High Ankle Sprain
The ATFL is the most injured ligament in the ankle, and an injury to the syndesmosis can account for around 10% of all ankle injuries, as reported by Boytim et al (1991) who studied professional (American) football players in a six-year study and found syndesmostic sprains accounted for 18 out of 98 ankle injuries reported. Hermans et al (2010) estimated that between 1-11% of all ankle injuries involved the syndesmosis.
Anatomy:
The distal tibiofibular joint is an articulation of the convex surface of the fibula, and the concave tibia (Norkus and Floyd, 2001). It is stabilised by the syndesmosis which contains the interosseus membrane which runs all the way between the tibia and fibula, and three other ligaments which provide stability at the distal end of the joint. The ligaments are the anteroinferior tibiofibular ligament, the posteroinferior tibiofibular ligament, a transverse ligament, and the previously mentioned interosseous membrane (Williams and Allen, 2010).
ogilvie-Harris et al (1994) completed a cadaver study investigating the amount of stability provided by these ligaments at the distal tibiofibular joint. they demonstrated that the ATFL accounts for 35% of the joints stability, the interosseus membrane 22% whilst the PTFL provides around 42%. therefore we can see that an injury to one or more of these ligaments can cause a significant amount of instability within the joint.
What is cause it:
An injury to the tibiofibular joint can be caused by contact or non contact. This could be in a tackle where a player’s foot is in contact with the ground and forcibly externally rotated, or when a player suddenly changes direction with the foot planted and moving into external rotation.
It has been shown that dorsiflexion and external rotation causes increased tension to the ligaments at the distal tibiofibular joint. This mechanism causes the talus to rotate and as a result can cause separation between the tibia and fibula stressing the ligaments, or worst case scenario, causing a rupture (Norkus and Floyd, 2001)
the external rotation mechanism has been shown to initially affect the ATFL, further rotation would then pose a risk to the interosseus membrane and PTFL (Hermans et al, 2010. Hunt, 2013). the normal gap between the tibia and fibula is around 5mm (Hunt, 2013) but even an extra 1mm increase in joint space can cause instability in the ankle.
Diagnosis:
Following a suspected syndesmosis injury, it is important to gather appropriate information from the subjective assessment such as: mechanism, swelling, location of pain etc.
Objectively a suspected syndesmosis injury may have pain and swelling over the distal tibiofibula joint, reduced range of movement and strength, difficultly weight bearing (or inability to be able to push off). It is important to consider other structures in the ankle such as the deltoid ligament, which has been shown to be injured in conjunction with the syndesmosis complex, due to its accessory role in stabilisation of the distal tibiofibula joint (Hunt, 2013).
The common test I use to test for a syndesmosis injury is the external rotation test. This can be done in sitting or (if the player can weight bear) in standing (replicating the mechanism of injury). In sitting the player is sat over the edge of the bed, the knee is stabilised and the foot moved into dorsiflexion and eversion. Pain would point towards a suspected syndesmosis sprain (Williams and Allen, 2010).
In a systematic review, Schwieterman et al (2013) looked at the diagnostic accuracy of special tests at the foot and ankle, their results (which didn’t include Pakarinen, I have just added it to the table) are below:
Test Sensitivity Specificity Paper Subjects
Cotton Test 0.25 N/A Beumer et al 28
0.25 0.98 Pakarinen 288
External Rotation 0.99 N/A Beumer et al 294
0.20 0.85 De Cesar et al 56
0.58 0.90 Pakarinen 288
Fibula Translation 0.75 0.88 Beumer et al 322
Squeeze Test 0.30 0.94 De Cesar et al 56