Normal neck motion

Abstract

Musculoskeletal disorders affect humankind perhaps more than any other category of malady, and at all ages. Prominent amongst such disorders are those apparently afflicting the vertebral column presenting with symptoms of headache and neck pain. Diagnosis of the cause of symptoms implicating structures or dysfunction of the neck as source is fraught with difficulty. Local neck joint kinetic behaviour and motion amplitude commands attention from those with an interest in manipulation, like chiropractors and physiotherapists, as well as surgeons, who all commonly examine patients for an association between perceived anomalies of local joint motion and such symptoms. Anecdotal impressions about the significance of findings made in this fashion form the rationale for therapy, including manual therapy. Although there are data on global neck kinematics, studies of local neck joint kinematic behaviour in appropriate age and gender cohorts of sufficient size to be clinically useful are scarce and contradictory. Remarkably, as investigators seek, but have yet to find, reliable and accurate diagnostic tests to quantify local neck joint motion, surgeons also seek surgically without any such data to relieve spondylotic myelopathy and/or radiculopathy caused by mechanical pathology in an intervertebral disc in the cervical spine with insertion of artificial disc prostheses. Thus, for those addressing the causes of otherwise unexplained neck related symptoms, especially surgeons and chiropractors, accurate data and a thorough understanding of neck kinematics (understanding of joint behaviour without consideration of forces) are essential, but absent. These deficiencies in the literature afford little confidence in other studies for which values for abnormal states or joint motion patterns are compared with the existing catalogue of “normal” rotational values or Instantaneous Centre of Rotation (ICR) locations derived from the suspect studies. A more useful catalogue is thus a necessary pre-requisite to full exploration of abnormal rotational joint motion and the locations of notionally normal ICRs (defined as X axis and Y axis positions on a typical Cartesian coordinate ‘map’ in which X axis is the left-right direction and Y axis is the up-down direction). This catalogue assembled from study of pain free volunteers uniquely and for the first time embraces the following characteristics: a. Since joints stiffen with age, data are from three age cohorts, from 30 years to 39 years, from 40 year to 49 years, and from 50 to 59 years. b. Since women are generally thought to be more flexible than men are, roughly half of the overall group of subjects is women and half men. c. Radiographs have been taken, each in the same fashion, with no prior nod of the chin down to the chest in flexion, but with the chin first protruded, then full active flexion. d. This study has a cohort in each sub-set of at least 30 volunteers. e. ICRs vary according to bone size, so radiographic measurements have been ‘standardized’ to account for such differences deriving from different regions of the neck and from images taken at different film focal distances and from one individual to another. This leads to six sets of values of sufficient size for each gender and three age ranges, accounting for inter-observer variation, which no previous study has undertaken in this way. Earlier reports of notional “normal” values for both motion amplitudes and ICR locations appear not to be based on equivalent data. This thesis reveals sufficient differences in values in enough joints for the three different age cohorts representing the commonest age groups presenting with neck pain and related disorders, and in both genders, to render current catalogues of normal motion somewhat unsatisfactory. For normal sagittal plane local joint motion from C2-3 to C6-7 in the human neck, for rotation amplitude values, the Null Hypotheses that no such data in neck kinematics can show differences in values from age cohort to age cohort and/or from gender cohort to gender cohort are rejected. The Null Hypotheses for Instantaneous Axes of Rotation are confirmed. Further, the thesis produces sufficient new evidence to propose more accurate ranges that can be considered as clinically relevant normals as the basis for investigations into clinical causes and assessment of treatment results for mechanically implicated neck pain and related disorders.