Ankle fractures

• introduction
• basic science
  • anatomy
  • movement
  • stability
  • contact and pressure
  • effects of injury
• classification
• clinical features
• imaging
• management
  • principles
  • undisplaced fractures
  • displaced fractures principles
  • displaced fractures ORIF
  • medial malleolar fractures
  • posterior malleolar fractures
  • syndesmosis injuries (this page)
  • post-op management
• ankle fractures in older patients
• ankle fractures in diabetics
• references

Last evidence check March 2008

Ankle fractures with a syndesmosis injury and interosseous membrane rupture (AO type C) are severe, potentially unstable injuries. egol (2009) found that the functional outcome of patients who required syndesmotic stabilisation was worse on both the short musculoskeletal function outcome instrument and the AOFAS ankle score than those who needed only malleolar stabilisation.

Biomechanical and clinical studies, particularly those of Boden (1989), clarified these injuries and suggeste selective syndesmotic stabilisation. As with other ankle fractures, an intact deep deltoid ligament would protect against tibio-talar displacement even with severe syndesmotic tears – tears up to 15cm above the ankle have been studied in cadaver experiments. However, if the medial malleolus was fractured or the DTTL torn, a low syndesmotic tear (existing data suggest <4.5cm from the ankle joint line) could still be stable if the fibula is anatomically reduced and fixed. Above this, a syndesmotic positioning screw is likely to be needed. van den Bekerom (2010) confirmed that Boden's criteria had a specificity of 0.96 but a sensitivity of only 0.39: they are good at ruling in the need for a syndesmosis screw but less at ruling it out.

There are a number of issues in translating these biomechanical studies into real life:

• A clinical study confirmed that if the medial malleolus and the fibula are fixed in a stable manner, the syndesmosis will normally be reduced and stable, and a syndesmotic stabilisation screw will rarely be required.
• However, fibular stabilisation may sometimes be relative in these severe injuries, which often have significant comminution.
• The level of the fracture does not predict the level of the tear of the interosseous membrane very accurately (Nielson 2004), so some fractures will be more unstable than the radiograph suggests. Indeed, there have been a number of papers which suggest that anything up to 30% of even trans-syndesmotic (AO type B) fractures may have significant syndesmotic injuries with residual instability even after ORIF.
• One some times sees small medial malleolar fractures, which usually represent the anterior colliculus of the malleolus only. The deep deltoid is not attached to this, but more posteriorly. Therefore, if the anterior colliculus is fractures and the mortise is incongruent, the deep deltoid ligament must also be torn. Fixation of the medial malleolar fragment in this situation will not stabilise the medial side.

Therefore, it is probably best to stress test all ankle fractures after bony stabilisation. The syndesmosis should be stressed laterally, anteroposteriorly and in external rotation – Briggs et al (2004) suggested the main direction of instability is anteroposterior rather than laterally.

Both Gardner (2006) and Rosarhelyi (2006) found that over 50% of ankle fractures with syndesmotic injuries showed some degree of malreduction on CT after apparently satisfactory ORIF.

Biomechanical studies suggest a single 3.5mm cortex screw, through 3 cortices, about 2cm above the ankle joint line, is adequate for stability. Additional, or larger, screws, do not normally resuce the risk of late displacement. The screw should be inserted with the ankle dorsiflexed to prevent narrowing of the mortise. It should be a neutral, not a lag screw. Occasionally, however, a second screw is required in a highly-unstable fracture or a very large patient.

Recent studies have explored the importance of the posterior malleolus in syndesmotic injuries. Gardner (2006) demonstarted in a cadaver model that posterior malleolar fixation resored 70% of syndesmosis stablity compared with 40% after syndesmotic screw insertion. Miller (2010) then demonstrated, in a small series, that open reduction and stabilisation of the syndesmosis produced equivalent clinical results to syndesmosis screw fixation. They recommended (Miller 2009a) direct visual confirmation of syndesmotic reduction and described the use of the posterolateral approach to achieve this (Miller 2009b). By using this method they reduced the rate of syndesmotic malreduction from 52% (Gardner 2006, Miller 2009) to 16% (Miller 2009).

Should syndesmosis screws be removed?

It is traditionally advised to keep patients with syndesmosis screws non-weightbearing until the screw is removed at 6-12 weeks, lest the screw should loosen or break, usually the former. Hamid (2009) found no difference in AOFAS ankle scores between patients who had retained syndesmosis screws, broken screws and retained screws. However, those with retained screws had slightly higher pain scores. Manjoo (2010) found better Olerud-Molander scores in patients who had screw removal or breakage, than in those with intact screws. The tibiofibular clear space was narrower with intact screws. Miller (2010) noted improvements in range of movement and ankle scores after implant removal in 25 patients who had syndesmotic screw and fibular plate removal.

It appears that it is intact, rather than broken, screws that can cause difficulties. Manjoo recommende offering screw removal six months after ORIF to patients whose screws are intact at that stage, which seems consistent with current evidence.