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Biomedical subjects

Gunnar B J Andersson

Publications and source records attributed to Gunnar B J Andersson.

At least 19 recordsLinked to original sources
PubMed2006

Inclusion of regional poroelastic material properties better predicts biomechanical behavior of lumbar discs subjected to dynamic loading.

Understanding the relationship between repetitive lifting and the breakdown of disc tissue over several years of exposure is difficult to study in vivo and in vitro. The aim of this investigation was to develop a three-dimensional poroelastic finite element model of a lumbar motion segment that reflects the biological properties and behaviors of in vivo disc tissues including swelling pressure due to the proteoglycans and strain-dependent permeability and porosity. It was hypothesized that when modeling the annulus, prescribing tissue specific material properties will not be adequate for studying the in vivo loading and unloading behavior of the disc. Rather, regional variations of these properties, which are known to exist within the annulus, must also be included. Finite element predictions were compared to in vivo measurements published by Tyrrell et al. (1985) of percent change in total stature for two loading protocols, short-term creep loading and standing recovery and short-term cyclic loading with standing recovery. The model in which the regional variations of material properties in the annulus had been included provided an overall better prediction of the in vivo behavior as compared to the model in which the annulus properties were assumed to be homogenous. This model will now be used to study the relationship between repetitive lifting and disc degeneration.

Biomechanical Phenomena↗
PubMed2006

Participation in occupational health longitudinal studies: predictors of missed visits and dropouts.

PURPOSE: The purpose of this study is to determine whether demographics, health, and job factors influence continued participation of employed persons in a longitudinal intervention study of tertiary prevention for work-related low-back disorders (WR-LBDs). METHODS: Four hundred fifty-four actively employed persons had enrolled in an intervention study of back supports and education to promote recovery from a WR-LBD. Baseline values were examined according to whether individuals continued in the study, missed a visit, or dropped out; frequency of missed visits; and early or late dropouts at follow-up intervals of 1, 2, 6, and 12 months. RESULTS: Workers who did not complete all study visits were significantly more likely to be younger and have poorer self-reported health. Individuals with a greater percentage of body fat dropped out early. Significantly more missed visits were observed among those who had arthritis and longer duration of low-back pain symptoms. Job factors did not influence study participation. CONCLUSIONS: Continued participation in a longitudinal study of working adults was influenced by age, health status, and factors related to the primary condition targeted by the intervention study. Strategies aimed at those who report lower levels of health and symptoms related to the condition under study may promote follow-up participation in longitudinal studies. Thus, even among actively employed persons, one should not assume that all workers are "healthy."

Adiposity↗
PubMed2006

Intradiscal injections of osteogenic protein-1 restore the viscoelastic properties of degenerated intervertebral discs.

BACKGROUND CONTEXT: Using biochemical, histological, and radiological parameters in a rabbit model of intervertebral disc (IVD) degeneration, the intradiscal injection of a growth factor, such as osteogenic protein-1 (OP-1), has been shown to regenerate the IVD. However, very little is known about how such a biological therapeutic approach affects the biomechanical properties of the degenerated IVD. PURPOSE: To investigate the effects of an intradiscal injection of OP-1 on the biomechanical properties of IVDs in the rabbit annular-puncture disc degeneration model and to determine their relationship to biochemical properties. STUDY DESIGN/SETTING: In vivo study on the effects of intradiscally administered OP-1 on the biomechanical and biochemical properties of IVDs in the rabbit annular-puncture disc degeneration model. METHODS: New Zealand White rabbits (n=16) underwent annulus fibrosus (AF) puncture, using an 18-gauge needle, at L2-L3 and L4-L5 (L3-L4: nonpunctured control). Four weeks later, the punctured discs received an injection of either 5% lactose (10 microL) or OP-1 (100 microg/10 microL of 5% lactose) into the nucleus pulposus (NP). The disc height was radiographically monitored biweekly. After sacrifice and removal of bone-disc-bone complexes 8 weeks postinjection, the dynamic viscoelastic properties of the IVDs were tested by applying a cycle of sinusoidal strain in uniaxial compression at six loading frequencies (0.05 to 2 Hz). The biochemical properties of the dissected IVDs were then analyzed and correlated with the biomechanical properties. RESULTS: A single injection of OP-1 significantly restored disc height when compared with the lactose-injected discs (OP-1 vs. lactose, p<.001). The elastic modulus of the IVDs in the OP-1-injected discs was significantly higher than that in the lactose-injected discs at all frequencies (mean: +43%, p<.001). The viscous modulus in the OP-1-injected discs was significantly higher at 0.05, 0.2, 0.5, and 1 Hz (mean: +55%, p<.001) and showed higher tendencies at other frequencies (p=.08-.09). For both moduli, no significant differences were observed between the OP-1-injected and the nonpunctured control discs. The OP-1 injection significantly increased the proteoglycan (PG) content in the NP and AF, and the collagen content in the NP (p<.001-.05). Both elastic and viscous moduli showed significant positive correlations with PG content in the NP and collagen content in the NP and AF (Rho=.357-.466, p=.010-.047). CONCLUSIONS: We have shown for the first time that an injection of the growth factor, OP-1, restored the biomechanical properties of IVDs in a rabbit model of IVD degeneration. Comparing biomechanical with biochemical data suggests that the OP-1-induced biomechanical restoration was a consequence of increased activities of anabolic pathways that resulted in biochemical changes in the IVD.

Animals↗
PubMed2006

Three-dimensional in vivo measurement of lumbar spine segmental motion.

STUDY DESIGN: Fifteen asymptomatic volunteers were externally rotated and CT scanned to determine lumbar segmental motion. OBJECTIVES: To measure three-dimensional segmental motion in vivo using a noninvasive measurement technique. SUMMARY OF BACKGROUND DATA: Spinal instability has been implicated as a potential cause of low back pain, especially, axial rotational instability. Typically, flexion-extension lateral radiographs were used to quantify instability, but inaccurately measured translations and inability to capture out-of-plane rotations are limitations. METHODS: Using a custom-calibrated rotation jig, L1-S1 CT reconstructions were created of volunteers in each of 3 positions: supine and left and right rotations of the torso with respect to the hips. Segmental motions were calculated using Euler angles and volume merge methods in three major planes. RESULTS: Segmental motions were small (< 4 degrees or 6 mm) with the greatest motions seen in axial rotation (range, 0.6 degrees to 2.2 degrees ), lateral bending (range, -3.6 degrees to 3.0 degrees ), and frontal translation (-1.2 mm to 5.4 mm). Largest motions were in the levels: L1-L2 to L3-L4. CONCLUSIONS: Complex coupled motions were measured due to external torsion and could be indicative of instability chronic patients with low back pain. The presented data provide baseline segmental motions for future comparisons to symptomatic subjects.

Adult↗
PubMed2006

Novel model to analyze the effect of a large compressive follower pre-load on range of motions in a lumbar spine.

A 3-D finite element model (FEM) of the lumbar spine (L1-S1) was used to determine the effect of a large compressive follower pre-load on range of motions (ROM) in all three planes. The follower load modeled in the FEM produced minimal vertebral rotations in all the three planes. The model was validated by comparing the disc compression at all levels in the lumbar spine with the corresponding results obtained by compressing 10 cadevaric lumbar spines (L1-S1) using the follower load technique described by Patwardhan et al. [1999. A follower load increases the load-carrying capacity of the lumbar spine in compression. Spine 24(10), 1003-1009]. Further validation of the model was performed by comparing the lateral bending and torsion response without pre-load and the flexion-extension response without pre-load and with an 800 N follower pre-load with those obtained using cadaver lumbar spines. Following validation, the FEM was subjected to bending moments in all three planes with and without compressive follower pre-loads of up to 1200 N. Disc compression values and the flexion-extension range of motion under 800 N follower pre-load predicted by the FEM compared well with in vitro results. The current model showed that compressive follower pre-load decreased total as well as segmental ROM in flexion-extension by up to 18%, lateral bending by up to 42%, and torsion by up to 26%.

Adaptation, Physiological↗
PubMed2006

Risk factors for recurrent episodes of work-related low back disorders in an industrial population.

STUDY DESIGN: An observational longitudinal design. OBJECTIVES: To characterize the rate of and risk factors for recurrent episodes of work-related low back disorder in industrial workers. SUMMARY OF BACKGROUND DATA: Little data exist on risk factors for recurrent episodes of work-related low back disorders in employed persons. METHODS: A total of 352 active hourly union employees who were diagnosed with a recent work-related low back disorder and who had at least one follow-up visit within 12 months enrolled for participation in a rehabilitation intervention study at the workplace. Information on clinical and job factors was obtained at each study visit. Job risk for low back disorder was quantified using the Lumbar Motion Monitor. The main outcome measure, recurrence of work-related low back pain, was derived from a computerized file of administrative records of visits to the plant's medical department. RESULTS: The rate of repeated episodes was 24.4%; an additional episode occurred in 2.3%. Adjusting for age, gender, health status and job exposures, lower levels of physical health, increasing back pain disability, spinal deformity, high stress, and increasing number of different jobs worked at the same plant were risk factors for a recurrent episodes of low back pain. CONCLUSIONS: Early identification of risk factors for a work-related low back disorder may signal the need for early and intense rehabilitation to prevent recurrent episodes. Because these findings were based on jobs with medium risk of low back disorders, other factors may be significant in higher risk jobs.

Adult↗
PubMed2006

Sexual dimorphism in degenerative disorders of the spine.

Sexual dimorphism is evident during formation, growth, and development of the spine. Pregnancy alters spine physiology and is a risk factor for back pain. The processes of aging and spinal degeneration adversely affect men and women slightly differently. Although degenerative changes are observed at similar rates in both sexes, women seem to be more susceptible to degenerative changes leading to instability and malalignment, structural deterioration, such a stenosis or disc degeneration. Surgical satisfaction is greater in men, which has been attributed to poorer preoperative function secondary to more advanced disease at time of surgery and lower patient expectations for clinical improvement, both observed in women.

Arthritis, Rheumatoid↗
PubMed2006

Modeling changes in intervertebral disc mechanics with degeneration.

Mechanical response of the spine to various dynamic loading conditions can be analyzed by way of in vitro and in vivo studies. Ethical concerns, interpretation of conclusions reached in animal studies, and lack of detailed stress distributions in the disc components are the major disadvantages of relying solely on in vivo studies. Intraspecimen variability, difficulty in including muscle activity, and inability to mimic fluid exchange into the disc during unloading are some of the disadvantages of in vitro models. The poroelastic finite element models can provide a method of understanding the relationship between biomechanical performance of the disc due to cyclic loading and disc degeneration. A poroelastic finite element model, including regional variation of strain-dependent permeability and osmotic pressure, was used to study the effect of disc degeneration on biomechanical properties as well as propagation of failure in the disc components when cyclic loading was applied to the lumbar disc. The results predicted that healthy discs were much more flexible than degenerated discs, and the disc stiffness decreased with increasing the number of load cycles independent of degenerative condition. Failure was found to progress as the drained elastic properties of the disc components decreased due to the presence of failure. Poroelastic finite element modeling, including strain-dependent permeability and osmotic pressure, is the most advanced analytical tool currently available that can be used to understand how cyclic loading affects the biomechanical characteristics of a degenerated lumbar disc. However, a complete understanding of behavior of the intervertebral disc will ultimately be achieved only with use of a combination of computational models together with in vitro and in vivo experimental methods. Finite element models of discs with varying degrees of disc degeneration will help clinicians understand the initiation and progression of disc failure and degeneration and will assist in the development of approaches to stimulate the regeneration of disc tissues.

Animals↗
PubMed2006

Nonsurgical management of acute and chronic low back pain.

A variety of nonsurgical treatment alternatives exists for acute and chronic low back pain. Patients should receive appropriate education about the favorable natural history of low back pain, basic body mechanics, and methods (eg, exercises, activity modification, behavioral modification) that can reduce symptoms. Nonprescription medication is efficacious for mild to moderate pain. Nonsteroidal anti-inflammatory drugs, alone or in combination with muscle relaxants, relieve pain and improve overall symptoms of acute low back pain. Exercise therapy has limited value for acute low back pain, but strong evidence supports exercise therapy in the management of chronic low back pain. Moderately strong evidence supports the use of manipulation in acute back pain. Evidence is weak for the use of epidural corticosteroid injections in patients with acute low back pain, strong for short-term relief of chronic low back pain, and limited for long-term relief of chronic low back pain. The use of facet injections in the management of acute low back pain is not supported by evidence, nor is the effectiveness of orthoses, traction, magnets, or acupuncture. Trigger point injections are not indicated for nonspecific acute or chronic low back pain, and sacroiliac joint injections are not indicated in the routine management of low back pain. Conflicting evidence exists regarding the use of transcutaneous electrical nerve stimulation.

Acute Disease↗
PubMed2006

Treatment of intractable discogenic low back pain. A systematic review of spinal fusion and intradiscal electrothermal therapy (IDET).

BACKGROUND: A growing number of patients suffer from severe low back pain of discogenic origin that is not responsive to conservative medical management. These patients must consider the option of surgical spinal fusion or minimally-invasive intradiscal electrothermal therapy (IDET). OBJECTIVE: To conduct a systematic review of clinical outcomes in patients undergoing spinal fusion or the intradiscal electrothermal therapy (IDET) procedure for intractable discogenic low back pain. DESIGN: Systematic literature review. METHODS: English-language journal articles published from January 1995 to December 2005 were identified through computerized searches of the PubMed database and bibliographies of identified articles and review papers. Articles were selected if disc degeneration or disruption was the primary indication for spinal fusion or the IDET procedure and if follow-up outcome data included evaluations of back pain severity, condition-specific functional impairment and/or health-related quality of life. The literature reviewed encompassed 33 spinal fusion articles: 10 randomized controlled trials, 1 nonrandomized controlled trial, 9 before-after trials, and 13 case series. There were 18 IDET articles: 2 randomized controlled trial, 2 nonrandomized controlled trials, 11 before- after trials, and 3 case series. Data were extracted and summarized on patient characteristics, surgical methods, and clinical outcomes. RESULTS: Overall, there were similar median percentage improvements realized after spinal fusion and the IDET procedure, respectively, for 2 of the 3 outcomes evaluated: pain severity (50%, 51%), back function (42%, 14%) and quality of life (46%, 43%). There was an identifiable randomized controlled trials trend of both treatments reporting a smaller magnitude of improvement in all 3 primary outcomes (pain severity, back function, quality of life) compared to other types of trials. Perioperative complications were commonly associated with spinal fusion (median: 14%, range: 2% to 54%, n = 31 study groups) whereas adverse events were rarely experienced with the IDET procedure (median: 0%, range: 0% to 16%, n = 14 studies). Randomized controlled trials of spinal fusion, in particular, had important methodological limitations. CONCLUSION: The majority of patients reported improvement in symptoms following both spinal fusion and the IDET procedure. The IDET procedure appears to offer sufficiently similar symptom amelioration to spinal fusion without the attendant complications.

Electric Stimulation Therapy↗
PubMed2005

A prospective cohort analysis of adjacent vertebral body bone mineral density in lumbar surgery patients with or without instrumented posterolateral fusion: a 9- to 12-year follow-up.

STUDY DESIGN: A prospective, cohort study of 11 patients who underwent either a posterior lumbar spinal fusion with instrumentation (n = 7) or a lumbar laminotomy and discectomy alone (n = 4) and who were evaluated by dual energy radiograph absorptiometry (DEXA) to determine bone mineral density (BMD) at the adjacent three cephalad vertebral levels. OBJECTIVES: To determine long-term BMD changes that occur at the adjacent three levels above an instrumented posterolateral lumbar fusion or an isolated laminotomy and lumbar discectomy. SUMMARY OF BACKGROUND DATA: No long-term prospective study has evaluated the affects of instrumented lumbar fusions on bone remodeling at adjacent vertebral levels. Several studies in animals and humans have reported a decrease in BMD at the adjacent level during the first 6 months after spinal fusion with a return to baseline at 1-year follow-up in up to 60% of patients. METHODS: DEXA was performed initially at a mean postoperative follow-up of 4 years (range, 2.3-5.5 years) and again at a mean of 10.8 years (range, 9.1-2.4 years). Eleven patients were divided into two groups: laminotomy and discectomy (n = 4) and instrumented posterior spinal fusion (n = 7). All patients underwent surgical procedures at the L4-L5 or L5-S1 levels with DEXA analysis being performed on the adjacent three cephalad levels. The discectomy group (mean age, 57.8 years) underwent lumbar hemilaminotomy without fusion whereas the other group (mean age, 60 years) underwent pedicle-screw instrumentation and posterolateral lumbar fusion. Peripheral sites, including the femoral neck, were included in the DEXA analysis to normalize for individual differences in bone mineral metabolism. RESULTS: At the mean 10.8-year follow-up, the fusion group was noted to have at the adjacent level, two levels cephalad, and three levels cephalad normalized BMDs of 1.47, 1.39, and 1.27, respectively. A 14.8%, 10.8%, and 9.5% increase respectively in normalized BMD was observed when compared with the mean 4-year fusion values (P < 0.05). This increase was also noted on comparative T-score, Z-score, and absolute BMD values (P < 0.05). The discectomy group when evaluated revealed no statistically significant change from the mean 4 to 10.8-year follow-up (BMD, normalized BMD, T-score, Z-score). No statistically significant difference was noted in hip BMD at the mean 4-year and 10.8-year follow-up (1.05 versus 1.03), suggesting that the effects were local. CONCLUSIONS: The local BMD adjacent to an instrumented lumbar fusion is increased at a mean of 10.8-years after surgery. There is a gradual decrease in BMD changes with increasing distance from the fusion level. Alterations in fusion site biomechanics and modulus mismatch between the host bone and the spinal instrumentation most likely result in chronic, localized bone remodeling with an increased BMD that decreases the greater the distance from the fusion mass.

Bone Density↗