Influence of bone mineral density on pedicle screw fixation: a study of pedicle screw fixation augmenting posterior lumbar interbody fusion in elderly patients

Some biomechanical studies have demonstrated that bone mineral density of the lumbar spine (BMD) affects the stability of pedicle screws in vitro. To investigate influence of BMD on loosening and related failure of pedicle screws in vivo. A clinical study of 52 patients who underwent pedicle screw fixation augmenting posterior lumbar interbody fusion (PLIF). There were 13 men and 39 women, with an average age of 63 years (range, 45-76 years) at the time of operation. The mean follow-up period was 2.8 years (range, 2-6 years). Relationship between BMD, screw loosening, and its related failures were statistically analyzed. BMD was measured by the dual energy X-ray absorptiometry (DEXA) method. Radiographic assessments were done by the first author and independently by another orthopedist who was not informed of the values of BMD. The mean BMD of all patients was 0.879 +/- 0.215 (mean +/- S.D.) g/cm2. The mean BMD in patients with and without screw loosening was 0.720 +/- 0.078 g/cm2 (n=11) and 0.922 +/- 0.221 g/cm2 (n=41). There was a significant difference between the mean BMD of patients with and without screw loosening (P