The effect of duration of symptoms on standard outcome measures in the surgical treatment of spinal stenosis.

The effect of the duration of symptoms on the outcome of lumbar decompression surgery is not known. The aim of our study was to determine the predictors of functional outcome of lumbar decompression surgery for degenerative spinal stenosis with particular emphasis on the duration of symptoms. In this prospective cohort study, we recruited 100 patients with a full data set available at 1-year and 85% at 2-year follow-ups: 49 females and 51 males with an average age of 62 (range 52-82). The pre- and post-operative outcome measures were Oswestry disability index (ODI), low back outcome score (LBOS), pain visual analogue score (VAS), modified somatic perception (MSP) and modified Zung depression (MZD) score. Dural tear occurred in 14%, and there was one post-operative extra-dural heamatoma. Overall, the ODI improved from a pre-operative of 56 (+/-13) to a 1-year ODI of 40 (+/-22) and at 2-year ODI of 40 (+/-21). The VAS improved from an average of 8 to 5.2 at 1 year and 4.9 at 2 years. There was a statistical significant association between symptom duration and the change in ODI (P=0.007 at 1-year follow-up, P=0.001 at 2-year follow-up), LBOS (P=0.001 at 1-year follow-up, P<0.001 at 2-year follow-up) and VAS (P=0.003 at 1-year follow-up, P=0.001 at 2-year follow-up). Subgroup analyses showed that patients with symptom duration of less than 33 months had a more favourable result. In addition, the patients who rated the operation as excellent had a statistically significantly shorter duration of symptoms. We have not found a predictive value for age at operation, MSP or MZD. The number of levels of decompression and the different types of decompression surgery did not influence the surgical results. Our study indicates that the symptom duration of more than 33 months has a less favourable functional outcome.