Screw Loosening in Posterior Spine Fusion: Prevalence and Risk Factors

Abstract

Study Design: Retrospective cohort study. Objective: Screw loosening in spinal fusion is poorly defined. Accordingly, its prevalence rates range from 1% to 60%, and its risk factors remain undefined. The goal of this study was to assess the prevalence of screw loosening, according to precise definitions, and to identify factors associated with it. Methods: We retrospectively reviewed records for 166 patients who underwent a posterior spinal fusion in our institution between 2011 and 2016. We recorded demographic data, osteoporosis, pelvic balance, surgery-related information, and postoperative radiographic data at a minimum follow-up of 6 months. Univariable and multivariable logistic regression models were used. Significance was defined by P < .05. Results: When loosening was defined by partial pull-out, its prevalence was 9.6% (95% CI 5.6-15); thoracic localization, the use of CrCo (chromium-cobalt) rods, osteoporosis, PI/LL (pelvic incidence/lumbar lordosis) mismatch (preoperative), and frontal imbalance (preoperative) were significant risk factors. When loosening was defined by osteolysis (radiolucent rim) >1 mm around at least 1 screw, its prevalence was 40.4% (95% CI 33-48) and age, scoliosis as indication for fusion, ASA (American Society of Anesthesiologists) 2 or 3, the use of CrCo rods, more than 5 levels fused, no circumferential arthrodesis, postoperative bracing, and sacrum or ilium as the inferior level of instrumentation were also significant risk factors. Conclusions: A clear definition of screw loosening seems essential for a useful analysis of the literature. Osteoporosis, sagittal imbalance, and rigid material appear to be risk factors, regardless of the definition.

Opportunistic Osteoporosis Screening Reveals Low Bone Density in Patients With Screw Loosening After Lumbar Semi-Rigid Instrumentation: A Case-Control Study

“…Certainly, screw loosening is a multifactorial process that cannot be reduced to impaired bone strength in osteoporosis. Complex biomechanics of the spine play a significant role and are influenced by load magnitude (BMI) and load direction (sagittal balance) as well as rigid material ( 32 ). Of note, BMI showed no significant difference between patients in the case and control groups; information about pre- or postsurgical sagittal balance was not available.…”

Correlation between Preoperative Serum Levels of Calcium, Phosphate, and Intact Parathyroid Hormone and Radiological Outcomes in Spinal Interbody Fusion among End-Stage Renal Disease Patients

“…Additionally, hyperphosphatemia induces hypocalcemia and hyperparathyroidism, both of which are causes of osteoporosis and poor bone quality in patients with ESRD [8,25,26]. In both our general practice and the previous literature, the incidence of implant loosening may be considerably higher in osteoporotic spines [27,28], and cage subsidence is relevant to low bone mineral density [29,30].…”

Influence of thread design on anchorage of pedicle screws in cancellous bone: an experimental and analytical analysis

“…Screw pull-out is not the most critical failure mode for pedicle screws. Recent studies report screw loosening with a prevalence of 15.2–40.4% 43 , 44 . The prevalence of screw pull-out, on the other hand, is reported to be 7.8–16.2% 43 – 45 .…”