Role of the posterior deep deltoid ligament in ankle fracture stability: A biomechanical cadaver study

Abstract

BACKGROUND The deltoid ligament is a key component of ankle fracture stability. Clinical tests to assess deltoid ligament injury have low specificity. In supination external-rotation (SER) type-IV ankle fractures, there is either a medial malleolus fracture or deltoid ligament injury. These injuries are often considered unstable, requiring surgical stabilisation. We look to identify the anatomical basis for this instability. This study investigates the anatomical basis for such instability by re-creating SER type ankle fractures in a standardised cadaveric study model, investigating the anatomical basis for such instability. AIM To investigate the anatomical basis for fracture instability in SER type ankle fractures. METHODS Four matched pairs of cadaveric limbs were tested for stability both when axially loaded and under external rotation stress. Four matched pairs of cadaveric limbs (8 specimens) were tested for stability when axially loaded to 750 N with a custom rig. Specimens were tested through increasing stages of SER injury in a stepwise fashion before restoring the lateral side with open reduction and internal fixation (ORIF). Clinical photographs and radiographs were recorded at each step. We defined instability in accordance with well accepted radiological parameters: > 4 mm medial clear space opening on a mortise-view radiograph or > 7 degrees of talar tilt. RESULTS All specimens with an intact posterior deep deltoid ligament were stable. Once the posterior deep deltoid ligament was sectioned there was instability in all specimens. Stabilisation of the lateral side prevented talar shift, but not talar tilt. CONCLUSION If the posterior deep deltoid ligament is intact then SER fractures can be managed without surgery. If the posterior deep deltoid is incompetent, ORIF and cautious rehabilitation is recommended because the talus can still tilt in the mortise.

Effects of Progressive Deltoid Ligament Sectioning on Weber B Ankle Fracture Stability

“…Our MCID for talar tilt instability was 7.0 degrees, consistent with a previous report. 16 No MCID value for defining rotational instability exists. Radiographic measurements were obtained using Sectra IDS7, version 23.2 (Sectra AB, Linköping, Sweden).…”

“…It has been suggested that these are termed SER4a fractures 7 ; acceptable clinical and functional outcomes in the short and midterm have been reported after nonoperative treatment. 3,[6][7][8]13,15,16 However, the primary concern with nonoperative treatment of SER4a fractures is the risk of occult instability leading to PTOA in the long term. 7,14 This study builds on Gougoulias and Sakellariou's theory advocating that the superficial layer and deep anterior deltoid ligaments are injured whereas the deep posterior deltoid ligament remains intact in SER4a fractures.…”

“…It has been suggested that these are termed SER4a fractures 7 ; acceptable clinical and functional outcomes in the short and midterm have been reported after nonoperative treatment. 3 , 6 - 8 , 13 , 15 , 16 However, the primary concern with nonoperative treatment of SER4a fractures is the risk of occult instability leading to PTOA in the long term. 7 , 14 …”

Concomitant Unstable and Stable Gravity Stress Tests on Weight-Bearing Stable Weber B Ankle Fractures Treated Nonoperatively

“…Instability is indicated in 35% to 48% of ankle fractures when gravity stress tests are used 2-5 , but in only 1% to 3% of fractures when weight-bearing radiographs are used 2-4 , meaning that the ankle mortise often changes from nonanatomic to anatomic (i.e., an apparently unstable fracture to an apparently stable one) after the orientation of the leg is shifted and weight is applied to it. This is rationalized by a possible partial rupture of the deltoid ligament, with the deep posterior portion of the ligament remaining intact 3,6,7 . Some authors have suggested classifying such an injury as SER4a 3,6 .…”

“…one) after the orientation of the leg is shifted and weight is applied to it. This is rationalized by a possible partial rupture of the deltoid ligament, with the deep posterior portion of the ligament remaining intact 3,6,7 . Some authors have suggested classifying such an injury as SER4a 3,6 .…”