Background
Minimally invasive distal metatarsal osteotomy (MIDMO) [
1‐
6] is to be indicated for all patients with angles of IMA <20° and HV <40° [
7‐
13], but many authors doubt whether this procedure is capable of correcting all types of hallux valgus deformities [
14‐
17]. Minimally, invasive distal metatarsal osteotomy (MIDMO) for hallux valgus treatment was originally introduced by Bösch in 1990 [
1,
2]; since then, several other authors have published their own modifications of the original technique [
3‐
7]. The common features of above techniques include subcapital osteotomy of the first metatarsal, lateral translation of the head, and blocking the head with a K-wire inserted proximally into the medullary canal of the first metatarsal. Many surgeons continue to use the MIDMO method, and studies from various independent sources report good to excellent results [
8‐
13] due to the small incision required, as well as less postoperative pain and wound healing problems [
5]. However, contrary reports tend to emphasize that MIDMO is not capable of correcting all types of hallux valgus deformities [
14]. No randomized studies in this field have been reported [
15]. Past studies underreported rates of complications (malunion, nonunion, and osteonecrosis) and recurrence, and the overall cost-effectiveness is unclear [
16,
17].
Both authors who report good clinical results and the authors who criticize the use of the MIDMO have thus far been using unchanged indications of the procedure as outlined by the original authors (IMA angle <20° and HV angle <40°) [
3‐
6]. Geometric analyses have been done for different types of distal metatarsal osteotomies [
18‐
22], but these analyses were not specific for 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]. MIDMO significantly differs from other distal osteotomy techniques, because it retains the medial bunion eminence, and the amount of contact and correction is invariably defined by the operative technique itself. Since lateral translation is driven by the K-wire insertion into the first metatarsal canal, the operative technique enables only one possible magnitude of the metatarsal head lateral translation with slight variations in the osteotomy inclination and dorsal or posterior displacement of the distal fragment [
3‐
6]. Thus, the geometric analyses published thus far are not suitable to answer the two important questions before the surgeon even considers using MIDMO in a given patient: (1) Will the given metatarsal head lateral translation with this technique result in sufficient contact between osteotomy fragments? (2) Will the given metatarsal head lateral translation result in sufficient hallux valgus correction with this technique? These two questions cannot be answered with the criteria of “IMA angle <20° and HV angle <40°” [
1‐
6] alone; thus far, there have there been no other specific epidemiological studies published to show which patients will benefit from MIDMO.
The aims of this study were to perform a geometric analysis of the indications for MIDMO in the treatment of hallux valgus and, thereby, to show which preoperative radiographic parameters are necessary to achieve sufficient contact between fragments and sufficient correction with this operative technique.
Conclusions
Minimally invasive distal metatarsal osteotomy (MIDMO) cannot sufficiently correct all deformations within the boundaries of IMA angle <20° and HV angle <40°. The presented study quantitatively shows how the size of the medial bunion eminence determines whether MIDMO is suitable for a given patient: in patients with large eminences and narrow metatarsals, complications related to insufficient postoperative contact between fragments (pseudoarthrosis, fragment displacement) can be expected, while in patients with small eminences and long metatarsals, the expected complications would be related to insufficient hallux valgus correction (persistent pain, early recurrence). The presented geometric analysis can be a useful preoperative planning tool to aid in deciding which patients will benefit most from MIDMO and to assess the possible causes of failed surgery.
Availability of supporting data
All computations described within this paper can be performed with the attached freeware computer program (.XLS file) Additional file
1.
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Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
BM performed all mathematical analyses, literature search, wrote the entire article, and created all tables/figures.