Normal Tibiofibular Joint Space Size on Radiography
The distal tibiofibular joint space refers to the clear space between the lateral border of the tibia and the medial border of the fibula at the level of the ankle syndesmosis. Accurate measurement of this space on plain radiographs is essential for identifying syndesmotic disruption, which can lead to ankle instability and accelerated joint degeneration if left untreated.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Anteroposterior, Mortise | <6 mm |
Clinical Significance
A tibiofibular joint space exceeding 6 mm on anteroposterior (AP) or mortise views is considered abnormal and strongly suggests disruption of the distal tibiofibular syndesmosis. Syndesmotic injury is commonly associated with high-energy ankle fractures and pronation-external rotation mechanisms. Even subtle widening may indicate partial ligamentous tear requiring close clinical correlation.
Failure to recognize syndesmotic instability can result in fibular malreduction, chronic lateral ankle pain, and post-traumatic osteoarthritis. The mortise view is particularly valuable because fibular overlap with the tibia is minimized, making subtle widening more apparent. Comparison with the contralateral ankle can be helpful when findings are equivocal.
- Distal tibiofibular syndesmosis rupture
- Maisonneuve fracture with syndesmotic disruption
- Bimalleolar or trimalleolar ankle fracture
- Isolated ligamentous syndesmotic sprain (high ankle sprain)
- Post-operative or post-traumatic fibular malposition
Reference: DiGiovanni CW, M.d. JG. Foot and Ankle, Core Knowledge in Orthopaedics. C.V. Mosby. (2007).
Imaging Notes
The tibiofibular joint space is measured on standard anteroposterior (AP) and mortise ankle radiographs. The mortise view, obtained with the ankle internally rotated approximately 15–20°, profiles the syndesmosis without fibular overlap and is the preferred projection for this measurement. The clear space is assessed approximately 1 cm above the tibial plafond, measured horizontally between the lateral cortex of the posterior tibial tubercle and the medial cortex of the fibula.
Ensure the patient is positioned correctly and weight-bearing views are obtained where clinically feasible, as stress across the mortise can unmask occult instability. External rotation stress radiographs may be performed under fluoroscopy when ligamentous injury is suspected but resting views appear normal.