The Orthopaedic Innovation Centre Canada investigates the effect of spine rod gripping on fatigue strength through cyclic biomechanical testing.
Thoracic and lumbar back pain is a highly prevalent issue that most adults will suffer from at some point in their lives. Severe back pain can be caused by mechanical issues and soft-tissue injury that may require treatment through surgical intervention. Spinal fusion is a common remedy that immobilises the affected area of the spine.
General practice for thoracic and lumbar spinal fusion is to implant pedicle screws into neighbouring vertebrae and connect levels with spinal rods. Rods are bent to the desired curvature using a rod bender, then strategically positioned into each pedicle screw head, or tulip, using a specialised surgical instrument known as a rod gripper to hold the rod tightly. As a result, the rod gripper can create notches on the rod surface that are generally situated in the span between vertebrae and are exposed to significant bending loads. Unfortunately, instrument-generated notching on spine rods may increase the risk of hardware failure from cyclic (fatigue) loading and fusion failure.
The effect of notching on spine rod fatigue life has been tested by the engineers and technologists at the Orthopaedic Innovation Centre (Winnipeg, Canada). They have combined orthopaedic practice with biomechanical testing to determine the effect of instrument-generated notching on the fatigue endurance of two rod materials. Defining the detrimental effects of rod notching will aid in establishing the importance of preventing these notches intra-operatively, thus ensuring a more durable construct.
Titanium and cobalt-chromium-molybdenum (CoCrMo) alloy 5.5mm and 6.0mm diameter spine rods were tested in pristine (unnotched) a