Resident Physician MedStar Georgetown University Hospital Washington, District of Columbia, United States
Disclosure(s):
Gnel Pivazyan, MD: K2M Stryker Spine: Grant/Research Support (Terminated, December 23, 2021)
Introduction: The biomechanics of fixation of the cervico-thoracic junction (CTJ) poses a significant challenge owing to the transition from the mobile cervical to rigid thoracic spine and the change in the alignment from lordosis to kyphosis. The objectives of the current investigation were to compare the multidirectional flexibility properties of the CTJ using a 4 rod versus traditional 2 rod constructs and evaluate the strain of different rod materials and diameters.
Methods: Multidirectional flexibility properties of ten cadaveric specimens were evaluated under flexion-extension, lateral bending, and axial rotation (± 4.5 Nm). The specimens were destabilized by performing laminectomies and medial facetectomies and instrumented from C3 – T4. The following reconstructions were tested: 3.5 mm Titanium (Ti) 2 rod, 3.5 mm Ti 4 rod, 4.0 mm Cobalt Chrome (CoCr) 2 rod, 4.0 mm CoCr 4 rod, and Ti 3.5 mm – 5.5 mm transition rod. Rod strain of the primary and accessory rods were measured.
Results: The addition of accessory rods to a traditional two rod construct improved the biomechanical stability of constructs in flexion-extension, lateral bending, and axial rotation. This biomechanical advantage was observed for all three loading modes for the Ti rods. Meanwhile, the accessory CoCr rods improved stability only in flexion-extension and axial rotation. The addition of accessory rods in Ti or CoCr reconstructions did not provide significant strain reduction. However, CoCr rods exhibited less strain than the Ti rods.
Conclusion : In summary, the addition of accessory rods to the traditional two rod constructs significantly improved stability of the constructs for Ti alloys as well as CoCr alloys. The 4.0mm CoCr rods provided greater stability than 3.5mm Ti rods. Lastly, while rod strain was not significantly reduced by the addition of accessory rods, it was reduced in CoCr rods treatment groups compared to the Ti rods.
