The association between pain intensity and disability in patients with failed back surgery syndrome, treated with spinal cord stimulation

Abstract

Objective

Pain researchers demonstrated that pain intensity is not the most reliable measure of the success of chronic-pain treatment. Several research groups have proposed “core outcome domains”, such as measurements of disability, to assess the effect of an intervention in pain patients. Up till now, studies investigating the relation between pain intensity and disability in patients treated with spinal cord stimulation (SCS) are lacking. Therefore, the current objective is to examine which pain-reporting strategy, routinely used in pain research, associates best with the degree of disability in these patients.

Methods

Eighty-one failed back surgery syndrome patients (37 males and 44 females, mean age 54.6 years), treated with high-dose spinal cord stimulation (HD-SCS) are recruited. Pain intensity was scored on an 11-point numerical rating scale (NRS) for leg and back pain, while disability was assessed with the Oswestry disability index (ODI). The association between both variables was investigated with Spearman’s correlation and Cramér’s V.

Results

Significant correlations (p < 0.001) are found between the absolute and relative differences of the ODI and NRS. Significant associations were found between reported cut-offs in literature (≤3, ≤5, and 50% pain relief) and the degree of disability. Finally, a significant association (p < 0.001) was found between the minimal clinical important difference.

Conclusions

In this study, we showed that the degree of disability was strongly associated with the pain intensity as measured using different methods. The standard method for reporting pain intensity reduction (50%) seems to associate the strongest with the degree of disability. However, a low degree of disability does not always reflect a low pain intensity.

Implications for rehabilitation

• The degree of disability reveals a good association with the reporting methods of pain intensity from the literature.

• The Oswestry disability index could serve as a valid tool to measure the effect of spinal cord stimulation on pain.

• Disability measures offer a better insight in the clinical profile of chronic pain patients than a pain intensity score.

Keywords:

• Spinal cord stimulation (SCS)
• failed back surgery syndrome (FBSS)
• chronic pain
• pain intensity
• disability

Acknowledgements

The investigators would like to thank all cooperating centers of the DISCOVER study (“High density in spinal cord stimulation: virtual expert registry”), more specifically: CHC Heusy Verviers, Jessa Hasselt, Ziekenhuis Oost Limburg, AZ Nikolaas Sint-Niklaas, Heilig Hart Ziekenhuis Lier, AZ Groeninge Kortrijk, CHR La Citadelle Liège, AZ Sint-Jan Brugge, OLV Aalst, CHU Charleroi, AZ Sint-Maarten Duffel, AZ Sint-Augustinus Wilrijk, UZ Leuven, AZ Delta Roeselare and UZ Brussel.

Disclosure statement

Maarten Moens has received speaker fees from Medtronic and Nevro. Sam Eldabe has received consulting fees from Medtronic, Boston Scientific and Saluda Medical, his department has received research funding from Medtronic, Nevro and Boston Scientific. There are no other conflicts of interest to declare.

Additional information

Funding

The DISCOVER-trial was supported by Medtronic Europe Sàrl that provided a research grant. Medtronic was not involved in the collection and analysis of the data or in writing the manuscript.