This is an excerpt from Orthopedic Joint Mobilization and Manipulation With Web Study Guide by Robert Manske,Bryan (BJ) Lehecka,Michael Reiman & Janice Loudon.
Clinicians use joint mobilization and manipulation for 2 main indications: joint pain and joint hypomobility. Three main categories of effects of mobilization or manipulation are described here: mechanical, neurophysiological, and psychological.
The mechanical effects of joint mobilization relate to the restoration of normal joint mobility or range of motion. This includes flexibility and mobility of capsular and other soft tissue structures such as ligaments and tendons. Following injury and immobilization, soft tissues can become shortened and limit overall joint mobility. Adequate force must be applied to the tissues to create mechanical effects. Higher grade mobilizations may increase the joint mobility back to normal by restoring relative amounts of play in the once-restricted joint motion. Another theory of mechanical effect is the releasing or freeing of the facet joint meniscoid entrapment. A meniscoid entrapment may include a locking caused by entrapment of a facet joint meniscoid in a groove formed in the articular cartilage or by a meniscus piece that has broken free and formed a loose body that is entrapped (Lewitt, 1985).These meniscoids can become extremely painful sources of dysfunction. Fortunately, either gapping or an isometric movement that pulls the facet laterally can theoretically dislodge the impingement; the result can be immediate pain relief and improvement of joint motion. Current evidence supports only transient biomechanical effects on studies quantifying motion (Colloca, Keller, Harrison, Moore, Gunzburg, and Harrison, 2006; Coppieters and Alshami, 2007; Coppieters and Butler, 2007; Gal, Herzog, Kawchuk, Conway, and Zhang, 1997)but not a lasting positional change (Hsieh, Vicenzino, Yang, Hu, and Yang, 2002; Tullberg, Blomberg, Branth, and Johnsson, 1998).Neurophysiological and psychological effects should therefore be strongly considered.
Applications of joint mobilizations and manipulation have been reported to create both local and distal neurophysiological effects (Bialosky, Bishop, and Bialosky, 2009; Bishop, Beneciuk, and George, 2011; Coranoda, Gay, and Bialosky, 2012; George, Bishop, and Bialosky, 2006). These effects may be especially enhanced when using the spine as the region of mobilization or manipulation application. Spinal soft tissues are highly innervated and may provide a large degree of afferent input into the central nervous system (Groen, Baljet, and Drukker, 1990). This input can come from multiple sources such as type I and II mechanoreceptors and free nerve endings found in cervical spine facet joints and muscle spindles of the cervical spine. Similar mechanisms might be seen in the remainder of the spine, but the number of nerve endings may be lower and less consistent in lower levels of the spine (McLain and Pickar, 1998). Movement such as mobilization or manipulation will fire these receptors and provide input to the central nervous system. These nerve receptors terminate in the spinal cord synapsing in the ventral and dorsal horn to signal proprioceptive and nociceptive information (Bolton, 1998).
Animal and human models have shown that the periaqueductal gray area of the midbrain is key for control of mediation of endogenous analgesia (Cannon, Prieto, and Lee, 1982; Hosobuchi, Adams, and Linchitz 1977; Reynolds, 1969). The periaqueductal gray area is in coordination with a complex network of systems including the nociceptive system, the autonomic nervous system, and the motor system. It has also been shown that type I and II mechanoreceptors from joints, muscles, and tendons project to the periaqueductal gray area (Yezierski, 1991). Evidence via postmanipulation sympathetic response combined with analgesia in symptomatic and asymptomatic subjects suggests a neurophysiologic response to spinal manipulation via mechanoreceptors (Wright, 1995). These effects may lie in the stimulation of the descending pain-inhibitory system of the central nervous system from midbrain to spinal cord.
Controversy persists regarding whether analgesic effects from mobilization and manipulation occur following treatment. Some reports suggest that mobilization or manipulation may stimulate a release of endogenous opioid peptides that bind to nervous system receptor sites, producing analgesia. Vernon and colleagues found increased levels of plasma beta-endorphin following manipulation, but these levels diminished to normal levels after only 15 minutes (Vernon, Dhami, Howley, et al., 1986). Controversy continues, as others have not succeeded in documenting these increased levels of endorphin compared to control groups (Christian, Stanton, and Sissons, 1998; Sanders, Reinnert, and Tepe, 1990).
The neurophysiological effect may also include a change in muscle activation patterns in which the motor system may be inhibited. The ability of mobilization and manipulation to inhibit muscle may vary depending on technique, location and nature of pain, and even the given muscles targeted with the manipulation. If mobilization or manipulation affects muscles, the neurophysiologic effects most likely occur locally at the targeted joint or region and the corresponding innervation distally associated with the shared innervation. The effects desired from performing the mobilization or manipulation are to increase facilitation of the deeper, more local muscles that assist with neuromuscular control of the area and, ideally, to inhibit the more superficial, global muscles that may be causing pain due to increased guarding of the joint or segments involved.
At least in the spinal model, evidence of improvement of psychological outcomes following manipulation is limited. In a meta-analysis, Williams, Hendry, Lewis, and colleagues (2007) reviewed 129 randomized controlled trials of spinal manipulation and identified 12 studies reporting psychological outcomes. These studies suggest that spinal manipulation may improve psychological outcomes compared to verbal interventions. Further, other variables, such as clinician and client expectations, may also play a role in the degree to which symptoms improve (Cross, Leach, Fawkes, and Moore, 2015; Riley, Bialosky, Cote, Swanson, Tafuto, Sizer, and Brismée, 2015). The greatest effect seems to be in those with a positive attitude and an expectation that the intervention will be helpful.