Larger sagittal inter-screw distance/tibial width ratio reduces delayed union or non-union after arthroscopic ankle arthrodesis

Abstract

Background: Arthroscopic ankle arthrodesis (AAA) has risks of complications, such as delayed union and non-union. The number and direction of the inserted screws have been reported as important factors affecting the time to union of AAA. However, the ratio of inter-screw distance (ISD) to tibial width (TW) in different planes has not been investigated. Therefore, we aimed to explore the effect of this ratio on bone union following AAA.

Methods: We retrospectively enrolled 63 patients (64 ankles) undergoing AAA from 2013 to 2019. Then, their age, body mass index (BMI), sex, diabetes mellitus (DM) status, Takakura-Tanaka classification, number of screws and radiographic parameters were analysed.

Results: The patients had a mean age of 70.3 (range, 45-91) years. Bone fusion was achieved in 57 ankles (89%) in a mean period of 3.3 (range, 2-6) postoperative months. There were four cases of delayed union and three of non-union. No significant differences in age, BMI, sex, DM, Takakura-Tanaka classification, and number of screws could be detected between the groups. However, the sagittal ISD/TW ratio was significantly larger in the union group than in the delayed/non-union group with a cut-off value of 57.0%.

Conclusion: Larger sagittal ISD/TW ratios result in reduced post-AAA delayed union or non-union. The surgeon should be aware that the anterior and posterior screw widths should be approximately 60% or more of the anteroposterior width of the tibia.

Keywords: Arthroscopic ankle arthrodesis; Coronal ratio; Delayed union; Inter-screw distance; Non-union; Sagittal ratio; Tibial width.