Hypothesis of the Etiology of Somatic Dysfunction

Author: J Michael Wieting, DO, MEd; Chief Editor: Consuelo T Lorenzo, MD

Manipulation is a mechanical intervention. Hypotheses that explain somatic dysfunction usually involve position and treatment of vertebral bodies, muscle, fascial segments, or other body parts, as well as soft tissue. Acute pathologies (eg, fractures, ligamentous tears, tumors, avulsions, joint inflammation) are not considered amenable to manipulation as a primary mode of treatment. Some pattern of neuromuscular behavior resulting in early localization of hypomobility may respond to manipulative care. Pain and edema may cause immobility, leading to contracture or an abnormal neuromuscular pattern. Precipitating pathology of somatic dysfunction may be largely resolved by the time diagnosis is made; however, pain also may arise from dysfunction and, along with impaired mobility, may be related directly to it. Pain and somatic dysfunction can create a self-perpetuating syndrome.

The musculoskeletal manifestation of restricted movement and impaired mobility of a body segment is known as somatic dysfunction. The condition has also been called an osteopathic lesion, a chiropractic subluxation, a joint blockage, and a loss of joint play, among other terms.

Barrier models have been suggested to explain palpable findings. Normal joints possess an active and a larger, passive ROM. A barrier or motion restriction produced by abnormal muscle contraction, ligamentous, or capsular shortening forms in 1 or more directions between the neutral position and normal limits so that patients are not able to achieve normal range. The manipulation practitioner then applies additional force to achieve normal passive ROM.

The facilitated segment model assumes that a vertebral body, chronically malpositioned by contracture, overly active muscle, or other somatic dysfunction, floods the segmentally related area of the spinal cord with inappropriate, nonfatiguing proprioceptive impulses. These impulses, in turn, spill over and facilitate outgoing motor neurons and autonomics in the same vertebral segment of the spinal cord. Pathways are then present for interaction between soma and viscera at related segments, and the palpatory diagnosis of visceral disease and the determination of influence on the viscera are possible. This phenomenon allows asymptomatic, abnormal segmental areas to develop symptoms from general illness, distant disease, or emotional stress. Physiatrists familiar with autonomic hyperreflexia and similar phenomena can relate easily to the concepts of somatovisceral reflexes and segmental spillover.

The mechanical model of altered joint play is distinct from the neurophysiologic hypothesis of somatic dysfunction. All normal voluntary joint motion is accompanied by a wiggling motion in a direction perpendicular or, possibly, tangential to the plane of that motion. This joint play exists because joint surfaces are not perfectly congruent. Loss of joint play because of soft-tissue restriction may inhibit voluntary motion from absence of the involuntary component. Passive intervention is needed to normalize function because lost joint play is in an involuntary direction. Pain arises, therefore, from poor mechanical function.

The concept of "ease and bind", central to functional and other indirect techniques, uses a model of vertebral motion around a symmetry point where motion in any direction encounters equal tissue resistance. In a dysfunctional vertebra or other musculoskeletal tissue, the balance point is not the anatomic neutral, so that movement in one direction of motion is met by more resistance (bind) than another (ease). The maintenance of asymmetry arises in proprioceptive and gamma motor spindle sensors, and treatment usually involves passive motion to and maintenance of the ease position so that the spindles can reset their output. The strain-counterstrain method suggests that the aberrant activity of the spindles can trigger reflex patterns and tender points, which can be used to monitor the positional resetting of the spindle output.^[29]

Hypothesis of action of manipulation

The overriding mechanism by which manipulative techniques relieve pain is not fully understood. A simple categorization separates treatments into those that mechanically lengthen tight soft tissues from those that alter the firing rate of inappropriately shortened muscles to achieve relaxation or ease. Either of these treatment techniques eliminates hypomobility of an offending segment if soft tissue is lengthened or the muscle is relaxed sufficiently. Functional, muscle energy, (most) myofascial release, and counterstrain techniques, using small forces, can work only on neuroreflexive alteration of muscle activity. Direct-thrust and articulatory techniques involve larger forces and, presumably, are able to stretch and elongate tissue.

Restricted motion arises from abnormal muscle contraction and shortened or stiffened soft tissues. All forms of manipulation interfere with abnormal muscular contraction, either by producing afferent stimuli that attenuate hyperexcitable, gamma-efferent systems or by elimination of proprioceptive input that stimulates the gamma-efferent system. Thrust and, possibly, articulatory and isometric techniques stimulate Golgi tendon organ input. Articulatory and isometric techniques may elicit permanent lengthening of collagenous tissue by inducing a permanent set with repeated stretching. Direct-thrust techniques result in high stress levels and probably in high strain levels in soft tissues over a short period of time. Nonuniform distribution of strain may develop, leading to localized tissue injury and subsequent healing with permanent elongation, with the net result being that vertebrae regain normal motion play; the forces needed to produce motion then are normalized.

Facet malposition or malfunction can be influenced directly with manipulation by passive joint motion. A bulging disk may be reduced or normalized by manipulation. The change in proprioceptive input to the spinal cord may close the gate on pain or remove abnormal, facilitating proprioceptive input.

Use of manipulation by physiatrists

The goals of manipulation are to restore or optimize biomechanical function by improving motion, thereby facilitating mobility, minimizing pain, and increasing the patient's overall level of wellness. Scientific evidence for the efficacy of manipulation has been mounting. General acceptance of the utility of manipulation in acute low back pain and other forms of musculoskeletal pathology has resulted in recommendations that manipulation be directed toward restoration of normal motion, reduction of pain, and overall increase of physical activity. There is also increasing evidence to support the use of manipulation in combination with other modalities to optimize the return of function.

A study by Childs and colleagues compared the use of exercise as a stand-alone therapy with the employment of spinal manipulation in combination with an exercise program, in patients suffering from low back pain.^[30] Improvements in disability and pain were, to a statistically significant degree, greater in the patients who received both therapies than in those in the low-stress aerobic and lumbar spine–stabilizing exercise group.

Subsequent literature reviews examining the use of manipulation in treating pain in the cervical and lumbar regions have also supported its use. Bronfort and colleagues found moderate evidence to support the use of spinal manipulation and mobilization in the treatment of chronic low back pain, stating that such treatment is "at least as effective as other efficacious and commonly used interventions."^[31]

Hurwitz and colleagues performed a comprehensive literature review of nonsurgical interventions for the treatment of patients with whiplash associated disorder (WAD) and for other neck disorders with or without trauma.^[32] The authors found that among the patients studied, treatment with mobilization and exercises seemed to be more effective than did treatment with the usual types of care or physical modalities.

The study also found evidence that for non-WAD neck disorders, in the absence of radicular signs or symptoms, it was more beneficial to treat patients with manual (manipulation or mobilization) and exercise interventions, low-level laser therapy, and perhaps acupuncture than it was to provide them with either sham or alternative treatments, or with no intervention at all. However, among the more successful "active" treatments, none was found to have a clear benefit over the others on either a short- or long-term basis. According to the report, for "WAD and neck disorders without trauma, the evidence favors supervised exercise sessions with or without manual therapy over usual or no care. Of the manual therapies, manipulation and mobilization yield comparable clinical outcomes."

Prescription of manipulation

Referral of a patient to another practitioner for manipulation requires a prescription, the contents of which may be communicated through conversation between the practitioners. Manipulative care also may be included as a portion of a general strengthening, conditioning, and musculoskeletal educational program. The specific region to be manipulated, potentially suggested techniques, and discussion of any medical issues, considerations, or side effects also must be a part of the prescription. Include patient age, precautions, diagnosis, treatment recommendations, frequency, duration, and other comments in all prescriptions for manipulation. Follow-up patient examination is essential. If treatment has been unsuccessful, consider reformulation of the diagnosis or of the therapeutic manipulative approach. If manipulation procedures are producing discomfort lasting more than 8 hours, consider changing to a less invasive, or possibly an indirect, technique.

The manipulative technique used in any intervention is determined by the time course of the problem and the patient's age and general physical condition, as well as past medical history, the presence of any contraindications, and the practitioner's expertise and training. These considerations underscore the need for a careful history and physical examination, structural examination, and functional diagnosis. A musculoskeletal problem amenable to manipulation must be identified in order for this approach to be effective. The identification of the source of pain is particularly important for patients with subacute or chronic pain. Note also that complete eradication of pain is rare. This fact may lead patients to become dependent on manipulation. Having well-defined biomechanical end points of treatment (eg, normal ROM and tissue texture) helps to formulate an effective end to treatment. Especially in the patient with chronic pain, manipulation should be directed toward obtaining an optimalbiomechanicalmusculoskeletal condition as quickly as possible.

Research relating to manipulation

Numerous clinical trials of spinal manipulative treatment have been summarized in the literature. Further, manipulative treatment has been the subject of multiple international consensus meetings. Trials have attempted to improve knowledge by comparing thrust with nonthrust (ie, direct with indirect) techniques and joint-specific with nonjoint-specific manual therapies, by varying the frequency and intensity of interventions and by comparing different types of joint-specific manipulation techniques. Studies in the literature have varied in terms of research design, criteria for improvement, time of evaluation, and techniques examined. The wide variations among studies have made blinded reviews and objective meta-analysis very difficult.

Anatomy and physics of manipulation

Understanding of the biomechanics of direct-thrust manipulation has significantly advanced. Indirect (ie, nonthrust) manipulation has been studied less. The external mechanical forces involved, the duration of the application of those forces, and the gross anterior/posterior displacements have been measured in human subjects, and relative displacements have been measured in cadaver studies. Study of internal forces and relative displacements of vertebral bodies resulting from applied forces still has not been performed. Some research has been conducted on the neurologic and neuromuscular responses to direct-thrusting procedures; however, little has been done to study other types of manipulative therapies in terms of biomechanical parameters or physiologic responses to them.

What has been learned about pain and mechanoreceptors, spinal cord physiology, and normal spinal biomechanics since the late 20th century has allowed this information to be applied and has facilitated contributions to the understanding of manual medicine and the treatment of somatic dysfunction. Knowledge about small tissue strains now is being accumulated and assimilated into manual medicine thinking. Two primary areas of research development and scholarly inquiry that relate to manual medicine at this time are the objective measurement of somatic dysfunction in patients and the examination of the association of somatic dysfunction with acute and chronic pain. Further inquiry also is warranted into questions concerning mechanism and (in the current era of health care – cost containment) efficacy.