Effect of osteoporosis on the clinical and radiological outcomes following one-level posterior lumbar interbody fusion

Background: Cage subsidence or pedicle screw loosening following lumbar fusion surgery is frequently reported in osteoporotic patients. However, few studies have analyzed clinical as well as radiological outcomes after such surgeries as a function of bone mineral density. We aimed to evaluate the impact of osteoporosis on the clinical and radiological outcomes of patients who underwent one-level posterior lumbar interbody fusion (PLIF). Methods: Fifty-five non-osteoporotic (T-score >= -1.0) and 31 osteoporotic (T-score <= -2.5) patients who underwent one-level PLIF were followed up for >2 years. Visual Analog Scale (VAS), Oswestry Disability Index (ODI), and EuroQol 5-Dimension (EQ-5D) parameters were assessed. Fusion success was identified with dynamic plain radiographs and computed tomography. Pedicle screw loosening and cage subsidence were evaluated. The clinical and radiological parameters were compared between osteoporotic and non-osteoporotic patients. Subgroup analysis was performed on cage subsidence or screw loosening. Results: Although VAS score for back pain was higher in osteoporotic patients than in non-osteoporotic patients at 6 months postoperatively (3.3 vs. 2.2, P = 0.062), this difference disappeared at 1 year postoperatively (2.9 vs. 2.5, P = 0.606). However, no differences were noted between the groups in ODI and EQ-5D grades. Cage subsidence (65.4% vs. 17.6%, P < 0.001) and screw loosening rates (32.3% vs. 12.7%, P = 0.029) were significantly higher in osteoporotic patients than in non-osteoporotic patients, but fusion rate did not differ between the groups. Although clinical outcomes did not differ between those who had cage subsidence or screw loosening and those who did not, fusion rate was lower in those who showed screw loosening than those who did not (71.4% vs. 93.9%, P = 0.038). Conclusions: Higher cage subsidence and pedicle screw loosening rates in osteoporotic patients did not significantly affect the clinical outcomes, but screw loosening, which occurred more frequently in older patients, significantly reduced the fusion success rate. Thus, PLIF procedure may be a good surgical treatment option to achieve good clinical outcomes, even in osteoporotic patients despite higher rates of cage subsidence and pedicle screw loosening. However, surgeons should monitor screw loosening because of its significant association with non-union. (C) 2018 Published by Elsevier B.V. on behalf of The Japanese Orthopaedic Association.