You are in: eMedicine Specialties > Orthopedic Surgery > FOOT AND ANKLE Morton NeuromaArticle Last Updated: May 9, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 13
  Author: Thomas M Schaller, MD, Clinical Assistant Professor, Department of Orthopedic Surgery, Kalamazoo Center for Medical Studies, Michigan State University Thomas M Schaller is a member of the following medical societies: Alpha Omega Alpha, American Academy of Orthopaedic Surgeons, American Medical Association, AO Foundation, and Orthopaedic Trauma Association Editors: Heidi M Stephens, MD, Associate Professor, Department of Surgery, Division of Orthopedic Surgery, Director of Diabetic Foot Clinic, Assistant Dean for Clinical Outreach, University of South Florida College of Medicine; Courtesy Joint Associate Professor, Department of Environmental and Occupational Health, University of South Florida College of Public Health; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Shepard R Hurwitz, MD, Executive Director, American Board of Orthopaedic Surgery; Dinesh Patel, MD, FACS, Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital; Jason H Calhoun, MD, FAAOS, Chairman, J Vernon Luck Distinguished Professor, Department of Orthopedic Surgery, University of Missouri Author and Editor Disclosure Synonyms and related keywords: interdigital neuroma, interdigital neuritis, forefoot pain, forefoot paresthesias, forefoot numbness, foot pain, Inge retractor, neurectomy, plantar keratosis INTRODUCTIONSection 2 of 13
  History of the ProcedureIn 1876, Thomas Morton first described interdigital nerve compression.1 Morton theorized that the nerve was being compressed between the metatarsal heads. Surgical procedures have historically been aimed either at directly dealing with the pathologic nerve or at altering the local biomechanical environment in which the nerve exists. The evolution of surgical care for Morton neuroma has resulted in some basic principles and goals, which are the foundation for the current surgical options. There is an increased body of literature that elaborates on many aspects of this seemingly simple problem. ProblemInterdigital neuritis is a mechanically induced nerve irritation due to intrinsic and extrinsic biomechanical factors that results in a combination of pain, paresthesias, and numbness in the forefoot. A greater understanding of forefoot anatomy and biomechanics has created an environment to further delineate the pathophysiology of interdigital neuroma. FrequencyMorton neuromas are more common in women, with a female-to-male ratio of 4:1. They tend to occur in the fifth decade of life and frequently are exacerbated by constrictive footwear.2 Symptoms are typically unilateral, with the third interspace most often involved followed by the second and the fourth interspaces.2 Simultaneous neuromas occurring in the same foot are rare.3 EtiologySee Pathophysiology. PathophysiologyThe term neuroma may be a misnomer for the condition. Morton neuroma may be best described as a clinical syndrome stemming from a constellation of factors related to the local anatomy and the forces applied on the forefoot with ambulation and shoe wear. Interestingly, it is not uncommon for the histopathology to be interpreted as relatively normal, even in light of classic preoperative findings and dramatic postoperative results. Clearly, the histopathology is not that of a typical neuroma,2 but some or all of the following may be observed:
Anatomic studies have revealed a wealth of information and helped to resolve some misconceptions regarding the etiology of this disease. The intermetatarsal space is narrower in the second and third interspaces than in the first and fourth interspaces, which correlates with the clinical presentation pattern.4 The composition of the tarsometatarsal articulation allows relative hypermobility between the second and third metatarsals, which contributes to mechanical irritation of the nerve. Narrow toe-box footwear can exacerbate the compression between the metatarsal heads, and hyperextension of the toes in high-heeled shoes tethers the nerve beneath the ligament and may expose it to more biomechanical stresses with gait.2 Less commonly, metatarsophalangeal (MTP) joint pathology, inflamed bursa, or lipomas can create compression at the level of the common digital nerve. ClinicalPatients typically present with pain and paresthesias localized to one interspace of the forefoot with radiation to the involved toes. The symptoms may wax and wane over many years and are exacerbated with compressive shoewear. Relief is common when the shoes are removed and the area is massaged. A provocative examination involves manually compressing the forefoot and simultaneously palpating the affected web space between the fingers of the other hand. The compression may result in the Mulder sign, which is a painful and palpable click that reproduces the symptoms.5 INDICATIONSSection 3 of 13
The indication for surgery is significant pain or dysfunction that is not tolerated by the patient and that fails to respond to conservative management. RELEVANT ANATOMYSection 4 of 13
In addition to the discussion above, key anatomic concepts must be considered when choosing the appropriate surgical treatment of an interdigital neuroma. The medial plantar nerve has 4 digital branches that begin at the medial aspect of the great toe and then form the common digital nerves of the first, second, and third web spaces. The lateral plantar nerve supplies the fourth web space and, in 27% of patients, contributes to the third web space. This increased thickness of the third digital nerve was hypothesized to predispose it to mechanical irritation; however, studies have shown no correlation between those patients with this anatomic variant and those with symptoms of Morton neuroma. The common digital nerves lie plantar to the intermetatarsal ligament and give off small branches to the plantar skin approximately 1-2 cm proximal to the bifurcation of the nerve. These branches also must be resected at the time of surgery because they may prevent nerve stump retraction after neurectomy and lead to a recurrent neuroma.1 CONTRAINDICATIONSSection 5 of 13
Once the diagnosis is made and conservative management has failed, few contraindications to surgical intervention exist. Local soft-tissue factors, such as infections or vascular insufficiency, are likely to be the only absolute contraindications. Patient psychosocial issues may be relative contraindications and must be addressed prior to surgical procedures of any kind. WORKUPSection 6 of 13
Imaging Studies
Diagnostic Procedures
Histologic FindingsSee Pathophysiology. TREATMENTSection 7 of 13
Medical therapyThe 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.13 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. 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. Surgical therapyCurrent surgical care for Morton neuroma involves a few different options for either decompressing or resecting the nerve. 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.14 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. 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. 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.15 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 detailsPostoperative 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. COMPLICATIONSSection 8 of 13
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.16 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.15 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. OUTCOME AND PROGNOSISSection 9 of 13
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.15 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:
FUTURE AND CONTROVERSIESSection 10 of 13
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. ACKNOWLEDGMENTSSection 11 of 13
The authors and editors of eMedicine gratefully acknowledge the contributions of previous coauthor Patrick L. O'Connor, MD, to the development and writing of this article. MULTIMEDIASection 12 of 13
REFERENCESSection 13 of 13
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