Surgery for Morton Neuroma Treatment & Management

The biomechanical goals of nonsurgical management are to reduce forefoot compression and to eliminate the effect of intermetatarsal ligament tension. In theory, this decreases the overall pressure on the nerve and allows it to function more normally. Shoe modifications are simple to understand but may be objectionable to some patients. High-heeled and narrow shoes should be avoided. The use of a metatarsal pad orthotic device can help keep pressure off the nerve.^[15]

The literature is conflicting regarding the success rate for nonsurgical management, but a reasonable estimate would be that 20-30% of patients would obtain either total resolution of symptoms or improvement to a satisfactory level with footwear modifications and restrictions.^[16]

Corticosteroid or local anesthetic injections may be helpful, especially when coupled with the aforementioned shoe modifications. Using 2 mL of corticosteroid with 1 mL of Marcaine in the same syringe, the injection should be given from the dorsal direction. Do not inject into the superficial subcutaneous tissue, so as to avoid steroid-induced skin necrosis. Injections should not be used indiscriminately, because the injection itself is associated with morbidities.

Current surgical care for Morton neuroma involves a few different options for either decompressing or resecting the nerve.^[17] The first consideration relates to the choice of surgical approach. The plantar approach is through a 3- to 4-cm longitudinal incision centered over the intermetatarsal space. This approach provides direct exposure of the nerve, since it lies plantar to the intermetatarsal ligament. The dorsal approach is through a similar-sized incision but must be taken down between the metatarsals and through the transected intermetatarsal ligament, a much less direct exposure of the nerve.^[18]

Current trends are toward the use of the dorsal incision for primary resection because it avoids the more debilitating problems of a plantar incision if a wound complication arises. Using a small Inge retractor to widen the intermetatarsal space and apply tension to the tissues facilitates the dissection and identification of the important structures. It is prudent to inspect the area carefully to look for concurrent pathology such as lipomas, osteophytes, or inflamed bursae. See the images below.

After deciding which approach to use, the definitive surgical procedure must be performed—another somewhat controversial issue. One surgical option is simply to divide the intermetatarsal ligament and thereby create a decompression of the intermetatarsal space. This may be coupled with a neurolysis, depending on the surgeon's preference. Proponents of this ideology generally believe that decreasing the stresses on the nerve is the key aspect of successful treatment and that, by preserving the nerve, some normal nerve function can return. Furthermore, by not resecting any nerve tissue, no chance of forming a recurrent (stump) neuroma exists.

A second option is to perform a neurectomy, as shown below. Proponents of neurectomy believe that the key to successful treatment is elimination of the pathologic nerve tissue, while decompression would only serve to decrease the ongoing mechanical stresses on that abnormally functioning nerve. As mentioned previously, it is very important to transect the nerve as far proximal to the bifurcation as possible. Many authors promote transecting the nerve 3 cm proximal to the proximal border of the intermetatarsal ligament, since this allows proper resection of the plantar branches that may otherwise prevent the nerve stump retraction away from the weightbearing surface.^{[19, 20]}

To this author's knowledge, no prospective, controlled trials exist to compare the 2 main surgical options. A review of the case series in the current body of literature indicates that the reported success rates are similar, generally with 80% satisfactory results.

Postoperative care consists of restricting the patient to weight bearing as tolerated in a postoperative shoe, with gradual introduction of appropriate footwear as tolerated once the wound has healed and swelling has resolved.

An expected complication of the neurectomy is loss of cutaneous sensation of the interdigital skin. For most patients, this is not clinically significant. A variable amount of numbness may be present on the plantar skin, just proximal to the web space. Some authors believe that this can be more problematic and may be more likely to perform surgical decompression of the nerve (and not resect it) to avoid this complication.^[1]

In the rare cases in which simultaneous adjacent neurectomies have been performed, the toe is affected by a more dense numbness from the metatarsal head to the tip of the digit. One study showed this increased numbness caused some awkwardness with nail care but no significant disability.^[21]

Intractable plantar keratosis underneath adjacent metatarsal heads has been identified as a potential complication, likely as a result of altered weight-bearing mechanics due to releasing the intermetatarsal ligament.^[19] Wound complications are typically minor when they occur. Antibiotic treatment, debridement, or both are used as indicated.

Recurrent or persisting symptoms after surgical intervention may relate to a number of factors and can be difficult to treat. Patients who have had the decompression type of procedure may continue to have problems if the decompression was incomplete or if the nerve simply remains irritable. Those who have had neurectomy may develop a stump neuroma that may be even more painful than the original problem. Surgical intervention may be indicated should the persisting symptoms be intolerable and fail to respond to conservative measures. When operating on a recurrent neuroma, the plantar approach provides more direct access to the nerve while avoiding the scarred tissue planes of the initial dorsal approach.

In general, review of the orthopedic literature from the last 20 years supports an estimate of 75-85% satisfactory results after surgical intervention. Nonsurgical management probably results in a 20-30% success rate.

Long-term postsurgical outcomes have been quantified thoroughly by Coughlin and Pinsonneault.^[19] Their study monitored 76 patients over an average of 5.8 years. A dorsal approach was used, and a neurectomy was performed 3 cm proximal to the intermetatarsal ligament. The results were as follows:

• Approximately one third of patients have some persisting scar sensitivity when examined that was not identified by the patients prior to being examined. Thus, it was likely minimally significant.
• Residual interspace tenderness was present in 61% when examined, but only 6 of those 45 patients had identified this as a persisting problem prior to being examined.
• No instances of metatarsal joint instability were reported.
• Intractable plantar keratosis developed in 15%.
• Subjective numbness was noted by 51% of patients, but only 4 of 71 patients found it problematic.
• Seventy percent of patients had footwear restrictions, and 38% had some persisting activity modifications.
• Wound complications occurred in 2 of 74 incisions and were mild.

This article outlines some current controversies regarding Morton neuroma; the fact that the eponym is likely a misnomer is a reflection of current controversies. The histology, use of adjunctive imaging modalities, and choice of surgical procedure all involve some degree of controversy. Current and future work is addressing these issues.