The Transverse Forefoot Arch Demonstrated by a Novel X-ray Projection

Objective: Metatarsalgia is often treated by metatarsal osteotomy. Exact knowledge of the normal anatomy of the forefoot is essential for pre-operative planning. The objective of this study was to investigate the forefoot arch during maximal loading in a randomly selected population sample.

Methods: Two hundred subjects randomly selected from a municipality representative of Denmark were invited to interview and forefoot X-ray examination, including a novel horizontal X-ray projection by which the height of each metatarsal from the floor can be measured under maximal loading.

Results: One hundred and thirty-four subjects (79%) presented themselves for interview and X-ray examination. The study group was representative of the randomly selected population sample in terms of age, sex and incidence of metatarsalgia. The study verified that the interrelated geometry of the metatarsal heads in the AP plane corresponds to a parabola as suggested previously (Le Lièvre's parabola). Also in the horizontal plane, the metatarsal heads generally form an arch, the transverse forefoot arch (TFA). Mean height was 3.91mm (S.E.=0.10). The individual height of the TFA varied from -1 to 10mm and was dependent on the width of the forefoot. The relative height of the arch (arch height divided by forefoot width) was independent of age and sex. A non-significant tendency towards a lower arch among subjects with metatarsalgia was observed.

Conclusion: This population study demonstrated that the metatarsal heads constitute arches in both planes (Le Lièvre's parabola in the AP plane and the transverse forefoot arch in the horizontal plane). This knowledge is essential for pre-operative planning in metatarsal osteotomy for metatarsalgia. Formulae for calculating the individual location of each metatarsal head were obtained.