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This companion article to interdigital perineural fibroma (a.k.a. Morton's neuroma [MN]) discusses the anatomy and physiology of the nerves in the forefoot, clinical presentation, diagnosis, and treatment of this painful fore foot condition. Although no empirical causal data exists to associate MN with Morton's syndrome or Morton's toe, a condition has been described in the literature whereby particular foot architecture has been linked to anomalies in the first and second metatarsals. This alteration in forefoot structure creates changes in foot biomechanics, precipitates foot pain, and alters foot functioning. To juxtapose this article with the possibility of Morton's syndrome, a family vignette referred to as "Jane's Genus" will be provided as an example of the prevalence of Morton's toe in one family.
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This companion article to interdigital perineural fibroma (a.k.a. Morton's neuroma [MN]) discusses the anatomy and physiology of the nerves in the forefoot, clinical presentation, diagnosis, and treatment of this painful fore foot condition. Although no empirical causal data exists to associate MN with Morton's syndrome or Morton's toe, a condition has been described in the literature whereby particular foot architecture has been linked to anomalies in the first and second metatarsals. This alteration in forefoot structure creates changes in foot biomechanics, precipitates foot pain, and alters foot functioning. To juxtapose this article with the possibility of Morton's syndrome, a family vignette referred to as "Jane's Genus" will be provided as an example of the prevalence of Morton's toe in one family.
Primary changes in form and function are followed by determinable changes in the outer shape and the inner architecture of the involved bone.
Weinmann & Sicher 1955, p. 174
Normal bipedal locomotion causes varying biomechanical stresses and strains on the feet. Ill-fitting shoes, repetitive movements, and everyday walking can affect soft tissue and osseous structures.
Minor alterations in foot biomechanics may, after many years, bring about chronic changes to foot structures precipitating painful foot syndromes and conditions such as Morton's neuroma (MN).
The literature has discussed a phenomenon called Morton's syndrome or Morton's toe. Morton's syndrome is a triad associated with a short first metatarsal segment, a long second metatarsal phalangeal joint, and hypermobile first metatarsophalangeal (MTP) segment with associated posteriorly placed sesamoids ossicles (see Figure 1).
Epidemiology
Interdigital perineural fibroma or Morton's neuroma is a painful benign mechanical entrapment neuropathy affecting a common digital nerve in the forefoot (Wu, 1996) (see Figure 2). The predominance of female to male ratio for this condition is 5:1, and the third interspace in the foot is the most common region affected. Multiple neuromata may be present in the same foot, as well as, bilateral foot involvement (Mollica, 1997). Daily activities requiring persistent and excessive squatting, sports, and vocations requiring forced dorsiflexion of the toes are precipitating factors.
Nerve Innervations in the Foot
The sensory cutaneous and muscular nerve innervation to the ankle and foot is derived from the femoral and sciatic nerves and their major branches. One branch includes the saphenous nerve. The saphenous nerve lies deep in the lower extremity and extends through the sartorius and gracilus muscles. It then passes medially about the tibia with terminal branches extending to the ankle, providing sensation to the medial malleolus and medial aspect of the foot. The sciatic nerve and its branches provide deeper sensation and muscular innervation of the ankle and foot. Theses branches include the sural nerve, common peroneal nerve, superficial peroneal nerve (musculocutaneous nerve), deep peroneal nerve, medial calcaneal nerve, medial and lateral plantar nerves, and proper digital nerves. Table I lists lower extremity nerves, their branches, and innervation properties (cutaneous sensory or motor).
The third web space in the foot receives branches from the medial and lateral plantar nerve. This nerve is wider and more easily irritated by the biomechanical forces between the bursa of the intermetatarsal ligament and the various structures in the foot (see Figure 3).
Altered foot biomechanics and other factors may precipitate the development of MN. Painful neuroma may alter gait patterns, activities of daily living, and job and athletic performance. They may also lead to a chronic pain syndrome (Mackinnon, 1998).
Clinical Presentation
The athlete or patient may complain of paroxysmal episodes of pain in the ball of the forefoot. This neuralgia-like pain may be described as sharp, burning (causalgia) or shooting in nature; the person may also have the sensation of having a stone/pebble in the shoe upon walking (Willick & Herring, 1998). Paresthesia to one or more toes is possible. Tight shoes, walking, and activities that require repetitive dorsiflexion of the toes aggravate pain. Rest usually relieves the pain.
Diagnosis
The process of diagnosing MN begins with a thorough history and physical examination. The specific nature of what part of the forefoot is involved, in conjunction with the pain distribution pattern, will be helpful in making a diagnosis. The differential diagnosis for forefoot pain is extensive. Table 2 includes a partial list of differential diagnoses attributing to forefoot pain.
Besides physical examination of the foot for deformities, variance in skin color, sensibility and motor function, and knowledge of preexisting medical morbidity (e.g., diabetes mellitus), a two-dimensional compression test (Wu, 1996), may assist with definitive diagnosis of MN. Compression or squeezing of the metatarsophalangeal (MTP) joints may produce an audible "click" and/or cause sudden pain in the forefoot. This click is referred to as Mulder's sign (Biasca et al., 1999; Mollica, 1997; Rosenberg & Sferra, 1998; Wu, 1996).
Performing compression of the five MTP heads and application of direct pressure over the third interspace (dorsal aspect of the foot) elicits neuralgia that is pathognomonic for MN. Figures 4a and b show the compression/ squeeze test and pressure over the third interspace in the foot. Another method used to diagnose MN includes imaging studies.
Imaging studies such as magnetic resonance (MR) (Biasca et al., 1999; Bencardino et al., 2000; Zonetti et al. 1999) and ultrasonography (US) (Mendicino & Rockett, 1997; Shapiro & Shapiro, 1995; Wu, 1996) have provided specific and sensitive data regarding MN. Plain radiographs are generally not helpful as a diagnostic means for MN. Some authors advocate using a local nerve block. If the nerve block produces pain relief, it is considered a positive diagnostic sign for MN (Basadonna et al., 1999; Rosenberg & Sferra, 1998; Younger & Claridge, 1998).
Treatment
The primary goal of treatment of MN is to interrupt pain. A thorough history and physical exam will identify the offending sources) of pain. Once identification is made, the causative factors may be halted. Conservative methods of treatment should initially be used (Bennett et al., 1995; Rosenberg & Sferra, 1998). Conservative treatments include shoe/footwear modifications, teaching correct vocational and sports biomechanics, and local anesthetic/corticosteroid injections. Bennett et al. (1995), Rosenberg & Sferra (1998), and Wu (1996) advocate using staged or tiered treatment protocols (noninvasive progressing to invasive therapies). Other conservative treatments are listed in Table 3.
If conservative treatments fail, surgery may be required. Two surgical interventions commonly used to treat MN are dividing the transverse metatarsal ligament to free the entrapped nerve and surgical excision of the offending neuromatous lesions (Mackinnon, 1998; Wolfort & Dellon, 2001).
Jane's Genus
Jane is a 45-year-old Caucasian female who came to see this author for a scheduled orthopaedic clinic appointment. She was complaining of pain in her right forefoot that she states began about 2 weeks after beginning a nonprescribed walking exercise program. Jane says she has been walking about 3 miles every evening after work on an asphalt track at the local high school, in flat, slip-on, nonsupportive shoes that she has had in her closet for about 7 years.
She described her pain as sharp, stabbing and throbbing at times; the level of pain is 6/10. Walking aggravated the pain. She had tried taking aspirin for the pain and had applied warm compresses to her foot after walking, without relief of her foot pain.
Jane cannot remember injuring her foot or ankle. Her past medical history was negative. Jane's ethnic heritage was German/Welch. tier family history was positive for a hammer-toe (mother), as well as her daughter, son, mother, brothers, niece, and nephew all having this "funny looking" long second toe.
Her review of systems was also negative. Subsequently, Jane was treated for Morton's neuroma by using a conservative, tiered approach. She stated at her last appointment that she had visited her family in St. Louis for a family reunion and had taken a picture of the feet of her family members.
This family vignette provides information that has been mentioned in the literature - that foot problems are hereditary (www.footcare4u.com/ ailments/neuroma.html).
If time and territory had permitted, it would have been interesting to perform a research study to ascertain more information regarding Jane's Genus and the possibility of Morton's syndrome in this family.
Jane's foot is shown in Figure S. Look at the praxis of Morton's toe in this family foot photograph (Figure 6). Very interesting! What questions would you ask the family members? History, examination, and imaging studies of the feet may have provided data as to the phenomenon of Morton's syndrome mentioned at the beginning of this article (short first MTP, hypermobile first MTP segment, and posterior displaced sesamoids).
Vilodot (1975) described foot types in a classic piece of literature (see Figure 7). The three types are:
1. Greek/Morton's type - this foot has a long second toe that is longer than all the other toes. The width tends to be narrow to medium.
2. Egyptian foot - this foot type has a long great toe while the other toes taper. The width is narrow to medium.
3. Giselle/peasant foot - This foot has three or more toes that are the same length and tend to be short. The width tends to be medium to wide.
Magee (1992), a physical therapist, also described various types of feet. He lists percentages of the population with varying foot types: Greek/ Morton's foot 22%, Egyptian foot 69%, and squared (Giselle/Peasant) foot 9%.
No matter what foot type we may have, Socrates said it the best: "O toys rodas avaon avaei ta ranta or, To him whose feet hurt, everything hurts." Well-stated, Socrates!
Reference
Basadonna, P.T., Rucco, B., Gasparini, D., & Onorato, A. (1999). Plantar fat pad atrophy after corticosteroid injection for an interdigital neuroma. American Journal of Physical Medicine and Rehabilitation, 78(3), 283-285.
Bencardino, J., Rosenberg, Z.S., Beltran, J., Liu, X., & Morty-Defaut, E. (2000). Morton's neuroma: Is it always symptomatic? American Journal of Roentgenology 175(3), 649-653.
Bennett, G.L., Graham, C.E., & Mauldin, D.M. (1995). Morton's interdigital neuroma: A comprehensive treatment pro
tocol. Foot and Ankle International 16(2), 760-763.
Biasca, N., Zanetti, M., & Zollinger, H. (1999). Outcomes after partial neurectomy of Morton's neuroma related to preoperative case history, clinical findings, and findings on magnetic resonance imaging scan. Foot and Ankle International, 20(9), 568-575.
Mackinnon, S. (1998). Neuromas. Foot and Ankle Clinics, 3(37), 385-404.
Magee, D.T. (1992). Orthopaedic physical assessment Philadelphia: Saunders. Mollica, M.B. (1997). Morton's neuroma:
Getting patients back on track. Physician and Sports Medicine, 25(5), 1-8.
Rosenberg, G.A., & Sferra, Jj. (1998). Morton's neuroma: Primary, recurrent, and their treatment. Foot and Ankle Clinics, 3(3), 473-484.
Senegar, M. (1991). Iatrogenic saphenous neuralgia: Successful therapy with neuroma resection. Neurosurgery, 28, 295.
Shapiro, PP., & Shapio, S.L. (1995). Sonographic evaluation of interdigital neuromas. Foot and Ankle International, 16, 604-606.
Vilodot. (1975). Patologia del antepie. Barcelona, Ediciones Toray, S.A.
Weinmann, J.P., & Sicher, H. (1955). Bone and Bones. Fundamentals of bone biology (2nd ed., p. 174). St. Louis: Mosby.
Willick, S.E., & Herring, S.A. (1998). Common lower extremity neuropathies in athletes. Journal of Musculoskeletal Medicine, 15(5), 48-58.
Wolfort, S.E, & Dellon. A.L. (2001). Treatment of recurrent neuroma of the interdigital nerve by implantation of the proximal nerve into muscle in the arch of the foot. Journal of Foot and Ankle Surgery, 40(6), 404-410.
Wu, K.K. (1996). Morton's interdigital neuroma: A clinical review of its etiology, treatment, and results. Journal Foot and Ankle Surgery, 35(2), 112-119.
Younger, A.S., & Claridge, RT. (1998). The role of diagnostic block in the management of Morton's neuroma. Canadian Journal of Surgery, 41(2), 127-130.
Zonetti, M., Strehle, J.K., Kundert, H.P, Zollinger, H., & Hodler, J. (1999). Morton's neuroma: Effect of MR imaging findings on diagnostic thinking and therapeutic decisions. Radiology, 213(2), 583-588.
Sharon G. Childs MS, CRNP-CS, CEN, ONC, is an Adult Nurse Practitioner and an Orthopaedic Trauma Critical Care Clinical Specialist at Concentra Medical Center in Baltimore, Maryland.
Copyright Anthony J. Jannetti, Inc. Nov/Dec 2002