Electrical stimulation predicts recovery potential after acute nerve injuries

Bottom line: This study found that, in rats, acute nerve injuries that may recover can be distinguished from those that are unlikely to recover based on the response to intraoperative electrical nerve stimulation in the acute clinical setting. Rather than requiring a greater amount of stimulation, researchers found that non-recoverable nerve stretch injuries demonstrate a complete lack of response to electrical stimulation immediately following nerve injury. Nerves that did not respond to stimulation had a very low chance to recover without surgical intervention, whereas responsive nerves showed a greater likelihood to recover on their own. 

Why this study is unique: There is at present no quick, reliable, and evidence-based way of evaluating the extent of nerve damage and need for surgical intervention after a patient experiences an acute injury. This study is the first to evaluate and distinguish the specific degrees of acute nerve injury using electrical nerve stimulation intraoperatively. The two injury levels tested in this study are both in-continuity stretch injuries, which means that they look similar from the outside and there is no way of determining the recovery potential by external observation alone.

Researchers may now have found a tool that can distinguish these injuries and predict recovery intraoperatively, opening the door for evidence-based surgical decision making and for patient-centered care tailored to a patient's individual needs and injury severity.

Why the study is important: Nerve injury is usually the limiting step in recovery after serious acute injury. If clinicians can more easily determine which injuries can recover without surgical intervention and which require surgery, patient outcomes can be significantly improved. This study promotes a novel approach for assessing a patient's regenerative potential after nerve stretch injuries, which could help prevent permanent functional deficits and improve outcomes for patients by supporting more accurate prognoses and more informed decisions about surgical treatment and patient care.

Researchers pursued this study to evaluate the predictive potential of a response to intraoperative electrical stimulation in injured nerves. As electrical stimulators are readily available in clinics, the results of this study can hopefully be quickly translated from bench to bedside.

How the research was conducted: Researchers used 22 rats in three separate groups: a sham-control group without any nerve injury, an epineuroclasis injury group (a milder injury typically associated with recovery), and an endoneuroclasis injury group (a more severe injury which typically leads to poor outcomes as the internal structures of the nerve are severely damaged).

These median nerve injury levels were induced using the novel neuroclasis animal model which, for the first time, induces specific degrees of structural nerve damage during stretching. This novel animal model, developed by researchers on this study, allows the precise induction of specific levels of nerve stretch injury on its subjects.

Researchers stimulated each nerve using a handheld electrical nerve stimulator, provided by Checkpont Surgical, immediately following the nerve injury and evaluated the rats' grip strength over the course of 12 weeks. A response to stimulation was observed when the nerve's target muscle contracted. Researchers first compared how many nerves in each injury group responded to stimulation and at which amount of stimulation a response to stimulation was seen. Using a mixed-effects model, they then evaluated whether a response to stimulation was associated with recovery of grip strength at 12 weeks after injury. 

Results: 15 of 16 nerves in the epineuroclasis injuries responded to intraoperative stimulation, whereas only 5 of 16 of the endoneuroclasis injuries responded to stimulation. This led to a three times greater likelihood that the milder epineuroclasis injury would respond to nerve stimulation, compared to the more severe endoneuroclasis nerve injury. 

Furthermore, retrospective contingency analysis of long-term functional outcomes showed that nerves that were unresponsive to stimulation had only an eight percent chance of functional recovery. Conversely, nerves that did respond to stimulation had a 75 percent probability of recovery. In summary, researchers found that responsiveness to stimulation is indicative of long-term functional recovery after nerve stretch injury and vice versa.

What this study means for patients: For patients, this could mean faster and more accurate diagnoses, fewer unnecessary procedures, and more personalized treatment plans, which ultimately could lead to more positive outcomes such as better functional recovery, reduced pain, and an overall improvement in quality of life.

What this study means for doctors: The predictive value of an intraoperative response to nerve stimulation, or lack thereof, may help in accurately assessing the severity of the nerve injury and the potential for recovery, allowing surgeons to more accurately determine the need for surgical treatment. The work in this project may help clinicians reach the "holy grail" of trauma and nerve injury by allowing them to predict which nerves will recover themselves, and which will require surgical treatment so that valuable time is not lost. This timely damage assessment and potential intervention are paramount in ensuring satisfactory patient outcomes and recovery from nerve injury. Recently published research from this team has already demonstrated similar predictive abilities of electrical nerve stimulation in patients when used for chronic nerve injuries.

What the next steps are for this work: Electrical nerve stimulators are already widely used during orthopedic surgery, often to locate and protect nearby nerves during surgeries such as fracture repair. This study now lays the foundation for the intraoperative use of electrical stimulation as a diagnostic tool for acute nerve injuries, and the next step will be to validate the findings of this study in patients.

Quotes: "Our recent work provides important insight into the capacity to accurately assess neurologic function in real time. We are excited to continue this body of work, furthering the capacity for important clinical translation," Dr. Cagle said.

"For the first time, surgeons now have a readily available intraoperative tool to evaluate the recovery potential of damaged nerves shortly after injury. We hope our findings will help to enhance our capacity to predict recovery and guide surgical intervention, leading the way towards more evidence-based surgical decision-making," Mr. Schroen said.