84: Bunion and Bunionette

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CHAPTER 84

Bunion and Bunionette

David Wexler, MD, FRCS (Tr & Orth); Dawn M. Grosser, MD; Todd A. Kile, MD

Synonyms

Hallux valgus

Lateral deviation of the great toe

ICD-9 Codes

727.1  Bunion

727.1  Bunionette

735.0  Hallux valgus (acquired)

ICD-10 Codes

M20.10  Hallux valgus (acquired), unspecified foot

M20.11  Hallux valgus (acquired), right foot

M20.12  Hallux valgus (acquired), left foot

Bunion

Definition

The term bunion stems from the Latin word bunio, which means “turnip,” an image suggestive of an apparent growth or enlargement around the joint. The medical term for this is hallux valgus. There is no similar Latin term for the fifth toe, so a similar process involving the fifth metatarsophalangeal (MTP) joint is called a bunionette. Hallux valgus is a common deformity of the forefoot and the most common deformity of the first MTP, often causing pain (Figs. 84.1 and 84.2). The pathophysiologic process stems from both the proximal phalanx and the metatarsal bone. The proximal phalanx deviates laterally on the head of the first metatarsal, exacerbated by the pull of the adductor hallucis muscle. The lateral capsule becomes contracted, and the medial structures are attenuated. The metatarsal deviates medially, but the underlying sesamoids remain in their relationship to the second metatarsal, thus creating dissociation of the metatarsal-sesamoid complex. As these two processes occur together, the pull of the abductor hallucis moves more plantarward and the pull of the extensor tendon moves laterally, causing pronation and further lateral deviation of the great toe, respectively. As the metatarsal head becomes more uncovered, a prominent medial eminence, or bunion, is apparent. There is a bursa between the metatarsal head and the skin that may become inflamed and painful. Depending on the amount of axial rotation of the first metatarsal and pronation of the toe, the first ray becomes dysfunctional, leading to increased weight bearing on the more lateral metatarsal heads and “transfer metatarsalgia,” causing pain under the plantar aspect of the forefoot [1].

f84-01-9781455775774
FIGURE 84.1 Anatomy of a bunion.
f84-02-9781455775774
FIGURE 84.2 Clinical photograph demonstrating a bunion or hallux valgus deformity. Note also the pronation of the digit.

The etiology of hallux valgus is multifactorial and can be either intrinsic or extrinsic [2]. The intrinsic causes are essentially genetic and are related to hypermobility of the first ray (hallux metatarsal) at its articulation with the medial cuneiform. Ligamentous laxity (e.g., Marfan syndrome, Ehlers-Danlos syndrome) can lead to this deformity as well as to variations in the shape of the metatarsal head (i.e., a rounder head is less stable than a flat one). Another contributing factor is metatarsus primus varus, or medial deviation of the first metatarsal, which is thought to be associated with a juvenile bunion [3]. Pes planus and first metatarsal length have also been evaluated for their contribution to hallux valgus, but findings are equivocal [4].

The principal extrinsic cause is inappropriate, nonconforming footwear, with abnormal valgus forces creating deformity [5]. This is particularly notable in women who wear high-heeled shoes with narrow toe boxes. The ratio of hallux valgus between women and men has been reported to be 15:1 [6].

Symptoms

Presenting symptoms can vary. The patient may complain only of a painless prominent medial eminence. However, more commonly, there will be pain that is worse when constrictive shoes are worn and relieved by walking barefoot or with open-toed shoes. If there is significant arthritis, patients may have pain throughout range of motion of the MTP joint while walking. The bunion may become red and inflamed as the bursa enlarges and overlying skin becomes abraded by the shoe. The patient will have difficulty finding comfortable shoes. As the hallux deviates into increased valgus, it tends to impinge on the medial aspect of the pulp of the second toe, causing pressure and soreness [7].

Physical Examination

There is generally an obvious medial enlargement overlying the metatarsal head, with occasional signs of inflammation (bursitis). The great toe will be laterally deviated, and with progression of deformity, it will be pronated (axially rotated). There may be splaying of the forefoot and callosities visible under the metatarsal heads of the lesser toes. Metatarsalgia—tenderness under the metatarsal heads—may also be seen even without a callus. Passive extension of the hallux MTP joint will reveal possible limitation of range of motion (normally approximately 70 degrees). This may indicate concomitant degenerative joint disease of the MTP joint. Mobility of the hallux at the first metatarsal–medial cuneiform joint is assessed in relation to the second ray. Hammer toes are commonly noted as a consequence of the crowding in the shoe by the great toe. Depending on the patient’s medical history (e.g., diabetes), the neuromuscular evaluation is important to assess for any vibratory loss, two-point discrimination loss, or other indications of neurologic compromise. Otherwise, the neurologic examination findings should be normal.

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