Susan R. Mercer

Biomechanics of the cervical spine. I: Normal kinematics

UNLABELLED This review constitutes the first of four reviews that systematically address contemporary knowledge about the mechanical behavior of the cervical vertebrae and the soft-tissues of the cervical spine, under normal conditions and under conditions that result in minor or major injuries. This first review considers the normal kinematics of the cervical spine, which predicates the appreciation of the biomechanics of cervical spine injury. It summarizes the cardinal anatomical features of the cervical spine that determine how the cervical vertebrae and their joints behave. The results are collated of multiple studies that have measured the range of motion of individual joints of the cervical spine. However, modern studies are highlighted that reveal that, even under normal conditions, range of motion is not consistent either in time or according to the direction of motion. As well, detailed studies are summarized that reveal the order of movement of individual vertebrae as the cervical spine flexes or extends. The review concludes with an account of the location of instantaneous centres of rotation and their biological basis. RELEVANCE The fact and precepts covered in this review underlie many observations that are critical to comprehending how the cervical spine behaves under adverse conditions, and how it might be injured. Forthcoming reviews draw on this information to explain how injuries might occur in situations where hitherto it was believed that no injury was possible, or that no evidence of injury could be detected.

Cervical transforaminal injection of corticosteroids into a radicular artery: a possible mechanism for spinal cord injury.

Spinal cord injury has been recognized as a complication of cervical transforaminal injections, but the mechanism of injury is uncertain. In the course of a transforaminal injection, an observation was made after the initial injection of contrast medium. The contrast medium filled a radicular artery that passed to the spinal cord. The procedure was summarily abandoned, and the patient suffered no ill effects. This case demonstrates that despite using careful and accurate technique, it is possible for material to be injected into a radicular artery. Consequently, inadvertent injection of corticosteroids into a radicular artery may be the mechanism for spinal cord injury following transforaminal injections. This observation warns operators to always perform a test injection of contrast medium, and carefully check for arterial filling using real-time fluoroscopy with digital subtraction.

Hamstring Muscles: Architecture and Innervation

Knowledge of the anatomical organization of the hamstring muscles is necessary to understand their functions, and to assist in the development of accurate clinical and biomechanical models. The hamstring muscles were examined by dissection in six embalmed human lower limbs with the purpose of clarifying their gross morphology. In addition to obtaining evidence for or against anatomical partitioning (as based on muscle architecture and pattern of innervation), data pertaining to architectural parameters such as fascicular length, volume, physiological cross-sectional area, and tendon length were collected. For each muscle, relatively consistent patterns of innervation were identified between specimens, and each was unique with respect to anatomical organization. On the basis of muscle architecture, three regions were identified within semimembranosus. However, this was not completely congruent with the pattern of innervation, as a primary nerve branch supplied only two regions, with the third region receiving a secondary branch. Semitendinosus comprised two distinct partitions arranged in series that were divided by a tendinous inscription. A singular muscle nerve or a primary nerve branch innervated each partition. In the biceps femoris long head the two regions were supplied via a primary nerve branch which divided into two primary branches or split into a series of branches. Being the only muscle to cross a single joint, biceps femoris short head consisted of two distinct regions demarcated by fiber direction, with each innervated by a separate muscle nerve. Architecturally, each muscle differed with respect to parameters such as physiological cross-sectional area, fascicular length and volume, but generally all partitions within an individual muscle were similar in fascicular length. The long proximal and distal tendons of these muscles extended into the muscle bellies thereby forming elongated musculotendinous junctions.

The ligaments and annulus fibrosus of human adult cervical intervertebral discs.

STUDY DESIGN Descriptive, microdissection study. OBJECTIVE To determine the morphology of the human adult cervical intervertebral disc and its ligaments. SUMMARY OF BACKGROUND DATA Some studies indicate that the cervical disc is distinctly different from the lumbar intervertebral disc, yet most clinical and anatomic texts appear content with extrapolating data from the lumbar spine. A detailed three-dimensional description of the cervical intervertebral disc and its surrounding ligaments is currently unavailable. METHODS Whole cervical spinal columns were freed from 12 human adult embalmed cadavers, and the posterior elements and soft tissues were removed. Using microdissection, the longitudinal ligaments and the fibrous components of 59 cervical intervertebral disc were resected systematically. The orientation, location, and attachments of each stripped bundle of collagen were recorded photographically and in sketches. RESULTS The cervical anulus fibrosus does not consist of concentric laminae of collagen fibers as in lumbar discs. Instead, it forms a crescentic mass of collagen thick anteriorly and tapering laterally toward the uncinate processes. It is essentially deficient posterolaterally and is represented posteriorly only by a thin layer of paramedian, vertically orientated fibers. The anterior longitudinal ligament covers the front of the disc, and the posterior longitudinal ligament reinforces the deficient posterior anulus fibrosus with longitudinal and alar fibers. CONCLUSIONS The three-dimensional architecture of the cervical anulus fibrosus is more like a crescentic anterior interosseous ligament than a ring of fibers surrounding the nucleus pulposus.

Musculoskeletal Abnormalities in Chronic Headache: A Controlled Comparison of Headache Diagnostic Groups

The presence of postural, myofascial, and mechanical abnormalities in patients with migraine, tension‐type headache, or both headache diagnoses was compared to a headache‐free control sample. Twenty‐four control subjects were obtained from a convenience sampling and each was matched by age and sex to three patients with headache (one with migraine [with or without aura], one with tension‐type headache, and one with diagnoses of both migraine and tension‐type headache [combined diagnosis]) who had been previously assessed by a physical therapist at a headache clinic. Physical therapy assessment findings were compared among the four groups.

Development of sensitivity to facial expression of pain

&NA; The ability to perceive pain in others is an important human capacity. Its development has not been studied. The present study examined the development of sensitivity to evidence of pain from childhood to early adulthood. One hundred and thirty‐four males and females from four age groups (5–6, 8–9, 11–12 years and young adult) took part. They judged the amount of pain displayed on videotaped excerpts of the facial expressions of pain patients. Excerpts were selected to display no pain, some pain and strong pain, based on facial measurements, and were displayed to participants in a signal‐detection paradigm. All participant groups were more sensitive to evidence of strong than some pain. The ability to detect pain expressions increased across the young, middle and older groups of children, but older children did not differ from adults. Increasing age was generally associated with increasing sensitivity to more subtle facial signs of pain. The results indicate that the ability to perceive pain in others is already significantly developed by the ages of five to six, but refinements in the ability continue through to early adulthood. These findings represent the first description of the development of the ability to perceive pain in others. Important areas for future research into the neurobiological, personal and social determinants of this ability are highlighted.

Nonpharmacological treatment for migraine: incremental utility of physical therapy with relaxation and thermal biofeedback

The identification of musculoskeletal abnormalities in headache patients has led to the incorporation of physical therapy (PT) into treatment programs for chronic headache. The current studies: (i) investigated the efficacy of FT as a treatment for migraine, and (ii) investigated the utility of PT as an adjunct treatment in patients who fail to improve with relaxation training/thermal biofeedback (RTB). PT alone is not effective in reducing headache, with only 14% of subjects reporting significant headache reduction (mean reduction of 15.6% in comparison with 41.3% in RTB). However, PT may have been a useful adjunct, with 47% of a group of 11 subjects who had failed to improve with RTB reporting improvement with the addition of PT. It is recommended that RTB remain the nonmedical treatment of choice for migraine, and that PT may be a useful adjunct for patients who fail to improve after such treatment.

Lateral Hip Pain: Findings From Magnetic Resonance Imaging and Clinical Examination

STUDY DESIGN Prospective cross-sectional study. OBJECTIVES To examine the radiological and physical therapy diagnoses of lateral hip pain (LHP), and determine the validity of selected clinical variables for predicting gluteal tendon pathology. BACKGROUND LHP is frequently encountered by clinicians. Further investigation is required to establish the specific pathologies implicated in the cause of LHP, and which clinical tests are useful in the assessment of this problem. METHODS AND MEASURES Forty patients with unilateral LHP underwent a physical therapy examination followed by magnetic resonance imaging (MRI) studies. Three radiologists analyzed the images of both hips for signs of pathology. Interobserver reliability of the image analyses, the agreement between the physical therapy and radiological diagnoses, and the validity of the clinical tests were examined. RESULTS Gluteus medius tendon pathology, bursitis, osteoarthritis and gluteal muscle atrophy (predominantly affecting gluteus minimus) were all implicated in the imaging report of LHP. While prevalent in symptomatic hips, abnormalities were also identified in asymptomatic hips, particularly relating to the diagnosis of bursitis. The strength of agreement between radiologists was variable and little agreement existed between the physical therapy and radiological diagnoses of pathology. Nine of the 26 clinical variables examined in relation to gluteal tendon pathology had likelihood ratios above 2.0 or below 0.5, but the associated 95% confidence intervals were large. CONCLUSIONS The diagnosis of LHP is challenging and our results highlight some problems associated with the use of MRI as a diagnostic reference standard. This factor, together with the imprecise point estimates of the likelihood ratios, means that no firm conclusions can be made regarding the diagnostic utility of the clinical tests used in the assessment of gluteal tendon pathology.

Revisiting the clinical anatomy of the alar ligaments.

PurposeThe morphology of the alar ligaments has been inconsistently described, particularly with regard to the existence of an atlantal portion. Despite these inconsistencies, these descriptions have been used to develop physical tests for the integrity of these ligaments in patients with cervical spine problems. The purpose of this study was to describe the detailed macrostructure of the alar ligaments.MethodsThe alar ligaments of 11 cervical spine specimens from embalmed adult cadavers were examined by fine dissection. A detailed description of the macrostructure of these ligaments and their attachment sites was recorded. Measurements were performed with respect to ligament dimensions and relations with selected bony landmarks.ResultsNo atlantal portion of the alar ligament was viewed in any specimen. The attachment of the ligaments on the odontoid process occurred on its lateral and posterolateral aspects, frequently below the level of the apex. The occipital attachment was on the medial surface of the occipital condyles in close proximity to the atlanto-occipital joints. The orientation of the ligaments was primarily horizontal. The presence of transverse bands extending occiput to occiput with minimal or no attachment to the odontoid process was a common variant.ConclusionsThe absence of findings with respect to the atlantal portion of the alar ligament suggests that it may be considered an anatomical variant, not an essential component for stability of the craniocervical complex. These findings may inform the use and interpretation of clinical tests for alar ligament integrity.

In response to Larkin, Carragee and Cohen letter “Transforaminal epidural steroid delivery…”

until the affected nerve root is identified. This approach should reduce the risk of misdiagnosing the level of the affected nerve root, which may occur with spread of LA to several levels during conventional diagnostic nerve root blocks. This method also enables several nerve roots to be tested or injected through a single needle, taking less time and causing less patient discomfort. But we believe the biggest advantage of this approach is that a flexible catheter is much less likely than a needle to enter an artery or the nerve root itself. When concordant stimulation is attained at low voltage, the chances of inadvertent intravascular injection are further reduced. To date, we have performed over 100 catheter-guided cervical TFESI without complications, suggesting greater safety. Comparative studies are needed to confirm the potential for both improved diagnostic accuracy and improved safety with this approach to cervical epidural steroid injection.