Search PubMed⌕ Search

Biomedical subjects

T Steffen

Publications and source records attributed to T Steffen.

At least 37 records · Page 2Linked to original sources
PubMed2000

Effect of implant design and endplate preparation on the compressive strength of interbody fusion constructs.

STUDY DESIGN: A human cadaveric study on the compressive strength of different lumbar interbody fusion implants and endplate preparation techniques was performed. OBJECTIVES: To assess the axial compressive strength of an implant with peripheral endplate contact as opposed to full surface contact, and to assess whether removal of the central bony endplate affects the axial compressive strength. SUMMARY OF BACKGROUND DATA: The compressive strength of interbody fusion constructs has been compared between implants and bone grafts. Neither implant design nor endplate preparation has been shown to affect strength. Removal of the central bony endplate for bone grafts was noted to improve graft incorporation but also to facilitate subsidence. METHODS: A total of 44 vertebrae were tested in four experimental groups by combining two interbody implants (full-surface vs peripheral surface support) with two endplate preparation techniques (intact bony endplate vs removal of the central bony endplate). Specimens were tested to ultimate compressive failure using a 50 N/second ramped load. Yield strength and ultimate compressive strength were compared between groups using two-factor analysis of covariance. A P value less than 0.05 was considered significant. Stepwise linear regressions assessed the predictive power of age, bone mineral content, and the implant's normalized endplate coverage on yield strength and ultimate compressive strength. RESULTS: Neither implant design nor endplate preparation technique affected yield strength or ultimate compressive strength. Age, bone mineral content, and the normalized endplate coverage were strong predictors of yield strength (P < 0. 0001; r2 = 0.459) and ultimate compressive strength (P < 0.0001; r2 = 0.510). CONCLUSIONS: An implant with only peripheral support resting on the apophyseal ring offers axial mechanical strength similar to that of an implant with full support. Neither supplementary struts nor a solid implant face has any additional mechanical advantage, but reduces graft-host contact area. Removal of the central bony endplate is recommended because it does not affect the compressive strength and promotes graft incorporation.

Adolescent↗
PubMed2000

Minimally invasive bone harvesting tools.

The most readily available source for autologous bone graft used in spinal fusion (the gold standard) is the iliac crest. However, the open surgical approach for harvesting corticocancellous iliac bone is associated with a marked increase in morbidity. This study suggests two alternatives to the traditional open harvesting procedure. For anterior interbody fusion procedures using a cage, the autologous bone is harvested regionally from a neighboring vertebral body. Alternatively, using minimally invasive techniques, a custom bone graft harvester with a flexible tube and cutting tip allows harvesting of autologous bone from a single entry point at the iliac crest. The effect on the mechanical strength of a lumbar vertebra of removing a cylindrical regional bone graft was studied in a cadaveric model. The bone defect was filled using three different filler materials: a porous tri-calcium phosphate plug, a porous tantalum plug, and a self-setting calcium phosphate cement. After plug removal, the vertebral body's strength in flexion/compression loading was reduced significantly, but could be restored to at least intact values with any of the three filler materials. The minimally invasive bone graft harvester was tested in three cadaveric pelves. With the cutting tip being guided within the cortical boundaries of the pelvis, cancellous bone volumes of 10-20 cc could be harvested from each iliac bone. Regional bone graft harvest in anterior spine surgery is suggested to be anatomically safe and biomechanically acceptable. Any of the three filler materials can restore the vertebral body's mechanical strength, but the filler's long-term resorption/remodeling or osteointegration behavior is unknown. The minimally invasive bone graft harvester is a novel tool, which performed satisfactorily under laboratory conditions, but clinical results are still missing.

Bone Transplantation↗
PubMed2000

Synframe: a preliminary report.

Both endoscopic lumbar spinal surgery and the non-standardized and unstable retractor systems for the lumbar spine presently on the market have disadvantages and limitations in relation to the minimally invasive surgical concept, which have been gradually recognized in the last few years. In an attempt to resolve some of these issues, we have developed a highly versatile retractor system, which allows access to and surgery at the lumbar, thoracic and even cervical spine. This retractor system - Synframe - is based on a ring concept allowing 360 degrees access to a surgical opening in anterior as well as posterior surgery. The ring is concentrically laid over the surgical opening for the approach and is used as a carrier for retractor arms, which are instrumented with either different sizes or types of blades and/or different sizes of Hohmann hooks. In posterior surgery, nerve root retractors can also be installed. This ring also functions as a carrier for fiberoptic illumination devices and different sizes of endoscopes, used to transmit the surgical procedure out of the depth of the surgical exposure for both teaching purposes and for the surgical team when it has no longer direct visual access to the procedure. The ring is stable, being fixed onto the operating table, allowing precise minimally open approaches and surgical procedures under direct vision with optimal illumination. This ring system also opens perspectives for an integrated minimally open surgical concept, where the ring may be used as a reference platform in computer-navigated surgery.

Equipment Design↗
PubMed2000

Cages: designs and concepts.

Many new interbody fusion cages have been recently developed, but clinical studies analyzing fusion outcome are still scarce. Radiological methods to assess fusion are not standardized and are often unreliable. Cages have been stated to provide good segmental distraction, provide axial load support and reduce segmental mobility, but there have been reports of failed fusions because of implant failure. This paper presents a critical opinion on current cage designs, stressing their clinical and biomechanical implications. Threaded cage designs compromise endplate integrity, and when placed in pairs have inherent limitations for distraction. Non-threaded cage designs usually preserve endplate integrity, but geometry may be inadequate to provide a good surface match to the endplate. The concept of an open frame type cage is believed to have biological advantages, because large graft volumes inside the cage can be in direct contact with host bone. Cadaveric tests suggest that open frame constructs have compressive strength similar to that of full surface contact cages. Restoration of segmental height, sagittal balance and increased neuroforaminal clearance are all functions of disc space distraction. The effect of cage instrumentation on axial load distribution, however, is not well understood. Biomechanical experiments strongly suggest supplementing cage instrumentation with posterior fixation, to achieve a marked increase in initial segmental stability. In the absence of gross segmental instability, micromotion at the host graft interface may still exist. As a result, fusion will never occur, instead a pseudoarthrosis will develop. For monitoring fusion, the use of non-metallic cages has distinct advantages, because no metal artifacts will disturb radiological assessment.

Equipment Design↗
PubMed2000

A surgical approach to the ventral aspect of the lumbar vertebrae in the sheep model.

The sheep model is frequently used for pre-clinical trials of spinal implants and vertebral interbody fusion devices. The lack of a well-documented multisegmental approach to the ventral aspect of the lumbar vertebrae has limited these trials to a posterior approach to the spine. A retroperitoneal approach to the sheep lumbar vertebrae was established and tested. One hundred and five sheep underwent the surgery. No major complications are reported. Major anatomical differences between sheep and humans were observed and documented. Anatomical variations in the sheep segmental vessel anatomy were also observed. Comprehensive knowledge of the retroperitoneal approach in sheep will facilitate pre-clinical studies testing ventral spinal implants or fusion techniques.

Animals↗
PubMed2000

Biomechanical stability of five stand-alone anterior lumbar interbody fusion constructs.

Anterior lumbar interbody fusion (ALIF) cages are expected to reduce segmental mobility. Current ALIF cages have different designs, suggesting differences in initial stability. The objective of this study was to compare the effect of different stand-alone ALIF cage constructs and cage-related features on initial segmental stability. Human multisegmental specimens were tested intact and with an instrumented L3/4 disc level. Five different ALIF cages (I/F, BAK, TIS, SynCage, and ScrewCage) were tested non-destructively in axial rotation, flexion/extension and lateral bending. A cage 'pull-out' concluded testing. Changes in neutral zone (NZ) and range of motion (ROM) were analyzed. Cage-related measurements normalized to vertebral dimensions were used to predict NZ and ROM. No cage construct managed to reduce NZ. The BAK and TIS cages had the largest NZ increase in flexion/extension and lateral bending, respectively. Cages did reduce ROM in all loading directions. The TIS cage was the least effective in reducing the ROM in lateral bending. Cages with sharp teeth had higher 'pull-out' forces. Antero-posterior and mediolateral cage dimensions, cage height and wedge angle were found to influence initial stability. The performance of stand-alone ALIF cage constructs generally increased the NZ in any loading direction, suggesting potential directions of initial segmental instability that may lead to permanent deformity. Differences between cages in flexion/extension and lateral bending NZ are attributed to the severity of geometrical cage-endplate surface mismatch. Stand-alone cage constructs reduced ROM effectively, but the residual ROM present indicates the presence of micromotion at the cage-endplate interface.

Adult↗
PubMed2000

[Tobacco prevention in apprentices--evaluation of a general practice project "not smoking is cool!"].

PURPOSE: In recent years the incidence of adolescent smokers has increased steeply. Taking this into account, current anti-smoker campaigns should be reconsidered. Great importance must be attached to the apprentice group, since adolescents in professional training have frequently not been reached sufficiently by the preventive efforts. This study presents a tobacco prevention campaign among adolescents which was conducted in a large Swiss industrial company in 1998. METHODS AND SAMPLE: A total of 430 apprentices took part in the prevention campaign which intentionally targeted adolescent behaviour. Of these, 40 apprentices were trained as mediators for tobacco prevention in advance. On the prevention day, the mediators communicated their know-how and experiences to their working groups. To evaluate the campaign, the apprentices were surveyed via standardised questionnaires on their smoking habits before the prevention campaign began. One month after the prevention day they were surveyed again on their current smoking habits and how the campaign had affected them. RESULTS: The study showed that apprentices smoke heavily despite high awareness of the negative consequences. Some 30% of the trainees admitted smoking regularly. Another 11% said they were occasional tobacco consumers. No significant gender difference was noticeable. Especially striking was that the adolescents often justified their own smoking as habit and dependence on tobacco. The prevention campaign was well received by the adolescents. It set about half of the smokers thinking over their smoking habits. No change in smoking habits, however, could be demonstrated one month after the campaign. CONCLUSIONS: Prevention among adolescents beyond the mandatory school period is a special challenge, since one cannot take advantage of the school's network. Within the scope of the campaign described here, it was possible to reach 430 apprentices of a major company. The study shows a great need for on-target smoking prevention in this sector. In the future, studies should examine whether tobacco prevention campaigns for apprentices should already contain secondary prevention elements from the outset. They should also assess if the effects could be further improved by introducing structural and other ongoing health-promotion measures.

Adolescent↗
PubMed2000

Posterolateral and anterior interbody spinal fusion models in the sheep.

Posterolateral and anterior interbody spinal arthrodesis is a frequent procedure, but high nonunion rates are reported and harvesting autologous bone graft from the iliac crest significantly increases morbidity. Bone graft substitutes are an alternative, but to date clinical results are not conclusive. Bone substitutes can be organic or inorganic, biologic or synthetic. They can have osteoconductive properties, inductive properties or both. Animal experiments are essential to investigating bone substitutes using biomechanical and histologic methods not available in clinical studies. Few authors reported on instrumented anterior fusion models, but none used the sheep model. In the current study posterolateral and anterior interbody fusion models in sheep are described. Both models used instrumented fusions, applying porous mineral scaffolds, alone or mixed with bone. The surgical techniques are described step-by-step and potential difficulties are highlighted. Preliminary results are reported for the posterolateral fusion model using coralline graft substitutes. The coral granules mixed with locally harvested bone had fusion outcomes similar to pure autologous bone. The graft substitute showed marked resorption between 12 and 20 weeks. All fusions had bone cortex and good trabecular connectivity. Histologic evaluation suggests after 20 weeks nearly the entire surface of the substitute is covered with new bone. Porous mineral bone substitutes mixed with locally harvested autologous bone are thought to be a valid alternative for posterolateral fusions.

Animals↗
PubMed1999

[Hepatitis B and C in intravenous drug abusers in Switzerland].

Since the 1980s hepatitis B and C have spread greatly among intravenous drug consumers. This shows up today in a high prevalence for both pathogens. It is striking that many patients who have only consumed drugs intravenously for a few years have already been infected with hepatitis B or C. The clear reduction in the spread of HIV within the drug-using community achieved by targeted measures during recent years has not had a similar impact on hepatitis B and C. Given this background, optimising preventive efforts among intravenous drug users is of great importance. Structural steps for therapy and damage-reduction should be optimised even more. Moreover, individual protective behaviour among patients should be improved. Medical advice and care is of great importance in this case. New studies show that many intravenous drug consumers are insufficiently informed on the risks of infection from shared use of injection utensils (spoons, filters, etc.) or drug sharing with used needles. Moreover, many drug consumers are not vaccinated against hepatitis B. Medical advice on protective behaviour should address these problems more directly. In the future, other sustainable intervention programmes based on this approach will need to be developed.

Adolescent↗
PubMed1999

[New treatment concepts in smoking cessation].

Although the smoking rate in Switzerland had declined during the 1970s and 1980s, it has not continued to decrease during the 1990s. About one third of the population in Switzerland smoked in 1997. Striking is a sharp increase in young female smokers during recent years. The portion of 15- to 25-year-old female smokers rose from 26% (1992) to 41% (1997). This undesirable development calls for making the most of preventive initiatives to date. Beside primary prevention steps, the range of assistance for smokers also needs to be extended. In addition to the smoking withdrawal counselling introduced, development of a range of programmes should also be expanded to assist smokers who have currently been unable to quit. Reduction in the number of cigarettes smoked within the framework of intensive specialist care can make sense in this situation. In the near future, pharmacological aids (nicotine substitute preparations) are also anticipated for this purpose. The most important resources for such smoker counselling will be presented. Future studies should focus on optimising reduction treatment as a new approach toward treatment.

Adolescent↗
PubMed1999

[Indications and results of thyroid gland ultrasound imaging of ambulatory care patients].

Sonography permits investigations which furnish impressive information whose practical benefit for the patient, however, has not been documented so far. The thyroid lends itself extremely well to sonographic study because of its superficial localization. The efficiency of this investigation has also not been elucidated. This study addresses the question of correlation between clinical and sonographic examination. Sonographic imaging did not have a great clinical impact and therapeutic consequences were rarely generated. A definitive diagnosis was usually possible after fine needle aspiration or hormonal analysis. Solitary thyroid nodules are an indication for sonography. Whether sonography is useful in patients with euthyreotic nodular goiter is debatable.

Adolescent↗
PubMed1999

[Smoking cessation in pharmacies--evaluation of the smoking cessation campaign "Tobacco adieu!" among pharmacists in Basel].

Now as in the past, tobacco consumption is a major health problem in Switzerland. Efforts to reduce tobacco consumption include different preventive strategies. Although dispensary pharmacists have increased their efforts in health promotion and prevention in recent years, their role in tobacco prevention has not been documented so far. The "Tobacco Adieu!" campaign to support smoking cessation was introduced in pharmacies as a low threshold offer in Basle in 1996. This paper assesses the process and the effect of this effort. Participating pharmacies were interviewed during the evaluation and all consultations in this area were recorded in questionnaires. Customers requesting counselling from pharmacies during the campaign were also asked to fill in a questionnaire regarding their smoking behaviour and their experiences in the pharmacy. The offer was well accepted by the public: During the four week period, about 2,000 client contacts for smoking cessation took place in the 63 participating pharmacies. Compared to the pre-campaign situation, more intensive counselling took place. Clients who received counselling in the pharmacies generally attested to its good quality. In addition to counselling, further care during the smoking cessation phase was offered to clients who wanted to quit smoking. Follow-up visits were agreed in 76 percent of the cases. The project shows that smokers can be motivated to consider cessation and supported in the process by pharmacists. Therefore, pharmacies can be used as a low threshold offer in this context. Expansion of this programme in public pharmacies seems justified. However, continuing education and a motivated team are the prerequisites for successful counselling of smokers in pharmacies.

Adolescent↗
PubMed1999

Motor conduction alterations in patients with lumbar spinal stenosis following the onset of neurogenic claudication.

The pathogenesis of neurogenic claudication is thought to lie in relative ischemia of cauda equina roots during exercise. In this study we will evaluate the effect of the transient ischemia brought on by exercise on motor conduction in patients suffering from lumbar spinal stenosis (LSS). We will also evaluate the sensitivity of motor evoked potentials (MEPs) in detecting motor conduction abnormalities before and after the onset of neurogenic claudication. Thirty patients with LSS and 19 healthy volunteers were enrolled in the study. All LSS patients had a history of neurogenic claudication and the diagnosis was confirmed with a CT myelogram. Both groups underwent a complete electrophysiological evaluation of the lower extremities. The motor evoked potential latency time (MEPLT) and the peripheral motor conduction time (PMCT) were measured. The subjects were asked to walk on a flat surface until their symptoms were reproduced. A new set of electrophysiological tests was then performed. Exercise did not produce claudication in any of the control group subjects. Twenty-seven patients did have claudication. The pre-exercise MEPLT and nerve conduction studies in the control group fell within the normal range. In the patient group, 19 patients had increased baseline values for MEPLT to at least one muscle. There was a significant difference between the MEPLT and the PMCT values measured before and after exercise in the patients with signs of neurological deficit. This difference was not found to be significant in patients without neurological deficits (t-test P < 0. 05). It may be concluded that exercise increases the sensitivity of MEPs in detecting the roots under functional compression in LSS.

Adult↗
PubMed1998

Quantitative magnetic resonance imaging in the assessment of degenerative disc disease.

Understanding degenerative intervertebral disc diseases hinges on the ability to objectively and noninvasively assess the disc matrix composition and integrity. The potential of quantitative magnetic resonance imaging to meet these demands was evaluated. Analyzing the T1 and T2 signal patterns in the nucleus pulposus with increasing Thompson morphological grade revealed a significant reduction related to grade. This significant decrease in T1 and T2 in the nucleus pulposus with grade 4 degeneration and the corresponding low correlation coefficients with respect to the content of individual matrix molecules suggest that matrix integrity plays an important and distinct role in determining T1 and T2 signal. Similarly, the significant increase in magnetization transfer in the nucleus pulposus observed in grade 4 degeneration did not correlate with the changes in molecular content in these highly degenerated discs. Again, this lack of correlation clearly indicates that the tissue integrity and matrix composition independently contribute to the magnetization transfer signal. This study presents the first clear evidence that quantitative magnetic resonance analysis reflects not only the disc matrix composition, but also the structural integrity of the matrix of the disc.

Adult↗
PubMed1998

[Economic evaluation in a trial of medically controlled prescription of narcotics to dependent users (PROVE)].

In the 1994-1996 trial of medically controlled prescription of narcotics to dependent users, 800 places were ascribed to heroin substitutes and another 200 for methadone and morphine substitutes. The trial was evaluated with the aid of an accompanying research. Among the results demonstrated in the evaluation was an improvement of the health of the participants. The economic assessment was drawn from observations of health effects within a sub-sample of 142 participants from four centers. In a retrospective statistical survey, for each acute illness which could be influenced through the trial, the number of diagnoses was recorded in the first and thirteenth month after study entry. Also, based on a number of representative cases for each of these acute illnesses, the resource use, i.e. the types and numbers of medical products and services rendered to the patients, was recorded. The results showed a clear decline in depressive episodes, skin diseases, digestive system disorders as well as epileptic attacks and intoxication. Treatment costs could be reduced from a total of CHF 94875.--to CHF 21,998.--/month or from CHF 22.27 to CHF 5.15/patient per day. The improvement of somatic and psychic health due to the medically controlled prescription of narcotics resulted in a benefit of CHF 17.11/person per day.

Depression↗
PubMed1998

Quantitative intramuscular myoelectric activity of lumbar portions of psoas and the abdominal wall during a wide variety of tasks.

PURPOSE: Since most previous reports of EMG activation profiles from psoas and the abdominal wall have been qualitative, the objective of this work was to document myoelectric activity from these deep muscles. This knowledge is required to assist in choosing specific training exercises and for making rehabilitation decisions that require knowledge of normalized and calibrated muscle activation levels in different tasks. METHODS: Intramuscular EMG was collected from five men and three women, in whom amplitudes were normalized to maximum contraction efforts and reported over a wide variety of clinical and rehabilitation tasks. Electrodes were inserted into vertebral portions of psoas and the three layers of the abdominal wall. Normalized signal amplitudes were reported as peak levels and time histories. RESULTS: All forms of sit-ups activated psoas (15-35% MVC) more than the curl-up (<10%); psoas was not highly activated during barbell lifting of loads up to 100 kg (< 16% MVC); psoas was most active during maximal hip flexion efforts; push-ups activated psoas up to 25% MVC. Several isometric abdominal exercises were evaluated using the criteria of maximizing abdominal activation while minimizing psoas activity: the side (bridge) support exercise proved the best training method for the abdominal wall. CONCLUSIONS: Consideration of deep muscle activity, provided in this report, is important for choosing the most appropriate rehabilitation and training program for an individual. Specific guidance is provided for choosing the best abdominal exercise, together with activation profiles during lifting, during twisting, and during hip rotation.

Abdominal Muscles↗