How To Address Stump Neuromas
Given the challenges of stump neuromas in the foot, this author offers insights on the etiology, conservative management and surgical options such as nerve capping and transplantation.
The stump neuroma is a natural and expected occurrence after nerve injury. When damaged, the proximal nerve segment attempts to regenerate, leading to a bulb-shaped thickening or stump. Trauma is a common cause for these injuries throughout the body.
In the foot, however, iatrogenic etiologies are more frequent. Researchers have reported that up to 30 percent of stump neuromas elicit pain.1 It is unclear why some are painful and others are not, but it most likely relates to the area and tissue into which the nerve regenerates.
Interdigital neuromas typically have fairly standard histological characteristics. Myelinated fibers degenerate, leading to thickening and fibrosis of the epineurium and perineurium. Additionally, thickening and hyalinization takes place in the walls of the epineural and endoneural vessels.2 This degenerative histology is in direct contrast to traumatically induced neuromas, which are more proliferative. The neural tissue demonstrates dense fibrous changes with tortuous irregular proliferation.
Nerves are remarkable in that they do go through some degree of repair and regeneration after injury. We are able to utilize this with surgical repair of transected nerves via direct end-to-end anastomosis, nerve grafting or by utilizing neural tunnels to guide the regenerating neurons to rejoin their distal segment. On the other hand, stump neuromas are characterized by disorganized architecture with nerve tissue growing out in no particular orientation.3
Dellon described neural regeneration as an expected biological consequence after a peripheral nerve divides.4 Wallerian degeneration is the process that nerves go through to repair themselves after injury. Nerve growth factors produced from Schwann cells support this process. After injury, these neurotrophic factors diffuse outward, inducing nerve fibers to grow outward in many different directions beyond the border of transection. This haphazard regrowth leads to a bulb-shaped thickening that is otherwise known as a stump neuroma.
This begs the question: if stump neuromas are a natural occurrence after nerve injury, why are they not all painful? Certainly, Morton’s neuroma excision is a fairly standard procedure performed by most foot and ankle surgeons. In fact, it is estimated that only 30 percent of stump neuromas become symptomatic after transection.1
The answer is not entirely clear but there are some theories. Most authors believe pain occurs when the haphazardly regenerating nerve fibers branch out into scar tissue or areas of adhesion.5 Weightbearing areas on the foot, locations prone to mechanical stimulation and areas that undergo repetitive trauma become problem spots as well. In short, the nerve fibers interact abnormally with surrounding connective tissue, leading to pain.
What You Should Know About The Etiology
As I noted earlier, the formation of a terminal or stump neuroma is a natural occurrence after nerve injury. In the foot and ankle, nerve injuries generally result from either a traumatic event or as part of a surgical procedure, be it intentional or unintentional.6 The soft tissue envelope is relatively small and this places subcutaneous and deep nerves in danger of damage during traumatic events. The dorsal neural structures are at risk with laceration type injuries. The plantar structures are prone to damage with puncture wounds.