Mitchell and Wilson Metatarsal Osteotomies for the Treatment of Hallux Valgus: Comparison of Outcomes Two Decades after the Surgery

Abstract

Background:

At short-term followup, the Mitchell osteotomy appears to provide more symptomatic improvement than the Wilson osteotomy. We compared the outcomes of the two procedures two decades after the surgeries.

Methods:

In a two-center retrospective study, 30 patients (35 feet) who had Mitchell osteotomies and 28 patients (35 feet) who had Wilson osteotomies were evaluated 20 to 22 years after surgery for correction of the hallux valgus angle (HVA) and intermetatarsal (IMA) angle, changes in the shortening of the first metatarsal and improvement in the overall status (a composite radiographic and clinical outcome according to Bonney and McNab).

Results:

With adjustment for the preoperative values and surgical center (analysis of covariance), the HVA (degrees) had a higher correction in the Mitchell group (p = 0.075), while IMA was comparably corrected by the two methods. Shortening of the first metatarsal was greater in the Wilson group (Mitchell- Wilson = −1.93, 95% CI −2.69 to −1.17,p < 0.001). Before the surgery, overall status was graded “poor” or “good” in all feet (28/7 Mitchell, 29/6 Wilson). After the surgery, the status was graded “excellent,” or “good” (29/6) in the Mitchell group, and “excellent,” “good” or “poor” (25/7/3) in the Wilson group. The status was improved by at least one grade-level in all 35 feet in the Mitchell group and in 31 of 35 feet in the Wilson group. With stratification for the preoperative status, the proportion of “improvements” was higher in the Mitchell group (Mitchell-Wilson = 11.1%, 95% CI 0.7 to 21.5%, p = 0.036). In an alternative analysis (logistic regression), with adjustment for the preoperative status, center, and IMA values, the Mitchell method also appeared superior in this outcome (likelihood ratio test p = 0.021).

Conclusions:

As assessed 20 to 22 years after the surgery, the Mitchell osteotomy resulted in less shortening of the first metatarsal in a somewhat greater proportion of feet with an improved overall status than the Wilson method.

Keywords

Hallux Valgus Mitchell Osteotomy Wilson Osteotomy

INTRODUCTION

More than 130 different operative methods have been described for correction of hallux valgus, most of which include a first metatarsal osteotomy (in various ways and at various sites).^6,7 However, the choice of suitable operation still remains controversial.⁴

The osteotomy first described by Mitchell et al.¹² in 1958, is a subcapital first metatarsal osteotomy with lateral displacement of the capital fragment. The method has been reported to yield good results at long-term followup.¹³ The Wilson osteotomy is a sagittal oblique osteotomy of the distal shaft.^5,10,14 Based on an assessment after an average followup period of around 3 years, Karataglis et al.⁸ suggested that the Mitchell osteotomy produced greater symptomatic improvements than the Wilson osteotomy. We compared radiographic and clinical outcomes of the Mitchell and the Wilson osteotomies for treatment of the hallux valgus 2 decades after the surgery.

MATERIALS AND METHODS

Design and patients

The study was approved by the local ethics committee (Zagreb University School of Medicine). The retrospective study was undertaken in 2003, at the Department of Orthopaedic Surgery, Zagreb University School of Medicine, and the Department of Orthopaedic Surgery at Holy Ghost General Hospital, Zagreb, Croatia. The two institutions share a common strategy in treatment of hallux valgus, which has largely been established by the first author (MM). Through the hospital database searches, we identified 77 patients who met predefined criteria: had either a Mitchell or Wilson osteotomy for the treatment of hallux valgus, unilaterally or bilaterally; the indication for the surgery was based on a hallux valgus angle of more than 20 degrees, an intermetatarsal angle of more than 10 degrees, pain from shoe pressure over the medial side of the metatarsophalangeal joint and aesthetic reasons; at least 20 years had elapsed since the surgery; hallux valgus had occurred before 55 years of age and the patient was at least 16 years old; at each facility, they were operated on by the same surgeon, and the preoperative radiographs of the affected foot (feet) were available. All 77 patients were asked to return for followup evaluation. A total of 58 patients (55 women, three men; 70 feet) responded and gave informed consent for radiographic and clinical assessment and the use of data for investigational purposes. Of the 19 patients (24 feet, 10 Mitchell and 14 Wilson osteotomies) who did not respond, three had died since the surgery and the reasons for nonresponding remained unknown for the remaining 16. We had no insight into the outcomes for these patients. To obtain followup of 20 years or more, only those feet operated on between 1981 and 1983 were included. In late 1980, we started a routine use of the Wilson method (introduced at both institutions by MM). Forty-eight patients (56 feet) were treated at the larger of the two centers (Department of Orthopaedic Surgery, Zagreb Medical School), 30 by the Mitchell and 26 by the Wilson method. The remaining 10 patients (14 feet) were treated at the second center, five by the Mitchell and nine by a Wilson osteotomy. There was no planned assignment of the patients to the centers or operative methods. Generally, a Wilson osteotomy was preferred for feet with higher intermetatarsal angle (IMA), but there was no specifically defined cut-off value, and the choice of the method was at surgeon's discretion. All of the 58 patients had a positive family history of hallux valgus. The two groups were comparable in terms of age at the time of surgery and duration of followup (Table 1).

Table 1:

General characteristics of the analyzed patients and feet and values of the radiographic outcomes before and 20 to 22 years after the surgery: hallux valgus angle (HVA), intermetatarsal angle (IMA), and shortening of the 1^st metatarsal.

	Type of surgery

	Mitchell	Wilson
Number of patients (Female/Male)	30 (29/1)	28 (26/2)
Number of feet	35	35
Age at surgery (years)	36 (16–45)	36 (16–45)
Follow-up (years)	21.5 (20–22)	21.5 (20–22)
HVA (degrees)
Before surgery	35.4 ± 8.7	33.9 ± 5.5
After surgery	16.9 ± 6.0	17.5 ± 4.6
Difference (after-before)	−18.5 (−20.9 to −16.0)	−16.4 (−18.3 to −14.5)
IMA (degrees)
Before surgery	15.1 ± 3.1	17.9 ± 5.6
After surgery	9.3 ± 2.3	7.8 ± 4.8
Difference (after-before)	−5.8 (−6.9 to −4.7)	−10.1 (−11.1 to −9.0)
Shortening of the first metatarsal
Before surgery	2.06 ± 1.63	1.89 ± 1.43
After surgery	5.63 ± 1.96	7.40 ± 1.99
Difference (after-before)	3.57 (3.09 to 4.05)	5.51 (4.90 to 6.13)

Data are counts, medians (ranges) or mean ± SD values. Paired mean differences (after the surgery-before the surgery) are given with 95% CI.

Operative Procedures

All operations were done with the use of spinal anesthesia and a pneumatic high-thigh tourniquet. A short dorsomedial skin incision was made over the first metatarsophalangeal joint and exostosectomy was routinely done. The capsule was incised medially in a U fashion.

Our modified technique for the Mitchell osteotomy used double incomplete step-off cuts instead of transverse cuts, reaching 50% to 75% across the metatarsal neck. This improved the degree of correction and maintained the length of the first metatarsal (Figure. 1). Plantar displacement of the metatarsal head was about 1 mm or equal to the cortical thickness. No lateral soft-tissue dissection was done. The distal fragment was fixed with a suture inserted from the dorsal and proximal fragment towards the plantar and distal direction. The medial capsule was tightened to maintain straight alignment of the hallux with the first metatarsal bone. The overhanging ledge of the proximal fragment was removed.

The Wilson osteotomy was a sagittal oblique osteotomy angled 45 degrees from distal and medial to proximal and lateral. The distal fragment was then displaced laterally. Permanent fixation was obtained with 2.7 ASIF cortical screws inserted from medial on the proximal fragment to lateral on the distal fragment (Figure 2). The overhanging ledge of the proximal fragment was removed. The medial capsule was tightened to maintain straight alignment of the hallux with the first metatarsal.

Postoperative Care

Postoperatively, the patients wore special plaster boots with heels adjusted for walking, and gradually increased weightbearing. Boots were removed 5 to 7 weeks after the Mitchell and 6 to 8 weeks after the Wilson osteotomy. Patients were advised to wear comfortable shoes for 2 to 3 months after the Mitchell or 3 to 4 months after the Wilson osteotomy, then they were allowed to use normal walking shoes. The slightly longer time with plaster boots and comfortable shoes after the Wilson osteotomy was a precautionary measure since, at the time, we had relatively less experience with the outcomes of this method. The policy of both institutions was to remove cortical screws to prevent the possibility of complications related to use of electrical currents in physical therapy procedures later in life. This was done 1 to 2 years after the surgery.

Assessment and Outcomes

All feet were assessed in a standardized manner. Before the surgery, standard weightbearing (standing) anteroposterior and lateral radiographs were taken, and the overall status was graded based on criteria by Bonney and McNab, modified by Helal.⁶ (Table 2). The same evaluations were done in November, 2003, when the patients operated on at one site were assessed at the other site. The radiographs were scanned and analyzed using custom-designed computer software to determine the preoperative and postoperative values of the hallux valgus angle (HVA), IMA and shortening of the first metatarsal bone. The overall status was graded without knowledge about the preoperative grade. Correction (reduction) of HVA, correction (reduction) of IMA, and change in the shortening of the first metatarsal were determined as differences between the postoperative and preoperative values.

Statistical Analysis

Each foot was considered as an independent case. Summary statistics are reported for patients’ demographics and preoperative and postoperative radiographic findings and overall status. Reductions in HVA and IMA and changes in shortening of the first metatarsal were each analyzed in a separate analysis of covariance with the type of surgery, center, and preoperative values of the outcome variable as independent variables. Least-square means from this analysis were used to determine mean differences between the two operative methods, together with the 95% confidence interval (CI). Proportions of feet with improved overall status in the two treatment groups were compared using a chi-square test with stratification by the preoperative status (random-effects pooled Mitchell-Wilson difference with 95% CI), and a binary logistic regression with independent variables of surgery, center, preoperative status, and preoperative IMA (since the Wilson method was preferred for feet with higher IMA values). NCSS 2004 software (NCSS, Kaysville, Utah, USA) was used.

Table 2:

Classification of the overall status of hallux valgus according to Bonney and McNab with modification by Helal.⁶

Overall status	HVA (degrees)	IMA (degrees)	Range of movement of first MTP joint	Subjective symptoms	Function
Excellent	0–20	0–12	Full	Without pain	Complete
Good	0–30	0–16	Partial reduction	Temporary pain	Satisfactory
Poor	>30	>16	Complete reduction	Permanent pain	Limited

HVA = hallux valgus angle; IMA = intermetatarsal angle, MTP = metatarsophalangeal.

RESULTS

Preoperative and postoperative values of the radiographic measurements are summarized in Table 1. With adjustment for center and the preoperative value of the outcome variable, the reduction of HVA was somewhat greater in the Mitchell group, with borderline significance (p = 0.075), while the reduction of IMA was comparable for the two procedures (Table 3). Shortening of the first metatarsal after the surgery was significantly less pronounced with the Mitchell osteotomy than with the Wilson osteotomy (p < 0.001) (Table 3).

Before the surgery, the overall status of the analyzed feet was graded (criteria in Table 2) mainly as “poor” (28 feet in the Mitchell and 29 in the Wilson group); a few were graded as “good” (seven feet in the Mitchell and six in the Wilson group) (Table 4). At the evaluation 20 to 22 years after the surgery, the overall status was graded mainly as “excellent” (29 feet in the Mitchell group and 25 in the Wilson group) or “good” (six feet in the Mitchell group and seven in the Wilson group), but three feet in the Wilson group were graded as “poor” (Table 4). After the surgery, status was improved by at least one level in all 35 feet in the Mitchell group and in 31 of 35 feet in the Wilson group (Table 4). Analysis of the outcome “status improved yes/no” stratified by the preoperative status (poor or good) indicated a significantly greater proportion of “improvements” in the Mitchell group (pooled random-effects Mitchell-Wilson difference 11.1%, 95% CI, 0.7 to 21.5%, chi-square 4.394, p = 0.036). A binary logistic regression analysis on this outcome with adjustment for the preoperative status, center and IMA (because the Wilson method was preferred in patients with higher IMA values), also indicated a significant difference between the treatments. (Chi-square value from the likelihood ratio test associated with factor “surgery” was 5.365, p = 0.021.)

There were no complications in the Mitchell group. In the Wilson group, superficial wound infections occurred in two feet that were successfully treated with antibiotics; however, contracture of the first metatarsophalangeal joint developed in both feet. Recurrence of hallux valgus occurred in one foot in the Wilson group.

DISCUSSION

A number of techniques (with a variety of modifications) are available for operative treatment of hallux valgus in adults.^2,3,9,15 In 2004, a systematic review of the published literature concluded that there was no compelling evidence of advantages of any of these methods over any other particular type of surgery.⁴ The Mitchell osteotomy has been reported to give good results at both short-term and long-term followup.^2,12,13 Some authors believe that the Wilson osteotomy tends to cause metatarsalgia and calluses because of a shift of the forefoot load distribution towards the lesser metatarsals, which is attributed to shortening of the first metatarsal and dorsal displacement of the distal fragment.^6,10,13,14 Merkel et al.¹³ has suggested that a shortening of more than 10 mm after the first metatarsal osteotomy resulted in a higher degree of patient dissatisfaction and an increased frequency of metatarsalgia.¹³ On the other hand, a high level of patient satisfaction has been reported at 10-year followup after the Wilson osteotomy,⁵ and this method has been reported to yield better short-term results than the chevron osteotomy.¹¹ Kalataglis et al.⁸ suggested that the Mitchell method improved symptoms more than the Wilson method at an average followup of 36 months. Our retrospective review compared the results of these two techniques at much longer followup (20 years) than any of the earlier studies.

Table 3:

Summarized results of analysis of covariance on the outcomes “correction (reduction) of the hallux valgus angle (HVA),” “correction (reduction) of the intermetatarsal angle (IMA),” and “change in the shortening of the first metatarsal”

	Correction of HVA (degrees)		Correction of IMA (degrees)		Shortening of the first metatarsal (mm)

Covariates	F-ratio	P value	F-ratio	P value	F-ratio	P value
Pre-surgical value	62.18	<0.001	120.74	<0.001	3.18	0.079
Center	1.43	0.236	0.00	0.984	0.21	0.646
Surgery	3.27	0.075	0.00	0.952	25.17	<0.001
LS-Mean Mitchell	18.61		6.83		3.51
LS-Mean Wilson	16.66		6.79		5.44
ΔM-W (95%CI)^*	1.94 (−0.16 to 4.05)		0.04 (−1.15 to 1.22)		−1.93 (−2.69 to −1.17)

Mean difference Mitchell-Wilson with 95% Tukey-Kramer's simultaneous confidence interval. These outcomes were determined as differences between the values after the surgery (i.e., at the assessment visit 20 to 22 years after the surgery) and the values before the surgery. A separate ANCOVA was performed on each outcome. The model always contained the following covariates: type of surgery, center, and preoperative values of the outcome variable.

Table 4:

Overall status (based on criteria listed in Table 1) before the surgery and 20 to 22 years after the surgery for the feet treated by the Mitchell and the Wilson methods (“transition” of the status)

Overall status - Mitchell method					Overall status - Wilson method

Before surgery	n		After surgery	n	Before surgery	n		After surgery	n
Poor	28	→	Excellent	22	Poor	29	→	Excellent	20
		→	Good	6			→	Good	6
		→	Poor	0			→	Poor	3
Good	7	→	Excellent	7	Good	6	→	Excellent	5
		→	Good	0			→	Good	1
		→	Poor	0			→	Poor	0
Total	35			35	Total	35			35

The main drawbacks of this comparison are related to its retrospective design, the lack of randomization, and the unavailability for evaluation of some of the patients meeting the predefined inclusion criteria. Therefore, a certain level of selection/attrition bias could not be ruled out. Also, the scoring system for the overall status⁶ is less precise and objective than the systems now available; however, in the early 1980s, when the surgeries were done, this was a recognized and accepted system. We used it for the post-operative evaluation to allow a postoperative-to-preoperative comparison. Despite these limitations, we believe that our results and conclusions are valid. The request for patients to return for evaluation clearly explained its purpose and offered an opportunity of an “easy access” to a detailed examination. We had no influence on whether the patients would respond to it or not. It is possible that the outcomes in the nonresponding patients were either better or poorer than in the analyzed sample, but we see no obvious reason to believe that either better or poorer outcomes would be confined to either of the procedures, which were comparably represented among the “nonevaluated” feet (10 Mitchell, 14 Wilson). The fact that at each center all feet were operated on by the same surgeon contributed to “uniformity” of the operative technique and reasoning in the choice of the method, and “center” was included in all analyses. Finally, both the preoperative and postoperative evaluations were conducted in a standardized manner at both sites, the radiographic outcomes were straightforward and objective, and the assessment of the overall post-operative status was unbiased by the knowledge about the preoperative status (blinding to the method was not possible).

Our data suggest that both the Mitchell and the Wilson osteotomies produce good long-term radiographic and clinical results. The shortening of the first metatarsal, which has been suggested to be correlated with the occurrence of metatarsalgia,¹³ was clearly less pronounced in the Mitchell group, and the combined radiographic-clinical outcomes also appeared to be better in this group. In this respect, the results are in agreement with the report on better short-term outcomes with the Mitchell method.⁸

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