Syndesmotic and Deltoid Injuries: Companions or Coincidences.

Background: Syndesmotic complex injuries are supposedly associated with injuries to the deltoid ligament (DL) complex. Several syndesmosis classifications take DL injuries into account when rating the stability of the syndesmotic injury. Still, no study has yet assessed the frequency and severity of DL injuries in unstable syndesmotic injuries. The aim of this retrospective cohort study was to assess both the severity of the syndesmotic and DL injury in patients undergoing surgery for an unstable syndesmotic injury.

Methods: The integrity of the syndesmotic and DL complex of 37 patients were assessed on MRI by 2 musculoskeletal radiologists. Eligible were adult patients with an acute, isolated, unstable syndesmotic injury (ligamentous or bony avulsions) who underwent surgery. The DL complex was classified as having 3 superficial (TNL/TSL/TCL) and 2 deep (aTTL/pTTL) components. Grade 0 indicated an intact ligament; grade I showed a periligamentous edema; grade II a partial tear presenting as laxity, irregular contour, or partial discontinuity with concomitant hyperintense signaling; grade III a complete tear; or grade IV in case of an avulsion fracture. Frequency and severity of DL injuries were assessed, and possible injury combinations analyzed using an h-cluster analysis and Mann-Whitney U test.

Results: Mean severity (grade 0-3) was 2.6 ± 0.8 for the syndesmotic complex and 1.6 ± 1.1 for the DL (superficial 1.5 ± 1.1, deep 1.6 ± 1.1). Seven patients (19%) had no (n = 3; 8%) or minor (grade 1: n = 4; 11%) DL injuries. Overall, 2 different patient clusters and 4 separate ligament clusters were identified.

Conclusion: Unstable syndesmotic injuries can occur isolated or with an accompanying DL injury. There appears to be a great heterogeneity between the severity of syndesmotic and deltoid ligament injuries.