The aim of this study is to assess the success of posterior lumbar interbody fusion in the treatment of degenerative spinal instability. Methods: Historical prospective study containing sixty-five consecutive patients who underwent posterior lumbar interbody fusion (PLIF) using carbon cages and pedicle fixation between 1993 and 2000.

Clinical outcome was assessed by the postoperative symptomatic relief, complications rate and the fusion rate. The fusion rate was assessed using plain radiographs and the Brantigan and Steffee scoring system. Functional outcome was measured by the improvement in the Oswestry disability index, PROLO score, return to work and satisfaction with the surgical outcome. The determinants of functional relief were analysed against the improvement in disability using multiple regression analysis. Results: Overall fusion rate was ninety eight percent. There was a significant improvement in Oswestry disability index P< 0.001. There was 85% satisfaction with the surgical procedure and 58% return to pre-disease activity level. We found preoperative level of disability to be best the determinant of functional recovery irrespective of age or the degree of psychological morbidity (p< 0.0001). Conclusion: The combination of posterior lumbar interbody fusion (PLIF) and posterior instrumented fusion is a safe and effective method of achieving segmental fusion with sustained functional relief and high satisfaction rate. Direct relationship between preoperative level of disability and functional recovery suggests that spinal fusion should be performed to alleviate disability caused by degenerative spine.