PubMed Health⌕ Search

Biomedical subjects

Max Aebi

Publications and source records attributed to Max Aebi.

18 recordsLinked to original sources
PubMed2006

Quantitative magnetic resonance imaging of enzymatically induced degradation of the nucleus pulposus of intervertebral discs.

STUDY DESIGN: The structural integrity of the nucleus pulposus (NP) of intervertebral discs was targeted by enzyme-specific degradations to correlate their effects to the magnetic resonance (MR) signal. OBJECTIVE: To develop quantitative MR imaging as an accurate and noninvasive diagnostic tool to better understand and treat disc degeneration. SUMMARY OF BACKGROUND DATA: Quantitative MR analysis has been previously shown to reflect not only the disc matrix composition, but also the structural integrity of the disc matrix. Further work is required to identify the contribution of the structural integrity versus the matrix composition to the MR signal. METHODS: The bovine coccygeal NPs were injected with either enzyme or buffer, incubated at 37 degrees C as static, unloaded and closed 3-disc segments, and analyzed by a 1.5-Tesla MR scanner to measure MR parameters. RESULTS: Collagenase degradation of the NP significantly decreased the relaxation times, slightly decreased the magnetization transfer ratio, and slightly increased the apparent diffusion coefficient. Targeting the proteoglycan and/or hyaluronan integrity by trypsin and hyaluronidase did not significantly affect the MR parameters, except for an increase in the apparent diffusion coefficient of the disc after trypsin treatment. CONCLUSIONS: Our results demonstrate that changes in the structural integrity of matrix proteins can be assessed by quantitative MR.

Animals↗
PubMed2006

Harvesting local cylinder autograft from adjacent vertebral body for anterior lumbar interbody fusion: surgical technique, operative feasibility and preliminary clinical results.

Autogenous iliac crest has long served as the gold standard for anterior lumbar arthrodesis although added morbidity results from the bone graft harvest. Therefore, femoral ring allograft, or cages, have been used to decrease the morbidity of iliac crest bone harvesting. More recently, an experimental study in the animal showed that harvesting local bone from the anterior vertebral body and replacing the void by a radio-opaque beta-tricalcium phosphate plug was a valid concept. However, such a concept precludes theoretically the use of posterior pedicle screw fixation. At one institution a consecutive series of 21 patients underwent single- or multiple-level circumferential lumbar fusion with anterior cages and posterior pedicle screws. All cages were filled with cancellous bone harvested from the adjacent vertebral body, and the vertebral body defect was filled with a beta-tricalcium phosphate plug. The indications for surgery were failed conservative treatment of a lumbar degenerative disc disease or spondylolisthesis. The purpose of this study, therefore, was to report on the surgical technique, operative feasibility, safety, benefits, and drawbacks of this technique with our primary clinical experience. An independent researcher reviewed all data that had been collected prospectively from the onset of the study. The average age of the patients was 39.9 (26-57) years. Bone grafts were successfully harvested from 28 vertebral bodies in all but one patient whose anterior procedure was aborted due to difficulty in freeing the left common iliac vein. This case was converted to a transforaminal interbody fusion (TLIF). There was no major vascular injury. Blood loss of the anterior procedure averaged 250 ml (50-350 ml). One tricalcium phosphate bone plug was broken during its insertion, and one endplate was broken because of wrong surgical technique, which did not affect the final outcome. One patient had a right lumbar plexopathy that was not related to this special technique. There was no retrograde ejaculation, infection or pseudoarthrosis. One patient experienced a deep venous thrombosis. At the last follow up (mean 28 months) all patients had a solid lumbar spine fusion. At the 6-month follow up, the pain as assessed on the visual analog scale (VAS) decreased from 6.9 to 4.5 (33% decrease), and the Oswestry disability index (ODI) reduced from 48.0 to 31.7 with a 34% reduction. However, at 2 years follow up there was a trend for increase in the ODI (35) and VAS (5). The data in this study suggest that harvesting a cylinder of autograft from the adjacent vertebral body is safe and efficient. Filling of the void defect with a beta-tricalcium phosphate plug does not preclude the use of posterior pedicle screw stabilization.

Adult↗
PubMed2005

The adult scoliosis.

Adult scoliosis is defined as a spinal deformity in a skeletally mature patient with a Cobb angle of more than 10 degrees in the coronal plain. Adult scoliosis can be separated into four major groups: Type 1: Primary degenerative scoliosis, mostly on the basis of a disc and/or facet joint arthritis, affecting those structures asymmetrically with predominantly back pain symptoms, often accompanied either by signs of spinal stenosis (central as well as lateral stenosis) or without. These curves are often classified as "de novo" scoliosis. Type 2: Idiopathic adolescent scoliosis of the thoracic and/or lumbar spine which progresses in adult life and is usually combined with secondary degeneration and/or imbalance. Some patients had either no surgical treatment or a surgical correction and fusion in adolescence in either the thoracic or thoracolumbar spine. Those patients may develop secondary degeneration and progression of the adjacent curve; in this case those curves belong to the type 3a. Type 3: Secondary adult curves: (a) In the context of an oblique pelvis, for instance, due to a leg length discrepancy or hip pathology or as a secondary curve in idiopathic, neuromuscular and congenital scoliosis, or asymmetrical anomalies at the lumbosacral junction; (b) In the context of a metabolic bone disease (mostly osteoporosis) combined with asymmetric arthritic disease and/or vertebral fractures. Sometimes it is difficult to decide, what exactly the primary cause of the curve was, once it has significantly progressed. However, once an asymmetric load or degeneration occurs, the pathomorphology and pathomechanism in adult scoliosis predominantly located in the lumbar or thoracolumbar spine is quite predictable. Asymmetric degeneration leads to increased asymmetric load and therefore to a progression of the degeneration and deformity, as either scoliosis and/or kyphosis. The progression of a curve is further supported by osteoporosis, particularly in post-menopausal female patients. The destruction of facet joints, joint capsules, discs and ligaments may create mono- or multisegmental instability and finally spinal stenosis. These patients present themselves predominantly with back pain, then leg pain and claudication symptoms, rarely with neurological deficit, and almost never with questions related to cosmetics. The diagnostic evaluation includes static and dynamic imaging, myelo-CT, as well as invasive diagnostic procedures like discograms, facet blocks, epidural and root blocks and immobilization tests. These tests may correlate with the clinical and the pathomorphological findings and may also offer the least invasive and most rational treatment for the patient. The treatment is then tailored to the specific symptomatology of the patient. Surgical management consists of either decompression, correction, stabilization and fusion procedures or a combination of all of these. Surgical procedure is usually complex and has to deal with a whole array of specific problems like the age and the general medical condition of the patient, the length of the fusion, the condition of the adjacent segments, the condition of the lumbosacral junction, osteoporosis and possibly previous scoliosis surgery, and last but not least, usually with a long history of chronified back pain and muscle imbalance which may be very difficult to be influenced. Although this surgery is demanding, the morbidity cannot be considered significantly higher than in other established orthopaedic procedures, like hip replacement, in the same age group of patients. Overall, a satisfactory outcome can be expected in well-differentiated indications and properly tailored surgical procedures, although until today prospective, controlled studies with outcome measures and pre- and post-operative patient's health status are lacking. As patients, who present themselves with significant clinical problems in the context of adult scoliosis, get older, minimal invasive procedures to address exactly the most relevant clinical problem may become more and more important, basically ignoring the overall deformity and degeneration of the spine.

Adult↗
PubMed2005

Internal strains in healthy and degenerated lumbar intervertebral discs.

STUDY DESIGN: A biomechanical study investigating the intradiscal mechanics of human lumbar intervertebral discs (IVDs). OBJECTIVES: To assess the relationship between nucleus pulposus migration and intradiscal strains as a function of degeneration. SUMMARY OF BACKGROUND DATA: Intradiscal deformation studies have documented the nucleus pulposus migration capabilities during bending but without assessing subsequent intradiscal strains of the anulus fibrosus. Degenerated IVDs show higher anular laxity, hypermobility, and, perhaps, segmental instability. It is unknown if nucleus pulposus migration might be the cause of increased intradiscal anular strains and if such a phenomenon is modulated by IVD degeneration. METHODS: Eighteen healthy and degenerated IVDs were subjected to compression, extension, flexion, and lateral bending. Craniocaudal radiographs at unloaded and loaded steps documented positions of wires placed within and beads glued to the external surface in the mid-transverse plane. Circumferential and radial strains from the anterior, lateral, and posterolateral regions during load were compared between healthy and degenerated IVDs. RESULTS: The nucleus pulposus migrated to the opposite side of bending regardless of bending direction and significantly more in degenerated IVDs. The highest nucleus pulposus migration was observed during lateral bending. Circumferential tensile strains were significantly higher in the posterolateral regions of degenerative IVDs during all loads. Degeneration significantly increased radial tensile and compressive strains during all bending loads. CONCLUSIONS: Increased nucleus pulposus migration in degenerated IVDs may result in increased shifting of the IVD pivot point during bending movements as well as intradiscal anular strains, particularly in the posterolateral anulus. This phenomenon may explain the segmental instability observed in degenerated segments as well as the associated anular tears present in the posterolateral region before IVD failure.

Aged↗
PubMed2005

Atlantoaxial fusion using anterior transarticular screw fixation of C1-C2: technical innovation and biomechanical study.

This study is an attempt to describe a new technique for anterior transarticular screw fixation of the atlantoaxial joints, and to compare the stability of this construct to posterior transarticular screw fixation with and without laminar cerclage wiring. Nine human cadaveric specimens were included in this study. The C1-C2 motion segment was instrumented using either anterior transarticular screws (group 1), posterior transarticular screws alone (group 2), or posterior screws with interlaminar cerclage wires (group 3). Using an unconstrained mechanical testing machine, the specimens were tested in rotation, lateral bending, and flexion-extension using nondestructive loads of +/-2 N m. The specimens were also tested in translation using nondestructive loads of +/-100 N. All values for the three groups with regards to anterior-posterior displacement, rotation, and lateral bending were similar as determined using a Kruskal-Wallis rank sum test with a significance level of p<0.05. The only significant difference was registered in flexion-extension where the cerclage wire added some strength to the construct. Anterior transarticular screw fixation of the atlantoaxial spine has several advantages over posterior fixation techniques, and is as stable as posterior transarticular fixation in all clinically significant planes of motion. The addition of posterior interlaminar cerclage wiring further improves resistance to flexion-extension forces. Anterior transarticular screw fixation of the atlantoaxial joint is a useful technique for achieving C1-C2 stabilization.

Adult↗
PubMed2004

Apparent diffusion coefficient of intervertebral discs related to matrix composition and integrity.

While tremendous work has been performed to characterize degenerative disc disease through gross morphologic, biochemical, and histologic grading schemes, the development of an accurate and noninvasive diagnostic tool is required to objectively detect changes in the matrix with aging and disc degeneration. In the present study, quantitative magnetic resonance was used to determine if the quality of the nutritional supply to the intervertebral disc at various ages and levels of degeneration could be assessed through measurement of the apparent diffusion coefficients (ADCs). Modifications of the nucleus pulposus matrix content, specifically of water and glycosaminoglycan contents, with age and disc degeneration, were reflected in correlating changes in the ADCs. From unforced stepwise linear regression analyses, relations were established showing that decreases in glycosaminoglycan or water contents in the nucleus pulposus resulted in direct decreases in the ADCs. Relations obtained for the ADCs of the nucleus pulposus were direction dependent, in conformity with the anisotropic diffusion in the intervertebral discs. Changes in matrix integrity, as evidenced by the percentage of denatured collagen, were also detected in the nucleus pulposus with a low positive correlation to the ADC along the height of the disc and an inverse statistically significant regression to the ADC along the anterior to posterior axis of the disc. Correlations between the matrix content and integrity of the annulus fibrosus and its ADCs were not as evident, with only the ADC in the lateral direction of the disc of the anterior annulus fibrosus able to reflect changes in matrix content. The information obtained by the ADCs, particularly of the nucleus pulposus, can potentially be used in combination with quantitative T1, T2, and MT parameters to noninvasively obtain a quantitative assessment of the disc matrix composition and structural integrity.

Adolescent↗
PubMed2003

Spinal metastasis in the elderly.

Bony metastases are a frequent problem in elderly patients affected by cancer, and those with bony metastases involve the spine in approx. 50%. The most frequent spinal metastases (60%) are from breast, lung, or prostate cancer. The chance that an elderly patient (60-79 years old) is affected by bony metastases is four times higher in men and three times higher in women than a middle-aged patient (40-59 years old). Since the medical treatment with all the adjuvant treatment options prolong the survival of this particular patient group, the spinal metastases may become a mechanical issue, thus requesting surgical treatment. Different classification systems have been proposed to rationalize surgical indications, some concentrating solely on the local spinal tumor involvement and some including the overall clinical situation. Since most of the surgical options are of palliative character, it is more important to base the decision on an overall clinical classification including the different treatment modalities-irradiation, chemotherapy, steroids, bisphosphonates, and surgery-to make a shared decision. In case surgery is indicated-neural compression, pathological fracture, instability, and progressive deformity, nursing reasons-the most straightforward procedures should be chosen, which may not need an intensive care unit stay. In the thoracolumbar spine a posterior decompression and posterolateral vertebral body resection through a posterior approach only, with a concomitant reconstruction and stabilization, has shown to work sufficiently well. In the middle and lower cervical spine the anterior approach with anterior decompression and anterior column reconstruction is most effective and has a low morbidity, whereas the occipitocervical junction can generally be treated by posterior resection and stabilization. The outcome should be determined by the survival time in an ambulatory, independent status, where pain is controlled, and the patient is not hospitalized. Surgical management shows the greatest improvement in pain reduction, but also in other domains of quality of life. Since prospective randomized studies comparing different treatment modalities for spinal metastases including surgery are not available and are ethically difficult to achieve, each case remains an interdisciplinary, shared decision making process for what is considered best for a patient or elderly patient. However, whenever surgery is an option, it should be planned before irradiation since surgery after irradiation has a significant higher complication rate.

Aged↗
PubMed2003

Anterior instrumentation for traumatic C1-C2 instability.

STUDY DESIGN: Technical note, case report. and review of literature. OBJECTIVE: Description of anterior transarticular internal fixation for traumatic C1-C2 instability. SUMMARY OF BACKGROUND DATA: The currently effective posterior approaches for instrumentation of the C1-C2 junction require considerable soft tissue dissection and prone patient positioning. Some medical and anatomic conditions restrict the posterior approach. MATERIALS AND METHODS: An odontoid screw and anterior transarticular C1-C2 screws were used to instrument an unstable injury at this junction. The lesion consisted of a type II dens fracture and C1 ring disruption. Two high-quality fluoroscopy machines, a radiolucent OSI fracture table, and the Synframe (Synthes, Paoli, PA) retraction system are used for this procedure. The implant of choice is the 4.0-mm cannulated titanium screw. RESULTS: At 4-month follow-up, successful stabilization without failure of hardware is documented. The patient's neurologic status is stable, with a minor residual left upper extremity motor deficit. The patient has restricted C-spine rotation but no neck pain with movement. CONCLUSION: Anterior stabilization through a standard Smith-Robinson approach of the C1-C2 junction with screws into the odontoid and the lateral masses of C1 is effective. Supine positioning and minimal soft tissue dissection are advantages of this method over standard posterior transarticular instrumentation. Knowledge of the local anatomy, strict adherence to the operative protocol, and high-quality fluoroscopy avoid potential surgical complications.

Bone Screws↗
PubMed2003

A synthetic peptide of link protein stimulates the biosynthesis of collagens II, IX and proteoglycan by cells of the intervertebral disc.

To date, there have been no reports on the effect on disc cells of the intervertebral disc (IVD) of the amino terminal peptide of link protein (DHLSDNYTLDHDRAIH) (link N) which is generated by the cleavage of human link protein by stromelysins 1 and 2, gelatinase A and B, and collagenase between His(16) and Ile(17). However, link N has been shown to act as a growth factor and stimulate synthesis of proteoglycans and collagen by chondrocytes of human articular cartilage. There are also no studies on the effect of link N on type IX collagen in any tissue. In the studies reported here, a serum-free pellet culture system has been used to examine whether link N can play a role in maintaining the integrity of disc matrix, specifically at the level of matrix assembly by cells of the IVD. Using this culture system, we determined the capacity of link N to stimulate accumulation of these matrix proteins in the annulus fibrosus (AF) and nucleus pulposus (NP). Gross inspection of separate AF and NP pellet cultures in the absence of link N revealed a progressive increase in size and a transition from "spherical" to "polygonal" pellets after centrifugation. Addition of 10 ng/ml link N resulted in increased pellet sizes for both AF and NP pellet cultures. Link N increased proteoglycan, type II and type IX collagen contents with an increase in DNA content over time. This study demonstrates that link N can act directly on disc cells to stimulate matrix production, which involves increased accumulation of proteoglycan, and types II and IX collagens. This study also identifies the value of pellet cultures for studies of the IVD cells in a serum-free chemically defined medium, in which pellets can continue growing in size in response to growth factors with minimal cell loss. Link N may have value in stimulating the growth and regeneration of the damaged IVD.

Amino Acid Sequence↗
PubMed2003

The potential and limitations of a cell-seeded collagen/hyaluronan scaffold to engineer an intervertebral disc-like matrix.

STUDY DESIGN: The use of a cell-seeded biomatrix for tissue engineering of the intervertebral disc. OBJECTIVE: To evaluate the ability of a biomatrix to support the viability of intervertebral disc cells and to accumulate the extracellular matrix that they produce. SUMMARY OF BACKGROUND DATA: Intervertebral disc degeneration is a common occurrence during adult life that has adverse economic consequences on the health care system. Current surgical treatments are aimed at removing or replacing the degenerate tissue, which can alter the biomechanics of the spine and result in degeneration at adjacent disc levels. The ideal treatment of the degenerate disc would involve biologic repair, and tissue-engineering techniques offer a means to achieve this goal. METHODS: Scaffolds of type I collagen and hyaluronan were seeded with bovine nucleus pulposus or anulus fibrosus cells and maintained in culture for up to 60 days in the presence of fetal calf serum or a variety of growth factors to try to generate a tissue whose properties could mimic those of the nucleus pulposus with respect to proteoglycan content. RESULTS: During the culture period, various proteoglycans (aggrecan, decorin, biglycan, fibromodulin, and lumican) and collagens (types I and II) accumulated in the scaffold. Proteoglycan accumulation in the scaffold was greatest under conditions in which transforming growth factor-beta1 was present, but under all conditions, more proteoglycan was lost into the culture medium than retained in the scaffold. Both the nucleus and anulus cells behaved in a similar manner with respect to their ability to synthesize matrix macromolecules and have them retained in the scaffold. By day 60 of culture, the proteoglycan content of the scaffolds never exceeded 10% of that present in the mature nucleus pulposus, although this figure could have been considerably increased if most of the proteoglycan being synthesized could have been retained. Furthermore, proteoglycan retention was not uniform within the scaffold, but increased near its periphery. CONCLUSIONS: This work demonstrates that although it is possible to maintain functional disc cells in a biomatrix, it will be necessary to optimize proteoglycan synthesis and retention if any resulting tissue is to be of value in the biologic repair of the degenerate disc. The ability of the anulus cells to replicate the matrix production of the nucleus cells, at least in the collagen/hyaluronan scaffold, suggests that repair may not be limited to the availability of authentic nucleus cells.

Animals↗
PubMed2003

Elective lumbar spinal decompression in the elderly: is it a high-risk operation?

INTRODUCTION: Spinal degeneration leading to spinal stenosis is increasingly common in an aging population. Many patients are not referred for operation because of the fear of severe complications. The purpose of this study was to relate the surgical risks involved in elective spinal decompression in elderly patients to those of total hip arthroplasty, a well-accepted procedure whose risks and benefits are well known. METHODS: We reviewed the charts of 6 8 consecutive patients who underwent elective spinal decompression and fitted our inclusion criteria (65-80 yr of age, no spinal or hip operations, no hip fractures, spine fractures or cauda equina syndrome and no bone or metastatic disease). This group was matched with a similar group of 68 randomly selected patients who underwent total hip arthroplasty during the same period. We recorded the age, gender, American Society of Anesthesiologists (ASA) score, early postoperative complication rate, operative time, hospital stay and blood lost. RESULTS: The 2 groups were well matched with respect to age, gender and ASA score. The only significant intraoperative difference was operative time, with the spine procedure taking longer to complete (191 min v. 278 min). Blood loss was not significantly different. Both groups had a similar number of lift-threatening complications (12 v. 14). The number of minor complications was greater in the spinal decompression group (62 v. 125). CONCLUSIONS: Elective lumbar spinal decompression in elderly patients suffering significant pain or disability due to degenerative lumbar spinal stenosis is worthwhile. We recommend judicious use of conservative measures, but encourage referral for surgical management when these fail. This operation, even when instrumentation and bone grafting are required, is not associated with more serious or life-threatening risks than a total hip replacement in elderly patients.

Aged↗
PubMed1998

Lumbar intradiscal pressure measured in the anterior and posterolateral annular regions during asymmetrical loading.

OBJECTIVE: To analyze the effect of asymmetrical loading on intradiscal pressure. DESIGN: Human cadaveric lumbar spines were instrumented with multiple pressure sensors and subjected to external mechanical loads. BACKGROUND: Tears and radial fissures in the posterolateral annulus with no evidence of annular protrusion or nuclear extrusion are frequently observed in non-degenerated intervertebral discs. Cadaveric studies have shown that asymmetrical loads lead to posterolateral herniation. Regional overload may be responsible for a progressive structural weakness of the posterolateral annular fibres. METHODS: Three needles each equipped with three independent pressure sensors were inserted in the midplane of the L(3)/L(4) intervertebral disc (n = 16) in the anterior, right posterolateral and left posterolateral regions. Axial rotation was applied in the upright, flexed and extended positions and the pressures recorded. RESULTS: The largest intradiscal pressure increase was observed in the posterolateral inner annular regions, more so in flexion than extension, when combined with axial rotation. Significant centripetal pressure gradients were found only in the posterolateral needles during the upright and flexed positions. CONCLUSIONS: When applying compression and axial rotation, the posterolateral inner annular zones of the intervertebral disc show high stress peaks and centripetal pressure gradients. Asymmetrical loads (rotation) combined with postural changes in the sagittal plane increase these effects, and may be responsible for a chronic mechanical overload of these regions. RELEVANCE: Our findings suggest a predilection for the posterolateral inner annular regions to mechanical failure, especially under asymmetrical loading.

Journal Article↗