Cath Lab Digest

   Generally speaking, one should treat most traumatic nerve injuries acutely with end-to-end endoneural repair. However, this is not the standard of care with injuries distal to the arch of the foot. Frenette and Jackson looked at a small series of patients in whom the smaller distal nerves of the foot underwent primary repair. The authors reported only a 25 percent return to normal sensation.⁷ It is therefore not recommended to attempt repair on these patients due to the small nerve size and minimal sensory deficit acquired when patients undergo conservative treatment.

   Iatrogenic nerve injury is certainly a possible complication after foot and ankle surgery but is luckily uncommon when one employs good surgical techniques. Regardless, painful stump neuromas do occur and are more frequently involved with common digital nerve resection or resection of Morton’s neuroma.

   Logic would tell us that the large volume of Morton’s neuromas removed each year is the reason for this. However, there are studies that explain why there may be other factors that predispose the patient to painful stump neuromas after these procedures.

   Amis and colleagues looked into this when they dissected second and third common digital nerves in fresh, frozen cadaveric feet.⁸ They found consistent, small, plantarly directed nerve branches along the course of these nerves that innervated the underlying skin. The authors hypothesized that these branches acted to anchor the nerves, preventing inadequate retraction deep into the foot after standard common digital nerve resection.

   Small communicating branches are also present in a certain percentage of the population between the second and third and/or third and fourth common digital nerves. These communicating branches travel transversely, deep to the metatarsals and are usually proximal to the actual Morton’s neuroma. When one does not identify this intraoperatively, the terminal nerve stump can become tethered once again and inadequate retraction deep into the foot can occur.⁹

Essential Diagnostic Insights

   Diagnosis of a stump neuroma is not always straightforward. A large part of the diagnosis draws from the clinical history and timing of symptoms. One should have heightened suspicions if the patient presents with classic nerve symptoms and a recent history of traumatic nerve injury or Morton’s neuroma surgery. Common complaints are burning pain, pins and needles sensations and/or electrical shooting or shocking.¹⁰ The pain is often localized to the area of nerve injury but may present more proximal.

   The timing of symptoms is also important. A classic stump neuroma does not become symptomatic for weeks to months after the initial insult. As I mentioned earlier, the terminal portion of the nerve goes through a certain amount of axonal regeneration after resection. However, this does take time and requires several weeks to have proliferated enough to become symptomatic.¹⁰

   When the symptoms become evident immediately or relatively soon after surgery, the surgeon needs to consider other diagnoses and rule them out. In the case of persistent pain after Morton’s neuroma resection, studies have shown that two-thirds of cases are due to incomplete excision of the nerve.¹⁰ Another potential cause is undiagnosed multiple neuromas, which reportedly occur 3.4 percent of the time.¹⁰ Lastly, one should consider that the wrong web space may have been diagnosed or the initial diagnosis was incorrect prior to surgery (see “What Common Conditions Can Be Misdiagnosed As Neuromas?” on page 74).