Osteotomies through the diaphysis of the first metatarsal are normally done in a horizontal or oblique plane which produces a large healing surface. The osteotomy is also at or near right angles to ground reaction force, so weightbearing can compress the osteotomy if the configuration is basically stable.
Being more proximal, it is possible to achieve greater correction of the intermetatarsal angle with a diaphyseal osteotomy, but as correction is with lateral displacement and contact needs to be maintained throughout the length, less correction is obtained than with a proximal osteotomy. Hybrid diaphyseal/proximal osteotomies, such as the rotational scarf and Ludloff, aim to get the best of both worlds.
The long osteotomy permits controlled shortening to reduce the 1st MTP joint without tension, and an angled cut allows controlled depression of the metatarsal head to offset shortening.
The long osteotomy requires a large exposure and periosteal elevation. This, together with the position in cortical bone, has the potential for long times to union, although this does not seem to be a problem in reported series