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Biomechanical effects of cement neck and interspinous process device on locking lumbar interbody cementation
Shang-Chih Lin1, Yu-Kun Xu2, Che-Wei Liu3
1Graduate Institute of Biomedical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.
Background:
Locking lumbar interbody cementation is a surgical option in patients with osteoporosis and low mobility. It can quickly stabilize the spine construct and prevent cage subsidence. However, establishing a stable bridging neck cement between the vertebrae and disc is a key procedure.
Methods:
The validated lumbosacral model analyzed the stress cracking risks for five cement neck diameters under flexion, extension, bending, and twisting. The key indices included disc mobility and neck stress. The biomechanical impact of the interspinous process device was evaluated in high-stress fracture-prone necks.
Findings:
The neck diameter has a significant impact on neck stress, especially extension. The maximum neck stress with a 4-mm diameter was very close to the ultimate tensile strength (25.4 MPa) of cement, inducing a high risk of neck fracture. Generally, neck fractures have little effect on disc mobility during flexion, bending, and twisting. However, after the fracture, neck failure led to a 17.1 % increase in disc mobility during extension. If the neck diameter was less than 5 mm on intraoperative radiography, the interspinous process device effectively reduced neck stress by 51.1 % during extension and 31.7 % during bending.
Interpretation:
To improve neck strength, the neck diameter should be increased to at least 5 mm during the surgery. If the strength is inadequate, an interspinous process device can be considered to further minimize the risk of fractures, particularly during extension and bending movements.
