CLINICAL OUTCOME OF INTERBODY CAGE FUSION WITH POSTERIOR INSTRUMENTATION

Abstract

Aim: To test the null hypothesis that interbody cage fusion does not improve clinical outcome.

Methods and materials: This is a prospective study of 87 patients. Seventy-one of the 87 patients followed to the conclusion of the study at two years. Inclusion criteria: Patients undergoing interbody cage fusion with the Ray threaded cage, made of Titanium, and posterior stabilisation with Diapason pedicle screw instrumentation, all operated by the same surgeon. Exclusions: Surgery for infection, or tumour. Tools used for assessment: Oswestry low back pain questionnaire; Visual analogue pain score (VAS); SF36 general health questionnaire. Assessment time points were 1) Pre-op, and post-operatively at 2) 3 months, 3) 6 months, 4) 1 year and 5) 2 years. SF 36 was introduced later recruiting 71 of the 87 patients.

Results: There were 31 males and 56 females. Average age was 46 years (range 14–76) Fifty-one of the patients had no previous surgery, while 36 had previous surgery.

There was a significant, gradual improvement in symptoms of an average of 20 points (p< .001) over the first year on the Oswestry score. However, this plateaued between the first and second years. Over two years there was a greater than 20 point increase in all but three concepts of SF36, general health, reported health and mental health improving around 15 points (p< .001). Sixty-five per cent of the patients reported an overall improvement and 12% were worse, with most changes occurring in the first year.

In assessing the symptoms with Oswestry questionnaire there was a significant difference between first time and revision surgical groups. The revision group showed an improvement of 11 points (p< .001) at two years, most occurring in the latter part of the first year followed by some deterioration between the first and second years. In the primary surgery group there is a 28 point (p< .0001) improvement by two years. Most of the improvement in the primary group is achieved by the first six months.

Conclusions: Interbody fusion can significantly improve health and function assessed by Oswestry and SF36 outcome tools. Additional observations – unsatisfactory outcome in 12% of patients; expected progress at fixed times after surgery can assist planned rehabilitation. This paper introduces the concept of time staged assessment of symptoms in spinal fusion.