Neck Ligament Disruption as
revealed by Digital Motion X-ray
John W. Baird, D.C.
Presented to the Inter-Urban Pain Association Conference,
Grand River Hospital, October 21, 2005, Waterloo, Ontario
Introduction:
Soft tissue injuries of the cervical spine pose a significant health challenge. Often elusive
to detection by static imaging methods, this type of injury is associated with high
morbidity and poor clinical outcomes. Patients often report intractable moderate to severe
pain and disability. Traditional plain film investigations often fail to identify ligamentous
injury. Stress study radiography will prove helpful in many but not all cases. CT and MRI
are often negative. Injuries arising from motor vehicle accidents often prove challenging,
particularly when the injured person carries the legal burden of proof and traditional
diagnostic investigation fails to identify the cause of the individual's impairment. Timely
access to rehabilitation is often affected by insurer denials. Undetected ligamentous
injury may pose a significant risk to force based interventions such as chiropractic
adjustment, manipulation, mobilization, stretching and long axis traction.
Anatomy:
Ligaments stabilize the cervical spine. The function of the cervical ligaments is to act as a
passive stabilizer, limiting the motion of the spine at the end ranges. Ligaments cannot
initiate movement. The fibers of ligaments align with the direction of the load. They have
elastic properties but serve mostly to hold a tensile load. Normal loading of ligaments
occurs up to the plastic limit of collagen and elastin. Ligaments demonstrate piezoelectric
properties and hysteresis. (1) Ligaments tend to follow Wolff's and Davis' Laws. (2)
Davis' Law states that soft tissue remodels to stress. This adaptation will always occur
and will be responsive to changes in stress. The mechanical behaviour of ligaments
depends not only on the material properties of the fibers themselves, but also on the
geometrical arrangement of collagen fibrils and fiber bundles, the proportioning of
different types of fibrous constituents. (3)
Unloading causes a shortening of the ligaments due to elastic contraction. Loading causes
stress relaxation and creep. Relaxation proceeds more rapidly than creep in a ligament.
(4) Mathematical models have been developed to explain how relaxation and creep
interrelate in a non-linear way. (5) Piezoelectric effects are reversible such that a
decreasing change in loading results in changes in creep. Once the added force is
removed, there is an initial elastic recovery; however, there is large hysteresis (energy
loss) in which some of the deformation remains permanent or plastic. (6) Some
permanent shortening can occur in unloaded ligaments known as negative “creep” and
contracture. Excessive loading can cause failure of the elastic elements known as plastic
deformity. There is a common misconception that chronically strained tissue atrophies.
The concept of shrinkage is totally false. Ligaments, including elastic ones, will respond
to increased stress by growing to withstand the increased strain. (7)
Non-surgical gains in marginal ligamentous instability is most attributable to negative
creep resulting from redistribution of postural loads in spinal modeling.
In more serious cases of ligamentous laxity, prolotherapy (8, 9, 10) may assist in
restoring stability and reducing pain. In cases of instability, surgical stabilization may be
necessary to protect neurological integrity.
Injury:
Ligamentous injuries typically result from tensile overload with varying degrees of
disruption. Mechanoreceptive innervation has been found in the cervical facet joints,
ligaments and intervertebral discs. (11, 12, 13, 14) Ligaments contain significant
innervation. The innervation of the ligamentous structures in the cervical spine includes
receptors that respond to slow tonic input, which is important in postural control, rather
than ballistic movement. (15)
Ligaments are injured by sudden loads. Ligament injury may lead to instability patterns
specific for the segmental location of the particular ligament and may be associated with
neurological impairment. Instability must be considered in anyone with neurological
symptoms, especially if the symptoms are persistent. (16) Rupture of stabilizing soft
tissues in the cervical spine results in biomechanical instability and a consequent positive
feedback loop or vicious circle of pain. Afferent noxious stimuli from injured paraspinal
tissues are transmitted via the recurrent meningeal nerve. (17, 18)
Videofluoroscopy is important in the evaluation of ligamentous instability. (19) In a
report from a group of 32, 117 patients with cervical spine trauma in San Diego, the
diagnoses were delayed or missed in 4.6%. Ten patients developed permanent sequelae as
a result. The single most common error identified in this group was failure to obtain an
adequate cervical spine series. (20)
Coupling patterns occur in all ranges of motion of the cervical spine and have been well
documented and described. (21, 22, 23, 24) Two or more individual motions are said to
be coupled (e.g. lateral bending and axial rotation or anterior translation with flexion)
when one motion is always accompanied by another motion. The motion being produced
by an external load is termed the main motion and all the accompanying motions are
called coupled motions. (25) Paradoxical motion occurs when normal coupling is not
observed. Since coupling patterns are the result of the structural relationships of vertebrae
in motion, paradoxical motion must be associated with abnormal coupling and therefore
abnormal structural relationships. Some authors suggest that paradoxical motion is
simply a normal variant with no clinical significance. (26)
While there remains some debate as to whether paradoxical motion is pathognomic,
identification is more straightforward. Videofluoroscopy provides visualization of normal
coupling patterns as well as paradoxical motion. Evidence of paradoxical motion along
with forensic determination of abnormal geometry is a consequence of traumatically
induced structural compromise.
DMX Digital/Dynamic Motion X-ray:
DMX is a form of videofluoroscopy adapted to the assessment of spinal injury. The
fluoroscopy output and external camera output are sent to a picture in picture mixer to
assist in patient recognition. The video stream is captured to DVD Video.
The DMX Digital / Dynamic Motion X-ray Cervical protocol consists of:
1. Lateral nodding, involving lateral observation of cervical motion when the centre of
mass of the head is rotated posteriorly by raising the chin.
2. Flexion and Extension involving lateral observation of the full range of cervical
motion in the sagittal plane. Freeze frame capture of representative neutral, flexion
and extension were obtained and digitized using DX Analyzer software with digital
zoom capabilities.
3. Left Posterior Oblique Flexion and Extension permits observation of the right
intervertebral foramina through flexion and extension. This examination is not
performed with plain film and provides a unique opportunity to appreciate the
patency of the foramina as well as the integrity of the capsular ligaments.
4. Right Posterior Oblique Flexion and Extension permits observation of the left
intervertebral foramina through flexion and extension. Comparison of oblique studies
may be helpful in cases of unilateral radicular complaints.
5. Anterior/Posterior Lateral Flexion permits observation of symmetry in cervical
motion as well as coupled spinous rotation, which is normally expected.
6. Anterior/Posterior Rotation permits observation of symmetry in cervical rotation in
the upper cervical spine and may reveal abnormalities associated with capsular
ligament injury.
7. Anterior/Posterior Open Mouth Lateral Flexion permits observation of alar and
accessory ligament function.
The DVD is finalized to create an original artifact. Video frames are captured in the
Flexion and Extension protocol as well as the Open Mouth Lateral Flexion protocol and
forensically evaluated for geometry using digital radiographic analysis.
Digital radiographic analysis combines the power of a digital microscope with powerful
Grey scale and composite filters. Abnormal geometry is identified and reported with
accuracy far exceeding manual methods. (27, 28, 29) Digital Radiographic Analysis is a
reliable and valid means of evaluating vertebral displacement on radiographic images.
(30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
A common nomenclature used to describe the mechanism of injury refers to the principle
of applied loading of the motion segments, i.e. the Major Injuring Vector (MIV), and not
the observed motions of the head, or the loads on the head required to produce the
resultant head motions. (41)
The Major Injuring Vector is described using the Cartesian coordinate system. The x, y
and z-axes follow the right hand rule when referring to the standard anatomical position,
The left shoulder is +x. The right shoulder is -x. Upward is +y. Forward is +z. (42)
The report of findings of the DMX cervical protocol may be stated in terms of known
abnormal geometry as well as Cartesian Coordinates and vectors. Due to the anatomical
orientation of ligaments, identification of ligament disruption provides identification of
the Major Injuring Vector. A forensic analysis of the DMX cervical protocol will
establish the Major Injuring Vector. Using Cartesian coordinates in relation to anatomical
position, the Major Injuring Vector can be described in terms of the x, y and z axes.
There is a direct correlation between a known Major Injuring Vector, resulting soft tissue
damage and the forces at impact.
More commonly, accident descriptions such as “rear-end collision” “head-on collision”
or “t-bone impact” are used among people discussing accidents causing personal injury.
(43)
Rehabilitation:
Rehabilitation of ligamentous injury must always be aimed at unloading injured
ligaments while creating plastic deformity by normalizing the global mechanically loaded
configuration of the injured spine. The ideal cervical spine configuration has been
validated. (44) Loss of lordosis is associated with chronic pain. (45) A vast amount of the
literature indicates that loss of cervical lordosis and kyphosis are risk factors for neck
pain, shoulder and upper back pain, headaches and a variety of neurological conditions.
(56, 47, 48, 49, 50)
Anatomical architectural variants of the facets and dens have no relationship to the
cervical lordosis. Surgical and rehabilitative methods that attempt restoration of the
cervical lordosis do not need to consider cervical articular pillar angle, height, nor C2
odontoid architecture. (51)
Isometric strengthening of the primary muscle groups assists in unloading injured
ligaments. A combination of loading of contracted ligaments and unloading of injured
ligaments in rehabilitation along with isometric strengthening of core musculature may
result in recovery of spinal stability in marginal cases. The most efficient means of
strengthening the core musculature is Mirror Image® exercises. (52)
Extension compression traction is essential for restoration of lordosis. (53, 54, 55) By
causing plastic deformity of buckled tissues, extension compression traction can reverse
kyphosis at a traumatically compromised motion segment. Structurally compromised
ligaments show marginal response to unloading. When lordosis is restored, posterior
ligaments may experience negative creep and return to stable pre-accident coupling
patterns.
When disruption of a ligament compromises innervation, loading injured and unstable
ligaments results in further trauma. Consideration of surgical intervention is imperative to
protect the nervous system from insult.
Case Studies:
Case 1:
43 year-old male patient was rear-ended while stopped in traffic. He was involved in a
second accident just 1 month later. In the second accident, he was riding as a front seat
passenger, with his wife driving and his daughter in the back. The car was rear-ended.
A s42 Occupational Therapy In-Home Assessment Report provided a Treatment
Recommendation that he receive “One to two follow-up visits recommended teaching the
patient the difference between hurt and harm”.
A s42 Assessment of Attendant Care Needs gave a total allowance of $1.62 for monthly
trimming of patient's toenails.
An assessment 1 month later with stress study radiographs found Loss of Motion
Segment Integrity at C4 in translation (4.3mm) and C5 in translation (3.5mm) indicating
a 25% impairment per the AMA Guides, 4th Edition.
A DMX assessment 15 months after the stress study found Loss of Motion Segment
Integrity at C3 in translation (4.35mm) indicating a 25% permanent impairment per
AMA Guides, 4th Edition.
Case 2:
A 29 year-old female patient was a passenger in a taxi van struck on the passenger door
making a left turn.
Hospital x-rays were negative.
An assessment 6 months later with stress study radiographs found Loss of Motion
Segment Integrity at C2 in translation (6.2mm) and angular (12.6) and C3 in translation
(4.2mm) indicating a 25% impairment per AMA Guides, 4th Edition.
A DMX assessment 15 months after stress study found Loss of Motion Segment Integrity
at C2 angular (23.65) and C3 in translation (3.97mm) indicating a 25% permanent
impairment per AMA Guides, 4th Edition.
Case 3:
A 38 year-old female patient was driving with left leg up on the dashboard and had a
front-end impact.
She developed a 4Hz post-accident tremor of the head. The tremor caused a vestibular
disturbance preventing her from walking any distance without assistance.
X-ray and initial MRI were not diagnostic due to motion artifacts.
A second MRI performed under sedation revealed compression of the anterior superior
endplate of C6.
DMX revealed Loss of Motion Segment Integrity at C2 in translation (4.20mm) and at
C4 in translation (3.71mm) and anterior buckling of C2 indicating a 25% permanent
impairment per AMA Guides, 4th Edition.
Paradoxical motion of the C6 spinous is observed in flexion and extension indicating
subfailure of the interspinous and capsular ligaments.
Case 4:
52 year-old male patient lost control of his car and rolled several times into a ditch.
Hospital x-rays and a CT scan were both negative for fracture.
An assessment 1year later found Loss of Motion Segment Integrity at C4 in translation
(3.8mm) indicating a 25% impairment per the AMA Guides, 4th Edition.
A DMX assessment 15 months after stress study found Integrity at C4 in translation
(3.66mm), C4 angular (14.30) and C5 angular (18.02) indicating a 25% permanent
impairment per the AMA Guides, 4th Edition.
An avulsion fracture of the C4 facet is visualized on the flexion and extension protocol.
Case 5:
A 72 year-old female patient was sitting in the driver's seat of her car when it was struck
by another car on the passenger side. Her car was a write-off. She was involved in a
second accident, where she swerved to avoid one car and hit another car with impact at
right front of her car.
Hospital x-rays and a CT scan were both negative for fracture.
3 separate Med-Rehab DAC Assessors found no significant neck injury.
An assessment 2 years post accident found Loss of Motion Segment Integrity at C2
angular (19.4) and C3 in translation (3.6mm) indicating a 25% impairment per the AMA
Guides, 4th Edition.
A DMX Assessment 15 months after the stress study found Loss of Motion Segment
Integrity at C3 in translation (4.35mm) indicating a 25% permanent impairment per
AMA Guides, 4th Edition.
The DMX also demonstrates an Unstable Type 2 fracture of the odontoid process
which, required surgical stabilization
Conclusion:
Ligaments are responsible for stabilization of the spine. Ligamentous disruption is
associated with chronic pain and impairment. Instability should be ruled out to protect
neurological integrity. Rehabilitation protocols should be aimed at optimizing the spinal
configuration as well as strengthening core musculature. Loading of injured ligaments
should be avoided to prevent further trauma. Restoration of cervical lordosis may result
in restoration of spinal stability in marginal cases of ligamentous injury.
Videofluoroscopy may explain poor clinical outcomes in cases with insufficient
evidence. Videofluoroscopy with digital radiographic analysis should be considered in
cases where clinical findings do not adequately explain the patient's complaints.
References:
1.
2.
3.
4.
5.
6.
7.
8.
Panjabi MM, White AA. Clinical Biomechanics of the Spine. Philadelphia JB
Lippincott, 2nd ed..1990
Cochran G, A Primer of Orthopedics Biomechanics. Curchill Livingstone, 1982
Noyes F, Torvik P, Hyde W, DeLucas J, Biomechanics of Ligament Failure.
Journal of Bone and Joint Surgery, 1974.
Thornton, G. M., Oliynyk, A., Frank, C. B., and Shrive, N. G., 1997, "Ligament
creep cannot be predicted from stress relaxation at low stress: a biomechanical
study of the rabbit medial collateral ligament", J. Orthop. Research., Vol. 15, pp.
652-656.
Lakes RS, Vanderby R, Interrelation of creep and relaxation: a modeling pproach
for ligaments. J Biomech. Engineering, 121, 612-615, Dec. (1999).
Harrison DE, Caillet R, Harrison DD, Troyanovich SJ, Harrison SO, A Review of
Biomechanics of the Central Nervous System -Part II: Spinal Cord Strains from
Postural Loads. JMPT 1999, 22(5):322
Harrison DD, Spinal Biomechanics: A Chiropractic Perspective. 1992.
Linetsky FS, Miguel R, Torres F. Treatment of cervicothoracic pain and
cervicogenic headaches with regenerative injection therapy. Curr Pain Headache
Rep. 2004 Feb;8(1):41-8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
Dagenais S, Haldeman S, Wooley JR. Intraligamentous injection of sclerosing
solutions (prolotherapy) for spinal pain: a critical review of the literature. Spine J.
2005 May-Jun;5(3):310-28.
Hooper RA, Ding M. Retrospective case series on patients with chronic spinal
pain treated with dextrose prolotherapy. J Altern Complement Med. 2004
Aug;10(4):670-4.
McLain RF. Mechanoreceptor Endings in Human Cervical Facet Joints. Spine, 1
994; 19(5): 495-501.
Jiang H, Russell G, Raso J, Moreau MJ, Hill DI, Bagnall KM. The Nature and
Distribution of the Innervation of Human Supraspinal and Interspinal Ligaments.
Spine, 1995; 20(8):869-876.
Roberts S, Eisenstein SM, Menage J, Evans EH, Ashton IK. Mechanoreceptors in
Intervertebral Discs, Morphology, Distribution, and Neuropeptides. Spine, 1995;
20(24): 2645-2651.
Mendel T, Wink CS, Zimny ML. Neural Elements in Human Cervical
Intervertebral Discs. Spine, 1992; 17(2):132-135.
Jacobs B. Cervical fractures and dislocations. Clin Orthop. 1975;109:18-32.
Prehospital Care of the Spine-Injured Athlete. National Athletic Trainers'
Association Task Force for Appropriate Care of the Spine-Injured Athlete. 1998
Foreman SM, Croft AC, Whiplash Injuries: The Cervical
Acceleration/Deceleration Syndrome. 2nd ed. Williams & Wilkins. 1995. 312
Cloward RB, J Neurol Neurosurg Psychiatry 23:321, 1960.
Foreman SM, Croft Ac, Whiplash Injuries: The cervical
Acceleration/Deceleration Syndrome, 3rd Ed. Lippincott Williams & Wilkins
2001.
Davis JW, Phreaner DL, Hoyt DB, etal: The etiology of the missed cervical spine
injuries. Journal of Trauma 34(3):342-246, 1993.
Penning L. Functional Pathology of the cervical Spine. Excerpta Medica
Foundation. Amsterdam 1962 pp16, 18, 27.
Penning L. Acceleration Injury of the Cervical Spine by Hypertranslation of the
Head: Part I. Effect of normal translation of the head on cervical spine motion: a
radiological study. Euro Spine J 1992; 1:7-12
Penning L. Normal Movements of the Cervical Spine. AM J Roentgenol 1978;
130:317-326.
Harrison De, Harrison DD, Haas JW. CBP Structural Rehabilitation of the
Cervical Spine. Harrison CBP Seminars.2002 pp15, 23-33.
Panjabi MM, White AA. Clinical Biomechanics of the Spine. Philadelphia JB
Lippincott, 2nd ed..1990
Corbett R, Is Paradoxical Motion Normal at the Occipito-Atlanto Joint (C0/C1)
On Flexion? Canadian Society of Chiropractic Evaulators- The Evaluator, 7(2)
2004 p3-7
Suh C: Minimum Error Point Search for Spinal X-ray Analysis. Chiropractic
Research Journal. 1 (1) 1988.
Panjabi M, Chang D, Dvorák J: An Analysis of Errors in kinematic Parameters
Associated with in Vivo Functional Radiographs. SPINE, 17(2), 1992.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
Shea K, Nelson M, et al: A comparison of manual versus computer assisted
radiographic measurement-intraobserver measurement variability for Cobb's
Angles. SPINE 1998:5:531-55.
Harrison D E, Cailliet R, Harrison D D, Janik T, Troyanovich S, Coleman R:
Lumbar coupling during lateral translations of the thoracic cage relative to a fixed
pelvis. CLINICAL BIOMECHANICS, 14(1999) 704-709.
Harrison D E, Harrison D D, Cailliet R, Janik T, Troyanovich S: Cervical
coupling during lateral head translations creates an S-configuration. CLINICAL
BIOMECHANICS, 15(2000) 436-440.
Harrison D, Harrison D, Cailliet R, Troyanovich S, Janik T, Holland B: Cobb
Method or Harrison Posterior Tangent Method: Which to Choose for Lateral
Radiographic Analysis. SPINE, 25(16), 2000.
Dvorák J, Panjabi M, Grob D, Novotny J, Antinnes J: Clinical Validation of
Functional Flexion/Extension Radiographs of the Cervical Spine. SPINE, 18(1),
1993.
Nelson D, Peterson E, Tilley B, O'Fallon W M, Chao E, Riggs B L and
Kleerekoper M,: Measurement of Vertebral Area on Spine X-rays in
Osteoporosis: Reliability of Digitizing Techniques. Journal of Bone and Mineral
Research, 5(7), 1990.
Osterhouse M, Tepe R, Kettner N, McVey M, Reliability of the Penning Method
for Cervical Intersegmental Motion Assessment: A Pilot Study; Journal of the
Neuromusculoskeletal System, Vol. 10, No.2, Summer 2002 p53
Rajnics P, Pomero V, Templier A, Lavaste F, Illes T: Computer-Assisted
Assessment of Spinal Sagittal Plain Radiographs. Journal of Spinal Disorders.
Vol. 14,No.2,pp135-142 2001
Troyanovich S, Harrison D, Harrison D, Holland B, Janik J: Further Analysis of
the Reliability of the Posterior Tangent Lateral Lumbar Radiographic
Mensuration Procedure: Concurrent Validity of Computer-Aided X-Ray
Digitization. JMPT, 21 (7), 1998.
Frobin W, Leivseth G, Biggemann M, Brinckmann P: Sagittal Plane segmental
motion of the cervical spine. A new precision measurement protocol and normal
motion data of healthy adults. CLINICAL BIOMECHANICS, 17 (2002) 21-31.
Troyanovich S, Harrison S, Harrison D, Holland B, Janik J. et al: Chiropractic
Biophysics Digitized Radiographic Mensuration Analysis of the Anteroposterior
Lumbopelvic View: A Reliability Study.. JMPT, 22 (5), 1999.
Troyanovich S, Harrison D, Harrison D, Harrison S, Holland B, Janik J. et al:
Chiropractic Biophysics Digitized Radiographic Mensuration Analysis of the
Anteroposterior Cervicothoracic View: A Reliability Study.. JMPT, 23 (7), 2000.
CERVICAL SPINE PROTECTION REPORT Prepared for NOCSAE, Manohar
M. Panjabi, Ph. D. Barry S. Myers, M.D., Ph.D. 30 May, 1995
Panjabi MM, White AA, Brand R. A Note on Defining Body Parts
Configurations. J. Biomechanics 7:385-387, 1974.
Nordhoff LS. Motor Vehicle Collision Injuries: Mechanisms, Diagnosis and
Management. Aspen. 1996.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
Harrison DD, Troyanovich SJ, Holland B. Comparisons of the lordotic cervical
spine curvatures to a theoretical ideal model of the static sagittal cervical spine.
Spine 1996; 19(6):398-405
Harrison DE, Harrison DE, Janik TJ, Caillet R, Ferrentelli JR, Haas JR, Holland
B, Modelling of the sagittal Cervical Spine as a Method to Discriminate Lordosis.
Spine 2004 29(22): 2485-2492
Harrison De, Harrison DD, Haas JW. CBP Structural Rehabilitation of the
Cervical Spine. Harrison CBP Seminars.2002 pp56
Hohl M, Soft-tissue injuries of the neck in automobile accidents. J Bone and Joint
Surgery 1974;56-A:1675-1682
Norris SH, WattI. The prognosis of neck injuries resulting from rear-end vehicle
collisions. J Bone and Joint Surgery 1983;65-B:608-611
Ettlin TM, Kischka U, Reichman S, Radii EW, Heim S, Wengen D, Benson DF.
Cerebral symptoms after whiplash ijury. J Neurol Neurosurg Psych 1992; 55:94348
Lowery G. Three-dimensional screw divergence and sagittal balance: a personal
philosophy relative to cervical biomechanics. Spine: State of the Art Reviews
1996;10:343-356.
Harrison DE, Harrison DD, Haas JW, Janik TJ, Holland B. Do Sagittal Plane
Anatomical Variations (Angulation) of the Cervical Facets and C2 Odontoid
Affect the Geometrical Configuration of the Cervical Lordosis? Clinical Anatomy
(author's proof)2004
Harrison De, Harrison DD, Haas JW. CBP Structural Rehabilitation of the
Cervical Spine. Harrison CBP Seminars.2002 pp100
Harrison DD, Jackson BL, Troyanovich SJ, Robertson GA, DeGeorge D, Barker
WF. The Efficacy of Cervical Extension-Compression Traction Combined with
Diversified Manipulation and drop Table Adjustments in the Rehabilitation of
Cervical Lordosis. J Manipulative Physiol Ther 1994;17(7):454-464.
Harison DE, Caillet R, Harrison DD, jaik TJ, Holland B. New 3-Point Bending
Traction Method of Restoring Cervical Lordosis Combined with Cervical
Manipulation: Non-randomized Clinical Control Trial. Archives Phys Med
Rehabil 2002; 83(4):447-53.
Harrison DE, Harrison DD, Betz J, Colloca CJ, Janik TJ, Holland B. Increasing
the Cervical Lordosis with Chiropractic Biophysics Seated Combined ExtensionCompression and Transverse Load Cervical Traction with Cervical Manipulation:
Non-Randomized Clinical Control Trial. J Manipulative Physiol Ther 2003 MarApr;26(3):139-51.