The Kinematic Effect of Anatomic Deep Deltoid Ligament Stabilization in a Cadaveric Model of Syndesmotic Instability with Deep Deltoid Ligament Instability

Category: Trauma; Sports Introduction/Purpose: The objective of this work was to investigate the utility of a suture augmented deep deltoid ligament (DDL) stabilization with different accepted treatments of distal tibiofibular syndesmosis injuries. We hypothesized that adding DDL stabilization would improve the rotational stability of the ankle. Also, that flexible syndesmotic stabilization using suture button fixation, AITFL suture stabilization, with DDL stabilization would restore the kinematics of an intact ankle most closely during external rotation stress (ERS). Methods: Ten matched pairs of through-the-knee cadaveric ankle specimens were mechanically tested in 5 Nm of ERS under 750 N of axial load. Specimens were tested intact, after transection of all the syndesmotic and deep deltoid ligaments and after each iteration of one of two stabilization sequences: 1) AITFL + suture button (SB) stabilization; AITFL+SB + DDL suture stabilization; syndesmotic screw with or without DDL stabilization; or 2) AITFL+SB+DDL; AITFL+SB; syndesmotic screw with or without DDL stabilization. Optical motion tracking was used to capture the kinematics of the tibia, fibula, and talus. CT scans of each specimen with markers were used to transform kinematic data into an anatomic coordinate system. Individual bony kinematics were extracted by decomposing the transformation matrices needed to align the starting test position to the ending test position and tracking points on the anterior medial and anterior lateral talus. Results: The average axial rotation of the talus was significantly increased after destabilization from 5.15 to 9.02 as compared to the intact state (P< 0.001). All the four fixation constructs reduced the axial rotation of the talus without significant difference when compared to intact (figure 1). Addition of DDL stabilization reduced the talar axial rotation with both screw and flexible stabilization. The axial plane translation direction changed from 16.22 degrees in intact stage to 53.21 after destabilization (P=0.044). The range of axial plane translation direction after all stabilizations was 35.02 to 44.43, however, they were not significantly different as compared to the intact state. Conclusion: DDL stabilization improved rotational stability of the talus. Although there were no significant changes in the axial plane translation direction of the talus after any stabilizations, there was a 19 to 28 degree difference as compared to the intact stage. This could be clinically significant over the course of years since the latency period of posttraumatic ankle arthritis is known to be approximately 20 years. The apparent over-tightening of both flexible and screw stabilization of syndesmosis with DDL stabilization should be thought of as time zero due to creep of flexible fixation that was observed at the conclusion of testing.