intervention are discussed. Understanding the varying mechanisms of injury as well as classification is imperative for preoperative risk stratification as well as management.

Clinical application of sensory protection of denervated muscle

Following proximal peripheral nerve injury, motor recovery is often poor due to prolonged muscle denervation and loss of regenerative potential. The transfer of a sensory nerve to denervated muscle results in improved functional recovery in experimental models. The authors here report the first clinical case of sensory protection. Following a total hip arthroplasty, this patient experienced a complete sciatic nerve palsy with no recovery at 3 months postsurgery and profound denervation confirmed electrodiagnostically. He underwent simultaneous neurolysis of the sciatic nerve and saphenous nerve transfers to the tibialis anterior branch of the peroneal nerve and gastrocnemius branch from the tibial nerve. He noted an early proprioceptive response. Electromyography demonstrated initially selective amelioration of denervation potentials followed by improved motor recovery in sensory protected muscles only. The patient reported clinically significant functional improvements in activities of daily living. The authors hypothesize that the presence of a sensory nerve during muscle denervation can improve functional motor recovery.

Topographic variations of the relationship of the sciatic nerve and the piriformis muscle and its relevance to palsy after total hip arthroplasty

The aim of this paper was to study the anatomical relationship between the piriformis muscle and the sciatic nerve with regard to the possibility of neurological deficit after THA. The incidence of anatomical variation of both structures is 15-30% in the literature. The authors studied 91 cadavers and found an atypical relationship in 19 cases (20.9%). In this study individual variations were found with the following frequency: The sciatic nerve exits below the piriformis muscle in 79.1% of the cases. The sciatic nerve separates into two divisions above the piriformis, one branch passing through the muscle, the other below it (14.3%). An unsplit nerve passes through the piriformis muscle in 2.2%. The nerve separates into two divisions above the piriformis, one branch exiting above the muscle and passing along its dorsal aspect, the second exiting distally below the muscle in 4.4%. The most common reasons for sciatic nerve injury in surgery of the hip joint are direct injuries, ischemia of the nerve tissue, compression or excessive distraction of the nerve, compression by bone cement, thermal damage during cement polymerization, injury during THA dislocation, compression by hematoma, bone prominence or an implanted acetabular component. According to the presented anatomical study, overstretching of the nerve itself or its branches in the area of the pelvitrochanteric muscles after their release from their origin can be another mechanism. Such overstretching can appear in the presence of some of the aforementioned anatomical variants.

Surgical maneuvers placing the sciatic nerve at risk during total hip arthroplasty as assessed by somatosensory evoked potential monitoring

The sciatic nerve in 52 hip arthroplasties was evaluated using intraoperative somatosensory evoked potentials (SSEPs). Twenty-nine of these cases involved the lateral transtrochanteric approach, and 23 involved the posterior approach. A total of 11 incidents of SSEP changes occurred in eight patients. Six episodes occurred during lateral retraction of the proximal femur, and three occurred during anterior retraction of the proximal femur. Tracings returned to baseline with prompt cessation of femoral retraction in each case. One SSEP change occurred in a revision following reduction of the prosthetic components, and this resolved with shortening of the prosthetic neck to less than anatomic length. One change occurred during tightening of cables securing strut allografts to the femur and this resolved spontaneously. No correlation was found between frequency of SSEP changes and age, sex, limb lengthening, or preoperative range of motion. It is concluded that routine lateral or anterior retraction may place the sciatic nerve at risk.