Evaluate heel aligment. Patients with hindfoot varus are at increased risk of recurrent instability / failure with operative and nonoperative treatment (Kuhn MA, Foot Ankle Int 2006;27:77).
Assess peroneal strength
Inversion stress test:
Anterior drawer test: the ankle is allowed to plantar-flex slightly, and an anterolateral rotatory force is applied to the heel. The talus will rotate anterolaterally as it slides forward due to the intact deltoid ligament; it will not displace forward if it is not allowed to rotate. Performed with the patient in the sitting position and the knee in flexion.
Document neurologic exam: recurrent inversion sprains may cause injury to branches of the superficial peroneal nerve with altered sensation or sensitivity in the anterolateral foot.
Recurrent instability characterized by: history of multiple ankle sprains, functional instability, pain, and difficulty walking on uneven ground.
Ankle Instability Xray / Diagnositc Tests
Complete radiographic examination = Lateral, mortise xrays of ankle and AP, lateral and oblique views of foot. Generally normal, evaluate for tibiotalar alignment, tibial marginal osteophytes, talar exostoses, osteochondral lesions of the talus, and os subfibulare lesions (avulsed bone fragment from the distal fibula consisting of the ATFL and CFL origins)
Consider stress xrays for chronic instability. Talar tilt angle 5 degrees greater than that of the normal side or an absolute value of 10 degrees = pathologic laxity. Talar tilt angle is the angle between the talar and tibial articular surfaces measured on the mortise view. Lateral stress views with forward translation of 3 mm more than the contralateral limb, or an absolute value of 10 mm indicates mechanical instability.
MRI: generally not indicated, except for chronic recurrent injury. Chronic injuries demonstrates: thickened (>3mm) ligaments, attenuation, abnormal signal intesity, retracted fibrosed ligaments). Anterior taolofibular ligament: best viewed in axial plane, generally bifasciculated. Calcaneofibular ligament: best seen in oblique axial or coronal images, deep to peroneal tendons
Ankle Instability Classification / Treatment
Grade I: Sprain of ATFL = mild swelling and tenderness, no instability.
Grade II: ATFL tear, CFL strain = moderate swelling and tenderness, moderate laxity with anterior drawer, normal talar tilt.
Grade III: ATFL and CFL complete rupture = severe swelling and tenderness, instability with anterior drawer and talar tilt.
Treatment= rest, ice, compression, and elevation (RICE) with early controlled motion in a functional Ankle Brace or cam walker. Physical therapy to improve proprioception and strengthening of the peroneal muscles. Functional bracing for strenuous/high risk activity.
A short period (10days) of immobilization in a below-knee cast or Aircast results in faster recovery than tubular compression bandage (Lamb SE, Lancet 2009;373:575).