Mechanical ankle instability is elicited through examination and imaging. A subset of patients however report “functional” instability ie/ instability without objective radiological evidence. Little research compares operative outcomes between these groups. We hypothesised patients with “mechanical instability” were more likely to benefit from operative intervention than those with “functional instability”.

This was a single centre, retrospective case note review of prospectively collected data. Inclusion criteria: over six months of symptoms, failed conservative management, surgical stabilisation between 2016–2018. Data collected: demographics, operative procedure, preoperative and postoperative PROMs.

Nineteen patients were included. All had preoperative MRIs determining ligamentous involvement. Nine had radiological evidence of instability, eight had negative radiographs. Two were excluded due to no intraoperative radiographs.

There was no statistical difference in preoperative MOxFQ scores between the groups (p=0.2039). Preoperative EQ5D-TTO scores were statistically different (mean mechanical 0.58 vs functional 0.26, p=0.0162) but not EQ5D-VAS scores (mean mechanical 77 vs functional 53, p=0.0806).

Mechanical group's preoperative, 26 and 52 week scores respectively: Mean MOxFQ= 57.88, 22.13, 18.5. Mean EQ5D-TTO= 0.58, 0.78, 0.84. EQ5D-VAS= 77, 82, 82.5.

Functional group's preoperative, 26 and 52 week scores respectively: Mean MOxFQ= 71.87, 37.75, 23. Mean EQ5D-TTO 0.26, 0.63, 0.76. EQ5D-VAS 53, 80, 88.

This trend of improvement in PROMs was not reflected in patient satisfaction scores. 75% of respondents in the functional group reported dissatisfaction at 26 weeks versus no dissatisfaction in the mechanical group. We should consider counselling patients accordingly when offering surgery.