Geometric analysis of indications for minimally invasive distal metatarsal osteotomy in treatment of hallux valgus.

Blaž Mavčič

doi:10.1186/s13018-015-0304-7

Abstract

BackgroundMinimally invasive distal metatarsal osteotomy (MIDMO) is to be indicated for all patients with angles of IMA <20° and HV <40°, but many authors doubt whether this procedure is capable of correcting all types of hallux valgus deformities. The aims of this study were to perform a geometric analysis of MIDMO indications and to show which preoperative radiological parameters are necessary to achieve sufficient contact between bone fragments and sufficient correction with this operative technique.MethodsA geometric mathematical model in AP and lateral radiographic plane was created based on preoperative measurements of the intermetatarsal angle (IMA), subcapital metatarsal width, medial bunion eminence, and metatarsal length. MIDMO was simulated with possible dorsal/plantar fragment displacement in order to assess postoperative contact between fragments (either 4–5 mm or half of the metatarsal width) and sufficient correction (postoperative IMA 8°).ResultsThe metatarsal neck should be at least 8 mm wider from the bunion eminence to achieve the minimally required contact between fragments. For sufficient correction, the metatarsal head translation should be at least 0.018 of the metatarsal length for every degree of IMA reduction. The medial bunion eminence, in comparison with metatarsal width/length size, determines whether MIDMO is a suitable procedure for a given patient.ConclusionsMIDMO cannot sufficiently correct all deformations within the boundaries of IMA angle <20° and HV angle <40°. In patients with large eminences and narrow metatarsals, complications related to insufficient postoperative fragment contact can be expected, while sufficient hallux valgus correction in patients with small eminences and long metatarsals is questionable.Electronic supplementary materialThe online version of this article (doi:10.1186/s13018-015-0304-7) contains supplementary material, which is available to authorized users.

Highlights

Invasive distal metatarsal osteotomy (MIDMO) is to be indicated for all patients with angles of intermetatarsal angle (IMA)
Invasive distal metatarsal osteotomy (MIDMO) for hallux valgus treatment was originally introduced by Bösch in 1990 [1, 2]; since several other authors have published their own modifications of the original technique [3,4,5,6,7]
Geometric analyses have been done for different types of distal metatarsal osteotomies [18,19,20,21,22], but these analyses were not specific for Minimally invasive distal metatarsal osteotomy (MIDMO) with perpendicular subcapital osteotomy, did not take into account the metatarsal length and dorsal/posterior displacement of the distal fragment [21], or were too complex to be used on larger numbers of patients in the clinical setting without 3D imaging [22]