The bunionette deformity is a prominence of the fifth metatarsal head, usually with medial deviation of the fifth toe. It is associated with
- wide fifth metatarsal head (Fallat and Bucholz 1980, Leach and Igou 1975) – Coughlin found this in 8/30 in his surgical series, but Nestor, in a large radiological series, did not find any significant difference in metatarsal head width between patients and controls
- lateral bowing of the 5 th metatarsal shaft (Fallat and Bucholz 1980) – however, Nestor et al (1990) did not find any increased lateral bowing in patients compared with controls; they considred this a normal variation which was made more symptomatic by increased 4 th-5 th MT angle
- an increased angle between the 4 th and 5 th metatarsal shafts - Fallat and Bucholz found a normal angle of 6.2deg, although some studies have used a value of 8deg as the upper limit of normal. Coughlin (1991) found an average angle of 10.6deg in surgically treated patients and Nestor (1990) an average of 10.8deg in 91 feet with bunionette compared with 9.1deg in 91 matched controls
- an increased incidence of hallux valgus – Nestor et al (1990) found a 23% prevalence of hallux valgus in patients with bunionette compared to 9% in controls, although there was probably some selection of controls implying that the difference with normal feet may be even higher
Almost half of the patients in Nestor et al’s radiological series had bilateral bunionettes.
Coughlin (1991) used the first three anatomical abnormalities described above to classify bunionettes;
- Type 1 – large, wide metatarsal head
- Type 2 – lateral metatarsal shaft bowing
- Type 3 – increased 4th/5th MT angle
Coughlin recognised that some bunionettes had features of more than one category. In addition, his system categorises the appearance of individual deformities rather than defining the way in which they differ from normality. Hence Nestor’s finding that the main difference between bunionettes and normal feet was an increased 4th/5th MT angle can be reconciled with Coughlin’s classification. No study has assessed the reproducibility of Coughlin’s classification, and series reporting the treatment of bunionettes have not generally used this or any other classification to select treatment.
Patients usually complain of:
- pain over the prominent 5th MT head
- difficulty in finding comfortable shoes
- rubbing between the 4th and 5th toes
- cosmetic concerns
As with hallux valgus, asymptomatic people with bunionettes may consult for advice about treatment “before it gets worse”.
Many patients have bilateral deformities and/or hallux valgus or other lesser toe problems.
All patients should be asked screening questions about:
- Inflammatory arthropathy
- Circulatory problems
- Neurological problems
Examination may occasionally show features of a generalised arthropathy or a more complex foot deformity. There is often a generally wide forefoot, and hallux valgus, hammertoes and congenital curly toes are frequently noted though not always symptomatic. The 5th metatarsal is laterally deviated and the head prominent. The 5th toe is medially deviated; the ease of reduction should be noted, along with any intrinsic toe deformity.
Occasionally, an underlying condition such as possible inflammatory arthropathy or neurological condition may need to be investigated appropriately.
The main investigation is plain radiology with standing AP and lateral radiographs of the forefoot. This allows assessment of the 5th MT shape and measurement of the 4th/5th MT angle. Any other forefoot abnormality, such as hallux valgus, can be assessed in the normal way.
Some patients only require explanation of the problem. We reassure asymptomatic people that there is no evidence that surgical correction of asymptomatic deformities will prevent later problems, and offer to see them again should problems develop.
As with most forefoot problems, simple advice on choice of shoes can help many people. There is no evidence that any from of strapping, splintage or insoles alter the natural history of bunionette.
A lateral or dorsolateral skin incision will give adequate access. If extending the incision to perform a proximal osteotomy, care should be taken with the branches of the sural nerve. If shaving the lateral prominence of the metatarsal head, the capsule can be opened with techniques analogous to those for bunion surgery. We normally use a longitudinal arthrotomy which can be double-breasted to repair the transverse tie-bar of the forefoot. However, some techniques perform a metatarsal osteotomy without opening the joint.
If desired, the lateral eminence of the metatarsal head can be excised. Shaving a metatarsal head prominence (Kitaoka and Holiday 1992) can give good results alone, but where angulation is present a metatarsal osteotomy would usually be added . Excision of the 5th MT head produced mostly poor results (Kitaoka 1991) and should be avoided.
An osteotomy is then performed according to choice. Options include:
- Distal osteotomies of various configurations with medial translation of the head fragment. Not all series used fixation of the osteotomy. Non-fixation was associated with delayed union (Sponsel 1976), a high incidence of transfer keratoses (Keating 1982) or malunion (Pontious 1996)
- Oblique (Sponsel 1976, Keating 1982)
- Transverse - (Weitzl et al 2007; a percutaneous technique was described by Legenstein et al (2007))
- Chevron (Moran and Claridge 1994, Boyer and Deorio 2003)
- Horizontal, analogous to a Weil osteotomy (London 2003, Radl et al 2005)
- Diaphyseal osteotomy through the proximal shaft with rotational correction of 5th MT angulation and screw fixation (Coughlin 1991, Vienne et al 2006)
- Basal osteotomy – both dome (“reverse Mann”) and “reverse proximal chevron” (relative to procedures for hallux valgus) have been described.
Series have reported varying amounts of splintage and weightbearing restriction post-operatively, mostly reflecting the culture of their publication dates. There seems little evidence that either casting or weightbearing restriction are necessary.
It has been suggested that Coughlin type 1 deformities should be treated with a head shaving, type 2 with a distal or diaphyseal osteotomy and type 3 with a basal osteotomy. However, published series have not allocated treatment according to classification of deformity, nor is there any discernable pattern of success or failure according to pattern.
Lateral condyle resection
Kitaoka (1992) reported 21 patients who had only lateral condylar resection. Although the 4-5IMA was comparable to most series of osteotomies, 20/21 patients were relieved of the callosity over the metatarsal head and 16 were pain-free. Deformity recurred in 2 patients at a mean follow-up of 6.6yr.
Keating (1982) described 22 oblique Sponsel osteotomies without fixation. No clinical results were reported, but the 4-5IMA improved from 9 to 8deg and the lateral deviation angle in patients with type 2 deformities from 7.5 to -9deg. However, there were 2 recurrences and 8 patients had symptomatic transfer lesions. Keating noted the tendency of the Sponsel osteotomy to dorsal malunion and recommended a double-oblique cut to prevent dorsal migration.
Kitaoka described 19 distal chevron osteotomies followed a mean of 7.1y. The author’s forefoot score improved from 35.8 to 73.9/75 and the 4-5IMA from 11.8 to 9.2deg. There was one transfer lesion but no other substantial complications and patient satisfaction was unrelated to objective correction. Moran also reported 16 distal chevron osteotomies with a mean follow-up of 3.2yr, all K-wired. Their forefoot score improved from 44.1 to 90.6/100 and the forefoot width from 9.1 to 8.5cm. There were 2 residual callosities and one transfer lesion. Boyer (2003) reported 10 patients who underwent chevron osteotomy. Mean correction of the 4-5IMA was 1.4deg and the lateral deviation angle was corrected by 1.3deg. Mean AOFAS score was 93/100 and there were no significant complications.
Legenstein reported 57 patients who had a percutaneous transverse distal osteotomy with intramedullary K-wire stabilisation. Mean AOFAS score improved from 59 to 95/100 and the 4-5IMA from 12 to 8deg. There were four infections but no recurrent deformities or non-unions. Weitzl (2007) reported 30 similar osteotomies followed up for an average of 7.7 years. Mean AOFAS score was 88/100. Mean 4-5IMA improved from 14.8 to 8.1deg in type 3 deformities; in type 2 deformities the lateral deviation angle was measured and improved from 9.6 to 3.7deg. Eight osteotomies healed with dorsal translation but only one had a transfer lesion. There were three infections, one delayed union and one recurrent deformity. They commented that the percutaneous technique and intramedullary fixation makes it difficult to remove the lateral shaft prominence, which can become symptomatic.
Steinke described a transverse osteotomy with a peg of proximal fragment impacted into a hole in the head. Of 44 feet, 38 were asymptomatic, four had residual pain and shoewear problems, and both feet of one patient were not improved. 4-5IMA appears not to have changed. There was one asymptomatic malunion and no other significant complications.
London (2003) reported 25 distal rotation osteotomies, cut close to horizontal, with screw fixation. Mean follow-up was 64m. Mean AOFAS score was 94/100 and mean 4-5IMA improved from 10.8 to 5.5deg. Four patients had some residual pain, seven had shoewear restrictions and there were three symptomatic calluses, though no transfer lesions. Radl (2005) reported 21 similar procedures. Mean AOFAS score improved from 42 to 87/100 and 4-5IMA from 14 to 9deg. There was one delayed union, three hardware problems and one painful callosities but no infections.
Vienne reported 33 diaphyseal rotation Coughlin osteotomies in 24 patients with an average of 39 months follow-up. Mean AOFAS score increased from 55 to 95/100 and the mean 4-5IMA improved from 10.4 to 1degree. On average the metatarsal head was translated 4.6mm medially. Six patients had the screws removed.
Glover (2009) described 60 examples of the “scarfette” osteotomy in 50 patients followed for a mean of 12months. 4-5IMA improved from 12.8 to 1.3deg. No clinical results were reported. There were 2 asymptomatic undercorrections and fixation pins were removed in 7 patients.
Diebold (1991) reported 22 oblique proximal chevron osteotomies with minimum 3y follow-up. Pain was absent in 14 and minor in 8. All calluses resolved and there were no infections or transfer lesions. The 4-5IMA improved from 12.1 to 1.3deg . Diebold also noticed a small improvement in the hallux valgus angle and 1-2IMA and suggested bunionette correction may improve overall forefoot balance.
Okuda (2002) reported 10 basal dome osteotomies (analogous to the Mann 1st MT osteotomy). All patients scored 100/100 on the OAFAS scale and the mean 4-5IMA was corrected from 18.9 to 2.6deg. The average time to union was 18 weeks with 3 delayed unions taking >30 weeks, and union was slower in the more proximally sited osteotomies. There were no infections or transfer lesions.