Role of subtalar arthroereisis as adjunct procedure in treating stage IIb adult-acquired flatfoot deformity

A. Bernasconi, M. Argyropoulos, S. Patel, Y. Ghani, N. Phyo, N. Cullen, D. Singh, M. Welck

Background: The role of subtalar arthroereisis (STA) in surgical management of adult acquired flexible flatfoot deformity (AAFD) is controversial. Our aim was to determine whether STA as adjunct procedure improved radiographic correction of stage IIb AAFD focusing on the longitudinal medial arch and forefoot abduction. We also reported complications after STA.

Methods: All patients diagnosed with stage IIb AAFD treated by medialising calcaneal osteotomy, flexor digitorum longus transfer, spring ligament repair with or without Cotton osteotomy and STA between 2004 and 2019 were retrospectively reviewed. Seven measurements were recorded on pre and minimum 24-week postoperative weightbearing radiographs by two observers. Interobserver reliability was assessed. Univariate analysis was used to test the association of demographic (sex, side, age, BMI) and surgical variables (Cotton osteotomy and STA) with change in radiographic angles. Significant variables were included in a multivariable regression model. Twentytwo feet (21 patients, mean±SD age: 55.2±2.4 years) with a mean±SD radiographic follow-up of 11.2±1.2 months were investigated.

Results: There was excellent interobserver reliability for all parameters (ICC range, 0.75-0.94).
The addition of STA correlated with greater change in the talonavicular coverage angle (TNCA) (p=0.04) and calcaneus-fifth metatarsal angle (CFMA) (p=0.01), while Cotton osteotomy did not (p>0.05). Multivariate regression showed that STA was the only predictor of change in TFNA (p=0.03) and in CFMA (p=0.02). The final regression model demonstrated that STA was associated to a greater change in TNCA by 10.1 degrees and in CFMA by 5 degrees. Four (33%) patients complained of sinus tarsi pain, requiring removal of the implant with resolution of symptoms in three quarters of cases.

Conclusion: Subtalar arthroereisis as an adjunct procedure to medialising calcaneal osteotomy, flexor digitorum longus transfer, spring ligament repair in the treatment of stage IIb AAFD leads to improved forefoot abduction, measured through TNCA and CFMA.