CHRONIC ANKLE INSTABILITY
ATFL Primary | CFL Secondary | Mechanical + Functional
Types of Instability
Critical Must-Knows
- ATFL is weakest and most commonly injured lateral ligament
- CFL is EXTRA-ARTICULAR - injured with increasing inversion force
- Anterior drawer tests ATFL; Talar tilt tests CFL
- Conservative treatment fails in 20-40% of patients
- Brostrom-Gould is gold standard surgical treatment
Examiner's Pearls
- "ATFL: resists anterolateral translation in plantarflexion
- "CFL: resists inversion throughout ROM (crosses subtalar joint)
- "Functional instability = proprioceptive deficit, peroneal weakness
- "Always exclude subtalar instability and OLT
Clinical Imaging
Imaging Gallery
Critical Chronic Ankle Instability Exam Points
Anatomy is Key
ATFL (anterior talofibular): weakest lateral ligament, taut in plantarflexion, resists anterior translation. CFL (calcaneofibular): extra-articular, taut in dorsiflexion, crosses subtalar joint. PTFL: rarely injured, strongest lateral ligament.
Distinguish Instability Types
Mechanical instability = true laxity (positive anterior drawer greater than 10mm, talar tilt greater than 10 degrees). Functional instability = giving way without laxity (proprioceptive deficit, peroneal weakness). Both types can coexist.
Examination
Anterior drawer (ATFL): 90 degrees knee flexion, ankle neutral, translate talus anteriorly. Talar tilt (CFL): invert hindfoot, compare to contralateral. Compare side-to-side - absolute values less reliable.
Surgical Decision
Brostrom-Gould = anatomic repair + IER reinforcement (first line). Non-anatomic reconstruction (tenodesis) for revision, generalized laxity, or poor tissue. Graft reconstruction increasingly popular.
Quick Decision Guide
| Presentation | Examination | Imaging | Management |
|---|---|---|---|
| Giving way, no objective laxity | Normal drawer/tilt, weak peroneals | XR normal, consider MRI | 6 months proprioceptive rehab |
| Recurrent sprains, mild laxity | Positive drawer, minimal tilt | Stress XR equivocal | Trial bracing + rehab first |
| Frequent giving way, clear laxity | Positive drawer AND tilt | Stress XR positive | Surgical stabilization |
| Previous failed surgery | Positive exam, generalized laxity | MRI shows tissue quality | Graft reconstruction |
ACPLateral Ligament Complex
Memory Hook:ACP = Anterior is weakest, Calcaneofibular is Central, Posterior is strongest!
PROPSCauses of Functional Instability
Memory Hook:PROPS support the ankle - without them, it gives way!
BGTSurgical Options
Memory Hook:BGT = Brostrom is Gold standard, Tenodesis for revisions!
Overview and Epidemiology
Chronic ankle instability (CAI) develops in 20-40% of patients following lateral ankle sprain. It is characterized by recurrent ankle sprains, episodes of giving way, and persistent symptoms lasting greater than 12 months despite conservative treatment. Athletes and active individuals are at highest risk.
Why Does Instability Develop?
Multifactorial: (1) Incomplete ligament healing with elongation/attenuation, (2) Proprioceptive deficit from mechanoreceptor damage, (3) Peroneal muscle weakness, (4) Altered neuromuscular control. Both mechanical and functional factors contribute.
Risk Factors
- Previous ankle sprain (strongest predictor)
- Inadequate initial treatment/rehab
- High-demand sports (basketball, soccer)
- Generalized ligamentous laxity
- Cavovarus foot alignment
Associated Conditions
- Osteochondral lesions of talus (15-25%)
- Subtalar instability
- Peroneal tendon pathology
- Anterior/posterior impingement
- Syndesmotic injury
Pathophysiology and Mechanisms
Critical Anatomy
The lateral ligament complex consists of three ligaments. The ATFL originates from anterior fibula and inserts on lateral talar body - it is the primary restraint against anterior translation in plantarflexion. The CFL is extra-articular, crosses the subtalar joint, and resists inversion throughout ROM.
Lateral Ankle Ligaments
| Ligament | Origin | Insertion | Injury Frequency | Function |
|---|---|---|---|---|
| ATFL | Anterior distal fibula | Lateral talar body | 85% (most common) | Resists anterior translation in PF |
| CFL | Distal fibula tip | Lateral calcaneus | 50-75% combined | Resists inversion, crosses STJ |
| PTFL | Posterior fibula | Posterior talus | Rare (5%) | Resists posterior translation in DF |
ATFL Biomechanics
ATFL taut in plantarflexion - this is why most ankle sprains occur with plantarflexion-inversion mechanism. ATFL provides 100% of resistance to anterior talar translation at 15 degrees plantarflexion. Sectioning ATFL increases anterior drawer by 4-5mm.
ATFL Details
- Length: 15-20mm, width: 7-8mm
- Weakest lateral ligament
- Intra-articular structure
- 3 distinct bands described
- Mean load to failure: 139N
CFL Details
- Length: 20-25mm, cord-like
- Extra-articular (key exam point)
- Crosses subtalar joint
- Overlapped by peroneal tendons
- Mean load to failure: 310N
Classification Systems
Mechanical vs Functional Classification
| Type | Definition | Examination | Treatment Focus |
|---|---|---|---|
| Mechanical | True ligamentous laxity | Positive drawer/tilt, stress XR abnormal | Surgical stabilization |
| Functional | Giving way without laxity | Normal exam, proprioceptive deficit | Proprioceptive rehabilitation |
| Combined | Both mechanical and functional | Laxity + neuromuscular deficit | Surgery + comprehensive rehab |
Clinical Significance
Functional instability can exist without mechanical laxity and responds well to rehabilitation. Mechanical instability requires structural restoration. Most patients with CAI have elements of both, requiring comprehensive management.
Classification guides treatment approach and rehabilitation focus.
Clinical Assessment
History
- Mechanism: Index injury and subsequent events
- Symptoms: Giving way, swelling, pain, difficulty on uneven ground
- Sports/Activity level: Demands and expectations
- Previous treatment: Bracing, rehab, surgery
Examination
- Inspection: Swelling, alignment (cavovarus)
- Palpation: ATFL, CFL, peroneal tendons, sinus tarsi
- ROM: Ankle and subtalar joint
- Stress tests: Anterior drawer, talar tilt
Complete Examination Required
Always assess: subtalar instability (Broden stress), peroneal tendon integrity (subluxation, tears), generalized ligamentous laxity (Beighton score), hindfoot alignment (cavovarus = higher recurrence), and contralateral ankle for comparison.
Clinical Tests for Lateral Ankle Instability
| Test | Technique | Positive Finding | Structure Tested |
|---|---|---|---|
| Anterior drawer | Stabilize tibia, translate talus anteriorly | Greater than 10mm or greater than 3mm vs contralateral | ATFL |
| Talar tilt | Stabilize tibia, invert hindfoot | Greater than 10 degrees or greater than 5 degrees asymmetry | CFL (+ ATFL if positive) |
| Inversion stress | Maximal inversion with ankle neutral | Pain, apprehension, increased motion | Lateral ligament complex |
| Peroneal test | Resist eversion, check for subluxation | Weakness, subluxation over malleolus | Peroneal tendons |
Comparison is Key
Absolute values are unreliable due to normal variability. Always compare to contralateral ankle. Asymmetry greater than 3mm (drawer) or greater than 5 degrees (tilt) is more significant than absolute measurements. Examine both ankles in the same position.
Investigations
Imaging Protocol
AP, lateral, and mortise views. Assess for malalignment, OLT, talar dome changes, arthritis. Weight-bearing views essential for alignment assessment. Often normal in isolated ligament injury.
Anterior drawer stress (Telos device) and inversion stress views. Quantify mechanical instability. Drawer greater than 10mm or tilt greater than 10 degrees (or asymmetry greater than 3mm/5 degrees) indicates instability.
Assess ligament quality, associated lesions (OLT, peroneal pathology, impingement), and tissue quality for surgical planning. Identifies chronic ligament changes (thickening, discontinuity, scarring).
Stress Radiograph Thresholds
Anterior drawer: greater than 10mm absolute or greater than 3mm asymmetry = ATFL incompetent. Talar tilt: greater than 10 degrees absolute or greater than 5 degrees asymmetry = ATFL + CFL involved. Always compare to uninjured side.
Radiographic Findings
- Stress XR: Quantify laxity
- Standard XR: Alignment, OLT, arthritis
- Broden stress: Subtalar instability
- Hindfoot alignment view: Cavovarus
MRI Findings
- ATFL: Thickened, attenuated, absent
- CFL: Integrity, scarring
- OLT: Location, size, stability
- Peroneal tendons: Tears, subluxation
Management Algorithm
Non-Operative Management Protocol
Goal: Restore proprioception, strength, and neuromuscular control.
Rehabilitation Phases
Acute management: RICE for any acute exacerbations. Ankle bracing for activity. Begin ROM exercises. Initiate proprioceptive training (single leg stance, wobble board).
Strengthening and proprioception: Progressive peroneal strengthening. Balance training progression. Sport-specific agility introduction. Continue bracing for activity.
Return to activity: Graduated return to sport. Continue proprioceptive maintenance. Brace use as needed. Monitor for recurrent symptoms.
Conservative Success Factors
60-80% success rate with comprehensive rehabilitation. Better outcomes with: functional instability only, good compliance, lower demands, and adequate peroneal strength. Failure indicators: mechanical laxity, cavovarus foot, high-demand athlete.
Minimum 6 months of supervised rehabilitation before considering surgery.
Surgical Technique
Modified Brostrom Procedure (Gold Standard)
Surgical Steps
Lateral decubitus or supine with bump. Thigh tourniquet. Mark landmarks: lateral malleolus, ATFL course, peroneal tendons, sinus tarsi.
Curvilinear incision anterior and distal to lateral malleolus (following ATFL). Identify and protect superficial peroneal nerve branches. Incise IER (inferior extensor retinaculum).
Identify ATFL (often attenuated, scarred). Assess CFL through same incision or separate distal limb. Evaluate tissue quality for repair vs reconstruction decision.
Incise ATFL capsule longitudinally at its talar attachment. Prepare fibular footprint with decortication. Pass suture anchors (2-3) into anterior fibula. Pants-over-vest imbrication of ATFL with ankle in neutral.
Key step: Advance IER (inferior extensor retinaculum) over ATFL repair and secure to fibula with sutures. This provides critical reinforcement and limits anterior translation.
If CFL involved, extend incision distally. Repair CFL to calcaneus with suture anchor or directly if tissue quality permits. Tension with ankle in neutral to slight eversion.
Technical Pearls
Tension repair with ankle in neutral - avoid over-tightening (causes stiffness) or under-tightening (recurrence). IER augmentation (Gould) is critical for improved outcomes. Consider arthroscopy first for OLT assessment and treatment.
Post-repair immobilization in walking boot for 2-4 weeks, then progressive weight-bearing and rehabilitation.
Complications
Potential Complications
| Complication | Risk Factors | Prevention | Management |
|---|---|---|---|
| Recurrent instability | Poor tissue quality, cavovarus, non-compliance | Proper patient selection, address alignment | Revision reconstruction with graft |
| Stiffness | Over-tensioning, prolonged immobilization | Appropriate tensioning, early ROM | Physiotherapy, possible MUA |
| Superficial peroneal nerve injury | Surgical approach | Careful dissection, identify nerve | Observation, most resolve |
| Wound complications | Diabetes, obesity, smoking | Meticulous technique, optimize health | Wound care, possible debridement |
| Subtalar stiffness (tenodesis) | Non-anatomic procedures | Use anatomic techniques | PT, accept some limitation |
Recurrence Risk Factors
Higher recurrence with: cavovarus foot (address surgically if significant), generalized ligamentous laxity (use graft augmentation), poor rehabilitation compliance, return to high-demand sport too early. Recurrence rate 5-15% even with modern techniques.
Cavovarus Foot
Cavovarus alignment places lateral ligaments at increased stress. If significant hindfoot varus present, consider calcaneal osteotomy (Dwyer) at time of ligament reconstruction to correct alignment and reduce recurrence risk.
Postoperative Care
Rehabilitation Protocol
Immobilization: Below-knee cast or controlled motion boot. Non-weight-bearing initially. Elevate, ice, wound care. Begin toe/knee ROM to prevent stiffness.
Protected mobilization: CAM boot weight-bearing as tolerated. Begin ankle ROM exercises out of boot. Avoid inversion initially. Start isometric strengthening.
Progressive loading: Wean from boot to supportive footwear. Progressive resistance training. Proprioception exercises. Gait training, stationary bike.
Return to activity: Sport-specific drills. Agility and plyometric progression. Criteria-based return to sport. Consider bracing for return.
Return Criteria
- Greater than 90% strength vs contralateral
- Full ROM without pain
- Passed functional hop tests
- Sport-specific drills tolerated
- Typically 4-6 months post-op
Bracing Post-Surgery
- Consider brace for first 6-12 months of sport
- May use permanently for high-demand activities
- Ankle support reduces re-injury risk
- Transition to tape if preferred
Outcomes and Prognosis
Outcomes by Procedure
| Procedure | Success Rate | Recurrence | Return to Sport |
|---|---|---|---|
| Brostrom-Gould (primary) | 85-95% | 5-10% | 85-90% |
| Anatomic graft reconstruction | 80-90% | 5-15% | 80-85% |
| Non-anatomic tenodesis | 70-80% | 10-20% | 70-80% |
| Revision surgery | 70-85% | 15-25% | 70-80% |
Long-Term Outcomes
Brostrom-Gould has excellent long-term outcomes with 20+ year follow-up studies showing maintained stability. Anatomic reconstruction approaches similar outcomes when properly indicated. Key to success: appropriate patient selection, address associated pathology, comprehensive rehabilitation.
Evidence Base
- Arthroscopy in 61 CAI patients revealed: OLT 22%, synovitis 75%, loose bodies 26%. Highlights importance of addressing associated pathology during stabilization.
- Long-term follow-up (26 years mean) of Brostrom procedure showed 87% good/excellent results. Stability maintained over time. Low rate of late arthrosis.
- Compared anatomic (Brostrom) vs non-anatomic (Evans, Watson-Jones) procedures. Anatomic repair superior for restoration of normal ankle kinematics and subtalar motion preservation.
- High rate of peroneal pathology (40%) in CAI patients. Longitudinal tears and tendinopathy common. Address at time of stabilization for optimal outcomes.
- Systematic review: 6 months conservative treatment first. Modified Brostrom is first-line surgery. Anatomic reconstruction for revision. Address associated pathology.
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Young Athlete with Recurrent Sprains
"A 22-year-old soccer player presents with recurrent ankle sprains over 2 years. He has completed 6 months of physiotherapy with bracing. Examination shows positive anterior drawer (12mm vs 6mm contralateral). He wants to return to competitive sport."
Scenario 2: Failed Previous Repair
"A 35-year-old woman had a Brostrom repair 3 years ago that failed after 18 months. She now has persistent instability, giving way episodes, and anterior drawer 14mm (vs 5mm contralateral). MRI shows attenuated ligament remnants."
Scenario 3: Instability with OLT
"A 28-year-old basketball player has CAI confirmed on stress XR. MRI also shows a 1.2cm medial talar dome osteochondral lesion with overlying cartilage damage. He has failed conservative treatment."
Scenario 4: Functional vs Mechanical Instability
"A 30-year-old recreational runner has recurrent giving way and ankle sprains. She has completed 3 months of physiotherapy. Examination shows negative anterior drawer and talar tilt. She has significant peroneal weakness and poor single-leg balance."
MCQ Practice Points
Primary Restraint
Q: Which ligament is the primary restraint against anterior translation of the talus in plantarflexion? A: Anterior talofibular ligament (ATFL) - The ATFL is taut in plantarflexion and provides 100% of resistance to anterior talar translation at 15 degrees plantarflexion. It is the weakest and most commonly injured lateral ligament.
CFL Unique Property
Q: What unique anatomical feature of the CFL makes it important for subtalar stability? A: CFL is extra-articular and crosses the subtalar joint - Unlike the ATFL which is intra-articular, the CFL crosses both the ankle and subtalar joints, contributing to stability of both articulations.
Stress Test Thresholds
Q: What is considered a positive anterior drawer stress test in chronic ankle instability? A: Greater than 10mm absolute OR greater than 3mm asymmetry compared to contralateral - Side-to-side comparison is more reliable than absolute values due to individual variation in ligamentous laxity.
Surgical Procedure
Q: What is the gold standard first-line surgical procedure for chronic ankle instability? A: Modified Brostrom-Gould - This anatomic repair involves ATFL imbrication to the fibula with suture anchors plus reinforcement with the inferior extensor retinaculum (Gould modification), achieving 85-95% success rates.
IER Augmentation
Q: What is the purpose of the Gould modification in the Brostrom procedure? A: Reinforcement with inferior extensor retinaculum (IER) - The IER is advanced over the ATFL repair and secured to the fibula, providing additional anterior restraint and improving outcomes compared to ATFL repair alone.
Australian Context
Clinical Practice
- Sports medicine physicians manage initial assessment
- Orthopaedic referral for failed conservative or mechanical instability
- Physiotherapy-led rehabilitation programs
- High participation in ankle-stressing sports (rugby, AFL, basketball)
Healthcare Setting
- Day surgery for Brostrom-Gould
- Public and private settings
- Sports clinics for comprehensive care
- Return-to-sport programs in sports medicine units
Orthopaedic Exam Focus
Australian examiners will expect: Understanding of mechanical vs functional instability, anatomy of lateral ligament complex (ATFL taut in plantarflexion, CFL extra-articular), stress radiograph thresholds, Brostrom-Gould technique, and indications for graft reconstruction in revision settings.
CHRONIC ANKLE INSTABILITY
High-Yield Exam Summary
Key Anatomy
- •ATFL: weakest ligament, intra-articular, taut in PLANTARFLEXION
- •CFL: EXTRA-ARTICULAR, crosses subtalar joint, taut in DF
- •PTFL: strongest, rarely injured
- •Anterior drawer tests ATFL; Talar tilt tests CFL
Instability Types
- •MECHANICAL: true laxity (positive stress tests/XR)
- •FUNCTIONAL: giving way WITHOUT laxity (proprioceptive deficit)
- •Most CAI patients have BOTH components
- •Surgery for mechanical; Rehab for functional
Stress Test Thresholds
- •Anterior drawer: greater than 10mm OR greater than 3mm asymmetry = positive
- •Talar tilt: greater than 10 degrees OR greater than 5 degrees asymmetry = ATFL + CFL
- •Always COMPARE to contralateral side
- •Asymmetry more reliable than absolute values
Surgical Approach
- •Brostrom-Gould = GOLD STANDARD (85-95% success)
- •Gould modification = IER reinforcement (critical)
- •Graft reconstruction for: revision, hyperlaxity, poor tissue
- •Non-anatomic tenodesis largely HISTORICAL
Exam Pearls
- •6 months conservative before surgery
- •ATFL provides 100% resistance to anterior translation at 15 degrees PF
- •Always assess for OLT (15-25%), peroneals, subtalar instability
- •Cavovarus = higher recurrence - consider calcaneal osteotomy