Morton’s Neuroma - Outcome of Surgical Excision

Fahim Anwar

Address for Correspondence:
F Anwar
9 Rowan Court
Cambuslang
Glasgow
G72 7FX
E-mail : fahim10@hotmail.com

Abstract:

Purpose: Morton’s neuroma is the painful condition of the foot caused by thickening and fibrosis of the interdigital nerve. The purpose of this study is to evaluate the outcome and complication of surgical treatment of Morton’s neuroma.

Patients and Methods: A retrospective descriptive study of all patients who underwent surgical excision of Morton’s neuroma between January 2002 to January 2005 in a District General Hospital under on consultant. Data was collected from the clinical notes, clinical letters and a short telephonic interview. The surgical involved excision of the neuroma and ligament release through either planter or dorsal incision. The follow up range was 6 to 36 months with an average of 15.1 months.

Results: There were 10 males and 37 females with an average age of 56.8years. Mean hospital stay was 1.4 days. Third inter-metatarsal space was the most common site of involvement followed by the 2^nd inter-metatarsal space. There were 3 (6.4%) superficial and 2 (4.3%) deep wound infections treated conservatively. 3 (6.4%) patients developed recurrence, 4 (8.5%) had stump neuroma and 7 (14.8%) had either persistent pain or swelling of the foot. Persistent pain on weight bearing was seen in 7 (14.8%) and 5 (10.6%) of patients had some sensory loss over the involved foot.

Conclusion: Surgical excision of the Morton’s neuroma after failure of conservative methods yields good results and patient satisfaction. Persistent pain and swelling after surgical excision are common problems.

J.Orthopaedics 2010;7(3)e8

Keywords:

Morton’s; Neuroma; Surgery; Complications.

Introduction:

Morton’s neuroma is a common cause of burning foot pain and tingling sensation at the base of toes. Its prevalence varies with different populations and found in 10% of feet worldwide and is more common in females with female-to-male ratio of 5:1¹. It usually occurs in middle-aged individuals and approximately 30% of asymptomatic middle-aged persons have the radiologic / pathologic findings of Morton’s neuroma. The exact aetiology of the condition is not clearly understood. It is caused by perinural fibrosis of a digital nerve leading to an abnormal growth². It can occur between any toes with either foot, but most commonly occurs between the third and fourth toes³. The condition is uncommon in first and fourth web space and an alternative diagnosis should be considered with this presentation⁴. Morton’s neuroma if not treated can become a disabling condition. It can lead to foot, knee, hip and back problems by affecting the normal gait pattern.

The pain of Morton’s neuroma is mainly over the metatarsal head on the planter surface of the foot. It radiates to the toes and often associated with numbness distal to the metatarsal head. Clinical examination will demonstrate considerable tenderness over the involved web space. Mulder⁵ in 1951 described a clinical test to diagnose Morton’s neuroma. The test is performed with thumb and index finger over the planter and dorsal surface of the foot at the level of metatarsophalangeal joint. The forefoot is squeezed gently with the other hand. A painful click is produced when the neuroma subluxes between the metatarsal heads. This sign is called as Mulder’s click or Mulder’s sign.

The diagnosis of Morton’s neuroma is mainly clinical and diagnostic radiological tests are rarely necessary. Ultrasound and magnetic resonance imaging have been recently used in cases where clinical diagnosis is doubtful. Ultrasound has been demonstrated to be effective tool in diagnosis of Morton’s neuroma⁶. However the use of ultrasound is operator dependent. Magnetic resonance imaging is more sensitive in confirming the diagnosis⁷ but its use is limited because of cost and availability.

Treatment of Morton’s neuroma is not always easy. Simple measures like; alteration of footwear, using wide toed shoes, avoid wearing high heels and the use of arch supports may help relieve pressure over the nerve and reduce the inflammation. Ultrasound guided local anaesthetics and steroid can help relieve the symptoms in majority of cases and delay the need for surgery⁸. There are varieties of minor surgical procedures described in literature to treat Morton’s neuroma in the event of failure of conservative treatment. Although minor the surgical treatment is not without complications. Wound infection, stump neuroma and persistent pain and swelling are the main surgical complications.

Materials and Methods:

This is a retrospective study of all patients who underwent surgical excision of Morton’s neuroma between January 2002 and January 2005. The data was collected from the clinical case notes, clinical letters and a telephonic interview. A total of 47 patients with clinical signs of Morton’s neuroma were identified who underwent surgical treatment. The diagnosis was made on clinical signs and symptoms. Clinical investigations such as ultrasound and MRI were performed only when the diagnosis was in doubt or when the other conditions of the forefoot were suspected. Conservative therapy was attempted for at least three months before proceeding with surgery. Non-steroidal anti-inflammatory medications and shoe wear modification were commenced initially. Patients whose symptoms did not settle with simple measures were offered metatarsal padding, orthotics or local steroid injections. Surgery was considered in patients where conservative measures fail to resolve the symptoms.

Surgery was performed as an in-patient. Both planter and dorsal approach were used for surgery and the procedure involved excision of neuroma and ligament release. The inclusion criteria were all patients undergoing either primary or revision surgical removal of Morton’s neuroma. Patients with a follow up of less then three months were excluded from the study. Post-operative complications like superficial and deep wound infections, recurrence, stump neuroma, persistent pain on weight bearing and prolonged swelling were noted. Two-tailed T Test was used to the show the difference between pre-operative and pot-operative Visual Analogue Scale (VAS) scores.

Results :

During January 2002 and January 2005, 47 patients underwent surgical treatment for Morton’s neuroma. There were 10 (21.3%) males and 37 (78.7%) females with a male to female ratio of 1: 3.7. The age range was 32 to 79 years with average age of 56.8 years. Right foot was involved in 29 (61.7%) patients and left foot in 18 (38.3%) patients. Hospital stay varied from 1 to 5 days with an average of 1.4 days (Table 1). Only 6 patients had revision surgery for their Morton’s neuroma and remaining 41 patients had primary excision of the lesion. All patients had a symptom of pain on weight bearing and a VAS score in the range of 5 to 10. Average VAS score before surgery was 7.9. Only 10 (21.3%) patients had resting pain.

Table 1: Demographic characteristics of patients

Table 2: Complications following Surgery for Morton’s Neuroma

Mulder’s sign was positive in 36 (76.6%) patients and negative in 11 (23.4%) patients. The surgery was carried out through planter incision in 26 (55.3%) patients and through dorsal approach in 21 (44.7%) patients. The position of the neuroma was in the third web space in 33 (70.2%) patients whereas 14 (29.8%) patients had it in the second web space. The diagnosis of Morton’s neuroma was confirmed post-operatively by pathological examination in 44 patients. Only three patients did not have their pathological diagnosis available.

Post-operative deep infection was encountered only in 3 (6.4%) patients whereas 2 (4.3%) patients had superficial wound infections and cellulitis. These infections were treated successfully with oral/intravenous antibiotics. 4 (8.5%) patients developed stump neuroma, whereas 7 (14.8%) had persistent postoperative swelling of the foot. Recurrence of the neuroma stump occurred in 3 (6.4%) patients and all of them had primary resection of the neuroma (Table 2).

Post-operatively VAS score reduced to zero in 34 (72.3%), 1 in 4 (8.5%) patients and to 2 in 2 (4.3%) patients (Figure 1).  However the VAS score remained high at 6 in 2 (4.3%) patients and 7 in 5 (10.6%) patients (all had planter approach for excision of the neuroma). The two-tailed P value was less than 0.0001, which showed a statistically significant difference between pain VAS score before and after the operation. Post-operative numbness of the foot in the distribution of the involved digital nerve was encountered in 5 (10.6%) patients with difficulty in wearing shoes. 53.2% of the patients reported excellent outcome, 14.9% reported very good, 12.8% good and 19.1% of patients reported poor outcome following surgical removal of the neuroma (Figure 2).

Figure 1: Pre and Post-operative VAS scores

Figure 2: Surgical outcome of Morton’s neuroma

Discussion :

Durlacher⁹ first reported Morton’s neuroma in the literature in 1845. However the disease itself was not popular until described by Sir Thomas Morton¹⁰ in 1876 as painful condition of the foot. The planter nerve within the foot lies between the deep transverse metatarsal ligaments and the planter skin in close proximity of the lumbrical muscle and the flexor tendon. The nerve divides into the planter digital nerves as it passes underneath the ligament. The planter digital nerves supply sensations to the sides of the adjacent toes in the inter-digital space. It is the entrapment and irritation of the planter digital nerve underneath the deep transverse metatarsal ligaments that give rise to the symptoms when they pass into the toes. The space between third and the fourth metatarsal³ is the most frequent location involved, however it can occur in any metatarsal space.

There is insufficient evidence about the effectiveness of surgical and non-surgical interventions for Morton's neuroma¹¹. Conservative methods can be tried before surgery¹² but they can lead to secondary complications and make subsequent surgical exposure difficult¹³. Surgery is the essential treatment of Morton’s neuroma and surgical removal of the neuroma is associated with the best outcome³. Either the planter or dorsal approach can be used to carry out the procedure. The planter approach is much simpler and does not involve opening through the transverse ligament and also provide adequate approach to deal with other related pathologies in and around the area^14,15. Karges¹⁶ also suggested that the planter approach has the ability to resect the nerve more proximally as compared to the dorsal approach resulting in higher success rate.

The dorsal approach however is technically difficult but associated with less local complications like wound dehiscence, haematoma and infection¹⁷. Our study also shows that there is significant reduction in persistent pain after the surgical excision of Morton’s neuroma. The persistent pain in 7 patients after removal of the neuroma was associated with planter approach. The reason for the persistent pain on weight bearing may be associated with thickened, nodular surgical scar and post-operative scarring in the fat cushions of the foot. Nashi et al in 1997¹⁸ compared the dorsal and planter surgical approach for surgical removal of Morton’s neuroma and showed that weight bearing and return to wok was faster in dorsal group as compared to planter group. Simple decompression of the nerve by dividing the transverse metatarsal ligaments has reported good results¹⁹. Hence this has been advocated as a treatment of choice for Morton’s neuroma by many authors^20,21. However long term follow up studies are required to establish the role of such treatment.

Excision of the neuroma in our study was associated with varying degree of numbness in the area of distribution of the digital nerve in about 10% of the cases. This is usually well tolerated in majority of patients. 14.8% of our patients still complained of persistent pain during weight bearing. If the numbness extends over the weight bearing area of the foot, wearing appropriate footwear may be difficult²². Mann and Reynolds¹⁹ reported that 75% of the patients would be limited with regards to the choice of appropriate footwear after surgical excision of Morton’s neuroma. The outcome of Morton’s neuroma surgery in our study was excellent to good in 80.9% and poor in 19.1%.  This is consistent with the literature where an 80% to 90% of patient’s satisfaction has been reported^23,24,25.

Conclusion:

Morton’s neuroma is a disabling condition and a very common cause of foot pain. Careful history, thorough clinical examination and a high index of suspicion allow the clinician to make a definitive diagnosis. Ultrasound examination helps to confirm the clinical diagnosis. Surgical treatment of the Morton’s neuroma should be considered once the conservative methods have failed. Surgical removal of the neuroma is associated with good patient satisfaction and outcome. Persistent or recurrent pain, post-operative infections and swelling along with numbness after excision of the neuroma present a challenging problem for both the surgeon and patient. It is therefore essential to have a detailed pre-operative discussion with the patient about these potential complications¹⁹.

Reference:

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5. Mulder JD. The causative mechanism in Morton’s metatarsalgia. J Bone Joint Surg (Br) 1951; 33-B: 94-95.

6. Redd RA, Peters VJ, Emery SF, Branch HM, Rifkin MD. Morton neuroma: sonographic evaluation. Radiology 1989; 171:415-417.

7. Mendicino SS, Rockett MS. Morton’s neuroma. Update on diagnosis and imaging. Clinical Podiatr Med Surg 1997;14:303-311.

8. Hassouna H, Singh D, Taylor H, Johnson S. Ultrasound guided steroid injection in the treatment of interdigital neuralgia. Acta Orthop Belg 2007; 73(2): 224-229.

9. Durlacher L. Treatise on Corns, Bunions, the Diseases of Nails and the General Management of the Feet. London, England, Simkin, Marshall, 1845, p 52.

10. Morton TG. A peculiar and painful affection of the fourth metatarsophalyngeal articulation. Am J Med Sci 1876; 71:37-45.

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12. Keh RA, Ballew KK, Higgins KR, Odom R, Harkless LB. Long-term follow-up of Morton’s neuroma. J Foot Surg 1992;31:93-95.

13. Greenfield J, Rea Jr J, Ilfeld FW. Morton’s interdigital neuroma: indications for treatment by local injections versus surgery. Clin Orthop 1984;185:142–4.

14. Barbosa GG, Tiradentes MG, Ignacio H, Filho GC, Chueire AG. Surgical treatment of Morton’s neuroma by planter approach: A retrospective study. Acta Ortop Bras 2005; 13(5): 258-260.

15. Wilson S, Kuwada GT. Retrospective study of the use of a plantar transverse incision versus a dorsal incision for excision of neuroma. J Foot Ankle Surg 1995;34(6):537–40.

16. Karges DE. Plantar excision of primary interdigital neuromas. Foot Ankle 1988;9(3):120–4.

17. Wilson S, Kuwada GT. Retrospective study of the use of a plantar transverse incision versus a dorsal incision for excision of neuroma. J Foot Ankle Surg 1995;34(6):537–40.

18. Nashi M, Venkatachalam AK, Muddu BN. Surgery of Morton’s neuroma: dorsal or plantar approach? J R Coll Surg Edinb 1997;42(1):36–7.

19. Mann RA, Reynolds JC. Interdigital neuroma—a critical clinical analysis. Foot Ankle 1983;3(4):238–43.

20. Dillon AL. Treatment of Morton’s neuroma as a nerve com- press ion. The role for neutralizes. J Am Podiatry Med Assoc 1992;82(8):399–402.

21. Okafor B, Shergill G, Angel J. Treatment of Morton’s neuroma by neurolysis. Foot Ankle Int 1997;18(5):284–7.

22. Stamatis ED, Myerson MS. Treatment of recurrence of symptoms after excision of interdigital neuroma. J Bone Joint Surg (Br) 2005; 86-B:48-53.

23. Thomson CE, Gibson JN, Martin D. Interventions in the treatment of Morton’s neuroma. Cochrane Database Syst Rev 2004;(3):CD003118.

24. Coughlin MJ, Pinsonneault T. Operative treatment of interdigital neuroma: a long-term follow-up study. J Bone Joint Surg 2001;83A:1321–8.

25. Keh R, Ballew K, Higgins K, Odom R, Harkless L. Long term follow-up of Morton’s neuroma. J Foot Surg 1992;31(1): 93–5.

This is a peer reviewed paper 

Please cite as: Fahim Anwar: Morton’s Neuroma - Outcome of surgical excision

J.Orthopaedics 2010;7(3)e8

URL: http://www.jortho.org/2010/7/3/e8

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