| | A Biomechanical Model for Mechanically Efficient Cavitation Production During Spinal Manipulation: Prethrust Position and the Neutral ZoneReceived 3 August 2004; received in revised form 2 August 2005 Spinal manipulative therapy (SMT) is the generic term commonly given to a group of manually applied therapeutic interventions.1 These are usually applied with the aim of inducing intervertebral movement by directing forces to vertebrae.2, 3 There are various theories for mechanisms to how SMT translates into clinical effects, in particular, for the treatment of spinal pain,4, 5, 6, 7, 8 making the selection of techniques difficult to explain or justify. In statistical terms, the clinical outcomes of SMT for spinal pain are significantly greater than those of placebo or sham.9, 10, 11, 12, 13 Consequently, notwithstanding the importance attached to the magnitude of these outcomes, some form of interface must exist between mechanical events that occur during the delivery of SMT and the clinical outcomes that result. At present, however, the exact location or even nature of this interface is as yet uncertain. Because the precise biomechanics involved in SMT are largely unknown, further exploration of this area would be valuable, if only to assist practitioners to better appreciate the mechanisms underlying their clinical observations and to justify their actions.14, 15, 16, 17 Spinal manipulative therapy includes both “manipulation” and “mobilization” procedures. Until now, force-time histories measured during spinal manipulation have been described as consisting of 3 distinct phases: the “preload” (or “prethrust”) phase, the “thrust phase,” and the resolution phase3 (Fig 1). Most of the force delivered during the prethrust and thrust phases is applied along the same line of action, perpendicular to the skin surface.18, 19 Therefore, a fourth “orientation” phase may be added to describe the period during which the patient is orientated into the appropriate position in preparation for the prethrust phase, as demonstrated in previous studies20, 21 (Fig 1). Forces applied during the orientation phase are likely variable but should gradually increase throughout the phase because restraining tissues provide increasing resistance to further departures from the resting neutral position. Within the thrust phase of a manipulation, a (usually) high-velocity “thrust” (which, in this context, refers to a rapidly delivered additional force) delivers an impulse (the time integral of applied force, equal to the difference in momentum) to 1 or more “target” vertebra. This impulse is represented in Fig 1 by the area under the curve of the thrust phase, within the limits of ΔF. This impulse is understood to create a very small amplitude movement between the surfaces of a target zygapophyseal joint.2 Hence, the given term high-velocity, low-amplitude thrust is derived from the mechanical characteristics commonly associated with the delivery of this intervention. Manipulation is usually associated with an audible “pop,” “click,” or “crack,” which is often viewed as signifying success in the technical delivery of the intervention,15, 19, 20, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 although this has yet to be directly linked to clinical effects.33 This cracking sound is caused by an event termed cavitation, occurring within the synovial fluid (SF) of the joint.34 Cavitation is the term used to describe the formation and activity of bubbles (or cavities) within fluid, formed when tension is applied to the fluid as a result of a local reduction in pressure.34, 35, 36 It can theoretically occur in any diarthrodial synovial joint in the body and is a consequence of certain types of motion between the articular surfaces.34, 37, 38 Cavitation can occur during both high- and low-velocity joint motion.39, 40 As such, high-velocity motion has to be considered an important yet not absolute requirement for the production of cavitation during spinal manipulation. Thus, it may be argued that cavitation is the only characteristic that truly distinguishes a manipulation from other SMT modalities. By contrast, mobilization of the spine is associated with relatively slow loading rates, ranging from almost static loading to cyclical (oscillatory) loading rates as high as 5 to 6 Hz.15 It is generally performed at less than 2 Hz15; causes very little, if any, intervertebral motion41, 42; and does not produce cavitation (the only factor that truly distinguishes it from manipulation). In the case of higher frequencies (5 Hz), the amplitude of oscillation is probably quite small so that tissue strain rates are likely to be small compared with manipulation. In addition, mobilization is usually characterized by a large number of loading cycles and a much longer duration of loading than manipulation.15 For clarity therefore, in the remainder of this article, the term manipulation will specifically refer to high-velocity, low-amplitude thrust manipulation (which, when successfully delivered, produces cavitation). Mechanisms of Action  Various theories have been proposed to explain the clinical effects of spinal manipulation. Essentially, 4 main theories emerge from the published literature. These are (1) release of trapped intra-articular material such as synovial folds or meniscoids; (2) relaxation of “hypertonic” muscle by sudden stretching, the “mechanoreceptor-pain gate” or “reflexogenic” theory; (3) disruption of articular or periarticular adhesions; and (4) “unbuckling” of motion segments that have undergone “disproportionate displacements.”6 A recent critical review of these 4 main theories4 argued that only one theory, namely, the release of trapped intra-articular material such as synovial folds or meniscoids, so far offers a plausible “mechanical” explanation for the measured clinical effects of spinal manipulation on spinal pain. It was also argued that, although cavitation seemed unlikely to be an absolute requirement for these intra-articular mechanical events to occur, it is at the very least an indicator of successful joint surface separation, which would be a requirement.4 There is also evidence that zygapophyseal joint cavitation, the distinguishing characteristic of spinal manipulation, appears to be associated with certain physiological outcomes.43, 44 To invoke these physiological outcomes, it is therefore reasonable to argue that cavitation is necessary. Hence, it would be useful to have more precise information about biomechanical factors that will facilitate cavitation production. Although previous work has already provided useful biomechanical data for spinal manipulation,3, 15, 25, 45, 46 most have not focused upon factors that facilitate cavitation. This article aims to explore some of these factors. Manipulation Kinematics Kinematics is the branch of mechanics that deals with motion (of an object) without reference to force or mass. With a few notable exceptions,2, 20, 21, 47, 48, 49, 50, 51, 52, 53 most biomechanical studies of spinal manipulation have given scant attention to kinematics. Hence, despite these novel efforts, accurate and complete kinematic data for vertebral movements during all phases of spinal manipulation throughout the spine are currently unavailable. Consideration of this area should reveal biomechanical factors that play an important role in cavitation production. Joint kinematics are largely determined by the morphology of the bones and the anatomical restraints influencing the articulations that they form. During spinal manipulation, the clinician applies a force to the spine, tending to translate a target vertebra (all points of the bone moving in parallel paths and to the same extent), and a moment, tending to rotate the target vertebra relative to its adjacent neighbors. The rotational movements similar to those created by the muscles are known as physiological movements, whereas the translational movements that are not normally produced voluntarily are known as accessory movements.15 In any diarthrodial synovial joint, including the zygapophyseal joints, translations will produce different types of articular surface motion depending on the line of action of the applied force relative to the morphology of that particular joint. These translations are gliding (a parallel motion of one surface across another), distraction (the separation of articular surfaces in a direction perpendicular to the surfaces), and compression (the apposition of the 2 articular surfaces toward one another to create equal and opposite loading). Joint movement can be further described in terms of dividing the resultant (total) movement into components of primary and coupled movements. In the spine, reference is usually made to the motion of an entire vertebra with one of its neighbors rather than to motion occurring at individual zygapophyseal joints. Therefore, in terms of spinal manipulation, the primary movement can be viewed as motion of an entire target vertebra that occurs in the same plane as, or rotation about an axis perpendicular to, the line of action of the applied force delivered by the clinician. Vertebral movements that occur concomitantly with the primary movement but in directions other than that expected of the externally applied force are known as coupled movements. Coupling of motion may be defined as the consistent association of rotation along or about an axis, with another translation or rotation along or about a second axis of a 3-dimensional orthogonal coordinate system.54 Vertebrae have 6 degrees of freedom: rotation about and translation along transverse, sagittal, and longitudinal axes. Fig 2 illustrates the 6 possible movement components: translations in 3 directions (1, 2, 3; the directions of the x-, y-, and z-axes) and rotations in 3 directions (4, 5, 6; about lines parallel to these 3 axes). Hence, in addition to a primary movement, there are 5 possible coupled movement components (Fig 2). The motion produced during flexion, extension, lateral flexion, and axial rotation between vertebrae is a complex combined motion resulting from simultaneous rotation and translation.55 An externally applied force such as that delivered during spinal manipulation has the potential to produce various combinations of physiological and accessory vertebral movements. Furthermore, passively generated movements are likely to result in vertebral motion that differs from that which occurs during active physiological movements.15, 24 This is because physiological coupling can be constrained during the application of an external nonphysiological force.56, 57 As such, zygapophyseal articular surface motion, occurring as a result of an externally applied force, may also differ from that which occurs during active movements. Manipulation Kinetics Kinetics is the branch of mechanics that deals with motion (of an object) under the action of given forces. This includes static (equilibrium) states in which no movement is occurring and dynamic states in which forces may vary as movement occurs. Most previous biomechanical analyses of spinal manipulation have been concerned with the forces and moments acting upon the bones that form the target joint. It is still not clear how the available kinetic data for spinal manipulation (as summarized in Fig 1) are representative of the forces that actually arrive at the target vertebra. Motion of the target vertebra will be heavily influenced by the morphologies of the intervertebral joints and the restraints offered by the connecting tissues. Indeed, several studies suggest that a substantial proportion of the kinetic energy transferred to the patient is likely to be used on the deformation of both superficial and restraining tissues.41, 42, 58 As such, it may be valid to discuss the production of cavitation in terms of the mechanical efficiency of manipulation delivery. Functional Spinal Units The bodies of 2 adjacent vertebrae with their strong and intimate connections, including their interconnecting ligaments, the intervertebral disc, and the zygapophyseal joints, form individual fundamental segmental units throughout the spine. Each of these fundamental units is known as a functional spinal unit (FSU). An FSU is defined as the smallest segment of the spine to exhibit biomechanical characteristics similar to those of the entire spine.54 The typical load-displacement behavior of a cadaveric FSU specimen is illustrated in Fig 3. Within the total range of passive motion of any FSU, the typical nonlinear load-displacement curve consists of 2 regions or “zones” that exhibit very different biomechanical behavior. In the vicinity of the resting neutral position of the FSU, this load-displacement behavior is highly flexible. This is the region known as the neutral zone,59 which may be defined as the motion region of the joint where the passive osteoligamentous stability mechanisms exert little or no influence. During passive physiological movement of the FSU, motion occurs in this region against minimal internal resistance. It is a region in which a small load causes a relatively large displacement. Certainly in the lumbar spine, exactly where the neutral zone motion region is situated (within the total range of motion of an FSU) is largely determined by the zygapophyseal joints.60 As such, the initial orientation of the zygapophyseal joints at the outset of a movement will have a significant effect on ensuing motion of the FSU.53, 61, 62, 63, 64 The “elastic zone” is the remaining region of FSU motion that continues from the end of the neutral zone to the point of maximum resistance (provided by the passive osteoligamentous stability mechanism), thus limiting the range of motion. Manipulation “Prethrust Position” As evident in Fig 1, previous kinetic data for spinal manipulation consistently demonstrate a preload force, a relatively constant force that may be applied for several seconds before the thrust phase.3, 18, 19, 52, 65, 66, 67 This phase may be more accurately described as the prethrust phase, given that it too involves significant applied force. Similarly, the position achieved at the end of the prethrust phase, upon which the additional thrust impulse will be delivered, may be described as the prethrust position. The prevailing kinematic model of motion for both the target FSU and target zygapophyseal joint during spinal manipulation68, 69, 70 is based entirely on observations of cavitation produced during distraction of metacarpophalangeal (MCP) joints.34, 71 As a result, this model has limited validity for predicting spinal motion. These studies undoubtedly provide insight into cavitation occurring in zygapophyseal joints. However, care is needed when transferring a model of motion based on a simple joint such as the MCP to a much more complex articular arrangement such as an FSU and its constituent zygapophyseal joints. Although the articulations at a MCP joint and an FSU each involve motion between 2 bones, motion at a MCP joint demands consideration of only one independent synovial joint. It therefore differs markedly from the 3-joint complex of an FSU (the so-called articular triad). Indeed, it was the simple anatomy and accessibility of the MCP joint that lent itself to the early studies of synovial joint cavitation,34, 71 which were not designed to provide models for spinal manipulation. Even so, the prevailing kinematic model fails to make a distinction between kinematics of the target FSU and those of the individual target zygapophyseal joint. The apparent confusion that this has created can be seen in the inconsistency of descriptions and supposed definitions of spinal manipulation throughout the literature.9, 28, 72, 73 During spinal manipulation, there is usually a designated target zygapophyseal joint (within the target FSU), in which cavitation is desired.31 The intent of the clinician is to efficiently deliver a suitable proportion of the thrust impulse to this target joint.74 As such, when discussing the production of cavitation, kinematics of the target joint must be clearly distinguished from those of the target FSU. Because we are specifically interested in the cavitation event, we will be primarily concerned with kinematics of the target joint for the remainder of this article. The modern graphical conceptualization of the prevailing kinematic model of manipulation is 2-dimensional and is represented by the area covered by one of the bones of a simple diarthrodial synovial joint as it travels through its entire range of physiological rotation, which is symmetrical and thus idealized (Fig 4).69 Here, another fundamental problem arises with the model in that inferences made from observations of an accessory movement (distraction) in a joint have been applied to describe a physiological movement (pure rotation about a fixed axis). As may be seen in Fig 4, the prevailing kinematic model describes the ideal prethrust position of a target joint as being located at the limit of the joint's passive range of motion in a single plane of motion, far into the elastic zone. If this model is used to predict the distribution of the often substantial force applied during the thrust phase,65, 66 most would be seen to pass directly to the restraining tissues surrounding the target zygapophyseal joint. If this occurred, these tissues could easily be damaged.75, 76, 77 Rather conveniently, a concept known as the physiologic barrier, which has evolved to account for the resistance provided by SF cohesion as described in studies of MCP joint distraction,34, 71, 78 is said to dissipate (in the form of SF cavitation) much of the force that reaches the target joint before it is able to reach the anatomical restraining tissues. The remaining portion of the elastic zone, beyond the physiologic barrier, is generally known as the paraphysiologic space (Fig 4). Some studies suggest that much of the substantial force applied during the thrust phase is unlikely to be transmitted directly to anatomical tissues surrounding the target joint.58, 79, 80 In addition, the contact forces applied during the orientation and prethrust phases have 3-dimensional components19 and create FSU motion in multiple planes,3, 20, 21, 51 indicating that the prevailing 2-dimensional kinematic model is in need of some revision. In recent years, some attempts have been made at revising this model, acknowledging the likely importance of complex combined FSU movements during the orientation and prethrust phases,24, 81 and problems encountered when transferring the model to clinical scenarios.82 However, such attempts have so far fallen short of providing a comprehensive revision that is entirely consistent with available empirical data. Assuming cavitation to be the mechanical goal of manipulation, the target joint must be placed in a prethrust position that facilitates efficient delivery of kinetic energy from the thrust impulse to the SF so that tension is applied to the fluid. For maximum mechanical efficiency, this must occur in a position that results in the minimum loss of kinetic energy (from the thrust impulse) to the surrounding tissues. In biomechanical terms, the motion region of the target joint that most suitably fulfills these requirements is the neutral zone (as defined previously). Therefore, for the safe and efficient delivery of the thrust impulse to the SF, the ideal prethrust position will be equivalent to the neutral zone of the target joint. This argument can be applied to any diarthrodial synovial joint in the body, including, of course, an individual zygapophyseal joint. Importance of Neutral Zone in Prethrust Position Conventionally, use of the term neutral zone in relation to the spine has been reserved for the description of the motion behavior of 1 or more complete FSU57, 59, 83, 84 (Fig 3). Even so, it may be argued that, within any individual FSU, each of its 2 constituent zygapophyseal joints will possess an independent motion region where the passive osteoligamentous stability mechanisms (of that individual joint) exert little or no influence. Certainly, the low restraint offered by zygapophyseal joint capsules85, 86 would lend support to this argument, on the condition that the FSU was orientated in such a way as to allow the target joint to exploit such freedom of motion,2 a concept possibly overlooked in previous investigations.87 The neutral zone of an FSU surrounds the resting neutral position of that FSU. There is a degree of preexisting tension that naturally exists in spinal ligaments and tissues surrounding the zygapophyseal joints, even when in this resting neutral position.88 In this neutral configuration, a perfectly formed FSU possesses reflectional (mirror image) symmetry about the sagittal plane, which divides the body into right and left halves. Indeed, this is the only form of symmetry that the FSU possesses. In this configuration, preexisting tension is uniformly distributed between the 2 constituent zygapophyseal joints, which offer equal restraint to motion. Only motion in the sagittal plane (rotation or translation) will retain this FSU symmetry. Motion in any other plane (such as axial rotation or lateral flexion) will create a departure from symmetry and a consequent nonuniform distribution of tension throughout the FSU, which will undoubtedly influence the restraint offered by each of the 2 zygapophyseal joints. The restraint offered in any one of these joints may increase or decrease, depending on the precise orientation of the FSU. Consequently, the orientation of a given FSU when in its position of overall restraint equilibrium (FSU neutral zone) may differ from its orientation when any one of its constituent zygapophyseal joints is positioned to encounter minimal restraint (target joint neutral zone). It is therefore likely that FSU motion outside the sagittal plane would be required to decrease the restraint offered by any one particular zygapophyseal joint so that it tends toward its neutral zone motion region. Theoretically, only from within the neutral zone of the target joint may tension be applied to the viscoelastic SF of that joint with minimal resistance from anatomical tissues. If the prethrust position is optimal, the additional force delivered during the thrust phase with the FSU in this position will travel through the path of least possible resistance and arrive at the target joint. Motion is likely to occur between the target joint surfaces in the form of a distraction or gliding translation or a combination of both,2, 38 ultimately transferring kinetic energy to the SF. If this kinetic energy is sufficient, cavitation will ensue.37 A New Model To follow convention, the simple anatomy of the MCP joint can be used to illustrate this concept for a new general model of manipulation (Fig 5). In every study to have studied cavitation in MCP joints, cavitation was achieved by distraction translation in the neutral position (which, in the MCP joint, is the midpoint of the neutral zone). Therefore, just as with the original model (Fig 4), care must be taken when using data from MCP joint motion to predict spinal motion. In particular, when transferring this model to a zygapophyseal joint, restraint provided by all components of the target FSU must be recognized. Furthermore, although, like the original model, this model is represented in Fig 5 by a 2-dimensional motion diagram along a single plane, the concept is actually 3-dimensional in that achieving the neutral zone in every plane would provide the optimal (most efficient) prethrust position. The further the target joint is positioned from its neutral zone (ie, into its elastic zone), the greater will be the force required, during the thrust phase, in overcoming the resistance provided by the surrounding tissues to achieve cavitation. Thus, cavitation will be more efficiently produced when the target joint is distracted within the neutral zone motion region. In the spine, although spinal manipulation is likely to create strain in the capsules of target zygapophyseal joints that is within physiological parameters, this may account for the observation of larger peak manipulation forces during manipulation regarded by clinicians as “satisfactory” (by way of producing cavitation), yet which possess largely identical kinematic characteristics to those that did not.52 What is occurring with the paraphysiologic space? If any extra motion becomes available to the target joint after cavitation occurs, as a result of reduced resistance offered by SF, then it is likely only to be available perpendicular to the joint surface, allowing joint gapping against less resistance2, 34, 37, 39, 71 (Fig 5). The available extra range of motion provided in this paraphysiologic space will then be limited only by the joint's anatomical restraining tissues. Zygapophyseal joint gapping has been confirmed during manipulation of the spine.2 For the surfaces of any zygapophyseal joint to separate, the motion of the FSU to which it belongs must depart from normal coupling, which is determined by joint morphology and restraining tissues. The motion of the target FSU that occurs during spinal manipulation must therefore be nonphysiological. Thus, considerable external force is required if the motion of the FSU is to deviate from normal coupling. A significant proportion of the force applied during the orientation phase will be used to overcome the restraint offered by the target FSU and constrain coupled movements that would normally occur. The almost constant force applied during the prethrust phase produces little additional motion and will therefore be primarily used to maintain this FSU orientation. In the case of “long-lever” manipulations, orientating the entire target FSU around the target joint neutral zone position (and sustaining this orientation) will require considerable forces because resistance will be simultaneously provided by several body segments such as the head, thorax, abdomen, pelvis, and extremities.20, 21, 53 Manipulation Accuracy and Specificity In the context of spinal manipulation, accuracy is achieved when cavitation occurs in the designated target zygapophyseal joint, regardless of whether it also occurs in any other joint(s). On the other hand, specificity is achieved when cavitation does not occur in any joint other than the target joint. Research has shown that accuracy is generally achieved at the cost of specificity.31 The resistance offered by tissues of the target joint in the optimal prethrust position should, by definition, be minimal. From this, the thrust impulse will provide the SF with the additional kinetic energy required to produce cavitation.37 Therefore, if cavitation is intended to be specific to a single target zygapophyseal joint, the target joint would need to be alone in being within its neutral zone motion region. This would apply to all other zygapophyseal joints, including the contralateral joint within the target FSU. Without obvious exception, all spinal manipulation procedures appear to entail some degree of motion outside the sagittal plane during orientation and prethrust phases, regardless of anatomical level.2, 20, 21, 47, 48, 49, 50, 51, 52, 53 Thus, the distribution of restraint and force transmission between the 2 zygapophyseal joints within a target FSU are intentionally altered during these phases by orientating the FSU further from its resting, neutral, symmetrical configuration. According to previous authors, motion in joints of neighboring FSUs may be reduced by applying a “short-lever” manipulation toward a target vertebra.31 In the case of long-lever manipulations, whereby the applied force is delivered to the target FSU through its contiguous neighbors, specificity may be increased during the orientation and prethrust phases by way of approximating articular surfaces of neighboring zygapophyseal joints in such a way as to effectively “lock” their FSU and permit force transmission between joint surfaces24, 89 or by confining them to their elastic zone regions to “saturate the capacity of local damping factors.”45 Failure to do so may mean that the ensuing thrust impulse will be dissipated throughout multiple FSUs and thus be less specific.31, 90 Without orientation and prethrust phases, the spine would be allowed to freely oscillate during the thrust phase, with its behavior being largely a function of its own resonant frequency and the “thrust-rise time” (Δt in Fig 1).17, 91, 92, 93 From this, we may deduce that the prethrust position effectively creates a damping effect, which limits the extent to which force is transmitted to the entire spine during the thrust phase. In doing so, the orientation and prethrust phases increase the likelihood of both accuracy and specificity of joint surface motion at the target zygapophyseal joint. Consequently, it obviates the need for a very high–velocity thrust impulse (short thrust-rise time), as predicted by Solinger93 for a specific spinal manipulation with no distinct prethrust phase or influence of coupling. Importantly, these prethrust forces are not unique to short-lever manipulations, in which manipulation forces are applied directly over the target FSU. They also appear during long-lever manipulations, in which forces are applied via limbs and through partial or entire body segments.3 This damping effect is thus unlikely to be the result of local compression of paraspinal soft tissues from direct contact pressure41, 42 or effects of direct compression on the low-friction skin-fascia interface94 but the upshot of an optimal prethrust position, produced by the skilful application of forces during the orientation and prethrust phases, that acts to form a path of least resistance for the ensuing thrust impulse. Clinical Relevance The existing theories for the mechanisms of action of spinal manipulation6 and the rationale for its use14 have been based on the prevailing kinematic model, which continues to inform contemporary opinion and even policy.9, 72, 73, 82 However, it is hoped that this new model will inform further explanatory work on the production of cavitation during spinal manipulation. In particular, further kinematic investigation should yield valuable information, which is likely to be of clinical relevance. If this model is ultimately verified by empirical research, future definitions of manipulation that give reference to biomechanical characteristics of the intervention should be modified accordingly. This proposed revision of the conceptual and kinematic model of manipulation is unlikely to have profound impact on the everyday technical delivery of particular spinal manipulation procedures because anecdotal evidence suggests that cavitation is already commonly achieved during current clinical practice. The presented model and the identification of characteristics that potentially facilitate the cavitation event are simply intended to bring explanations of clinical effects and empirical research into closer accord. Nonetheless, the model proposed may offer a starting point for clinicians and researchers alike to develop more mechanically efficient manipulative approaches and techniques. The presence of pain in the spine has been shown to produce abnormal kinematic behavior,95, 96, 97 which in turn may influence or even limit movements that result from externally applied forces such as those applied during the various phases of spinal manipulation. With the ideal prethrust position described as being equivalent to the neutral zone of the target joint, it is no longer a function of the total range of motion of that joint. Essentially, the location of the neutral zone should be the same for joints with a normal range of motion as with joints with an increased range of motion (hypermobility) or a decreased range of motion (hypomobility). This circumvents some problems identified with the previous model.82 Previously injured FSUs and peripheral joints are known to be associated with less passive restraint and have been characterized by proportionally larger neutral zones.59, 98, 99 If the passive retraining tissues of a particular target joint are influenced in this way, it may explain why cavitation is more easily achieved in some joints than others100 because the probability of that joint being in its neutral zone region at any particular time will be greater. This may also explain why habitual “knuckle crackers” seem to have lax joints, in which cavitation may be more readily achieved. The opposite may be true (smaller neutral zone) for joints in which cavitation cannot be achieved. Finally, if cavitation is judged to be the mechanical goal of a manipulation, then maximal mechanoreceptor stimulation will indicate a less mechanically efficient impulse delivery. When the target joint is moved into the elastic zone motion region, there is likely to be increased tissue resistance (to the thrust impulse), which will result in increased high-threshold mechanoreceptor stimulation. Mechanoreceptor stimulation has often been suggested as the most likely route through which spinal manipulation provides clinical effects.25, 27, 69, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111 The mechanoreceptor-pain gate theory thus seems to be mutually exclusive from the notion that cavitation is the goal of manipulation. However, future research is needed to investigate whether either of these factors constitutes the interface between the biomechanics of spinal manipulation and the clinical outcomes that result. Conclusions Biomechanical factors that facilitate mechanically efficient cavitation production during manipulation have been explored, and a revision of the conceptual and kinematic model has been proposed. Central to this model, mechanically efficient cavitation production during manipulation requires a prethrust position, in which the target joint is ideally positioned into its own neutral zone motion region, thus maximizing the efficiency of the manipulation. Future research is needed to test this model. References 1. 1Harvey E, Burton AK, Moffett JK, Breen A. Spinal manipulation for low-back pain: a treatment package agreed to by the UK chiropractic, osteopathy and physiotherapy professional associations. Man Ther. 2003;8:46–51. |
CrossRef
2. 2Cramer GD, Gregerson DM, Knudsen JT, Hubbard BB, Ustas LM, Cantu JA. The effects of side-posture positioning and spinal adjusting on the lumbar Z joints: a randomized controlled trial with sixty-four subjects. Spine. 2002;27:2459–2466.
CrossRef
3. 3Herzog W, Symons B. The biomechanics of spinal manipulation. Crit Rev Phys Rehabil Med. 2001;13:191–216. 4. 4Evans DW. Mechanisms and effects of spinal high-velocity, low-amplitude thrust manipulation: previous theories. J Manipulative Physiol Ther. 2002;25:251–262. Abstract | Full Text |
Full-Text PDF (129 KB)
|
CrossRef
5. 5Hearn A, Rivett DA. Cervical SNAGs: a biomechanical analysis. Man Ther. 2002;7:71–79. |
CrossRef
6. 6Shekelle PG. Spinal manipulation. Spine. 1994;19:858–861. MEDLINE 7. 7Wright A. Hypoalgesia post-manipulative therapy: a review of a potential neurophysiological mechanism. Man Ther. 2000;1:11–16. |
CrossRef
8. 8Zusman M. What does manipulation do? The need for basic research. In: Boyling JD, Pastalanga N editor. Grieve's modern manual therapy. Edinburgh: Churchill Livingstone; 1994;p. 651–659. 9. 9Assendelft WJ, Morton SC, Yu EI, Suttorp MJ, Shekelle PG. Spinal manipulative therapy for low back pain. A meta-analysis of effectiveness relative to other therapies. Ann Intern Med. 2003;138:871–881. 10. 10Hurwitz EL, Aker PD, Adams AH, Meeker WC, Shekelle PG. Manipulation and mobilization of the cervical spine. A systematic review of the literature. Spine. 1996;21:1746–1759. MEDLINE |
CrossRef
11. 11Koes BW, Assendelft WJ, van der Heijden GJ, Bouter LM. Spinal manipulation for low back pain. An updated systematic review of randomized clinical trials. Spine. 1996;21:2860–2871. MEDLINE |
CrossRef
12. 12Shekelle PG, Adams AH, Chassin MR, Hurwitz EL, Brook RH. Spinal manipulation for low-back pain. Ann Intern Med. 1992;117:590–598. MEDLINE 13. 13van Tulder MW, Koes BW, Bouter LM. Conservative treatment of acute and chronic nonspecific low back pain. A systematic review of randomized controlled trials of the most common interventions. Spine. 1997;22:2128–2156. MEDLINE |
CrossRef
14. 14Haas M, Groupp E, Panzer D, Partna L, Lumsden S, Aickin M. Efficacy of cervical endplay assessment as an indicator for spinal manipulation. Spine. 2003;28:1091–1096.
CrossRef
15. 15Lee M, Gál JM, Herzog W. Biomechanics of manual therapy. In: Dvir Z editors. Clinical biomechanics. Philadelphia: Churchill Livingstone; 2000;p. 209–238. 16. 16Rebain R, Baxter GD, McDonough S. The passive straight leg raising test in the diagnosis and treatment of lumbar disc herniation: a survey of United Kingdom osteopathic opinion and clinical practice. Spine. 2003;28:1717–1724.
CrossRef
17. 17Solinger AB. Theory of small vertebral motions: an analytical model compared to data. Clin Biomech (Bristol, Avon). 2000;15:87–94. Abstract | Full Text |
Full-Text PDF (265 KB)
|
CrossRef
18. 18Herzog W, Kawchuk GN, Conway PJW. Relationship between preload and peak forces during spinal manipulative treatments. J Neuromusculoskelet Syst. 1993;1:52–58. 19. 19Van Zoest GG, Gosselin G. Three-dimensionality of direct contact forces in chiropractic spinal manipulative therapy. J Manipulative Physiol Ther. 2003;26:549–556. Abstract | Full Text |
Full-Text PDF (302 KB)
|
CrossRef
20. 20Klein P, Broers C, Feipel V, Salvia P, Van Geyt B, Dugailly PM, et al. Global 3D head-trunk kinematics during cervical spine manipulation at different levels. Clin Biomech (Bristol, Avon). 2003;18:827–831. Abstract | Full Text |
Full-Text PDF (252 KB)
|
CrossRef
21. 21Triano JJ, Schultz AB. Motions of the head and thorax during neck manipulations. J Manipulative Physiol Ther. 1994;17:573–583. MEDLINE 22. 22Denslow J. Pathophysiologic evidence for the osteopathic lesion: the known, unknown, and controversial. In: Beal M editors. The principles of palpatory diagnosis and manipulative technique. Newark (Ohio): American Academy of Osteopathy; 1989;p. 134–138. 23. 23Gibbons P, Tehan P. Manipulation of the spine, thorax and pelvis. An osteopathic perspective. Edinburgh: Churchill Livingstone; 2000;. 24. 24Gibbons P, Tehan P. Patient positioning and spinal locking for lumbar spine rotation manipulation. Man Ther. 2001;6:130–138. |
CrossRef
25. 25Herzog W. The mechanical, neuromuscular, and physiologic effects produced by spinal manipulation. In: Herzog W editors. Clinical biomechanics of spinal manipulation. New York: Churchill Livingstone; 2000;p. 191–207. 26. 26Livingstone WK. Pain mechanisms. New York: Macmillan Co; 1947;. 27. 27Maigne JY, Vautravers P. Mechanism of action of spinal manipulative therapy. Joint Bone Spine. 2003;70:336–341.
CrossRef
28. 28Mierau D, Cassidy JD, Bowen V, Dupuis P, Noftall F. Manipulation and mobilization of the third metacarpophalangeal joint. A quantitative radiographic and range of motion study. Man Med. 1986;3:135–140. 29. 29Reggars JW. The therapeutic benefit of the audible release associated with spinal manipulative therapy. A critical review of the literature. Aust Chiropr Osteopath. 1998;7:80–85. 30. 30Sandoz R. The significance of the manipulative crack and of other articular noises. Ann Swiss Chiro Assoc. 1969;4:47–68. 31. 31Ross JK, Bereznick DE, McGill SM. Determining cavitation location during lumbar and thoracic spinal manipulation: is spinal manipulation accurate and specific?. Spine. 2004;29:1452–1457.
CrossRef
32. 32Vernon H. Qualitative review of studies of manipulation-induced hypoalgesia. J Manipulative Physiol Ther. 2000;23:134–138. Abstract | Full Text |
Full-Text PDF (43 KB)
|
CrossRef
33. 33Flynn TW, Fritz JM, Wainner RS, Whitman JM. The audible pop is not necessary for successful spinal high-velocity thrust manipulation in individuals with low back pain. Arch Phys Med Rehabil. 2003;84:1057–1060. Abstract | Full Text |
Full-Text PDF (131 KB)
|
CrossRef
34. 34Unsworth A, Dowson D, Wright V. “Cracking joints”. A bioengineering study of cavitation in the metacarpophalangeal joint. Ann Rheum Dis. 1971;30:348–358. MEDLINE |
CrossRef
35. 35Young FR. Cavitation. London: Imperial College Press; 1999;. 36. 36Trevena DH. Cavitation and tension in liquids. Bristol: Adam Hilger; 1987;. 37. 37Watson P, Kernohan WG, Mollan RAB. A study of the cracking sounds from the metacarpophalangeal joint. Proc Inst Mech Eng (H). 1989;203:109–118. MEDLINE |
CrossRef
38. 38Chen YL, Kuhl T, Israelachvili J. Mechanism of cavitation damage in thin liquid films: collapse damage vs. inception damage. Wear. 1992;153:51. 39. 39Meal GM, Scott RA. Analysis of the joint crack by simultaneous recording of sound and tension. J Manipulative Physiol Ther. 1986;9:189–195. MEDLINE 40. 40Suter E, Herzog W, Conway PJ, Zhang YT. Reflex response associated with manipulative treatment of the thoracic spine. J Neuromusculoskelet Syst. 1994;2:124–130. 41. 41McGregor AH, Wragg P, Gedroyc WM. Can interventional MRI provide an insight into the mechanics of a posterior-anterior mobilisation?. Clin Biomech (Bristol, Avon). 2001;16:926–929. Abstract | Full Text |
Full-Text PDF (163 KB)
|
CrossRef
42. 42Powers CM, Kulig K, Harrison J, Bergman G. Segmental mobility of the lumbar spine during a posterior to anterior mobilization: assessment using dynamic MRI. Clin Biomech (Bristol, Avon). 2003;18:80–83. Abstract | Full Text |
Full-Text PDF (226 KB)
|
CrossRef
43. 43Brennan PC, Kokjohn K, Kaltinger CJ, Lohr GE, Glendening C, Hondras MA, et al. Enhanced phagocytic cell respiratory burst induced by spinal manipulation: potential role of substance P. J Manipulative Physiol Ther. 1991;14:399–408. MEDLINE 44. 44Brennan PC, Triano JJ, McGregor M, Kokjohn K, Hondras MA, Brennan DC. Enhanced neutrophil respiratory burst as a biological marker for manipulation forces: duration of the effect and association with substance P and tumor necrosis factor. J Manipulative Physiol Ther. 1992;15:83–89. MEDLINE 45. 45Triano JJ. The mechanics of spinal manipulation. In: Herzog W editors. Clinical biomechanics of spinal manipulation. New York: Churchill Livingstone; 2000;p. 191–207. 46. 46Triano JJ. Biomechanics of spinal manipulative therapy. Spine J. 2001;1:121–130. Abstract | Full Text |
Full-Text PDF (171 KB)
|
CrossRef
47. 47Cramer GD, Skogsbergh D, Tuck NR, Floyd J, Allen S, Fonda S, et al. In: The effects of spinal manipulative therapy on the L5 intervertebral foramina as evaluated by magnetic resonance imaging. Des Moines: Foundation for Chiropractic Education and Research; 1996;p. 158–160. 48. 48Cramer GD, Tuck NR, Knudsen JT, Fonda SD, Schliesser JS, Fournier JT, et al. Effects of side-posture positioning and side-posture adjusting on the lumbar zygapophysial joints as evaluated by magnetic resonance imaging: a before and after study with randomization. J Manipulative Physiol Ther. 2000;23:380–394. Abstract | Full Text |
Full-Text PDF (601 KB)
|
CrossRef
49. 49Gál JM, Herzog W, Kawchuk GN, Conway PJ, Zhang YT. Biomechanical studies of spinal manipulative therapy (SMT): quantifying the movements of vertebral bodies during SMT. J Can Chiropr Assoc. 1994;38:11–24. 50. 50Gal JM, Herzog W, Kawchuk GN, Conway PJ, Zhang YT. Forces and relative vertebral movements during SMT to unembalmed post-rigor human cadavers: peculiarities associated with joint cavitation. J Manipulative Physiol Ther. 1995;18:4–9. MEDLINE 51. 51Gal J, Herzog W, Kawchuk G, Conway PJ, Zhang YT. Movements of vertebrae during manipulative thrusts to unembalmed human cadavers. J Manipulative Physiol Ther. 1997;20:30–40. MEDLINE 52. 52Kawchuk GN, Herzog W. Biomechanical characterization (fingerprinting) of five novel methods of cervical spine manipulation. J Manipulative Physiol Ther. 1993;16:573–577. MEDLINE 53. 53Maigne JY, Guillon F. Highlighting of intervertebral movements and variations of intradiskal pressure during lumbar spine manipulation: a feasibility study. J Manipulative Physiol Ther. 2000;23:531–535. Abstract | Full Text |
Full-Text PDF (104 KB)
|
CrossRef
54. 54White AA, Panjabi MM. Clinical biomechanics of the spine. Philadelphia: JB Lippincott; 1990;. 55. 55Lindh M. Biomechanics of the lumbar spine. In: Nordin M, Frankel VH editor. Basic biomechanics of the musculoskeletal system. London: Lea & Febiger; 1989;p. 183–207. 56. 56Bogduk N, Yoganandan N. Biomechanics of the cervical spine part 3: minor injuries. Clin Biomech (Bristol, Avon). 2001;16:267–275. Abstract | Full Text |
Full-Text PDF (138 KB)
|
CrossRef
57. 57McClure P, Siegler S, Nobilini R. Three-dimensional flexibility characteristics of the human cervical spine in vivo. Spine. 1998;23:216–223. MEDLINE |
CrossRef
58. 58Herzog W, Kats M, Symons B. The effective forces transmitted by high-speed, low-amplitude thoracic manipulation. Spine. 2001;26:2105–2110. MEDLINE |
CrossRef
59. 59Panjabi MM. The stabilizing system of the spine. Part II. Neutral zone and instability hypothesis. J Spinal Disord. 1992;5:390–396. MEDLINE |
CrossRef
60. 60Thompson RE, Barker TM, Pearcy MJ. Defining the neutral zone of sheep intervertebral joints during dynamic motions: an in vitro study. Clin Biomech (Bristol, Avon). 2003;18:89–98. Abstract | Full Text |
Full-Text PDF (258 KB)
|
CrossRef
61. 61Edmondston SJ, Allison GT, Gregg CD, Purden SM, Svansson GR, Watson AE. Effect of position on the posteroanterior stiffness of the lumbar spine. Man Ther. 1998;3:21–26. |
CrossRef
62. 62Panjabi M, Yamamoto I, Oxland T, Crisco J. How does posture affect coupling in the lumbar spine?. Spine. 1989;14:1002–1011. MEDLINE |
CrossRef
63. 63Vicenzino G, Twomey L. Side flexion induced lumbar spine conjuct rotation and its influencing factors. Aust J Physiother. 1993;9:115–123. 64. 64Panjabi MM, Oda T, Crisco JJ, Dvorak J, Grob D. Posture affects motion coupling patterns of the upper cervical spine. J Orthop Res. 1993;11:525–536. MEDLINE |
CrossRef
65. 65Conway PJW, Herzog W, Zhang Y, Hasler EM, Ladly K. Forces required to cause cavitation during spinal manipulation of the thoracic spine. Clin Biomech. 1993;8:210–214. 66. 66Herzog W, Conway PJ, Kawchuk GN, Zhang Y, Hasler EM. Forces exerted during spinal manipulative therapy. Spine. 1993;18:1206–1212. MEDLINE 67. 67Kawchuk GN, Herzog W, Hasler EM. Forces generated during spinal manipulative therapy of the cervical spine: a pilot study. J Manipulative Physiol Ther. 1992;15:275–278. MEDLINE 68. 68Kimberley PE. Formulating a prescription for osteopathic manipulative treatment. J Am Osteopath Assoc. 1980;79:506–513. MEDLINE 69. 69Sandoz R. Some physical mechanisms and effects of spinal adjustments. Ann Swiss Chiropr Assoc. 1976;6:91–141. 70. 70Sandoz R. Some reflex phenomena associated with spinal derangements and adjustments. Ann Swiss Chiropr Assoc. 1981;7:45–65. 71. 71Roston JB, Wheeler-Haines R. Cracking in the metacarpo-phalangeal joint. J Anat. 1947;81:165–173. 72. 72American Chiropractic Association . Spinal manipulation policy statement (updated version). Arlington: American Chiropractic Association; 2003;. 73. 73Haldeman S, Hooper PD. Mobilization, manipulation, massage and exercise for the relief of musculoskeletal pain. In: Wall PD, Melzack R editor. Textbook of pain. Edinburgh: Churchill Livingstone; 1999;p. 1399–1418. 74. 74Herzog W, Zhang YT, Conway PJ, Kawchuk GN. Cavitation sounds during spinal manipulative treatments. J Manipulative Physiol Ther. 1993;16:523–526. MEDLINE 75. 75Myklebust JB, Pintar F, Yoganandan N, Cusick JF, Maiman D, Myers TJ, et al. Tensile strength of spinal ligaments. Spine. 1988;13:526–531. MEDLINE 76. 76Winkelstein BA, Nightingale RW, Richardson WJ, Myers BS. The cervical facet capsule and its role in whiplash injury: a biomechanical investigation. Spine. 2000;25:1238–1246. MEDLINE |
CrossRef
77. 77Yoganandan N, Kumaresan S, Pintar FA. Geometric and mechanical properties of human cervical spine ligaments. J Biomech Eng. 2000;122:623–629. MEDLINE |
CrossRef
78. 78Semlak K, Ferguson AB. Joint stability maintained by atmospheric pressure. An experimental study. Clin Orthop Relat Res. 1970;68:294–300. 79. 79Ianuzzi A, Khalsa PS. Comparison of human lumbar facet joint capsule strains during simulated high-velocity, low-amplitude spinal manipulation versus physiological motions. Spine J. 2005;5:277–290. Abstract | Full Text |
Full-Text PDF (657 KB)
|
CrossRef
80. 80Symons BP, Leonard T, Herzog W. Internal forces sustained by the vertebral artery during spinal manipulative therapy. J Manipulative Physiol Ther. 2002;25:504–510. Abstract |
Full-Text PDF (99 KB)
|
CrossRef
81. 81McCarthy CJ. Spinal manipulative thrust technique using combined movement theory. Man Ther. 2001;6:197–204. |
CrossRef
82. 82Vernon H, Mrozek J. A revised definition of manipulation. J Manipulative Physiol Ther. 2005;28:68–72. Full Text |
Full-Text PDF (274 KB)
|
CrossRef
83. 83Klein GN, Mannion AF, Panjabi MM, Dvorak J. Trapped in the neutral zone: another symptom of whiplash-associated disorder?. Eur Spine J. 2001;10:141–148. MEDLINE |
CrossRef
84. 84Kumar S, Panjabi MM. In vivo axial rotations and neutral zones of the thoracolumbar spine. J Spinal Disord. 1995;8:253–263. MEDLINE |
CrossRef
85. 85Adams MA, Hutton WC. The relevance of torsion to the mechanical derangement of the lumbar spine. Spine. 1981;6:241–248. MEDLINE |
CrossRef
86. 86Onan OA, Heggeness MH, Hipp JA. A motion analysis of the cervical facet joint. Spine. 1998;23:430–439. MEDLINE |
CrossRef
87. 87Cascioli V, Corr P, Till A, Ag G. An investigation into the production of intra-articular gas bubbles and increase in joint space in the zygapophyseal joints of the cervical spine in asymptomatic subjects after spinal manipulation. J Manipulative Physiol Ther. 2003;26:356–364. Abstract | Full Text |
Full-Text PDF (294 KB)
|
CrossRef
88. 88Hukins DW, Kirby MC, Sikoryn TA, Aspden RM, Cox AJ. Comparison of structure, mechanical properties, and functions of lumbar spinal ligaments. Spine. 1990;15:787–795. MEDLINE |
CrossRef
89. 89Nyberg RE. Manipulation: definition, types, application. In: Basmajian JV, Nyberg RE editor. Rational manual therapies. Baltimore: Williams & Wilkins; 1993;p. 21–47. 90. 90Reggars JW, Pollard HP. Analysis of zygapophyseal joint cracking during chiropractic manipulation. J Manipulative Physiol Ther. 1995;18:65–71. MEDLINE 91. 91Keller TS, Colloca CJ, Fuhr AW. In vivo transient vibration assessment of the normal human thoracolumbar spine. J Manipulative Physiol Ther. 2000;23:521–530. Abstract | Full Text |
Full-Text PDF (142 KB)
|
CrossRef
92. 92Solinger AB. The physics of spinal manipulation: a critical review of four articles by Haas. J Manipulative Physiol Ther. 1996;19:141–145. MEDLINE 93. 93Solinger AB. Oscillations of the vertebrae in spinal manipulative therapy. J Manipulative Physiol Ther. 1996;19:238–243. MEDLINE 94. 94Bereznick DE, Ross JK, McGill SM. The frictional properties at the thoracic skin-fascia interface: implications in spine manipulation. Clin Biomech (Bristol, Avon). 2002;17:297–303. Abstract | Full Text |
Full-Text PDF (485 KB)
|
CrossRef
95. 95Pearcy M, Portek I, Shepherd J. The effect of low-back pain on lumbar spinal movements measured by three-dimensional x-ray analysis. Spine. 1985;10:150–153. MEDLINE |
CrossRef
96. 96Amevo B, Aprill C, Bogduk N. Abnormal instantaneous axes of rotation in patients with neck pain. Spine. 1992;17:748–756. MEDLINE 97. 97Lund T, Nydegger T, Schlenzka D, Oxland TR. Three-dimensional motion patterns during active bending in patients with chronic low back pain. Spine. 2002;27:1865–1874.
CrossRef
98. 98Abumi K, Panjabi MM, Kramer KM, Duranceau J, Oxland T, Crisco JJ. Biomechanical evaluation of lumbar spinal stability after graded facetectomies. Spine. 1990;15:1142–1147. MEDLINE |
CrossRef
99. 99Tochigi Y, Amendola A, Rudert MJ, Baer TE, Brown TD, Hillis SL, et al. The role of the interosseous talocalcaneal ligament in subtalar joint stability. Foot Ankle Int. 2004;25:588–596. MEDLINE 100. 100Fryer GA, Mudge JM, McLaughlin PA. The effect of talocrural joint manipulation on range of motion at the ankle. J Manipulative Physiol Ther. 2002;25:384–390. Abstract | Full Text |
Full-Text PDF (215 KB)
|
CrossRef
101. 101Brodeur R. The audible release associated with joint manipulation. J Manipulative Physiol Ther. 1995;18:155–164. MEDLINE 102. 102Buerger AA. Experimental neuromuscular models of spinal manual techniques. Man Med. 1983;1:17. 103. 103Gillette RG. Potential antinociceptive effects of high-level somatic stimulation—chiropractic manipulation therapy may coactivate both tonic and phasic analgesic systems. Some recent neurophysiological evidence. In: Coyle BA, Konsler GR, Adams AH editor. Proceedings of the Pacific Consortium for Chiropractic Research: a series of communications. First Annual Conference on Research and Education. 1986 Jun 28-29. Belmont (Ca): Pacific Consortium for Chiropractic Research; 1986;p. 1–9. 104. 104Gillette RG. A speculative argument for the coactivation of diverse somatic receptor populations by forceful chiropractic adjustments. A review of the neurophysiological literature. Man Med. 1987;3:1–14. MEDLINE 105. 105Katavich L. Differential effects of spinal manipulative therapy on acute and chronic muscle spasm: a proposal for mechanisms and efficacy. Man Ther. 1998;3:132–139. |
CrossRef
106. 106Korr IM. Proprioceptors and somatic dysfunction. J Am Osteopath Assoc. 1975;74:638–650. MEDLINE 107. 107Pickar JG. Neurophysiological effects of spinal manipulation. Spine J. 2002;2:357–371. Abstract | Full Text |
Full-Text PDF (298 KB)
|
CrossRef
108. 108Wyke BD. The neurology of the cervical spinal joints. Physiotherapy. 1979;65:72–76. MEDLINE 109. 109Wyke BD. Receptor systems in lumbosacral tissues in relation to the production of low back pain. In: White AA, Gordon SL editor. Idiopathic low back pain. London: Mosby Co; 1982;p. 97–107. 110. 110Wyke BD. Articular neurology and manipulative therapy. In: Glasgow EF, Twomey LT, Scull ER, Kleynhans AM, Idczak RM editor. Aspects of manipulative therapy. Edinburgh: Churchill Livingstone; 1985;p. 72–77. 111. 111Zusman M. Spinal manipulative therapy; review of some proposed mechanisms and a new hypothesis. Aus J Physiother. 1986;32:89–99. a Researcher, School of Health and Rehabilitation, Keele University, Staffordshire, UK; Associate Researcher, Research Centre, British School of Osteopathy, London, UK b Director, Institute for Musculoskeletal Research and Clinical Implementation, AECC, Bournemouth, UK  Submit requests for reprints to: David W. Evans, School of Health and Rehabilitation, MacKay Building, Keele University, Staffordshire, ST5 5BG, UK.
Sources of support: No external funds were provided for this research. PII: S0161-4754(05)00353-2 doi:10.1016/j.jmpt.2005.11.011 © 2006 National University of Health Sciences. Published by Elsevier Inc. All rights reserved. | |
|
FULL TEXT00353-2/journalimage?img=PIIS0161475405003532.gr1.lrg.gif&fig=fig1&kwhquery=&issn=0161-4754&ishighres=false&allhighres=false&free=yes','journalimage');)
00353-2/journalimage?img=PIIS0161475405003532.gr2.lrg.gif&fig=fig2&kwhquery=&issn=0161-4754&ishighres=false&allhighres=false&free=yes','journalimage');)
00353-2/journalimage?img=PIIS0161475405003532.gr3.lrg.gif&fig=fig3&kwhquery=&issn=0161-4754&ishighres=false&allhighres=false&free=yes','journalimage');)
00353-2/journalimage?img=PIIS0161475405003532.gr4.lrg.gif&fig=fig4&kwhquery=&issn=0161-4754&ishighres=false&allhighres=false&free=yes','journalimage');)
00353-2/journalimage?img=PIIS0161475405003532.gr5.lrg.gif&fig=fig5&kwhquery=&issn=0161-4754&ishighres=false&allhighres=false&free=yes','journalimage');)