36. FLOATING FIRST METATARSAL: THREE CASES

Abstract

Purpose of the study: Bipolar dislocation of the first metatarsal, also called floating metatarsal, remains a rare traumatic injury of the first ray of the foot. This is an acute unstable post-traumatic metatarsophalangeal and cuneometatarsal injury occurring simultaneously or successively. Most earlier reports have been single case reports. We report here three successive cases in adults to study the mechanism of the injury, the clinical forms and the different therapeutic modalities.

Material and method: The patients were three males aged 35 years on average who presented a bipolar dislocation of the first metatarsal.

Results: The causal event was an automobile accident for two patients and a work accident for one. There was an open wound in two cases over the metatarsophalangeal joint. Orthopaedic metatarsophalangeal reduction was achieved in two cases and open cuneometarsal reduction in one. The cuneometatarsal reduction was maintained with a pin for six weeks. The auto-reduction was then continued.

Discussion: Described for the first time by English as a paired dislocation, in 1997 Liebner coined the term of a floating metatarsal. We were able to identify eight publications in the literature. The causal mechanism would be successive dislocation of themetatarsophalangeal joint first followed by the cuneometatarsal joint. The metatarsophalangeal dislocation was dorsal in two patients and lateral in one. The sesamoid girdle remained intact (Jahns 1) and in all cases followed the first phalanx in its displacement (Garcia Mata S+). The cuneometatarsal dislocation was dorsal in all cases. The skin opening involved the plantar surface in one case and was medial in the other, allowing externalisation of the first metatarsal head. The floating metatarsal was isolated in one case and associated with a fracture of the second metatarsal in two. Primary reduction of the metatarsophalangeal joint then the cuneometatarsal joint was achieved in all cases. Irreducibility due to a button effect was noted in one case. At minimum three months follow-up, there has been no evidence of deformity. The foot has remained pain free with correct shoe wearing. The control x-rays have not shown any subluxation.

Conclusion: The floating first metatarsal is an exceptional foot injury. Primary reduction of the metatarsophalangeal joint appears to be the rule. Adequate primary treatment ensures satisfactory outcome.