First Metatarsal Rotation After Scarf Osteotomy for Hallux Valgus.

BACKGROUND: Recurrence after surgical correction of hallux valgus may be related to coronal rotation of the first metatarsal. The scarf osteotomy is a commonly used procedure for correcting hallux valgus but has limited ability to correct rotation. Using weight-bearing computed tomography (WBCT), we aimed to measure the coronal rotation of the first metatarsal before and after a scarf osteotomy, and correlate these to clinical outcome scores. METHODS: We retrospectively analyzed 16 feet (15 patients) who had a WBCT before and after scarf osteotomy for hallux valgus correction. On both scans, hallux valgus angle (HVA), intermetatarsal angle (IMA), and anteroposterior/lateral talus-first metatarsal angle were measured using digitally reconstructed radiographs. Metatarsal pronation angle (MPA), alpha angle, sesamoid rotation angle, and sesamoid position were measured on standardized coronal WBCT slices. Preoperative and postoperative (12 mo) clinical outcome scores (Manchester Oxford Foot Questionnaire and Visual Analogue Scores) were captured. RESULTS: Mean HVA was 28.6 ± 10.1° preoperatively and 12.1 ± 7.7° postoperatively (P < .001). Mean IMA was 13.7 ± 3.8° preoperatively and 7.5 ± 3.0° postoperatively (P < .001). Before and after surgery, there were no significant differences in MPA (11.4 ± 7.7 and 11.4 ± 9.9°, respectively; P = .75) or alpha angle (10.9 ± 8.0 and 10.7 ± 13.1°, respectively; P = .83). There were significant improvements in sesamoid rotation angle (SRA) (26.4 ± 10.2 and 15.7 ± 10.2°, respectively; P = .03) and sesamoid position (1.4 ± 1.0 and 0.6 ± 0.6, respectively; P = .04) after a scarf osteotomy. There were significant improvements in all outcome scores after surgery. Poorer outcome scores correlated with greater postoperative MPA and alpha angles (r = .76 (P = .02) and .67 (P = .03), respectively). CONCLUSION: A scarf osteotomy does not correct first metatarsal coronal rotation, and worse outcomes are linked to greater postoperative metatarsal rotation. Rotation of the metatarsal needs to be measured and considered when planning hallux valgus surgery. Further work was needed to compare postoperative outcomes with rotational osteotomies and modified Lapidus procedures when addressing rotation.Level of Evidence: 4.