Syndesmosis Injury

1. Clinical Overview

Summary

Syndesmosis injuries, commonly referred to as "High Ankle Sprains", represent 1-11% of all ankle sprains but account for disproportionate morbidity, with recovery times 2-3 times longer than lateral ankle ligament injuries. [1] The syndesmosis is a fibrous joint between the distal tibia and fibula, stabilized by four ligamentous structures: the anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), transverse tibiofibular ligament, and interosseous ligament/membrane (IOL/IOM). [2]

Injury typically occurs through combined external rotation and dorsiflexion forces, most commonly in collision sports such as American football, rugby, ice hockey, and skiing. [3] The spectrum of injury ranges from isolated AITFL sprains (Grade I) to complete disruption of all syndesmotic structures with frank diastasis (Grade III), the latter often associated with fractures. [4]

Clinical diagnosis relies on a combination of examination findings—including the squeeze test, external rotation stress test, and Cotton test—supplemented by imaging. Plain radiographs may appear normal in up to 50% of cases of syndesmotic instability, making advanced imaging (MRI or weight-bearing CT) essential for diagnosis. [5,6]

Management is determined by stability: isolated stable injuries without diastasis are treated conservatively with protected weight-bearing for 6-12 weeks, while unstable injuries with diastasis require surgical fixation to prevent chronic instability and post-traumatic arthritis. [7] Even 1mm of lateral talar shift reduces tibiotalar contact area by 42%, accelerating degenerative change. [8]

Key Facts

• Anatomy of the Syndesmosis: The syndesmosis is a complex of 4 ligamentous structures:

  1. AITFL (Anterior Inferior Tibiofibular Ligament): Contributes 35% to syndesmotic stability. Originates from the anterolateral tubercle of the tibia (Tillaux-Chaput tubercle) and inserts on the anterior fibula. Weakest of the major ligaments, typically the first to fail. [9]
  2. PITFL (Posterior Inferior Tibiofibular Ligament): Contributes 40-42% to syndesmotic stability, making it the strongest component. Runs from the posterior tibial tubercle to the posterior fibula. [9]
  3. Transverse Tibiofibular Ligament: Deep inferior portion of the PITFL, forms a labrum-like structure at the posterior ankle joint.
  4. Interosseous Ligament/Membrane: Thickened distal extension of the interosseous membrane, contributes 20-25% to stability. [9]

• Incidence in Sports: Accounts for 10-20% of all ankle injuries in collision sports, with the highest rates in American football (45% of all ankle sprains) and ice hockey. [3,10]

• Recovery Timeline: Unlike lateral ankle sprains (return to sport 2-4 weeks), syndesmosis injuries require 6-12 weeks for stable injuries and 3-6 months for surgically stabilized injuries. [11]

• Diagnostic Challenge: Standard anteroposterior (AP) and mortise radiographs have sensitivity of only 50-60% for detecting syndesmotic instability. Weight-bearing views, MRI, or bilateral comparison imaging significantly improve diagnostic accuracy. [5,6]

• The 1mm Rule: Each millimeter of lateral talar shift reduces tibiotalar contact area by 42% and increases peak contact pressures, dramatically accelerating arthritic change. [8]

Clinical Pearls

"The Hop Test": Inability to perform 10 single-leg hops on the injured extremity without pain is highly suggestive of syndesmotic injury. Pain localized above the ankle joint line (at the syndesmosis) rather than laterally distinguishes this from lateral ligament injuries. Sensitivity is moderate (70%) but specificity is high (85%). [12]

"Proximal Fibula Tenderness = Maisonneuve": Always palpate the proximal fibula and entire fibular shaft in suspected syndesmosis injuries. Proximal tenderness suggests a Maisonneuve fracture—a proximal fibular fracture with syndesmotic disruption and deltoid ligament injury. This is a rotationally unstable injury requiring surgical fixation. [13]

"Look for the Flake Sign": Small avulsion fractures are pathognomonic for ligamentous injury. The Chaput (Tillaux-Chaput) tubercle avulsion indicates AITFL injury; the Wagstaffe-Le Fort fracture (anterior fibular flake) also signals AITFL avulsion. Posterior malleolar fractures > 25% of the joint surface indicate PITFL disruption and are inherently unstable. [14]

"Weight-Bearing is Diagnostic": Many syndesmotic injuries appear normal on non-weight-bearing radiographs but demonstrate clear diastasis with axial loading. Always obtain weight-bearing or gravity stress views when syndesmotic injury is suspected. [6]

"Malreduction is the Enemy": The most common complication of syndesmotic screw fixation is malreduction, particularly placing the fibula too anterior or lateral within the incisura. This occurs in 16-52% of cases and leads to persistent pain, stiffness, and arthritis. Intraoperative CT or fluoroscopy from multiple angles is essential. [15]

---

2. Epidemiology

Incidence and Prevalence

• Overall Incidence: 1-11% of all ankle sprains in the general population. [1]
• Sports-Specific Incidence:
  • American football: 10-45% of ankle injuries
  • Rugby: 15-20% of ankle injuries
  • Ice hockey: 20-25% of ankle injuries
  • Alpine skiing: 10-15% of ankle injuries [3,10]
• Associated Fractures: 20-40% of ankle fractures have an associated syndesmotic injury. This rises to 60-70% in pronation-external rotation (Weber C) and pronation-abduction fracture patterns. [4]

Demographics

• Age: Bimodal distribution—peak in young athletes (18-35 years) and older individuals with fragility fractures (> 65 years).
• Sex: Male predominance (2:1 to 3:1) in sports-related injuries, reflecting higher participation rates in collision sports.
• Activity: Predominantly athletic injuries (70-80%), with the remainder from motor vehicle accidents, falls from height, and occupational injuries.

Injury Mechanism

The syndesmosis is injured through:

1. External Rotation + Dorsiflexion (Most Common, 60-70%): The anterior talus is wider than the posterior talus. During forced dorsiflexion, the wider anterior dome is driven into the mortise like a wedge, forcing the tibia and fibula apart. Superimposed external rotation further stresses the ligaments. Classic mechanism: opponent landing on the lateral leg while the foot is planted. [3]

2. Pronation-External Rotation: Deltoid ligament fails first (or medial malleolar fracture), followed by sequential anterior-to-posterior disruption of the syndesmosis (AITFL → IOM → PITFL), and ultimately a high fibular fracture (Maisonneuve). [13]

3. Hyperdorsiflexion: Pure hyperdorsiflexion can injure the syndesmosis in the absence of rotation, particularly in snow sports (ski boot holds ankle in dorsiflexion).

4. Direct Blow: Less common—direct trauma to the lateral fibula drives it posteriorly, disrupting the syndesmosis.

---

3. Pathophysiology

Functional Anatomy

The distal tibiofibular syndesmosis is a fibrous joint (amphiarthrosis) that allows minimal physiologic motion—approximately 1-2mm of fibular translation and 2-5° of external rotation during ankle dorsiflexion. [2] This motion accommodates the wider anterior talar dome during gait.

Ligamentous Contributions to Stability: [9]

• PITFL: 42% (strongest, primary stabilizer)
• AITFL: 35% (most commonly injured)
• IOL: 22%
• Deltoid ligament: Indirect stabilizer—resists medial talar translation

The Fibular Incisura: The fibula sits within a concave recess (incisura) on the lateral tibia. Its position is slightly posterior and tilted ~20-30° from vertical. Anatomic reduction requires precise restoration of this 3D relationship.

Injury Classification

West Point Grading System: [4]

• Grade I (Stable Sprain): AITFL sprain without complete tear. No diastasis. Stable on stress testing. Represents 40-50% of syndesmotic injuries.
• Grade II (Partial Instability): Complete AITFL tear ± partial IOL tear. Diastasis may occur only under stress (dynamic instability). Represents 30-40% of injuries.
• Grade III (Complete Diastasis): Complete disruption of AITFL, IOL, and PITFL. Frank diastasis present at rest. Often associated with deltoid injury or fracture. Represents 10-20% of injuries.

Alternative Classification by Ligamentous Injury: [14]

• Latent (Occult): AITFL injury with intact PITFL and IOL. Stable at rest, unstable under stress.
• Frank: Complete disruption of all components with visible diastasis on standard radiographs.

Sequential Failure Pattern

Syndesmotic ligaments fail in a predictable sequence with increasing energy:

1. AITFL (weakest, fails first)
2. Interosseous ligament (distal extension)
3. Interosseous membrane (progressive proximal tear)
4. PITFL (strongest, fails last)
5. Deltoid ligament or medial malleolar fracture (if pronation component)

In Maisonneuve fractures, the entire syndesmosis and IOM fail, with the fibular fracture occurring at the weakest point proximally. [13]

Biomechanical Consequences of Diastasis

The 42% Rule: Biomechanical studies demonstrate that 1mm of lateral talar shift decreases tibiotalar contact area by 42% and increases peak contact stress by 40-50%. [8] This concentration of force accelerates cartilage breakdown.

Rotational Malreduction: External rotation malreduction of the fibula (> 5°) reduces contact area by 30% even without lateral shift. Internal rotation or anterior positioning similarly reduces contact area by 15-20%. [15]

---

4. Clinical Presentation

History

• Mechanism: Patient reports external rotation injury with foot planted, often with another player falling on the leg. "My ankle twisted outward and I heard/felt a pop."
• Pain Location: Pain is localized to the anterolateral ankle above the joint line, rather than over the lateral malleolus (which suggests lateral ligament injury).
• Inability to Weight Bear: Unlike many lateral ankle sprains where patients can limp, syndesmosis injuries often prevent immediate weight-bearing.
• Delayed Presentation: Athletes may continue playing initially, with pain and swelling worsening over 24-48 hours.

Physical Examination

Inspection:

• Swelling is often less dramatic than lateral ankle sprains but is "high and tight" (above the ankle joint).
• Ecchymosis may extend proximally along the lateral leg.
• Ankle deformity is rare unless frank diastasis or fracture is present.

Palpation:

• Syndesmotic Tenderness: Palpate the AITFL just anteromedial to the distal fibula and 1-2cm proximal to the joint line. Point tenderness here is 92% sensitive for syndesmotic injury. [12]
• Proximal Fibula: Always palpate entire fibular shaft to rule out Maisonneuve fracture.
• Medial Ankle: Palpate deltoid ligament and medial malleolus. Tenderness suggests associated injury.
• Posterior Ankle: Palpate posterior malleolus for fracture.

Special Tests:

1. Squeeze Test: [12]

   • Technique: Compress tibia and fibula together at mid-calf level.
   • Positive: Pain at the syndesmosis (ankle level).
   • Sensitivity: 30-50%, Specificity: 88-94%
   • Interpretation: Low sensitivity limits utility as screening tool, but high specificity makes positive test highly suggestive.

2. External Rotation Stress Test (ERST): [12]

   • Technique: Stabilize leg with knee flexed 90°. Dorsiflex ankle to neutral. Apply external rotation force to foot.
   • Positive: Pain over syndesmosis (anterolateral ankle).
   • Sensitivity: 71-88%, Specificity: 83-94%
   • Interpretation: Most accurate single clinical test.

3. Cotton Test: [12]

   • Technique: Grasp heel and apply lateral translation force to talus within mortise.
   • Positive: Lateral translation > 3mm or side-to-side difference > 2mm compared to contralateral ankle.
   • Sensitivity: 71%, Specificity: 97%
   • Interpretation: High specificity; best for detecting frank instability.

4. Fibular Translation Test:

   • Technique: Translate fibula anteroposteriorly relative to tibia.
   • Positive: Excessive motion or pain.
   • Sensitivity/Specificity: Not well validated.

5. Crossed-Leg Test: [12]

   • Technique: Patient places injured ankle on contralateral knee (figure-4 position).
   • Positive: Pain at syndesmosis from external rotation stress.
   • Sensitivity: 62%, Specificity: 88%

Combined Test Interpretation: No single test has sufficient sensitivity and specificity to rule in or out syndesmotic injury. A combination of positive squeeze test + ERST + syndesmotic tenderness has positive predictive value of 95%. [12]

Functional Assessment

• Hop Test: Ask patient to hop 10 times on injured leg. Inability to complete due to pain above the ankle joint suggests significant syndesmotic injury. [12]
• Gait: Patients typically exhibit antalgic gait with shortened stance phase and external foot progression angle.

---

5. Investigations

Plain Radiography

Standard Views: AP, mortise (15-20° internal rotation), and lateral ankle radiographs.

Radiographic Measurements on Mortise View: [6]

1. Tibiofibular Clear Space (TFCS): Measured 1cm proximal to tibial plafond. Normal less than 6mm. > 6mm suggests diastasis.
2. Tibiofibular Overlap (TFO): Overlap of tibia and fibula. Normal > 6mm on AP view, > 1mm on mortise view. Absence of overlap suggests injury.
3. Medial Clear Space (MCS): Space between medial malleolus and medial talar border. Normal less than 4mm and equal to superior clear space. Widening > 5mm suggests deltoid injury and instability.

Limitations: Static radiographs miss 40-50% of syndesmotic instabilities because ligamentous injuries without bony avulsion or fracture appear normal at rest. [5]

Weight-Bearing Views: Bilateral weight-bearing AP and mortise views increase sensitivity to 75-80% by unmasking dynamic instability. [6] Compare side-to-side measurements.

Gravity Stress Views: External rotation stress applied under fluoroscopy while obtaining mortise view. Diastasis > 2mm compared to contralateral side indicates instability. Sensitivity 71%, specificity 97%. [16]

Advanced Imaging

MRI: [5]

• Indications: Suspected syndesmotic injury with normal radiographs, assessment of extent of ligamentous injury, preoperative planning.
• Findings:
  • Direct visualization of AITFL, PITFL, IOL, and deltoid ligament tears
  • Bone marrow edema at syndesmosis
  • Extent of IOM disruption (defines "high" vs "low" injury)
  • Associated injuries (osteochondral lesions, peroneal tendon injuries)
• Accuracy: Sensitivity 100%, specificity 93% for complete tears. [5]
• Limitations: Cost, time, tendency to over-diagnose clinically insignificant injuries.

CT Scan: [6]

• Indications: Assessment of syndesmotic reduction after fixation, identification of subtle fractures (posterior malleolus, avulsion fragments).
• Weight-Bearing CT: Emerging modality with sensitivity 92%, specificity 95% for syndesmotic instability. Allows bilateral comparison and 3D assessment of fibular position within incisura. [6]
• Post-Operative CT: Gold standard for assessing adequacy of reduction. Detects malreduction in 16-52% of cases not apparent on fluoroscopy. [15]

Arthroscopy: [17]

• Direct Visualization: Allows assessment of syndesmotic stability by attempting to pass a 3-4mm probe through the syndesmosis from anterior to posterior. Passage of probe indicates disruption.
• Diagnostic Accuracy: Sensitivity and specificity approach 100% (gold standard).
• Therapeutic: Allows débridement of interposed soft tissue, assessment of reduction, and treatment of concomitant intra-articular pathology.
• Indications: Uncertain diagnosis, concomitant injuries, assessment of intraoperative reduction.

Diagnostic Algorithm

SUSPECTED SYNDESMOSIS INJURY
         ↓
Weight-Bearing AP + Mortise Radiographs
         ↓
    ┌────────────┴────────────┐
DIASTASIS PRESENT          NO DIASTASIS
(TFCS > 6mm, MCS > 5mm)           ↓
    ↓                    Clinical Tests +
UNSTABLE - SURGICAL      (Squeeze, ERST, Tenderness)
                              ↓
                    ┌─────────┴──────────┐
                NEGATIVE           POSITIVE
                    ↓                    ↓
            Low Suspicion         MRI or WB-CT
            Treat as Sprain           ↓
                         ┌─────────────┴──────────┐
                    NEGATIVE                 POSITIVE
                         ↓                        ↓
                 Stable Injury           Grade Injury
                 Conservative       ┌───────┴────────┐
                                Stable          Unstable
                                   ↓                ↓
                            Conservative      Surgical

---

6. Management

Conservative Management

Indications:

• Grade I injuries: AITFL sprain without complete tear, stable on stress testing, normal radiographic measurements
• Grade II injuries with negative stress radiographs (controversial—some advocate fixation for all complete AITFL tears)

Protocol: [11]

Phase 1: Protection (0-3 weeks)

• CAM walker boot or short leg cast
• Partial weight-bearing (20-30 kg) with crutches
• Ice, elevation, NSAIDs for pain
• Isometric exercises (ankle pumps, quadriceps sets)
• Key Point: Avoid external rotation and dorsiflexion stress

Phase 2: Mobilization (3-6 weeks)

• Progress to weight-bearing as tolerated in boot
• Remove boot for ROM exercises (avoid external rotation)
• Begin proprioception training (single-leg balance)
• Strengthening: Resistance band exercises (plantarflexion, inversion, eversion)
• Pool therapy if available
• Milestone: Full weight-bearing without pain

Phase 3: Strengthening (6-12 weeks)

• Wean from boot to lace-up ankle brace
• Progressive resistance exercises
• Plyometric training (jumping, hopping)
• Sport-specific drills
• Milestone: Single-leg hop test equal to contralateral side

Phase 4: Return to Sport (12+ weeks)

• Gradual return to full training
• Consider external support (bracing or taping) for initial return
• Full ROM, strength, and proprioception
• Criteria: Symmetrical hop test, pain-free cutting/pivoting

Outcomes: Grade I stable injuries treated conservatively achieve good-to-excellent outcomes in 80-90% of cases at 6 months. Return to sport averages 10-12 weeks. [11]

Surgical Management

Indications: [7]

• Absolute:
  • Frank diastasis on weight-bearing radiographs (TFCS > 6mm)
  • Syndesmotic injury with ankle fracture requiring ORIF
  • Failed conservative management (persistent instability > 3 months)
• Relative:
  • Complete AITFL tear with positive stress test (Grade II unstable)
  • High-level athletes desiring expedited return
  • Maisonneuve fracture

Surgical Options:

1. Syndesmotic Screw Fixation: [7,14]

• Technique:

  • Reduce syndesmosis anatomically (key: fibula must sit posteriorly in incisura)
  • Insert 3.5mm or 4.5mm cortical screw 2-3cm proximal to joint line, 25-30° anteroposterior angulation
  • Tricortical (3 cortices) or quadricortical (4 cortices)—debate continues
  • Position ankle in neutral (not dorsiflexed) during insertion

• Post-Operative Protocol:

  • Non-weight-bearing or protected weight-bearing 6-8 weeks
  • Remove screw at 8-12 weeks (controversial) or allow in situ breakage

• Advantages: Low cost, familiar technique, strong initial fixation

• Disadvantages:

  • Screw breakage in 10-30% if not removed and patient weight-bears [7]
  • Malreduction in 16-52% [15]
  • Second surgery for removal
  • Restricts physiologic fibular motion

2. Suture-Button Fixation (TightRope®): [18]

• Technique:

  • Reduce syndesmosis anatomically
  • Drill 3.5-4mm hole through fibula and tibia 2-3cm above joint line
  • Pass suture with attached buttons, tension to compress syndesmosis
  • Buttons sit on lateral fibula and medial tibia

• Post-Operative Protocol:

  • Weight-bearing as tolerated immediately or at 2 weeks (surgeon-dependent)
  • No removal required
  • Return to sport 10-12 weeks

• Advantages:

  • Allows physiologic fibular motion (dynamic fixation)
  • No routine implant removal
  • Earlier weight-bearing
  • Lower malreduction rate (preserves reduction during tensioning) [18]
  • Superior functional outcomes vs screws in multiple RCTs [18]

• Disadvantages:

  • Cost (4-5× screw cost)
  • Button prominence/irritation in 5-10%
  • Potential for loss of reduction if under-tensioned
  • Technically demanding

3. Hybrid Techniques:

• Suture-button for primary fixation + screw for temporary stability (screw removed at 6-8 weeks)
• Anatomic AITFL repair with suture anchors augmented by screw or button

Intraoperative Pearls: [15]

• Avoid Malreduction: Most common error. Use intraoperative fluoroscopy with perfect lateral view to confirm fibula is reduced posteriorly. CT scan post-op if any doubt.
• Clamp Application: Reduction clamp should be angled 30° from posterior to anterior (parallel to AITFL), not perpendicular to floor.
• Assess Reduction: Pass 3-4mm arthroscopic probe from anterior to posterior. Probe should not pass through joint if reduced.
• Fracture Fixation First: Always fix fibular or posterior malleolar fractures before syndesmotic fixation.

Special Considerations

Maisonneuve Fracture: [13]

• Proximal fibular fracture + syndesmotic disruption + deltoid ligament injury (or medial malleolar fracture)
• Highly unstable, always requires ORIF
• Fibular fracture typically does not require fixation (treat syndesmosis and medial injury)
• Outcomes similar to other syndesmotic injuries if adequately reduced

Posterior Malleolar Fracture: [14]

• Fragments > 25% of joint surface indicate PITFL disruption and instability
• Fixation of posterior malleolar fragment indirectly stabilizes syndesmosis
• If fragment is fixed anatomically, isolated syndesmotic fixation may not be required
• Assess syndesmotic stability after fragment fixation with Cotton test and fluoroscopy

Pediatric Syndesmotic Injury:

• Rare in skeletally immature patients (physis is weaker than ligaments)
• More common in adolescents approaching skeletal maturity
• Conservative management preferred; surgical indications same as adults
• Avoid trans-physeal screws if physis still open (use suture-button or extra-physeal screw)

---

7. Complications

Early Complications

Malreduction (16-52%): [15]

• Most common complication
• Fibula positioned too anterior, lateral, or externally rotated
• Results in: persistent pain, stiffness, reduced contact area, arthritis
• Prevention: Meticulous technique, intraoperative CT/fluoroscopy, post-op CT to verify
• Treatment: Revision surgery within 3-6 months; outcomes inferior to primary reduction

Wound Complications (2-5%):

• Infection (superficial or deep)
• Dehiscence
• Risk factors: smoking, diabetes, open injuries

Nerve Injury (1-3%):

• Superficial peroneal nerve most at risk (anterior approach)
• Sural nerve (lateral approach)
• Usually neuropraxia; permanent injury rare

Screw Breakage (10-30%): [7]

• Occurs with early weight-bearing on quadricortical screws
• Often asymptomatic
• Prevention: tricortical screws, protected weight-bearing, early removal, or use suture-button

Late Complications

Heterotopic Ossification/Synostosis (2-8%):

• Bony bridge forms between tibia and fibula
• Presentation: pain, stiffness, loss of dorsiflexion
• Risk factors: severe injury, surgical trauma, delayed fixation
• Treatment: excision after maturation (12-18 months) ± indomethacin prophylaxis

Chronic Instability (5-15%): [11]

• Recurrent "giving way," difficulty with uneven terrain
• Etiology: inadequate initial treatment, unrecognized injury, failed healing
• Diagnosis: stress radiographs, MRI, examination under anesthesia
• Treatment: delayed reconstruction (AITFL repair/reconstruction, syndesmotic fixation)

Post-Traumatic Arthritis (10-20% at 5 years): [8]

• Accelerated by: malreduction, chronic instability, delayed treatment, severe cartilage injury
• Presentation: pain, stiffness, swelling with activity
• Treatment: conservative (activity modification, NSAIDs, injections) → ankle arthrodesis or arthroplasty

Recurrent Diastasis (3-8%):

• Loss of reduction after hardware removal or suture-button loosening
• Requires revision fixation if symptomatic

Hardware Irritation:

• Screw prominence: rare
• Button prominence: 5-10% with suture-button; may require removal [18]

---

8. Prognosis and Return to Sport

Return to Sport Timeline: [11]

• Conservative (Grade I): 10-12 weeks
• Surgical (Grade II/III): 12-24 weeks
• Elite Athletes: May return as early as 8-10 weeks post-surgery with accelerated rehab

Functional Outcomes:

• Good-Excellent Results: 75-85% at 1 year following appropriate treatment [11]
• Residual Symptoms: 15-25% report mild pain or stiffness at 1 year
• Return to Pre-Injury Level: 70-80% of athletes return to same level of sport [11]

Factors Predicting Outcome:

• Positive Predictors: Anatomic reduction, early diagnosis, compliance with rehab, stable injury pattern
• Negative Predictors: Malreduction, delayed diagnosis (> 3 weeks), chronic instability, concomitant chondral injury, Maisonneuve fracture

---

9. Evidence & Guidelines

Systematic Reviews and Meta-Analyses

Suture-Button vs Screw Fixation: [18]

• Meta-analysis of 10 RCTs (n=629 patients) by Manjoo et al. (2010):
  • Suture-button: superior AOFAS scores (91 vs 87, p=0.02)
  • Suture-button: faster return to work (9 vs 12 weeks, p=0.01)
  • Suture-button: lower reoperation rate (8% vs 23%, pless than 0.001)
  • No difference in malreduction rates, infection, or loss of reduction
• Conclusion: Suture-button fixation offers functional and practical advantages over screws

Clinical Examination Tests: [12]

• Systematic review by Sman et al. (2013):
  • External rotation stress test: most sensitive (88%) and specific (94%) single test
  • Squeeze test: high specificity (94%) but low sensitivity (30%)
  • Combination of tenderness + squeeze + ERST: PPV 95%
• Conclusion: Clinical diagnosis requires combination of tests; no single test is definitive

Conservative vs Surgical for Isolated Injuries:

• No high-quality RCTs comparing conservative vs surgical for isolated Grade II injuries
• Retrospective studies suggest similar outcomes at 1 year, but surgical treatment may reduce time to return to sport by 2-4 weeks in athletes [11]

Clinical Practice Guidelines

Current Evidence Recommendations:

1. Weight-bearing radiographs for all suspected syndesmotic injuries [6]
2. MRI or weight-bearing CT if clinical suspicion high with normal radiographs [5,6]
3. Surgical fixation for all frank diastasis (Grade III) [7]
4. Suture-button fixation preferred over screws for improved outcomes and lower reoperation rate [18]
5. Post-operative CT to verify reduction [15]
6. Conservative management acceptable for Grade I stable injuries [11]

---

10. Patient Explanation

What is a Syndesmosis Injury?

Your ankle is made up of three bones: the tibia (shin bone), fibula (smaller outer bone), and talus (ankle bone). The tibia and fibula are held together tightly by strong ligaments called the "syndesmosis." These ligaments act like the laces on a boot—they keep the two bones together so they can form a stable socket for your ankle bone.

A high ankle sprain occurs when these ligaments are torn. This usually happens when your foot is planted and someone or something twists your leg outward forcefully. Unlike a regular ankle sprain (which affects ligaments on the outside of your ankle), a high ankle sprain affects the ligaments above the ankle joint.

Why Does It Take Longer to Heal?

Regular ankle sprains heal in 2-4 weeks. High ankle sprains take 6-12 weeks (or longer if surgery is needed). Here's why:

1. High Forces: Every time you take a step, your body weight spreads the tibia and fibula apart like a wedge. This constantly stresses the healing ligaments.
2. Motion Required: Your ankle needs the fibula to move slightly during normal walking. This movement slows healing.
3. Importance: If this ligament doesn't heal properly, your ankle becomes unstable and develops arthritis quickly.

Do I Need Surgery?

It depends on how badly the ligaments are torn:

• Mild Tear (Stable): If the bones stay together when you stand on them, you can heal without surgery. You'll wear a walking boot for 6-8 weeks and do physical therapy.

• Severe Tear (Unstable): If the bones separate when you stand, surgery is needed. We place a strong "button and rope" device (or sometimes a screw) to hold the bones together while the ligaments heal. This takes about 3 months.

What Happens If It's Not Treated Properly?

If the bones don't heal in the correct position, even being 1-2 millimeters out of place can:

• Cause chronic pain and weakness
• Make your ankle arthritis develop within 2-5 years instead of decades
• Require additional surgery to correct

This is why proper diagnosis and treatment are so important.

---

11. Viva Vault (Examination Focus)

Core Knowledge Questions

Q1: Describe the anatomy of the syndesmosis and the contribution of each ligament to stability.

A: The syndesmosis is a fibrous joint between the distal tibia and fibula, consisting of four structures:

1. AITFL (Anterior Inferior Tibiofibular Ligament): 35% stability. Runs from the anterolateral tibial tubercle (Tillaux-Chaput) to the anterior fibula. Weakest component.
2. PITFL (Posterior Inferior Tibiofibular Ligament): 42% stability. Strongest component. Runs from the posterior tibial tubercle to the posterior fibula.
3. Transverse Tibiofibular Ligament: Deep portion of PITFL, acts as posterior labrum.
4. Interosseous Ligament: 22% stability. Distal thickening of the interosseous membrane.

The deltoid ligament provides indirect medial stability.

---

Q2: What is the mechanism of injury for a syndesmosis injury?

A: The most common mechanism is external rotation combined with dorsiflexion (60-70% of cases). During dorsiflexion, the wider anterior talus is driven into the mortise, spreading the tibia and fibula apart like a wedge. Superimposed external rotation further stresses the ligaments. This typically occurs when an opponent lands on the lateral leg while the foot is planted.

Alternative mechanisms include:

• Pronation-external rotation: Deltoid fails first, followed by sequential syndesmotic disruption and high fibular fracture (Maisonneuve)
• Hyperdorsiflexion alone: Seen in skiing
• Direct trauma: Rare

---

Q3: What are the clinical tests for syndesmotic injury and their diagnostic accuracy?

A:

1. Squeeze Test: Compress mid-calf → pain at ankle. Sensitivity 30%, specificity 94%.
2. External Rotation Stress Test: ER of foot in neutral dorsiflexion → pain. Sensitivity 88%, specificity 94%. Most accurate single test.
3. Cotton Test: Lateral translation of talus. Sensitivity 71%, specificity 97%.
4. Crossed-Leg Test: Figure-4 position → pain. Sensitivity 62%, specificity 88%.

No single test is definitive; combination of positive tests increases diagnostic accuracy (PPV 95% for tenderness + squeeze + ERST).

---

Q4: What radiographic measurements are used to diagnose syndesmotic injury?

A: On AP and mortise views, measured 1cm above the tibial plafond:

1. Tibiofibular Clear Space (TFCS): Normal less than 6mm. > 6mm suggests diastasis.
2. Tibiofibular Overlap (TFO): Normal > 6mm on AP, > 1mm on mortise. Loss of overlap indicates injury.
3. Medial Clear Space (MCS): Normal less than 4mm and equal to superior clear space. > 5mm suggests deltoid injury and instability.

Limitations: 40-50% of injuries appear normal on static radiographs. Weight-bearing views or MRI improve sensitivity.

---

Q5: What is the West Point classification?

A:

• Grade I: AITFL sprain without complete tear. No diastasis. Stable on stress testing.
• Grade II: Complete AITFL tear ± partial IOL tear. Dynamic instability (diastasis only under stress).
• Grade III: Complete disruption of AITFL, IOL, and PITFL. Frank diastasis at rest. Often associated with deltoid injury or fracture.

---

Q6: What is the biomechanical significance of the "1mm rule"?

A: Biomechanical studies by Ramsey and Hamilton demonstrated that 1mm of lateral talar shift reduces tibiotalar contact area by 42%. This dramatically increases peak contact stress (by 40-50%), which accelerates cartilage breakdown and leads to post-traumatic arthritis. This underscores the critical importance of anatomic reduction in syndesmotic injuries.

---

Clinical Decision-Making

Q7: What are the indications for surgical fixation of a syndesmosis injury?

A: Absolute Indications:

• Frank diastasis on weight-bearing radiographs (TFCS > 6mm, MCS > 5mm)
• Syndesmotic injury associated with ankle fracture requiring ORIF
• Failed conservative management (persistent instability > 3 months)

Relative Indications:

• Complete AITFL tear (Grade II) with positive stress testing
• High-level athletes requiring expedited return to sport
• Maisonneuve fracture

---

Q8: Compare syndesmotic screw fixation vs suture-button fixation.

A:

Evidence: Meta-analyses favor suture-button for superior functional outcomes, lower reoperation rates, and faster return to work/sport.

---

Q9: What is malreduction and why does it occur?

A: Malreduction refers to fixation of the fibula in an anatomically incorrect position within the tibial incisura. It occurs in 16-52% of syndesmotic fixations and is the most common complication.

Common Errors:

• Fibula positioned too anterior (most common)
• Fibula positioned too lateral
• Fibula externally rotated > 5°

Why It Occurs:

• Reduction clamp applied perpendicular to floor rather than angled 30° (parallel to AITFL)
• Inadequate fluoroscopic views (perfect lateral required to assess posterior position)
• Interposed soft tissue preventing reduction
• Inaccurate fibular fracture reduction (in fracture cases)

Consequences: Malreduction reduces tibiotalar contact area by 15-30%, causes persistent pain, stiffness, and accelerates arthritis.

Prevention: Meticulous technique, multiple fluoroscopic views, intraoperative arthroscopy to assess reduction, post-operative CT scan to verify.

---

Q10: Describe the management of a Maisonneuve fracture.

A: A Maisonneuve fracture is a proximal fibular fracture with complete syndesmotic disruption and deltoid ligament injury (or medial malleolar fracture). It is a rotationally unstable injury.

Management:

1. Surgical fixation is mandatory (ORIF)
2. Medial injury: Fix medial malleolar fracture with screws or repair deltoid ligament
3. Syndesmosis: Stabilize with screw or suture-button (2-3cm above joint line)
4. Proximal fibula fracture: Typically does NOT require fixation (treat syndesmosis and medial side)
5. Post-op: Protected weight-bearing 6-8 weeks, same rehab protocol as other syndesmotic injuries

Prognosis: Similar outcomes to other Grade III syndesmotic injuries if anatomically reduced. Malreduction and chronic instability are main risks.

---

Evidence-Based Medicine

Q11: What does the evidence say about conservative vs surgical management for Grade II injuries?

A: This remains controversial due to lack of high-quality RCTs.

Conservative Management:

• Retrospective studies suggest good outcomes (80-85% good-excellent) for isolated AITFL tears without diastasis on stress testing
• Return to sport: 10-12 weeks
• Risk: chronic instability in 10-15% if injury was actually unstable

Surgical Management:

• May reduce return to sport time by 2-4 weeks in athletes
• Guarantees stability but carries surgical risks (malreduction, infection, hardware complications)

Current Approach: Most surgeons treat Grade II injuries conservatively if stress radiographs are negative, with close follow-up. If pain persists > 6 weeks or instability develops, consider surgical stabilization. High-level athletes may opt for surgery to expedite return.

---

Q12: A patient presents 4 weeks post-screw fixation with persistent pain. Post-operative CT shows the fibula is 3mm anterior to its normal position. What is your management?

A: This is malreduction, which will lead to poor outcomes (persistent pain, stiffness, arthritis).

Management:

1. Explain to patient: Incorrect position will cause long-term problems; revision recommended
2. Timing: Ideally within 3-6 months (while soft tissue is still amenable to mobilization)
3. Procedure: Remove screw, mobilize fibula, achieve anatomic reduction (use intraoperative fluoroscopy/CT or arthroscopy), re-fix with suture-button or screw
4. Prognosis: Outcomes after revision are inferior to primary anatomic reduction but better than leaving malreduced

Alternative: If patient is low-demand or unwilling to undergo revision, can trial conservative management (PT, activity modification, NSAIDs), but warn of high risk of symptomatic arthritis.

---

12. References

1. Hunt KJ, Phisitkul P, Pirolo J, et al. High ankle sprains and syndesmotic injuries in athletes. J Am Acad Orthop Surg. 2015;23(11):661-673. doi:10.5435/JAAOS-D-13-00135

2. Hermans JJ, Beumer A, de Jong TA, Kleinrensink GJ. Anatomy of the distal tibiofibular syndesmosis in adults: a pictorial essay with a multimodality approach. J Anat. 2010;217(6):633-645. doi:10.1111/j.1469-7580.2010.01302.x

3. Waterman BR, Belmont PJ, Cameron KL, et al. Epidemiology of ankle sprain at the United States Military Academy. Am J Sports Med. 2010;38(4):797-803. doi:10.1177/0363546509350757

4. Edwards GS Jr, DeLee JC. Ankle diastasis without fracture. Foot Ankle. 1984;4(6):305-312. doi:10.1177/107110078400400607

5. Takao M, Ochi M, Oae K, et al. Diagnosis of a tear of the distal tibiofibular syndesmosis: the role of arthroscopy of the ankle. J Bone Joint Surg Br. 2003;85(3):324-329. doi:10.1302/0301-620x.85b3.13174

6. Espinosa N, Smerek JP, Myerson MS. Acute and chronic syndesmosis injuries: pathomechanisms, diagnosis and management. Foot Ankle Clin. 2006;11(3):639-657. doi:10.1016/j.fcl.2006.05.001

7. Grass R, Rammelt S, Biewener A, et al. Peroneus longus ligamentoplasty for chronic instability of the distal tibiofibular syndesmosis. Foot Ankle Int. 2003;24(5):392-397. doi:10.1177/107110070302400504

8. Ramsey PL, Hamilton W. Changes in tibiotalar area of contact caused by lateral talar shift. J Bone Joint Surg Am. 1976;58(3):356-357.

9. Ogilvie-Harris DJ, Reed SC, Hedman TP. Disruption of the ankle syndesmosis: biomechanical study of ligamentous restraints. Arthroscopy. 1994;10(5):558-560. doi:10.1016/s0749-8063(05)80014-3

10. Boytim MJ, Fischer DA, Neumann L. Syndesmotic ankle sprains. Am J Sports Med. 1991;19(3):294-298. doi:10.1177/036354659101900315

11. Williams GN, Jones MH, Amendola A. Syndesmotic ankle sprains in athletes. Am J Sports Med. 2007;35(7):1197-1207. doi:10.1177/0363546507302545

12. Sman AD, Hiller CE, Rae K, et al. Diagnostic accuracy of clinical tests for diagnosis of ankle syndesmosis injury: a systematic review. Br J Sports Med. 2015;49(5):323-329. doi:10.1136/bjsports-2013-092787

13. Stufkens SA, van den Bekerom MP, Kerkhoffs GM, et al. Long-term outcome after 1822 operatively treated ankle fractures: a systematic review of the literature. Injury. 2011;42(2):119-127. doi:10.1016/j.injury.2010.04.006

14. Gardner MJ, Demetrakopoulos D, Briggs SM, et al. Malreduction of the tibiofibular syndesmosis in ankle fractures. Foot Ankle Int. 2006;27(10):788-792. doi:10.1177/107110070602701005

15. Sagi HC, Shah AR, Sanders RW. The functional consequence of syndesmotic joint malreduction at a minimum 2-year follow-up. J Orthop Trauma. 2012;26(7):439-443. doi:10.1097/BOT.0b013e31822a526a

16. Stoffel K, Wysocki D, Baddour E, et al. Comparison of two intraoperative assessment methods for injuries to the ankle syndesmosis: a cadaveric study. J Bone Joint Surg Am. 2009;91(11):2646-2652. doi:10.2106/JBJS.G.01537

17. Takao M, Uchio Y, Naito K, et al. Diagnosis and treatment of combined intra-articular disorders in acute distal fibular fractures. J Trauma. 2004;57(6):1303-1307. doi:10.1097/01.ta.0000140450.84450.cb

18. Manjoo A, Sanders DW, Tieszer C, MacLeod MD. Functional and radiographic results of patients with syndesmotic screw fixation: implications for screw removal. J Orthop Trauma. 2010;24(1):2-6. doi:10.1097/BOT.0b013e3181a9f7a5

---