Syndesmotic Behavior after Sequential Sectioning: Simulation of Ligamentous Ankle Injuries in Vitro

Category: Ankle, Trauma, Distal Tibiofibular Joint Introduction/Purpose: Ankle fractures are often associated with ligamentous injuries of the distal tibiofibular syndesmosis and the deltoid ligament. These injuries may predispose to instability, early joint degeneration and long-term ankle dysfunction. In the classic article of Boden it was made clear that injuries of the syndesmotic ligaments were of no importance in absence of a deltoid ligament rupture. Even in the presence of a deltoid ligament rupture, the interosseous membrane withstood lateralization of the talus in fixated fibula fractures up to 4.5 mm above the ankle joint. However, detection of ligamentous injuries and the need for treatment remain subject of ongoing debate. Syndesmotic injuries are often treated operatively by temporary fixation performed with positioning screws. But do isolated syndesmotic injuries need to be treated operatively at all? Methods: Ten fresh-frozen, exarticulated through the knee, human cadaveric lower limbs were tested under axial compressive loads of 50 and 700 N, simulating non-weightbearing and weightbearing conditions. All specimens were tested with different foot positions (plantigrade, dorsiflexion, inversion, eversion, and 10 Nm external rotational torque) during sequential sectioning of the syndesmotic ligaments and the deltoid ligament. We triangulated Boden’s classic findings with an active motion capture system (0.1 mm accuracy) to track the translations and rotations of the fibula relative to the tibia. Results: Isolated sectioning of the AITFL resulted in an increase of external fibula rotation up to 8.9 degrees (doubling the physiological 4.0 degrees) with an external rotation stress of 10 Nm in non-weightbearing conditions. However, weightbearing appeared somewhat protective, reducing the external rotation to 7.9 degrees. Sectioning of all syndesmotic ligaments with an intact deltoid ligament resulted in a syndesmotic widening of 0.9 mm in weightbearing conditions with a plantigrade foot. Dorsiflexion of the foot resulted in a significant increase of syndesmotic widening for all conditions of the syndesmotic ligaments. Sectioning of the deltoid ligament resulted in a significant increase of all fibula translations in all foot positions during weightbearing conditions. Conclusion: The results of our study have implications for common ligamentous ankle injuries and their treatment. In isolated syndesmotic injuries with a plantigrade foot, weightbearing seemed protective and limiting syndesmotic widening probably due to the saddle shape of the tibiotalar surface. Conservative treatment in a cast seems justifiable. External rotation stress causes the “open-book-phenomenon” in isolated AITFL injuries, especially in non-weightbearing conditions. Protection with cast or surgery is necessary. The deltoid ligament prevents lateralization of the talus but allows increased syndesmotic widening and external rotation of the fibula in dorsiflexion and external rotation stress due to the shape of the talus.

Upper Cervical Spine Stability: Maximum Rotation and the Rotation Stress Test in Clinics

The rotation stress test is used to evaluate stability of the craniocervical junction by assuming that it gives the maximum rotation. However, a more complex manipulation might show a higher rotation: the rotation with extension and contralateral bending. This was tested in vitro with ten upper cervical spine specimens.

3D Talar Kinematics During External Rotation Stress Testing in Hindfoot Varus and Valgus Using a Model of Syndesmotic and Deep Deltoid Instability

Background: External rotation stress (ERS) identifies ankle instability after fibular reduction of rotational ankle injuries. Combined hindfoot and ankle motions and an inconsistent starting position could mask differing degrees of instability resulting from syndesmotic and/or deltoid ligament disruption. The goal of this work was to use full 3D talar kinematics to evaluate the effects of hindfoot orientation and foot starting position during ERS on the ability to detect instability caused by ligament disruptions. Methods: Six cadaveric ankles with metallic fiducial markers were CT scanned in neutral and 3 stress positions: varus hindfoot internal rotation stress (IRS-var), valgus hindfoot ERS (ERS-val), and varus hindfoot ERS (ERS-var). Scans were obtained in stress positions after transecting the deep deltoid ligament (tDDL) and then the syndesmotic ligaments (tDDL+Syn). Talar rotations and translations were computed in the axial, coronal, and sagittal planes in each stress position. Changes in a fixed center of rotation (CoR) relative to the intact sequence were calculated. Results: Axial plane rotation beginning from IRS-var increased significantly for each level of ligamentous instability ( P < .05 for all conditions) (10.9 degrees, intact; 14.1 degrees, tDDL; 22.7 degrees, tDDL+Syn during ERS-val; and 16.4 degrees, intact; 23.1 degrees, tDDL; 29.9 degrees, tDDL+Syn during ERS-var). With ERS-val, the talar CoR moved medially (3.6-5.4 mm) and posteriorly (0.5-5.2 mm); ERS-var moved anterior/laterally or posterior/medially depending on the specific ligamentous instability. With tDDL+Syn the ankle became grossly unstable and there were no clear trends in sagittal/coronal rotation or translation. Conclusion: An ERS test from internal to external rotation consistently differentiates between normal, tDDL, and tDDL+Syn. Talar CoR moved outside the mortise with ligamentous instability. Clinical Relevance: Significant residual deep deltoid instability is likely underrecognized with current practice. The most discriminatory test for detecting such instability in our laboratory was an ERS test performed by internally rotating the foot to a hard, bony endpoint, positioning the hindfoot in varus, and then performing the entire external rotation maneuver while maintaining the varus hindfoot position.

Intraoperative Torque Test to Assess Syndesmosis Instability

Background: In this cadaveric study, a new “torque test” (TT) stressing the fibula posterolaterally under direct visualization was compared with the classical external rotation stress test (ERT) and lateral stress test (LST). Methods: The anteroinferior tibiofibular ligament (AiTFL), the interosseous membrane (IOM), and the posteroinferior tibiofibular ligament (PiTFL) were sectioned sequentially on 10 fresh-frozen human ankles. At each stage of dissection, instability was assessed using the LST, ERT, and TT under direct visualization. Anatomical tibiofibular diastasis measurements were taken directly on cadavers and compared using the Wilcoxon signed rank test. Results: All 3 tests showed statistically significant motion in the syndesmosis when at least 2 ligaments were sectioned. The mean increase across diastasis with a 2-ligament section was 3.0 mm ( P = .005), 3.2 mm ( P = .005), and 4.8 mm ( P = .005) for the LST, ERT, and TT, respectively. The largest mean increase in diastasis was obtained with a complete injury using the TT and was 6.2 mm ( P = .008). With the TT, a 3.5-mm tibiofibular diastasis was 90% sensitive and 100% specific when 2 or more syndesmotic ligaments were sectioned. Conclusion: The TT was a more sensitive and specific tool for detecting syndesmosis instability than classic LST and ERT. Clinical relevance: Stressing the fibula in a posterolateral direction created a larger distal tibiofibular diastasis, which would be easier to detect in the intraoperative setting. The TT was more sensitive and specific to detecting a 2-ligament syndesmotic injury than the classic test and required less force to perform.