What is the growth rate of peripheral nerves?

From the Guidelines

Peripheral nerves typically regenerate at a rate of 1-3 millimeters per day or about 1 inch per month following injury. This growth rate varies based on several factors including the person's age, overall health status, the type and severity of injury, and the specific nerve affected 1. The regeneration process involves Wallerian degeneration, where the distal portion of the damaged nerve degenerates while the proximal segment forms a growth cone that advances toward the target tissue. Key factors influencing nerve regeneration include:

• The location of the injury, with proximal injuries (closer to the spinal cord) having a poorer prognosis than distal injuries because the nerve must regenerate over a longer distance to reach its target
• The presence of inflammation, which can decrease neurite outgrowth and increase calcium influx across cell membranes, causing axonal degeneration 1
• The use of anti-inflammatory therapy, such as topical corticosteroids, which can promote nerve regeneration by reducing inflammation 1
• The role of neurotrophic factors, such as nerve growth factor (NGF), which can alleviate patient symptoms and promote neuronal regeneration 1

The slow growth rate explains why recovery from peripheral nerve injuries often takes months to years, and why early intervention with appropriate surgical repair or nerve grafting may be necessary for optimal functional recovery, especially for injuries with nerve gaps exceeding 5mm. Schwann cells play a crucial role by forming bands of Büngner, which guide regenerating axons. Recent studies have shown that therapeutic strategies targeting neuronal regeneration, such as autologous serum tears (AST) and neurotrophic factors, can alleviate patient symptoms and promote nerve regeneration 1.

From the Research

Growth Rate of Peripheral Nerves

The growth rate of peripheral nerves is a complex process that involves various molecular mechanisms and factors. Research studies have investigated the growth rate of peripheral nerves in different contexts, including after injury and during regeneration.

• The growth rate of axons in peripheral nerves has been reported to be around 1.5-2.0 mm per day 2.
• A study found that the sensory potential evoked by stimuli to digits III and I and recorded proximal to the suture line at the wrist appeared after a delay of three to four months, corresponding to a growth rate of 1.5-2.0 mm per day 2.
• The cumulative amplitude of the sensory potential increased for two years slowly and thereafter at a two times faster rate 2.
• The overall increase in the amplitude of the sensory potentials in children aged 10 and 12 years was three times faster than in adults 2.

Factors Influencing Growth Rate

Several factors can influence the growth rate of peripheral nerves, including:

• Growth factors, such as insulin-like growth factors (IGFs) and mesencephalic astrocyte-derived neurotrophic factor (MANF) 3, 4.
• The presence of molecules in situ that promote the effective elongation of neurites, such as laminin and heparan sulfate proteoglycan 5.
• The use of artificial nerve conduits (NCs) and growth factor delivery systems to improve therapeutic performance 6.

Regeneration and Repair

The regeneration and repair of peripheral nerves is a complex process that involves the coordinated action of multiple cell types and molecular factors.

• Research has shown that the effective regeneration of severed neuronal axons in the peripheral nerves of adult mammals may be explained by the presence of molecules in situ that promote the effective elongation of neurites 5.
• The use of NCs and growth factor delivery systems has been shown to improve significantly the axonal outgrowth in nerve defect models 6.