eMedicine Specialties > Orthopedic Surgery > Foot & Ankle
Morton Neuroma
Updated: May 9, 2008
Introduction
History of the Procedure
In 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.
Problem
Interdigital 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.
Frequency
Morton 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
Etiology
See Pathophysiology.
Pathophysiology
The 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:- Sclerosis of the endoneurium
- Hyalinization of the walls of endoneurial vessels
- Thickened perineurium
- Demyelinization of nerve fibers
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.
Presentation
Patients 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
Indications
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 Anatomy
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
Contraindications
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.
Workup
Imaging Studies
- A large body of literature addresses the use of imaging modalities to aid in the diagnosis of Morton neuroma. The condition is most commonly diagnosed based strictly upon the history and physical examination findings. In equivocal cases, the use of ultrasound, magnetic resonance imaging (MRI), or both may be helpful.6,7,8
- The skill of the technologists and physicians performing and interpreting these studies plays a key role in determining just how valuable these modalities can be in clinical practice.
- The ultrasound appearance is typically that of a hypoechoic oblong mass that is oriented along the long axis of the foot. Prospective studies in symptomatic patients reveal that ultrasound can be used reliably to detect the neuromas.9 Furthermore, they can be helpful in identifying contributing pathologic lesions, such as lipomas or bursae.10
- MRI technology and applications continue to evolve and can provide reliable information regarding the pathoanatomy of the forefoot. The characteristic MRI findings of a Morton neuroma are low intensity on T1- and T2-weighted sequences due to the high degree of fibrous content. In contrast, an intermetatarsal bursa is associated with increased intensity on the T2-weighted images due to its fluid content.11 MRI with gadolinium contrast enhancement and with fat suppression probably provides the most reliable images for diagnosis.12
Diagnostic Procedures
- An injection of local anesthetic with sterile technique may be useful in the diagnostic evaluation of Morton neuroma. The temporary resolution of pain, paresthesias, or both in response to the injection may confirm the location of the pathology. A positive response to the injection tends to be predictive of satisfactory postsurgical outcomes.
Histologic Findings
See Pathophysiology.
Treatment
Medical Therapy
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.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 Therapy
Current 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 Details
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.
Complications
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 Prognosis
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:
- 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.
Future and Controversies
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.
Multimedia
Media file 1: Plantar view showing the relationships between the metatarsal heads, the intermetatarsal ligament, and the neuroma.
Media file 2: This image demonstrates the key provocative physical examination maneuver: simultaneous forefoot compression coupled with intermetatarsal space compression.
Media file 3: The histopathology reveals nerve fibers and pacinian corpuscles entrapped within fibromyxoid connective tissue.
Media file 4: Typical incision location.
Media file 5: Superficial exposure.
Media file 6: Deeper dissection.
Media file 7: Neuroma and adherent fibrofatty tissue.
References
Weinfeld SB, Myerson MS. Interdigital Neuritis: Diagnosis and Treatment. J Am Acad Orthop Surg. Nov 1996;4(6):328-335. [Medline].
Coughlin MJ, Mann RA. Surgery of the Foot and Ankle. 7th ed. Mosby-Year Book;1999.
Thompson FM, Deland JT. Occurrence of two interdigital neuromas in one foot. Foot Ankle. Jan 1993;14(1):15-7. [Medline].
Levitsky KA, Alman BA, Jevsevar DS. Digital nerves of the foot: anatomic variations and implications regarding the pathogenesis of interdigital neuroma. Foot Ankle. May 1993;14(4):208-14. [Medline].
Mulder J. The Causative Mechanism in Morton's Metatarsalgia. J Bone Joint Surg Br. 1951;33:94-95.
Lee MJ, Kim S, Huh YM, Song HT, Lee SA, Lee JW, et al. Morton neuroma: evaluated with ultrasonography and MR imaging. Korean J Radiol. Mar-Apr 2007;8(2):148-55. [Medline].
Zanetti M, Weishaupt D. MR imaging of the forefoot: Morton neuroma and differential diagnoses. Semin Musculoskelet Radiol. Sep 2005;9(3):175-86. [Medline].
Giannini S, Bacchini P, Ceccarelli F, Vannini F. Interdigital neuroma: clinical examination and histopathologic results in 63 cases treated with excision. Foot Ankle Int. Feb 2004;25(2):79-84. [Medline].
Read JW, Noakes JB, Kerr D. Morton''s metatarsalgia: sonographic findings and correlated histopathology. Foot Ankle Int. Mar 1999;20(3):153-61. [Medline].
Iagnocco A, Coari G, Palombi G. Sonography in the study of metatarsalgia. J Rheumatol. Jun 2001;28(6):1338-40. [Medline].
Timins ME. MR imaging of the foot and ankle. Foot Ankle Clin. Mar 2000;5(1):83-101, vi. [Medline].
Terk MR, Kwong PK, Suthar M. Morton neuroma: evaluation with MR imaging performed with contrast enhancement and fat suppression. Radiology. Oct 1993;189(1):239-41. [Medline].
Saygi B, Yildirim Y, Saygi EK, Kara H, Esemenli T. Morton neuroma: comparative results of two conservative methods. Foot Ankle Int. Jul 2005;26(7):556-9. [Medline].
Valente M, Crucil M, Alecci V. Operative treatment of interdigital Morton's neuroma. Chir Organi Mov. Mar 14 2008;[Medline].
Coughlin MJ, Pinsonneault T. Operative treatment of interdigital neuroma. A long-term follow-up study. J Bone Joint Surg Am. Sep 2001;83-A(9):1321-8. [Medline].
Benedetti RS, Baxter DE, Davis PF. Clinical results of simultaneous adjacent interdigital neurectomy in the foot. Foot Ankle Int. May 1996;17(5):264-8. [Medline].
Keywords
interdigital neuroma, interdigital neuritis, forefoot pain, forefoot paresthesias, forefoot numbness, foot pain, Inge retractor, neurectomy, plantar keratosis
Contributor Information and Disclosures
Author
Thomas M Schaller, MD, Clinical Assistant Professor, Department of Orthopedic Surgery, Kalamazoo Center for Medical Studies, Michigan State University; Medical Director of Orthopedic Trauma, Bronson Methodist Hospital
Thomas M Schaller, MD 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
Disclosure: Nothing to disclose.
Medical Editor
Heidi M Stephens, MD, MBA, Associate Professor, Department of Surgery, Division of Orthopedic Surgery, 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
Heidi M Stephens, MD, MBA is a member of the following medical societies: Alpha Omega Alpha, American Academy of Orthopaedic Surgeons, American Medical Association, American Orthopaedic Foot and Ankle Society, and Florida Medical Association
Disclosure: Nothing to disclose.
Pharmacy Editor
Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment
Managing Editor
Shepard R Hurwitz, MD, Executive Director, American Board of Orthopaedic Surgery
Shepard R Hurwitz, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Association for the Advancement of Science, American College of Rheumatology, American College of Sports Medicine, American College of Surgeons, American Diabetes Association, American Orthopaedic Association, American Orthopaedic Foot and Ankle Society, Association for the Advancement of Automotive Medicine, Eastern Orthopaedic Association, Orthopaedic Research Society, Orthopaedic Trauma Association, and Southern Orthopaedic Association
Disclosure: Nothing to disclose.
CME Editor
Dinesh Patel, MD, FACS, Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital
Dinesh Patel, MD, FACS is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Association of Physicians of Indian Origin, American College of International Physicians, and American College of Surgeons
Disclosure: Nothing to disclose.
Chief Editor
Jason H Calhoun, MD, FACS, Frank J Kloenne Chair in Orthopedic Surgery, Professor and Chair, Department of Orthopedics, The Ohio State University Medical Center
Jason H Calhoun, MD, FACS is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American College of Surgeons, American Diabetes Association, American Medical Association, American Orthopaedic Association, American Orthopaedic Foot and Ankle Society, Missouri State Medical Association, Musculoskeletal Infection Society, Southern Medical Association, Southern Orthopaedic Association, Texas Medical Association, and Texas Orthopaedic Association
Disclosure: Nothing to disclose.