During the study period March 2004 to November 2008, consecutive patients who met the inclusion-exclusion criteria for posterior interbody fusion (PLIF) surgery were entered into this prospective study at a university hospital in the north east of England. Inclusion criteria were as follows: 1) LBP greater than 2 years duration not responding to conservative therapy including rehabilitation programs, physiotherapy and epidural steroid injections, 2) Oswestry Disability Index (ODI) >30; 3) degenerative disc disease with or without modic changes, 4) spondylolisthesis grade I to III, 5) postlaminectomy/post-discectomy syndrome, and 6) broad based disc prolapse with low back and leg pain. Exclusion criteria were previous spinal infection and spondylolisthesis >grade III.
Patients were assessed preoperatively and at follow-up using a self-administered questionnaire consisting of the MSPQ, Zung, ODI, and visual analogue scale (VAS) for back and leg pain.
The MSPQ is a 13 item 4 point self-report questionnaire that measures heightened somatic awareness (somatic anxiety) in chronic back pain patients. The MSPQ has been shown to be a valid and reliable instrument in this patient group. The 13 statements (for example feeling hot all over, nausea, stomach churning) have 4 responses (not at all, little/slightly, a great deal/quite a bit, extremely/could not have been worse) and are scored 0 to 3 respectively, giving a score range of 0 to 39. The higher the score, the more marked the somatic symptoms.
The Zung depression scale is a 23 item self-report questionnaire that measures depression in LBP patients. Each of the statements (e.g., I feel downhearted and sad, I feel guilty) has 4 choices (rarely or none of the time, some or little of the time, a moderate amount of the time, most of the time), scored either 0 to 3 or 3 to 0 depending on the statement. This results in a score range of 0 to 69. The higher the score, the more marked the depression.
Psychological status was measured preoperatively using the decision rules of the DRAM (). This classifies patients into one of 4 types based on a combination of scores from the MSPQ and modified Zung questionnaires: normal (N, Zung score <17) at risk (R, Zung score 17-33 and MSPQ score <12), distressed somatic (DS, Zung score 17-33 and MSPQ score >12) and distressed depressive (DD, Zung score >33). In the context of spinal surgery, patients who are classified as DD and DS are regarded as those who may have poor outcome after fusion.
The primary outcome measure was the ODI ver. 2.1. A reduction of 16 points on the ODI was considered to be a minimum clinically significant outcome [12,13
]. Secondary outcomes were the VAS for back and leg pain severity. A decrease pre- to postoperative of 2 was considered as being clinically significant [12,13
]. The ODI and VAS were measured pre- and postoperatively at 2 years follow-up.
Each patient was seen by a consultant spinal surgeon and offered PLIF. All operations were performed by the same consultant surgeon (MK) assisted by a specialist registrar. PLIF is an impatient procedure performed under general anaesthesia. Instrumentation and carbon fibre cages packed with locally harvested bone were used for interbody fusion.
Statistics were obtained using SPSS ver. 14 (SPSS Inc., Chicago, IL, USA). Where the data was skewed, the median in addition to the mean is reported. Before applying parametric methods, the data was checked for normality. If there was significant deviation from normality, non-parametric methods were used. The assumptions of statistical tests were verified before use. Statistical significance was designated at p < 0.05. The paired samples t-test was used to determine significance between pre- and postoperative outcome scores. All Students' t-tests were two-tailed. One-way analysis of variance (ANOVA) was used to determine statistical significance between the preoperative outcome scores for the DRAM categories.