Chronic lateral ankle instability

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Chronic lateral ankle instability

Recurrent feeling of “giving way” sensations or instability.

Functional Instability – clinical syndrome in which the patient complains of giving way while physical and radiographic examination reveals a stable ankle.
Mechanical Instability - clinical syndrome in which the patient complains of giving way while physical and radiographic examination reveal an abnormal displacement of talus in ankle mortise.

Aetiology:
Mechanical instability:
• hypermobile ankle  increased risk for inversion sprains

Subtalar mechanical instability:
hypermobile STJ
calcaneofibular and interosseous ligaments in sinus tarsi may play a role
very difficult to distinguish from ankle instability
have normal finding on anterior draw test and talar tilt
increased talus/calcaneus joint space on AP view

Proprioceptive deficit:
• often can follow ligament and joint capsule trauma  affect muscular control of ankle

Central control:
• decreased central control may be a factor

Peroneal muscle weakness:
• may be secondary to adequate rehabilitation
• Tropp (1986) demonstrated that the was a peroneal weakness in those with functional instability of the ankle joint

Lateral deviated subtalar joint axis:
• If axis is lateral, the lever arm for ground reaction force to supinate he foot will be greater (Payne; Kirby) –
• The pronator muscles will have a shorter level arm and may be unable resist supinatory forces, the shorter lever arm would account for the muscle apparent muscle weakness demonstrated by Tropp (1986). The muscle may not be weak, they just have a short level arm to evert the foot or resist inversion.

Supinatory foot type:
• pes cavus, forefoot valgus with restricted midfoot ranges of motion, laterally deviated subtalar joint axis,

Low supination resistance:
• easy to supinate and sprain ankle
• associated with lateral deviated subtalar joint axis (peroneal muscles may not be weak, but may have poor lever arm to joint axis)

Management:
Conservative:
• proprioceptive exercise/neuromuscular control – tilt/wobble boards
• taping and bracing; ankle orthoses (eg Ritchie brace)

Surgical:
• usually involve a reconstruction in which another structure is used to replace or help the injured ligament

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