The clinical and radiological outcome of 34 patients who were treated with PDN-Solo and PDN-Solo XL devices for symptomatic degenerative lumbar discs is described.

34 patients had PDNs implanted in their lumbar spines between September 2002 and August 2004. Suitable patients, with proven discogenic back pain, who failed at least six months of conservative treatment, were fully consented prior to surgery. The approach was retroperitoneal in all cases except at L5/S1 when it was transperitoneal. The primary clinical outcome measure was the Low Back Outcome Score (LBOS). X-rays were taken at these follow-up points to assess the integrity and effectiveness of the implants.

36 operations were performed in 15 males and 19 females (including 2 early revision PDNs). All patients were between 20 and 65 years old, with a mean age of 42. 17 patients were treated with PDN alone and 17 with PDN as an adjunct to an interbody fusion.

There were 10 device related complications, two being amenable to early PDN revision and six requiring revision to fusion. Two patients remain symptom-free.

According to the LBOS, only 19 of 29 patients who have not been revised to fusion have had successful outcomes (65.5% of unrevised patients, 56% of all patients). Final follow-up x-rays show that when the PDN remains intact the disc space height is very similar to its neighbours. If the device has dissociated, the disc is narrowed.

Fifty years after lumbar disc nucleus replacement was first attempted by Fernstrom, the success rate is no higher and the reasons for revision are the same. Clearly there has to be a major improvement in this technology before it can be widely adopted. Until such a time as that improvement has occurred, we cannot recommend this device as a treatment for back pain.

Statement of purposes of the study and background: Validated outcome measures should be an essential tool in clinical practice. The Oswestry Disability Index (ODI), since its publication in 1980, is now a principle measure of condition-specific outcome in spinal management. The Low Back Outcome Score (LBOS), another popular measure, emphasises objective questions and gives a broad based status for low back illness. We have analysed the use of these instruments to see if they were directly comparable.

Method: Fifty five consecutive patients attending our clinic between February and June 2005 for treatment of low back disorders completed the questionnaires. These were then scored in the conventional manner. To directly compare LBOS with ODI the LBOS score was converted to a percentage and inversed. The individual LBOS evaluations were then marked in two ways. Firstly the questions that did not appear to correlate to the ODI were removed. Secondly the weighting system was adjusted to match the ODI weighting. Statistical regression analysis was performed.

Results: Direct comparison of ODI versus an inverse of the LBOS percentage score gave a scatter of results. The R squared result was 0.117

Removing the non-core answers from the LBOS gave an R squared value of 0.130

Removing the weighting of the LBOS gave an R squared value of 0.132

Removing the non-core questions and weighting system of the LBOS gave an R squared value of 0.133

Conclusion: These two validated disease specific outcome tools provide very different results when applied to the same group of patients. This has significant implications for outcome research especially when comparing studies which do not use similar instruments.