3rd generation MICA with the "K-wires-first technique" - a step-by-step instruction and preliminary results.

Background: Minimally-invasive techniques for hallux valgus correction are becoming increasingly popular. In the last decades, multiple techniques for minimally-invasive hallux valgus correction have been described. MICA (Minimally-invasive Chevron & Akin), representing the 3rd generation of minimally-invasive hallux valgus correction, combines the advantages of an extraarticular osteotomy, stable internal fixation, and high potential for correction. This report aims to provide a step-by-step instruction of the surgical technique with the "K-wires-first" MICA modification, illustrated by detailed imaging of both intraoperative fluoroscopy and clinical imaging as well as corresponding sawbone models for each step. Preliminary results including radiological outcome and complications of the first 50 cases will be discussed.

Methods: Between May 2018 and May 2021, 50 consecutive MICAs in 47 patients were performed with the K-wires-first technique. There were 40 women and 7 men with an average of 57.4y (range 25-78). The mean preoperative IMA was 16.2° (range 11.0-21.5), the HVA 30.6° (range 21.8-42.1).

Results: There was one intraoperative conversion to an open surgical bunion correction corresponding to a 2% conversion rate respectively (1/50). On 3 feet (2 patients), removal of the Chevron screws was performed after 7, 9, and 12 months due to prominent and disturbing screw heads at the level of the medial cortex, accounting for a revision rate of 6% (3/50). There were no other secondary revision surgeries. The IMA decreased after MICA by a mean of 10.8° from 16.2° to 5.4° and the HVA by a mean of 22.1° from 30.6° to 8.5°, demonstrating MICA's high potential for correction.

Conclusions: Compared to other MICA techniques, the K-wires-first modification helps to reduce hardware malpositioning and the risk of conversion to open surgery. Furthermore, our preliminary results demonstrate a high potential for correction even for severe hallux deformities.

Trial Registration: Retrospectively registered, swissethics BASEC-ID 2021-01537, July 16th, 2021 ( www.raps.swissethics.ch ).