Bunionette

NB This page is from the 2005 Hyperbook.
Last evidence check February 2005.

Pathological anatomy

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 4 th/5 th 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 4 th/5 th 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.

Clinical features

Patients usually complain of:

• pain over the prominent 5 th MT head
• difficulty in finding comfortable shoes
• rubbing between the 4 th and 5 th 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
• Diabetes
• Circulatory problems
• Neurological problems
• Trauma

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 5 th metatarsal is laterally deviated and the head prominent. The 5 th toe is medially deviated; the ease of reduction should be noted, along with any intrinsic toe deformity.

Investigation

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 5 th MT shape and measurement of the 4 th/5 th MT angle. Any other forefoot abnormality, such as hallux valgus, can be assessed in the normal way.

Non-surgical management

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.

Surgery

Various surgical procedures have been proposed:

• Excision of the 5 th MT head – produced mostly poor results (Kitaoka 1991) and shold be avoided
• Shaving a metatarsal head prominence
• Distal osteotomies of various configurations:
  • Oblique, analogous to a Wilson 1 st MT osteotomy
  • Transverse, analogous to a Hohman 1 st MT osteotomy
  • Chevron
• Diaphyseal osteotomy
• Basal osteotomy – concerns about union in the proximal part of the 5 th MT mean that “basal” osteotomies are generally performed through the proximal diaphysis. Nevertheless Okuda (2002) had 3/10 delayed unions, though clinical outcome was not affected.

Most clinical series report success rates of 80-90% irrespective of technique. There are no RCTs or, indeed, any other comparative series.

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)

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.