Background:​ Very little objective data are available regarding medial ankle instability.

Hypothesis:​ Several structures contribute to the stabilization of the medial ankle, and, in the case of injury, they are not involved in a uniform way.

Study Design:​ Explorative, prospective case series.

Methods:​ Fifty-one patients (52 ankles;​ males 27, females 25;​ age 36.4 [16 to 60] years) were surgically treated because of medial ankle instability. All clinical findings and structural changes, as found by arthroscopy and surgical exploration, were compared with the clinical diagnosis and then addressed for surgical reconstruction.

Results:​ Pain in the medial gutter was noted in all ankles (100%). Arthroscopy verified a clinically expected additional lateral instability in 40 ankles (77%). At 4.43 years (2 to 6.5 years) after surgical reconstruction, the clinical result was considered to be good/excellent in 46 cases (90%), fair in 4 cases (8%), and poor in 1 case (2%).

Conclusion:​ The clinical characteristics of medial ankle instability are a feeling of giving way, pain on the medial gutter of the ankle, and a valgus and pronation deformity of the foot that can typically be actively corrected by the posterior tibial muscle. Arthroscopy was shown to be a very helpful diagnostic tool in verifying medial instability.