A Biomechanical Model for Mechanically Efficient Cavitation Production During Spinal Manipulation: Prethrust Position and the Neutral Zone

Spinal manipulative therapy (SMT) is the generic term commonly given to a group of manually applied therapeutic interventions.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: 46-51Abstract Full Text PDF PubMed Scopus (65) Google Scholar These are usually applied with the aim of inducing intervertebral movement by directing forces to vertebrae.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: 2459-2466Crossref PubMed Scopus (70) Google Scholar, 3Herzog W Symons B The biomechanics of spinal manipulation.Crit Rev Phys Rehabil Med. 2001; 13: 191-216Crossref Google Scholar There are various theories for mechanisms to how SMT translates into clinical effects, in particular, for the treatment of spinal pain,4Evans DW Mechanisms and effects of spinal high-velocity, low-amplitude thrust manipulation: previous theories.J Manipulative Physiol Ther. 2002; 25: 251-262Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar, 5Hearn A Rivett DA Cervical SNAGs: a biomechanical analysis.Man Ther. 2002; 7: 71-79Abstract Full Text PDF PubMed Scopus (23) Google Scholar, 6Shekelle PG Spinal manipulation.Spine. 1994; 19: 858-861Crossref PubMed Scopus (83) Google Scholar, 7Wright A Hypoalgesia post-manipulative therapy: a review of a potential neurophysiological mechanism.Man Ther. 2000; 1: 11-16Abstract Full Text PDF Scopus (192) Google Scholar, 8Zusman M What does manipulation do? The need for basic research.in: Boyling JD Pastalanga N Grieve's modern manual therapy. Churchill Livingstone, Edinburgh1994: 651-659Google Scholar 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.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: 871-881Crossref PubMed Scopus (337) Google Scholar, 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: 1746-1759Crossref PubMed Scopus (403) Google Scholar, 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: 2860-2871Crossref PubMed Scopus (243) Google Scholar, 12Shekelle PG Adams AH Chassin MR Hurwitz EL Brook RH Spinal manipulation for low-back pain.Ann Intern Med. 1992; 117: 590-598Crossref PubMed Scopus (357) Google Scholar, 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: 2128-2156Crossref PubMed Scopus (797) Google Scholar 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.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: 1091-1096PubMed Google Scholar, 15Lee M Gál JM Herzog W Biomechanics of manual therapy.in: Dvir Z Clinical biomechanics. Churchill Livingstone, Philadelphia2000: 209-238Google Scholar, 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: 1717-1724PubMed Google Scholar, 17Solinger AB Theory of small vertebral motions: an analytical model compared to data.Clin Biomech (Bristol, Avon). 2000; 15: 87-94Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar 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 phase3Herzog W Symons B The biomechanics of spinal manipulation.Crit Rev Phys Rehabil Med. 2001; 13: 191-216Crossref Google Scholar (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.18Herzog W Kawchuk GN Conway PJW Relationship between preload and peak forces during spinal manipulative treatments.J Neuromusculoskelet Syst. 1993; 1: 52-58Google Scholar, 19Van Zoest GG Gosselin G Three-dimensionality of direct contact forces in chiropractic spinal manipulative therapy.J Manipulative Physiol Ther. 2003; 26: 549-556Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar 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 studies20Klein 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: 827-831Abstract Full Text Full Text PDF PubMed Scopus (33) Google Scholar, 21Triano JJ Schultz AB Motions of the head and thorax during neck manipulations.J Manipulative Physiol Ther. 1994; 17: 573-583PubMed Google Scholar (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.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: 2459-2466Crossref PubMed Scopus (70) Google Scholar 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,15Lee M Gál JM Herzog W Biomechanics of manual therapy.in: Dvir Z Clinical biomechanics. Churchill Livingstone, Philadelphia2000: 209-238Google Scholar, 19Van Zoest GG Gosselin G Three-dimensionality of direct contact forces in chiropractic spinal manipulative therapy.J Manipulative Physiol Ther. 2003; 26: 549-556Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar, 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: 827-831Abstract Full Text Full Text PDF PubMed Scopus (33) Google Scholar, 22Denslow J Pathophysiologic evidence for the osteopathic lesion: the known, unknown, and controversial.in: Beal M The principles of palpatory diagnosis and manipulative technique. American Academy of Osteopathy, Newark (Ohio)1989: 134-138Google Scholar, 23Gibbons P Tehan P Manipulation of the spine, thorax and pelvis. An osteopathic perspective. Churchill Livingstone, Edinburgh2000Google Scholar, 24Gibbons P Tehan P Patient positioning and spinal locking for lumbar spine rotation manipulation.Man Ther. 2001; 6: 130-138Abstract Full Text PDF PubMed Scopus (20) Google Scholar, 25Herzog W The mechanical, neuromuscular, and physiologic effects produced by spinal manipulation.in: Herzog W Clinical biomechanics of spinal manipulation. Churchill Livingstone, New York2000: 191-207Google Scholar, 26Livingstone WK Pain mechanisms. Macmillan Co, New York1947Google Scholar, 27Maigne JY Vautravers P Mechanism of action of spinal manipulative therapy.Joint Bone Spine. 2003; 70: 336-341Crossref PubMed Scopus (83) Google Scholar, 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: 135-140Google Scholar, 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: 80-85PubMed Google Scholar, 30Sandoz R The significance of the manipulative crack and of other articular noises.Ann Swiss Chiro Assoc. 1969; 4: 47-68Google Scholar, 31Ross JK Bereznick DE McGill SM Determining cavitation location during lumbar and thoracic spinal manipulation: is spinal manipulation accurate and specific?.Spine. 2004; 29: 1452-1457Crossref PubMed Scopus (110) Google Scholar, 32Vernon H Qualitative review of studies of manipulation-induced hypoalgesia.J Manipulative Physiol Ther. 2000; 23: 134-138Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar although this has yet to be directly linked to clinical effects.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: 1057-1060Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar This cracking sound is caused by an event termed cavitation, occurring within the synovial fluid (SF) of the joint.34Unsworth A Dowson D Wright V "Cracking joints". A bioengineering study of cavitation in the metacarpophalangeal joint.Ann Rheum Dis. 1971; 30: 348-358Crossref PubMed Scopus (130) Google Scholar 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.34Unsworth A Dowson D Wright V "Cracking joints". A bioengineering study of cavitation in the metacarpophalangeal joint.Ann Rheum Dis. 1971; 30: 348-358Crossref PubMed Scopus (130) Google Scholar, 35Young FR Cavitation. Imperial College Press, London1999Crossref Google Scholar, 36Trevena DH Cavitation and tension in liquids. Adam Hilger, Bristol1987Google Scholar 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.34Unsworth A Dowson D Wright V "Cracking joints". A bioengineering study of cavitation in the metacarpophalangeal joint.Ann Rheum Dis. 1971; 30: 348-358Crossref PubMed Scopus (130) Google Scholar, 37Watson P Kernohan WG Mollan RAB A study of the cracking sounds from the metacarpophalangeal joint.Proc Inst Mech Eng (H). 1989; 203: 109-118Crossref PubMed Scopus (22) Google Scholar, 38Chen YL Kuhl T Israelachvili J Mechanism of cavitation damage in thin liquid films: collapse damage vs. inception damage.Wear. 1992; 153: 51Google Scholar Cavitation can occur during both high- and low-velocity joint motion.39Meal GM Scott RA Analysis of the joint crack by simultaneous recording of sound and tension.J Manipulative Physiol Ther. 1986; 9: 189-195PubMed Google Scholar, 40Suter E Herzog W Conway PJ Zhang YT Reflex response associated with manipulative treatment of the thoracic spine.J Neuromusculoskelet Syst. 1994; 2: 124-130Google Scholar 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.15Lee M Gál JM Herzog W Biomechanics of manual therapy.in: Dvir Z Clinical biomechanics. Churchill Livingstone, Philadelphia2000: 209-238Google Scholar It is generally performed at less than 2 Hz15Lee M Gál JM Herzog W Biomechanics of manual therapy.in: Dvir Z Clinical biomechanics. Churchill Livingstone, Philadelphia2000: 209-238Google Scholar; causes very little, if any, intervertebral motion41McGregor 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: 926-929Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar, 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: 80-83Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar; 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.15Lee M Gál JM Herzog W Biomechanics of manual therapy.in: Dvir Z Clinical biomechanics. Churchill Livingstone, Philadelphia2000: 209-238Google Scholar 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). 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."6Shekelle PG Spinal manipulation.Spine. 1994; 19: 858-861Crossref PubMed Scopus (83) Google Scholar A recent critical review of these 4 main theories4Evans DW Mechanisms and effects of spinal high-velocity, low-amplitude thrust manipulation: previous theories.J Manipulative Physiol Ther. 2002; 25: 251-262Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar 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.4Evans DW Mechanisms and effects of spinal high-velocity, low-amplitude thrust manipulation: previous theories.J Manipulative Physiol Ther. 2002; 25: 251-262Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar There is also evidence that zygapophyseal joint cavitation, the distinguishing characteristic of spinal manipulation, appears to be associated with certain physiological outcomes.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: 399-408PubMed Google Scholar, 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: 83-89PubMed Google Scholar 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,3Herzog W Symons B The biomechanics of spinal manipulation.Crit Rev Phys Rehabil Med. 2001; 13: 191-216Crossref Google Scholar, 15Lee M Gál JM Herzog W Biomechanics of manual therapy.in: Dvir Z Clinical biomechanics. Churchill Livingstone, Philadelphia2000: 209-238Google Scholar, 25Herzog W The mechanical, neuromuscular, and physiologic effects produced by spinal manipulation.in: Herzog W Clinical biomechanics of spinal manipulation. Churchill Livingstone, New York2000: 191-207Google Scholar, 45Triano JJ The mechanics of spinal manipulation.in: Herzog W Clinical biomechanics of spinal manipulation. Churchill Livingstone, New York2000: 191-207Google Scholar, 46Triano JJ Biomechanics of spinal manipulative therapy.Spine J. 2001; 1: 121-130Abstract Full Text Full Text PDF PubMed Scopus (99) Google Scholar most have not focused upon factors that facilitate cavitation. This article aims to explore some of these factors. Kinematics is the branch of mechanics that deals with motion (of an object) without reference to force or mass. With a few notable exceptions,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: 2459-2466Crossref PubMed Scopus (70) Google Scholar, 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: 827-831Abstract Full Text Full Text PDF PubMed Scopus (33) Google Scholar, 21Triano JJ Schultz AB Motions of the head and thorax during neck manipulations.J Manipulative Physiol Ther. 1994; 17: 573-583PubMed Google Scholar, 47Cramer GD Skogsbergh D Tuck NR Floyd J Allen S Fonda S et al.The effects of spinal manipulative therapy on the L5 intervertebral foramina as evaluated by magnetic resonance imaging. 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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 biomechanical factors that an important role in cavitation production. kinematics are largely by the of the and the the that spinal manipulation, the a force to the spine, to a target of the in and to the same and a to the target relative to The movements to those by the are as physiological the movements that are not produced are as M Gál JM Herzog W Biomechanics of manual therapy.in: Dvir Z Clinical biomechanics. Churchill Livingstone, Philadelphia2000: 209-238Google Scholar In any diarthrodial synovial the zygapophyseal will produce different types of articular surface motion on the line of action of the applied force relative to the of that joint. These are motion of one surface (the of articular surfaces in a perpendicular to the and (the of the 2 articular surfaces one to create equal and movement can be further described in of the movement into of and In the spine, reference is usually to the motion of an with one of than to motion occurring at zygapophyseal Therefore, in of spinal manipulation, the movement can be viewed as motion of an target that in the same or rotation about an perpendicular the line of action of the applied force delivered by the movements that occur with the movement but in other than that of the applied force are as of motion may be as the association of rotation along or about an with or rotation along or about a of a Clinical biomechanics of the spine. Scholar have 6 of rotation about and along and Fig 2 the 6 movement in 3 the of the and and in 3 about to these 3 Hence, in to a are 5 movement (Fig The motion produced during and rotation between vertebrae is a motion from simultaneous rotation and M Biomechanics of the lumbar M biomechanics of the Scholar An applied force such as that delivered during spinal manipulation has the potential to produce various of physiological and vertebral movements are likely to result in vertebral motion that from that which during physiological M Gál JM Herzog W Biomechanics of manual therapy.in: Dvir Z Clinical biomechanics. Churchill Livingstone, Philadelphia2000: 209-238Google Scholar, 24Gibbons P Tehan P Patient positioning and spinal locking for lumbar spine rotation manipulation.Man Ther. 2001; 6: 130-138Abstract Full Text PDF PubMed Scopus (20) Google Scholar This is because physiological can be during the of an N N Biomechanics of the cervical spine 3: Biomech (Bristol, Avon). 2001; 16: Full Text Full Text PDF PubMed Scopus Google Scholar, P S R characteristics of the human cervical spine in 1998; 23: PubMed Scopus Google Scholar As such, zygapophyseal articular surface occurring as a result of an applied force, may also from that which during is the branch of mechanics that deals with motion (of an object) under the action of given This includes static in which movement is occurring and dynamic in which forces may as movement Most previous biomechanical of spinal manipulation have been with the forces and upon the that form the target joint. It is not how the data for spinal manipulation in Fig are of the forces that at the target vertebra. of the target will be by the of the intervertebral joints and the by the studies that a of the to the patient is likely to be used on the of both and restraining 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: 926-929Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar, 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: 80-83Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar, W M Symons B The forces by low-amplitude thoracic manipulation.Spine. 2001; 26: PubMed Scopus Google Scholar As such, it may be to the production of cavitation in of the mechanical of manipulation The bodies of 2 vertebrae with their and their the intervertebral and the zygapophyseal form throughout the spine. of these is as a spinal An is as the of the spine to biomechanical characteristics to those of the Clinical biomechanics of the spine. Scholar The of a is in Fig Within the range of passive motion of any the curve of 2 or that very different biomechanical In the of the resting neutral position of the this is This is the as the neutral The of the spine. and Spinal 1992; PubMed Scopus Google Scholar which may be as the motion of the joint the passive mechanisms or passive physiological movement of the motion in this It is a in which a small causes a relatively large in the lumbar spine, the neutral motion is the range of motion of an is largely by the zygapophyseal MJ the neutral of intervertebral joints during dynamic motions: an in Biomech (Bristol, Avon). 2003; 18: Full Text Full Text PDF PubMed Scopus Google Scholar As such, the orientation of the zygapophyseal joints at the of a movement will have a effect on motion of the JY Guillon F Highlighting of intervertebral movements and variations of intradiskal pressure during lumbar spine manipulation: a feasibility study.J Manipulative Physiol Ther.

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