Showing papers by "Patricia Dolan published in 2000"

Mechanical Initiation of Intervertebral Disc Degeneration

Abstract: volves gross structural disruption as well as cell-mediated changes in matrix composition, but there is little evidence concerning which comes first. Comparatively minor damage to a vertebral body is known to decompress the adjacent discs, and this may adversely affect both structure and cell function in the disc. Methods. In this study, 38 cadaveric lumbar motion segments (mean age, 51 years) were subjected to complex mechanical loading to simulate typical activities in vivo while the distribution of compressive stress in the disc matrix was measured using a pressure transducer mounted in a needle 1.3 mm in diameter. “Stress profiles” were repeated after a controlled compressive overload injury had reduced motion segment height by approximately 1%. Moderate repetitive loading, appropriate for the simulation of light manual labor, then was applied to the damaged specimens for approximately 4 hours, and stress profilometry was repeated a third time. Discs then were sectioned and photographed. Results. Endplate damage reduced pressure in the adjacent nucleus pulposus by 25% 6 27% and generated peaks of compressive stress in the anulus, usually posteriorly to the nucleus. Discs 50 to 70 years of age were affected the most. Repetitive loading further decompressed the nucleus and intensified stress concentrations in the anulus, especially in simulated lordotic postures. Sagittal plane sections of 15 of the discs showed an inwardly collapsing anulus in 9 discs, extreme outward bulging of the anulus in 11 discs, and complete radial fissures in 2 discs, 1 of which allowed posterior migration of nucleus pulposus. Comparisons with the results from tissue culture experiments indicated that the observed changes in matrix compressive stress would inhibit disc cell metabolism throughout the disc, and could lead to progressive deterioration of the matrix. Conclusions. Minor damage to a vertebral body end

Effects of backward bending on lumbar intervertebral discs. Relevance to physical therapy treatments for low back pain.

Abstract: Study design Mechanical testing of cadaveric motion segments. Objectives To test the hypothesis that backward bending of the lumbar spine can reduce compressive stresses within lumbar intervertebral discs. Summary of background data Lumbar extension affects the distribution of compressive stress inside normal cadaveric discs, but little is known about its effect on mechanically disrupted and degenerated discs. Methods Nineteen lumbar motion segments (mean donor age, 48 years) were subjected to complex mechanical loading to simulate the following postures: moderate lumbar flexion, 2 degrees of extension, 4 degrees of extension, and the neutral position (no bending). The distribution of compressive stress within the disc matrix was measured in each posture by pulling a miniature pressure transducer along the midsagittal diameter of the disc. Stress profiles were repeated after a mechanical treatment that was intended to simulate severe disc degeneration in vivo. Results The "degeneration" treatment reduced pressure in the nucleus pulposus and generated stress concentrations within the anulus, in a manner similar to that found in severely degenerated discs in vivo. When all discs were considered together, 2 degrees of extension increased the maximum compressive stress within the posterior anulus by an average of 16%, compared with the neutral posture. The size of localized stress peaks within the posterior anulus was increased by 43% (P = 0.02). In 4 degrees of extension, changes observed between 0 degree and 2 degrees were usually exaggerated. In contrast, moderate flexion tended to equalize the distribution of compressive stress. In 7 of the 19 discs, 2 degrees of lumbar extension decreased maximum compressive stress in the posterior anulus relative to the neutral posture by up to 40%. Linear regression showed that lumbar extension tended to reduce stresses in the posterior anulus in those discs that exhibited the lowest compressive stresses in the neutral posture (P = 0.003; R2 = 41%). Conclusions The posterior anulus can be stress shielded by the neural arch in extended postures, but the effect is variable. This may explain why extension exercises can relieve low back pain in some patients.

Can exercise therapy improve the outcome of microdiscectomy

Abstract: Study Design. A prospective randomized controlled trial of exercise therapy in patients who underwent microdiscectomy for prolapsed lumbar intervertebral disc. Results of a pilot study are presented. Objective. To determine the effects of a postoperative exercise program on pain, disability, psychological status, and spinal function. Summary of Background Data. Microdiscectomy is often used successfully to treat prolapsed lumbar intervertebral disc. However, some patients do not have a good outcome and many continue to have low back pain. The reasons for this are unclear but impairment of back muscle function due to months of inactivity before surgery may be a contributing factor. A postoperative exercise program may improve outcome in such patients. Methods. Twenty patients who underwent lumbar microdiscectomy were randomized into EXERCISE and CONTROL groups. After surgery, all patients received normal postoperative care that included advice from a physiotherapist about exercise and a return to normal activities. Six weeks after surgery, patients in the EXERCISE group undertook a 4-week exercise program that concentrated on improving strength and endurance of the back and abdominal muscles and mobility of the spine and hips. Assessments of spinal function were performed in all patients during the week before surgery and at 6, 10, 26, and 52 weeks after. The assessment included measures of posture, hip and lumbar mobility, back muscle endurance capacity and electromyographic measures of back muscle fatigue. On each occasion, patients completed questionnaires inquiring about pain, disability and psychological status. Results. Surgery improved pain, disability, back muscle endurance capacity and hip and lumbar mobility in both groups of patients. After the exercise program, the EXERCISE group showed further improvements in these measures and also in electromyographic measures of back muscle fatigability. All these improvements were maintained 12 months after surgery. The only further improvement showed by the CONTROL group between 6 and 52 weeks was an increase in back muscle endurance capacity. Conclusion. A 4-week postoperative exercise program can improve pain, disability, and spinal function in patients who undergo microdiscectomy.

Sudden and unexpected loading generates high forces on the lumbar spine.

Abstract: Study Design. A cross-sectional study of spinal loading in healthy volunteers. Objectives. To measure the bending and compressive forces acting on the lumbar spine, in a range of postures, when unknown loads are delivered unexpectedly to the hands. Summary of Background Data. Epidemiologic studies suggest that sudden and unexpected loading events often lead to back injuries. Such incidents have been shown to increase back muscle activity, but their effects on the compressive force and bending moment acting on the spine have not been fully quantified. Furthermore, previous investigations have focused on the upright posture only. Methods. In this study, 12 volunteers each stood on a force plate while weights of 0, 2, 4, and 6 kg (for men, 40% less for women) were delivered into their hands in one of three ways: 1) by the volunteer holding an empty box with handles, into which an unknown weight was dropped; 2) by the same way as in 1, but with volunteer wearing a blindfold and earphones to eliminate sensory cues; or 3) by the volunteer sliding a box of unknown weight off a smooth table. Experiments were carried out with participants standing in upright, partially flexed, and moderately flexed postures. Spinal compression resulting from muscular activity was quantified using electromyographic signals recorded from the back and abdominal muscles. The axial inertial force acting up the long axis of the spine was calculated from the vertical ground reaction force. The bending moment acting on the osteoligamentous spine was quantified by comparing measurements of lumbar curvature with the bending stiffness properties of cadaveric lumbar spines. Results. The contribution from abdominal muscle contraction to overall spinal compression was small (average, 8%), as was the axial inertial force (average, 2.5%), and both were highest in the upright posture. Peak bending moments were higher in flexed postures, but did not increase much at the moment of load delivery in any posture. Peak spinal compressive forces were increased by 30% to 70% when loads were suddenly and unexpectedly dropped into the box, and by 20% to 30% when they were slid off the table, as compared with loads simply held statically in the same posture (P < 0.001). The removal of audiovisual cues had little effect. Conclusions. Sudden and alarming events associated with manual handling cause a reflex overreaction of the back muscles, which substantially increases spine compressive loading. Manual handling regulations should aim to prevent such events and limit the weight of objects to be lifted.

Spinal position sense is independent of the magnitude of movement.

Abstract: STUDY DESIGN Position sense in the spine was recorded at T1, T7, L1, and S2 in three incremental angular ranges of flexion and on return to upright standing from these movements. OBJECTIVES To determine the effect of angular range of movement on position sense. The main purpose was to establish a protocol for whole spine assessment of position sense in healthy and pathologic spines. SUMMARY OF BACKGROUND DATA Position sense is one dimension of proprioception, classically assessed by the ability to reproduce preselected target positions. This approach was used in the current study to determine whether spinal position sense is affected by the magnitude of movement traversed in repositioning tasks. METHODS Spinal position sense was assessed in 20 healthy subjects during repeated flexion movements carried out in one-third, half, and two thirds of the full range of movement in the sagittal and coronal planes. During each movement, the 3-Space Fastrak (Polhemus Inc., Colchester, VT) was used to record angular movement of the spine at four sensor locations (T1, T7, L1, and S2). The absolute difference in the sensor angles between repeated trials was calculated for each flexed position and on return to upright standing from these. These absolute differences were used as a measure of position sense. RESULTS Absolute position sense after one-third angular movements was accurate to within 4.30 degrees +/- 2.84 degrees in flexed positions and 2.70 degrees +/- 2.20 degrees in upright postures. Corresponding results for two-thirds movements were 4.75 degrees +/- 2.63 degrees and 3.33 degrees +/- 2.60 degrees, respectively. Range of movement had no significant influence on the accuracy of position sense. CONCLUSIONS 1) Healthy individuals are able to reposition their spine accurately under conditions of incremental increases in angular range. 2) Range-related variations in position sense are small and unlikely to be of clinical significance.

When do Bending Stresses on the Spine Rise to Damaging Levels

Abstract: Experiments on cadaver spines have quantified the bending stresses (bending moment) required to cause overload injury or fatigue failure to the lumbar spine. This paper reviews subsequent experiments in living people which sought to identify the circumstances that cause spinal bending to rise to potentially damaging levels in life. Healthy volunteers performed various bending and lifting activities in the laboratory, and peak bending moment was quantified from measurements of lumbar flexion, obtained using the 3-Space Isotrak. Bending stresses approached or even exceeded estimated fatigue limits in some subjects when they performed lifting tasks in the early morning (when the spine's bending stiffness is increased), and following fatigue of the back muscles. Individuals with a small range of lumbar flexion were particularly likely to exceed safe limits. These findings may explain why repeated bending and lifting are so closely associated with low back problems.

Biomechanical Factors Affecting The Disc

Abstract: Introduction There is no longer any doubt that lumbar intervertebral discs can directly cause low back pain. Anatomical studies have identified nociceptive nerve endings within the outer annulus fibrosus (Bogduk 1994), and pain-provocation studies on sedated patients have demonstrated that their symptoms of severe back pain can be reproduced by direct mechanical stimulation of the posterior annulus fibrosus (Kuslich et al. 1991). The purpose of the present paper is to suggest how mechanical loading might cause lumbar discs to become painful in some people. The first section, which describes experiments on cadaveric spines, shows how mechanical loading can lead to disc injury (including prolapse) or fatigue failure, and how sustained loading in certain postures can lead to high concentrations of compressive stress within the annulus. Later sections describe experiments on living people which indicate the everyday circumstances which could lead to disc injury and/or pain.