ANKLE FRACTURES - WEBER CLASSIFICATION
Syndesmotic Level | Stability Determines Treatment | Ring Injury Concept
WEBER CLASSIFICATION
Critical Must-Knows
- Weber classification is based on fibular fracture level relative to syndesmosis
- Ankle is a ring structure - isolated fractures rare, look for second injury
- Weber B stability determined by deltoid ligament and syndesmosis integrity
- Medial clear space greater than 4.5mm indicates deltoid rupture = unstable
- Syndesmotic screws placed 2-4cm above joint, parallel to joint line
Examiner's Pearls
- "Weber C = syndesmosis disrupted by definition = unstable
- "Mortise view: 15-20 degree internal rotation shows true joint space
- "Maisonneuve = proximal fibula fracture + syndesmosis rupture - examine whole leg
- "Lauge-Hansen describes mechanism; Weber describes fibula level
Clinical Imaging
Imaging Gallery
Critical Ankle Fracture Exam Points
Ring Concept
Ankle is an osseoligamentous ring. Isolated malleolar fractures rare - always look for second lesion (deltoid rupture, syndesmosis injury, proximal fibula fracture).
Stability Assessment
Stress radiographs critical for Weber B. If medial clear space greater than 4.5mm on gravity or external rotation stress = unstable = surgical.
Weber vs Lauge-Hansen
Weber = fibula level (A/B/C). Lauge-Hansen = mechanism (SER, SAD, PER, PAB). Both useful but Weber guides treatment.
Syndesmosis Fixation
Screw placement 2-4cm above joint. 3.5-4.5mm cortical, 3-4 cortices. Remove at 8-12 weeks before weight-bearing.
Quick Decision Guide
| Fracture Pattern | Stability | Key Finding | Treatment |
|---|---|---|---|
| Weber A (isolated) | Stable | Below syndesmosis, no medial injury | Moon boot, weight-bear as tolerated |
| Weber B (isolated) | Potentially stable | Medial clear space normal on stress | Cast/boot, close follow-up |
| Weber B + deltoid rupture | Unstable | Medial clear space greater than 4.5mm | ORIF fibula + deltoid exploration |
| Bimalleolar/Trimalleolar | Unstable | Multiple malleoli fractured | ORIF all fragments |
| Weber C | Always unstable | Above syndesmosis = disrupted | ORIF + syndesmosis fixation |
ABCWeber Classification Memory Aid
Memory Hook:A is Always stable (below), B is Borderline (stress it), C is Clearly unstable (above)!
DIMSAnkle Stability Assessment
Memory Hook:If DIMS are disrupted, surgery will FIX it - assess all four before deciding treatment!
SPEPLauge-Hansen Mechanism
Memory Hook:SPEP: First letter = foot position, Second = force direction. SER is most common - Spiral fibula at Syndesmosis level!
2-3-4Syndesmosis Screw Placement
Memory Hook:2-3-4 rule: 2cm up, 3-4 cortices, 3.5-4.5mm screw. Remove before full weight-bearing at 8-12 weeks!
Overview and Epidemiology
Clinical Significance
Ankle fractures are the most common lower limb fracture requiring surgical intervention. Correct assessment of stability is paramount - unstable fractures treated non-operatively have poor outcomes with post-traumatic arthritis in up to 50% at 20 years.
Demographics
- Bimodal distribution: young males (sports/high-energy), elderly females (low-energy/osteoporotic)
- Female predominance increases with age
- Winter peaks (ice-related falls)
- Sports: soccer, basketball, skiing
Mechanism
- SER (Supination-External Rotation): 40-75% - most common
- PER (Pronation-External Rotation): 5-20%
- SAD (Supination-Adduction): 10-20%
- PAB (Pronation-Abduction): 5-20%
Anatomy and Biomechanics
The Ring Concept
The ankle mortise functions as an osseoligamentous ring. Just like a pretzel, you cannot break a ring in one place - there must be a second disruption. Always look for the second lesion!
Key Anatomical Structures
| Structure | Function | Clinical Relevance |
|---|---|---|
| Syndesmosis (AITFL, PITFL, IOL, ITL) | Maintains tibiofibular relationship | Weber C = always disrupted. Squeeze test positive. |
| Deltoid ligament (superficial + deep) | Primary medial stabilizer | Deep portion critical - resists lateral talar shift |
| Lateral ligaments (ATFL, CFL, PTFL) | Lateral ankle stability | Commonly injured in Weber A, usually heal well |
| Posterior malleolus | PITFL attachment, articular surface | Fix if over 25% articular surface or greater than 2mm step |
Syndesmosis Components
- AITFL: Anterior inferior tibiofibular ligament - first to tear
- PITFL: Posterior inferior tibiofibular ligament - strongest
- IOL: Interosseous ligament
- ITL: Inferior transverse ligament (deep PITFL)
Deltoid Complex
- Superficial: Tibionavicular, tibiocalcaneal, tibiotalar
- Deep: Anterior and posterior tibiotalar (critical)
- Deep deltoid resists lateral talar shift
- Rupture = medial clear space widening
Exam Trap: Superficial Peroneal Nerve
The superficial peroneal nerve crosses the surgical field anterolaterally, 7-10cm proximal to the tip of the fibula. It becomes subcutaneous at this level and is at risk during lateral approach. Always identify and protect!
Classification Systems
Weber Classification (Danis-Weber)
| Type | Fibula Level | Syndesmosis | Stability | Treatment |
|---|---|---|---|---|
| Weber A | Below syndesmosis | Intact | Stable | Non-operative usually |
| Weber B | At syndesmosis | Partial/Intact | Variable | Stress testing required |
| Weber C | Above syndesmosis | Disrupted | Unstable | Surgical fixation |
Key Point
Weber classification correlates with syndesmotic injury. Higher fracture = greater syndesmotic disruption = more unstable. Weber C is unstable by definition.
Clinical Assessment
History
- Mechanism: Twisting, inversion/eversion, direct blow
- Ability to weight-bear: Ottawa rules
- Previous ankle injuries: Instability, arthritis
- Medical comorbidities: Diabetes, PVD, smoking
Examination
- Look: Swelling, deformity, skin condition, blisters
- Feel: Bony tenderness (medial, lateral, posterior malleoli)
- Move: ROM (limited by pain), stability testing
- Neurovascular: Dorsalis pedis, posterior tibial, sensation
Don't Forget the Proximal Fibula!
Maisonneuve fracture: Proximal fibula fracture with syndesmotic rupture. Always palpate full length of fibula and get full-length tibia/fibula views if suspicious. The ankle may look relatively benign!
Special Tests
| Test | Technique | Positive Finding | Interpretation |
|---|---|---|---|
| Squeeze Test | Compress fibula to tibia at mid-calf | Pain at ankle syndesmosis | Syndesmosis injury |
| External Rotation Stress | ER force to foot with knee at 90 degrees | Pain at syndesmosis, widening on fluoro | Syndesmosis instability |
| Cotton Test | Lateral translation of talus | greater than 3mm translation | Deltoid insufficiency |
| Fibula Translation | Direct AP stress to fibula | greater than 3mm translation | Syndesmosis disruption |
Ottawa Ankle Rules
X-rays indicated if: Bone tenderness at posterior edge or tip of either malleolus OR Inability to weight-bear 4 steps immediately and in ED. Sensitivity over 98% for fractures.
Investigations
Imaging Protocol
Three views essential: AP, Lateral, Mortise (15-20 degree internal rotation). Mortise view critical for assessing joint congruency and clear spaces.
Gravity stress or external rotation stress views. Essential to determine stability if isolated Weber B with normal mortise. Widening greater than 4.5mm medial clear space = unstable.
Indicated for: posterior malleolus assessment, pilon fracture exclusion, preoperative planning for complex patterns, syndesmosis evaluation.
Rarely needed. May help assess deltoid ligament integrity if unclear. Useful for occult fractures or persistent symptoms.
Radiographic Parameters
| Measurement | Normal Value | Abnormal | Significance |
|---|---|---|---|
| Medial clear space | less than 4mm | greater than 4.5mm | Deltoid rupture, talar shift |
| Superior clear space | less than 4mm | greater than 4mm | Talar subluxation |
| Tibiofibular clear space | less than 6mm | greater than 6mm | Syndesmosis widening |
| Tibiofibular overlap | greater than 6mm (AP), greater than 1mm (mortise) | Reduced | Syndesmosis injury |
| Talar tilt | 0 degrees | greater than 2 degrees | Ligamentous instability |
Mortise View Technique
15-20 degrees internal rotation of the leg to parallel the intermalleolar axis with the X-ray beam. This provides a true AP view of the ankle mortise and allows accurate measurement of clear spaces.
Management Algorithm
Non-Operative Management
Indications:
- Stable, isolated Weber A fractures
- Stable Weber B fractures (negative stress views, MCS normal)
- Non-ambulatory or severely comorbid patients
- Significant soft tissue compromise
Non-Operative Protocol
Below-knee backslab, elevation, ice. Non-weight-bearing or TTWB as tolerated.
Convert to CAM boot or below-knee cast. Check alignment with repeat X-rays.
Progressive weight-bearing as pain allows. Physiotherapy for ROM and strength.
Return to normal activities. May take 3-6 months for full recovery.
Close Follow-Up Essential
Non-operative Weber B fractures need weekly X-rays for first 2 weeks to ensure no late displacement. If any widening occurs, convert to operative management.
Surgical Technique
ORIF Lateral Malleolus
Supine with bump under ipsilateral hip. Tourniquet to thigh. May use lateral decubitus for posterior work.
Direct lateral incision over fibula. Protect superficial peroneal nerve (anterolateral). Full-thickness skin flaps.
Anatomic reduction with pointed reduction clamp. Assess length, rotation, alignment. Fibula is key to ankle stability.
1/3 tubular plate or anatomic plate. Interfragmentary lag screw if oblique fracture. 3+ screws proximal, 2+ distal.
Intraoperative stress test under fluoro. Hook test, external rotation. If positive, syndesmosis screw required.
Medial Malleolus Fixation
- Two 4.0mm partially threaded screws (most common)
- Perpendicular to fracture line
- Alternative: tension band wire, plate
- Small fragments: K-wires + tension band
Posterior Malleolus Fixation
- Fix if over 25% articular surface or greater than 2mm step
- Posterolateral approach or anterior-to-posterior screws
- Reduces PITFL, improves syndesmosis stability
- May allow avoidance of syndesmosis screw
Complications
Complications and Management
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Wound complications | 10-20% | Diabetes, smoking, swelling | Staged surgery, optimize soft tissues |
| Malreduction | 5-15% | Technical error, inadequate imaging | Revision if symptomatic, prevent with good technique |
| Syndesmosis malreduction | 15-25% | CT shows up to 50% in some series | Intraoperative CT, careful reduction |
| Post-traumatic arthritis | 10-30% | Initial cartilage damage, malreduction | Depends on initial injury severity |
| Hardware irritation | 10-30% | Subcutaneous implants | Removal after union if symptomatic |
| Nonunion | under 5% | Smoking, diabetes, osteoporosis | Bone graft, revision fixation |
| DVT/PE | 1-5% | Immobilization, tourniquet | Chemoprophylaxis, early mobilization |
Syndesmosis Malreduction
CT studies show 16-50% syndesmosis malreduction rate with screws alone. Consider intraoperative CT if available. Even 2mm of malreduction associated with worse outcomes. Ensure fibula is in incisura with reduction clamp before screw insertion.
Postoperative Care and Rehabilitation
Rehabilitation Timeline
Backslab, strict elevation. Wound check at 10-14 days. Non-weight-bearing.
CAM boot. Begin ROM exercises out of boot. Touch weight-bearing progressing to partial.
Remove syndesmosis screws. Progress to full weight-bearing. Active mobilization.
Wean from boot. Full weight-bearing. Proprioception and strength training.
Sport-specific rehabilitation. Full return when strength 90% of contralateral.
Outcomes and Prognosis
Prognostic Factors
| Factor | Impact | Notes |
|---|---|---|
| Anatomic reduction | Most important | 1mm talar shift reduces contact area 42% |
| Syndesmosis reduction | Critical | Malreduction = worse outcomes |
| Initial cartilage damage | Significant | Cannot be modified surgically |
| Age | Moderate | Younger better functional outcomes |
| Diabetes | Negative | Higher complication rates |
| Smoking | Negative | Impaired healing, higher infection |
The 1mm Rule
1mm of lateral talar shift reduces tibiotalar contact area by 42%. This dramatically increases contact pressures and accelerates post-traumatic arthritis. Anatomic reduction is the single most important factor for outcomes.
Evidence Base
Syndesmosis Screw vs Suture Button
- RCT of 97 patients: suture button showed improved functional outcomes (AOFAS 93 vs 88) and less syndesmosis widening at 2 years compared to screw fixation.
Early vs Delayed Weight-Bearing
- Meta-analysis of 6 RCTs (724 patients): Early WB (before 6 weeks) resulted in earlier return to work with no increase in complications or loss of reduction.
Posterior Malleolus Fixation Threshold
- Fragment size over 25% of articular surface or greater than 2mm step-off associated with worse outcomes. Posterior malleolus fixation restores syndesmosis stability.
Syndesmosis Malreduction Rates
- CT analysis of syndesmosis reduction: 39% malreduction rate when assessed by CT vs 4% on plain radiographs. External rotation most common malreduction.
Australian Registry Data - Ankle Fractures
- Ankle fractures account for approximately 4% of all fractures in Australia. Incidence increasing in elderly population. Average hospital stay 2.4 days for operative cases.
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Classification and Initial Management (~2-3 min)
"A 45-year-old woman presents after twisting her ankle stepping off a curb. She is unable to weight-bear. X-rays show a spiral oblique fracture of the lateral malleolus at the level of the syndesmosis with no obvious medial injury. How would you classify and manage this fracture?"
Scenario 2: Surgical Technique (~3-4 min)
"You decide to proceed with ORIF for an unstable Weber B fracture with positive stress views. The patient is in theatre. Walk me through your surgical technique."
Scenario 3: Complication Management (~2-3 min)
"You review a patient 6 months post ankle ORIF in clinic. They have persistent lateral ankle pain and stiffness. CT shows malreduced syndesmosis with external rotation of the fibula. How do you manage this?"
MCQ Practice Points
Anatomy Question
Q: Which structure is the primary restraint to lateral talar shift? A: The deep deltoid ligament (specifically the deep tibiotalar fibers). The superficial deltoid resists eversion. Disruption of the deep deltoid allows the talus to shift laterally, increasing medial clear space.
Classification Question
Q: A Weber B fracture is defined by the fibula fracture being at what level? A: At the level of the syndesmosis. This correlates with partial syndesmosis injury potential. Weber A is below (intact syndesmosis), Weber C is above (disrupted syndesmosis).
Radiographic Question
Q: What is the upper limit of normal for medial clear space on a mortise view? A: 4mm (or equal to superior clear space). Greater than 4-4.5mm suggests deltoid ligament rupture and indicates an unstable injury requiring surgical management.
Treatment Question
Q: What is the effect of 1mm lateral talar shift on tibiotalar contact? A: 42% reduction in contact area. This is the basis for emphasis on anatomic reduction - even small amounts of talar shift dramatically increase contact pressures and accelerate post-traumatic arthritis.
Syndesmosis Question
Q: At what level should a syndesmosis screw be placed above the joint line? A: 2-4cm above the joint line, parallel to the tibial plafond. Some surgeons prefer 3-4cm to minimize risk of articular damage. Screw directed 25-30 degrees anterior to coronal plane.
Australian Context and Medicolegal Considerations
Australian Data
- 4% of all fractures in Australia
- Incidence increasing in elderly population
- Average LOS 2.4 days for operative cases
- Most managed in public hospital system
RACS/AOA Guidelines
- Competency in ankle fracture management expected of all orthopaedic trainees
- orthopaedic exam frequently includes ankle fracture scenarios
- Weber classification standard for communication
- Stress testing for Weber B considered standard of care
Medicolegal Considerations
Key documentation requirements:
- Document examination of full length of fibula (Maisonneuve)
- Document neurovascular status pre and post-operatively
- Document stress testing results for Weber B fractures
- Informed consent must include: infection, DVT, malunion, nonunion, post-traumatic arthritis, need for hardware removal
- If non-operative: document patient informed of need for close follow-up and risk of late displacement
Consent for Ankle ORIF
Specific risks to discuss: Wound complications (especially if swollen, diabetic, smoker), superficial peroneal nerve injury, need for syndesmosis screw removal, hardware irritation requiring removal, post-traumatic arthritis regardless of treatment, DVT/PE.
ANKLE FRACTURES
High-Yield Exam Summary
Key Anatomy
- •Ring structure - isolated injury rare, look for second lesion
- •Syndesmosis: AITFL, PITFL, IOL, ITL - PITFL strongest
- •Deep deltoid = primary restraint to lateral talar shift
- •Superficial peroneal nerve 7-10cm above fibula tip
Weber Classification
- •Weber A = below syndesmosis = stable
- •Weber B = at syndesmosis = need stress views
- •Weber C = above syndesmosis = unstable by definition
- •Lauge-Hansen describes mechanism (SER most common 40-75%)
Treatment Algorithm
- •Stable Weber A/B: Non-operative, CAM boot, close follow-up
- •Unstable Weber B (MCS greater than 4.5mm): ORIF fibula +/- syndesmosis
- •Weber C: ORIF fibula + syndesmosis fixation always
- •Bimalleolar/Trimalleolar: ORIF all components
Surgical Pearls
- •Operate within 6-8h or wait for wrinkle sign (7-14 days)
- •Protect superficial peroneal nerve anterolaterally
- •Always stress syndesmosis intraoperatively
- •Syndesmosis screw: 2-4cm above joint, 3-4 cortices, parallel to plafond
Complications
- •Syndesmosis malreduction 15-50% (CT > XR detection)
- •1mm talar shift = 42% reduction in contact area
- •Wound complications 10-20% (higher if swollen/diabetic)
- •Post-traumatic arthritis 10-30% at 10 years