Ankle Instability

Ligamentous Stabilisers of the Ankle

Lateral Ligaments

• ATFL – Primary restraint to anterior translation, especially if foot not plantigrade
• CFL – Restraint to varus force – lies deep to peronei
• PTFL – Strongest and least ruptured of the three lateral ligaments
• SPR – At level of lateral malleolus – rupture = peroneal instability
• IPR – Continuation of IER, stabilises peronei distally
• IER – Y-shaped, vertical limb crosses ankle & STJ – weak stabiliser
• AITFL – Stabilises inferior tibiofibular joint – most commonly injured
• PITFL – Stronger than AITFL and less commonly injured
• IOTFL – Proximal extent is IOM

Talocalcaneal Ligaments

• Lateral, interosseus, and cervical – stabilise talus in and around sinus tarsi

Deltoid Ligament

• Superficial – Fan-shaped, attaching to navicular, calcaneus, and talus
• Deep – More important for stability, attaches only to talus

Spring Ligament

• Runs under sustentaculum from calcaneus to navicular like a sling
• Has superior & inferior portions
• Supports TNJ and medial arch

Posterior Structures

• Intermalleolar Ligament – Between malleoli at level of joint
• PITFL – Strongest stabiliser of the syndesmosis, least frequently torn
• PTFL – Lies on posterior aspect, rarely injured
• Posterior Talar Tubercle – If fails to ossify, forms an Os Trigonum, can impinge

Ankle Movements

• Axis of motion is between malleoli – oblique
• Ankle is most stable on axial loading and plantigrade – congruent bones
• On dorsiflexion:
  • Fibula externally rotates 11 degrees & moves slightly proximal
  • To accommodate wedge-shaped talus and oblique axis

Classification of Instability

• Most useful classification:
  • Functional Instability – Feeling of giving way or actual giving way but with no clinical laxity
  • Mechanical Instability – Clinically reproducible laxity – may or may not be symptomatic

Risk Factors for Instability

Hindfoot Varus

• Most important predisposing factor for recurrent lateral instability
• Main cause of surgical failure is not recognising varus

Equinus

• Inability to get foot plantigrade means ATFL is constantly working
• Can lead to chronic rupture or incompetence

Hindfoot Valgus

• Less common than varus but can cause chronic medial instability

Other Risk Factors

• Pivoting Sports
• Obesity
• Hyperlaxity

Clinical Features

History

• Acute, chronic, or acute on chronic
• What actually happens on giving way?
• Number of episodes
• Are they painful?
• Treatment history
• Symptoms:
  • Locking, clicking, or giving way
  • Global hyperlaxity

Examination

• Beighton’s Score – for hyperlaxity
• Screen for deformity – varus, valgus, or equinus
• Passive ROM – is there pain or stiffness?
• Palpation – lateral, medial & syndesmotic ligaments for pain
• Joint line pain – synovitis from chronic impingement
• Evidence of peroneal subluxation

Special Tests

• Anterior Draw – Tests ATFL
  • 30° plantar flexion, fix tibia, and draw hindfoot forward
  • Positive if sulcus appears or more laxity than the other side
• Tilt Test – Primarily for lateral laxity
  • Ankle plantigrade, STJ locked, apply varus stress
  • Valgus stress will test medial structures
• Syndesmosis Stability
  • Squeeze Test – Useful in acute injuries, pain over AITFL
  • External Rotation Test – More useful in chronic injury
    • Foot plantigrade, hanging off couch, knee flexed
    • Fix tibia and externally rotate foot
    • Positive if increased rotation or pain → impingement

Imaging

X-Ray (XR)

• Standing AP and Lateral Views – Show mortise reduction
• Stress Views – May be useful
• Plain X-rays miss 50% of OCDs

MRI

• Indicated in:
  • Non-recovering ankle sprains at 4-8 weeks
  • Chronic instability cases with pain → may have OC lesion
• Arthrogram – Probably better than plain MRI

Management

Acute Injuries & Instability

• No evidence to support acute ligament repair over non-operative treatment
• Evidence-based approach:

Minor Stable Sprains

• RICE, early weight-bearing (WB), and ROM

Severe Stable Sprains

• Physiotherapy – muscle rehab and proprioceptive training

Severe Unstable Sprains

• Diagnosed by a clinician
• Supportive brace + early WB with physiotherapy
• MRI if no improvement after 4-6 weeks to rule out OCD

Chronic Instability

• Patients with functional instability often improve with arthroscopy
  • Instability often due to intra-articular pathology
• Patients with true mechanical instability can be offered stabilisation

Good Practice Approach

1. Perform Examination Under Anaesthesia (EUA)
2. Arthroscopy – improves many cases
3. If no improvement & mechanical instability → Stabilisation Procedure

Stabilisation Procedures

Brostrum (with Gould Modification)

• Direct repair of ATFL and CFL
• Techniques:
  • End-to-end repair or anchors depending on ligament tear location
• Gould Modification:
  • Reinforces with part of the inferior retinaculum
• Advantages:
  • Very good, reproducible long-term result
  • Preferred as it is an anatomic repair

Non-Anatomic Repairs

• Examples: Evans, Watson Jones, or Sammarco (actually anatomic)
• Indications:
  • Insufficient ligamentous tissue for Brostrum
  • More robust repair required:
    • Varus hindfoot
    • Severe instability
    • High-demand patient needing stability at the expense of flexibility
    • Ligamentous laxity (try to avoid surgery in this group)
• Techniques:
  • Splitting Peroneus Brevis
  • Re-rooting the tendon around talus, fibula, and calcaneus
  • Uses anchors or drill holes
• Outcomes:
  • Good results
  • Robust
  • Not as anatomic as Brostrum – may alter ankle kinematics and stiffen