The effects of joint manipulation: reciprocal relationships

INTRODUCTION The joint manipulation (JM) is a manual technique widely used for the treatment of mechanical musculo-skeletal disorders. A number of studies have analyzed the clinical effects of JM. Despite this, the mechanisms involved in manipulative therapy - and the possible reciprocal influences between the effects - remain partially unclear. OBJECTIVES The purpose of this narrative review of the literature is the collection and the comparison of data related to physiological and clinical effect of manipulative therapy, as well as the identification of the possible reciprocal influences between these two areas. METHODS Between December 2006 and November 2008 a research has been performed in the medical Databases PubMed, Embase, Cinhal, and PEDro, using the keywords “manipulation”, “manipulative therapy” and “manual therapy”. In this study we included only the experimental clinical trials and the systematic reviews of the literature that employed manipulation with thrust, and that provided objective quantifiable outcomes (i.e. blood test) or subjective – but validated – outcomes (i.e. Visual Analogical Scale). Other data from narrative reviews of the literature, reports of meetings, case reports and anecdotical studies have been excluded. RESULTS In our study we performed a narrative review of 30 selected studies. The evidence related to physiological effects has been divided into bio-mechanical (inclusive of intra-articular and intra-discal pressure), neurophysiological (related to the effect on muscular tone), cardiovascular, autonomic (related to skin conductance) and psychological. The clinical evidence, instead, has been divided into effects on pain, on level of functional disability, on variations of articular range of motion, and on increase of maximal muscular recruitment. Finally, analyzing the obtained data, we defined some unidirectional and reciprocal relations between the effects of manipulation. DISCUSSION Even excluding some direct relations, as between the cracking sound and clinical effects, in some others contexts it is debatable that some relationships should be excluded, even if there is no evidence to define it. On the whole, for instance, it is true that a limitation of ROM - even if asymptomatic - can have an effect on functional disability, but it is impossible to take it for granted, nor that the transient increase of ROM after manipulation can affect this hypothetical relationship. CONCLUSIONS Joint Manipulation brings out physiological and clinical effects that are partially quantifiable and related, even if circumscribed by the lapse immediately subsequent to the treatment. In order to get a better understanding of the mechanisms implied in the effects of MT, more research needs to be carried out, with more homogeneity in the outcome measures and in the type of manipulative technique.