How to avoid complications of distraction osteogenesis for first brachymetatarsia

Background and purpose Distraction osteogenesis may be used for the treatment of brachymetatarsia. However, few reports have been published on first metatarsal lengthening by this method. We evaluated the complications of distraction osteogenesis for first brachymetatarsia and here we provide a solution. Patients and methods 16 patients (27 feet) underwent distraction osteogenesis for first brachymetatarsia. Mean age at time of surgery was 20 (12–34) years and mean duration of postoperative follow-up was 5 (2–13) years. A unilateral external fixator was fixed at the medial aspect of the metatarsus. The distraction axis was parallel to the plantar surface of the foot in the sagittal plane and to the second metatarsal axis in the transversal plane. Results First metatarsal length expressed as a proportion of second metatarsal length was 60% (55–64). Average degree of metatarsal lengthening was 42% (34–54), and the average lengthening index was 64 (39–93) days/cm. The most common complication was stiffness of the metatarsophalangeal joint (12 feet). Deformities that included cavus foot and hallux valgus occurred in 3 feet each, and callus fractures occurred in 3 feet. The other complications were pin breakage and pin tract infection in 2 feet each. Interpretation Distraction osteogenesis for first brachymetatarsia can give satisfactory cosmetic and functional results. However, several complications are commonly encountered. This report on complications and their solutions may help those attempting distraction osteogenesis for first brachymetatarsia.


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Brachymetatarsia is a congenital deformity and involves an abnormally short metatarsal caused by premature closure of the epiphysis. The fourth toe is most commonly involved, followed by the first and the fifth toes (Viladot 1973). The deformity is not only cosmetically disturbing but also impairs the weight-bearing mechanism of the foot. In first brachymetatarsia, excessive weight bearing is loaded onto the second and third metatarsus by a change in weight, and pressure and pain can develop during shoe wearing and walking because of the deformity and overlapping adjacent toes (Tanaka et al. 1995, Baek andChung 1998). Surgery should be planned on the basis of functional recovery and anatomical restoration that restores proper weight bearing in addition to addressing cosmetic problems. Several techniques have been described for the treatment of brachymetatarsia; these include onestage lengthening using an interpositional bone graft, gradual lengthening by distraction osteogenesis with or without shortening of the adjacent metatarsals and phalanges, and shortening of adjacent metatarsals and phalanges (Harris and Beath 1949, Hughes et al. 1990, Kawashima et al. 1994, Choi et al. 1999, Masada et al. 1999, Oh et al. 2004.
The most widely used procedures are one-stage lengthening or distraction osteogenesis. Each method has its own advantages and disadvantages. The advantages of one-stage lengthening include a shorter period of bony union, better patient compliance, and less scar formation. However, this method has the disadvantages of donor site morbidity, neurovascular impairment, and smaller length gain (Harris andBeath 1949, Hughes et al. 1990). Congenital shortness of the metatarsal bone represents one of the best indications for distraction osteogenesis in the foot (Martin 2001). The advantages of distraction osteogenesis include: no need for bone grafting, easier tendon stretching, fewer neurovascular complications, early weight bearing, and a larger length gain, whereas disadvantages include stiffness or subluxation of the metatarsophalangeal (MTP) joint, cavus or angulation deformity, pin tract infection, and a longer period of bony union (Kawashima et al. 1994, Takakura et al. 1997, Choi et al. 1999, Masada et al. 1999, Oh et al. 2004, Shim and Park 2006. However, few reports have been published on first metatarsal lengthening by this method (Takakura et al. 1997, Oh et al. 2004, Kim et al. 2003, Shim and Park 2006. We evaluated the results and complications that occurred in 27 feet with brachymetatarsia of the first ray treated with distraction osteogenesis, and here we provide solutions for complications.

Patients and methods
16 patients (15 women) underwent distraction osteogenesis for first brachymetatarsia from January, 1998 to June, 2006 at our institution (27 feet). Metatarsal shortening was congenital in all patients. The mean age at time of surgery was 20 (12-34) years and mean duration of postoperative follow-up was 62 (26-126) months. All the patients except 3 (nos. 1, 2, and 8) were treated after epiphyseal closure of the metatarsus. Before surgery, we made patients and parents aware of the various complications associated with distraction osteogenesis (e.g. loss of motion, sensitivity about the scar). Surgery was aimed at functional recovery and anatomical restoration to recover proper weight bearing and to minimize cosmetic problems. 11 patients underwent bilateral first metatarsal lengthening, and 9 patients (13 feet) underwent simultaneous lengthening of the fourth metatarsal bone. 14 of the 16 patients had occasional pain around adjacent toes when wearing shoes and walking. 2 other patients complained of psychological distress caused by the cosmetic appearance of their deformity.

Operative technique
Under fluoroscopic guidance, 2 miniature half-pins were inserted into the proximal metaphysis and 2 into the distal metaphysis, and directed medial to lateral. When the first metatarsal bone was too short to accept all 4 half-pins, 1 proximal pin was inserted in the medial cuneiform. A unilateral external fixator (Dyna-EXTOR, BK meditech, Seoul, Korea) was fixed at the medial aspect of the metatarsus, as parallel to the plantar surface as possible in the sagittal plane, and as parallel to the second metatarsal axis in the transversal plane to prevent malalignment during metatarsal lengthening ( Figure  1). A medial longitudinal incision of 1.5 cm was made at the metatarsal shaft and corticotomy was performed perpendicular to the plantar surface of the foot. We did not perform plantar fascia release or flexor tenotomy to lengthen soft tissue. The

Evaluation of radiographic and clinical outcome
Radiographs were taken with the foot plantigrade on the floor, and the radiation beam was directed at the center of the forefoot and was inclined 15 degrees from the vertical at a distance of 100 cm above the film to obtain anteroposterior radiographs. We evaluated first metatarsal lengths as percentages of second metatarsal lengths, lengthening gains and percentages, external fixation periods, lengthening index, and ranges of motion of first MTP joints. First and second metatarsal lengths were measured according to Tanaka et al. (1995). Briefly, the axes of the first and second metatarsals were lines that connected the mid-points of the proximal and distal ends of their diaphysis. Metatarsal length is the distance between the points of intersection of the axes of the metatarsals with the distal ends and proximal ends of the metatarsals.
External fixation period was from the date of surgery to fixator removal. Lengthening index was calculated by dividing the length of the external fixation period by the length gained. Patients were allocated to 3 groups with respect to MTP joint motion (dorsiflexion plus plantarflexion), i.e. normal or mild restriction (≥ 75˚), moderate restriction (30˚-74˚), or marked restriction (< 30˚). We defined stiffness as being moderate or marked restriction of MTP joint motion. The outcome was assessed clinically according to the American Orthopaedic Foot and Ankle Society (AOFAS) hallux metatarsophalangeal-interphalangeal scale (Kitaoka et al. 1994) and graded as excellent (> 85), good (71-85), fair (56-70), or poor (< 56).

Results
Mean length of the first metatarsal expressed as a proportion of that of the second metatarsal was 60% (55-64). Average length gained was 17 (13-21) mm, and average length gained as a proportion of the original metatarsal length was 42% (34-54). Bony consolidation was achieved in all 27 metatarsals. proper direction of the metatarsal lengthening was confirmed by a predistraction of about 5 mm by intraoperative fluoroscanning.
Postoperatively, 0.25 mm of distraction was applied 3 times a day after a 7-day latent period. Radiographs were checked every other week to inspect the degree of osteogenesis and joint condition. We controlled distraction rate and rhythm according to radiographic findings and the clinical condition of the patient. Distraction was continued until a satisfactory metatarsal length had been achieved. Patients were permitted full weight-bearing ambulation with heel touching using postoperative shoes on the second postoperative day. The external fixators were removed when calluses had matured.
The mean AOFAS score was 87 (85-90) points preoperatively and improved to 92 (80-100) points at the last follow-up; 19 cases had excellent results ( Figure 2) and 8 had good results. 3 patients whose epiphysis of the metatarsus was not fused before surgery had no problems associated with residual growth at the last follow-up. The 3 patients (nos. 14, 15, and 16) with the shortest follow-up after external fixator removal (22, 23, and 22 months) had no complications.

Complications
The most common complication encountered was MTP joint stiffness, which was seen in 12 feet. 3 patients (3 feet) had moderate hallux valgus deformity. 2 of these patients accepted their results because of cosmetic improvement and no bunion pain (Figure 3). 1 patient developed painful hallux valgus, which was later corrected by distal chevron osteotomy. Cavus deformity of the metatarsus occurred in 2 patients who had no cavus deformity before surgery (3 feet). 1 patient with bilateral deformity underwent dorsal closing wedge osteotomies at the metatarsal base and correction was achieved (Figure 4). Another patient accepted the deformity cosmetically and functionally. All 3 feet were plantigrade without any symptoms at final follow-up. Callus fractures occurred in two patients who underwent simultaneous distraction osteogenesis for bilateral

Discussion
Various complications of distraction osteogenesis, as now generally performed to correct first brachymetatarsia have been reported, e.g. stiffness or subluxation of the MTP joint, cavus or other angulation deformity of the metatarsus, prolonged time for bony consolidation, and pin tract infection (Table 2) (Kawashima et al. 1994, Takakura et al. 1997, Masada et al 1999, Oh et al. 2004. The most common complication is MTP joint stiffness. Although loss of any motion or loss of more than 50% of dorsiflexion has been considered to be MTP joint stiffness in several studies (Takakura et al. 1997, Masada et al 1999, Shim and Park 2006, we considered MTP joint motion of below 75 degrees to be stiffness. In healthy individuals, the average length of the first metatarsal expressed as a proportion of of the length of the second metatarsal is about 86% (Kitaoka et al. 1994). Moreover, a few authors (Takakura et al. 1997, Masada et al 1999, Shim and Park 2006 have   reported greater reduction in motion in patients with a length gain of more than 40%, and have emphasized that the amount of lengthening should not exceed 40%. To avoid excessive lengthening, Kim et al. (2003) recommended shortening of an adjacent bone for the treatment of first brachymetatarsia when the amount of lengthening is expected to exceed 40%. Also, Kawashima et al. (1994) reported that a distraction rate of 0.35 mm twice a day is too fast for tendon elongation, although adequate for bone distraction. Choi et al. (1999) reported that a distraction rate of 0.25 mm twice a day is optimal for soft tissue elongation and bone formation. In our study, distraction was performed at 0.25 mm 3 times a day and MTP joint stiffness was observed in 13 of the 27 feet. Based on our results, MTP joint stiffness may be caused by an excessive amount of lengthening, a distraction rate and rhythm that are too rapid, or a long period of external fixation. The best prevention against joint stiffness is stretching therapy, if it can be instituted safety (Martin 2001). If therapy is unable to restore adequate motion, then tendon lengthening may be necessary (Martin 2001). Shim and Park (2006) reported improvement of 7 cases who underwent plantar capsular release on flexion contracture or subluxation of the MTP joint after distraction osteogenesis. Thus, we consider that the amount of lengthening should be less than 40%, and that a distraction rate of 0.25 mm twice a day is optimal; and furthermore, that postoperative active and passive MTP joint mobilization exercises are essential for preventing MTP joint stiffness. Malalignments after distraction osteogenesis, such as cavus or hallux valgus deformities, are also important complications. Oh et al. (2004) reported 2 cases of cavus deformity due to tight plantar soft tissues in 2 patients who had undergone considerable lengthenings (56% and 66%). The other factor that favors cavus deformity concerns the anatomical orientation of the first metatarsal (Oh et al. 2004). Normally, the first metatarsal has approximately 30 degrees of inclination in the sagittal plane. If lengthening is performed along the anatomical axis of the first metatarsal, the head of the first metatarsal will be situated at a lower position than the plantar surface in the final lengthened state. Thus, in an attempt to prevent the development of cavus deformity during and after lengthening, the axis of the external fixator must be as parallel as possible to the plantar surface at the medial aspect of the first metatarsal bone. Even so, in our study, cavus deformity developed in 2 patients (3 feet). In 1 patient, the deformity was bilateral with painful plantar callosities, and the patient underwent dorsal closing wedge osteotomies at the metatarsal base. We did not perform plantar fascia release and flexor tenotomy to prevent cavus deformity during the index procedure. Thus, we believe that the soft tissue procedure will also be needed in cases with tight plantar soft tissue.
Hallux valgus deformity was caused by the anatomical orientation of the first metatarsal. If lengthening is performed along the anatomical axis of the first metatarsal with an increased intermetatarsal angle, the hallux valgus angle will be increased after final lengthening. Thus, to prevent the development of hallux valgus deformity, the axis of the external fixator must be aligned parallel to the anatomical axis of the second metatarsal in the transversal plane.
In cases treated at our institution before this study was initiated, the external fixator was attached at the dorsal aspect of the first metatarsal, and complications such as cavus deformity and angulation deformity occurred frequently. We therefore changed the external fixator position from the dorsal side to the medial aspect of the first metatarsal, and found that complications of malalignment were markedly reduced.
Callus fractures occurred in 2 patients (3 feet) who were allowed to walk with heel weight bearing as soon as they could tolerate the pain. However, they walked using the entire sole. We believe that the callus fractures may have been caused by too rapid a distraction rate and walking with weight bearing using the whole sole, which would result in overloading of the callus during ambulation. We thus advocate that full weightbearing ambulation postoperatively without support should be delayed in patients who have undergone simultaneous correction for bilateral first brachymetatarsia.
We conclude that distraction osteogenesis for first brachymetatarsia can give satisfactory cosmetic and functional results. However, several complications are commonly encountered. We consider that these could be reduced by using the technique described above.