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Research Article Open Access
Introduction: Pedicle screw fixation is frequently applied to treat patient with degenerative diseases of lumbar spine and the reported rate of screw loosening may achieve the level of over 50% in case of osteoporosis. In this study, we hypothesized that a threshold of bone density in HU could be identified, below which the risk of pedicle screws loosening may be significantly increased.
Materials and methods: This is a prospective non-randomized study of patients with degenerative diseases of lumbar spine that underwent spinal instrumentations with pedicle screw fixation, 110 patients were enrolled. Preoperatively computed tomography was administered and bone density of trabecular bone of vertebra body was measured. Standard intervention includes pedicle screw fixation, unilateral foraminotomy and transforaminal interbody fusion with cage and autograft. Minimal follow-up period accounted for 18 months, cases with evident pedicle screw loosening on CT scans were registered. Logistic regression analysis was used to estimate the relationship between bone density loss and probability of implant instability.
Results: Logistic regression analysis demonstrated a strong inverse relationship between bone density measured in Hounsfield units and frequency of all cases of pedicle screws loosening. The obtained logistic regression equation analysis using derivatives of a high order showed a critical point of 81 HU that corresponds to the acceleration of total implant instability probability growth per unit of bone density loss.
Conclusion: Bone density in HU can be used as a criterion for implant instability prediction as far as a strong relation has been estimated between screw loosening probability growth and the decrease in bone density. Breakpoint of 81 HU corresponds to the increased risk of pedicle screws instability development.
Computed tomography, Spinal instrumentations, Screw loosening, Hounsfield units, Ankylosing Spondylitis Arthritic Disease Arthritis Arthritis Surgery