The influence of age, sex, and posture on the measurement of atlantodental interval in a normal population.

OBJECTIVE: The atlantodental interval (ADI) is used in assessing atlantoaxial stability. This measurement may potentially be affected by several features encountered during patient examination. This study examined the influence of 3 features: age, sex, and posture, on the measurement of ADI in a normal population. METHODS: The ADI was measured sequentially on 269 lateral cervical radiographs of adults with no demonstrated bony injury. Images were stratified by age and sex with equal representation in each age group. A further 25 asymptomatic adults were assessed for posture using craniovertebral angle measured from digital lateral photographs. The ADI was then measured from a lateral radiograph. The data were examined for correlation between age, craniovertebral angle, and ADI using Spearman rank correlation. The ADI of age groups was compared by Kruskal-Wallis test. The relationship between ADI and sex was examined using Wilcoxon rank sum test. Interaction between age and sex was explored using an interaction term in regression analysis. RESULTS: The ADI decreased with age, median measurements reducing from 2.07 to 0.85 mm across age groups (P < .01). No significant relationship was demonstrated between ADI and sex. No significant interaction was demonstrated between age and sex. Measurements of craniovertebral angle did not correlate with ADI (ρ = 0.03, P = .90). CONCLUSION: The magnitude of ADI decreases with advancing age. Age should be considered a modifying factor when interpreting measurement of ADI, particularly in consideration of potential minor instabilities. Patient sex does not appear to influence ADI, either independently or in interaction with age. Craniocervical posture variation does not influence ADI in an asymptomatic adult population.

Toward understanding normal craniocervical rotation occurring during the rotation stress test for the alar ligaments.

BACKGROUND: The rotation stress test is recommended for assessing alar ligament integrity. Although some authors, in the literature regarding the rotation stress test, accept that rotation will occur during testing, estimates of range occurring with a normal test response vary between 20 and 40 degrees. None of these estimates are based on formal examination of the test. OBJECTIVE: The purposes of this study were: (1) to examine the range of craniocervical rotation occurring during rotation stress testing for the alar ligaments in individuals who are healthy and (2) to investigate a measurement protocol for quantifying rotation. DESIGN: A within-subject experimental study was conducted. METHODS: Sixteen participants underwent magnetic resonance imaging in neutral and end-range rotation stress test positions. Measurements followed a standardized protocol relative to the position of the axis. A line connecting the transverse foramena of the axis created a reference plane. The position of the occiput in the head-neutral position was calculated as the angle formed between a line joining the foramena lacerum and the reference plane. Measurements were repeated at the end-range test position. Total rotation of the occiput was calculated as the difference in angles measured in neutral and test positions. Measurement was performed on 4 occasions, and reliability of measurements was assessed using the standard error of measurement (SEM) and the intraclass correlation coefficient (ICC). RESULTS: Measurement of rotation of the occiput relative to a stabilized axis ranged between 1.7 and 21.5 degrees (X=10.6, SD=5.1, SEM=1.14, ICC=.96, 95% confidence interval=.90-.98). LIMITATIONS: Sustaining the test position for imaging increased the potential for loss of end-range position and image quality. Testing could be performed only in the neutral position, not in 3 planes as commonly described. CONCLUSIONS: The range of craniocervical rotation during rotation stress testing of intact alar ligaments should typically be 21 degrees or less. Rotation may be quantified using the method protocol outlined.

The anterior shear and distraction tests for craniocervical instability. An evaluation using magnetic resonance imaging.

Screening for integrity of the ligaments of the craniocervical complex has been suggested prior to the application of manual techniques to the upper cervical spine. However, most tests proposed lack validation limiting their usefulness clinically. This study examined the effect of the anterior shear test for the transverse ligament and the distraction test for the tectorial membrane in normal volunteers. MRI was performed in supine in neutral and end-range stress test positions in 16 individuals using proton density-weighted sequences and a standard head coil in a 3-T system. Measurements were made with respect to a strictly standardised protocol. The anterior shear test was assessed using changes in atlantodental interval and distance from the anterior arch of the atlas to the posterior aspect of the odontoid process. Distraction testing for the tectorial membrane was assessed by changes in basion-dental interval and by direct measurement of the tectorial membrane. Differences were compared using Wilcoxon Sign Rank tests or paired t-test depending upon each variables assessment of normality. Anterior shear testing resulted in a 0.41 mm mean increase in atlantodental interval (p = 0.03) and 0.35 mm mean increase in axial plane distance (p = 0.05). Distraction testing for the tectorial membrane resulted in a 0.64 mm increase in basion-dental interval (p < 0.01) and a 1.11 mm increase in direct ligament length measurement (p = 0.02). Reliability of measurements ranged from moderate to substantial. These results indicate that these tests produce a consistent direct effect on the transverse ligament and the tectorial membrane which is consistent with their theorised mechanism for clinical use.

Construct validity of clinical tests for alar ligament integrity: an evaluation using magnetic resonance imaging.

BACKGROUND: The alar ligaments are integral to limiting occipito-atlanto-axial rotation and lateral flexion and enhancing craniocervical stability. Clinical testing of these ligaments is advocated prior to the application of some cervical spine manual therapy procedures. Given the absence of validation of these tests and the potential consequences if manipulation is applied to an unstable upper cervical spine segment, exploration of these tests is necessary. OBJECTIVE: The purpose of this study was to examine the direct effect of the side-bending and rotation stress tests on alar ligaments using magnetic resonance imaging (MRI). DESIGN: This was a within-participant experimental study. METHODS: Sixteen participants underwent MRI in neutral and end-range stress test positions using proton density-weighted sequences in a 3-Tesla system. Measurements followed a standardized protocol relative to the position of the axis. Distances were measured from dens tip to the inferior margin of the foramen magnum and from midsubstance of the dental attachment of the ligament to its occipital insertion. Between-side differences were calculated for each measurement to account for inherent asymmetries in morphology. Differences were compared between the test and neutral positions using a Wilcoxon signed rank test. RESULTS: Side-bending stress tests produced a median between-side difference in ligament length of +1.15 mm. Rotation stress tests produced a median between-side difference in ligament length of +2.08 mm. Both results indicate increased measurement of the contralateral alar ligament. Limitations Assessment could be made only in the neutral position due to imaging limitations. Clinical texts state that tests should be performed in 3 positions: neutral, flexion, and extension. CONCLUSIONS: Both side-bending and rotation stress testing result in a measurable increase in length of the contralateral alar ligament. This finding is consistent with mechanisms that have been described to support their use in clinical practice.

The relationship between dens height and alar ligament orientation: a radiologic study.

OBJECTIVE: This study examined the anatomical assumptions underlying multiplanar alar ligament stress testing. The alar ligament has been described as occurring in 1 of 3 planes: caudocranial, horizontal, and craniocaudal. This has been stated to result from variation in dens height. Stress testing in all 3 planes is suggested, with increased translation present in all positions to infer instability. METHODS: Computed tomography scans with no diagnosed bony or ligamentous abnormally were prospectively collected over a 3-month period from a teaching hospital in Newcastle, Australia, and sequentially analyzed. The height of the dens relative to the occipital condyles was measured using McRae's line and the bimastoid line. The orientation of the alar ligament was measured relative to the vertical axis of the dens as well as a vertical line defined by specified occipital and spinal bony landmarks. These results were correlated with dens height. RESULTS: After exclusions, 42 individual computed tomography studies were analyzed yielding 64 clearly discernible ligaments. A vertical line derived from the digastric line provided the smallest variation in results. The mean ligament orientation given by this measure was 110.06° (85°-127°). There was no correlation between measured dens height relative to the occiput and ligament orientation. CONCLUSION: Our findings reinforce the existence of normal anatomical variation in dens height and alar ligament orientation. However, variation in dens height as a cause of variation in ligament orientation was not supported by this study.

Factors related to thumb pain in physiotherapists.

The aim of this study was to determine whether differences exist between physiotherapists with work-related thumb pain and physiotherapists without thumb pain. Twenty-four physiotherapists with work-related thumb pain (Pain Group) and 20 physiotherapists without thumb or wrist pain (Non-pain Group), who were working at least 20 hours per week in an outpatient musculoskeletal setting, were compared on a number of attributes: generalised joint laxity, hand and thumb strength, height, weight, working environment, hand position and force applied during mobilisation, mobility at individual thumb joints, extent of osteoarthritis at the thumb and radial-sided wrist joints, and demographic data including age, gender and years of experience. All physiotherapists in the Pain Group reported their thumb pain was related to and initially caused by the performance of manual techniques, and 88% had altered their manual techniques because of pain in the thumb. There was extreme variability in hand position and force applied during mobilisation, and a slightly high prevalence of osteoarthritis (22.7%) considering the mean age of the total sample (38.6 years). Statistically significant differences between groups included increased right carpometacarpal joint laxity (6.4%, 95% CI 0.19 to 12.6), decreased right tip pinch strength (0.84 kg, 95% CI 0.01 to 1.68), and lower body mass index (2.0, 95% CI 0.11 to 3.9) for the Pain Group. Other factors were not statistically different between groups. These results indicate that work-related thumb pain affects physiotherapists ability to administer manual treatments, and suggest that decreased stability and strength of the thumb may be associated with work-related thumb pain.