Scarf osteotomy for hallux valgus surgery: determining indications for an additional Akin osteotomy

INTRODUCTION: There is a lack of clear indications to carrying out an Akin osteotomy in addition to scarf osteotomy. Recent studies have shown that a proximal distal phalangeal articular angle (PDPAA) of > 8° as an indication to carrying out additional Akin osteotomy correlates with better radiological outcomes with lesser risk of recurrence. Our study aimed to validate carrying out the additional Akin osteotomy at a PDPAA > 8° while looking into functional outcomes which have not been studied. METHODS: Patients who underwent scarf and combined scarf and Akin osteotomy in our institutional registry was identified. Patient reported outcome measures were compared between patients who underwent scarf and combined scarf and Akin osteotomy. The Visual Analogue Scale (VAS), American Orthopedic Foot and Ankle Score (AOFAS), Short Form-36 Physical Component Score (PCS) and Mental Component Score (MCS) were measured pre-operatively and across a follow up period of 2 years. RESULTS: A total of 212 cases were identified. At a PDPAA > 8, there was no difference in VAS, AOFAS, PCS and MCS between patients that had isolated scarf osteotomy and those that received combined scarf and Akin osteotomy pre-operatively, and at 6 months. However, at 2 years post-operatively, patients that received scarf and Akin osteotomy had a significantly better AOFAS score as compared to patients with isolated scarf osteotomy (82.3 ± 15.3 vs 88.4 ± 13.0, p = 0.0224). On the contrary, at a PDPAA < 8, patients who underwent combined scarf and Akin osteotomy had a significantly lower VAS score at 6 months (1.16 ± 2.16 vs 0.321 ± 1.09, p = 0.00633) and 2 years (0.698 ± 1.73 vs 0.333 ± 1.46, p = 0.0466). They also had a higher AOFAS score at 6 months (80.7 ± 14.3 vs 85.4 ± 12.5, p = 0.0123) and 2 years (83.0 ± 14.0 vs 90.7 ± 9.9, p < 0.0001). CONCLUSION: PDPAA > 8° can serve as a valid indication to carrying out additional Akin on top of scarf osteotomy based on functional outcomes. However, further studies should investigate a PDPAA threshold that is lower than 8°, which can potentially allow more patients to receive the additional Akin osteotomy that can bring better functional outcomes.