A rationale for the treatment of back pain and joint pain by manual therapy.

The manual therapist is concerned with the prevention and treatment of musculoskeletal pain and dysfunction problems by the application of primary physical modalities incorporating exercise, passive joint movement (including mobilization and manipulation), traction, and massage.[1-3] Today, most manual therapists have usually received additional pathology, diagnosis, and skill training beyond that traditionally obtained at the undergraduate level and have had an extended period of supervised clinical practice.[1] Although the historical focus of manual therapy has been directed toward the treatment of back and peripheral joint pain and dysfunction, a survey of Grieve's Modem Manual Therapy of the Vertebral Column[1] shows that it now encompasses the wider musculoskeletal field. This article considers the biomechanical effects that manual therapy can have on the musculoskeletal system of the body.

Back pain appears to be an inevitable accompaniment of the human life cycle. Approximately 80% of persons in western society experience back pain at some stage during their life, and this pain is sufficient to cause an alteration in lifestyle for at least a period of time and drives individuals to seek some form of treatment.4 Back pain is the single most expensive musculoskeletal ailment in western society,[5] although only 8% of those with back pain or dysfunction account for almost 80% of the costs involved.[6] Until recently, it was believed that back pain was not a problem in "underdeveloped countries," but recent evidence clearly shows that its incidence in such countries is similar to that in the "developed" world and that when back pain clinics are made available, local people flock to them for treatment.[7] Backache is as universal as headache, but it is often impossible to be accurate about the source of the pain, as most demonstrable pathology is also visible in the symptom-free population.[8]

As current knowledge of the pathogenesis of back pain is incomplete and many of the diagnostic labels attached to patients are unclear, it is little wonder that treatment remains largely empirical.[8] Nevertheless, in recent years fundamental biological studies have added considerably to the current understanding of age changes, related pathology, and the effects of trauma on spinal structures.[8-11] Although knowledge of basic biologic information is still proceeding, it forms the basis of understanding of the effects of physical and manual therapy on the tissues of the spine and thus on low back pain.

Research into the musculoskeletal system of the body as a whole has demonstrated the beneficial effects of movement on all joint tissues, particularly articular cartilage (AC) and ligaments; it has also shown that the stress of exercise is essential, not only for physical fitness but also for the maintenance of muscle bulk and bone mass, and that problems such as back and joint pain respond favorably to movement and activity and adversely to rest.[11-13] Similarly, experience in the physical treatment of athletes who have severe musculoskeletal injuries to many regions of the body has provided the initial stimulus for the development of the highly successful approach to the treatment of chronic back pain by aggressive, intensive physical therapy and work conditioning.[11,13,14] There is now a better knowledge of the effects of movement and exercise on all elements of the musculoskeletal system, which needs to be understood by physical therapists if they wish to optimize the effects of their manual treatment of back pain and dysfunction problems.

Effect of Movement and Exercise on Back and Joint Pain

There is no reliable evidence that prolonged bed rest or the avoidance of exercise brings about a reduction in back pain; current research clearly demonstrates that, apart from a quite short period of time immediately after injury, bed rest has no effect on the natural history of back pain.[12,13] Similarly, a consideration of current research makes it abundantly clear that physical activity is beneficial and necessary to patients with musculoskeletal dysfunction (acute and chronic), including joint and back pain, and that the active rehabilitation of those with disorders such as chronic back pain not only restores function, but is also associated with a reduction in pain intensity.[8,13-15] indeed, the opposite position appears to be true, that is, that prolonged rest or the avoidance of activity increases the duration and severity of the back pain.[16] Despite this evidence, however, it is clear that bed rest, analgesics, corsets, and the avoidance of physical activity are still the most commonly prescribed forms of medical treatment.[12,13]

Inactivity and especially bed rest cause substantial weakness and loss of tissue from all elements of the musculoskeletal system.[17,18] These changes include a loss of bone, muscle, and connective tissues; a reduction in joint range of motion (ROM), muscle strength, and endurance; and a marked decline in physical fitness in all individuals whose activity levels have been considerably reduced.[17-19] This situation applies equally to the elderly, and there is no truth in the old adage that elderly people do not require as much exercise as younger people,17 that exercise is somehow dangerous to them, and that they have earned their rest after a lifetime of work. The weight of current research evidence reveals that the musculoskeletal system (including the vertebral column) demands the stress of movement and activity at all stages of the life cycle, even into extreme old age.[17,18,20,21] Old people with back pain need a strong, ongoing program of physical activity to reduce their pain levels and improve their function.[19]

In the spine, the health of the joints is largely dependent on repeated low-stress movements. The intervertebral disks and zygapophyseal (facet) joints require movement for the proper transfer of fluid and nutrients across joint surfaces.[22,23] Movement and active exercise are unlikely to reduce the number of episodes of back pain that a person suffers, but they will ensure that those affected will be better able to cope with the problem, to recover from it more rapidly, to remain at or return to productive work more quickly, and to have a much improved quality of life.[13]

Manual Therapy and the Musculoskeletal System

The manual therapist primarily uses movement and exercise as the principal tools in the treatment of peripheral joints and low back pain. In recent years, there has been an abundant amount of research that shows the value of movement to the joints[24] and the musculoskeletal system[25] and that provides strong support to explain the success of manual and physical therapy for back pain.13 Much of the evidence will be considered and applied in this article.

Joints

The function of AC is to facilitate free movement and load bearing of joints, and it is particularly well adapted to meet its dual tasks of reducing friction and alternating load bearing on subchondral bone.[26] Cartilage degeneration is associated with disease processes, whereas localized damage to AC surfaces and to the ligaments and capsule of spinal joints may result from trauma, particularly if repetitive in nature. The effects of pathology need to be clearly distinguished from the results of the "normal" process of attrition and aging[8] if manual therapy is to be effective. Aging is characterized by a small amount of AC dehydration, by fatigue and splitting of collagen bundles, and by changes in the ratios of proteoglycans in the matrix.[26,27] These changes are reflected by an increased compliance of AC to pressure and a considerable reduction in cartilage thickness in old age in all weight-bearing joints.[27-29] The cartilage changes are accompanied by a reduction in the volume of synovial fluid and in its osmolarity, usually with atrophic changes to underlying bone.[24,30] Similarly, age changes (which may be primarily due to disuse) and repetitive minor trauma bring about substantial atrophy of joint capsule and ligament; increasing age also causes ligament stiffening" as the numbers of cross-linkages between adjacent collagen fibrils increase substantially, making the fibers less compliant.[25,31] The principal findings from animal studies show that early lesions in joints occur not where the joint is loaded, but where it is not loaded.[27] The softening and fibrillation of AC is indicative of tissue falling apart from inactivity, not from overuse.[27,32,33] Thus, Many of the joint changes associated with aging are likely to be due more to disuse than to any genetic predisposition of AC and collagen.[23,33]

The physical therapist using manual therapy continually works with joints affected by age and pathological change and attempts to improve movement and reduce pain by passive and active movement techniques. It is therefore important for the physical therapist to understand the physiological effects that movement has on the various elements of synovial joints. All collagenous tissues rely heavily on movement to ensure adequate nutrition.[23,34] Articular cartilage demands regular mechanical loading to remain healthy.[32] Exercise and movement ensure the passage of synovial fluid over its surface and, together with the alternate compression and relaxation of AC that occur during movement, enable the synovial fluid to be expressed and then "sucked back" into the AC as the area of pressure changes over the surface.[11,22,23,29] The regular physical loading and unloading of joint cartilage that occurs with movement during manual therapy facilitates this process. Although cartilage responds very favorably to movement, it responds poorly to prolonged rest and immobilization, particularly under loading.[29] There is overwhelming evidence that shows atrophy and degeneration of AC and underlying subchondral bone during immobilization and especially under conditions of constant loading.

Similarly, ligaments, as dynamic collagenous structures, undergo hypertrophy with exercise and considerable atrophy with disuse. Systemic exercise results in thicker, stronger ligaments that maintain their compliance and flexibility and that also become stronger at the bone-ligament-bone complex.[22]

In the same way, the intervertebral disks (IVDs), which are the largest avascular collagenous structures in the adult, gain their nutrition by the diffusion of nutrients from a distance, primarily via the vertebral end-plate and secondarily by diffusion through the annulus.[9,34] Disk nutrition is heavily dependent on movement, and recent studies[35,36] show that movements in the sagittal plane bring about the greatest transfer of fluid into and out of the disk. These studies indicate the importance of regular, large-range spinal movements so that adequate IVD nutrition is ensured. Similarly, other recent studies[8,37] demonstrate that sustained disk loading (eg, at the limit of flexion) is associated with advanced disk degeneration and low back pain. Movement therapy in all of its forms considerably assists disk nutrition and health.

All of the cartilagenous structures of the body respond adversely to disuse and to conditions of prolonged loading and positively to movement and exercise. Physical therapy procedures, including passive mobilization techniques, utilize both the "stirring" and movement of synovial fluid and the compression and relaxation of cartilage. In addition, full ROM reduces the tendency toward the adaptive shortening of connective tissues and muscles about the joints and minimizes the tendency toward stiffening with age.[8] Recent research has also shown that long-duration, high-mileage weight-bearing exercise such as walking, jogging, or running is not associated with premature joint degeneration or osteoarthritis but is strongly associated with increased bone mineral content in the lower limbs and back.[8,38,39] This evidence is clearly at odds with the often expressed clinical view that repetitive exercise, and particularly running, is associated with the "wearing out" of AC because of the constant stresses of impaction and loading. Current research, however, shows that the old concept of "wear and tear" cartilage loss and osteoarthritis was incorrect and that osteoarthritic joint changes begin in areas where collagen is not often stressed by movement and pressure.[27,32] This knowledge reinforces and vindicates the value of exercise and movement in the physical therapy of joint and back problems.

Bone and Muscle

Bone and muscle are both dynamic structures that respond positively to exercise and adversely to disuse. A strong inverse relationship exists between muscle mass and osteoporosis such that a decline in muscle mass is matched by an increasing fragility of bone.[40] Much of the reduction in muscle mass that occurs with increasing age in western society is due to disuse and can be substantially reversed by a program of activity.[17,25] This knowledge is fundamentally important for the manual therapist because it focuses attention on the need for both specific and general exercise to be prescribed, particularly for the middle-aged and elderly, as an essential part of treatment programs for most individuals. In this regard, Pardini[19] has demonstrated that most elderly Americans can show up to 50% improvement in muscle strength after a relatively short exercise program. High activity levels are particularly essential to the elderly, if independence is to be valued and if the quality of life is to be maintained into old age.

Numerous controlled studies[41-46] have demonstrated the requirements of bone and muscle for exercise throughout the life cycle. Smith et al[41] examined 30 elderly-women with a mean age of 84 years. The women were placed in two groups that were matched for age, weight, and degree of ambulation. The experimental group participated in a 30-minute exercise program, 3 days a week for 3 years. At the end of this period, there was a 5.6% difference in bone mineral content between the groups, consisting of a 2.3% gain in the experimental group and a 3.3% loss in the control group. These results support the findings of Aloia et al,[42] who reported a significant increase in total body calcium in postmenopausal women who exercised regularly for 1 year, in contrast with a fall in total body calcium in a matched sedentary group. Similarly, Ayalon et al,[43] in a study of the effects of dynamic loading exercises for the forearms of postmenopausal women (53-74 years of age), showed an increase of 3.8% in bone density of the radius and ulna after 5 months of exercise compared with controls, who continued to show a decline in bone density. Other recent studies have demonstrated that bone gain after exercise is both site specific and exercise-type specific. Thus, Aisenbrey[47] has shown that among athletes, weight lifters have the greatest bone density and swimmers have the least. Nevertheless, there are some recent indicators showing that habitual swimmers have greater bone mass than do sedentary individuals.48 These studies are a small part of an increasing body of evidence supporting the value of high levels of regular exercise in preserving skeletal health. This is true for both genders, but is particularly the case for women after menopause, when hormonal deprivation adds considerably to involutional bone loss.

Similarly, other studies show that it is possible to increase muscle strength, endurance, and hypertrophy into old age.[44,46] Aniansson et al,[45] in a controlled study of the effects of exercise in old men, showed a significant increase in muscle power and an increased aerobic capacity after a 12-week program of dynamic and static exercise. Walker,[44] in a review article on exercise and aging, demonstrated that muscles in older individuals responded favorably to exercise programs, particularly if the strengthening programs are individualized and consistent with personal goals.

It is not only the middle-aged and elderly who can benefit from increased levels of activity. It has been found that young people who are immobilized for long periods of time also show alterations usually attributable to muscle and bone aging. It is clear that many of the changes attributed to aging are due to disuse.[25,49] Exercise, properly prescribed and applied in the early stages, can reverse most of these changes.

Based on the understanding of the needs that all elements of the human musculoskeletal system have for movement and exercise throughout life, manual therapists have the responsibility to include exercise as an essential part of prophylaxis and treatment in addition to their other more passive treatment modalities such as massage, mobilization, manipulation, and traction.

Education, Lifestyle, and Risk Factors

An essential part of manual therapy is the education of a patient in regard to appropriate musculoskeletal structure and function, to the basic pathology of the patient's problem, and to lifestyle adaptations that may be necessary for the future. This is particularly true for neck and back pain problems, because there is a mythology associated with the region and a dearth of knowledge about spinal morphology among the general public.[4,8] Education concerning the spine should include an understanding of age changes in the region, as they substantially affect the physical behavior of the vertebral column, and should explain the vulnerability of the spine to stress under particular loading conditions.[4,8,9,37] I will now discuss some important aspects of the biomechanics of the spine that are necessary for manual therapists to appreciate if they are to better understand the effects of their treatment.

Spinal Posture

The usual position of lumbar lordosis assists in the effective transmission of loads applied to the spine and provides the most efficient position from which to move the spine.[50] Flattening of the spine occurs with increasing age[51] and has been associated with low back pain in some studies,[52] although others53 have not shown such an association. An essential feature of McKenzie's[52] approach to treatment has centered on the need to maintain a normal pelvic tilt and associated lordosis. Many sitting and working postures involve an individual working at or near the end-range of flexion for considerable periods of time. These postures have profound effects on the nutrition and mechanical behavior of spinal tissues, which need to be understood so that the effects of such sustained postures can be readily managed.

Loading at the Limit of Spinal Movement (End-range)

Although sustained postures in spinal extension are rare, there are many occupations and recreational pursuits that involve a position of full lumbar flexion sustained for long periods of time. Where the spine is loaded at end-range, "creep" (movement further into range) occurs because of an internal adjustment of forces within the tissues involving fluid transfer.[54,55] This process squeezes a considerable amount of fluid out of the compressed intervertebral disks, the cartilage of the facet joints, and the stretched spinal ligaments and also redistributes the remaining fluid within the structures. Thus, creep in flexion is observed as increased forward movement that takes the spine beyond its usual range of movement. This prolonged process not only deprives the soft tissues of part of their nutrition,[56] but the natural collagen "crimp," which is a feature of the resting state of collagen, progressively straightens out as the fibrils elongate under the sustained load.[31,57] Recovery from this position, once the load is removed, takes a considerable period of time.[55] Such situations occur as a usual part of the working pattern of occupational groups such as bricklayers, stonemasons, and sheepshearers and to all individuals who sit in full flexion, under the load of their own body weight, for long periods.

The tissue fluid redistribution described changes the shape of the elements of the mobile segments; places the collagen in the disks, facet joints, and ligaments under sustained load (to which it reacts adversely); increases intradiskal pressure; and leaves the lumbar spine literally "hanging" on its facet joints.29,58 This situation progressively brings about deleterious changes to all the collagenous structures thus placed under loading[37] and makes those individuals particularly vulnerable to injury after periods of sustained flexion loading. It is for this reason that individuals should avoid lifting heavy loads after long periods of driving.[8]

Physical therapy procedures of active and passive lumbar movement aid nutrition of the disks and facet joints, help preserve a hill range of movement, and ensure strong ligaments and tendons.[22,29] Lumbar sagittal movements, in particular, bring about the largest fluid exchange between the disks and the interstitial fluid surrounding the spine.[35,36,59]

This explanation indicates the need for the utilization of large-range trunk movement in the sagittal plane in the early stages of disk and facet joint degeneration. Movement also prevents the adaptive shortening of ligaments and maintains spinal flexibility.[37] The major problem of spinal flexion creep is best managed by ergonomic advice that emphasizes the need for good static and dynamic postures, by regular "pause" exercises (ie, short periods of exercise focusing on mobility and relaxation) that encourage spinal movement, and particularly by the use of the extension component of sagittal movement as the most efficient means of "unloading" the previously loaded elements of the spine and of rehydrating disks, AC, and soft tissues. This explanation provides an understanding of why extension postures and movements are important in the management of low back pain and why extension movements are so useful as a primary form of manual treatment.

Conversely, back pain associated with prolonged standing involves axial creep, that is, relative movement into lumbar extension.[8] Axial creep is best treated by postures and movements that "unload" those previously "compressed" and stretched structures, that is, by movements that emphasize spinal flexion.

Spinal Manipulative Therapy 

The Spinal Lesion

In essence, the pathology of the spinal lesion in most back pain circumstances is still unknown, although there are complex hypotheses produced to explain how spinal manipulative therapy (SMT) exerts its mechanical effects. The current literature suggests that SMT is most unlikely to work by reducing subluxations, correcting vertebral alignment, adjusting nuclear prolapse, or tearing joint adhesions,[60-63] although all of these treatments have strong advocates. Under very particular circumstances, SMT is likely to exert a truly mechanical effect in regard to the acute, painful locked back syndrome.

The early consideration of this situation led to diagnostic labeling such as the "osteopathic lesion," joint "subluxation" "vertebral blockage," "stiff segments," and the like.[60,64] Appropriate pathology necessary to explain or validate such diagnoses, however, has never been demonstrated. These titles have formed useful descriptive labels, based on subjective palpation rather than on more solid criteria.[61] There are no published data to support the view that vertebral malalignment can be corrected by SMT, although there is some research indicating that spinal ROM can be increased by manipulation.[8,61]

Similarly, although Cyriax[60] asserted that nuclear disk herniation was reducible under specific manipulative circumstances, there is no evidence in the literature to justify this view.[10] Indeed, current knowledge of the pathogenesis of nuclear disk lesions shows that the pathology is much less common than believed a decade or more ago[9,64] and that it is extremely unlikely that SMT could have any positive effect on the reduction of nuclear material.[8]

Other explanations provided for the apparent success of SMT encompass neurophysiological reasons, which are beyond the scope of this article. Useful hypotheses, however, are provided by Haldeman,[61] Paris,[62] and Zusman.[63] In particular, Zusman[63] refers to physiological mechanisms and demonstrates how SMT is likely to have an inhibitory effect on reflex muscle contraction (spasm). Zusman also provides an interesting explanation concerning a hysteresis or delayed effect for neural discharge in joint afferents after repetitive end-range passive movement. More recently, Butler[65] has linked the neurophysiological concepts related to a mechanical compromise of neural tissue and axoplasmic flow to provide a challenging explanation for the effects of manipulative therapy.

Acute, Painful Locked Back

Although this article has shown that physiological processes can help explain the direct effect repetitive passive or active movement can have on synovial joints and intervertebral disks, it has proved to be more difficult to explain how movement or manipulation can be so effective in the case of acute, painful locked back. This syndrome refers to acute low back pain that is often attributed to a particular movement and that is sometimes associated with a "click" or noise from the back. Patients with this syndrome are usually flexed and rotated, unable to extend, complain of constant severe back pain, and sometimes experience pain that is referred down one or both legs. On examination, there appears to be a mechanical block to movement, particularly into extension. Such patients often respond favorably to a specific lumbar manipulation or mobilization or to some form of active-assisted movement. The response to a single manipulation is often dramatic, with a sudden reduction of back and leg pain and a full restoration of movement and function.

In attempting to explain the reasons for this condition, a number of alternative ideas have been proposed. Although in the past a few clinicians and researchers have implicated the intervertebral disk,[60] most currently believe that it is impossible (given present knowledge of the structure, function, and pathology of the lumbar disk) for it to be the primary cause and consider the facet joints to be the source of the problem.[8,66] The two most usual explanations provided as to the facet joint structures likely to be involved are (1) nipping of synovial joint fringes of the capsule and (2) entrapment of menisci. Although both the capsule and the menisci are well innervated,[67,68] they are small, "slippery" structures that are unlikely to be entrapped. Bogduk and Engel,[66] however, propose a mechanism by which the menisci might be so involved.

In a study of the lumbar zygapophyseal joints, Taylor and Twomey[69] showed the presence of "joint inclusions" of AC at the posterior-lateral margins of the joint in some individuals (Fig. 1). Under conditions of impaction and torsion, the AC may be split (Fig. 2), parallel to the joint surface. The continuity of these inclusions with a well-innervated capsule, present a situation that is analogous to a tom meniscus in the knee joint. There is the likelihood that should such damage occur, the piece of firm AC may be caught between the articular surfaces, block movement, and, because it is connected to a well-innervated capsule, cause considerable pain.[69] "Gapping," or separation of the joint surfaces by manipulation or movement, would allow the piece of firm AC to return to its normal position, take the load off the capsule, and result in restoration of movement and a reduction in pain. This remains a hypothesis, but is a reasonable explanation for the dramatic effects, often of a single manipulation, in the case of acute, painful locked back,

Although a thorough consideration of the merits of this research extend beyond the scope of this article, readers are referred to the article by Taylor and Twomey,[69] which establishes the validity of the histological sections, demonstrates the pathology, and postulates the clinical situation of the acute, painful locked back.

Summary

Movement and exercise are essential for the development, maintenance, and continuing strength of the musculoskeletal system throughout life and form a vital part of treatment directed toward improving the function or reducing pain from the musculoskeletal system after inactivity, trauma, or disease.[12,13,22,29,63,65] The techniques of manual therapy all utilize movement, stress, and loading to the body and are directed toward functional improvement and pain reduction.[61] Although many of the effects that mobilization and manipulation have on joint pain and mobility (particularly for the vertebral column) remain largely speculative, there is a growing body of evidence that suggests a useful biomechanical model to explain the often dramatic relief that follows such procedures.[61,62,69] Nevertheless, over the last decade, the major advances made in the area of back pain treatment and the management of other musculoskeletal disorders have been based on intensive, aggressive, active physical treatment.[12-14] In addition, recent research has demonstrated that habitual and working postures are important factors in back and regional pain problems.[35,36] Sustained postures near or at the limit of joint ROM, and especially when under loading (of body weight or external objects), substantially reduce the hydration of tissues and the ability of an individual to respond rapidly to environment change.[37]

References

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