Clinical results of modified Mitchell s osteotomy for hallux valgus augmented with oblique lesser metatarsal osteotomy

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1 Journal of Orthopaedic Surgery 2005:13(3): Clinical results of modified Mitchell s osteotomy for hallux valgus augmented with oblique lesser metatarsal osteotomy K Yamamoto, A Imakiire, Y Katori, T Masaoka, R Koizumi Department of Orthopedic Surgery, Tokyo Medical University, Tokyo, Japan ABSTRACT Purpose. To evaluate postoperative results of modified Mitchell s osteotomy and its combination with oblique metatarsal osteotomy for the treatment of hallux valgus. Methods. A total of 93 feet of 53 patients (2 men and 51 women) with hallux valgus underwent modified Mitchell s osteotomy and were followed up for at least 5 years. Patients age ranged from 17 to 83 years, and the duration of follow-up ranged from 5 years one month to 18 years 4 months. Modified Mitchell s osteotomy was performed on 53 feet in 31 patients (group A), whereas modified Mitchell s osteotomy augmented with oblique lesser metatarsal osteotomy was performed to the remaining 40 feet in 22 patients (group B). Postoperative results were assessed using a clinical assessment system developed by the Tokyo Medical University based on 5 categories: pain in the first metatarsophalangeal, deformity of the metatarsophalangeal, plantar callosity and/or metatarsalgia of lesser metatarsals, the use of commercially available shoes, and local inflammatory symptoms. Results. Mean total score improved from 3.8 to 7.9 on a 10-point scale. Scores for 2 categories plantar callosity and/or metatarsalgia and the use of commercially available shoes were significantly higher in group B at postoperative 5 years. Before surgery, at postoperative 3 weeks, and at postoperative 5 years, respectively, the mean hallux valgus angles were 34.2 Ο, 12.0 Ο, and 17.1 Ο ; mean M1-M2 angles were 16.7 Ο, 7.4 Ο, and 8.7 Ο ; mean M1-M5 angles were 34.9 Ο, 25.8 Ο, and 26.6 Ο ; and mean sesamoid bone shifts were 8.7 mm, 4.3 mm, and 5.9 mm. Conclusion. Modified Mitchell s osteotomy shortens the length of the first metatarsal bone and thus relieves tension in soft tissues such as the adductor hallucis. Nonetheless, the procedure can induce metatarsophalangeal joint malalignment and metatarsalgia, and plantar callosity may develop or persist after surgery. Combining oblique metatarsal osteotomy of the lesser metatarsal bones is useful in patients with uneven metatarsal bone lengths and metatarsophalangeal joint malalignment. Key words: callosities; hallux valgus; metatarsal bones; metatarsalgia; metatarsophalangeal joint; osteotomy Address correspondence and reprint requests to: Dr Kengo Yamamoto, Department of Orthopedic Surgery, Tokyo Medical University, Nishishijujku, Shinjuku-ku, Tokyo , Japan. kengo-y@tkg.att.ne.jp

2 246 K Yamamoto et al. Journal of Orthopaedic Surgery INTRODUCTION Mitchell s osteotomy is an osteotomy of the distal first metatarsal for the treatment of hallux valgus and was originally described in It provides stable surgical results and is a relatively convenient surgical procedure consisting of a step metatarsal osteotomy of the first metatarsal, exostosis resection, and reefing of the medial articular capsule of the first metatarsophalangeal (MTP) joint. Mitchell s osteotomy has been performed to treat mild-to-moderate hallux valgus, while its combination with proximal metatarsal osteotomy and first MTP joint lateral soft-tissue dissection has been used to treat severe hallux valgus. We have been treating severe hallux valgus using a modified Mitchell s osteotomy combined with first MTP joint lateral soft-tissue dissection as needed. 2,3 Postoperative metatarsalgia and plantar callosity have been associated with surgery for hallux valgus. We obtained favourable results by performing oblique metatarsal osteotomy for the second to fifth metatarsals (the lesser metatarsals). This article discusses the postoperative results of the modified Mitchell s osteotomy, how this procedure can be used to treat hallux valgus, and the usefulness of combining this technique with oblique lesser metatarsal osteotomy. MATERIALS AND METHODS We have performed modified Mitchell s osteotomy to treat hallux valgus since However, some patients have experienced persistent postoperative metatarsalgia and plantar callosity. After 1986, modified Mitchell s osteotomy augmented with oblique lesser metatarsal osteotomy was used when the patient s preoperative pain on the plantar side of the second to fifth metatarsal heads was severe, or when distribution of plantar pressure was considerably higher on the plantar surfaces of the second to fifth metatarsals compared with the plantar surface of the first metatarsal as measured by a foot pressure distribution device (Predas MP4800; Anima, Tokyo, Japan). Between July 1987 and September 2000, 84 feet in 55 patients underwent modified Mitchell s osteotomy. Of these, 53 feet in 31 patients (one man and 30 women) who were followed up for at least 5 years comprised group A. 67 feet in 36 patients underwent modified Mitchell s osteotomy augmented with oblique lesser metatarsal osteotomy. Of these, 40 feet in 22 patients (one man and 21 women) who were followed up for at least 5 years comprised group B. In group B, oblique lesser metatarsal osteotomy was performed on the second and third metatarsal bones in 22 feet, on the second metatarsal bone in 7 feet, and on other metatarsal bones in 11 feet. The age of the patients at the time of surgery ranged from 19 to 68 years (mean, 49.6 years; standard deviation [SD], 14.5 years) in group A, and 17 to 83 years (mean, 47.4 years; SD, 15.9 years) in group B. The duration of follow-up ranged from 5 years 4 months to 18 years 4 months (mean, 8 years 2 months) in group A, and from 5 years 1 month to 12 years 6 months (mean, 7 years 5 months) in group B. Since postoperative follow-up period varied between the 2 groups, outcomes were compared at 5 years after surgery. Postoperative results for hallux valgus have been assessed by different standards developed by Shapiro and Heller, 4 Glynn et al., 5 and, more recently, the American Orthopedic Foot and Ankle Society s Hallux Metatarsophalangeal Interphalangeal Scale. In the present study, the Tokyo Medical University Classification was used 3 an assessment system that takes into account both subjective complaints and objective findings: pain in the first MTP joint, deformity, plantar callosity and/or metatarsalgia of lesser metatarsals, use of commercially available shoes, and local inflammatory symptoms are quantified, with highest total score being 10 (Table 1). The Mann-Whitney U test, paired t-test, and Chi squared test were used for statistical analyses with the significance level set at p<0.01. Several parameters were measured before and after surgery. The hallux valgus angle, M1-M2 angle, M1- Table 1 Tokyo Medical University Classification 3 for postoperative clinical assessment of hallux valgus Pain in the first metatarsophalangeal (MTP) joint (excluding callus) No pain 2 Pain during walking or exercising 1 Pain at rest 0 Deformity of the first MTP No deformity 2 Mild protrusion 1 Severe protrusion (overlapping with the second toe) 0 Plantar callosity and/or metatarsalgia of lesser metatarsals No callus or pain 3 Have callus but no pain 2 Pain during walking 1 Pain on pressure 0 Use of commercially available shoes Yes 2 Some 1 No 0 Local inflammatory symptoms No 1 Yes 0

3 Vol. 13 No. 3, December 2005 Modified Mitchell s osteotomy 247 Figure 2 The osteotomised region was securely fixed using 2 cross-inserting Kirschner wires. Figure 1 Radiological measurement: (1) hallux valgus angle, (2) M1-M2 angle, (3) M1-M5 angle, (4) length of the first metatarsal bone, and (5) degree of sesamoid bone shifting. M5 angle, degree of sesamoid bone shift, and length of the first, second, and third metatarsal bones were measured in a weight-bearing, standing position on anterior radiographs (Fig. 1). Sesamoid bone shift was defined as the distance between the centre line of the first metatarsal and the medial border of the sesamoid. Surgery was performed when conservative treatments such as pharmacotherapy, orthosis, and exercise therapy were ineffective, and when activities of daily living were hindered, such as when pain made it difficult for the patient to wear shoes. Surgery was not performed when pain or hindrance of activities of daily living were absent, even if the hallux valgus was severe. Surgical technique was similar to the original Mitchell s osteotomy. An arced dorsomedial skin incision was made in the first MTP joint without damaging the dorsomedial cutaneous nerve. A Y- shaped incision in the capsule was then made without removing the bursa. The V -shaped portion of the Y was bent back and both sides of the stem of the Y were inverted peripherally to expose the MTP joint. Figure 3 A plantar orthosis is used 3 weeks after surgery. The first metatarsal bone was dissected subperiosteally from the caput to the centre of the shaft, and the exostosis on the medial side of the metatarsal bone was resected. After cleaning the resection margin using a Surgairtome (Hall Surgical, Largo [FL], US), bone wax was used for haemostasis. In the articular cartilage, a longitudinal sagittal groove was seen, but if the exostosis was resected from the groove, excessive resection could lead to a poor joint fit, and thus resection was conducted while leaving the sagittal groove intact, as far as possible. In the original Mitchell s osteotomy, the first metatarsal was dissected between 1.3 cm and 1.9 cm (1/2 3/4 inch) from the MTP joint, but we moved the dissection slightly proximally, at 2.0 cm to 2.5 cm from the MTP joint. Osteotomy was performed perpendicular to the bone

4 248 K Yamamoto et al. Journal of Orthopaedic Surgery axis using a bone micro saw, and the distal fragment was shaped into a proximally extending lateral step to achieve the planned shifting and shortening. Pronation was corrected while shifting the metatarsal head laterally, and 3-dimensional correction was performed to avoid dorsal flexion. The M1-M2 angle was also corrected. The osteotomised region was securely fixed using 2 cross-inserting Kirschner wires (Fig. 2). If the hallux valgus could not be corrected intraoperatively by gently pulling the medial capsule attached to the proximal phalanx toward the centre of the metatarsal, lateral soft-tissue dissection of the first MTP joint was performed. The skin on the lateral side of the first MTP joint was incised, but when oblique osteotomy was performed on the second metatarsal bone, the skin incision made for the oblique osteotomy was used for soft-tissue dissection. If minimal dissection was desired, a small incision on the lateral capsule was made inside the joint, but if a more extensive dissection was necessary through the joint capsule, a new skin incision was made in order to dissect the adductor hallucis, because dissection performed in a blind manner can lead to the onset of osteoarthritis in MTP joints soon after surgery. Three of 6 feet with hallux valgus angles over 50 Ο, and 3 of 22 feet with angles between 40 Ο and 49 Ο underwent such a procedure. If the hallux valgus could be corrected intraoperatively by gently pulling the medial capsule, the articular capsule that had been opened in a Y shape and inverted was reefed with a slight over-correction in the shape of a letter V. The Kirschner wires were embedded subcutaneously. When one oblique lesser metatarsal osteotomy was included, an approximately 3-cm vertical incision was made above the target metatarsal bone. When 2 oblique lesser metatarsal osteotomies were performed, a skin incision was made between the 2 target metatarsal bones. When combined surgery of lateral soft-tissue dissection of the first MTP joint and an oblique osteotomy of the second metatarsal bone was performed, a skin incision was also made between the first and second metatarsal bones. This oblique lesser metatarsal osteotomy was performed according to Helal, 6 but internal fixation of the osteotomised region was not performed, and shortening was achieved by sliding fragments and by early loading. Caution should be exercised in such situations because excessive periosteal dissection may lead to lateral dislocation of the metatarsal head. Immediately after surgery, several 2.5-cm wide elastic adhesive bandages were used to maintain the surgically corrected position. Once the surgical wound was stabilised, a plaster cast was wrapped over the bandages, and as soon as the swelling subsided, patients were allowed to initiate weight-bearing walk. A plantar orthosis was used 3 weeks after surgery (Fig. 3). Kirschner wires were removed under local anaesthesia 6 to 8 weeks after surgery following radiographic confirmation of bone union. The guidelines for the start of weight-bearing walk were also applicable when an oblique lesser metatarsal osteotomy was performed. Because Japanese people walk barefoot indoors and contracture of the first MTP joint may hinder activities of daily living, it was important to initiate range of motion exercises 3 weeks after surgery when the cast was removed. The orthosis was used day and night for 6 months after surgery, and patients were instructed to do Hohmann s exercises. RESULTS According to the clinical assessment system developed by the Tokyo Medical University, 3 mean preoperative and postoperative 5-year scores, respectively, were 0.9 and 1.7 points in the pain category, 0.4 and 1.5 points in deformity, 1.3 and 2.3 points in plantar callosity and metatarsalgia, 1.0 and 1.6 points in use of commercially available shoes, and 0.3 and 1.0 points in local inflammatory symptoms, with total scores of 3.8 and 7.9. The results demonstrate significant improvement in each of these parameters (Mann-Whitney U test, p<0.005). Comparison between groups A and B revealed no significant differences in pain, deformity, or inflammation scores, but showed a significant difference in the scores of plantar callosity and metatarsalgia, use of commercially available shoes, and total score. These findings demonstrate the effectiveness of oblique lesser metatarsal osteotomy in alleviating plantar callosity and metatarsalgia (Table 2). Before surgery, at postoperative 3 weeks, and at postoperative 5 years in the radiological assessment, respectively, the mean hallux valgus angles, M1-M2 angles, M1-M5 angles, and sesamoid bone shifts are shown in Figure 4. There was significant improvement in each of these parameters at postoperative 3 weeks, but a slight increase was found at postoperative 5 years. Because the hallux valgus angle and sesamoid bone shift are more likely to be affected by soft-tissue dissection, the degree of increase was slightly larger (paired t-test) (Fig. 4). Hallux valgus angles of 30 Ο accounted for 73.1% of the cases, while severe hallux valgus of 40 Ο accounted for 30.1%. Comparison within each severity group showed no significant differences in the hallux valgus angle at postoperative 3 weeks or at postoperative 5 years (Mann-Whitney U test; Table 3). The mean hallux valgus angle at postoperative 5

5 * Vol. 13 No. 3, December 2005 Modified Mitchell s osteotomy 249 Table 2 Clinical assessment scores for groups A and B* Clinical assessment Preoperative Postoperative 5 years Group A Group B Group A Group B Pain in the first metatarsophalangeal (MTP) joint 0.9 (0.6) 0.9 (0.4) 1.6 (0.6) 1.7 (0.6) (excluding callus) [2 points] Deformity of the first MTP (2 points) 0.4 (0.7) 0.4 (0.5) 1.3 (0.7) 1.5 (0.6) Plantar callosity and/or metatarsalgia of lesser 1.4 (1.1) 1.5 (0.9) 1.6 (1.2) 2.7 (0.5) metatarsals (3 points) Use of commercially available shoes (2 points) 1.0 (0.4) 1.4 (0.5) 1.0 (0.5) 1.7 (0.5) Local inflammatory symptoms (1 point) 0.4 (0.5) 0.3 (0.4) 1.0 (0.0) 0.9 (0.3) Total (10 points) 4.0 (2.2) 4.0 (1.5) 6.9 (2.2) 8.5 (1.6) * Values are expressed as mean (standard deviation) Mann-Whitney U test, p<0.005 Mann-Whitney U test, p<0.01 (a) Hallux valgus angle 50 Ο 34.2± Ο (b) M1-M2 angle 25 Ο 16.7± Ο * p<0.01 ** p< Ο 20 Ο 17.1± ± Ο 10 Ο 7.4± ± Ο 5 Ο 0 Ο Preoperative Postoperative 3 weeks Postoperative 5 years 0 Ο Preoperative Postoperative 3 weeks Postoperative 5 years (c) M1-M5 angle (d) Sesamoid bone shift 40 Ο 15 Ο 30 Ο 34.9± Ο 8.7± ± Ο 10 Ο 25.8± ±4.6 5 Ο 4.3±2.1 0 Ο Preoperative Postoperative 3 weeks Postoperative 5 years 0 Ο Preoperative Postoperative 3 weeks Postoperative 5 years Figure 4 Comparison of preoperative and postoperative changes in (a) hallux valgus angle, (b) M1-M2 angle, (c) M1-M5 angle, and (d) sesamoid bone shift using paired t-test.

6 250 K Yamamoto et al. Journal of Orthopaedic Surgery Table 3 Changes in hallux valgus angle in relation to severity Hallux valgus angle No. of feet Hallux valgus angle (mean, SD) Preoperative Postoperative 3 weeks Postoperative 5 years 50 o o (5.2 o ) 18.8 o (13.0 o ) 20.0 o (15.0 o ) 40 o 49 o o (2.7 o ) 13.1 o (6.1 o ) o (7.3 o )2 30 o 39 o o (2.7 o ) 12.6 o (4.5 o ) o (6.2 o )2 20 o 29 o o (2.6 o ) 29.4 o (3.3 o ) o (5.7 o )2 <20 o o (1.6 o ) 26.2 o (2.2 o ) o (3.9 o )2 Group A (42 feet) Group B (51 feet) Total (93 feet) 20 feet 22 feet 43 feet 8 feet 63 feet 30 feet Improved Persistent 0% 20% 40% 60% 80% 100% Figure 5 Comparison of the results of 2 surgical methods in improvement in plantar callosity or metatarsalgia. years was 17.5 Ο (SD, 7.2 Ο ) in group A, and 16.6 Ο (SD, 7.6 Ο ) in group B. No significant difference was found between these 2 groups. Intra-operatively, we empirically concluded that it was necessary to perform first MTP joint lateral softtissue dissection in 6 feet: 3 with hallux valgus angles over 50 Ο and 3 with angles of 40 Ο to 49 Ο. When comparing the postoperative hallux valgus angles between these 6 feet and the other 22 feet not requiring lateral soft-tissue dissection although their hallux valgus angles were also either >50 Ο or 40 Ο 49 Ο, the mean hallux valgus angle of the first group at postoperative 5 years was 20.7 Ο (SD, 13.1 Ο ), and that of the second group was 19.8 Ο (SD, 11.3 Ο ). No significant difference was found between the 2 groups (Mann-Whitney U test). The mean decrease in the length of the first, second, and third metatarsal bones was 3.7 mm (6.4%), 6.2 mm (9.0%), and 4.2 mm (6.3%), respectively. Plantar callosity and metatarsalgia persisted in 53.1% and 14.7% of feet in group A and group B, respectively. These observations confirmed the effectiveness of oblique metatarsal osteotomy (Chi squared test, p<0.0005; Fig. 5). DISCUSSION There are more than 130 surgical methods for the treatment of hallux valgus. Several attempts have been made to develop a surgical method to treat all hallux valgus regardless of the severity. In recent years, surgical methods have been selected based on severity and condition: parameters such as hallux valgus angle or M1-M2 angle. As a general rule, a hallux valgus angle

7 Vol. 13 No. 3, December 2005 Modified Mitchell s osteotomy 251 of <20 Ο is considered mild, 20 Ο 39 Ο moderate, and >40 Ο severe. Distal metatarsal osteotomies such as Mitchell s osteotomy or Hohmann s osteotomy are performed to treat mild-to-moderate hallux valgus, whereas proximal osteotomy such as Mann s osteotomy with soft-tissue dissection is combined to treat moderate-to-severe hallux valgus. The indication for Mitchell s osteotomy varies among authors: Mann 7 suggested it be performed when the M1-M2 angle is <20 Ο and the hallux valgus angle is <40 Ο, Tanaka et al. 8 suggested an M1-M2 angle of <15 Ο and hallux valgus angle of <33 Ο. Modified Mitchell s osteotomy and MTP joint lateral soft-tissue dissection have been combined to treat severe hallux valgus in our department, and relatively favourable results have been obtained. Senba and Nomura 9 combined the Hammond osteotomy (distal osteotomy) and MTP joint lateral soft-tissue dissection for the treatment of severe hallux valgus and recommended that this method be used when the hallux valgus angle is 35 Ο and the M1-M2 angle is 20 Ο. It was once reported that combining distal osteotomy and lateral soft-tissue dissection increased the risk of osteonecrosis, 10 which was also true when proximal metatarsal osteotomy and first MTP joint softtissue dissection were performed to treat severe hallux valgus. However, we did not experience osteonecrosis following lateral soft-tissue dissection because vascularisation in the plantar and medial sides of the first metatarsal bone was rich. We compared the results of modified Mitchell s osteotomy with its combination with lateral soft-tissue dissection in cases with hallux valgus angles of >40 Ο and found a similar degree of recovery for both groups. We therefore concluded that a combination of modified Mitchell s osteotomy and first MTP joint lateral soft-tissue dissection is viable in the treatment of severe hallux valgus. Hallux valgus is often complicated by flat foot or metatarsus latus, and MTP joint malalignment often leads to metatarsalgia or plantar callosity. There have been numerous reports on the incidence of postoperative metatarsalgia and callosity: Mitchell at al. 1 reported 32%, Mann et al %, Wilson %, Glynn et al. 5 20%, Shapiro and Heller 4 33%, and Lindgren and Turan %. In order to avoid inducing MTP joint malalignment, we performed oblique osteotomy on the other metatarsal bones, particularly the second and third metatarsal bones. Nonetheless, in some cases, 3-dimensional corrective osteotomy of the first metatarsal bone is sufficient for correcting broad foot and improving metatarsalgia and plantar callosity. Therefore, whether to perform oblique lesser metatarsal osteotomy should be based on the severity of metatarsalgia or plantar callosity, length of the first and second metatarsal bones, and distribution of plantar pressure. The shortening of the first metatarsal by different osteotomies varies: 6 7 mm by Mitchell s osteotomy, 1 2 mm by Mann s osteotomy, 14 and 2.7 mm by Lindgren s osteotomy. 15 All of the osteotomies can shorten the first metatarsal and effectively relieve tension in the adductor hallucis, but may exacerbate MTP joint malalignment and lead to postoperative metatarsalgia and plantar callosity. Therefore, shortening of the first metatarsal bone is safe if MTP joint alignment is normal, but shortening should be minimised if MTP joint malalignment is detected or postoperative misalignment is expected. Correction of the M1-M2 angle largely depends on the amount of peripheral fragment displacement following osteotomy. During preoperative planning, if the metatarsus primus varus is marked and the M1-M2 angle is large, the lateral step should also be large. If the degree of lateral shift of the metatarsal head is too great, the osteotomised region will become unstable and hinder bone fusion. Mitchell et al. 1 suggested that the upper limit of displacement was one third of the horizontal diameter. We recommend an upper limit of displacement of about 40%. CONCLUSION Modified Mitchell s osteotomy is a fine surgical method for the treatment of hallux valgus providing stable results. Despite slightly poorer results in severe cases, the use of additional procedures allows successful treatment of the condition. Numerous further modifications to the modified Mitchell s osteotomy are performed in our department, including osteotomy methods, location, fixation, first MTP joint lateral soft-tissue dissection, and oblique osteotomy. Therefore, it may not be appropriate to refer our method as modified Mitchell s osteotomy because it is no longer a simple procedure like the original Mitchell s osteotomy. ACKNOWLEDGEMENT The authors wish to thank Prof J Patrick Barron of the International Medical Communications Center of the Tokyo Medical University for reviewing this manuscript.

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