Ankle Syndesmosis Fixation

Surgical Indications

Absolute Indications

• Weber C or pronation-external rotation (Lauge-Hansen) ankle fracture with confirmed intra-operative syndesmotic instability after anatomic fibular plate fixation — demonstrated by the hook test, external rotation stress test, or Cotton test under fluoroscopy
• High ankle sprain (isolated syndesmotic disruption) with Grade III instability — complete disruption of the AITFL, PITFL, and interosseous ligament confirmed on MRI or stress radiography, and clinical or radiographic talar shift
• Syndesmotic diastasis greater than 6 mm on the AP radiograph (compared with the contralateral side) with clinical instability

Relative Indications

• Maisonneuve fracture (proximal fibular fracture with syndesmotic disruption and medial injury) — fixation of the syndesmosis after anatomic fibular reduction or fixation
• Chronic syndesmotic instability with persistent pain and confirmed diastasis on weight-bearing CT or stress radiography — delayed reconstruction using suture-button or screw with ligamentous repair
• Ankle fracture with associated posterior malleolar fracture involving greater than 25% of the articular surface and PITFL disruption where posterior fixation alone does not restore syndesmotic stability on intra-operative testing

Contraindications

Absolute:

• Syndesmotic instability that resolves after anatomic fibular plate fixation — do not over-fix a stable syndesmosis
• Active deep infection or open fracture contamination at the planned fixation site
• Significant tibial plafond or pilon fracture that precludes accurate syndesmotic assessment

Relative:

• Poor skin condition or significant soft tissue compromise at the lateral ankle (delay fixation until soft tissue recovery)
• Severe osteoporosis where screw purchase is unreliable (consider suture-button or larger diameter screws with bicortical purchase)
• Patient non-compliance with weight-bearing restrictions (suture-button may be preferred over screw fixation)

Intra-operative Syndesmotic Instability Tests

Hook Test

• Technique: After anatomic fibular plate fixation, insert a bone hook or clamp around the distal fibula and apply lateral traction while viewing the syndesmosis on fluoroscopy
• Positive finding: Lateral translation of the fibula away from the tibia (widening of the tibiofibular clear space greater than 5 mm compared to the fixed position) with lateral traction
• Limitations: Operator-dependent force; does not detect pure rotational instability; may give false-negative if AITFL is partially intact
• Evidence: Widely used and accepted as a standard intra-operative test; sensitivity and specificity vary by study but it is a reliable practical bedside tool

External Rotation Stress Test

• Technique: Apply external rotation force to the foot (or the talus directly) while the ankle is held in neutral or slight dorsiflexion, under fluoroscopic imaging of the mortise view
• Positive finding: Widening of the medial clear space greater than 5 mm (or greater than 2 mm compared to the contralateral side) on the mortise view with external rotation
• Limitations: Requires adequate imaging quality; medial clear space interpretation depends on the quality of the medial-sided repair (if deltoid is ruptured); a valgus stress component may produce a false-positive in pure deltoid insufficiency
• Evidence: Considered the most specific test for syndesmotic instability when performed after fibular fixation; best assessed on the mortise view

Cotton Test

• Technique: Apply lateral or medial talar shift force (manual or with a laminar spreader) under fluoroscopy while viewing the mortise view
• Positive finding: Asymmetric talar shift within the mortise; widening of the medial clear space suggesting residual instability despite lateral fixation
• Limitations: Does not isolate syndesmotic instability from pure deltoid incompetence; lateral talar shift may occur from deltoid rupture alone
• Evidence: Useful adjunct but least specific of the three tests — interpret in conjunction with the hook test and external rotation stress test

Trampoline Test (Ballottlement)

• Technique: With the ankle in neutral, palpate the anteroinferior tibiofibular ligament (AITFL) region. Press on the fibula laterally — a springy or bouncy feel (like a trampoline) indicates disruption of the AITFL and syndesmotic instability
• Positive finding: Loss of normal firm resistance; a spongy, springy feel when the fibula is depressed laterally
• Limitations: Subjective and examiner-dependent; does not quantify the degree of instability
• Evidence: Described in clinical practice as a useful adjunct; most valuable when combined with fluoroscopic stress testing

Evidence for Fixation Methods

Syndesmotic Screws

Positional screw fixation (3.5 or 4.5 mm cortical screw) is the historical gold standard for syndesmotic stabilisation. The screw is placed through the fibula into the tibia at a level 2-4 cm above the tibial plafond (above the synovial reflection), angled 25-30 degrees anteriorly in the coronal plane.

• Quadricortical fixation (4 cortices): Screw engages both tibial cortices and both fibular cortices — provides rigid fixation but eliminates all physiological tibiofibular motion. Screws frequently break with weight-bearing (10-30% rate).
• Tricortical fixation (3 cortices): Screw engages both fibular cortices and the medial tibial cortex only — leaves the lateral tibial cortex free, permitting some tibiofibular motion. Theoretically lower breakage rate but higher risk of loosening. Less commonly used.
• Number of screws: Biomechanical studies show two screws (placed at 2 cm and 3-4 cm above the plafond) provide greater torsional stability than one screw. One screw is acceptable in smaller frames or less severe disruptions; two screws are preferred in larger patients and high-energy injuries.
• Screw removal: Typically removed at 8-12 weeks post-operatively to restore tibiofibular motion and reduce the risk of breakage. The evidence for routine removal is debated — some studies show no difference in outcome with retained screws, but breakage and subsequent removal difficulty are practical concerns. Removal carries a small risk of re-diastasis.

Suture-Button Fixation (TightRope)

A suture-button device (e.g. TightRope, ZipTight) passes a fibre-wire loop through 4-cortex drill holes (fibula to tibia) and is secured with metallic or bioabsorbable buttons on the lateral fibula and medial tibia.

• Advantages: Does not require routine removal; allows earlier weight-bearing (protocols vary but many permit partial weight-bearing from 2-4 weeks); provides dynamic flexible fixation that permits physiological tibiofibular micromotion while maintaining reduction
• Biomechanics: Suture-button constructs match or exceed the stiffness of 3.5 mm quadricortical screws in biomechanical models for resistance to diastasis under physiologic loading; however, they are less stiff under high-load torsional stress
• Complications: Knot or button irritation over the medial tibial cortex (5-15% of cases — may require later removal of the button); skin irritation or wound problems at the button site; rare device failure or breakage
• Evidence: Multiple RCTs and meta-analyses have compared suture-button with screw fixation. Overall, functional outcomes at 1-2 years are comparable between the two methods. Suture-button shows advantages in earlier return to weight-bearing and absence of planned hardware removal.

Key Evidence

Distal Tibiofibular Syndesmosis

Ligamentous Complex

The syndesmosis is a fibrous joint connecting the distal tibia and fibula, stabilised by four key structures:

Incisura Fibularis

The incisura fibularis (also called the tibial incisure or fibular notch) is the groove on the distal lateral tibia where the fibula sits. Its anatomy varies:

• Deep (concave) incisura: More stable anatomically — the tibial surface cups the fibula, providing inherent bony stability. Less dependent on ligamentous restraints.
• Shallow (flat) incisura: Less bony stability — the syndesmotic ligaments bear a greater proportion of the stabilising load. These patients are more vulnerable to syndesmotic instability from relatively lower-energy injuries and may be over-represented in high ankle sprain cohorts.

Clinical importance: The incisura depth varies between individuals. A shallow incisura is a risk factor for syndesmotic instability and malreduction. Pre-operative contralateral CT can characterise the incisura shape and serve as a reference for reduction.

Tibiofibular Relationship — Radiographic Landmarks

Structures at Risk During Surgery

Peroneal tendons: Pass posterior to the distal fibula in the retromalleolar groove. Drill trajectories directed too far posteriorly during screw or suture-button placement risk penetrating the retromalleolar groove and irritating or injuring the peroneal tendons. Drilling should be performed under direct visualisation or fluoroscopic guidance with the trajectory angled anteriorly.

Superficial peroneal nerve: Crosses the lateral aspect of the fibula approximately 6-8 cm above the lateral malleolus tip. At risk during exposure of the proximal fibular fracture (in Maisonneuve injuries) or during dissection for syndesmotic screw placement if the incision is extended proximally. Identify and protect in all lateral approaches.

Saphenous nerve and vein: Located anteromedially, at risk during medial malleolar exposure, deltoid repair, or medial placement of suture-button button. The great saphenous vein runs with the saphenous nerve in the subcutaneous tissue anteromedially.

Deep peroneal nerve and dorsalis pedis artery: Located in the anterior interval between tibia and extensor hallucis longus. At risk during anterior ankle arthrotomy for direct incisura visualisation. Retract the EHL laterally to protect the neurovascular bundle.

Positioning and Preparation

Patient position: Supine on a radiolucent table with a bump under the ipsilateral hip to internally rotate the leg and bring the lateral malleolus into a more accessible position. Place a small sandbag or rolled towel under the ipsilateral buttock to improve the AP fluoroscopic view of the ankle.

Fluoroscopy: A true AP view (the malleoli should appear equidistant from the talus, with the talar dome appearing symmetric) and a true mortise view (15-20 degrees internal rotation so the talar dome is perfectly symmetric and the medial and lateral clear spaces are equal) must be obtainable before draping. Verify with the uninjured contralateral ankle for comparison images.

Anaesthesia: General or spinal anaesthesia. A well-padded high thigh tourniquet inflated to 250-300 mmHg. Prophylactic antibiotics (single dose of cefazolin 2 g IV at induction, or alternative based on local protocol and allergy status).

Consent: Counsel regarding: malreduction and its consequences (chronic pain, early arthritis), hardware breakage (screws), need for planned screw removal (second procedure), suture-button knot or button irritation, wound infection, non-union or malunion of associated fractures, complex regional pain syndrome, and the possibility of eventual ankle fusion or replacement for post-traumatic arthritis.

Step 1: Anatomic Fibular Reduction and Plate Fixation

Before assessing or treating the syndesmosis, the fibula must be anatomically reduced and stabilised with plate osteosynthesis. This is the prerequisite step — failure to restore fibular length and rotation guarantees syndesmotic malreduction.

Exposure: Use the standard lateral approach to the fibula (longitudinal incision along the posterior border of the fibula, centred over the fracture). Protect the superficial peroneal nerve (crosses 6-8 cm above the lateral malleolus). Develop the interval between peroneal muscles posteriorly and the extensor compartment anteriorly. Expose the fracture, irrigate, and remove haematoma.

Reduction: Reduce the fibular fracture anatomically using pointed reduction clamps, checking length (fibular shadow alignment with the tibial shadow on AP view), rotation (the lateral malleolar tip should point directly laterally on the mortise view), and translation (the fibula should sit centrally within the incisura). Confirm reduction on AP, lateral, and mortise fluoroscopic views before applying the plate.

Plate fixation: Apply a one-third tubular plate or pre-contoured anatomical locking plate along the lateral fibula. A minimum of 3 cortices (preferably 6 cortices) proximal and distal to the fracture are recommended. Use an interfragmentary lag screw where possible to achieve compression.

Step 2: Intra-operative Syndesmotic Stability Testing

With the fibular plate securely fixed, perform the following tests sequentially:

Hook Test

Apply lateral traction to the distal fibula using a bone hook or pointed reduction clamp. Apply gentle, progressive lateral force while a colleague holds the tibia. View the tibiofibular clear space on fluoroscopy during traction.

Positive: Greater than 5 mm widening of the tibiofibular clear space on AP view compared to the fixed position. The fibula visibly moves laterally away from the incisura.

External Rotation Stress Test

Apply external rotation force to the hindfoot while the ankle is in neutral or slight dorsiflexion. View the mortise view on fluoroscopy.

Positive: Widening of the medial clear space greater than 5 mm (or greater than 2 mm compared to the contralateral pre-operative mortise view). The talus shifts laterally within the mortise.

Cotton Test

Apply lateral translation force to the talus (manual or with a small spreader). View the mortise view on fluoroscopy.

Positive: Talar shift within the mortise; widening of the medial clear space; loss of congruence between the talar dome and the plafond.

Step 3: Syndesmotic Reduction

If instability is confirmed, reduce the syndesmosis before placing any fixation.

Dorsiflexion Position

Place the ankle in neutral or slight dorsiflexion (10-15 degrees). Maximum dorsiflexion brings the wider anterior talar dome into the mortise and can over-compress the syndesmosis if fixation is placed in this position. Neutral to slight dorsiflexion is preferred.

Reduction Technique

• Direct visualisation (preferred): Through the existing fibular fracture site or through a small anterolateral arthrotomy (2-3 cm incision anteroinferior to the fibula), directly visualise the anterior incisura. The fibular articular cartilage should sit congruently within the tibial incisura. If exposed, the AITFL fibres should realign anatomically.
• Pointed clamp: Apply a pointed reduction clamp to the fibula and tibia at the level of planned fixation (typically 2-4 cm above the plafond). Ensure the clamp engages the lateral fibular cortex and the medial tibial cortex. Tighten gradually while checking reduction on fluoroscopy.

Fluoroscopic Confirmation

Check the following on fluoroscopy after clamping:

Intra-operative CT (when available)

If intra-operative CT is available, perform a scan of the distal tibiofibular joint after clamping. Compare with the contralateral ankle (pre-operative CT). This is the gold standard for confirming anatomic reduction and detecting malreduction that is invisible on plain fluoroscopy.

Step 4: Fixation Placement

Option A — Syndesmotic Screws (Quadricortical)

Implant: 3.5 mm cortical screw (most common) or 4.5 mm cortical screw in larger patients. Fully threaded positional screw — do NOT use as a lag screw.

Drilling:

1. Identify the drill entry point on the lateral fibular cortex at the level of the plate or 2 cm above the plafond
2. Aim the drill 25-30 degrees anteriorly in the coronal plane (to match the slope of the tibiofibular joint) and perpendicular to the long axis in the sagittal plane
3. Drill through 4 cortices (lateral fibula, medial fibula, lateral tibia, medial tibia) using a 2.5 mm drill bit for a 3.5 mm screw, or a 3.2 mm drill bit for a 4.5 mm screw
4. Confirm trajectory on fluoroscopy — the drill should pass through the tibia at the level of the syndesmosis, approximately 2-4 cm above the plafond

Screw insertion:

1. Measure screw length with a depth gauge (typically 35-50 mm for quadricortical purchase)
2. Tap the tibial cortices (the fibula is usually tapped through the plate if using a self-tapping screw; the tibia may require tapping for 4.5 mm screws)
3. Insert the fully threaded cortical screw with the ankle in the same position used for reduction (neutral or slight dorsiflexion)
4. Tighten the screw to secure reduction — do not over-compress (check the medial clear space on mortise view)

One versus two screws:

• One screw: Adequate in smaller patients, lower-energy injuries, and when the syndesmotic disruption is confined to a single level. Place at 2 cm above the plafond.
• Two screws: Preferred in high-energy injuries, larger patients, and when the interosseous ligament disruption extends more proximally. Place the first screw at 2 cm and the second at 3-4 cm above the plafond, through separate plate holes or through separate stab incisions. Biomechanically, two screws provide greater rotational stability.

Tricortical option: Drill and insert a screw engaging only 3 cortices (both fibular cortices plus the medial tibial cortex), leaving the lateral tibial cortex free. This preserves some tibiofibular motion. Technically more demanding; less commonly used but supported by some biomechanical evidence.

Option B — Suture-Button (TightRope)

Implant: Commercially available suture-button device (e.g. Arthrex TightRope, Zimmer Biomet ZipTight, Stryker TENODEX). The device consists of a fibre-wire loop with metallic or bioabsorbable buttons on each end.

Drilling:

1. Identify the drill entry point on the lateral fibula, 2 cm above the plafond (through the plate or a separate stab incision)
2. Use a 3.5-4.0 mm drill bit (device-specific) and drill through 4 cortices with the same trajectory as for a syndesmotic screw (25-30 degrees anteriorly)
3. Confirm trajectory on fluoroscopy

Device passage and fixation:

1. Pass the guide wire from lateral (fibula) to medial (tibia) through the drilled hole
2. Pass the suture-button construct over the guide wire from lateral to medial, deploying the lateral button on the fibular cortex
3. Pull the fibre-wire loop taut from the medial side to reduce the syndesmosis
4. Deploy the medial button on the medial tibial cortex
5. Tighten the construct by tying knots or using the tensioning mechanism (device-specific) while monitoring reduction fluoroscopically
6. Verify: medial clear space, tibiofibular clear space, and tibiofibular overlap should match the contralateral side

Two devices: Some surgeons use two suture-button devices (one at 2 cm, one at 3-4 cm above the plafond) for additional stability, analogous to two screws. The biomechanical advantage of a second device is less well established than for two screws.

Step 5: Final Intra-operative Confirmation

After fixation is placed, perform the following checks:

1. External rotation stress test: The syndesmosis should be stable with no widening of the medial clear space on the mortise view
2. AP and mortise views: Tibiofibular clear space less than 6 mm, tibiofibular overlap greater than 6 mm, medial clear space equal to superior clear space and to contralateral side
3. Lateral view: Fibular reduction maintained, posterior malleolus congruent
4. Intra-operative CT (if available): Compare syndesmotic reduction with the contralateral pre-operative CT. Confirm no anterior subluxation of the fibula within the incisura
5. Range of motion: Check that the ankle moves through a functional range (neutral to 20 degrees dorsiflexion) without crepitus or impingement — excessive restriction may indicate over-compression

Step 6: Wound Closure and Post-operative Immobilisation

Close the lateral fibular incision in layers. If an anterior arthrotomy was made for incisura visualisation, close the capsule with absorbable suture. Apply a below-knee backslab or well-padded removable boot with the ankle in neutral.

Weight-Bearing Protocol

Syndesmotic Screw Fixation

The weight-bearing protocol for syndesmotic screws is determined by whether the surgeon plans routine removal. The principle is that syndesmotic screws are positional screws designed to hold reduction while ligaments heal — they are not designed to bear axial load.

Standard protocol (screw removal planned):

• Weeks 0-2: Non-weight-bearing in a below-knee plaster backslab or rigid boot with the ankle in neutral. Elevate limb. Begin gentle ankle dorsiflexion and plantarflexion exercises out of the boot under physiotherapy guidance (if a boot is used).
• Weeks 2-6: Non-weight-bearing continues. Transition to a removable boot if in a cast. Increase range-of-motion exercises. Start active-assisted ankle circumduction. Proprioception exercises seated.
• Weeks 6-8: Partial weight-bearing (25-50% body weight) in the boot, progressing as tolerated. Continue range-of-motion and strengthening exercises.
• Weeks 8-12: Planned syndesmotic screw removal. After removal, protected weight-bearing in boot for 2-3 weeks while monitoring for re-diastasis. Then transition to full weight-bearing.
• Weeks 12-16: Progressive weight-bearing without boot. Return to light activities. Proprioception and balance training.
• 3-6 months: Gradual return to sport-specific activities. Full return to sport at approximately 6 months for high-demand athletes, earlier for lower-demand activities.

Protocol without planned removal (retained screw):

• Non-weight-bearing for 8-10 weeks, then gradual transition to full weight-bearing over 4-6 weeks. The screw may break (10-30%) but broken retained screws are often asymptomatic. Functional outcomes are generally satisfactory even if the screw breaks, provided the initial reduction was anatomic.

Suture-Button Fixation

The suture-button construct allows earlier weight-bearing because it is a dynamic fixation that permits physiological tibiofibular micromotion.

Standard protocol (suture-button):

• Weeks 0-2: Non-weight-bearing or touch-weight-bearing (up to 15 kg) in a boot. Early ankle range-of-motion exercises out of the boot under supervision.
• Weeks 2-4: Progressive weight-bearing from 25% to 50% in the boot. Continue range-of-motion, strengthening (resistance band), and proprioception exercises.
• Weeks 4-6: Weight-bearing as tolerated in the boot. Begin weaning from boot as comfort permits.
• Weeks 6-12: Full weight-bearing in a normal shoe. Continue progressive strengthening (calf raises, single-leg balance). Proprioception training with wobble board.
• 3-6 months: Sport-specific rehabilitation. Return to sport approximately 4-6 months depending on injury severity and functional recovery.

Rehabilitation Milestones

Phase 1: Protection (Weeks 0-6)

• Goal: Protect fixation, control swelling, restore pain-free range of motion
• Elevation: Above heart level for the first 48 hours, then continue intermittent elevation for 2 weeks
• Ankle ROM: Gentle dorsiflexion and plantarflexion within the boot or cast; avoid forced inversion/eversion in the early weeks (protects the healing syndesmotic ligaments)
• Strengthening: Isometric quadriceps and gluteal exercises to maintain proximal leg strength; gentle toe curls and ankle pumps
• Modalities: Ice, compression, elevation for oedema control

Phase 2: Mobilisation (Weeks 6-12)

• Goal: Restore full range of motion, begin weight-bearing, early strengthening
• Weight-bearing: Gradual progression (protocol depends on fixation type)
• ROM: Active-assisted to active range of motion; target full dorsiflexion (ideally match contralateral) and full plantarflexion
• Strengthening: Resistance band exercises for dorsiflexors, plantarflexors, invertors, and evertors; calf raises (bilateral progressing to single-leg)
• Proprioception: Single-leg balance (eyes open progressing to eyes closed); wobble board
• Gait re-education: Normalise gait pattern with physiotherapy guidance

Phase 3: Strengthening and Return to Activity (Weeks 12-24)

• Goal: Functional strengthening, proprioceptive recovery, gradual return to sport and work
• Strengthening: Eccentric loading of the gastrocnemius-soleus complex; single-leg squat; lateral agility drills
• Proprioception: Advanced balance training (unstable surfaces, perturbation training)
• Running: Begin straight-line jogging at approximately 12-16 weeks if pain-free, full ROM, and adequate strength (greater than 80% of contralateral side)
• Sport-specific: Agility drills, cutting, jumping at 16-24 weeks
• Full return to sport: Typically 4-6 months after injury for competitive athletes; individualised based on functional testing

Factors Influencing Recovery

Expected Outcomes

Short term (3-6 months):

• Most patients achieve weight-bearing by 3-4 months (suture-button) or 3-4 months after screw removal (screw fixation)
• Ankle range of motion typically recovers to 80-90% of contralateral by 6 months
• Mild residual swelling and stiffness are common and expected

Medium term (1-2 years):

• Functional outcome scores (AOFAS, OMAS) are generally good to excellent in patients with anatomic reduction
• Malreduced patients have significantly worse scores and higher rates of early post-traumatic arthritis
• Return to sport rates of 70-85% at 1 year in competitive athletes (lower in high-demand pivoting sports)

Long term (greater than 2 years):

• Anatomic reduction with any fixation type provides the best long-term prognosis
• Post-traumatic ankle arthritis develops in 15-30% of patients at 5-10 years (higher in malreduced or chondrally injured ankles)
• Ankle arthrodesis is the definitive salvage procedure for end-stage post-traumatic arthritis