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° (5.1°)) than in controls (88.4° (7.2°); 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.Ankle ligament injuries are the most common injuries in sport and recreational activities.¹ The anterior talar‐fibular ligament is affected in 85% of ankle sprains.^2,3,4 This type of injury represents a sprain with a major component in the sagittal plane.^5,6 This kind of injury is therefore best investigated using lateral views of the ankle, where the osseous containment of the talus in the tibia can be assessed. Although most of these ligamentous ankle injuries can be successfully treated with physical rehabilitation and non‐operative treatment, 20–40% of patients with ankle injuries develop chronic ankle instability (CAI) and experience recurrent sprains.^7,8,9,10 Many of these patients with CAI can be satisfactorily treated with reconstruction of the injured ligaments.^{3,11,12,13,14,15,16} However, good results of surgery and physical rehabilitation notwithstanding, some patients keep experiencing persistent symptomatic ankle instability^10,17 and have the propensity to develop post‐traumatic ligamentous ankle osteoarthritis.¹⁸The risk of spraining an ankle depends on both intrinsic factors (hindfoot alignment, ligament laxity, muscular force, neuromuscular control and so on) and extrinsic factors (shoes worn, type and intensity of sport, warm up and so on).^19,20,21 The shoulder, a rather unstable joint, is characterised by a humeral head that is large compared with the glenoid, whereas in the hip, a stable joint, the femoral head and the acetabulum are of equal size. This suggests that there is a relationship between joint stability and osseous joint configuration, but to date, the effect of the osseous configuration on the predisposition to develop CAI has not been investigated.The current study examines whether the osseous joint configuration of the ankle joint plays a role in the development of CAI. The hypotheses of this study were that (a) a flat talus, characterised in terms of a large radius, contributes to CAI; (b) a lack of restraint of the talus in the tibia, characterised in terms of a small tibiotalar coverage, contributes to CAI; and (c) a higher talar body with consequently more torque forces contributes to CAI.