Background In 2015 a study of isolated lateral malleolar fractures (AO/OTA44-B1) treated at Sahlgrenska University hospital (SU) during two consecutive years revealed large-scale variation in the choice of treatment and planned follow-up. The study resulted in the development of a structured treatment algorithm (TA) for ankle fractures. We investigated the effects of this well-implemented TA on the classification, treatment and follow-up of lateral malleolar fractures. Methods The current study is an uncontrolled, non-randomized, retrospective before-and-after study comparing a group of AO/OTA44-B1 fractures treated at SU before the introduction of the TA for ankle fractures (1 April 2012 to 31 March 2014) with a group treated after the introduction of the TA (1 September 2017 to 31 August 2019). Results In all the studied parameters regarding treatment for AO/OTA44-B1 fractures, a statistically significant change was seen after the introduction of the TA. Surgical treatment reduced from 32% (95% CI 27.5 – 36.5) pre-TA to 10% (95% CI 6.9 – 13.1) post-TA, while the number of patients permitted full weight-bearing increased from 41% (95% CI 36.3 – 45.7) to 84% (95% CI 80.1 – 87.9). Conclusions A thoroughly implemented treatment algorithm can reduce the number of surgical treatments for stable ankle fractures. The current study demonstrates that a structured treatment algorithm can standardize the management of ankle fractures and make decisions less dependent on the surgeon’s discretion.