Bunionette

Paulo Carvalho

♦ INTRODUCTION

Bunionette or tailor’s bunion is a forefoot deformity characterized by a bony prominence in the lateral aspect of the fifth metatarsal (M5) head, accompanied, in most cases, by varus deviation of the fifth toe (Figure 9.1).

The bunionette was first described by Davies in 1949.¹ The name “tailor’s bunion” derives from the pressure and callous over the lateral aspect of the M5 head tailors would experience after spending long periods in a cross-legged sitting position.

The main classifications commonly accepted are those described by Fallat and Buckholz,² DuVries,³ and Coughlin.⁴ These classifications are based on the anatomical characterization of M5. There are three anatomical variants that define three types of bunionette: M5 in normal position with hypertrophic metatarsal head and prominent lateral condyle (type 1); M5 with lateral bowing, often called saber deformity (type 2); and M5 in valgus alignment where a wider intermetatarsal angle (IMA) exists between the fourth metatarsal (M4) and M5 (type 3) (Figure 9.2). The latter is the more frequent type, varying between authors (50% to 74%).²,⁵ Combinations of the three types are often observed,²,⁵,⁶ defined as type 4 by some authors.²

Bunionette deformity is much more frequent in women than in men. There are few demographic studies with a large series of patients. In two studies with more than 100 cases, very different female-male ratios were found.²,⁶ Fallat and Buckholz found a ratio of 2:1,² and Shimobayashi et al. found a ratio of 21:1.⁶ Based on the average of seven studies frequently cited in the literature, the author found a 5:1 female to male ratio.²,⁵,⁶,⁷,⁸,⁹,¹⁰

♦ PATHOGENESIS

There are intrinsic and extrinsic causes of bunionette deformity. In intrinsic causes, the three anatomical variants previously described play an important role in the pathogenesis of the bunionette causing an increased pressure over the lateral aspect of M5, resulting in local hyperkeratosis and inflammation with swelling and bursitis. In extrinsic causes, footwear, especially women’s narrow toe box footwear, may promote or exacerbate symptoms through constant rubbing and pressure over the head of M5.

♦ CLINICAL PRESENTATION

Patients present with pain over the lateral and/or plantar aspect of the M5 head that worsens with footwear and activity. On physical examination, callous and local inflammation such as swelling and erythema are typically present. Bursitis or even ulceration may be noted as well. In addition, very often, there is an associated varus of the fifth toe, which can present a supradductus or infradductus component as well as a claw deformity (Figure 9.3).

♦ IMAGING STUDIES

Standard weight-bearing radiographs (lateral, anteroposterior, and oblique views) are recommended and typically the only imaging required. In the anteroposterior plane, the fourth-fifth IMA, the fifth metatarsophalangeal angle (MPA), lateral deviation angle, as well as the width of the M5 head should be assessed (Figure 9.2).

The IMA is formed by the lines of the longitudinal axis of the fourth and fifth metatarsals. The normal IMA is proposed to be less than 8°.¹⁰ In normal feet, the average IMA is 6.5°, whereas it is greater than 9.6° in feet with symptomatic bunionette.²,¹⁰,¹¹,¹²

The MPA is the angle between the axis of the M5 and the axis of the proximal phalanx of the fifth toe. A normal angle is considered to be 14° or less.¹⁰,¹³

The lateral deviation angle is formed between a line connecting the midpoint of the width of the head and the midpoint of the neck of the M5 and a line along the proximal one-half of the medial cortex of the M5’s shaft. Normally, this measures less than 3°, but it is considered normal up to 7°.² However, according to some studies, there is no difference in the lateral deviation angle between patients with and without bunionette complaints.⁶,¹⁰ The width of the M5 head is considered normal up to 13 mm.¹⁰

Spreading between the first metatarsal (M1) and the second metatarsal (M2), spreading between M4 and M5, or spreading between all the metatarsals (“splayfoot”) is frequently present in patients with a bunionette⁵,⁶,¹⁰,¹⁴
(Figure 9.4). A splayfoot may also be present with a normal M4-M5 IMA. Therefore, it is possible to encounter patients with a symptomatic bunionette in the setting of a normal IMA, lateral deviation angle, and M5 head width, due to a large width between the M1 and M5.

Figure 9.1 Bunionette with varus of the fifth toe.

Figure 9.2 Types of bunionette, (A) type 1, large head; (B) type 2, saber deformity; (C) type 3 increased intermetatarsal angle.

♦ TREATMENT

Conservative treatment is the recommended initial approach. This includes adapted shoes (with a wide toe box or with cutouts or stretching) that can accommodate the prominent M5 head, padding the inflamed area, hyperkeratosis débridement, and the use of anti-inflammatory drugs or corticosteroids to treat the inflammation, pain, and bursitis.

Surgical treatment is indicated when conservative measures fail to control the symptoms or in patients with special demands, such as high-performing athletes.

The aim of surgery is to decrease the width of the forefoot and the prominent M5 lateral condyle. Anatomical characteristics such as IMA, MPA, lateral deviation angle, and width of the M5 head should be evaluated as it may influence the correct surgical technique. In the author’s opinion, the angle between M1 and M5 should also be evaluated, as there may be a bunionette in a splayfoot with a normal IMA.

Several open surgical procedures have been described in the literature such as condylectomy, osteotomy, phalanx or metatarsal head resection, and amputation. Phalanx or metatarsal head resection and amputation should be reserved for salvage procedures.¹⁵,¹⁶

Lateral condylar resection was described by Davies. The lateral condylectomy of the M5 head does not change the IMA, and therefore, it is only indicated for type 1 deformities without splayfoot. It is also not effective for bunionette with associated plantar keratosis. The presence of pes planus or forefoot pronation can also be a relative contraindication as the pressure will continue due to position of the hindfoot and forefoot. Other disadvantages to simple condylectomy
that have been reported include recurrence of deformity, joint instability with incongruous joint (Figure 9.5), and residual pain.¹⁷

Figure 9.3 Different presentations of the fifth toe, (A) claw toe, (B) supradductus, (C) infradductus.

Recurrence may be seen as the IMA is not decreased with isolated exostectomy, and a type 3 deformity or a splayfoot may develop. Weakening of the lateral capsular structures might also play a role in postoperative instability.

Metatarsal osteotomies are used to decrease the width of the forefoot and M5 head prominence. Several open M5 osteotomies have been described (oblique, transverse, chevron, crescentic, peg-in-hole, etc.), which can be grouped into proximal, diaphyseal, or distal. Although prospective, randomized, and comparative studies are lacking,¹⁸ the existing literature reveals that the outcome of metatarsal
osteotomies seems to be satisfactory. However, according to the only published meta-analysis of the M5 osteotomies,¹⁹ a relatively high degree of complications has been reported. An overall complication rate of 14% was found, 6% of them being major. Proximal and diaphyseal osteotomies have higher complication rate, respectively, 22% and 21%. Distal osteotomies have a complication rate of 11%.¹⁹ In this metaanalysis, percutaneous osteotomies were included as distal osteotomies.