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
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