Abstract
Purpose. The objective of this retrospective study was to evaluate the long-term follow-up results of neurectomy clinical outcomes and complications in the treatment of Morton’s neuroma. Materials and methods. A total of 19 patients (19 different feet) were treated for Morton’s neuroma by excision of the interdigital nerve at our institute between May 1997 and May 1999. Thirteen (13 feet) of them were followed up. The 13 patients were female and had an average age of 43 years (range 34-54 years) at the time of the operation. The patients were followed-up for a mean of 10.5 years (range 10.0-12.2 years) and scored using the American Orthopaedic Foot & Ankle Society (AOFAS) forefoot scoring system and Visual Analogue Scale (VAS) score. Subjective satisfaction was evaluated at the final follow-up. Results. Eight patients scored more than 90 on the AOFAS forefoot scoring system. The VAS score was improved in all patients. The mean preoperative VAS score was 8.6 ± 0.8 cm (7-10) and the mean follow-up VAS score was 2.4 ± 1.8cm (0-6), which indicated no significant difference (P > .05). The final follow-up satisfaction results indicated that 4 patients were completely satisfied with the operation, 4 were satisfied with minor reservations, 5 were satisfied with major reservations, and no patient was unsatisfied. Neurectomy to treat Morton’s neuroma had a good satisfaction rate (61%). Eleven of the patients complained of numbness on the plantar aspect of the foot adjacent to the interspace, and 2 of these 11 patients complained of disability induced by severe numbness. There was a complaint of residual pain by 1 patient. There were no skin problems on the operation lesions. Conclusion. The long-term results of neurectomy clinical outcomes in Morton’s neuroma are slightly worse than the short- and mid-term results.
“. . . the cause of Morton’s neuroma remains unclear, and its etiology and treatment remain matters of controversy.”
Morton’s neuroma is one of the most common causes of forefoot pain. Viladot 1 reported that Morton’s neuroma was the cause of metatarsalgia in 33% of patients who had forefoot pain. However, the cause of Morton’s neuroma remains unclear, and its etiology and treatment remain matters of controversy.
Various conservative and operative treatments for Morton’s neuroma have been reported. In particular, there have been numerous reports detailing the results of operative treatment and the risk factors of their outcomes for Morton’s neuroma. However, these results, including clinical results and risk factors, are far from conclusive.2-7 Moreover, most of the reports are on mid-term follow-up results after a surgery, with only a few studies reporting on the clinical outcomes and complications after neurectomy for Morton’s neuroma.
Thus, in this study we evaluated the long-term (>10 years) follow-up results of neurectomy clinical outcomes and complications and compared them with the short- and mid-term results of neurectomy.
Materials and Methods
Between May 1997 and May 1999, 19 patients (19 different feet) were treated surgically for suspected Morton’s neuroma at our institution, the Foot and Ankle Service at Eulji Hospital. Because 6 of these patients could not be contacted, only 13 patients (13 feet) were followed and evaluated retrospectively. The medical notes for the patients were reviewed, including preoperative and postoperative notes, radiographs, and pathology reports and the patients’ personal interviews were followed up at outpatient clinics. This was performed independently by an investigator who was not directly involved in the procedure. All the patients were female, and the average age was 43 years (range 34-54 years) at the time of the operation.
In all patients, a diagnosis of Morton’s neuroma was confirmed by the clinical symptoms found after examination. Mulder’s sign 8 and diagnostic testing had ruled out other possible etiologies of the symptoms.
Ten of the 13 patients were evaluated by ultrasonography. Ultrasonography has been performed for diagnostic evaluation of the interspaces to calculate the diameter of the neuroma. 9 The neuroma appeared as an ovoid mass with a hypoechoic signal and was parallel to the long axis of the metatarsals in the coronal view. 10 We have calculated and recorded the longest diameter of the neuroma. The mean follow-up period was 10.5 years (range 10.0-12.2 years; Table 1).
Summary of Cases
Abbreviations: U/S, ultrasound sonography; HV, hallux valgus; AOFAS, American Orthopaedic Foot & Ankle Society; VAS, Visual Analogue Scale.
Satisfaction: 1 = complete satisfaction, 2 = minor reservation, 3 = major reservation, 4 = dissatisfied.
AOFAS score ranges from 0 to 100.
VAS score: 0 cm (no pain) to 10 cm (severe pain).
For more than 6 months at least, all patients were offered conservative treatments, such as nonsteroidal anti-inflammatory medications, metatarsal pads, shoe modification, and steroid injection. These, however, did not improve the patients’ conditions.
All patients were operated on by one surgeon using the same technique consistently. The operations were performed under ankle nerve block anesthesia and tourniquet control. A 3-cm dorsal longitudinal incision was centered over the involved interspace. And then, the transverse intermetatarsal ligament was identified. After sectioning this structure, the common digital nerve was identified (Figure 1).
A dorsal longitudinal incision is made in the affected interspace and the neuroma is identified.
The digital nerves distal to the bifurcation of the common digital nerve were transected. The dissection was then carried proximally into the interspace, isolating the common digital nerve approximately 3 cm proximal to the bifurcation (Figure 2).
Excised neuroma.
From this group, 3 patients experienced additional sources of pain in the forefoot (hallux valgus) and were treated surgically.
We evaluated the clinical outcomes by using the American Orthopaedic Foot & Ankle Society (AOFAS) scoring system and Visual Analogue Scale (VAS) and questioned patients regarding subjective satisfaction at the final follow-up. The AOFAS scoring system and VAS were applied preoperatively and postoperatively at the final follow-up.
In the AOFAS scoring system, each part of the forefoot is scored in terms of pain (40 points), function (45 points), and alignment (15 points) with a maximum score of 100. The VAS is a 10-cm scale ranging from 0 cm (no pain) to 10 cm (severe pain).
For statistical analysis, a χ 2 test was used to calculate any statistical differences, with statistical significance set at P < .05. The calculations were performed using SPSS (version 18.0.0 for Windows; IBM SPSS, Chicago, IL).
The patients were asked to rate their overall subjective satisfaction after the operation. The satisfaction scale was a slight modification of that reported by Johnson et al. 11 According to this scale, the patients were divided into 4 groups. Group 1 consisted of those who were completely satisfied and reported no pain, no restriction of activity, and no or mild restriction of footwear; group 2 included patients who were satisfied with minor reservations and reported mild pain, no or mild restriction of activity, and mild or moderate restriction of footwear; group 3 comprised those who were satisfied with major reservations and reported moderate pain, mild or moderate restriction of activity, and moderate restriction of footwear; and group 4 consisted of patients who were dissatisfied and reported severe pain, moderate or severe restriction of activity, and moderate or severe restriction of footwear.
According to the published reports,2,3,6,7 postoperative complications include residual pain, numbness in the web space, and scar sensitivity. The sensory disturbance and numbness involving the web spaces located around the neuroma before and after the operation were reported as none, mild, moderate, and severe (Table 1).
We defined severe numbness as the condition in which the sensory changes on the normal side are more than 70% on physical examination, causing disturbance in routine activities, such as walking and running.
Results
There were 13 patients in the study, all of whom were females. The main preoperative symptom was pain in the plantar aspect of the foot, which was increased by walking and relieved by rest. There were no underlying diseases and high activity in the patients.
Eight of the 13 patients scored more than 90 on the AOFAS scoring system, with 4 patients scoring 100 (maximum score). The average preoperative AOFAS forefoot score was 55.6 ± 10.2 (range 42-72), whereas the average postoperative AOFAS forefoot score was 89.1 ± 9.7 (range 72-100; Table 1). Although this indicated an improvement, there was no statistically significant difference (P = .538, χ 2 test).
The VAS score also improved from 8.6 ± 0.8 cm (range 7-10 cm) preoperatively to 2.4 ± 1.8 cm (range 0-6 cm) postoperatively, but no statistically significant difference was observed here either (P = .086, χ 2 test).
Pain on performing specific activities was improved postoperatively. However, 4 of the patients (33.3%) complained of footwear restriction due to footwear-induced pain. Three patients suffered from hallux valgus and were treated by using a concomitant procedure, proximal chevron osteotomy.
At final follow-up, 4 patients (30.7%) were completely satisfied with the procedure, 4 patients (30.7%) were satisfied with minor reservations, 5 patients (38.4%) were satisfied with major reservations, and no patient reported dissatisfaction.
Our study revealed a postoperative satisfaction rate with a good outcome of 61%. We observed that 2 of the 5 patients (cases 4 and 6) who were satisfied with major reservations suffered from a combination of hallux valgus, whereas the remaining 3 did not suffer from the additional ailment.
All 5 patients were recommended for revision surgery or further evaluation, but all of them refused to have the surgery performed. Four of the 5 patients (cases 1, 4, 6, and 12) had a postoperative VAS score of more than 5 cm and complained of footwear restriction.
On sensory physical examination, 9 of 11 patients (81.8%) who did not experience sensory disturbance had new complaints regarding numbness of the plantar aspect of the involved web spaces (Table 1). Three of 11 patients (27.2%) who experienced numbness of the plantar aspect reported a rating of uncomfortable, whereas 2 patients (18.2%) complained of restriction of activity. Finally, 2 patients complained of a residual pain. There were no complications, such as skin problems, or scar sensitivity.
Discussion
The main symptoms of Morton’s neuroma include a burning pain between a pair of metatarsal heads with radiation into the corresponding toes. The pain is aggravated by walking or standing, whereas rest or the removal of shoes brings relief. Clinically, there may be tenderness in the intermetatarsal space. When squeezing pressure is applied to the intermetatarsal space, a painful and palpable clicking sensation is induced (Mulder’s sign).8,12
Pain is the most common complaint of patients with neuroma, and this can be affected by other factors, such as footwear and walking. We evaluated pain by using a VAS scoring system since this has been shown to be a valid measure of pain, and we chose to use the AOFAS forefoot system to assess the overall status of the forefoot.7,13
The results from both assessments reported improvements postoperatively, which correlated with the published findings of other studies. Four of the 5 patients who were satisfied with major reservations scored more than 5 cm in the VAS.
Among the operative treatments for neuroma, neurectomy is the most commonly accepted procedure. Its reported success rate ranges from 57% to 85%2-7 (Table 2). There are many factors that affect the result of the operation, such as prior operations, concomitant forefoot surgery, duration of symptoms, size of the neuroma, and location of the neuroma.6,11,14-17 One group 7 reported that neuroma in the second web space led to poor outcomes. However, none of the factors has been conclusively shown to be a risk factor for neurectomy outcomes.
Reported Results of Neurectomy in Morton’s Neuromas
Our study revealed a postoperative success rate of 61%, which is lower than the average results from published reports. Previous studies could not find a relationship between size of the neuroma and the combined conditions and outcomes. Most neuromas are located in the third intermetatarsal space, between the third and fourth metatarsal heads. 18
The patients often complained about footwear restriction and numbness in the web space, postoperatively.13,16 Other investigators 19 reported that 70% of patients still had some degree of footwear restriction that may have been affected by the outcome of surgery in spite of its providing good pain relief. In addition, numbness in the web space postoperatively was reported to range from 38% to 67%.2,5,6,16 However, in our study, 1 patient (7.6%) complained of footwear restriction due to the presence of residual pain; there would have been no footwear restriction if pain had improved. New numbness in the web space showed a high incidence, and in 9 (81.8%) of 11 patients, previous numbness had become worse. Among 9 patients who had new numbness, 7 reported numbness in the plantar web space and 2 between the digits. Two of 11 patients (18.1%) complained of restriction of activity due to severe numbness and were not completely satisfied with the operation. The numbness did not disappear or improve over a long period of time, specifically for more than 10 years.
This study has a few limitations, including a small sample population consisting only of females and recall bias since it is a long-term retrospective review. We need a bigger sample population to confirm our findings.
Conclusions
The long-term results of neurectomy in the treatment of Morton’s neuroma were slightly worse than the mid- and long-term results in other published reports. Complications, including numbness and residual pain, were present, which likely induced footwear restriction and poor outcomes.
There was a great deal of numbness reported by patients, thus we assumed that continued numbness postoperatively may have affected the results and could be one of several considerations in terms of postoperative results. We conclude that surgeons should be aware of the long-term prognosis of neurectomy in Morton’s neuroma and should explain this to patients when discussing treatment options.