Nerve and tendon lacerations (i.e. deep cuts) of the hand are a relatively common injury. Treating these injuries appropriately is important to maintain long-term sensation and motor functions of the injured hand.

The Anatomy of the Hand

There are 3 major nerves in the hand: the radial nerve, the ulnar nerve, and the median nerve

  • Located at the level of the hands, the radial nerve is purely a sensory nerve. It supplies sensation to the back (dorsum) of the thumb index finger and hand. 
  • The median nerve is a mixed nerve. It supplies sensation to the palm side of the thumb, index finger, little finger, and half of the ring finger. It also supplies motor power to the thenar muscles, or muscles of the thumb. 
  • The ulnar nerve is also a mixed nerve. It supplies sensation to the palm (dorsum) of the small finger and half of the ring finger. The ulnar nerve also supplies motor power to the muscles of the little finger (hypothenar muscles) and the small intrinsic muscles in the hand.

The Symptoms of Injury

The symptoms of a nerve laceration are highly variable, particularly in the hand.

  • There may be loss of sensation or numbness (which can be total or partial). 
  • There may be nerve irritability with hypersensitivity to touch.
  • There may be tingling over the distribution of the nerve. 
  • There may be a partial laceration of the nerve which initially heals, producing a painful nerve scar (neuroma) and creating a painful sensitive area. 
  • Motor or muscle weakness may also result (either complete or partial). 
  • There may be wasting (atrophy) of the affected muscles. This may result in weakness of grip.
  • Chronic weakness of certain muscles may result in an imbalance of muscle forces and produced a chronic deformity of the fingers, such as a claw finger deformity (which can result from the intrinsic weakness seen with an ulnar nerve laceration).

Note that after nerve laceration, the distal portion (end towards the fingers) begins to degenerate, as part of a process called Wallerian degeneration. When this happens, the nerve ends may retract from each other, particularly in cases of a complete laceration. Eventually, scar tissue forms at both ends. 

In motor nerves and the motor endplate, the attachment of the nerve to the muscle may also degenerate after a period of time. 

All of these factors can work against the complete return of nerve function after repair. 

The Types of Injury

The nature of a laceration is important for us to understand when making a treatment plan. 

  • Dirty, jagged, ripping injuries (such as chainsaw laceration) damage a far bigger segment of the nerve then a clean, sharp laceration from glass or a sharp knife. 
  • A tearing or avulsion injury – in which a segment of nerve is torn - damages a far bigger section then a simple laceration. 
  • The condition of the tissue around the nerve (nerve bed) and any contamination of the area also affects nerve healing. 
  • Finally, a patient's age and overall health are important. Several studies have shown that nerve repair results over the age of 50 do not compare to nerve repairs in younger adults. Additionally, smoking and nicotine use can impair microcirculation which affects the results of nerve repair. Malnutrition and alcoholism can also impact results.

The Treatment

Treatment of nerve lacerations in the hand requires a detailed, complete assessment of nerve function and hand function.

  • In cases of partial sensation loss, patients may require sensory mapping with two-point discrimination (a tool to determine the amount of sensation that remains) in order to determine whether protective sensation is still present. 
  • Electrodiagnostic studies may be required in chronic cases to determine exactly which muscles are affected in cases of a partial nerve laceration.

These studies (and others if needed), as well as a very detailed hand examination, help to provide a complete picture of the functional loss caused by the hand nerve laceration. 

When treating patients, we must also consider the level of their original injury. Lacerations that injure tiny small nerves and lacerations in mixed nerves (those with both sensory and motor nerve branches) are more difficult to treat.

Our assessment is ultimately coupled with the decision on how much functional loss can be well tolerated in order to create a plan to restore function. 

  • For example, numbness can sometimes be tolerated on the inner aspect of several fingers. It usually cannot be tolerated on the thumb or outer aspect of the index and little finger due to risk of burns or injury to those fingers.
  • Numbness is better tolerated than numbness and pain and hypersensitivity. 
  • Partial weakness, motor loss or lack of coordination are also better tolerated in some patients than others (consider the needs of a pianist, surgeon, artist, etc.).

Early Treatment

Early treatment of lacerations will consist of:

  • cleaning up any debris in the surrounding area of the laceration.
  • repairing any other structures that were damaged.
  • repairing the nerves directly with microsurgical techniques.

Early treatment can be accomplished immediately after an injury or approximately 2 weeks later. Sometimes, prior to coming to us the wounds have been cleaned and the skin repaired by the emergency room. The results in such cases are approximately the same.

In surgery for early treatment, an operating microscope or loupe magnification is used to trim the nerve ends carefully and repair the nerve with several sutures that are smaller than a human hair. If a large segment of nerve has been damaged and needs to be resected or is missing, a nerve graft (section of matching nerve taken from another donor area) may be used to bridge the gap between the nerve ends. 

A newer surgical technique involves using a neural tube (a small tube of collagen) that surrounds both ends of the nerve repair and allows the nerve to heal down the tube, bridging the gap. 

Both surgical techniques can allow function to return when there has been a missing segment of nerve or damaged nerve. The results of the newer procedure, however, are not as good as a direct primary repair of the nerve ends.

Delayed Treatment

For delayed repairs of a nerve laceration, the ends of both nerves must be found in the scar tissue of an already healed wound and freed up; then the ends of the nerve must be trimmed back to the viable section nerve. 

  • Often in these cases, the nerve ends have retracted, and cannot be reapproximated. In these cases, a nerve graft or nerve tube are often utilized. 
  • In cases where a partial nerve laceration has healed, producing a painful neuroma and painful sensation (dysethesia), there is still partial nerve function. A decision is made at the time of surgery whether to completely divide the nerve, take out the section of scar tissue and repair it, or to simply take out a wedge of diseased nerve tissue and repair that (leaving the more normal appearing nerve intact). 
  • Finally, in chronic cases with chronic weakness or deformity (and where nerve repair is not felt to be possible) other surgical procedures such as a microvascular nerve transfer, tendon transfers or joint fusions are utilized to restore her hand function. 

Each nerve laceration case and patient requirements are individual and unique, requiring a different approach.

Nerve repair surgery is usually performed under general anesthesia to avoid any patient motion. The patient is often placed in a protective splint post-op to avoid any tension on the nerve repair. 

The actual nerve repair site takes 4 to 6 weeks to heal and avoid tearing. Mobilization exercises of the hand are then begun to regain motion. Return to work and normal activities are usually allowed after the nerve repair site is healed and function and strength are within acceptable limits.

Approximately 2 weeks after nerve repair, the nerve starts the slow process of regeneration at about the rate of an inch a month. This process may take place more quickly in younger healthier patients. Regeneration is also faster in primary nerve repairs than with nerve grafts.

It may be months before the return of sensation is noted. Return of muscle function often takes longer. Ultimately, it is important to remember that despite our best efforts and advanced microsurgical technique, all nerve function does not return in every patient.