Background: Peripheral nerve injury commonly results in long-term disability and pain for patients. Recovery after nerve traction or crush injury is unpredictable and depends on the degree of injury. Our inability to accurately assess the severity or degree of injury hampers our ability to predict the chances for recovery or need for surgical intervention in the form of neurolysis, nerve repair, or nerve graft. An investigation into the histologic sequence and mechanics of nerve failure under tension may help in the process of accurately assessing the severity of the nerve injury, the prognosis for recovery, and the need for surgical treatment. Questions/purposes: Using an in vivo rat model, we asked: (1) What is the pattern of mechanical failure during nerve stretch? (2) Is there staggered disintegration of specific anatomic substructures when mechanical failure occurs? Methods: To answer our first research question about the pattern of mechanical failure during nerve stretch, four 12-month-old male Sprague-Dawley rats were enrolled in a load-to-failure experiment generating load-deformation curves of the rat median nerve. Under anesthesia, the median nerves of both forelimbs were surgically exposed and secured under two blunt metal pins 1 cm apart. A metal hook was attached to a load-cell and raised from beneath the nerve at a speed of 0.2 mm/second until complete rupture occurred. Applied forces were monitored in real time via a force-time curve. All experiments were filmed, and the rats were euthanized afterward. Based on load-to-failure experiments, we identified two distinct events of sudden force reduction during stretching in the load-deformation curve of the rat median nerve. We labeled the first of these two events as epineuroclasis and the second as endoneuroclasis. Neuroclasis derives from the Greek term “neuron” for nerve, and the suffix “-clasis” means breaking or fracture. An additional eight rats were used to investigate whether this staggered mechanical failure was caused by staggered disintegration of specific anatomical substructures. Under anesthesia, eight left median nerves were stretched to the epineuroclasis point and eight right nerves to the endoneuroclasis point. Induction of injury was confirmed by load-time curves, and nerves were held in place for 5 minutes before tension was released. Nerve function was assessed before and after injury using a handheld electrical nerve stimulator. The nerves were harvested for histology (to assess integrity of the epineurium, axons and intraneural vasculature, endoneurial collagen [dis-]organization, as well as molecular collagen damage), and the rats were euthanized immediately after. The uninjured median nerves of two additional rats were harvested for histology as control tissue. Mechanical, functional, and histologic findings were compared between both injury levels and with uninjured nerves. Results: Load-to-failure experiments revealed a characteristic failure pattern of the rat median nerve with two distinct events of mechanical failure that occurred at a mean ± SD resistance force of 2.3 ± 0.5 N and 1.4 ± 0.2 N (mean difference 0.9 ± 0.6 N [95% confidence interval 0.4 to 1.4]; p = 0.003), respectively. Additional experiments investigating both mechanical failure points revealed that the first failure point (epineuroclasis) was associated with epineurium rupture and plastic deformation of nerve fibers, whereas the second injury point (endoneuroclasis) was associated with failure of endoneurial tubes, axons, and intraneural vasculature. Epineuroclasis severely impaired nerve conductivity (median stimulation of 25 nC [range 25 nC to 50 nC] preinjury and 170 nC [range 25 to 300 nC] after epineuroclasis, difference of medians 145 nC; p < 0.001). Endoneuroclasis induced an even greater functional impairment than epineuroclasis (median stimulation of 400 nC [range 300 to 2000 nC] after endoneuroclasis, difference of medians 230 nC; p = 0.005). Both injury levels could be induced through live analysis of resistance forces during nerve stretch. Conclusion: Peripheral nerve injuries follow a characteristic sequence of mechanical and structural failure, with two distinct injury levels preceding nerve transection. Clinical Relevance: The order and degree of failure in the rat median nerve seems to follow a predictable “outside-in” pattern. This sequence of mechanical and structural failure may inform a classification system of nerve stretch injuries that may more accurately reflect the pathoanatomy and prognosis. We offer a new classification of nerve injuries based on the sequence of nerve failure in rats. However, future studies are needed to validate the applicability of the neuroclasis classification to human peripheral nerves before clinical implementation and use can be proposed. The characterization of specific injury levels using an animal model provides a framework that could facilitate the development of novel diagnostic tools, potentially identifying the specific structural changes found in this study in the acute clinical setting.

Functional recovery from peripheral nerve injuries remains unpredictable and continues to pose a major clinical challenge to surgeons. This study sought to investigate the utility of intraoperative nerve stimulation following neurolysis surgery as a prognostic indicator of functional recovery. A retrospective chart review of adult patients who underwent peripheral nerve neurolysis between September 2021 and December 2022 was performed. A handheld nerve stimulator was used intraoperatively before and after neurolysis. Patients with preoperative motor deficits corresponding to the nerve that underwent neurolysis, intraoperative nerve stimulation, and postoperative follow-up length of at least 3 months were included. Muscle strength as measured by the Medical Research Council scale was used to evaluate nerve function. A scale grade of 0 or 1 meant “no recovery,” between 2 and 4 was classified as “partial recovery,” and 5 was classified as “full recovery.” Fisher exact tests were employed to test for an association between stimulation thresholds and functional recovery. A total of 27 patients and 45 nerves were included in the study, with a mean follow-up of 8.0 months. Intraoperative stimulation at 0.5 mA was observed in 73% (33/45) of nerves, with 76% achieving full recovery, 18% partial recovery, and 6% no recovery. Two nerves stimulated at 2 mA and one at 20 mA, with both showing partial recovery. In contrast, 22% (10/45) of nerves showed no stimulation, leading to full recovery in 20%, partial recovery in 30%, and no recovery in 50% of cases. A significant (P < .001) association was found between stimulation thresholds and functional recovery. Intraoperative nerve stimulation is strongly linked to functional recovery postneurolysis, demonstrating its potential as a prognostic tool for guiding surgical decisions. Prognostic, IV.

Background: Peripheral nerve injury commonly results in pain and long-term disability for patients. Recovery after in-continuity stretch or crush injury remains inherently unpredictable. However, surgical intervention yields the most favorable outcomes when performed shortly after injury. Our inability to accurately distinguish injuries that will recover naturally from those needing immediate surgical intervention makes surgical decision-making highly challenging and often results in delayed surgery with unsatisfying outcomes. A prognostic tool with the ability to distinguish different degrees of nerve injury and to predict recovery in the acute clinical setting could thus be very useful. Questions/purposes: Using a previously validated in vivo rat model, we asked: (1) Can intraoperative electrical stimulation be used to distinguish two distinct degrees of acute stretch injury in the rat median nerve? (2) Is a response to intraoperative stimulation associated with functional recovery after stretch injury in the rat median nerve? Methods: To answer our first research question, we included 22 male Sprague-Dawley rats, all 12 months of age, in a sham control (6 rats), an epineuroclasis (8 rats), and an endoneuroclasis (8 rats) group. Epineuroclasis and endoneuroclasis describe the first and second degree of mechanical and structural failure during stretching in the rat median nerve and serve as the first and second (more severe) stretch injury levels in this study. Under anesthesia, the median nerves of both forelimbs were surgically exposed and probed with a handheld electrical stimulator to identify the stimulation threshold required to induce digit flexion. In both injury groups, nerves were then stretched to their respective injury levels using a hook attached to a load cell that generated the load-deformation curve of the nerve in real time. Nerves were secured under two metal pins 1 cm apart and stretched at a speed of 0.2 mm per second until a first (epineuroclasis) or second (endoneuroclasis) sudden force reduction was observed on load-deformation curves. After the stretch injury, rats in both injury groups were again probed with the stimulator to identify differences in stimulation thresholds between both injury levels. To answer our second question, the grip strength of all rats was assessed using the grasping test at 1 week preoperatively, as well as at 1, 3, 6, 9, and 12 weeks postoperatively. Twelve weeks served as the final follow-up, after which the rats were euthanized. Stimulation thresholds at time 0 were compared using Wilcoxon tests (within one group) and Mann-Whitney tests (between groups). Grip strength test data were compared using a two-way mixed-effects model and Tukey multiple comparisons test. Recovery was defined as rats reaching a grip strength similar to sham control rats at 12 weeks, and lack of recovery was defined as similar grip strength at 1 and 12 weeks after injury within the same group. An association between response to stimulation and recovery was tested for using a chi-square test. From the corresponding 2 × 2 contingency table (motor response present/absent versus recovery/no recovery), an OR was calculated, as well as a positive predictive value (defined as the fraction of nerves without a response that actually did not recover). Results: Intraoperative electrical stimulation allowed for differentiation of both injury levels based on the nerve’s overall responsiveness to stimulation. Both injury levels required similarly high stimulation thresholds to induce digit flexion after stretch injury, with a median (range) of 200 nanocoulombs (nC) (100 to 1600) after epineuroclasis and 200 nC (100 to 400) after endoneuroclasis (median difference 0 nC; p = 0.74). However, 15 of 16 nerves induced digit movement after epineuroclasis, whereas only 5 of 16 nerves in the endoneuroclasis group induced a response at any stimulation threshold (OR 33 [95% confidence interval (CI) 3.91 to 373.0]; p < 0.001). These results demonstrate that lack of responsiveness at time 0 was strongly associated with a lack of functional recovery. Both injury levels exhibited an acute loss of grip strength 1 week after injury. However, at 12 weeks, rats in the sham control and epineuroclasis groups demonstrated a similar grip strength, with a mean ± SD of 12.97 ± 2.88 N and 13.18 ± 2.59 N, respectively (mean difference -0.21 N [95% CI -3.85 to 3.43]; p = 0.99). Endoneuroclasis resulted in a sustained loss of function compared with rats in the control group, with 2.51 ± 1.06 N at 12 weeks (mean difference 10.46 N [95% CI 6.81 to 14.1]; p < 0.001). Based on a retrospective contingency table analysis, nerves that were unresponsive to stimulation had a 92% likelihood of no functional recovery (negative predictive value 0.92 [95% CI 0.64 to 1]). Conversely, nerves that responded to simulation had a 75% probability of recovery (positive predictive value 0.75 [95% CI 0.53 to 0.89]). Conclusion: Two distinct degrees of acute stretch injury in the rat median nerve can be distinguished based on the ability to induce digit movement using a handheld electrical stimulator. In the rat median nerve, responsiveness to stimulation is indicative of long-term recovery after stretch injury and vice versa. Clinical Relevance: The ability to predict recovery using intraoperative nerve stimulation could allow surgeons to distinguish injuries that will likely recover naturally from those likely to benefit from immediate surgical intervention. To identify the clinical scenarios in which patients may benefit from the use of intraoperative stimulation as a prognostic tool, future prospective preclinical studies using larger animal models such as rabbits should evaluate the prognostic abilities of handheld stimulators for multiple types of nerve injury, including crush injury.

Reverse total shoulder arthroplasty (RTSA) has seen a tremendous increase in popularity over the last 2 decades. While initially developed for use in patients with irreparable rotator cuff disorders and cuff arthropathy, the evolution of RTSA and associated implants has led to implantation for a variety of pathologies. A literature search was performed to examine outcomes of RTSA based on specific preoperative diagnoses. Articles including individual pathologies as well as articles comparing outcomes between different pathologies were included. Preoperative diagnoses include rotator cuff arthropathy/massive irreparable rotator cuff tears, primary glenohumeral arthritis with intact rotator cuff, inflammatory arthritis, proximal humerus fractures, and failed prior arthroplasty, as well as miscellaneous diagnoses such as tumor resection, septic arthritis, avascular necrosis, and glenohumeral arthritis following shoulder dislocation. RTSA provides generally satisfactory outcomes regardless of preoperative pathology. Direct comparison studies revealed overall superior outcomes of RTSA for glenohumeral arthritis with intact rotator cuff as compared to patients with rotator cuff arthropathy. Patients with diagnoses portending higher preoperative outcome scores were at risk for less overall improvement. Patients undergoing RTSA for inflammatory conditions, fractures, and arthroplasty revision are at higher risk for complications, which may explain the increased variability of outcomes in these groups. RTSA produces reliable improvements in function and pain, with small differences in risks and outcomes based on preoperative diagnosis. Patients should be adequately counseled in order to create appropriate expectations. Further long-term studies are needed to differentiate outcome differences between specific preoperative pathologies.

Background: Across many sports, injuries to the upper extremity (UE) are prevalent due to falls on an outstretched hand (FOOSH) and overuse. This retrospective analysis aimed to characterize sports-related UE injuries in the United States (US) over the past decade, examining injury frequency, affected body part, diagnosis, and hospital disposition across age, sex, and sport. Methods: The National Electronic Injury Surveillance System (NEISS) was queried for sports injuries presented to US emergency departments (EDs) from 1 January 2014 to 31 December 2023. Patient demographics, injury site, diagnosis, and disposition were recorded. Annual injury trends were evaluated by linear regression. All statistical analysis was conducted using SPSS (version 30.0) software. Results: There were 1,330,108 nationally estimated (NE) UE sports injuries (47,371 NEISS Cases) that were presented to US EDs from 2014 to 2023. Linear regression revealed a significant decrease in annual injuries across the study period (β = −0.63, R² = 0.40 p = 0.05). For many sports, including football, basketball, soccer, baseball, softball, wrestling, volleyball, hockey, and rugby, rates of UE injury decreased significantly during the study period. Fractures were the predominant diagnosis across all age groups, observed among 99.3% of patients. Football was the most common sport associated with UE injury in elementary to high school-age children, with basketball becoming more common in patients from 19 to 50 years old. Tennis-related injuries were the most common for patients above 50 years old. Across all sports, the most commonly injured body parts were fingers (33.5%), wrists (20.3%), and lower arms (17.3%). Notably, shoulder injuries accounted for 99.1% of all wrestling cases and 71.5% of all lacrosse injuries included in this study. Conclusions: Sports-related UE injuries decreased significantly from 2014 to 2023, with notable declines during the COVID-19 pandemic. The injuries included in this study varied depending on sport, age, and sex, allowing for the recommendation of specific interventions. While few injuries led to hospitalization, those that did typically involved lower arm injuries; further efforts to reduce these injuries will reduce the burden placed on US hospitals.