Classification
- Type: Syndesmosis (fibrous joint bound by the interosseous membrane and tibiofibular ligaments)
- Degrees of freedom: Minimal — slight lateral fibular spread and rotation during ankle dorsiflexion
- Region: Ankle complex (mechanically linked to anatomy/joints/proximal-tibiofibular and anatomy/joints/talocrural)
Articular Surfaces
- Fibular notch of the tibia (concave): A shallow depression on the lateral distal tibia
- Medial surface of the distal fibula (convex): Fits into the fibular notch, bound by strong ligamentous structures
- No articular cartilage — this is a fibrous joint, not synovial
Movements and ROM
| Movement |
Description |
Mechanism |
| Lateral fibular spread |
1–2 mm widening of the mortise |
During ankle dorsiflexion, the wider anterior talus wedges between the malleoli, forcing them apart |
| Fibular rotation |
Slight external rotation of the fibula |
Accompanies dorsiflexion and eversion |
| Superior glide |
Slight superior fibular movement |
During weight-bearing dorsiflexion |
The ankle mortise must widen during dorsiflexion. The talus is wider anteriorly than posteriorly. As the ankle dorsiflexes, the wider anterior portion enters the mortise, forcing the fibula laterally by 1–2 mm. A rigid syndesmosis that cannot accommodate this spread limits dorsiflexion.
Capsular Pattern
Not applicable — this is a syndesmosis, not a synovial joint.
Resting and Close-Packed Positions
Not applicable for a syndesmosis in the traditional sense. The syndesmosis is maximally stressed in ankle dorsiflexion with eversion.
Ligaments
Anterior Inferior Tibiofibular Ligament (AITFL)
- Attachments: Anterior distal tibia → anterior distal fibula
- Function: Resists fibular displacement anteriorly and laterally. The most commonly injured syndesmotic ligament (first structure damaged in high ankle sprain).
- Assessment test: Squeeze test (compress the tibia and fibula at mid-calf level — pain at the syndesmosis is positive). External rotation stress test (externally rotate the foot with the knee at 90° — pain at the syndesmosis is positive).
Posterior Inferior Tibiofibular Ligament (PITFL)
- Attachments: Posterior distal tibia → posterior distal fibula
- Function: The strongest syndesmotic ligament. Resists fibular displacement posteriorly and laterally. A posterior malleolar fragment in ankle fractures often avulses this ligament.
Transverse Tibiofibular Ligament
- Attachments: Posterior tibial ridge → posterior distal fibula (deep to the PITFL)
- Function: Forms a labrum-like extension of the tibial articular surface posteriorly, deepening the ankle mortise
Interosseous Membrane
- Attachments: Along the interosseous borders of the tibia and fibula from proximal to distal
- Function: Binds the tibia and fibula along their entire length; the distal portion (interosseous ligament) is the most critical for syndesmotic stability
Mobilization Techniques
Hands-on instruction is required. The descriptions below provide clinical reference detail for understanding and supervised practice. They are not a substitute for instructor-led technique training. Correct hand placement, force dosage, and tissue response interpretation require hands-on coaching and feedback.
General Contraindications
- Absolute: Syndesmotic disruption (high ankle sprain with instability), malleolar fracture, active infection
- Relative: Healing syndesmotic sprain (follow rehabilitation timeline — typically 6–12 weeks for full syndesmotic healing)
Anteroposterior Fibular Glide at the Distal Tibiofibular Joint
Purpose: Restores syndesmotic mobility when ankle dorsiflexion is limited by a rigid distal tibiofibular syndesmosis. The fibula must glide posteriorly and laterally to accommodate the widening mortise during dorsiflexion.
Patient position:
- Supine or long sitting with the ankle over the edge of the table
- Ankle in neutral or slight dorsiflexion
Hand placement:
- Stabilizing hand: Grips the distal tibia medially, stabilizing it
- Mobilizing hand: Thumb and fingers grip the lateral malleolus (distal fibula). For posterior glide: direct force posteriorly on the lateral malleolus. For anterior glide: direct force anteriorly.
Technique execution:
- Apply an oscillatory force directing the distal fibula posteriorly (to restore dorsiflexion) or anteriorly (to restore plantarflexion)
- Grade I–II: Gentle oscillations for assessment and pain modulation
- Grade III: Oscillations into end-range for syndesmotic mobilization
- Duration: 20–30 seconds, 2–3 sets
Indications:
- Restricted ankle dorsiflexion that persists after talocrural mobilization and gastrocnemius/soleus stretching
- Post-ankle sprain stiffness with syndesmotic involvement
- Decreased distal fibular mobility on accessory motion testing
Technique notes:
- Critical: Ensure syndesmotic integrity before mobilizing. If the squeeze test and external rotation stress test are positive (indicating syndesmotic disruption), do not mobilize — the syndesmosis needs to heal.
- Reassessment: Re-test ankle dorsiflexion. Improvement confirms syndesmotic restriction.
Distal Tibiofibular Distraction (Mortise Spreading)
Purpose: Restores the ability of the mortise to widen during dorsiflexion. Gently separates the tibia and fibula at the distal syndesmosis.
Patient position: Same as above.
Hand placement:
- One hand on the medial malleolus (tibia), one on the lateral malleolus (fibula). Apply gentle opposing forces — spreading the malleoli apart.
Technique execution:
- Gentle oscillatory or sustained distraction spreading the mortise
- Grade I–II only — the syndesmosis has limited extensibility by design; aggressive spreading risks ligamentous damage
- Duration: 15–20 seconds, 2–3 sets
Indications:
- Decreased mortise width on accessory testing (compare bilaterally)
- Post-immobilization (cast or boot) syndesmotic stiffness
Muscles Crossing This Joint
No muscles directly cross the distal tibiofibular syndesmosis. Muscles that affect fibular position include:
Conditions Affecting This Joint
- High ankle sprain (syndesmotic sprain) — disruption of the AITFL and potentially the interosseous membrane; more serious and slower to heal than lateral ligament sprains; positive squeeze test and external rotation stress test; recovery 6–12 weeks (vs. 2–6 weeks for lateral sprains)
- Ankle fracture with syndesmotic disruption — Weber B and C fractures (fibular fractures at or above the syndesmosis) often involve syndesmotic injury; surgical fixation with a syndesmotic screw may be required
- Syndesmotic impingement — thickened or scarred AITFL tissue impinges on the anterolateral talus during dorsiflexion; anterior ankle pain; common after ankle sprains
Clinical Notes
- High ankle sprains are frequently underdiagnosed. A patient with an ankle sprain who has pain above the lateral malleolus (at the syndesmosis level), a positive squeeze test, and pain with external rotation stress has a syndesmotic injury — not a simple lateral ligament sprain. The recovery timeline is 2–3 times longer. Misdiagnosis leads to premature return to activity and chronic instability.
- The syndesmosis must be assessed in all ankle dorsiflexion limitations. If talocrural mobilization and gastrocnemius/soleus stretching do not restore dorsiflexion, the syndesmosis or proximal tibiofibular joint may be the limiting factor. Assess distal fibular AP and lateral mobility.
- Post-fracture syndesmotic stiffness is common. After ankle fractures treated with a syndesmotic screw, the screw is often removed at 6–12 weeks. The syndesmosis may be fibrosed and stiff, limiting dorsiflexion. Gentle syndesmotic mobilization is an important component of post-fracture rehabilitation.
Key Takeaways
- The ankle mortise must widen 1–2 mm during dorsiflexion to accommodate the wider anterior talus — syndesmotic rigidity limits dorsiflexion.
- High ankle sprains (syndesmotic disruption) are 2–3 times slower to heal than lateral ligament sprains — the squeeze test and external rotation stress test differentiate them.
- Always assess syndesmotic integrity (squeeze test, ER stress test) before mobilizing — disrupted syndesmosis is a contraindication.
