Manual therapy has shown a positive effect in patients with musculoskeletal pain, although discussion exists on the strength of this effect and on the indicated patient groups (Kent et al., 2010, Miller et al., 2010, Slater et al., 2012). Insight, in the mechanical and/or physiological mechanisms on which manual therapy is based, can contribute to its use in clinical practice.
Although the effects of manual therapy are classically explained within a biomechanical paradigm, research now points to the important role of neurophysiological processes at both spinal and supraspinal levels in the modulation of nociceptive information (Bialosky et al., 2009). Pain modulation is an attribute of the nervous system and is conceptualized as the net result of complex neural interactions in which physiological and psychological information is integrated into a concrete and individual pain experience (Ossipov et al., 2010, Garland, 2012). Manual therapy techniques can play a role in these interactions as they trigger a cascade of neurophysiological events starting from some form of mechanical (manual) stimulation of the body (Bialosky et al., 2009). Evidence for these neurophysiological events comes from clinical research which show increases in pain thresholds (PTs) directly after spinal manual therapy interventions in healthy participants, in participants subjected to experimentally induced pain, and in patients with musculoskeletal pain (Coronado et al., 2012, Millan et al., 2012). In the reviews of Millan et al. (2012) and Coronado et al. (2012), it was concluded that manual therapy techniques carried out at the spinal column have significant pain modulating effects, although the clinical relevance of these effects remain unclear. No studies on the effects of manual therapy techniques on peripheral joints were included in these studies.
To add to the ongoing debate it is important to fill this gap and to reflect on the analgesic effect of manual therapy interventions, including the clinical relevant effects on pain modulation of both spinal and peripheral joint techniques (Bialosky et al., 2009). This can provide a sound rationale for manual therapy praxis and can therefore contribute to the acceptance of manual therapy as a legitimate therapy of choice for the treatment of musculoskeletal pain.
To summarize the specific pain modulatory effects of manual therapy in this review, PTs are selected as outcome criteria. PTs are defined as the minimal amount of pressure, temperature or chemical stimulation, which participants perceive as painful (Chesterton et al., 2007). The measurement of PTs is reliable and valid, and is widely used in the clinic as well as scientific research to evaluate the effect of different therapeutic interventions (Persson et al., 2004, Prushansky et al., 2004, Chesterton et al., 2007) and to evaluate the pain modulating system (Walton et al., 2014).
The present systematic review aims to add to the current knowledge, by studying the effects of manual therapy interventions directed to both spinal and peripheral joints on pain thresholds of patients with musculoskeletal pain. In addition, this review aims to give an interpretation of the clinical significance of these effects. To date contradictory results of manual therapy on pain thresholds are reported on populations with various forms of spinal and peripheral musculoskeletal pain, and a systematic overview of the effect of manual therapy techniques on pain thresholds in patients with musculoskeletal pain is to the best of our knowledge still lacking.
