Hardware failure in an unconstrained lumbar pedicle screw system - A 2-year follow-up study

Study Design. A consecutive study of patients who underwent lumbar spinal a rthrodesis with an unconstrained pedicle screw system. Objectives. To determine the rate of arthrodesis and of clinical success an d to examine and characterize the cases of hardware failure with the AO/Dyn amic Compression Plate system (Synthes, Paoli, PA). Summary of Background Data. Although the advantages and disadvantages of no nconstrained versus constrained systems have been studied extensively, inst rumentation failure has not. Additionally, the association between pseudart hrosis and hardware failure per se is unclear. Methods. Seventy-four consecutive cases of lumbar spinal fusion are reviewe d. Standard outcome scores based on pain relief and medication usage were t abulated, along with pertinent demographic data. The patients were observed at five intervals after surgery for at least 2 years (range, 24 to 35 mont hs; mean, 27 months). Standard statistical analyses were used to analyze da ta. Status of the arthrodesis was determined by standard radiographic crite ria. Results. The overall fusion rate was 61%. At final follow-up, 60% of patien ts believed that their back pain had improved, whereas 70% believed that th eir limb pain had improved. The presence of a solid fusion (r = 3.3, P = 0. 010) was correlated positively with a successful clinical outcome; the pres ence of pseudarthrosis and preoperative narcotic use were negatively correl ated with a successful clinical outcome. Twenty-two percent of patients (16 ) experienced hardware failure. Twelve of the 16 had pseudarthrosis; in the majority of these patients, hardware failure occurred at the level of the pseudarthrosis. Conclusions. The results of this study demonstrate an extremely high rate o f hardware failure and pseudarthrosis using an unconstrained pedicle screw system. Interestingly, the initial rate of pain relief was higher and decli ned over time and was quite possibly associated with loosening of the hardw are. Based on these data, it is difficult to recommend the use of an uncons trained fixation system in the lumbar spine.