OTA 2005 Posters
Scientific Poster #63 Basic Science
Fracture Fixation in Anterior Colliculus Ankle Fractures: An In Vitro Biomechanical Analysis
Purpose: This biomechanical study compares fixation with two screws to medial malleolar tension band (MMTB) wiring in simulated anterior colliculus fractures with posterior deltoid and syndesmotic disruption (OTA 44-B2).
Methods: 11 frozen cadaveric lower limb specimens were thawed and dissected. The interosseous membrane, subtalar and ankle ligament complexes were carefully maintained. The specimens were potted in acrylic cement, then mounted in a servohydraulic mechanical testing apparatus. Reflective markers were mounted on anatomic points on the ankles that were digitally acquired, representing the lateral and medial radiographic clear spaces of the ankle. Displacement and torque/rotation data were collected for each specimen using an optical tracking system. An external rotation force was applied in a stepwise fashion from 0 to 7.5 Nm of torque. This was done for the intact specimen, then after simulated injury with osteotomy of the anterior colliculus with sectioning of remaining posterior deltoid ligament and distal syndesmosis ligaments. The fibula was left intact to simulate anatomic reduction and rigid fibular fixation. The specimen then was treated with anterior collicular reduction and either repair with two screws (n=6) or MMTB (n=5). Syndesmosis reduction and fixation was performed, then each specimen was stressed to failure.
Results: Specimens showed significant instability and displacement with external rotation torque after sectioning. This improved with both medial repair techniques (P=0.02). At 2.5 Nm of torque, intact specimens displaced an average of 0.12 mm through the lateral clear space versus sectioned specimens 3.32 mm (P=0.03). Screw repair stabilized displacement to 1.79 mm, while MMTB reduced displacement to 0.36 mm (P=0.033). At 2.5 Nm torque, syndesmosis fixation reduced lateral clear space displacement to 0.31 mm (P=.027). At torques 5 Nm, syndesmosis fixation was required to reduce displacement to < 1 mm for both repair types.
Discussion: Previous studies have investigated purely bony or ligamentous injuries of the medial ankle. We investigated combined injuries. Syndesmosis fixation was only required for torques > 5 Nm in MMTB versus 2.5 Nm in the screw fixation group. MMTB shows superiority at low torques. This is likely due to better ligamentous restitution of the deltoid ligament.
Conclusion/Significance: In anterior collicular fractures with ligament disruption, MMTB was better able to restore stability to external rotation stress in a cadaver ankle model. MMTB shows superiority at low torques in biomechanical testing. This may obviate the need for syndesmosis fixation in some clinical cases.