Causes / typical injury mechanism: Bunionette deformity, also known as tailor's bunion, is a bony deformity of the fifth metatarsal head on the lateral, dorsolateral, or plantar face. It is caused by bony abnormalities or biomechanical stress on the lateral face of the fifth metatarsal head, commonly from ill-fitting footwear. It presents as a painful and/or erythematous lateral prominence over the head of the fifth metatarsal and commonly presents bilaterally. Bunionette deformities are seen in adolescents and adults and are 2-4 times more common in women than men.

The most common causes of bunionette deformity are preexisting bony abnormalities or biomechanical stress. Bony abnormalities that contribute to bunionette deformity include a prominent metatarsal head (type 1, 16%-33%), lateral bowing of the metatarsal shaft (type 2, 10%), an increase in the fourth-fifth intermetatarsal angle (type 3, 57%-74%), and a combination of an enlarged metatarsal head and lateral bending of the shaft or increased intermetatarsal angle (type 4). Biomechanical stress of constrictive footwear causes most symptoms of bunionette deformity. Both the various anatomical variations and biomechanical stress can lead to hypertrophy of the tissue over the fifth metatarsal head, hyperkeratosis, and bursal thickening.

Classic history and presentation: A painful deformity of the lateral aspect of the fifth metatarsal head, often presenting as an erythematous, hyperkeratotic lesion. Pain associated with lateral pressure with footwear is a common complaint. Associated soft tissue keratosis, bursitis, and contractures can also trigger pain. Pes planus deformity or hallux valgus deformity may be noted on examination along with a bunionette deformity. Bunionette deformity is quite common among athletes, especially downhill skiers. Bilateral bunionette deformities are common.

Prevalence:

• Age – Adolescents and adults.
• Sex / gender – More common in women. Ratios range from 3:1 to 10:1.

Risk factors:

• Bony abnormalities, including a prominent fifth metatarsal head, lateral bend of the fifth metatarsal shaft, increased fourth-fifth intermetatarsal angle, splay foot deformity, and congenitally plantarflexed or dorsiflexed metatarsals, put patients at risk for bunionette deformity.
• Coexisting plantar callosity due to a plantarflexed fifth metatarsal shaft can cause metatarsalgia.
• Ankle and hindfoot deformities like flat-foot deformity can exacerbate the risk of bunionette deformity.

Pathophysiology: Frequent pressure and irritation on the lateral border of the foot, often from ill-fitting footwear and/or bony abnormalities, causes thickening or inflammation of the bursa overlying the fifth metatarsal head and may increase the symptoms.

Grade / classification system: 

Classifications of anatomical anomalies that lead to bunionette deformity include:

• Type 1 – Prominent fifth metatarsal head
• Type 2 – Lateral bowing of the fifth metatarsal shaft
• Type 3 – Increase in the fourth-fifth intermetatarsal angle
• Type 4 – Combination of an enlarged fifth metatarsal head and lateral bending of the fifth metatarsal shaft