A multicenter, prospective, randomized trial evaluating a new hemostatic agent for spinal surgery

STUDY DESIGN

A prospective, randomized trial comparing Proceed, a gelatin-based hemostatic sealant (treatment), with Gelfoam-thrombin (control) in stopping intraoperative bleeding during spinal surgery.

OBJECTIVES

To determine the effectiveness and safety of Proceed.

SUMMARY OF BACKGROUND DATA

Proceed has been tested in animal models to determine its safety and effectiveness as a hemostatic agent. The current study was conducted under a Food and Drug Administration-approved Investigational Device Exemption to evaluate the effectiveness and safety of Proceed in humans.

METHODS

For this study, 127 patients undergoing spinal surgery were randomized into either the treatment or control group after standard surgical means to control bleeding had failed. The bleeding site was evaluated at 1, 2, 3, 6, and 10 minutes after the hemostatic agent was applied. The application was considered successful if the bleeding stopped within 10 minutes. Follow-up evaluation was performed at 12 to 36 hours, then at 6 to 8 weeks after surgery.

RESULTS

Proceed stopped bleeding in 98% of the patients (first bleeding site only) within 10 minutes, as compared with 90% of the control patients (P = 0.001). At 3 minutes, successful hemostasis had been achieved in 97% of the Proceed group, as compared with 71% of the control group (P = 0.0001). There was no difference in the adverse event profile between the two groups.

CONCLUSIONS

A significantly larger number of bleeding sites had achieved hemostasis with Proceed than with Gelfoam-thrombin at 1, 2, and 3 minutes after application. Proceed was as safe as Gelfoam-thrombin when used for hemostasis during spinal surgery procedures.

Effect of endplate conditions and bone mineral density on the compressive strength of the graft-endplate interface in anterior cervical spine fusion

STUDY DESIGN

Destructive compression tests and finite element analyses were conducted to investigate the biomechanical strength at the graft-endplate interface in anterior cervical fusion.

OBJECTIVES

To investigate the effect of endplate thickness, endplate holes, and bone mineral density of the vertebral body on the biomechanical strength of the endplate-graft interface in an anterior interbody fusion of the cervical spine.

SUMMARY OF BACKGROUND

Subsidence of the graft into the vertebral body is a well-known complication in anterior cervical fusion. However, there is no information in the literature regarding the compressive strength of the graft-endplate interface in relation to the endplate thickness, holes in the endplate, and bone mineral density of the vertebral body.

METHODS

Biomechanical destructive compression tests and finite element analyses were performed in this study. Cervical vertebral bodies (C3-C7) isolated from seven cadaveric cervical spines (age at death 69-86 years, mean 79 years) were used for compression tests. Bone mineral density of each vertebral body was measured using a dual energy radiograph absorptiometry unit. Endplate thickness was measured using three coronal computed tomography images of the middle portion of the vertebral body obtained using a computer-assisted imaging analysis. Then each vertebral body was cut into halves through the horizontal plane. A total of 54 specimens, consisting of one endplate and half of the vertebral body, were obtained after excluding eight vertebrae with gross pathology on plain radiograph. Specimens were assigned to one of three groups with different endplate conditions (Group I, intact; Group II, partial removal; and Group III, complete removal) so that group mean bone mineral density became similar. Each endplate was slowly compressed until failure using an 8-mm-diameter metal indenter, and the load to failure was determined as a maximum force on a recorded force-displacement curve. The effect on the strength of the graft-endplate interface of various hole patterns in the endplate was studied using a finite element technique. The simulatedhole patterns included the following: one large central hole, two lateral holes, two holes in the anterior and posterior portion of the endplate, and four holes evenly distributed from the center of the endplate. Stress distribution in the endplate was predicted in response to an axial compressive force of 110 N, and the elements with von Mises stress greater than 4.0 MPa were determined as failed.

RESULTS

The endplate thickness and bone mineral density were similar at all cervical levels, and the superior and inferior endplates had similar thickness at all cervical levels. There was no significant association between bone mineral density and endplate thickness. Load to failure was found to have a significant association with bone mineral density but not with endplate thickness. However, load to failure tends to decrease with incremental removal of the endplate, and load to failure of the specimens with an intact endplate was significantly greater than that of the specimens with no endplate. Finite element model predictions showed significant influence of the hole pattern on the fraction of the upper endplate exposed to fracture stress. A large hole was predicted to be more effective than the other patterns at distributing a compressive load across the remaining area and thus minimizing the potential fracture area.

CONCLUSION

Results of this study suggest that it is important to preserve the endplate as much as possible to prevent graft subsidence into the vertebral body, particularly in patients with poor bone quality. It is preferable to make one central hole rather than multiple smaller holes in the endplate for vascularity of the bone graft because it reduces the surface area exposed to fracture stresses.

Comparison of biomechanical response to surgical procedures used for cervical radiculopathy: posterior keyhole foraminotomy versus anterior foraminotomy and discectomy versus anterior discectomy with fusion

The objective of this study was to compare the change in flexibility of C5-C6 caused by three procedures using a three-dimensional nonlinear finite element model: posterior foraminotomy (keyhole procedure), anterior foraminotomy with discectomy, and anterior discectomy with fusion. The keyhole procedure produced a minor increase in motion. The anterior foraminotomy and discectomy produced one to two times greater motion. Anterior discectomy with fusion produced 50% to 100% reduction in motion. The posterior keyhole foraminotomy has a much lesser effect on the stability of the cervical spine segment than does an anterior procedure, and fusion is a requisite part of the anterior decompression procedure.

The effect of disc degeneration and facet joint osteoarthritis on the segmental flexibility of the lumbar spine

STUDY DESIGN

A biomechanical and imaging study of human cadaveric spinal motion segments.

OBJECTIVE

To investigate the effect of both disc degeneration and facet joint osteoarthritis on lumbar segmental motion.

SUMMARY OF BACKGROUND DATA

Spinal degeneration includes the osteoarthritic changes of the facet joint as well as disc degeneration. Disc degeneration has been reported to be associated with spinal motion. The association of facet joint osteoarthritis with lumbar segmental motion characteristics and the combined influence of disc degeneration and facet osteoarthritis has not yet been investigated.

METHODS

A total of 110 lumbar motion segments (52 female, 58 male) from 44 human lumbar spines were studied (mean age = 69 years). Magnetic resonance images were used to assess the disc degeneration from Grade I (normal) to Grade V (advanced) and the osteoarthritic changes in the facet joints in terms of cartilage degeneration, subchondral sclerosis, and osteophytes. Disc height, endplate size, and facet joint orientation and width also were measured from the computed tomographic images. Rotational movements of the motion segment in response to the flexion, extension, lateral bending, and axial rotational moments were measured using a three-dimensional motion analysis system.

RESULTS

Female motion segments showed significantly greater motion (lateral bending: P < 0. 001, flexion: P < 0.01, extension: P < 0.05) and smaller endplate size (P < 0.001) than male ones. The segmental motion increased with increasing severity of disc degeneration up to Grade IV, but decreased in both genders when the disc degeneration advanced to Grade V. In male segments, the disc degeneration-related motion changes were significant in axial rotation (P < 0.001), lateral bending (P < 0.05), and flexion (P < 0.05), whereas female segments showed significant changes only in axial rotation (P < 0.001). With cartilage degeneration of the facet joints, the axial rotational motion increased, whereas the lateral bending and flexion motion decreased in female segments. In male segments, however, motion in all directions increased with Grade 3 cartilage degeneration and decreased with Grade 4 cartilage degeneration. Subchondral sclerosis significantly decreased the motion (female: axial rotation, P < 0. 05; extension, P < 0.05 vs.- male:flexion,P < 0.05). Severity of osteophytes had no significant association with the segmental motion.

CONCLUSION

Axial rotational motion was most affected by disc degeneration, and the effects of disc degeneration on the motion were similar between genders. Facet joint osteoarthritis also affected segmental motion, and the influence differed for male and female spines. Further studies are needed to clarify whether the degenerative process of facet joint osteoarthritis differs between genders and how facet joint osteoarthritis affects the stability of the spinal motion segment.

Effects of a lifting belt on spine moments and muscle recruitments after unexpected sudden loading

STUDY DESIGN

Ten men and eight women participated in a repeated-measures experiment in which sudden loads were applied unexpectedly to a container held in the hands. Three independent variables were investigated: lifting belt use, preload, and load symmetry.

OBJECTIVES

To determine whether a lifting belt would help protect the spine in sudden symmetric and asymmetric loading situations.

SUMMARY OF BACKGROUND DATA

Unexpected loading events have long been associated with the onset of back pain. Based on work showing that lifting belts restrict motion of the torso, the hypothesis was that a lifting belt would stiffen the spine, thereby protecting its supporting tissues.

METHODS

A weight, equal to 7.5% of the subjects' trunk extension force, was allowed to fall 1 m before the bottom of a box held by blindfolded subjects was pulled. Kinetic and kinematic data, obtained from two force plates and a magnetic motion measurement system, were used in a three-dimensional, dynamic, linked-segment biomechanical model to calculate spine moments. Electromyogram data were simultaneously obtained from eight trunk muscles.

RESULTS

The belt reduced the forward bending of the spine during the symmetric loadings. In the men, the belt also reduced the forward flexion moment acting on the spine. The belt restricted lateral bending in the women and men, when the box was preloaded. The peak electromyogram amplitudes from posterior contralateral erector spinae and latissimus dorsi muscles increased during the asymmetric loadings, whereas three ipsilateral muscles were less active.

CONCLUSIONS

The conflicting moment and electromyographic results, combined with the influence of load symmetry, preload, and gender make the benefits of the lifting belt difficult to delineate. Although the data support the hypothesis that the belt stiffens the torso's response to sudden loading, the effects are small, and considerable individual differences exist. The findings show that during unexpected sudden loading, a belt may reduce the net external moment loading. At the same time the belt appears to alter the muscle response strategy so that the belt's overall effect on an individual's safety is hard to determine.

Association between recovery outcomes for work-related low back disorders and personal, family, and work factors

STUDY DESIGN

Incident cases of work-related low back disorders were identified in an automotive metal stamping plant. Individuals were asked to recall health and work habits at the time of diagnosis of the work-related disorder and to report their current low back pain and physical functioning.

OBJECTIVES

To evaluate five measures of health outcomes for work-related low back disorders in an industrial population and to determine potentially modifiable correlates of recovery.

SUMMARY OF BACKGROUND DATA

The factors that influence recovery in actively working adults and how to best measure recovery outcome in this population are not well known.

METHODS

Eighty-eight hourly employees of a metal stamping plant who experienced a work-related low back disorder were interviewed. Health status, health habits, and family and work relations were assessed with a structured interview to determine their association with various recovery outcomes (low back pain, low back pain disability, physical functioning, general physical health, and lost workdays). Interview information was supplemented with data from the plant's Occupational Safety and Health Administration Form 200 log.

RESULTS

The clinical measures of recovery from the work-related low back disorders examined had similar overall predictive ability. However, in multivariate analyses, different potentially modifiable prognostic variables emerged as significant among them. Poorer self-rated health status and high personal stress were correlated with low back pain disability. Higher levels of cigarette smoking were correlated with higher levels of low back pain disability, lower physical functioning, and more severe low back pain at follow-up.

CONCLUSION

The choice of measure of recovery from work-related low back disorders should be made in the context of the rehabilitation intervention goal. Interventions designed to modify and promote healthful personal behavior should be given more emphasis in rehabilitation efforts for work-related low back disorders.

Anterior cervical fusion: a finite element model study on motion segment stability including the effect of osteoporosis

STUDY DESIGN

Three-dimensional, nonlinear finite element models were used to evaluate the stability of the mid cervical spine after anterior fusion in patients with and without osteoporosis.

OBJECTIVES

The objective of this study was to compare the change in flexibility of C5-C6 after anterior discectomy with both loose-fitting and tight-fitting fusion graft.

SUMMARY OF BACKGROUND DATA

Many factors such as surgical technique, osteoporosis, and excess neck motion during the postoperative period may contribute to fusion failure. Knowledge about changes in biomechanical properties after the surgical procedure is important for selection of grafts with appropriate strength and for guiding patients in postoperative care and rehabilitation.

METHODS

Analyses with anterior fusion models with both loose-fitting and tight-fitting graft were performed in a normal and an osteoporotic spine. The motion of the C5 vertebra in relation to the C6 vertebra were calculated, after multidirectional moment loads of 0.5 Nm combined with a compressive preload of 105 N.

RESULTS

Loose-fitting graft produced both an increase and a decrease in motion under various external moment loads, with graft compressive stress below the compressive strength of the graft material. A reduction in motion was observed under all moment loads when a tight-fitting graft was used. The compressive stress in the tight-fitting graft was higher than the strength of the graft material. Osteoporosis increased the principal motions with both the loose-fitting graft and tight-fitting graft. Maximum increase in motion with a loose-fitting graft construct was observed under extension and axial torsion moment loads.

CONCLUSIONS

Anterior discectomy and insertion of the loose graft resulted in increased motion. A tight-fitting graft is beneficial in reducing motion, but the stress within the graftincreases beyond the graft strength. The presence of osteoporosis was nominally significant when the graft was tight fitting.

Abnormalities in muscle function during gait in relation to the level of lumbar disc herniation

STUDY DESIGN

A comparison between gait in patients undergoing surgery for L4 and L5 lumbar disc herniations and that in an age- and weight-matched control group.

OBJECTIVES

To study whether changes in the moments produced at the ankle and knee joints during walking reflect the neurologic level of a herniated nucleus pulposus.

SUMMARY OF BACKGROUND DATA

Lumbar herniated discs often cause muscle weakness, reduced motor function, and change in walking capacity. The specific effects of a disc herniation on muscle function during gait is poorly documented.

METHODS

Conventional physical examination and kinetic analysis of gait were performed on 16 patients who subsequently underwent surgery for herniated discs (eight with L4-L5 and eight with L5-S1 disc herniations) and 16 healthy control subjects. The three components of the external moment at the ankle and knee were computed. The peak magnitudes of specific components of the external moments were compared with those of the control group.

RESULTS

Reduced external ankle plantar flexion moment, indicating a decreased function of the ankle dorsiflexors, was found in patients with herniated nucleus pulposus of both L4-L5 and L5-S1. Reduced external ankle dorsiflexion moment, indicating a decreased function of the ankle plantar flexors, was found only in patients with a lesion to the L5-S1 disc, but not in those with herniations at L4-L5.

CONCLUSIONS

Preoperative gait analysis identified functional deficits of the muscles about the ankle and foot that relate to the level of the herniation. Kinetic measurements can assist in understanding the functional limitations associated with specific levels of a herniation.

Effect of lifting belts on trunk muscle activation during a suddenly applied load

The National Institute for Occupational Safety and Health suggests there is insufficient biomechanical or epidemiological evidence to recommend the use of back belts in industry. From a biomechanical perspective, previous work suggests that lifting belts stiffen the torso, particularly in the frontal and transverse planes. To determine whether lifting belts stiffen the torso and alter the trunk muscle response during a sudden loading event, we tested the hypotheses that (a) lifting belts alter peak muscle activity recorded with electromyography (EMG) during sudden loading and (b) lifting belts have a larger impact on trunk muscle response when sudden loads are applied asymmetric to the torso's midsagittal plane. A sudden load was delivered to 10 men and 10 women without history of low back disorder via a cable attached to a thoracic harness; motion was restricted to the lumbar spine. Results indicate that gender was not a significant factor in this study. The lifting belt reduced the peak normalized EMG of the erector spinae muscles on average by 3% during asymmetric loading, though peak normalized EMG was increased by 2% during symmetric loading. Lifting belts have been shown to slightly reduce peak erector spinae activity during asymmetric sudden loading events in a constrained paradigm; however, the effects of lifting belts are too small to provide effective protection of workers. Actual or potential applications include the assessment of lifting belts as protective devices in workers based on the effects of lifting belts on the trunk muscle activity.

A comparison of osteopathic spinal manipulation with standard care for patients with low back pain

BACKGROUND

The effect of osteopathic manual therapy (i.e., spinal manipulation) in patients with chronic and subchronic back pain is largely unknown, and its use in such patients is controversial. Nevertheless, manual therapy is a frequently used method of treatment in this group of patients.

METHODS

We performed a randomized, controlled trial that involved patients who had had back pain for at least three weeks but less than six months. We screened 1193 patients; 178 were found to be eligible and were randomly assigned to treatment groups; 23 of these patients subsequently dropped out of the study. The patients were treated either with one or more standard medical therapies (72 patients) or with osteopathic manual therapy (83 patients). We used a variety of outcome measures, including scores on the Roland-Morris and Oswestry questionnaires, a visual-analogue pain scale, and measurements of range of motion and straight-leg raising, to assess the results of treatment over a 12-week period.

RESULTS

Patients in both groups improved during the 12 weeks. There was no statistically significant difference between the two groups in any of the primary outcome measures. The osteopathic-treatment group required significantly less medication (analgesics, antiinflammatory agents, and muscle relaxants) (P< 0.001) and used less physical therapy (0.2 percent vs. 2.6 percent, P<0.05). More than 90 percent of the patients in both groups were satisfied with their care.

CONCLUSIONS

Osteopathic manual care and standard medical care had similar clinical results in patients with subacute low back pain. However, the use of medication was greater with standard care.

The influence of lumbar disc height and cross-sectional area on the mechanical response of the disc to physiologic loading

STUDY DESIGN

The influence of lumbar disc height and cross-sectional area on the mechanical response of the disc to physiologic loading was determined using a finite element model.

OBJECTIVES

To identify which geometric characteristics are potentially related to motion segment mechanical response to applied load, such as flexibility, fiber stress, disc bulge, and nucleus pressure.

SUMMARY OF BACKGROUND DATA

The height and area of the lumbar disc varies within the disc itself, between disc levels, between people, between men and women, with aging, and during the day. Mechanical theory dictates that the height and area influence the mechanical response of the disc to loading. This could have important consequences in risk of injury.

METHODS

Three-dimensional finite-element models representing three disc heights (5.5 mm, 8.5 mm, and 10.5 mm) and three disc areas (1060 mm2, 1512 mm2, and 1885 mm2) were generated. The effect of disc geometry on the mechanical properties of the disc were studied for four moment loads (magnitude, 7.5 Nm) with compressive preload (400 N) and for three different direct forces. Commercially available finite-element software was used.

RESULTS

Discs with a ratio of small disc area to disc height were more prone to larger motion, higher anular fiber stresses, and larger disc bulge. When the disc height alone was increased by a factor, its flexibility also increased, either by the same amount or by a much larger ratio.

CONCLUSIONS

Discs with the most height and smallest area are exposed to much higher risk of failure than other combinations of disc height and geometry.

Epidemiological features of chronic low-back pain

Although the literature is filled with information about the prevalence and incidence of back pain in general, there is less information about chronic back pain, partly because of a lack of agreement about definition. Chronic back pain is sometimes defined as back pain that lasts for longer than 7-12 weeks. Others define it as pain that lasts beyond the expected period of healing, and acknowledge that chronic pain may not have well-defined underlying pathological causes. Others classify frequently recurring back pain as chronic pain since it intermittently affects an individual over a long period. Most national insurance and industrial sources of data include only those individuals in whom symptoms result in loss of days at work or other disability. Thus, even less is known about the epidemiology of chronic low-back pain with no associated work disability or compensation. Chronic low-back pain has also become a diagnosis of convenience for many people who are actually disabled for socioeconomic, work-related, or psychological reasons. In fact, some people argue that chronic disability in back pain is primarily related to a psychosocial dysfunction. Because the validity and reliability of some of the existing data are uncertain, caution is needed in an assessment of the information on this type of pain.

Comparison of five methods used to determine low back disorder risk in a manufacturing environment

STUDY DESIGN

Five methods for quantifying work-related low back disorder (LBD) risk were used to assess 178 autoworkers from 93 randomly selected production jobs.

OBJECTIVE

To determine if five occupational LBD risk evaluation methods yielded similar assessments of manual material handling tasks.

SUMMARY OF BACKGROUND DATA

Several techniques are available for quantifying LBD risk in the workplace and are used in industry for job evaluation and redesign. It is unknown whether the methods yield similar results.

METHODS

The five job evaluation methods were the 1993 National Institute for Occupational Safety and Health model, the Static Strength Prediction Program, the Lumbar Motion Monitor model, and two variations of the United Auto Workers (UAW)-General Motors Ergonomic Risk Factor Checklist. These methods were selected because they represent common practice within the automotive industry, the result of governmental efforts to protect the workforce, or models thought to be the most scientifically advanced.

RESULTS

Intercorrelations between methods ranged between 0.21 and 0.80. Pairwise analysis of risk group classifications identified biases on the part of the National Institute for Occupational Safety and Health equation, which considered jobs to be of higher risk relative to other methods, and on the part of the Static Strength Prediction Program, which considered nearly all the jobs sampled to be low risk.

CONCLUSIONS

There is little agreement among the five quantitative ergonomic analysis methods used. In part, this may be because of their differential focus on acute versus cumulative trauma, thereby suggesting that greater consideration needs to be given to the underlying causes of LBD within a facility before selecting an ergonomic evaluation method.

Study on effect of graded facetectomy on change in lumbar motion segment torsional flexibility using three-dimensional continuum contact representation for facet joints

Facet joints provide rigidity to the lumbar motion segment and thus protect the disk, particularly against torsional injury. A surgical procedure that fully or partially removes the facet joints (facetectomy) will decrease the mechanical stiffness of the motion segment, and potentially place the disk at risk of injury. Analytical models can be used to understand the effect of facet joints on motion segment stability. Using a facet joint model that represents the contact area as contact between two surfaces rather than as point contact, it was concluded that a substantial sudden change in rotational motion, due to applied torsion moment, was observed after 75 percent of any one of the facet joints was removed. Applied torsional moment loading produced coupled extension motion in the intact motion segment. This coupled motion also experienced a large change following complete unilateral facetectomy. Clinically, the present study showed that surgical intervention in the form of unilateral or bilateral total facetectomy might require fusion to reduce the primary torsion motion.

The effects of lifting speed on the peak external forward bending, lateral bending, and twisting spine moments

Lifting tasks that involve twisting have been repeatedly implicated as contributing to the onset of occupational back injuries in epidemiological studies. The objective of this work was to quantify the three directional external moments acting on the spine during a sagittally symmetric and two asymmetric lifting tasks. A total of 15 subjects participated in the three lifting tasks. All tasks were performed at two qualitatively defined lifting speeds, 'slow' and 'fast', and with two load magnitudes: 10 and 20% of the subject's body weight. The mid-sagittal plane lifts were performed using two horizontal reach distances: 40 and 60 cm. A four-camera, two-forceplate motion and force measurement system were used to obtain the kinematic and kinetic data as the lifts were performed. A dynamic link-segment biomechanical model was used to quantify the reaction forces and moments at the ankle, knee, and hip and L5/S1 joints. Results from all tasks showed increased sagittal plane (forward bending) spine moments with the heavier load and at the faster lifting speed (p < 0.001). Spine lateral bending and twisting moments increased during the mid-sagittal plane lifts with the greater reach distance and the faster lifting speed, respectively. The twisting moments on the spine were greatest as subjects lifted from in front and placed the load to the side but were dependent upon the lifting speed and the load magnitude. The lateral bending moments increased during this same task with the heavier load. However, the spine lateral bending moments were greatest when lifting from one side to the other.

A prospective study of 342 patients using transpedicular fixation instrumentation for lumbosacral spine arthrodesis

The objective of this research was to determine the efficacy and safety of an experimental instrumentation device designed for transpedicular spinal fixation by evaluating fusion rates and clinical pain and function scores; to determine complication rates associated with the device; and to compare the obtained data with that previously published in the literature. Four hundred forty-two consecutive patients were enrolled in this 4-year, Food and Drug Administration-monitored investigational device exemption trial to undergo surgery for implantation of the device. Eighteen surgeons at 11 nationwide medical centers performed the operations and subsequent evaluations. The study population was derived from three diagnostic categories: degenerative disc disease, multioperated back, and vertebral fracture. The data source consisted of radiographs, clinical examination, and structured forms and questionnaires. Patients were evaluated preoperatively, intraoperatively, and postoperatively at 3, 6, 12, and 24 months. By the 24-month postoperative interval, attrition had reduced the study population to 342 patients, among whom bony fusion was obtained in 91.5%. Pain scores demonstrated a statistically significant improvement in clinical outcome. Intraoperative complications occurred in 21.9% of patients. Of the 442 study patients, 2.9% experienced device-related complications. Moreover, a total of 2,304 screws and bolts were implanted in this patient population. Of these, 0.39% were reported to have fractured. Among the 342 study patients observed during 24 months, the breakage rate of device components (bolt or screw) was 2.63%. These data compare favorably to existing reports of spinal arthrodesis effected with other types of instrumentation and without device implantation. In a 4-year trial, the experimental transpedicular fixation instrumentation produced successful spinal fusion in the majority of our study population, with acceptable complication rates.

A new culture system to study the metabolism of the intervertebral disc in vitro

STUDY DESIGN

This study determined whether entrapment of a rabbit intervertebral disc in alginate gel helped to promote the retention of normal metabolic activities by the nucleus pulposus and anulus fibrosus in tissue culture.

OBJECTIVES

To establish an in vitro culture system to study the metabolism of the intervertebral disc as a whole integral organ.

SUMMARY OF BACKGROUND DATA

In vitro studies of the metabolism of intervertebral discs have been scarce because of the difficulties involved in maintaining the integrity of the tissues, especially that of the nucleus pulposus, in culture medium.

METHODS

Rabbit intervertebral discs were embedded in alginate gel and maintained in culture for as long as 1 month. At weekly intervals, experiments were performed to measure the rate of proteoglycan synthesis and to characterize proteoglycans newly synthesized by cells in the anulus fibrosus and nucleus pulposus. In addition, at these same time intervals, the contents of sulfated proteoglycans, antigenic keratan sulfate, hyaluronan, and collagen in these two intervertebral disc tissues were measured to evaluate tissue integrity. Intervertebral discs cultured in medium alone were used as controls and analyzed in parallel.

RESULTS

The anulus fibrosus and nucleus pulposus of intervertebral discs cultured in alginate gel sustained a higher rate of proteoglycan synthesis and maintained a higher content of extracellular matrix components than the respective controls at all times.

CONCLUSIONS

This new alginate tissue culture system should prove useful for studying the metabolism of whole intervertebral discs.

Trunk kinematics and trunk muscle activity during a rapidly applied load

This study investigated the trunk kinematics and electromyographic (EMG) activity of eight trunk muscles when "expected" and "unexpected" loads were applied directly to the torso. Twenty individuals (mean age: 25.1 yr; range 20-33 yr) participated in this mixed model study in which gender was the between-subjects factor, and expectancy and symmetry of the applied load were within-subject factors. The sudden load was delivered to the subject via a cable attached to a thoracic harness and motion was restricted to the lumbar spine by strapping the pelvis to a rigid fixation apparatus. Surface EMG was recorded bilaterally from the longissimus thoracis (LGT), erector spinae (ERS), rectus abdominis (RAB) and the external obliques (EXO). Trunk kinematics were measured with a Lumbar Motion Monitor. During expected loading conditions, the peak muscle activity was reduced for the RAB and EXO bilaterally, and for the ERS(R) (p < 0.01) relative to the unexpected conditions. Conversely, the normalized area of EMG activity prior to the onset of load was increased for the ERS and EXO bilaterally, and for the RAB(R) (p < 0.05) during an expected loading event. Trunk motion in the sagittal and frontal planes was reduced during expected loading. Activation of the trunk muscles just prior to a rapid loading event increases trunk stiffness, decreasing trunk displacement and peak muscle activity.

Diagnostic considerations in patients with back pain

It should be obvious from this article that usually only a focused history and physical examination are needed to evaluate a back patient. A summary of guideline recommendations presented by the Agency for Health Care Policy and Research is provided in Table 7. If followed, few serious mistakes will occur, and a more cost-effective management of the back patient will be possible.

Trunk muscle use during pulling tasks: effects of a lifting belt and footing conditions

Pulling tasks require the torso to act as a rigid link in order to facilitate the force transmission between the ground and the hands. In this study, we tested the hypothesis that a lifting belt increases the rigidity of the torso, thereby increasing pulling strength or reducing trunk muscle forces, or both, as pulling tasks are performed. Twelve volunteers performed maximal and submaximal isometric pulling exertions; the latter were performed on nonslippery and slippery surfaces. Electromyographic data from 8 trunk muscles, trunk kinematic data, and ground reaction forces were sampled during each exertion. Results indicated that the lifting belt had no effect during maximal exertions on the maximal pull forces generated or the muscle recruitment levels, irrespective of the pulling posture. The lifting belt did not affect the EMG data obtained during the submaximal (40% of maximum) exertions, even when participants pulled on a slippery surface. However, the slippery surface increased the coactivation within the trunk musculature, perhaps stiffening the torso in the event of a slip. The absence of a statistical interaction effect between the lifting belt and the footing condition (slipperiness) indicates that the belt did not alter the coactivation pattern and hence was not relied upon by the participants as a protective mechanism. The data presented here will assist those who must make decisions regarding lifting-belt use and those who train individuals in manual materials handling techniques.

What are the age-related changes in the spine?

Degenerative changes of the spinal column have long been and continue to be confused with the presence of spinal distress and pain. All parts of the spine undergo degenerative changes as we age. The purpose of this chapter is to describe the degenerative process and its clinical consequences. The disc degenerative process will be discussed; its consequences on the facet joint and osteophyte formation are considered. The prevalence of disc degeneration, the role of physically demanding work and leisure and the interference of spinal deformity is clarified. A section particularly important for the clinician deals with the clinical consequences of the degenerative process in disc herniation, degenerative spondylolisthesis, spondylolysis and stenosis. This chapter tries to put the degenerative changes of the spine into the context of a normal ageing process.

Metabolism of the extracellular matrix formed by intervertebral disc cells cultured in alginate

STUDY DESIGN

Cells from normal rabbit nucleus pulposus (NP) and anulus fibrosus (AF) were cultured in alginate beads for as long as 14 days to allow them to reform a matrix made up of two compartments: the cell-associated matrix (CM) and further removed matrix (FRM). At different time points, the CM and FRM made by each cell population were analyzed using histologic, biochemical, and immunologic assays.

OBJECTIVES

To study the metabolism of normal rabbit NP and AF cells in alginate by characterizing the CM and FRM formed by each cell population, and to identify metabolic properties that may shed light on mechanisms at play in disc degeneration.

SUMMARY OF BACKGROUND DATA

Little is known about the metabolism of intervertebral disc cells, in part because of the lack of microculture systems appropriate for the study of these cells in vitro. In recent studies from our laboratories, it was suggested that articular chondrocytes cultured in alginate beads remain phenotypically stable and reform a matrix similar to the one they populate in vivo. This culture system appears ideally suited for the study of intervertebral cells available only in limited numbers.

METHODS

Rabbit NP and AF cells released from the matrix by sequential enzyme digestion were encapsulated in alginate beads (20,000 cells/bead) and cultured for as long as 14 days. At selected time points, beads were solubilized with calcium chelating agents, and the CM and FRM were isolated. The rate of 35S-sulfate incorporation into proteoglycans, and the contents of various extracellular matrix molecules (total sulfated proteoglycans, antigenic keratan sulfate, hyaluronan, collagen, and pyridinium crosslinks) were measured.

RESULTS

Both NP and AF cells remained phenotypically stable in the alginate gel throughout the culture period and reestablished a matrix composed of CM and FRM compartments. The two cell populations exhibited numerous differences in their metabolic activities in vitro. Nucleus pulposus cells synthesized fewer proteoglycan and collagen molecules and were less effective in incorporating these into the CM than AF cells.

CONCLUSIONS

Intervertebral disc cells, especially NP cells, are extremely sluggish in reforming a CM, a protective shell rich in proteoglycans and collagen molecules. This may help explain why damage to the NP often is accompanied by progressive degeneration of the disc in vivo.

History and physical examination in patients with herniated lumbar discs

To outline the usefulness of the medical history and physical examination in the diagnosis of herniated lumbar discs, and to review the essential properties of a test, including sensitivity, specificity, and clinical value. None of the tests that are part of a history and physical examination of a patient with a disc herniation has a high diagnostic accuracy by itself. This is because positive and negative predictive values of common clinical indicators are limited. Confirmatory tests are necessary for a definitive diagnosis when making management decisions. Combining the results of history and physical findings will increase the predictive value of these basic diagnostic tools.

Consensus summary of the diagnosis and treatment of lumbar disc herniation

Clinicians must not simply decide that a patient with symptoms and a positive diagnostic test has a reason for a specific treatment, and likewise clinicians must not decide that a patient with symptoms and a negative test does not have a clinically important problem. We must also consider the sensitivity, specificity and predictive value of the diagnostic test and the individual characteristics of the patient. Treatment outcome depends on many factors. Point of service decisions vs population based decisions are obviously different. Each patient presents to the treating practitioner on a given day, at a given time, and it is this picture upon which a plan of care is formulated.

Factors influencing the cost of chronic low back injuries: An analysis of data from independent medical examinations

Cost factors were examined in 157 patients with work- related spine injuries who were referred to a second opinion program between 1985 and 1991. The independent medical examination (IME) included a history, physical examination, and review of imaging and other studies. Data on demographic variables, litigation, work, injury history, physical examination, and imaging studies were recorded. A standard measure of psychological status (Low Back Pain Symptom Check List) was filled out. The instrument uses pain language as a clinical marker of psychological disturbance linked to a range of conflictual issues such as suppressed anger, burdensome feeling of inferiority, damaged self- esteem, role confusion, abnormal mentation, fear of responsibility or intimacy, gender issues, sexual concerns, disturbing arousal, and the like. Since it relies exclusively on pain language for diagnosis, it does not identify the specific nature of the psychological conflict. Data on treatment, final resolution, and cost were obtained from computerized files of the insurance company. The total cost incurred was $6,551,139. This averaged to $41,727 per case. More expensive cases were associated with a surgical intervention, psychological disturbance, litigation, motor weakness, and positive radiographs. These five variables accounted for 48% of the cost variance. Surgery accounted for 19.9% of the variance and contained the most expensive cases ($68,310 vs. $31,423). Psychological disturbance was detected in 27% of the sample and accounted for 10.5% of the cost variance. Litigation was present in 72% of the cases and accounted for 9.1% of the cost variance. Motor strength and radiographs taken together accounted for 8.4% of the variance. The usefulness of this information was explored from an actuarial and medical perspective.

Bacterial discitis caused by limb gangrene requiring below-knee amputation

Two patients presented with disabling back pain and were unable to participate in physical therapy activities after being admitted to an acute rehabilitation center. Both patients had bacterial discitis of the lumbar spine that was apparently caused by infected ischemic limb tissue, ultimately removed at below-knee amputation. The literature describes many cases of bacterial discitis infected from many sources, but not from ischemic limb tissue requiring subsequent amputation. Many such cases may exist, however, and earlier recognition of this condition will enable appropriate treatment before vertebral destruction and/or neurological sequelae.

Effect of lifting belts, foot movement, and lift asymmetry on trunk motions

Whether or not lifting belts protect workers from injury is a topic of considerable interest in industry. Not only is the protective effect uncertain, but the biomechanical basis for belt function is unclear. The objective of this study was to determine if lifting belts provide a means for controlling trunk motions during asymmetric material-handling tasks. We recruited 16 nursing personnel as experienced lifters to participate in two lifting sessions. A lifting belt was worn in one session and for a week prior to this session during the subjects' routine work activities. Each session required 42 lifts, distributed across three asymmetry conditions (0, 45, and 90 deg) and temporally spaced 30 s apart. Foot motion was not permitted in half the lifts. Results indicated that during lifting, lateral bending and twisting motions were reduced by both the lifting belt and foot motion; the most pronounced effect was observed at 90 deg of asymmetry. Trunk motions in the sagittal plane during lifting were not affected by the lifting belt. These results appear to support the use of lifting belts in asymmetric lifting conditions, but more research is needed to determine whether the muscles in the torso benefit from the reduced motion or are working harder to overcome this resistance to motion, causing increased internal loads on the spine during asymmetric material-handling tasks.

Epidural administration of methylprednisolone and morphine for pain after a spinal operation. A randomized, prospective, comparative study

The results of postoperative epidural administration of saline solution (a placebo), morphine, methylprednisolone, and a combination of morphine and methylprednisolone for the reduction of pain after an operation for spinal stenosis or a herniated intervertebral disc were compared in a prospective, randomized blinded study. Epidural administration of morphine and methylprednisolone--either alone or in combination--significantly reduced the need for analgesia after an operation for spinal stenosis (p < 0.05) but not after an operation for a herniated intervertebral disc. Morphine and methylprednisolone did not have an addictive effect on the reduction of pain. Itching was significantly more common in the patients who had received morphine than in those who had received the placebo (p = 0.04). Although urinary retention was more frequent after the use of morphine than after the use of the placebo, the difference was not significant with the size of the sample that was analyzed (p = 0.25).

The influence of initial horizontal weight placement on the loads at the lumbar spine while lifting

STUDY DESIGN

This was a biomechanical study of the effect of the initial horizontal distance between a person lifting and the load. Experimental data were analyzed using a dynamic rigid link model.

OBJECTIVE

To determine the effect of the initial horizontal load placement on the moments acting on the lumbar spine and the lower extremity joints during lifting, and to determine the role of the lower extremities during lifting from the floor.

SUMMARY OF BACKGROUND DATA

Epidemiologic studies have implicated lifting as a cause of back pain, and over 80% of all worker's compensation back injuries are considered to be caused by manual material handling Guidelines have been proposed to increase the safety of lifting, but they are primarily based on static biomechanical analyses, psychophysical data, and physiologic limitations.

METHODS

Each of 12 male subjects lifted a weight box containing 0 to 300 N, in 100-N increments. Each subject performed 20 lifts--four weights at five horizontal distances (20, 30, 40, 50 and 60 cm). Motion was measured with an optoelectronic system, ground reaction forces were measured with a force plate, and moments were calculated using a rigid link model.

RESULTS

The peak predicted L5-S1 moment increased as the weight and horizontal distance increased. The influence of horizontal distance on moment magnitude was nonlinear. As the distance changed from 20 to 40 cm, the distance-related rate of increase was approximately one-half of that occurring with a distance change from 40 to 60 cm. This can be explained by the need to reach out further, beyond 40 cm, which is accomplished by a deeper flexion of the knees and ankles and an anterior translation of the upper body and arms.

CONCLUSION

As the horizontal distance at the start of a lift increased, the peak moment acting on the lumbar spine also increased, but the increase was nonlinear. This is explained by a change in the technique of lifting when the distance is 40 cm or greater.

Variance in the measurement of sagittal lumbar spine range of motion among examiners, subjects, and instruments

STUDY DESIGN

Repeated measurements were made of lumbar sagittal range of motion by 14 examiners using three different measurement instruments.

OBJECTIVES

To determine the reliability of lumbar range of motion measurements among examiners, subjects, and instruments, and to determine whether variance is due to subject inconsistency, examiner inconsistency, differences between examiners, or differences between instruments.

SUMMARY OF BACKGROUND DATA

Measurements of lumbar spine range of motion are widely used in research and clinical applications as well as in disability rating systems for patients with low back pain.

METHODS

Fourteen examiners measured the sagittal range of motion. Using three instruments, 18 healthy subjects were measured twice in a randomized sequence with blinded readings when performing full flexion, and partial flexion to a defined midpoint. None of the examiners routinely used the particular instruments in their practices.

RESULTS

The mean test-retest reliability was 4.9 degrees. The intraexaminer reliability did not differ significantly among the examiners. Furthermore, there was no systematic difference resulting from instruments or posture condition. However, there was a statistically significant variance among examiners--i.e., a poor interexaminer reliability.

CONCLUSION

The most likely explanation for these findings is the variability among examiners in locating bony landmarks. The results indicate that range of motion measurements must be interpreted with caution in clinical, research, and disability applications. Test administrator training may improve results, but this could not be determined from this study.

The effects of lateral trunk bending on muscle recruitments when resisting nonsagittally symmetric bending moments

STUDY DESIGN

Surface electromyographic activities were measured in 15 subjects as they maintained a static laterally bent trunk posture and resisted sagittally symmetric and asymmetric moments applied to their torsos. The moment magnitudes were 20 and 40 Nm and had transverse plane directional components in 30 degrees increments surrounding the subjects' torsos.

OBJECTIVES

To quantify the myoelectric responses from eight trunk muscles as asymmetric loads were applied to the laterally bent torso.

SUMMARY OF BACKGROUND DATA

Asymmetric material handling frequently results in lateral bending of the torso. Each of these factors have been linked via epidemiologic investigations to the incidence of low back disorders. Little information is available that describes the response of the trunk muscles when the trunk is bent to the side.

METHODS

Subjects stood in a reference frame and adjusted their trunk posture to marks on a video display that indicated when a 20 degrees lateral bend to the right had been achieved. Moments were applied to the torso by connecting weights via cables and pulleys to a chest harness. Electromyographic activities were recorded bilaterally from the erector spinae, latissimus dorsi rectus abdominis, and external oblique muscles.

RESULTS

The electromyographic data indicated that the muscles showed the greatest activity when they were in opposition to the applied sagittal and frontal plane moments. The left external oblique showed the greatest response and was sensitive to the widest range of moment direction conditions. All of the muscles, except for the left latissimus dorsi, at times contributed antagonistic moments in the sagittal plane or the frontal plane, or in both planes. These data were compared with previously obtained data from an upright neutral posture.

CONCLUSIONS

Statistical analyses indicated that the responses of both external obliques and the left erector spinae to the moment direction conditions were significantly different between the laterally bent and neutral postures.

Trunk strength testing in patient evaluation and treatment

A wide variety of trunk strength testing devices has been developed, the goal being to quantify back strength, patient effort, and spinal function or dysfunction. Although the idea of applying quantitative values to spine function is appealing, controversy exists regarding the reliability and validity of these testing systems. In this issue, two experienced investigators give their opinions as to the values and pitfalls of lumbar trunk strength testing, and provide insight into the most appropriate applications of these often costly systems.

Evaluation of muscle force prediction models of the lumbar trunk using surface electromyography

Optimization-based models for prediction of muscle forces in the lumbar region of the torso are used to estimate the forces acting on spinal motion segments, especially for asymmetric tasks. The objectives of this study were to determine (a) which of four torso model formulations best predicted the electromyographic data, (b) the difference in muscular contribution to spinal compression force for the four models, and (c) the effect of using the lowest possible muscle stress bound in the model formulation. An approach for the investigation of competing optimization model formulations was developed and was illustrated with electromyographic data from static asymmetric loading conditions. This method is based on (a) the choice of experimental conditions in which models predict decidedly different muscle forces, and (b) the ability to ensure that the experimental conditions are such that the minimum number of assumptions about the force-electromyogram relationship must be made in order to choose between competing model predictions. Of the four models analyzed, only the formulation with an objective function that was the sum of cubed muscle stresses predicted the electromyographic data acceptably. The muscular contribution to spinal compression force predicted by these models differed by as much as 160% for some experimental conditions. The use of the lowest possible muscle stress bound does not appear to predict muscle forces that are in agreement with electromyographic data.

The dose-related effect of intradiscal chymopapain on rabbit intervertebral discs

STUDY DESIGN

This study analyzed the histological and biochemical responses of intervertebral disc tissue to intradiscal injection of varying amounts of chymopapain.

OBJECTIVE

To determine the appropriate amount of chymopapain needed to accomplish effective degradation of proteoglycans (PG) in the nucleus pulposus of intervertebral discs.

SUMMARY OF BACKGROUND DATA

Chymopapain is an accepted treatment alternative for patients with disc herniations. The recommended clinical dose of 2,000-4,000 pKats per injection is derived from early animal studies and empirical results in man. A lower effective dose could reduce the complication rate while providing similar clinical results.

METHODS

Twenty to 4,000 pKat of chymopapain was injected into rabbit discs, and the level of keratan sulfate (KS) epitope in serum was measured at different times after the injection. The animals were killed after 6 days and the injected and two neighboring discs were examined histologically.

RESULTS

The serum KS level did not change appreciably after injection of 20 pKat, rose moderately at 100 and 200 pKat, and rose strongly at 500 pKat. Doses greater than 500 pKat did not result in further increase in the KS level.

CONCLUSION

Degradation of the disc proteoglycans is dose dependent and reaches a maximum at 500 pKat. Higher doses appear not to cause further loss of aggrecan molecules, and injection of more than 1,000 pKat produces significant annular destruction.

Trunk muscle activation. The effects of torso flexion, moment direction, and moment magnitude

OBJECTIVES

This study was performed to quantify the electromyographic trunk muscle activities in response to variations in moment magnitude and direction while in forward-flexed postures.

METHODS

Recordings were made over eight trunk muscles in 19 subjects who maintained forward-flexed postures of 30 degrees and 60 degrees. In each of the two flexed postures, external moments of 20 Nm and 40 Nm were applied via a chest harness. The moment directions were varied in seven 30 degrees increments to a subject's right side, such that the direction of the applied load ranged from the upper body's anterior midsagittal plane (0 degree) to the posterior midsagittal plane (180 degrees).

RESULTS

Statistical analyses yielded significant moment magnitude by moment-direction interaction effects for the EMG output from six of the eight muscles. Trunk flexion by moment-direction interactions were observed in the responses from three muscles.

CONCLUSIONS

In general, the primary muscle supporting the torso and the applied load was the contralateral (left) erector spinae. The level of electromyographic activity in the anterior muscles was quite low, even with the posterior moment directions.

A model to study the disc degeneration process

Initiation and propagation of different types of events that lead to disc degeneration and the effect of the degenerating process on the disc mechanical performance is difficult to study by experimental methods. This study aimed to develop and use a finite element model of a motion segment without posterior elements to study the disc degeneration process. The model was used to study the development of anular tears, nuclear clefts, and endplate fractures and subsequent propagation of these degenerative processes due to compressive and bending loads. The analyses showed that the failure always started at the end plates indicating that they are the weak link in the body-disc-body unit. The analyses also showed that anular injuries are unlikely to be produced by pure compressive loads. The model predicted that it would require a larger extension moment as compared to flexion moment to initiate and propagate failure in a motion segment, which leads to the conclusion that the motion segment is stiffer in extension. The model also suggested that the presence of discrete peripheral tears in the anulus fibrosus may have a role in the formation of concentric anular tears and in accelerating the degenerating process of the disc.

The influence of load knowledge on lifting technique

The purpose of this study was to analyse the influence of load knowledge on lifting technique. Ten men lifted a box containing either no weight or weights of 150, 250 or 300 N with and without knowledge of what was inside the box. The kinetics and kinematics of the lift were analysed using a force plate, an optoelectronic motion analysis system, and a rigid body link model. At 0 N lifting, the unknown load resulted in a jerk-like motion and a significantly increased peak L5-S1 flexion-extension moment. At 150 N there was also a significant increase in the speed of trunk extension with unknown weights, but the L5-S1 moment remained unchanged. At higher load levels there were only minor differences between lifting techniques when knowing and not knowing the load. We conclude that lifts are approached assuming a certain weight, and that when the assumption is wrong and the load lighter than anticipated lifting is performed with a 'jerking' motion, creating unnecessary loads on the lower back.