Mark J. Pearcy

The differences in toxicity and release of bone-resorbing mediators induced by titanium and cobalt-chromium-alloy wear particles.

We investigated the relationship between the toxic effects of metal wear particles and their ability to stimulate the release of inflammatory mediators implicated in bone resorption. In vitro studies were carried out with use of rat peritoneal macrophages, which were exposed to either cobalt-chromium-alloy or titanium-aluminum-vanadium particles, milled from the metal components of hip prostheses. The particles were in the size-range of, and at concentrations similar to, those found in the tissues surrounding failed prostheses in humans. The titanium-aluminum-vanadium particles showed little toxicity even at high concentrations, while the cobalt-chromium particles were very toxic. The titanium-aluminum-vanadium particles induced significantly more release of prostaglandin E2 than did the cobalt-chromium particles, and this was true for a wide range of concentrations. Exposure to titanium-aluminum-vanadium increased the release of prostaglandin E2, interleukin-1, tumor necrosis factor, and interleukin-6. In contrast, exposure to cobalt-chromium particles was associated with a decreased release of prostaglandin E2 and interleukin-6, and it had little effect on the release of interleukin-1 and tumor necrosis factor.

Three-dimensional x-ray analysis of normal movement in the lumbar spine.

Biplanar radiography was used to assess the normal three-dimensional movements of the lumbar spine in the erect posture in a group of asymptomatic volunteers. The primary movements investigated were flexion and extension, while the three-dimensional analysis also measured any associated coupled lateral bends and axial rotations. The results showed that each intervertebral joint had a total range of flexion and extension of approximately 14°, the lower levels moving slightly more than the upper levels. All the intervertebral joints had more movement in flexion than extension from the upright position, except for the L5/S1 joint, which showed no consistent pattern, some subjects extending more than flexing. Coupled movements of 4° or more in flexion and 3° or more in extension were shown to be abnormal.

Axial rotation and lateral bending in the normal lumbar spine measured by three-dimensional radiography.

A three-dimensional radiographic technique was used to investigate the ranges of active axial rotation and lateral bending plus the accompanying rotations in the planes other than that of the primary voluntary movements in two groups of normal male volunteers. There was approximately 2 degrees of axial rotation at each intervertebral joint with L3-4 and L4-5 being slightly more mobile. Lateral bending of approximately 10 degrees occurred at the upper three levels, while there was significantly less movement of 6 degrees and 3 degrees at L4-5 and L5-S1, respectively. In the upper lumbar spine, axial rotation to the right was accompanied by lateral bending to the left and vice versa. At L5-S1, axial rotation and lateral bending generally accompanied each other in the same direction, while L4-5 was a transitional level. These measurements in vivo demonstrated that there was no simple mechanical coupling of the rotations, and that the lordotic shape of the lumbar spine together with muscular control are probably the two principal factors determining the relation between the primary and accompanying rotations.

A universal model of the lumbar back muscles in the upright position

A model of the lumbar back muscles was constructed incorporating 49 fascicles of the lumbar erector spinae and multifidus. The attachment sites and sizes of fascicles were based on previous anatomic studies, and the fascicles were modeled on radiographs of nine normal volunteers in the upright position. Calculations revealed that the thoracic fibers of the lumbar erector spinae contribute 50% of the total extensor moment exerted on L4 and L5; multifidus contributes some 20%; and the remainder is exerted by the lumbar fibers of erector spinae. At upper lumbar levels, the thorecic fibers of the lumbar erector spinae contribute between 70% and 86% of the total extensor moment. In the upright posture, the lumbar back muscles exert a net posterior shear force on segments L1 to L4, but exert an anterior shear force on L5. Collectively, all the back muscles exert large compression forces on all segments. A force coefficient of 46 Ncm-2 was determined to apply for the back muscles. These results have a bearing on the appreciation of the effects on the back muslces of surgery and physiotherapy.

Instantaneous axes of rotation of the lumbar intervertebral joints

Lateral radiographs of ten normal individuals were studied to determine the location of the instantaneous axis of rotation (IAR) of every lumbar vertebra for the movements, of flexion and extension from the upright position and flexion from the fully extended position; and errors involved in the technique were quantified to establish confidence limits for the results of the calculations. The distribution of the IARs was found to fall within a small range from the mean location at each level, particularly for the movement of flexion from the extended position. Within-observer and between-observer errors occurred in tracing and superimposing radiographs and marking x and y coordinates. Unacceptably large errors occur when the movement of the joint is less than 5°, and only the IAR for flexion from extension can be plotted with acceptable confidence. This result invalidates the notion that plotting centrodes may be of diagnostic value in recognizing mechanical disorders. The determination of a single extension to flexion IAR may be of more value clinically, to which end this study provides essential normative data.

Stereo radiography of lumbar spine motion

The technique of Biplanar Radiography for the computer analysis of orthogonal radiographs of the human spine enables the calculation of three-dimensional coordinates for anatomical landmarks on the vertebrae. Three-dimensional intervertebral movements are deduced from the changes in the relative orientations of the vertebrae as a subject moves from one position to another. The three-dimensional coordinates of the anatomical landmarks on the vertebrae were found to have an RMS error of less than 1 mm. The RMS errors for translational movements were less than 2 mm and for rotations were less than 1.5 degrees. This study of normal subjects has defined the ranges of voluntary flexion and extension, axial rotation, and lateral bending in the lumbar spines of young males. The range of flexion plus extension at each lumbar intervertebral joint is approximately 14 degrees with the L4/5 level being slightly more mobile than the others. There are approximately 2 degrees of axial rotation at each joint with L3/4 and L4/5 being slightly more mobile. Lateral bending of approximately 10 degrees occurs at the upper three levels while there is significantly less movement of 6 degrees and 3 degrees at L4/5 and L5/S1 respectively. In flexion and extension accompanying axial rotation of 2 degrees or more and lateral bending of 3 degrees or more occurred rarely and any larger accompanying rotation at an intervertebral joint should be considered abnormal. During twisting and side bending axial rotation to the right is accompanied by lateral bending to the left and vice versa at the three upper levels. At L5/S1 axial rotation and lateral bending generally accompany each other in the same direction while L4/5 is a transitional level. During lateral bending there is also generally extension at the upper levels and flexion at L5/S1. The measurement in vivo of the accompanying rotations in the other planes has demonstrated that there is no simple mechanical coupling of the rotations. Finally, this study has provided a base line of normal movements to which the movements seen in pathological conditions can be compared.

Anatomy and biomechanics of psoas major

The fascicular anatomy of the psoas major was determined by dissection in three cadavers. Its actions on the lumbar spine in the sagittal plane were modelled on erect, flexion, and extension radiographs of ten adult males. Calculations revealed that psoas exerts only very small moments that tend to extend the upper lumbar spine and to flex the lower lumbar spine, but at maximum contraction the psoas exerts severe compression forces on the lumbar segments, and large shear forces.

Failure strengths of different meniscal suturing techniques

The aim of this study was to measure the failure strengths of three arthroscopic meniscal suturing methods. The techniques investigated were a single horizontal loop, a double vertical loop, and a single vertical loop. Eleven human, lateral menisci obtained at autopsy were cut with a scalpel to simulate peripheral longitudinal tears. The menisci were then repaired with one suture at a time, using each of the three methods in turn. The two parts of the meniscus were then pulled apart using a computer-controlled materials testing machine until failure occurred, either by the suture itself failing or by the suture pulling out because of tearing of the meniscus. The horizontal sutures had a mean failure strength of 29.3 N, whereas the double vertical loop failed at 63.2 N and the single vertical loop at 67.3 N. The horizontal loop sutures and the double vertical loop sutures all failed by pulling out of the meniscus. The single vertical loop sutures failed by rupture of the suture itself. This study showed the superior mechanical characteristics of the single vertical loop suturing system over the other techniques tested. Owing to the more consistent failure strength, decreased costs, and shorter surgical time over the double vertical loop system, the single vertical loop technique is recommended for arthroscopic meniscal repair.

The Effect of Low-back Pain on Lumbar Spinal Movements Measured by Three-dimensional X-ray Analysis

Back pain patients have restricted spinal movements, and the pattern of disturbance from normal movements may indicate the pathology and the functioning of the lumbar spine. Biplanar radiography was used to measure the three-dimensional Intervertebral movements of patients with back pain alone and with back pain plus nerve tension signs demonstrated by restricted straight leg raise. Statistically significant decreases in flexion/extension compared with a normal control group were demonstrated for both groups. Accompanying coupled movements were increased only in those patients without nerve tension signs indicating asymmetrical muscle action, while those with tension signs had symmetric splinting particularly of the lower levels. Conservative treatments had no effect either clinically or on the movements. Caudal epidural injections produced clinical improvement and increased movements demonstrating relaxation of muscle splinting. Biplanar radiography, although capable of differentiating between the groups was not able to provide clinically useful information concerning individual patients with this type of back pain.

Three-dimensional analysis of active cervical motion: the effect of age and gender

OBJECTIVE: To describe the effects of age and gender on three-dimensional (3D) active cervical spine motion. DESIGN: This was a descriptive study. BACKGROUND: This study expanded on previous investigations of age and gender effects on single plane motion of the cervical spine. METHODS: Sixty female and 60 male asymptomatic, normal volunteers, aged between 20 and 59 years, were examined in a standardized seated position. The 3 SPACE Isotrak system was used to measure simultaneous 3D motion of the cervical spine. RESULTS: The mean range of all the primary movements decreased significantly with age. For flexion/extension the greatest decrease occurred between the 20- and 30-year-olds, whereas for both lateral flexion and rotation, significant differences were demonstrated in subjects aged two decades apart. The coupling of motion associated with rotation was significantly related to age. CONCLUSION: Age had a significant effect on all of the primary movements. Age had less effect on the range of the coupled movements, in that the only movements to be affected were lateral flexion and extension occurring during cervical rotation. Gender had no marked effect on the primary or the coupled movements. RELEVANCE: This study provides normative data for the effects of age and gender on three-dimensional analysis of active cervical spine motion, which can be used for comparison with specific patient populations. The high level of intra-subject test-retest reliability renders the3 SPACE system of value for clinical measurement of movement pre- and post-treatment intervention for cervical spine disorders.