What is a nerve?
Nerves are part of something called the peripheral nervous system. This system connects the central nervous system (brain + spinal cord) to the rest of the body. Nerves are responsible for all types of sensation, and also controls the muscles, like an electrical cord for a motor.
Why do nerve lacerations occur?
Nerves of the hand and wrist are fairly superficial (i.e. close to the skin), so a knife or other sharp object does not have to cut very deep in order to damage a nerve. We see nerve lacerations commonly from accidents in the kitchen such as cutting bagels, separating frozen meats with a knife, glasses breaking while washing dishes, and especially pitting an avocado with a knife. In general we recommend that a knife never be pointed back towards your hand.
Another common source of nerve lacerations is from using power tools, especially a table saw. Often patients will report being momentarily distracted and/or having taken the safety guard off of the power tool to help facilitate work efficiency. However, these safety guards are in place for a reason, please don't take them off. It only takes a split second for a table saw to do extreme damage to a finger.
The most common symptom after nerve laceration is numbness. The location of this numbness depends on the location of the laceration. The numbness will always be distal (i.e. below) to the level of the laceration. Patients may also experience weakness of the muscles the nerve supplies if a nerve contains both motor and sensory fibers.
The area of the nerve laceration can be particularly sensitive and painful however. Especially over time, a cut nerve will sprout new nerve endings in the hopes of trying to connect and mend the nerve. However, because nerve endings that are cut tend to retract back, the sprouting nerves do not connect to the other side. When this happens, the sprouting nerves become a hypersensitive ball of nerves called a Neuroma.
While nerve lacerations are primarily a clinical diagnosis, Dr. Steven Lee may order an Electromyography/Nerve Conduction Velocity (EMG/NCV) test to further evaluate nerve function. However, an EMG/NCV is typically useful for this purpose only 6 weeks after the laceration. It may also be used to follow progression or lack of progression during the healing process.
Pretty much all nerve lacerations will require surgical exploration and possible repair. An exception to this rule might be a nerve that has been lacerated so distally that the size of the nerve is too small to be repaired.
TIMELY TREATMENT IS EXTREMELY IMPORTANT. Surgery should ideally be done within 2 weeks of the date of injury. Delaying treatment longer than two weeks increases the chance that the repair will not be able to be repaired primarily and a nerve graft will be needed, which further increases the chance of a poorer outcome.
Nerve repair is completed under the guidance of a high-powered microscope. Special sutures the size of human hair are used to sew the lacerated ends back together. Once the nerve ends are reconnected, nerve fibers can form new pathways to the the target tissues they supply. This nerve regeneration is a slow process and can take a long time. The farther the nerve laceration is from the target tissue it supplies, the longer it takes to regain back sensation and motor activity. In general, after repair, the nerve does nothing for about a month, then the nerve can regenerate at a rate of 1 mm/month.
Nerve grafting serves to provide a source of an "empty tube" through which new nerve fibers can grow. Nerve grafting might be needed if there is a gap between the cut ends that is big enough that a tension free repair cannot be performed, or in chronic nerve injuries.
The results of surgery are dependent on number of factors. One of the most important factors is how the nerve was cut. Those that are cut the cleanest with the sharpest knife have a better prognosis. Those that were crushed, the worst prognosis. Patients with Diabetes or have pre-existing neurologic disorders, those that smoke, or don't closely follow the postoperative instructions also have a worse prognosis. Even in the most ideal conditions however, the results of the surgery are probably not as good as patients would hope. Patients can regain some sensation and motor control, but it is often not as normal as it was. Sometimes the nerve just doesn't recover.
Because there are many factors working against you with nerve lacerations, it's important that you choose a hand surgeon with a high level of skill and a steady hand! Dr. Steven Lee has over 20 years of experience in microscopic hand surgery.
Learn more about scheduling surgery.
All surgical patients are immobilized in a non-removable splint for 7-10 days following surgery. During this time, patients are encouraged to elevate their hand above their heart and keep their dressings clean and dry.
Patients are then transferred into a custom splint and remain immobilized for approximately 2 more weeks. The nerve needs to heal in an immobilized position as any tension placed on the nerve jeopardizes the healing process. Once healed, the patient will begin a period of hand/physical therapy designed to restore adequate mobility and strength. Hand/physical therapy usually lasts 2-3 months.
Learn more about post-operative care.
*It is important to note that all of the information above is not specific to anyone and is subject to change based on many different factors including but not limited to individual patient, diagnosis, and treatment specific variables. It is provided as an educational service and is not intended to serve as medical advice. Anyone seeking specific orthopedic advice or assistance should consult Dr. Steven Lee or an orthopedic specialist of your choice.
*Dr. Steven Lee is a board certified orthopedic surgeon and is double fellowship trained in the areas of Hand and Upper Extremity Surgery, and Sports Medicine. He has offices in New York City, Scarsdale, and Westbury Long Island.