Screw Loosening After Posterior Dynamic Stabilization--review of the Literature

Purpose Of The Study: The malposition of pedicle screws in the lumbar spine is associated with a potential risk of iatrogenic injury of neurological structures but also with a decrease of biomechanical stability. The correct position of the pedicle screws of a dynamic stabilization device, as a long-term implant, seems to be of great importance. A high incidence of screw loosening could influence both the rate of revision surgeries and the clinical results.We compared screw loosening in our own patients with published data after navigated and non-navigated implantation of Dynesys.

Material And Methods: Posterior instrumentation with the Dynesys system was performed in 19 patients after improvement of facet joint infiltrations. Seven (37%) patients underwent conventional surgery (group I), five (26%) were operated on using a CT-based navigation (group II) and seven (37%) using a fluoroscopic-based navigation (group III). Pre-operatively, the "Oswestry Low Back Pain Disability Questionnaire (OQ)" and the "Short Form 36 Health Survey Questionnaire (SF-36)" were used to obtain pain and functional scores. Furthermore, radiographs, MRI and CT examinations were performed before surgery. Screw position was analyzed on post-operative CT scans. At a minimum follow-up of twelve months, clinical examination, plain and dynamic X-rays were performed, and pain and functional scores (OQ, SF-36) were obtained.

Results: Pedicle perforation of minimum 2 mm was detected in two group I patients, in one group II and in two group III patients. Regarding OQ and SF-36, an improvement was observed in all patients, except for one column of SF-36. One patient (group I) underwent revision surgery due to symptomatic screw loosening and another patient (group III) due to persistent pain without signs of screw loosening.

Discussion: In former publications the majority of patients improved after Dynesys implantation with or without the use of navigation methods.Malposition of screws was not always followed by screw loosening. Revision surgery due to screw loosening, but without clinical symptoms, was not necessary in the majority of cases.

Conclusions: It still remains unclear if screw loosening after Dynesys implantation influences the clinical results or the rate of revision surgery and if malposition of screws will be followed by a higher rate of screw loosening.