Brachymetatarsia is a congenital condition characterised by the abnormal shortening of the metatarsals due to the premature closure of the metatarsal epiphyseal growth plate, either unilaterally or bilaterally.
While any of the metatarsals could be affected by this condition, there is an increased incidence of brachymetatarsia affecting the fourth metatarsals of young women.
In their morphofunctional study of Brachymetatarsia of the fourth metatarsal, Martínez et al. categorise the aetiology of the condition as – acquired, associated congenital and idiopathic congenital.
Acquired aetiology involves the premature closure of the epiphyseal plate following trauma, a neurotrophic disorder or excessive exposure to x-rays. This could also be caused by improper surgical interventions or infections such as osteomyelitis, osteochondrosis or Freiberg’s infraction.
The authors describe associated congenital aetiology as the occurrence of this deformity in conjunction with chromosomal conditions such as Down’s syndrome or Turner’s syndrome, or diseases such as enchondromatosis and dystrophic dwarfism.
Considered to be the most frequent among the three aetiologies, idiopathic congenital could easily be linked to hereditary factors, as it was observed by the authors to be present in up to three members of the same family.
Brachymetatarsia causes metatarsodigital alterations in the forefoot such as the floating toe syndrome where the affected metatarsal remains shortened and dorsiflexed in comparison to the rest of the digits of the foot.
As a result of this excessive shortening, the other metatarsals appear deviated and undergo rotation and medial displacement, occupying the space left by the affected metatarsal and increasing its instability.
The affected toe loses its function and does not make ground contact during weightbearing because of weak plantar fascia insertion, articular capsule and retraction of the skin; this causes luxation of the fourth metatarsophalangeal articulation.
There is an overall impairment in the optimal displacement of weight in the foot in addition to soft tissue imbalance which can lead to metatarsalgia and callosities over the second and third metatarsal heads.
Treatment modalities for Brachymetatarsia should involve a combination of palliative care and supportive foot devices to correct uncompensated ankle equinus and to promote even distribution of pressure across the plantar surface of the foot through all stages of gait.
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Repetitive plantarflexion can lead to pain and mechanical limitation in the posterior ankle joint which is known as posterior ankle impingement syndrome. This pathology commonly occurs in ballet dancers and football players.