A biomechanical study with human cadaveric osteopenic lumbar vertebrae evaluating a novel method for cement augmentation of pedicle screw fixation.Objectives.
To examine (1) the resistance to toggling and (2) ease of screw removal following cement augmentation of pedicle screw fixation via a novel, cannulated cement delivery device, allowing placement of a standard pedicle screw into a cement-augmented tract.Summary of Background Data.
Some recent studies have investigated various cannulated pedicle screws through which polymethylmethacrylate (PMMA) is injected and found improved fixation in osteopenic spines. However, when necessary because of revision surgery, extraction of screws cemented via a cannulated system is exceedingly difficult.Methods.
Novel cannulated screws were fabricated with fenestrations in the distal one-third of the screws. Fresh osteopenic (by dual energy x-ray absorptiometry) cadaveric lumbar vertebrae were instrumented with an uncemented pedicle screw in 1 pedicle and the novel cemented screw in the opposite pedicle. Vertebral augmentation was performed by placement of the novel screw and injection of 2.5 mL of PMMA. Before final cement hardening, the novel screw was removed and replaced with a standard pedicle screw. The pedicle screws in 13 vertebral bodies were subjected to 10,000 cycles of cephalocaudal toggling. In another 10 vertebral bodies, we measured the torque required to remove uncemented, cemented screws, and cemented fenestrated screws left in place until hardening.Results.
There was 63% less cephalocaudal motion with cemented screws using the new technique versus uncemented screws. Torque required for screw removal was similar for uncemented screws (mean, 358 Nmm) and PMMA-augmented screws via this new technique (mean, 343 Nmm). However, fenestrated screws cemented into place required an average of 4100 Nmm.Conclusion.
This novel cement-delivery screw and injection technique provides a significant increase in resistance to pedicle screw motion, allowing placement of a standard screw that can be removed in revision surgery.