Factors Associated With Failure of Trigger Point Injections

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Abstract
The purpose of this study was to investigate factors that may influence the outcome of trigger point injections for myofascial pain syndrome. No prior studies have correlated preexisting factors with treatment outcome or assessed the magnitude of risk of treatment failure associated with such factors. Thirty-one factors derived from patient evaluation and physical examination were selected according to prior studies of mixed pain groups focusing on clinical importance and ease of assessment in a typical clinic setting. Included in the analysis were 193 patients who received trigger point injections and who completed baseline questionnaires. Factors were analyzed via univariate and logistic regression analyses both for independent association with short-term treatment outcome and for magnitude of risk of failure associated with each factor following adjustment for other factors. In univariate analysis an increased risk of treatment failure was associated with unemployment due to pain at the start of treatment, no relief from analgesic medication, constant pain, high levels of pain-at-its-worst and pain-at-its least, prolonged duration of pain, change in social activity, and lower levels of coping ability. Alcohol use was associated with a decreased risk of treatment failure. In logistic regression analysis, only lack of employment, prolonged duration, and change in social activity were independently associated with treatment outcome. Constant-versus-intermittent pain was included in the logistic model because there was an increase in risk that may be clinically important and because it influenced the effect of change in social activity. These results were not affected by the number or type of additional treatments the patients had. These results suggest that several factors should be considered in treating myofascial pain patients with trigger point injections, and this study supports the belief that pain is a multidimensional problem and that a variety of factors may influence treatment outcome.

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