Does First Metatarsal Head Lowering During Minimally Invasive Chevron Akin Osteotomy Yield No Significant Difference...

Hallux valgus is a common forefoot deformity that alters forefoot loading and often leads to secondary complications such as intractable plantar keratosis beneath the second metatarsal head. Although the link between hallux valgus and intractable plantar keratosis is recognized, whether two procedures that correct intractable plantar keratosis through different mechanisms-minimally invasive chevron Akin osteotomy (MICA) with first metatarsal head lowering and conventional MICA combined with second distal metatarsal minimally invasive osteotomy (DMMO)-have differential effects on symptom improvement has not, to our knowledge, been assessed.

(1) Do patients with hallux valgus and intractable plantar keratosis beneath the second metatarsal head have distinctive radiographic features compared with those with hallux valgus alone? (2) How do the two different surgical strategies (MICA with first metatarsal head lowering versus MICA with second DMMO) differ in terms of lesser metatarsal head height and intractable plantar keratosis resolution? (3) What are the differences in the Foot and Ankle Ability Measure (FAAM), including the subscales for activities of daily living (ADL) and sports, and other complications between these techniques?

Between January 2017 and June 2024, two surgeons treated 194 feet with hallux valgus using MICA after predefined exclusions. Of these, 113 feet did not have preoperative intractable plantar keratosis beneath the second metatarsal head; after excluding 13 feet without a minimum 1-year follow-up, 100 feet were included as a reference cohort. The remaining 81 feet had preoperative intractable plantar keratosis beneath the second metatarsal head and constituted the primary study cohort. Within this group, 34 feet underwent MICA with first metatarsal head lowering and 47 feet underwent MICA with second DMMO. From 2017 to 2020, MICA with second DMMO was routinely used for patients with intractable plantar keratosis beneath the second metatarsal head. Beginning in 2021, we gradually incorporated first metatarsal head lowering, and both procedures were used thereafter based on first-ray sagittal alignment, intraoperative loading patterns, and patient preference. After excluding feet without a minimum 1-year follow-up, 30 feet in the MICA with first metatarsal head lowering group and 42 feet in the MICA with second DMMO group were available for comparative analysis. There was no differential loss to follow-up between study groups for analysis in this retrospective study (12% [4 of 34] and 11% [5 of 47]). Follow-up completeness was comparable between groups, with similar mean ± SD follow-up durations (15 ± 3 months versus 17 ± 4 months). The study population had a mean age of 57 years and was predominantly female (approximately 90%), with comparable demographic characteristics between groups. To answer our first study question, we compared preoperative radiographic characteristics-including hallux valgus angle, first-to-second intermetatarsal angle, and the relative length and height of the lesser metatarsals-between patients with and without intractable plantar keratosis beneath the second metatarsal head. To address our second study question, we evaluated the changes in the relative height of the lesser metatarsals and postoperative resolution of intractable plantar keratosis following two different techniques. To answer our third study question, we compared the FAAM-ADL and sports scores and procedure-related complications between the two surgical techniques. All p values were adjusted using the Holm-Bonferroni method. Because some patients contributed bilateral feet, analyses were adjusted for the nonindependence of observations using a mixed-effects model with patient as a random effect; within-patient correlation was negligible, supporting inclusion of both feet in the analysis.

Patients with hallux valgus and intractable plantar keratosis beneath the second metatarsal head had a larger hallux valgus angle (mean ± SD 35° ± 8° versus 31° ± 8°, mean difference 4° [95% confidence interval (CI) 1° to 5°]; p < 0.001) and lower second (3 ± 2 mm versus 1 ± 2 mm, mean difference 2 mm [95% CI 1.5 to 2.7]; p < 0.001) and third metatarsal heads (4 ± 2 mm versus 2 ± 1 mm, mean difference 2 mm [95% CI 1.3 to 2.5]; p < 0.001) than those without intractable plantar keratosis. Both procedures resolved intractable plantar keratosis at similar percentages (87% [26 of 30] versus 91% [38 of 42], OR 0.7 [95% CI 0.2 to 3.0]; p = 0.71). However, MICA with first metatarsal head lowering elevated both the second (-2 mm [95% CI -4.2 to 0]) and third metatarsal heads (-2 mm [95% CI -3.8 to 0]), whereas MICA with second DMMO elevated the second (-2 mm [95% CI -4.7 to -0.1]) but lowered the third (1 mm [95% CI -0.4 to 2.4]), producing a between-group difference of 3 mm (95% CI 1.9 to 3.9; p < 0.001). Functional outcomes improved in both groups, but MICA with first metatarsal head lowering showed greater improvement in FAAM-sports scores (24% versus 21%, mean difference 3% [95% CI 2% to 7%]; p = 0.04). Postoperatively, MICA with second DMMO resulted in new intractable plantar keratosis beneath the third metatarsal head (10% [4 of 42]). In contrast, first metatarsal head lowering more frequently caused plantar discomfort beneath the first metatarsal head (17% [5 of 30]).

Accurate assessment of metatarsal height in the axial plane is essential when surgically treating hallux valgus with intractable plantar keratosis. Although both adjunctive procedures-first metatarsal head lowering and second DMMO-effectively improved intractable plantar keratosis, they differ in their corrective mechanisms and associated risks: adding only second DMMO may predispose patients to new keratosis beneath the third metatarsal head, whereas lowering the first metatarsal head may result in postoperative plantar discomfort beneath the first metatarsal head.

Level III, therapeutic study.