Tommy Hansson

A prospective study of work perceptions and psychosocial factors affecting the report of back injury

A longitudinal, prospective study was conducted on 3,020 aircraft employees to identify risk factors for reporting acute back pain at work. The premorbid data included individual physical, psychosocial, and workplace factors. During slightly more than 4 years of follow-up, 279 subjects reported back problems. Other than a history of current or recent back problems, the factors found to be most predictive of subsequent reports in a multivariate model were work perceptions and certain psychosocial responses identified on the Minnesota Multiphasic Personality Inventory (MMPI). Subjects who stated that they “hardly ever” enjoyed their job tasks were 2.5 times more likely to report a back injury (P = 0.0001) than subjects who “almost always” enjoyed their job tasks. The quintile of subjects scoring highest on Scale-3 (Hy) of the MMPI were 2.0 times more likely to report a back injury (P = 0.0001) than subjects with the lowest scores. The multivariate model, including job task enjoyment, MMPI Scale-3, and history of back treatment, revealed that subjects in the highest risk group had 3.3 times the number of reports in the lowest risk group. These findings emphasize the importance of adopting a broader approach to the multifaceted problem of back complaints in industry and help explain why past prevention efforts focusing on purely physical factors have been unsuccessful.

The bone mineral content and ultimate compressive strength of lumbar vertebrae.

The bone mineral content of 109 lumbar vertebrae from 36 different subjects was determined by dual photon absorptiometry. The mean age of the subjects was 58.5 years (range, 31 to 79 years). The ultimate strength of the vertebral bodies was determined during axial compression. Bone mineral content and ultimate compressive strength were correlated (r = 0.86) and the strength was found to increase linearly with increasing amounts of bone mineral content. No differences in this correlation were found in the four vertebral levels (L1–4) included in the study, but a difference in this correlation was found between specimens taken from male and female subjects. The results make it possible to estimate the strength of a vertebral body from the knowledge of its bone mineral content as determined by dual photon absorptiometry and provide a basis for estimations of normal and abnormal amounts of bone mineral content in the vertebrae of the lumbar spine.

Rapid atrophy of the lumbar multifidus follows experimental disc or nerve root injury

Study Design. Experimental study of muscle changes after lumbar spinal injury. Objectives. To investigate effects of intervertebral disc and nerve root lesions on cross-sectional area, histology and chemistry of porcine lumbar multifidus. Summary of Background Data. The multifidus cross-sectional area is reduced in acute and chronic low back pain. Although chronic changes are widespread, acute changes at 1 segment are identified within days of injury. It is uncertain whether changes precede or follow injury, or what is the mechanism. Methods. The multifidus cross-sectional area was measured in 21 pigs from L1 to S1 with ultrasound before and 3 or 6 days after lesions: incision into L3–L4 disc, medial branch transection of the L3 dorsal ramus, and a sham procedure. Samples from L3 to L5 were studied histologically and chemically. Results. The multifidus cross-sectional area was reduced at L4 ipsilateral to disc lesion but at L4–L6 after nerve lesion. There was no change after sham or on the opposite side. Water and lactate were reduced bilaterally after disc lesion and ipsilateral to nerve lesion. Histology revealed enlargement of adipocytes and clustering of myofibers at multiple levels after disc and nerve lesions. Conclusions. These data resolve the controversy that the multifidus cross-sectional area reduces rapidly after lumbar injury. Changes after disc lesion affect 1 level with a different distribution to denervation. Such changes may be due to disuse following reflex inhibitory mechanisms.

Intervertebral Stiffness of the Spine Is Increased by Evoked Contraction of Transversus Abdominis and the Diaphragm : In Vivo Porcine Studies

Study Design. In vivo porcine study of intervertebral kinematics. Objectives. This study investigated the effect of transversus abdominis and diaphragm activity, and increased intra-abdominal pressure on intervertebral kinematics in porcine lumbar spines. Background. Studies of trunk muscle recruitment in humans suggest that diaphragm and transversus abdominis activity, and the associated intra-abdominal pressure contribute to the control of intervertebral motion. However, this has not been tested in vivo. Methods. Relative intervertebral motion of the L3 and L4 vertebrae and the stiffness at L4 were measured in response to displacements of the L4 vertebra imposed via a device fixed to the L4 vertebral body. In separate trials, diaphragm and transversus abdominis activity was evoked by stimulation of the phrenic nerves and via electrodes threaded through the abdominal wall. Results. When intra-abdominal pressure was increased by diaphragm or transversus abdominis stimulation, the relative intervertebral displacement of the L3 and L4 vertebrae was reduced and the stiffness of L4 was increased for caudal displacements. There was no change in either parameter for rostral displacements. In separate trials, the diaphragm crurae and the fascial attachments of transversus abdominis were cut, but intra-abdominal pressure was increased. In these trials, the reduction in intervertebral motion was similar to trials with intact attachments for caudal motion, but was increased for rostral trials. Conclusions. The results of these studies indicate that elevated intra-abdominal pressure, and contraction of diaphragm and transversus abdominis provide a mechanical contribution to the control of spinal intervertebral stiffness. Furthermore, the effect is modified by the muscular attachments to the spine.

Dynamic effects on the lumbar spinal canal : Axially loaded CT myelography and MRI in patients with sciatica and/or neurogenic claudication

Study Design. In patients with sciatica or neurogenic claudication, the structures in and adjacent to the lumbar spinal canal were observed by computed tomographic myelography or magnetic resonance imaging in psoas‐relaxed position and during axial compression in slight extension of the lumbar spine. Objectives. To determine the mechanical effects on the lumbar spinal canal in a simulated upright position. Summary of Background Data. For years, functional myelographic investigation techniques were shown to be of value in the evaluation of suspected encroachment of the spinal canal. Since the advent of computed tomography and magnetic resonance imaging, there have been few clinical and experimental attempts that have imitated these techniques. The data indicate that the space within the canal is posture dependent. Methods. Portable devices for axial loading of the lumbar spine in computed tomographic and magnetic resonance examinations were developed. Fifty patients (94 sites) were studied with computed tomographic myelography, and 34 patients (80 sites) with magnetic resonance in psoas‐relaxed position followed by axial compression in slight extension. The dural sac cross‐sectional area at L2 to S1, the deformation of the dural sac and the nerve roots, and the changes of the tissues surrounding the canal were observed. Results. In 66 of the investigated 84 patients, there was a statistically significant reduction of the dural sac cross‐sectional area in at least one site during axial compression in slight extension. Of the investigated patients, 29 passed the borderlines for relative (100 mm2) or absolute stenosis (75 mm2) in 40 sites. In 30 patients, there was deformation of the dural sac in 46 sites. In 11 of the patients investigated with magnetic resonance imaging, there was a narrowing of the lateral recess in 13 sites, during axial compression in slight extension. Conclusions. Axial loading of the lumbar spine in computed tomographic scanning and magnetic resonance imaging is recommended in patients with sciatica or neurogenic claudication when the dural sac cross‐sectional area at any disc location is below 130 mm2 in conventional psoas‐relaxed position and when there is a suspected narrowing of the dural sac or the nerve roots, especially in the ventrolateral part of the spinal canal in psoas‐relaxed position. The diagnostic specificity of the spinal stenosis will increase considerably when the patient is subjected to an axial load.

Experimental instability in the lumbar spine.

Study Design. An in vivo animal model of lumbar segmental instability, involving both passive and active stabilizing components of the spine, was developed. Objective. The aim of this investigation was to dynamically study the alterations in segmental kinematics as a result of interventions to the passive stabilizing components and to the lumbar musculature. Summary of Background Data. Segmental instability in the lumbar spine is associated with abnormal intervertebral motion. The majority of biomechanical studies have examined the in vitro effects of transecting individual stabilizing structures (i.e., intervertebral disc, facet joints, and ligaments), and have not simultaneously considered the effects of active musculature on spinal kinematics, which exist in the in vivo environment. Also, few studies have evaluated the kinematic behavior in the neutral region, for example, the transition phase between flexion and extension. Methods. Four experimental groups comprised 33 pigs, each of which followed different surgical injury sequences to the L3-L4 motion segment. An instrumented linkage attached to the L3-L4 motion segment was used to measure the sagittal kinematics during dynamic flexion-extension after each surgical injury and after bilateral stimulation of the lumbar paraspinal musculature. Results. Injuries to the disc resulted in greater overall axial translation. Graded injuries to the facet joint mainly caused changes in sagittal rotation and shear translation. When the facet injuries were compounded by removal of the transverse processes, there was significantly greater coupled motion and increased hysteresis in the neutral region for rotation. Extensive muscular stimulation after each of the injuries caused significantly greater rotation and shear translation, along with a tendency toward reduced axial translation, when compared to the unstimulated case. Although increasing the range of motion, increased muscular activity stabilized the injured motion segment by smoothing the erratic rotation pattern of motion, particularly in the neutral region. Conclusions. Because of the direct attachment to the vertebrae, both passive and active strain from the musculature influence the spinal kinematics in normal or destabilized motion segments. Although increasing the range of motion, stimulation of the musculature surrounding the injured motion segment has a stabilizing effect by reducing abrupt kinematic behavior, particularly in the neutral region where the muscles are under reduced tension. A facetectomy produces a paradoxical kinematic behavior, which enhances the unstable condition of the motion segment. Surgical and rehabilitative treatments for patients with segmental instability need to consider the physiologic influences of the spinal musculature.

Experimental disc degeneration due to endplate injury.

The aim of this study was to create an experimental model of disc degeneration that closely mimicked human disc degeneration. In six domestic pigs, an L4 cranial endplate perforation into the nucleus pulposus was made. Three months postoperatively, compressive testing was performed on the L2–L4 motion segments, and intradiscal pressure was measured in the intervening discs. Histochemical and morphologic examinations were made on the excised degenerated and adjacent discs. A significant reduction in water content was observed in the outer anterior annulus of the degenerated disc. In the nucleus, the proteoglycan content was significantly reduced, as well as the cellularity, although not significantly. The nucleus lost its gel-like structure and was discolored, and there was delamination of annular layers. Intradiscal pressure in the nucleus was significantly lower in the degenerated disc. In conclusion, experimental degeneration of the intervertebral disc induced by endplate penetration resembled human disc degeneration, as exemplified by biochemical and structural changes.

Primary Prevention of Back Symptoms and Absence from Work: A Prospective Randomized Study Among Hospital Employees

The personnel at a geriatric hospital were randomized into two groups. One group was allowed to exercise during working hours to improve back muscle strength, endurance, and coordination. The other group did not participate in the exercise program and received no further advice or information. After 13 months, the training group had increased back muscle strength. One subject had been absent from work 28 days in the training group whereas 12 subjects had been absent 155 days from work because of low back pain in the control group (P<0.004). The back pain complaints and intensity of back pain in the training group also decreased in a statistically significant way. Every hour spent by the physiotherapist on the training group reduced the work absence among the participants by 1.3 days, resulting in a cost/benefit ratio greater than 10.

Isometric lifting strength as a predictor of industrial back pain reports

The objective of our investigation was to study Isometric lifting strength in a population of industrial workers who perform a great variety of manual tasks, and to determine whether isometric strength is predictive of future back problems in such a population. Of 3,020 study sub]ects, 2,178 (72%) underwent strength testing In three standard lifting positions. During a 4-year follow-up period, 172 subjects tested reported back problems. When examining each isometric lift separately as a predictor of industrial back pain reports, those with greater Isometric strength were at significantly greater risk than were weaker workers. However, after controlling for the effects of age, only a slight trend remained. For the blue collar workers in this study, isometric lifting strength testing was ineffective in identifying individuals at risk for industrial back problems.

Muscular and kinematic behavior of the lumbar spine during flexion-extension

Reduction in lumbar muscular activity at full body flexion, known as flexion relaxation, has been studied in relation to overall trunk, lumbar spine, and hip flexion, but has not been evaluated in conjunction with motion on the segmental level. In this study, intervertebral motion in a lumbar motion segment, trunk flexion, and the electromyographic activity in the lumbar erector spinae muscles were simultaneously measured during dynamic flexion-extension in seven patients with chronic low back pain with symptoms suggesting segmental instability and in six asymptomatic controls. A linkage system, which attached directly to the spinous processes of a lumbar motion segment, was used to continuously measure the sagittal plane intervertebral motion, while a potentiometric goniometer measured trunk flexion; myoelectric activity was measured using surface electrodes. It was found that intervertebral motions, as well as trunk mobility, were significantly less in the patients, both in terms of range and pattern of motion. Flexion relaxation was demonstrated in the controls by a 78% decrease in myoelectric activity at full flexion, whereas in the patients, only a 13% reduction was found, with most of the patients experiencing no reduction at all. Flexion relaxation occurred only in subjects in whom intervertebral rotation had reached a stage of completion considerably before full trunk flexion was achieved. These findings suggest that persistent muscle activation, which restricts intervertebral motion, is a means by which the neuromuscular system provides stability to help protect diseased passive spinal structures from movements that may cause pain.