A finger injury that results in a cut nerve immediately disrupts the communication between the hand and the brain. Peripheral nerves in the finger are complex structures containing thousands of microscopic fibers that transmit sensory and, sometimes, motor information. These nerves are responsible for the detailed sense of touch and proprioception, the awareness of the finger’s position in space. A complete severance instantly halts these signals, resulting in an immediate loss of function in the area the nerve serves.
The Immediate Impact of Nerve Injury
The consequence of a completely cut finger nerve is an immediate loss of function distal to the injury site. Since digital nerves in the finger are primarily sensory, the most noticeable effect is anesthesia, or complete numbness, in a specific distribution of the fingertip or side. This sensory loss means the finger can no longer detect fine touch, temperature, or pain.
The sudden inability to feel prevents the brain from receiving feedback necessary for precision grip and object manipulation. While injuries higher up in the hand or wrist may cause motor deficits, a direct cut to a digital nerve usually causes a pure sensory deficit. This leaves the affected area vulnerable to unnoticed burns or cuts. The cut nerve ends may also generate a sensation of electric shock or shooting pain, indicating the raw nerve tissue is irritated.
Surgical Repair Options
When a nerve is completely severed, the ends must be surgically reconnected to provide a path for regeneration, as the nerve cannot heal this type of injury on its own. The preferred method is primary neurorrhaphy, which involves microsurgical stitching of the nerve’s outer sheath (epineurium) to precisely align the two ends. This procedure uses an operating microscope to ensure the delicate nerve fascicles—the bundles of nerve fibers—are matched up as closely as possible.
The goal is to create a tension-free connection, since pulling on the nerve ends can compromise the repair and hinder regrowth. If the injury caused a loss of nerve tissue resulting in a gap, a nerve graft becomes necessary. An autologous nerve graft, often taken from a less functionally important sensory nerve, is the standard for bridging these gaps. This transplanted segment acts as a scaffold, guiding regenerating nerve fibers across the defect and into the distal pathway.
Understanding Nerve Regeneration
Following successful surgical repair, the biological process of nerve regeneration begins. The segment of the nerve disconnected from the cell body undergoes Wallerian degeneration, where the nerve fibers and myelin sheath break down. Schwann cells within the remaining sheaths form structures that guide new axonal sprouts from the proximal nerve end across the repair site.
The rate at which these new axons grow is approximately 1 millimeter per day, or about one inch per month. This slow pace means recovery of sensation in the fingertip can take many months or even over a year. Physical and occupational therapy is an important element of recovery, focusing on sensory re-education. This retraining is necessary because new fibers may not reach their original sensory receptors, causing a mismatch between the touch stimulus and the perceived sensation.
Managing Long-Term Sensations
Even after successful surgery and regeneration, patients may experience persistent altered feelings. One common long-term issue is paresthesia, which includes chronic tingling, burning, or “pins and needles” sensations. Other potential complications include hyperalgesia (increased sensitivity to pain) or allodynia, where light touch is perceived as painful.
A specific long-term complication is the formation of a neuroma, a disorganized, painful tangle of regenerating nerve fibers at the injury site. This mass forms when growing axons fail to find their way into the distal nerve sheath and instead proliferate into a sensitive lump of scar tissue. A symptomatic neuroma causes chronic, shooting, or burning pain that affects the patient’s ability to use the finger, sometimes requiring further surgery.