Double versus triple arthrodesis for adult-acquired flatfoot deformity due to stage III posterior tibial tendon insufficiency: a prospective comparative study of two cohorts

PURPOSE: The study aims to prospectively compare double and triple arthrodesis in terms of functional outcomes and deformity correction. To the best of our knowledge, this is the first prospective comparative study in the literature to date. METHODS: This is a prospective comparative cohort study carried out between May 2017 and May 2019. The study was approved by the IRB at Assiut University and done according to the Helsinki declaration. Patients with AAFD stage III aged between 15 and 40 years old were assigned to double arthrodesis or triple arthrodesis. The groups were prospectively followed for one year. Primary outcomes were union rates, AOFAS scores, and radiological parameters of deformity correction on AP and lateral plain radiographs. Secondary outcomes were operative time, time to union, and complications. The double arthrodesis was done through the medial approach, while the triple arthrodesis was done through dual medial and lateral approaches. The post-operative protocol was standardized for both groups. RESULTS: A total of twenty-three patients matched the inclusion criteria and provided their consent to participate in the study. Thirteen (all males) patients underwent double arthrodesis, while ten (nine males and one female) patients underwent triple arthrodesis. The mean age for double and triple arthrodesis was 20.15 ± 5.63 and 25.10 ± 8.36 years, respectively, and the mean follow-up lengths were 12.46 and 12.9 months, respectively. There were no statistically significant differences between both groups in age, gender, laterality, or duration of follow-up. There were no statistically significant differences between both groups in AOFAS hindfoot scores or radiographic parameters. All patients were available for the final follow-up evaluation. All patients in both groups achieved union by four months post-operatively. The mean time to union in the double and triple arthrodesis groups was 3.39 ± 0.65 vs. 3.31 ± 0.6 months, respectively, with no statistically significant differences (p = 0.77). The mean operative time was significantly shorter in the double arthrodesis group than the triple arthrodesis group, 55.77 ± 15.18 vs. 91.6 ± 24.14 min (p < 0.001), respectively. Both double and triple arthrodesis groups had a statistically significant improvement of the mean AOFAS hindfoot score post-operatively (71.46 ± 7.77 vs. 88.38 ± 3.66, p < 0.001) and (66.9 ± 7.69 vs. 85 ± 5.83, p < 0.001), respectively. In the double arthrodesis group, the mean calcaneal pitch angle increased from 11.46° pre-operatively to 19.34° (MD = 8.45°, p < 0.001). The mean Meary’s angle improved from − 4.19 to 2.9° (MD = 7.32°, p < 0.001). Hibbs angle had a mean reduction of 6.45° post-operatively (p = 0.069). In the triple arthrodesis group, the mean calcaneal pitch angle improved from 10.06° pre-operatively to 17.49° post-operatively (MD = 7.12°, p < 0.001). The mean Meary’s angle improved from − 4.72 to 2.29° (MD = 7.09°, p < 0.001). The mean Hibbs angle decreased from 153.07 to 142.32° (MD = 10.54°, p < 0.001). The double vs. triple arthrodesis groups had no statistically significant differences in AOFAS hindfoot score improvement (16.92 vs. 19.1, p = 0.44), respectively. The two groups had no statistically significant differences in the magnitude of correction of all the radiographic parameters. CONCLUSION: Double arthrodesis is an equally reliable surgical option for AAFD stage III for achieving union, improving the functional outcomes, and deformity correction as triple arthrodesis with a significantly shorter operative time in the former. The authors recommend double arthrodesis if the calcaneocuboid joint is unaffected.