The effect of osseous ankle configuration on chronic ankle instability.

Background: Chronic ankle instability (CAI) is a common orthopaedic entity in sport. Although other risk factors have been studied extensively, little is known about how it is influenced by the osseous joint configuration.

Aim: To study the effect of osseous ankle configuration on CAI.

Design: Case-control study, level III.

Setting: Radiological examination with measurement of lateral x rays by an independent radiologist using a digital DICOM/PACS system.

Patients: A group of 52 patients who had had at least three recurrent sprains was compared with an age-matched and sex-matched control group of 52 healthy subjects.

Main Outcome Measures: The radius of the talar surface, the tibial coverage of the talus (tibiotalar sector) and the height of the talar body were measured.

Results: The talar radius was found to be larger in patients with CAI (21.2 (2.4) mm) than in controls (17.7 (1.9) mm; p<0.001, power >95%). The tibiotalar sector, representing the tibial coverage of the talus, was smaller in patients with CAI (80 degrees (5.1 degrees )) than in controls (88.4 degrees (7.2 degrees ); p<0.001, power >95%). No significant difference was observed in the height of the talar body between patients with CAI (28.8 (2.6) mm) and controls (27.5 (4.0) mm; p = 0.055).

Conclusion: CAI is associated with an unstable osseous joint configuration characterised by a larger radius of the talus and a smaller tibiotalar sector. There is evidence that a higher talus might also play some part, particularly in women.