DIAGNOSIS AND TREATMENT OF INTERDIGITAL NEURITIS (MORTON'S NEUROMA)
July 24th, 1996
Steven B. Weinfeld, MD, and Mark S. Myerson, MD
Abstract
Because controversy still exists as to whether this syndrome results from true neuromatous proliferation or from inflammation in the region of the interdigital nerve, we prefer to use to use the term interdigital neuritis instead of Morton's neuroma. We review the etiology, diagnosis, and management of interdigital neuritis, including the controversies of a plantar versus dorsal approach and neurectomy versus incision of the transverse metatarsal ligament with or without neurolysis. We recommend that diagnosis be made through history and clinical examination, that surgery be performed through a dorsal approach with release of the transverse ligament but without neurectomy, and that revision surgery also be performed through a dorsal incision with excision of the nerve 3 cm proximal to the transverse ligament.
Introduction
Our understanding of interdigital nerve compression syndrome as originally described by Morton in 1876 has evolved into a complex entity involving a myriad of structures in the vicinity of the transverse metatarsal ligament. Thomas G. Morton1 originally described this condition in 1876, suggesting that nerve irritation resulted from compression between the metatarsal heads. Despite the fact that clinicians now recognize this concept to be incorrect since no true neuroma formation occurs, the terminology has remained unchanged, and many continue to refer to this condition as "Morton's neuroma". In the current discussion, however, we will use the term interdigital nerve compression syndrome or interdigital neuritis (IDN).
Pathogenesis
Morton1 postulated that interdigital nerve irritation was caused by pinching of the nerve between the metatarsal heads, but this theory was incorrect since the nerve lies plantar to the intermetatarsal ligament and metatarsal heads (Fig. 1). In 1940, Betts2 first recognized that stretching, rather than compression, of the nerve was the cause of neuritis; this finding was confirmed in a pathologic study by Graham and Graham.3 They demonstrated that the interdigital nerve was distinctly larger in diameter just distal to the intermetatarsal ligament, substantiating earlier work indicating that the edge of the intermetatarsal ligament causes compression of the nerve. They also documented an increased number of blood vessels per fascicle, increased diameter of the nerve, increased perineural width, and increased fascicle diameter just distal to the intermetatarsal ligament. The difference in the number of blood vessels distal and proximal to the intermetatarsal ligament led these investigators3 to suggest that venous congestion was initially responsible for enlargement of the nerve and that, therefore, enlargement and disruption of the fascicles are secondary changes due to increased venous pressure.
In 1948, Nissen4 suggested that the pain of IDN was ischemic in origin, which was confirmed by histologic examination that demonstrated degenerative changes in the arterial wall associated with thrombosis. Nissen5 examined nerve specimens and demonstrated a continuous progression of neurovascular changes that occurred with increasing duration of symptoms. Although neuromatous proliferation6 and inflammatory processes7 have been proposed as etiologies of IDN, later studies, such as that by Graham and Graham,3 disproved these theories. In fact, neither nerve proliferation nor any specific inflammatory process occurs and, structurally, the nerves demonstrate well-formed myelin sheaths with no evidence of Schwann cell proliferation. However, proliferation of fibrous connective tissue in the surrounding stroma and within the plantar digital nerve does occur,8 as does arterial sclerosis with disruption of the internal elastic lamina associated with intimal fibrosis and narrowing of the arterial lumina. Degenerative changes of the arterial wall and disruption of the internal elastic lamina lead to narrowing of the digital vessel. This contributes to local ischemia and further tissue atrophy, leading to sensitivity and pain. Based on these findings, Ha'Eri et al.8 suggested that repetitive neurovascular trauma occurs in the web spaces, leading to connective tissue scarring that then produces the enlarging mass incorrectly referred to as a neuroma.
The most common histologic findings associated with IDN are perineural fibrosis, neural degeneration, and thickening and hyalinization of the walls of the endoneurial blood vessels. However, the pathology of a recurrent IDN is completely different: this condition is characterized by pathological features of a typical traumatic neuroma, ie dense fibrous tissue associated with an irregular pattern of nerve tissue.
Anatomical, histological, and radiological investigations of the intermetatarsophalangeal bursae in the second and third interspaces have demonstrated that the bursae are distal to the transverse metatarsal ligament and are close to the neurovascular bundle. Inflammation of these bursae may cause secondary fibrosis leading to classic symptoms of IDN. Bossley and Cairney9 have suggested that bursitis may occur in the web space, causing inflammatory changes in the nerve. They demonstrated that in the web spaces between the second, third, and fourth intermetatarsals, the bursa lies superior to the transverse metatarsal ligament and projects distally to it, but appears closely approximated to the neurovascular bundle. Pathologic specimens demonstrated lymphocytic infiltration with fibrinoid necrosis of the bursal wall. Bossley and Cairney9 also have suggested that inflammatory changes in this bursa may account for the pathologic findings with IDN, since injection of steroid into the bursa under radiographic control alleviated symptoms of IDN in their patients albeit temporarily. Although their results suggest that some of the symptoms of IDN may be secondary to bursitis, this finding has not been corroborated, and the bursal click proposed by Mulder10, thought to be pathognomonic of IDN, is only occasionally present.
During the latter part of the stance phase of gait, increased pressure is present under the lesser metatarsal heads, which is transmitted to the intermetatarsal space, located immediately underneath the deep plantar fascia. The anterior edge of the coalesced portion of the plantar fascia irritates and tethers the interdigital nerve, causing the syndrome of pain ultimately recognized as IDN.2 The high incidence of this condition in the third web space may be due to the anatomic branching of the medial and lateral plantar nerve in this location. With the majority of neuromas occurring in the second and third interspace, repetitive trauma -- particularly that related to footwear, ie tight shoes and high heels -- has been implicated as a major cause of neuritis. In this situation, the more mobile fourth and fifth metatarsals may cause tethering of the digital nerve against the immobile second metatarsal, resulting in inflammation of the nerve.11
Although the distribution of IDN has been reported to occur equally in the second and third interspace,12 most authors have identified a much higher percentage of neuromas in the third interspace.2,6 IDN does not occur in the first or fourth web space; if symptoms suggestive of nerve irritation occur in this location, an alternative source of the pain should be investigated. Symptomatic IDN may occur concurrently in both the second and third web space,13,14 but an attempt should be made to localize the symptoms to one or the other web space, perhaps with diagnostic lidocaine injection, to focus treatment efforts. For the patient with pain in both second and third web spaces, further work-up may be indicated to rule out other causes, such as rheumatoid arthritis. Identifying the symptomatic web space may be difficult at times since symptoms may be vague. In these cases, diagnosis may be facilitated by ultrasound or magnetic resonance imaging.
In 1940, Betts2 suggested that the third digital nerve is the largest digital nerve, formed by branches of both the medial and lateral plantar nerve, and is predisposed to neuroma formation. He also believed that the nerve s dual origins anchor the nerve around the flexor digitorum brevis, resulting in increased tethering of the nerve over the transverse metatarsal ligament with toe dorsiflexion. With contraction of the flexor muscle, the proximal end of the digital nerve is fixed, restricting the ability of the nerve to slide longitudinally, thereby increasing compression of the nerve from the transverse metatarsal ligament.2 This theory has been refuted by Levitsky et al.15 who, in an anatomic study, showed that neuromas can occur in nerves without internervous connection and that a third web space nerve formed by dual innervation is no larger than a nerve originating from a single innervation. They also stated that Betts theories did not explain the substantial incidence of second web space neuromas. The investigation by Levitsky et al.15 documented a relative decrease in space in the metatarsal head-transverse ligament region in the second and third web spaces, supporting a mechanical theory for neuroma formation.
Diagnosis
Most patients with symptoms consistent with IDN are women (average age, 50 years); their chief complaint is pain, often associated with burning or tingling of the involved toes. Occasionally a patient may report only a decrease in sensation. The symptoms are exacerbated by shoe wear, particularly shoes with a tight toe box or those with high heels, which increase the plantar pressure in the forefoot over the metatarsal heads and indirectly lead to further tethering of the nerve as the toes assume a more dorsiflexed or extended position at the metatarsophalangeal joint. Typically, pain is relieved by removing the shoe and massaging the toes or forefoot. Occasionally, the symptoms are atypical and pain may be localized to only one toe, or on the plantar aspect of the forefoot. It is extremely uncommon for diffuse, poorly localized pain associated with paresthesias to be caused by IDN of the forefoot.
Patients with IDN rarely walk with a limp, although occasionally a patient with a painful static forefoot deformity (such as hallux rigidus or hallux valgus) may supinate the forefoot at toe off and cause irritation of the lateral forefoot, leading to IDN. Generally, the configuration of the arch of the foot is normal, and no study has indicated an association of foot shape, either planus or cavus, with IDN.
Pain in the involved interspace can be reproduced by digital manipulation with pressure applied just proximal to the metatarsal heads by squeezing the forefoot between the index finger and thumb (Fig. 2). This pain can be exacerbated by simultaneously squeezing the forefoot with one hand and squeezing the web space with two fingers of the opposite hand (Fig. 3). Palpation of the involved web space usually causes radiation of the pain toward the involved digit or digits; usually both toes are involved. Squeezing the forefoot and the metatarsal heads together may elicit a palpable click in the involved web space due to pressure on the intermetatarsal bursa, and may reproduce the patient's symptoms.
It is important to distinguish the pain of IDN from that of other associated conditions of the forefoot, including synovitis, bursitis, and metatarsalgia. In metatarsalgia, the pain is localized directly under the involved metatarsal and is usually accompanied by callosity. Synovitis is often confused with neuritis and, not infrequently, patients with second metatarsophalangeal joint synovitis are mistakenly diagnosed and treated for neuritis, with excision of a presumed neuroma but no resolution of symptoms.16 The pain of synovitis is located immediately distal to the metatarsal head. Digital manipulation by attempting to subluxate the digit from a plantar-to-dorsal direction may tether the nerve and reproduce some symptoms, but the pain associated with this maneuver is more characteristic of synovitis.17 Patients with a cross-over toe deformity (characterized by dorsomedial deviation of the second toe) may present with symptoms of neuritis in addition to the metatarsophalangeal synovitis. The dorsomedial deviation of the toe probably causes traction on the digital nerve and aggravates tethering of the nerve under the intermetatarsal ligament. Treatment of the toe deformity usually resolves the symptoms of neuritis, and nerve resection should not be required.18,19
It is occasionally difficult to distinguish the pain of bursitis from that of neuritis, since the location of the pain is similar. If the intermetatarsal bursa enlarges, as is found in patients with rheumatoid arthritis, the diagnosis is more clear. However, some patients may present with a thickening or swelling in the web space associated with symptoms of IDN. Swelling is not a normal finding of IDN and, if present, another source of the pain should be investigated since patients not yet diagnosed with rheumatoid arthritis may present for the first time with an enlarged intermetatarsal bursa.16
The diagnosis of IDN is made from the history and findings on physical examination. If the diagnosis is in doubt, 1 cc of lidocaine may be injected into the distal web space beneath the intermetatarsal ligament; resolution of the symptoms provides clinical confirmation.
It is unlikely that radiological studies are required to confirm the diagnosis. There have been some reports of the successful use of ultrasound20 and magnetic resonance imaging21,22 in the diagnosis of IDN, but we believe, positive reports not withstanding, that these studies are rarely necessary. Magnetic resonance imaging should not be routinely used to diagnose IDN because of the expense involved and because the definitive diagnosis can usually be made by physical examination. High resolution ultrasound has been demonstrated to be effective in the diagnosis of IDN and the typical reported sonographic appearance is that of an oval hypoechoic mass orientated parallel to the long axis of the metatarsals. Because ultrasound does not routinely visualize normal digital nerves and because structures less than 5 mm in diameter are difficult to identify,20 the use of ultrasound as a diagnostic tool is probably limited to patients for whom the diagnosis is unclear or the clinical presentation is atypical. Shapiro and Shapiro23 reported that ultrasound was useful in diagnosing neuromas in 98% of 50 patients, but that the successful use of ultrasound was highly operator-dependent. Resch et al24 evaluated the use of ultrasound and magnetic resonance imaging in the diagnosis of Morton's neuroma and reported these modalities to be of limited use. We have found it difficult to differentiate the symptoms of neuritis from those of bursitis and synovitis in patients who have previously undergone forefoot surgery, including resection of an interdigital nerve. Sonographic evaluation has been useful and has confirmed surgical findings in such patients.
Treatment
Nonsurgical Management
Nonsurgical treatment should always be tried first. Although the results of these treatment modalities are unpredictable, approximately 20% of patients will have complete resolution of symptoms.3 The goal of this treatment should be to alleviate pressure on the nerve by decreasing the tension on the intermetatarsal ligament and/or reducing compression of the forefoot. This can be accomplished by increasing the space between the metatarsal heads. Fashionable shoe wear, particularly shoes with high heels and a narrow toe box, should be avoided since they serve to increase, rather than decrease, lateral compression of the metatarsal heads. A firm crepe sole, which can prevent excessive extension of the metatarsophalangeal joints during toe-off, is ideal but, unfortunately, not always tolerated nor accepted by patients. A metatarsal pad placed directly behind the metatarsal heads will relieve the pressure on the nerve and may increase the space between the metatarsal heads during toe off. Custom orthoses have met with mixed success in the treatment of IDN.12 Other recommended treatments include the use of a more rigid arch support.25 Rarely does antiinflammatory medication have any benefit. Although injection of corticosteroid has been reported to have some clinical benefit,26 our experience indicates that the effect is often temporary. Repeated steroid injections have not provided long-term relief and should be avoided because of serious complications such as atrophy of the plantar skin and potential systemic side effects.
Surgical Management
General considerations. Numerous surgical techniques for the treatment of IDN have been reported, including nerve resection from a plantar or dorsal approach or release of the intermetatarsal ligament with or without neurolysis. Each modality has its merits, but also potential drawbacks, since most large series on surgical treatment report a success rate of approximately 80%.12
Proponents of a plantar incision for neurectomy maintain that this is a more direct approach since the nerve is superficial in this location. Although the nerve is not difficult to identify and resect, any complication resulting from the plantar incision can be problematic. Therefore, most clinicians reserve the use of a plantar incision for the treatment of recurrent neuroma formation.
The dorsal approach to neurectomy is technically easier but adequate nerve resection must be performed. It is important to resect the nerve sufficiently proximally to avoid recurrent neuroma formation. A small incision immediately proximal to the web space cleft cannot visualize nor address the entire nerve and its branches. This concept was highlighted by the anatomic study of Amis et al.27 demonstrating the plantarly directed nerve branches from the interdigital nerve. These plantar nerve branches are found immediately proximal to the intermetatarsal ligament corresponding to the usual sites of neurectomy during IDN surgery (Fig. 4). These findings are clinically important for two reasons. First, if a neurectomy is performed 1 to 2 cm proximal to the nerve bifurcation, as has been suggested by Betts2 and others,12 the plantar nerve branches may prevent retraction of the transected nerve stump proximally into the intrinsic muscle and, therefore, off the weight-bearing surface of the foot. Second, because these plantar branches each represent a small nerve bundle, and intraoperative injury to them could give rise to a traumatic neuroma with recurrence of symptoms, it is important to identify and resect these nerve branches -- a procedure that cannot be performed through a limited distal web space incision. We -- and other investigators -- recommend excision of the common digital nerve at least 3 cm proximal to the proximal edge of the transverse metatarsal ligament to reduce the likelihood of tethering or producing a traumatic neuroma.27
Release of the transverse metatarsal ligament. As an alternative to neurectomy, some clinicians have proposed division of the intermetatarsal ligament with or without neurolysis as an effective treatment for IDN.28,29 After resection of any interdigital nerve, neural regeneration and neuroma formation occurs. If these neuromas form on the plantar aspect of the foot, particularly distally in the region of the metatarsal heads, they are symptomatic. Gauthier29 was the first to report on this procedure. He treated 206 patients with 304 nerve lesions by dividing the intermetatarsal ligament and performing an epineural neurolysis; he reported resolution of symptoms in 83% and improvement but persistence of some pain in 15% of the patients. Dellon28 and Diebold14 reported similar results, although they had smaller patient groups. Because these three authors believed that IDN is a nerve entrapment syndrome that should be treated as other nerve entrapments, ie with release of the offending structures, they released the intermetatarsal ligament without neurectomy, but recommended a neurolysis in addition to ligament release. Dellon28 also recommended opening the epineurium in the region of compression. If good perineurial markings were not present and the fascicles were not soft, then an interfascicular dissection was performed and the epineurium was resected. However, neither Dellon28 nor Diebold14 entirely clarified the rationale for performing the neurolysis.
Currently, our surgical approach to IDN is ligament release, not neurectomy, without simultaneous neurolysis. The theoretical advantages of this procedure are that the nerve remains intact, no sensory loss occurs, and there is no potential for recurrent and possibly refractory plantar neuroma formation, which may be more difficult to treat than the original problem. Our preliminary results have been good, although long-term follow-up is not yet available for this group of patients (work in progress). The morbidity of the operation is minimal, and our clinical impression is that patients are able to resume activities more rapidly than after neurectomy. No study has indicated that widening of the forefoot occurs by dividing either one or both second and third web space intermetatarsal ligaments. Strapping the forefoot is therefore not necessary during recovery and rehabilitation. We -- and other investigators12 -- have identified ligamentous tissue that reforms between the metatarsals after reoperation through a dorsal approach for recurrent neuroma. Although this is fibrous scar, it seems to represent some reconstitution of the intermetatarsal ligament. Mann and Reynolds12 believed that the presence of this fibrous scar would argue against simple division of the intermetatarsal ligament as the sole treatment for IDN. Although this theory is anatomically correct, it is not supported by long-term clinical results,29 and recurrent IDN occurs only rarely with this technique.
Neurectomy. Neurectomy remains a simple and popular procedure for the treatment of IDN; it has been performed via a dorsal web-space, a plantar longitudinal, or a transverse incision.13,30,31 If neurectomy is performed, we recommend a dorsal approach for either primary IDN or recurrent neuroma formation, with wide exposure of the dorsal soft tissues through a 3-cm dorsal longitudinal incision. The superficial soft tissues are dissected and the interosseous muscles are separated. Insertion of a retractor or a laminar spreader between the metatarsals is helpful to place tension on the intermetatarsal ligament and more fully visualize the soft-tissue structures (Fig. 5). The intermetatarsal ligament is then divided from distal to proximal using a scissors with the tips pointed dorsally to avoid incision of the nerve that lies immediately beneath it. The nerve is then identified and dissected distally to its bifurcation where it is transected. Traction with slight dorsal elevation on the distal stump of the nerve aids in visualization of the nerve, which is carefully dissected and divided as proximally as possible. When performing the dissection, it is important to identify and release any branches from the main trunk of the nerve into the plantar tissue, which may be the source of a recurrent neuroma. Patients are able to bear weight on the affected extremity immediately after surgery.
Some clinicians advocate a plantar approach for excision of a primary interdigital neuroma. Betts2 initially described successful resection of a digital nerve through a plantar incision without complications. This was reenforced by Nissen in 1948.4 Richardson et al.31 reported a 5% incidence of incisional complications with 172 plantar procedures. Beskin and Baxter13 reported successful resection of recurrent neuromas through a transverse plantar incision. These investigators2,4,13,31 believed that the plantar approach allows resection of the nerve proximally off the weight-bearing surface without resection of the transverse metatarsal ligament and allows access to both digital nerves if two adjacent web spaces are involved. The most commonly reported complications of plantar incisions are localized scar tenderness, wound drainage, and plantar keratosis.31
The plantar incision can be made longitudinally or transversely, depending on the location of symptoms (relevant to one or two web spaces) or on the surgeon's personal preference. The longitudinal plantar incision, which is positioned parallel to the elastic fibers of the plantar skin to decrease tension on the wound, provides nearly unlimited access to the digital nerve. Advocates of the transverse plantar incision cite the excellent exposure and the position of the scar distal to the metatarsal heads, which should decrease the incidence of a painful scar.32
Although the plantar approach facilitates visualization of the nerve and has been shown to have a low complication rate, incisional complications, when they do occur, can be devastating. A scar on the plantar aspect of the foot may occasionally hypertrophy and become symptomatic. It is rare, however, to experience pain from a symptomatic scar on the dorsum of the foot. Patients also may weight-bear immediately after surgery with a dorsal incision as opposed to a period of non-weight-bearing with a plantar approach. Most surgeons are also more comfortable with a dorsal incision.
Complications of neurectomy. The cutaneous innervation of the interdigital skin is variable. However, excision of the interdigital nerve is predictably associated with numbness of the web space and, to some extent, of the plantar aspect of the foot, just proximal to the level of the web space. Although most patients tolerate the numbness in between the toes, loss of sensation occurring more proximally on the weight-bearing surface of the foot can be quite troublesome. Even a patient with a successful neuroma excision may still have some difficulty with shoe wear; it is reported that 75% of patients are still limited as to choice of shoe type, particularly with reference to those with high heels.12
Recurrent Neuroma
Persistent pain may be quite problematic after excision of a neuroma and reported symptoms are similar to, if not worse than, those before neurectomy. To prevent an amputation neuroma when the interdigital nerve is cut, some clinicians have recommended using silicon caps, metal ligation clamps, or topical steroids or implanting the resected nerve stump into an interosseous muscle.28,33 However, an anatomic study by Amis et al.27 seemed to indicate that adequate proximal dissection of the nerve should decrease the incidence of recurrence. This theory is further supported by Johnson et al,34 who demonstrated that amputation neuroma and incomplete resection of the initial neuroma result in persistent pain. Therefore, as we have no experience with the supplemental methods listed above, we prefer to avoid the problem of recurrent neuroma by dividing the nerve as far proximally as possible.
In one series, the cause of recurrent symptoms was identified as adhesion of a traumatic neuroma to the plantar aspect of the metatarsal head.12 However, this finding has not been supported by other studies.27 Although this situation can occur in some patients, in most, the traumatic neuroma is directly in the web space, tethered to the skin through plantar neural branches, as demonstrated by Amis et al.27 In some patients, the traumatic neuroma adheres to the undersurface of the intermetatarsal ligament or lies just distal to it; in others, it lies proximal to the transverse metatarsal ligament and adheres to the skin.
Most plantar nerve branches occur on the distal portion of the digital nerve, adjacent to the intermetatarsal ligament, corresponding to the site at which a neurectomy is commonly performed. If the neurectomy is performed 1 cm proximal to the bifurcation of the nerve, then plantar nerve branches may still be present. Therefore, it is unlikely that pulling the nerve distally out of the wound will enable the cut end to retract proximally off the weight-bearing area of the forefoot since these nerve branches tether the nerve stump distally. Our current recommendation, therefore, is that the nerve should be transected at least 3 cm proximal to the proximal edge of the transverse metatarsal ligament.
Conclusion
Interdigital nerve compression syndrome (IDN) results from a constellation of factors in the area of the transverse metatarsal ligament, including hypertrophy of the intermetatarsal bursa, connective tissue, and/or vascular tissue. We are currently treating IDN as other compressive neuropathies in the extremities are treated, with release of the offending structures via a dorsal approach, not by resection of the digital nerve. Because the long-term results of ligament release alone are not yet available, the standard treatment remains resection of the interdigital nerve. Recurrent neuromas should be treated with neurectomy either through a plantar or dorsal approach, although the latter may be safer since it provides full visualization of the nerve. In any neurectomy, the nerve should be transected at least 3 cm proximal to the intermetatarsal ligament to allow retraction of the nerve stump into the intrinsic muscle, preventing recurrent traumatic neuroma formation.
References
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2. Betts LO: Morton's metatarsalgia: neuritis of the fourth digital nerve. Med J Aust 1940;1:514-515.
3. Graham CE, Graham DM: Morton's neuroma: a microscopic evaluation. Foot Ankle 1984;5:150-153.
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10. Mulder JD: The causative mechanism in Morton's metatarsalgia. J Bone Joint Surg 1951;33B:94-95.
11. Ouzounian TJ, Shereff MJ: In vitro determination of midfoot motion. Foot Ankle 1989;10:140-146.
12. Mann RA, Reynolds JC: Interdigital neuroma--a critical clinical analysis. Foot Ankle 1983;3:238-243.
13. Beskin JL, Baxter DE: Recurrent pain following interdigital neurectomy--a plantar approach. Foot Ankle 1988;9:34-39.
14. Diebold PF, Delagoutte JP: [True neurolysis in the treatment of Morton's neuroma]. Acta Orthop Belg 1989;55:467-471.
15. Levitsky KA, Alman BA, Jevsevar DS, et al: Digital nerves of the foot: anatomic variations and implications regarding the pathogenesis of interdigital neuroma. Foot Ankle 1993;14:208-214.
16. Awerbuch MS, Shephard E, Vernon-Roberts B: Morton's metatarsalgia due to intermetatarsophalangeal bursitis as an early manifestation of rheumatoid arthritis. Clin Orthop 1982;167:214-221.
17. Fortin PT, Myerson MS: Second metatarsophalangeal joint instability. Foot Ankle Int 1995;16:306-313.
18. Myerson MS: Arthroplasty of the second toe. Semin Arthroplasty 1992;3:31-38.
19. Myerson M: Claw toes, crossover toe deformity, and instability of the second metatarsophalangeal joint, in Myerson M (ed): Current Therapy in Foot and Ankle Surgery, St. Louis: Mosby-Year Book Inc, 1993, pp 19-26.
20. Redd RA, Peters VJ, Emery SF, et al: Morton neuroma: sonographic evaluation. Radiology 1989;171:415-417.
21. Terk MR, Kwong PK, Suthar M, et al: Morton neuroma: evaluation with MR imaging performed with contrast enhancement and fat suppression. Radiology 1993;189:239-241.
22. Erickson SJ, Canale PB, Carrera GF, et al: Interdigital (Morton) neuroma: high-resolution MR imaging with a solenoid coil. Radiology 1991;181:833-836.
23. Shapiro PP, Shapiro SL: Sonographic evaluation of interdigital neuromas. Foot Ankle Int 1995;16:604-606.
24. Resch S, Stenstrom A, Jonsson A, et al: The diagnostic efficacy of magnetic resonance imaging and ultrasonography in Morton's neuroma: a radiological-surgical correlation. Foot Ankle Int 1994;15:88-92.
25. Kilmartin TE, Wallace WA: Effect of pronation and supination orthosis on Morton's neuroma and lower extremity function. Foot Ankle Int 1994;15:256-262.
26. Greenfield J, Rea J, Jr., Ilfeld FW: Morton's interdigital neuroma. Indications for treatment by local injections versus surgery. Clin Orthop 1984;185:142-144.
27. Amis JA, Siverhus SW, Liwnicz BH: An anatomic basis for recurrence after Morton's neuroma excision. Foot Ankle 1992;13:153-156.
28. Dellon AL: Treatment of Morton's neuroma as a nerve compression. The role for neurolysis [see comments]. J Am Podiatr Med Assoc 1992;82:399-402.
29. Gauthier G: Thomas Morton's disease: a nerve entrapment syndrome. A new surgical technique. Clin Orthop 1979;142:90-92.
30. Karges DE: Plantar excision of primary interdigital neuromas. Foot Ankle 1988;9:120-124.
31. Richardson EG, Brotzman SB, Graves SC: The plantar incision for procedures involving the forefoot. An evaluation of one hundred and fifty incisions in one hundred and fifteen patients. J Bone Joint Surg 1993;75A:726-731.
32. Viladot A: Morton's neuroma. Int Orthop 1992;16:294-296.
33. Young G, Lindsey J: Etiology of symptomatic recurrent interdigital neuromas. J Am Podiatr Med Assoc 1993;83:255-258.
34. Johnson JE, Johnson KA, Unni KK: Persistent pain after excision of an interdigital neuroma. Results of reoperation. J Bone Joint Surg 1988;70A:651-657.
Figure Legends
Fig. 1. Normal anatomy of the plantar aspect of the foot.
Fig. 2. Clinical photograph showing digital manipulation with pressure applied just proximal to the metatarsal heads by squeezing the forefoot between the index finger and thumb.
Fig. 3. Clinical photograph showing simultaneous compression of the forefoot with one hand and of the web space with two fingers of the opposite hand.
Fig. 4. Lateral view of the plantar branches of the digital nerve. A, previously recommended level of neurectomy (1 cm proximal to ligament). B, current recommended level of neurectomy (3 cm proximal to ligament).
Fig. 5. Resection technique using a lamina spreader.
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