Syndesmotic Instability

West Point Ankle Grading System

This is the most commonly used classification for syndesmotic instability:

This classification is based on the clinical finding and assists in treatment decisions.

Lauge-Hansen Classification (Ankle Fractures with Syndesmotic Injury)

Syndesmotic injuries occur in specific fracture patterns:

Supination-External Rotation (SER):

• Stage I: AITFL disruption
• Stage II: Spiral oblique fibula fracture (at joint level)
• Stage III: PITFL disruption or posterior malleolus fracture
• Stage IV: Transverse medial malleolus fracture or deltoid rupture

Pronation-External Rotation (PER):

• Stage I: Transverse medial malleolus fracture or deltoid rupture
• Stage II: AITFL disruption
• Stage III: Spiral oblique fibula fracture (above joint level)
• Stage IV: PITFL disruption or posterior malleolus fracture

Pronation-Abduction (PAB):

• May have syndesmotic disruption in later stages
• Typically transverse fibula fracture at joint level

Understanding the Lauge-Hansen mechanism helps predict associated injuries.

Edwards and DeLee Classification (Isolated Syndesmotic Injuries)

This classification focuses on isolated syndesmotic injuries without fracture:

Implications:

• Type I: Usually conservative management
• Type II and III: Higher likelihood of requiring surgical stabilization

This classification emphasizes the importance of identifying associated medial or lateral injuries.

Squeeze Test:

• Compress tibia and fibula together at mid-calf level
• Positive: pain at the ankle (distal syndesmosis), not at the compression site
• Sensitivity: 30-92%, Specificity: 88-95%
• Most sensitive clinical test for syndesmotic injury

External Rotation Stress Test:

• Stabilize leg, externally rotate foot with knee flexed to 90 degrees
• Positive: pain at anterior or posterior syndesmosis
• Sensitivity: 20-71%, Specificity: 85-97%
• Most specific clinical test

Cotton Test (Fibular Translation Test):

• Grasp calcaneus and talus, translate laterally
• Positive: greater than 2mm lateral shift of fibula relative to tibia
• More commonly performed intraoperatively under anesthesia
• Compares to contralateral side

Dorsiflexion-External Rotation Test:

• Dorsiflex ankle and apply external rotation force
• Positive: pain at syndesmosis
• May be difficult to perform acutely due to pain

This section covers the examination findings used to assess syndesmotic stability.

Palpation sequence:

1. Anterior syndesmosis: palpate just above the ankle joint, between tibia and fibula

   • Tenderness here suggests AITFL injury

2. Posterior syndesmosis: palpate posterolateral ankle

   • Tenderness suggests PITFL injury

3. Proximal fibula: always palpate the fibular head and neck

   • Tenderness indicates possible Maisonneuve fracture

4. Medial structures: palpate medial malleolus and deltoid ligament

   • Often injured in combination with syndesmotic disruption

5. Interosseous membrane: palpate along the length of the leg

   • Proximal tenderness may indicate high interosseous membrane injury

Comparison to contralateral side is essential to detect subtle abnormalities.

This systematic approach ensures you do not miss associated injuries.

Gait assessment:

• Inability to weight bear suggests significant injury
• Antalgic gait with external rotation of foot to avoid pain
• Push-off weakness (due to pain with dorsiflexion)

Range of motion:

• Pain at end-range dorsiflexion (talus widens mortise)
• Pain with plantarflexion and external rotation
• Compare to uninjured side

Strength testing:

• Gastrocnemius strength: heel raise test (often painful)
• Tibialis anterior: resisted dorsiflexion
• Eversion and inversion strength

Single leg hop test (subacute phase):

• Inability to hop suggests persistent instability
• Useful for return-to-sport decisions

Functional assessment helps gauge severity and recovery progress.

Standard ankle series (AP, mortise, lateral):

AP view measurements:

• Tibiofibular overlap: should be greater than 6mm
  • Less than 6mm suggests diastasis
• Tibiofibular clear space: measure 1cm above plafond
  • Greater than 6mm suggests instability

Mortise view measurements (most important):

• Medial clear space: distance between medial malleolus and talus
  • Should be equal to superior clear space (ankle joint space)
  • Widening greater than 1mm compared to superior = deltoid injury
• Tibiofibular clear space: greater than 6mm abnormal
• Tibiofibular overlap: less than 1mm abnormal
• Talocrural angle: should be symmetric

Lateral view:

• Assess for posterior malleolus fracture (associated with PITFL injury)
• Greater than 25% articular surface involvement may need fixation

Weight-bearing radiographs:

• May reveal diastasis not apparent on non-weight-bearing films
• Useful in chronic or subtle cases

Plain radiographs are the initial imaging modality and often diagnostic.

External rotation stress view:

• Apply external rotation force to foot while taking mortise radiograph
• Can be performed manually or with device
• Positive: widening of medial clear space or tibiofibular clear space
• Compare to contralateral side (bilateral views essential)

Gravity stress view:

• Patient positioned lateral decubitus
• Foot hangs off table, gravity provides stress
• Less painful than manual stress

Cotton test (radiographic):

• Apply lateral translation force to foot
• Measure fibular displacement
• Greater than 2mm compared to contralateral side indicates instability

Indications for stress views:

• Equivocal findings on static radiographs
• High clinical suspicion despite normal static films
• Assessment of isolated syndesmotic injury (West Point latent vs subluxation)

Stress radiographs are the gold standard for diagnosing latent syndesmotic instability.

MRI:

• Indications:
  • Confirm extent of ligamentous injury
  • Assess for associated injuries (osteochondral lesions, deltoid, lateral ligaments)
  • Chronic syndesmotic pain with normal radiographs
• Findings:
  • AITFL disruption: fluid signal, discontinuity
  • PITFL disruption: similar findings
  • Bone bruising in distal tibia/fibula
  • Associated deltoid or lateral ligament injuries

CT scan:

• Indications:
  • Assess posterior malleolus fracture size
  • Evaluate syndesmotic reduction after fixation
  • Assess for malreduction (fibular malposition)
• Axial CT at level of tibial plafond:
  • Measure fibular position in incisura
  • Assess for rotational malreduction

Ultrasound:

• Dynamic assessment of syndesmotic stability
• Less commonly used
• Operator-dependent

Arthroscopy:

• Can directly visualize syndesmotic widening
• Greater than 2mm widening on arthroscopic visualization = instability
• Useful intraoperatively to assess reduction

Advanced imaging is helpful for equivocal cases or surgical planning.

Indications for conservative management:

• West Point latent (stable on stress testing)
• Isolated AITFL sprain without diastasis
• No associated fractures
• Patient can bear weight without significant pain

Acute phase (0-2 weeks):

• RICE protocol: rest, ice, compression, elevation
• Controlled Ankle Motion (CAM) boot or below-knee cast
• Non-weight bearing initially, progress as tolerated
• NSAIDs for pain (short course to avoid delayed healing)
• Crutches until comfortable single-leg standing

Intermediate phase (2-6 weeks):

• Progress to protected weight bearing in boot
• Begin gentle range of motion exercises
  • Alphabet exercises
  • Plantarflexion and dorsiflexion
  • Avoid inversion/eversion initially
• Progressive resistance exercises
• Continue boot for 4-6 weeks total

Late phase (6-12 weeks):

• Wean from boot to lace-up ankle brace
• Proprioceptive training: balance exercises, single leg stance
• Strengthening: gastrocnemius, tibialis anterior, peroneals
• Sport-specific drills (if athlete)
• Gradual return to activity

Return to sport criteria:

• No pain with weight bearing or running
• Full range of motion compared to contralateral
• Single leg hop test 90% of contralateral
• Typically 8-12 weeks (2-3x longer than lateral ankle sprain)

Follow-up radiographs at 2-4 weeks to ensure no delayed diastasis develops.

Absolute indications for surgery:

• Frank diastasis on static radiographs (West Point dislocation)
• Unstable ankle fracture with syndesmotic injury
• Maisonneuve fracture with syndesmotic disruption
• Greater than 2mm fibular translation on Cotton test

Relative indications:

• West Point subluxation in high-demand athletes
• Persistent instability despite 6 weeks conservative treatment
• Chronic syndesmotic instability with pain

Intraoperative assessment (for ankle fractures):

• After fibula fixation, perform Cotton test under fluoroscopy
• Assess for greater than 2mm lateral translation of fibula
• Compare to contralateral side if uncertain
• Assess medial clear space on mortise view
• If unstable, proceed with syndesmotic fixation

Goals of surgery:

1. Anatomic reduction of tibiofibular relationship
2. Maintain reduction while ligaments heal
3. Allow early range of motion (if using suture button)
4. Prevent post-traumatic arthritis

Surgical decision-making is based on stability assessment and fracture pattern.

Traditional syndesmotic screw fixation:

Setup:

• Patient supine, bump under ipsilateral hip
• Thigh tourniquet (optional)
• Fluoroscopy available (AP, mortise, lateral views)

Step 1: Reduction of syndesmosis

• Ensure fibular length restored (if fracture present)
• Position ankle in dorsiflexion and neutral rotation
  • Dorsiflexion widens anterior talus, preventing over-compression
• Apply reduction clamp from fibula to tibia
  • Place clamp 2cm above joint line
  • Apply gentle compression (avoid over-compression)
• Confirm reduction on fluoroscopy:
  • AP: tibiofibular overlap greater than 6mm
  • Mortise: clear space less than 6mm, overlap greater than 1mm
  • Lateral: fibula centered in incisura

Step 2: Screw insertion

• Insert screw 2-3cm above tibial plafond
• Direction: 30 degrees anterior to posterior (parallel to joint line)
• Size: 3.5mm or 4.5mm cortical screw
• Drill perpendicular to long axis of fibula
• Purchase: 3 cortices (both fibular cortices + near tibial cortex) or 4 cortices (all four)
  • 3 cortices: allows some motion, screw less likely to break
  • 4 cortices: more rigid, higher breakage rate
• Do not lag the screw (use non-lag technique)

Step 3: Optional second screw

• Some surgeons place 2 screws for increased stability
• Second screw 1-2cm proximal to first
• Same trajectory and technique

Step 4: Confirm reduction

• Remove clamp
• Obtain final fluoroscopy images (AP, mortise, lateral)
• Ensure clear space, overlap, and fibular position anatomic

Screw removal:

• Remove at 8-12 weeks if non-bioabsorbable
• Prevents screw breakage with weight bearing
• Protected weight bearing until screw removed or bioabsorbable screw incorporated

This is the traditional technique with proven long-term results.

Suture button (TightRope) fixation:

Advantages:

• Allows physiologic motion of syndesmosis (1-2mm)
• No need for implant removal
• Early weight bearing and range of motion
• Lower re-operation rate

Disadvantages:

• Higher cost
• Technically more demanding
• Potential for over-compression if not careful

Setup:

• Same positioning as screw fixation
• Ankle in dorsiflexion and neutral rotation

Step 1: Reduction

• Reduce syndesmosis as with screw technique
• Confirm on fluoroscopy

Step 2: Device insertion

• Drill 4mm hole from fibula to tibia
  • Entry point 2-3cm above plafond on fibula
  • Trajectory 30 degrees anterior to posterior
• Pass suture button device through drill hole
• Fibular button sits on lateral fibula
• Tibial button flips on medial tibial cortex

Step 3: Tensioning

• Apply tension to suture (usually pre-loaded with specific tension)
• Buttons compress fibula to tibia
• Avoid over-compression: should restore normal anatomy, not compress excessively
• Confirm reduction on fluoroscopy

Step 4: Final checks

• Remove clamp if used
• Assess stability by manually stressing ankle
• Confirm measurements on final images

Post-operative protocol:

• Early weight bearing as tolerated (advantage over screw)
• Early range of motion (within days)
• No implant removal needed

Suture button is increasingly popular, especially in athletic populations.

Common pitfalls in syndesmotic fixation:

1. Malreduction (most critical):

• Over-compression: clamp applied too aggressively
  • Narrows mortise excessively
  • Prevention: gentle clamp application, check on all views
• External rotation malreduction: fibula externally rotated
  • Narrowing of posterior mortise
  • Prevention: neutral rotation during fixation, check lateral view
• Anterior/posterior malposition:
  • Fibula translated anteriorly or posteriorly in incisura
  • Prevention: lateral fluoroscopy view, compare to contralateral CT if needed

2. Screw placement errors:

• Too distal: less than 2cm above plafond
  • Risk of intra-articular placement
• Wrong trajectory: not parallel to joint
  • Causes eccentric fibular position
• Lagging the screw:
  • Causes over-compression and malreduction

3. Inadequate assessment:

• Failure to assess stability after fibula fixation
  • Cotton test essential in fracture cases
• Not comparing to contralateral side
  • Normal anatomy varies; comparison is key

4. Post-operative management errors:

• Early weight bearing with rigid screw fixation
  • Leads to screw breakage
• Failure to remove screw
  • Screw breakage, difficulty with removal later

Recognition and management:

• Intraoperative: check fluoroscopy on all views before final fixation
• Post-operative: CT scan if malreduction suspected
• Revision if more than 1mm malreduction on post-op imaging

Awareness of pitfalls and meticulous technique prevent complications.

Intraoperative complications:

1. Malreduction (20-50% incidence):

• Over-compression of syndesmosis
• Fibular malposition (rotation, translation)
• Recognition: intraoperative fluoroscopy on multiple views
• Prevention: ankle in dorsiflexion, neutral rotation, gentle clamp application

2. Intra-articular screw placement:

• Screw placed too distal or wrong trajectory
• Recognition: pain, limited motion, radiographic signs
• Prevention: stay 2cm above plafond, confirm on lateral view

3. Neurovascular injury:

• Superficial peroneal nerve (at fibular incision site)
• Deep peroneal nerve or anterior tibial vessels (rare, with anterior approach)
• Prevention: careful dissection, knowledge of anatomy

Early post-operative complications:

4. Wound complications:

• Incidence: 5-10% in ankle fracture surgery
• Risk factors: diabetes, smoking, soft tissue injury
• Prevention: delay surgery if blisters present, careful soft tissue handling

5. Screw breakage (early):

• If weight bearing too early with rigid fixation
• Usually asymptomatic if syndesmosis healed
• Prevention: protected weight bearing until screw removal or union

6. Loss of reduction:

• Syndesmosis re-widens despite fixation
• May indicate inadequate fixation or continued instability
• Management: revision fixation if detected early

These complications can often be prevented with careful technique and appropriate post-operative protocols.

Chronic complications:

1. Post-traumatic arthritis (long-term most significant):

• Incidence: 10-30% at 5-10 years
• Malreduction is the primary risk factor
• Even 1mm malreduction significantly increases risk
• Presentation: pain, stiffness, crepitus
• Management: conservative initially (activity modification, bracing, NSAIDs), ankle fusion or replacement for end-stage

2. Chronic syndesmotic instability:

• Persistent or recurrent diastasis
• Causes: inadequate initial fixation, premature screw removal, high-energy injury
• Presentation: chronic pain, feeling of "giving way", difficulty with push-off
• Diagnosis: weight-bearing radiographs, stress views, MRI
• Management: syndesmotic reconstruction (see Chronic Instability tab)

3. Heterotopic ossification:

• Bone formation in syndesmotic region
• Incidence: 20-30% after syndesmotic injury
• Usually asymptomatic, found incidentally on radiographs
• Rarely requires excision

4. Screw-related issues:

• Screw breakage: 25-50% if not removed by 12 weeks
  • Usually asymptomatic if syndesmosis healed
  • Remove if symptomatic
• Difficulty removing screw: osseointegration, stripped head
• Prevention: remove at 8-12 weeks, use bioabsorbable screws

5. Stiffness and limited dorsiflexion:

• More common with rigid fixation and prolonged immobilization
• Prevention: early motion (especially with suture button), aggressive PT
• Treatment: stretching, manipulation under anesthesia if severe

6. Complex regional pain syndrome (CRPS):

• Rare but can be devastating
• Presentation: disproportionate pain, allodynia, autonomic changes
• Management: early recognition, desensitization, pain management referral

Long-term outcomes depend primarily on achieving and maintaining anatomic reduction.

Chronic syndesmotic instability:

Definition:

• Persistent diastasis or recurrent instability more than 6 months after injury

Causes:

• Inadequate initial treatment (missed diagnosis)
• Premature implant removal
• Malreduction with initial surgery
• High-energy injury with extensive soft tissue damage

Presentation:

• Chronic anterolateral ankle pain
• Pain with push-off or cutting activities
• Feeling of ankle "giving way"
• Difficulty returning to sport

Diagnosis:

• Weight-bearing radiographs: diastasis on static films
• Stress radiographs: compare to contralateral side
• MRI: assess ligamentous healing, rule out other pathology
• CT scan: assess arthritis, fibular position

Non-operative management (trial first):

• Activity modification
• Lace-up ankle brace or custom orthosis
• Physical therapy: proprioception, strengthening
• NSAIDs for pain
• Consider PRP or other biologics (limited evidence)

Operative management:

1. Syndesmotic screw or suture button (if ligaments have potential to heal):

• Reduce syndesmosis under fluoroscopy
• Fix with screw or button as acute injury
• Outcomes variable, better if less than 6 months from injury

2. Direct ligament repair/reconstruction:

• Open repair of AITFL and PITFL with suture anchors
• Augmentation with suture tape or internal brace
• Autograft reconstruction: free tendon graft (gracilis, semitendinosus) through drill holes
• Allograft reconstruction: similar technique with allograft

3. Arthroscopic debridement + fixation:

• Remove scar tissue and synovitis
• Assess reduction arthroscopically
• Fix with screw or button

Outcomes:

• Chronic instability surgery has less predictable results than acute fixation
• Earlier intervention (less than 6 months) has better outcomes
• Presence of arthritis worsens prognosis

Chronic syndesmotic instability is a challenging problem that is best prevented.

Post-operative protocol for screw fixation:

Phase 1: Protection (0-2 weeks)

• Splint or boot with non-weight bearing
• Elevate leg above heart level
• Ice for swelling control
• DVT prophylaxis if indicated
• Suture removal at 10-14 days

Phase 2: Early mobilization (2-6 weeks)

• Transition to CAM boot
• Non-weight bearing continues (if quadricortical screw)
• Partial weight bearing (if tricortical screw, some protocols)
• Begin gentle ROM exercises (plantarflexion/dorsiflexion)
• Avoid inversion/eversion

Phase 3: Screw removal and progressive loading (6-12 weeks)

• Screw removal at 8-12 weeks (if not bioabsorbable)
• After removal, progress to full weight bearing over 2 weeks
• Wean from boot to ankle brace
• ROM exercises progress to include inversion/eversion
• Begin strengthening exercises

Phase 4: Return to activity (12+ weeks)

• Progress strengthening
• Proprioceptive training: balance board, single leg exercises
• Sport-specific drills
• Gradual return to sport at 12-16 weeks post-screw removal

Total timeline: 20-28 weeks (5-7 months) from surgery to full sport

This protocol protects the syndesmosis during ligament healing.

Post-operative protocol for suture button fixation:

Phase 1: Protection (0-2 weeks)

• Splint or boot
• Weight bearing as tolerated (major advantage over screw)
• Ice and elevation
• DVT prophylaxis if indicated
• Suture removal at 10-14 days

Phase 2: Early mobilization (2-6 weeks)

• Continue boot
• Full weight bearing progressed rapidly
• Early ROM exercises (within days of surgery)
  • Ankle pumps immediately
  • ROM in all planes by 2 weeks
• Begin resistance band exercises

Phase 3: Strengthening (6-12 weeks)

• Wean from boot to ankle brace (by 6 weeks)
• Progressive strengthening program
  • Gastrocnemius: heel raises (bilateral, then unilateral)
  • Tibialis anterior: resisted dorsiflexion
  • Peroneals and invertors: resistance band
• Proprioceptive training: balance exercises

Phase 4: Return to activity (12+ weeks)

• Sport-specific training
• Agility drills
• Gradual return to sport at 12-16 weeks

Total timeline: 12-16 weeks (3-4 months) from surgery to full sport

Advantages:

• Faster return to activity (no screw removal wait)
• Early motion reduces stiffness
• No re-operation for implant removal

This accelerated protocol is a major benefit for athletes.

Detailed rehabilitation exercise progression:

Early phase exercises (0-6 weeks):

• Ankle pumps: plantarflexion and dorsiflexion in boot
• Alphabet exercises: trace alphabet with foot (ROM)
• Towel scrunches: picking up towel with toes (intrinsic strengthening)
• Isometric contractions: push against resistance without motion

Intermediate phase (6-12 weeks):

• Resistance band exercises:
  • Dorsiflexion: band around forefoot, pull toes toward shin
  • Plantarflexion: push forefoot away against band
  • Inversion: pull foot inward against band
  • Eversion: push foot outward against band
• Heel raises: bilateral progressing to unilateral
• Toe raises: strengthen tibialis anterior
• Balance exercises: single leg stance on firm surface
  • Progress to unstable surface (foam pad, balance board)

Advanced phase (12+ weeks):

• Plyometrics: box jumps, single leg hops
• Agility drills: ladder drills, cone drills, cutting
• Sport-specific exercises: simulate sport movements
• Single leg hop test: assess readiness for return to sport

Return to sport criteria:

• No pain with running or cutting
• Full ROM compared to contralateral (especially dorsiflexion)
• Strength 90% of contralateral (heel raise, single leg hop)
• Passed functional testing (hop test, agility)
• Confidence with sport-specific movements

Brace recommendations:

• Lace-up ankle brace for first 3-6 months of sport participation
• Taping may be used as alternative
• Gradual weaning from brace as confidence improves

Structured rehabilitation is essential for optimal outcomes.