Sagittal Plane Flexion Research Articles

The direction of progressive herniation in porcine spine motion segments is influenced by the orientation of the bending axis

Background. It has been shown that disc herniations are a cumulative injury created by repetitive flexion motion while under modest compressive loads. There is a lack of data linking the direction of nucleus tracking to the orientation of the bending motion axis. Our purpose was to determine if the direction that the nucleus tracks through the annulus during progressive herniation is predictable from the direction of bending motion (i.e. a specific side with posterio-lateral herniation). Methods. Matched cohorts (nu = 16) of porcine cervical spine (C3/4 and C5/6) motion segments were potted in aluminum cups and bent at an angle of 30° to the sagittal plane flexion axis while under a sustained compressive load of 1472 N. Findings. The direction of bending motion affected the tracking pattern of the nucleus through the annular fibres in a predictable pattern. Specifically, bending the motion segments at an angle of 30° to the left of the sagittal plane flexion axis biased the movement of the nucleus toward the posterior right side of the disc in 15 of the 16 specimens. Interpretation. Based on this animal model, shown to have similar biomechanical behaviour to humans, the direction that the nucleus tracks through the annular fibres appears to be dependent upon the direction of bending motion. This may have implications on both herniation prevention and rehabilitation of posterio-lateral bulges and herniations.

Poster 152: Sagittal plane biomechanics and low back pain in transfemoral amputees.

Objectives: To document the extent of static lumbar lordosis and dynamic lumbar spine motion in the sagittal plane in transfemoral amputees and to determine whether excessive lumbar lordosis and excessive sagittal plane spine motion are related to low back pain (LBP) in transfemoral amputees. Design: A cross-sectional observational study. Setting: Motion analysis laboratory at a Veterans Affairs tertiary care facility. Participants: 6 ambulatory transfemoral amputees with a history of significant chronic LBP (CLBP) beginning after amputation and 3 ambulatory transfemoral amputees without history of CLBP since amputation. Interventions: Not applicable. Main Outcome Measures: L1-S1 Cobb angle from a lateral upright radiograph. Peak lumbar sagittal plane flexion and extension measured by a video-based motion analysis system. Results: The mean L1-S1 Cobb angle ± SD (range) were 62°±10° (44°–77°) for transfemoral amputees with LBP and 58°±3° (54°–61°) for transfemoral amputees without LBP. The mean maximum degrees of flexion (range) were 4.2°±5.9° (−8.0° to 13.7°) for transfemoral amputees with LBP and 3.0°±3.4° (−2.7° to 8.8°) for transfemoral amputees without LBP. The mean maximum degrees of extension (range) were −5.7°±6.4° (−21.0° to 2.3°) for transfemoral amputees with LBP and −5.9°±4.1° (−12.1° to 1.0°) for transfemoral amputees without LBP. Conclusions: The L1-S1 Cobb angle showed a significant relationship with LBP in transfemoral amputees ( P<.0313). The most extreme L1-S1 Cobb angles were seen in transfemoral amputees with LBP. There was no difference between the groups in either maximum lumbar flexion or extension ( P<0.3). From this data, static lumbar angles appear to be more related to LBP than the sagittal flexion and extension range of dynamic lumbar motion during gait; perhaps it is not the extremes of sagittal plane lumbar motion that place this population at risk. However, type II error cannot be excluded.

Comparison of Surface Sensor and Bone-Fixed Measurement of Humeral Motion

A common method of tracking humeral motion involves securing a thermoplastic cuff to the humerus with an electromagnetic sensor attached. The data on the accuracy of this technique are limited. This study addressed two questions: (a) How similar are surface and bone-fixed measurements of 3-D humeral rotations? (b) How similar are surface and bone-fixed measurements of 3-D humeral translations? Electromagnetic motion sensors were secured to a bone-fixed external humeral fixator, a surface humeral cuff, and the skin over the sternum and scapular acromion process. The 3-D data were collected during successive slow velocity (10–20°/second) repetitions of humeral active-assisted scapular plane abduction, sagittal plane flexion, and internal/external rotation with the arm adducted. Root mean square errors of surface measures compared to bone-fixed angular and translational values were calculated, and pairedt-tests were computed between the two methods. Root mean square errors for humeral rotations ranged from 1° (1%) for humeral elevation during scapular plane abduction to 7.5° (9%) for humeral internal/external rotation. Peak errors were under-representations of 5.7° for internal/external rotation during scapular plane abduction and 15.6° for internal rotation with the arm adducted at the side. Average translation errors ranged from 0.1 to 2.1 mm. Data from this study suggest that dynamic measurement of humeral motion with a surface humeral cuff sensor can be performed for certain slow velocity motions with root mean square errors less than 8°. Caution is called for when interpreting internal/external rotation values, which were underrepresented. Results may vary with one’s age, weight, or general physical condition, with different velocities of movement, or with different movements.

Quantitative anthropometry of the subatlantal cervical longitudinal ligaments.

The quantitative anthropometry of the cervical longitudinal ligaments was determined in 20 human cadaveric subatlantal cervical spines at the limits of flexion and extension. To provide measurements of cervical anterior and posterior longitudinal ligament lengths, widths, and cross-sectional areas at segmental levels. Although mathematical models of the cervical spine require specific data to predict kinematics, the anthropometry of the cervical spine has not been examined in detail. The dimensional changes of ligaments in physiologic motion are not well characterized. Segmental lengths and widths of the cervical longitudinal ligaments were measured in sagittal plane flexion and extension, using a three-dimensional electromagnetic digitizer. The cross-sectional areas of the ligaments at resting length were measured with a laser micrometer system. Comparisons between anterior and posterior location and among segmental levels were made. Several ligaments were examined histologically to determine the insertion sites and, thus, to define the segmental length. The anterior longitudinal ligaments were shorter in flexion than in extension. In extension, they were longer than the posterior longitudinal ligaments in flexion. The resting isolated ligaments were longer than the longest in situ lengths at several vertebral levels. The anterior longitudinal ligaments were wider at the disc than at the body. The cross-sectional area at C2-C3 was smaller than at subaxial levels. The longitudinal ligaments were observed to insert along the entire underlying vertebral body. The quantitative anthropometry of the cervical longitudinal ligaments is important in the development of accurate mathematical models of the cervical spine. The in situ ligaments may not be under tension in the physiologic range of motion.

The effect of head position on scapular orientation and muscle activity during shoulder elevation

The purposes of this study were to compare the effects of flexed head positions on scapular orientation and muscle activity during humeral elevation, and to determine any association of kinematic and electromyographic (EMG) responses. Twenty-five subjects, 19-37 years old and without any recent history of shoulder or neck symptoms, were evaluated. Three-dimensional scapular coordinate data and surface EMG signals from the trapezius (upper and lower), levator scapulae, and serratus anterior were collected at static positions (0°, 90°, and 140°) of humeral elevation in the scapular plane and head positions (0°, 25°, and 50°) of sagittal plane flexion. Scapular upward rotation and tipping were significantly decreased in flexed head positions. The effect of head position on scapular tipping increased as humeral elevation increased. Mean EMG activity of the levator scapula, upper trapezius, and serratus anterior was unchanged across head positions. The lower trapezius demonstrated small but statistically significant increases in mean activity at the 0° and 140° arm positions when the head was flexed to 50°. Significant correlations were found between some EMG and kinematic responses in flexed head positions, however, no consistent patterns were apparent across muscles or positions.