The Benefit of Hydroxyapatite-augmented Pedicle Screw Fixation in Degenerative Spondylolisthesis Patients with Osteoporosis

Abstract

Objective A key determinant of the performance of pedicle screw systems is the strength of their attachment to the spine. The authors initially injected hydroxyapatite cement into the prepared screw hole before actual screw insertion in order to provide additional strength to this system and assessed its benefit in the fusion operation for the patients with osteoporosis. Methods Among the 21 patients who were diagnosed as grade I degenerative spondylolisthesis on L4-5 level with osteoporosis, nine patients were treated by transforaminal lumbar interbody fusion (TLIF) with screw augmentation with hydroxyapatite and the rest 12 patients underwent TLIF only. The plain radiographs were periodically checked during and up to 2 years after the operation. The changes of the angles between the vertebral bodies, between the upper and lower screws, between the screw and lower endplate of each body, and posterior disc height changes were serially measured and compared between these two groups. Results The angle between the upper screw and the lower endplate of upper vertebral body showed gradual decrease from 8.93° to 5.79° for the TLIF only group while well maintained for the augmentation group from 6.84° to 6.93° (p=0.053). Most of these significant angle changes occurred between 1 month and 6 months after the operation (p<0.05). Conclusion Most of the screw construct changes occurred in the upper level of fixation during 1 month to 6 months after fusion surgery in spondylolisthesis patients with osteoporosis. For these, the screw augmentation with hydroxyapatite demonstrated the improvement in maintaining the screw construct especially in the upper level of fixation.

Keywords

• hydroxyapatite
• osteoporosis
• screw augmentation