Abstract
Objective
From our series of 570 Dynesys flexible stabilisation procedures, we studied two prospective series of patients with a minimum one-year follow-up comparing uncoated and hydroxyapatite-coated (HA) screws.
Methods
Patients were entered prospectively and followed up at 6 weeks, 3, 6, and 12 months and annually thereafter. Plain radiographs were obtained annually. 58 patients who underwent Dynesys stabilisation with HA coated screws (312 screws) were evaluated. The data was compared with 71 patients who underwent Dynesys stabilisation with non-coated pedicle screws (366 screws). Outcome measures were screw loosening, breakage, implant removal or revision. Follow up was 96 %.
Results
In the HA coated group there were five screw breakages in three patients, all affecting S1 screws. There was evidence of loosening in one patient. In the non-HA coated group there were two cases of infection, both had their implants removed. Further 11 patients had screw loosening and required implant removal. There was a significant improvement of anchorage of the HA coated screws. There was no correlation between numbers of level stabilised, or previous surgery and screw loosening. Average time to revision surgery for loosening was 23 months in the non-coated group. Screw fractures occurred at 11 months in the HA coated group. There was no correlation between screw loosening or fracture and gender or age.
Conclusions
Change to HA coating was investigated because of high loosening in plain screws. Secure pedicle screw fixation is crucial in dynamic stabilisation as the implant remains under constant load. This study demonstrated the significant improved anchorage of HA coated pedicle screws in dynamic posterior stabilisation of the lumbar spine. HA coating has eliminated the problem of screw loosening irrespective of gender, age, number of level stabilised or whether there was previous lumbar surgery.
