Work History Is An Important Factor in Disc ReplacementFinding the ideal patient for total disc replacement (TDR) surgery helps ensure successful results. Identifying subgroups of patients who should not have TDR surgery is also important. As the authors of this study sum it up so nicely, Patient selection is the primary key to achieving a favorable outcome.
One way to sort out factors in good and bad results for TDR is to perform retrospective studies. This means the surgeons take a look at the medical records of patients who have had TDR in the past. They analyze all the data collected and look for patterns that would sort patients into subgroups by best and worst outcomes for each type of implant.
In this study, the records of 203 patients at the Texas Back Institute Research Foundation who had a total disc replacement (Charite or ProDisc) were evaluated after the fact. Before and after testing of pain and function were used as the primary measures of success or failure. The data was collected from patients involved in two Food and Drug Administration (FDA) clinical trials.
Measures of success or failure are rather subjective. There is no standard definition of success/failure for this type of spine surgery. Each researcher makes his or her own definition, making it difficult to compare the results of one study to another. And depending on how broad or narrow the definition is that's used, success rates can range from 23 per cent to 60 per cent. Without a set standard, what is one surgeon's success could very well be another's failure.
In order to avoid patients in the gray zone, the authors of this study evaluated patients at either extreme (very best and very worst cases). The gray zone refers to patients who could easily be considered a success or a failure depending on how those terms are defined. By looking at the results of patients who are at the extremes of outcomes, factors that relate to both conditions can be identified.
Patients in both implant groups had degenerative disc disease that did not respond to conservative (nonoperative) care. They did not have a history of previous spine surgery, osteoporosis (brittle bones), or significant arthritic changes of the facet (spinal) joints. Ages ranged from as young as 18 to as old as 60. Obese patients were not included. Everyone was followed for at least two years to be included.
Using a cluster analysis of the data, they found 40 of the 203 patients who fit in the best and worst subgroups. A long list of variables was considered when comparing both groups. Gender, age, body mass index, and smoking status were included. They also paid attention to surgical factors such as the number of spinal levels operated on and the final position of the implant (as seen on X-rays). Occupation, time off from work, and type of insurance coverage (Workers' Compensation versus non-Workers' compensation) were also included.
As might be expected, before and after improvements were very different between the best and worst groups. The two implants performed equally well so that was not the reason for differences between the two groups. The biggest factor separating the best from the worst was work status. Patients who were off work (sick leave or disability) the longest before surgery had the worst results.
The results of this study support findings of other studies that suggest it's best to stay at work if at all possible for as long as possible despite ongoing back and/or leg pain. If surgery is eventually needed, the results may be better in the long-run. Other studies have reported that implant positioning made a difference in the final results. This study was unable to show the same type of relationship between implant position and clinical outcomes.
Patients are screened very carefully before receiving a total disc replacement. Yet, despite very rigorous rules for inclusion versus exclusion, there are still some patients who do not respond well after surgery. According to the results of this study, careful screening is important and should also include work history/work status. Anyone who is not working at the time of surgery (and especially those who have been off work for a long time) should be reviewed carefully before being considered for a total disc replacement.
Richard D. Guyer, MD, et al. Lumbar Spinal Arthroplasty. In Spine. November 1,2008. Vol. 33. No. 23. Pp. 2566-2569.
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