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Submit responseThe question regarding subgroup analysis is a logical one considering the positive message of our study (1). Our study was designed to examine the efficacy of additional manipulative treatment for shoulder complaints. At baseline all the included patients experienced manifest pain in or dysfunction of the shoulder, while at the same time the physical examination also demonstrated a concomitant dysfunction of the cervicothoracic spine and the adjacent ribs (shoulder girdle dysfunction). We did not perform subgroup analyses on the efficacy of manipulative treatment with regard to specific conditions for several reasons. Subgroup analysis should be based on theoretical considerations. We do not expect large differential effects of manipulative techniques in treatment of shoulder complaints for various postulated specific dysfunctions of the shoulder girdle. A firm theory regarding subgoup effects according to specific shoulder girdle dysfunction is lacking. Moreover, to our opinion there are more similarities than differences between available manipulative techniques for specific conditions of the cervicothoracic spine and adjacent ribs. In addition, physical examination has not shown to contribute to the accurate location of such specific conditions or differentiation between them (2). A recent study demonstrated that by physical examination a distinction between neck and shoulder complaints cannot be made accurately (3). Finally, with our sample size of 150 patients we were able to demonstrate significant results in our main analysis. Any subgroup analysis would require a larger sample size, because statistical power of such additional analyses is likely to be insufficient (4).
References
(1) Bergman GJD, Winters JC, Groenier KH, Pool JJM, Meyboom-de Jong B, Postema K et al. Manipulative therapy in addition to usual medical care for patients with shoulder pain and dysfunction. A randomized, controlled trial. Ann Intern Med. 2004;141:432-39.
(2) Pool JJ, Hoving JL, de Vet HC, van Mameren H, Bouter LM. The interexaminer reproducibility of physical examination of the cervical spine. J Manipulative Physiol Ther. 2004;27:84-90.
(3) Groenier KH, Winters JC, de Jong BM. Classification of shoulder complaints in general practice by means of nonmetric multidimensional scaling. Arch Phys Med Rehabil. 2003;84:812-17.
(4) Brookes ST, Whitely E, Egger M, Smith GD, Mulheran PA, Peters TJ. Subgroup analyses in randomized trials: risks of subgroup-specific analyses; power and sample size for the interaction test. J Clin Epidemiol. 2004;57:229-36.
Gert JD Bergman, MSc Department of General Practice, University of Groningen, Groningen, The Netherlands Center for Rehabilitation, University Hospital of Groningen, The Netherlands
Jan C Winters, MD, PhD, Department of General Practice, University of Groningen, Groningen, The Netherlands
Geert JMG van der Heijden, PT, PhD Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, The Netherlands
Conflict of Interest:
None declared
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The use of manipulative therapy in shoulder dysfunction is analogous to using "medicine" to treat chest pain. Both the nature of condition and the specific treatment need to be identified. The authors described the type of treatments utilized in the study but did not classify the nature of the underlying cause For example, shoulder dysfunction can be caused by dysfunction of the spine, ribs, and shoulder articulations, etc. Have they performed an analysis of the efficacy of treatment with regard to specific conditions? If yes, what are the results of the subset analysis?
Conflict of Interest:
None declared