Acute Ankle Instability
Introduction
The ATFL, which is the weakest of the three lateral ankle ligaments, is involved in the majority of lateral ankle sprains; the CFL is involved in 50% to 75% of such injuries and the PTFL in less than 10%. Clinical assessment is based on the history of inversion and internal rotation of the foot. Examination is focussed on excluding the fracture and generally include swelling and localised tenderness on palpation. Imaging starts from plain radiographs of the ankle in acute injuries; stress radiographs are not helpful initially, and are painful to perform.
Be mindful of associated injuries: osteochondral lesions and peroneal tendon injuries.
Treatment
Initial treatment is usually non-operative:
- Treated sprains lead to a better outcome than untreated
- Immobilisation (splint, boot, or cast for 2-3 weeks)
- Rest, ice, compression, elevation, analgesia
- Physiotherapy
Studies have compared various braces with little long-term benefit of one over the other. In a systematic review, lace-up supports were found most effective, tapes were associated with skin irritation and elastic bandages were found least effective.
Functional recovery provides the best long-term outcomes; initial period of rest followed by a rehabilitation programme that comprises ROM exercises, strengthening, proprioception, and activity-specific training. Proprioceptive training programmes after an ankle sprain have shown effective prevention of recurrent episodes in athletes.
A Cochrane review comparing surgical versus non-surgical management of acute ankle sprains found that all available trials had methodological flaws and it was not possible to demonstrate a clearly superior management option based on the available pooled data.
Chronic Ankle Instability
Introduction
About 20% of acute ankle sprain patients develop chronic ankle instability; repeated episodes of instability that result in recurrent ankle sprains
Symptoms:
- persistent pain
- giving way
- recurrent sprains
- loss of confidence / apprehension
- avoidance of unpredictable ground e.g. cobbles
Chronic ankle instability can be:
- functional:
- patient-generated reports
- no structural laxity
- often due to sudden pain (e.g. impingement / loose body) causing muscle inhibition and sensation of 'giving way'
- mechanical:
- structural ligament defect or laxity
- confirmed on clinical examination
Examination:
- varus stress test
- anterior drawer test
- look for other contributory factors:
- hindfoot varus (sometimes subtle)
- plantar-flexed 1st ray
- midfoot cavus
- hypermobility
Investigations:
- Standing xrays
- MRI shows associated pathologies:
- chondral injury
- occult fractures
- bone bruising
- peri-articular tendon tears
- degeneration
- sinus tarsi injury
- impingement syndrome
The main signs of ligament injury on MRI scans are ligament swelling, discontinuity, a lax or wavy ligament, and non-visualisation.
Examination under anaesthesia (EUA) can also be helpful when comparing with the opposite side.
Treatment
- Always consider dedicated physio prior to any surgical consideration; balance, strength, proprioception; this may prevent progression to surgery, or help post-op recovery
- Indication for surgery in chronic instability is a failure of conservative management
- Differentiate between functional and mechanical ankle instability to guide the proper treatment
- Surgical techniques include anatomical and non-anatomical repairs
Anatomical repairs aim to:
- restore normal anatomy and joint mechanics
- seek to maintain movement of the ankle and subtalar joints
The most common anatomical repair is the Broström-Gould repair:
- mid-substance imbrication
- suture of the ruptured ends of the ligament
- augmented with the mobilised lateral portion of the extensor retinaculum attached to the fibula
- anatomic repairs have shown good or excellent results in 85% of patents
- arthroscopy is often routinely performed to identify and treat associated lesions
There has been a move towards augmentation of anatomical repairs with artificial adjuncts (e.g. Internal Brace™), particularly for revision procedures or for those at higher risk of recurrence.
Non-anatomical repairs are considered when the injured and attenuated ligament is not repairable. Local tendon or allograft can be used to restrict movement, but without repair of the injured ligaments and result in altered biomechanics.
Techniques include:
Evans:
- distally-attached peroneus brevis graft through an oblique posteriosuperior drill hole in the distal fibula
- does not replicate the ATFL or the CFL but lies in a position in between these two ligaments
Chrisman-Snook:
- a split peroneus brevis tendon graft (in order to maintain some function of PB)
- more closely approximates the ATFL and the CFL
*awaiting image upload*
A) Watson-Jones, B) Evans, C) Chrisman-Snook (reproduced from World Journal of Orthopaedics)
Arthroscopic repairs are also used and employ the reconstruction of autogenous plantaris tendon of the CFL and ATFL by using a 3-portal arthroscopic approach. For chronic ankle instability with no ligamentous repair, arthroscopic thermal capsular shrinkage has also been recommended.
Complications
- higher for non-anatomic repairs
- stiffness (common but well-tolerated)
- recurrent instability (look for varus heel / hyperlaxity)
- nerve issues
- degenerative disease
References