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Biomedical subjects

G Scheller

Publications and source records attributed to G Scheller.

At least 19 recordsLinked to original sources
PubMed2005

[Initial stability of press-fit acetabular cups--an in-vitro study].

AIM OF THE STUDY: Mechanical lever-out tests were performed in vitro to investigate the initial stability of press fit acetabular cups. METHOD: Five different uncemented, hemispherical press-fit cups were implanted in a standardized manner into Sawbones, Polyurethane foam blocks. Each cup was levered-out by using a 250 mm stainless steel rod, which was connected to the acetabular cup. Loads were then applied to the rod causing the cup to be diplaced. Lever-out forces were recorded by a computer. RESULTS: The results of the lever-out forces ranged between 39,2 and 50,8 Nm. The highest initial stability was achieved by two Titanium cups with a Titanium plasmaspray coating, a flattened pole and a sharp equatorial edge. According to our trials the equatorial rim of the polyurethane cavity is the crucial area for the implant's initial stabilty. There the highest amount of attrition was observed. CONCLUSION: To guarantee a high reproducibilty of the tests it is essential to pay particular attention to the quality of the polyurethane foam blocks, to the exactness of the reaming procedure and to a defined cup insertion. However as our trials were carried out under optimized labaratory conditions one must be careful not to over-interpret its results. Intraoperatively primary stability is also influenced by the quality of the bone.

Acetabulum↗
PubMed2003

Primary stability of threaded cups in THR--an experimental study.

Four threaded cups were tested up to their lever-out moments, torque-in moments and their resistance to failure. A was a parabolic-shaped, B was a spherical, C was a spherical-shaped too, and D was a conical shaped cup. Cup A and D represent cups which have proven themselves in clinical applications, but not cup B. The threads were determined and showed different constructive features. The cups were torqued into precise cavities in PVC foam cubes, after that they were levered out in a testing machine. The lever-out moments of all the cups showed significant differences; the results were: A: 78.4 Nm, B: 88.7 Nm, C: 117.5 Nm, D; 136.6 Nm. In the case of the torque-in moments there were no significant differences between A and B, neither between C and D. The differences in stiffness between B and C were not significant, but they were between the others. The primary stability against lever-out and the torque-in moment of threaded cups for artificial hip replacement can be basically influenced by different constructive features. Hence lever-out moment and torque-in moment should be understood and tested as independent variables.

Arthroplasty, Replacement, Hip↗
PubMed2002

[Results of treating slipped capital femoral epiphysis by pinning in situ].

The primary aim in treatment of chronic SCFE consists of immediate stabilization of the epiphysis to prevent further slipping. For mild degrees of slipping (<30 degrees ), pinning in situ is the treatment of choice. With slips between 30 and 50 degrees, the decision should be based on individual factors (age, functional limitation of the hip joint) whether pinning in situ is sufficient or whether an additional intertrochanteric osteotomy according to Imhäuser should be performed.The choice of implant should ensure a safe and stable connection between the epiphysis and the femoral neck without resulting in a substantial impairment of growth of the femoral neck due to premature closure of the growth plate. Since 1982 we have used K wires for in situ pinning of the affected hip as well as for prophylactic pinning of the nonaffected hip with a low complication rate. In a clinical and radiological study, 65 patients with a chronic slip of less than 50 degrees could be assessed after in situ pinning. Almost 75% were pain-free after a follow-up interval of 9.8 years, and 92% achieved a good or very good result according to the criteria of the Iowa hip score, the mean score being 95.1 points. According to the radiological score of Schulitz, five patients (7.7%) demonstrated a grade I osteoarthritis. One patient showed a partial necrosis of the femoral head; chondrolysis was not observed.

Adolescent↗
PubMed2002

[Improvement of osseointegration of bio-inert ceramics by modification of the surface--results of an animal experiment].

The aim of this experimental study was to screen different surface structures of alumina and zirconia ceramic implants for their osteointegration properties. Alumina and zirconia ceramic test implants having different surface structures (smooth, macro-structured, corundum-blasted, porous) were implanted in the femora of mini-pigs, and left in situ for 12 weeks. After removal, the implants were evaluated macroradiographically and histologically. The smooth and macro-structured ceramic surfaces showed virtually no bony ingrowth, neither in the cortical nor the cancellous bone areas. In contrast, a rough surface finish or a porous surface structure allowed extensive bony ingrowth. The osteointegration rates varied between 20.5% and 41.7% (cancellous bone), and between 26.0% and 52.8% (cortical bone). With regard to the development of ceramic implants for clinical use, for example in the field of total hip replacement, these data provide a basis for further, more comprehensive studies.

Aluminum Oxide↗
PubMed2001

[Long-term results with the cement-free Spotorno CLS shaft].

This retrospective study reviews 298 sequential cementless CLS Spotorno stems, which achieved their primary fixation and bony in- or ongrowth predominantly in the metaphyseal region. The minimum follow-up was 10 years and the average follow-up 11.7 years (range 10-14). The mean age at surgery was 55.2 years (range 32.2-68.9). Of the patients, 76.2% (227 stems) were followed up: 172 patients (57.7%) underwent clinical and radiological examination and 52 patients (55 stems, 18.5%) were interviewed by telephone. Of 298 stems, 13 (4.4%) had been replaced in the mean time, only 6 stems (2.0%) because of an aseptic loosening. The evaluation included both clinical (Merle d'Aubigne and Harris hip score) and radiographic parameters (plain X-rays). The mean Merle d'Aubigne score was 16.7 points, and the mean Harris hip score was 94.3 points. Radiolucent lines were detected in 33.7%; 5.8% showed enlargement within the last 3 years. Focal osteolyses were present in 30.8% of patients; 2.9% had progressed within the last 3 years. At follow-up, one patient presented with new clinical and radiological evidence of aseptic stem loosening. The current study showed an aseptic loosening of the CLS stem in 2.3%, a good osseointegration and good functional score results in more than 90%. The primary fixation and bony in- or ongrowth predominantly in the metaphyseal region seems to achieve good clinical results. Wear is the main reason for the osteolytic changes. Frequent clinical and radiological follow-up is important to detect bone reactions and loosening of the stem.

Adult↗
PubMed2001

Mid-term results of the cementless CLS stem. A 7- to 11-year follow-up study.

Between 1986 and 1990, 335 primary total hip arthroplasty (THA) were performed using the cementless CLS stem. The mean age at surgery was 55.3 years. The retrospective study was performed at an average follow-up time of 8.9 years. A total of 232 patients (69.3%) underwent clinical and radiological examination, 33 patients (9.9%) were interviewed by telephone, and 9 stems (2.7%) had been replaced meanwhile. The mean Harris hip score was 91.7 points, and the mean Merle D'Aubigne score was 16.8 points. One stem had subsided during the first postoperative year. Ectopic ossifications classified as Brooker III were noted in 5.7%, with no Brooker IV being seen. Radiolucent lines were found in 43.5%, and 11% showed enlargement with time. Focal osteolyses were present in 36%, of which 24% progressed with time. At the latest follow-up, we did not find any stem loosening clinically or radiologically.

Adult↗
PubMed2000

[Simulator for migration processes and wear in the artificial hip acetabulum for radiologic measurement].

For assessing migration of cups, standard X-rays or stereo radiological images (SRI) are available. In addition, software is also available for measurements. The accuracies of the various systems are established statistically, in part combined with phantoms, and compared. To date, no known phantom is available for the simulation of acetabular cup migration with account being taken of the position of the pelvis in the X-ray beam. Such an appliance covering 8 different parameters has now been developed, the cup can be moved horizontally, vertically and in the loading direction. Angular accuracy is +/- 0.5 degree, and wear of a magnitude of 0.25 mm can be simulated. Two degree elevation of the pelvis, left or right, can be simulated. The position of the pelvis around the horizontal axis permits continuous variation. This appliance can simulate migratory movements of the acetabular cup within a pelvis, and wear within the cup. In addition, the spatial position of the pelvis can be varied. The X-ray images can be used to investigate the accuracy of evaluation strategies.

Acetabulum↗
PubMed1999

Simulator trials to determine the wear of the combination aluminium oxide ceramic-carbon fibre reinforced plastic (CFRP) used as an insert in a hip socket.

Hip simulator trials were conducted to determine the initial wear between alumina femoral heads and carbon fibre reinforced plastic (CFRP, CAPROMAN) insert in a titanium socket. A force of 2500 N and a frequency of 0.857 H were applied. Using surface and sphericity measurement techniques, the amount of wear was determined. After 500,000 cycles, the centre of the head had moved by 10 microm into the insert, and the average radius increased by 2 microm. After 1 million cycles, the additional changes were less than 1 microm. Based on an examination of retrieved implants (wear rate: 6.1 microm/year) and based on the simulator results, the combination alumina-CFRP inserts could be approved for total hip replacement.

Biomechanical Phenomena↗
PubMed1999

[Primary stability of cement-free press-fit acetabulum cups. In vitro displacement studies].

The initial stability of 6 different hemispherical press-fit titanium acetabular cups was investigated by lever-out tests using a foam model. Each cup was implanted in a standardised manner into machined PVC-foam blocks with an underreaming of 1/2/3 mm, and levered out 5 times. A computer recorded the load-displacement curves. Both insertion forces and lever-out forces increased with increasing press-fit from 1 to 2 mm. With underreaming of 2 mm, insertion forces varied between 9 and 34 Nm, and lever-out torques between 13 and 23 Nm. The cup made up of multi-layer irregular titanium wire mesh had the highest initial stability of all the cups tested. 3 mm underreaming was associated with insertion difficulties, so that lever-out is difficult to compare with that with 1 and 2 mm. The amount of contact on the equatorial rim, where we saw the most attrition after lever-out, is the most important factor for determining the lever-out torque. The quality of the PVC foam blocks, the accuracy of reaming, and the definition of cup insertion are very important parameters for test reproduction. Since the trials were conducted under laboratory conditions, translation of the results to the intraoperative situation should be undertaken only with certain reservations.

Acetabulum↗
PubMed1998

Advantages of patellar resurfacing in total knee arthroplasty. Two-year results of a prospective randomized study.

Complications of patellar resurfacing in total knee arthroplasty have rekindled the interest of many surgeons in patellar retention. In a prospective study 20 randomly selected patients of 40 underwent patellar resurfacing in combination with their total knee arthroplasty. The other 20 patients were left with an unresurfaced patella. Within 24 months of follow-up, the advantages of patellar resurfacing could be seen according to the Knee Society Score. Especially in advanced osteoarthritis of the knee joint, the patients achieved better scores in climbing stairs and in function. The superior functional results are arguments for patellar resurfacing, at least in knees with advanced osteoarthritis.

Aged↗
PubMed1998

[Patellar resurfacing. Results of a prospective randomized study].

The mid-term results of this prospective randomized study illustrate why it is difficult to define a clear position concerning the issue of patellar resurfacing in total knee arthroplasty. In both groups of 20 patients typical complications for the respective procedures have occurred. One patient from group A with patellar resurfacing had to be revised for loosening of the patellar implant. In group B without resurfacing 3 patellae subluxated, 2 having been revised. Furthermore 4 patients complained about mild to moderate anterior knee pain. The Knee and Function Scores of the patients without revision were not significantly different except for the parameter pain (Knee Score Gr. A:84.8, Gr. B:77.8; pain Gr. A:46.9, Gr. B:41.9; Function Score Gr. A:78.5, Gr. B:71.9; climbing stairs Gr. A:38.5, Gr. B:33.8). The radiological measurements found the patellae with resurfacing significantly less tilted with 3.8 degrees than the patellae without resurfacing with 6.4 degrees. With the correct implantation technique patellar resurfacing guarantees a good clinical result within the first 5 years. Leaving the patella unresurfaced was associated with a higher rate of anterior knee pain and revision in our study.

Aged↗
PubMed1997

[Effect of integrated distance studs on cement thickness of implanted PE-acetabulum cups--experimental in vitro studies for improved cementing technique].

Variations in cement thickness between PE cups and acetabular bone are biomechanically unfavourable, and may contribute to prosthetic loosening. Integrated distance studs should in the first instance, prevent local thinning of the cement. In an experimental study we compared the thickness of the cement mantel of implanted PE cups without such studs. In the case of cups with studs, significantly fewer areas of thin cement (0-1 mm) were found in comparison with cups with no studs. "Bald" areas of cement (0-0.2 mm) were virtually prevented by the studs. We are of the opinion that PE cups with integrated studs on the surface ensure a uniform cement thickness around the cup, as well as decreasing the risk of "bald" areas in the cement, thus reducing loosening.

Acetabulum↗
PubMed1996

Follow-up (6-9 years) results of the uncemented CLS Spotorno stem.

The aseptic loosening rate in uncemented hip endoprostheses, especially the stem, is one of the most discussed problems among hip surgeons within the last few years. The first generation of uncemented stems had an essentially higher loosening rate compared with cemented stems. Although there are many reasons for this disappointing fact, the type of primary fixation and polyethylene wear are the two main ones. We reviewed 145 sequential uncemented CLS Spotorno stems, which achieved their primary fixation and bony in- or ongrowth predominantly in the metaphyseal region. The mean age of the patients was 54.9 years (range 37-76 years), and average follow-up was 7.8 years. The evaluation included both clinical (Merle d'Aubigne and Harris Hip Score) and radiographic parameters (plain X-rays). The medium-term follow-up showed a survival rate of 96.7% and good functional score results in more than 90%. Special attention was paid to the so-called thigh pain phenomenon which, despite current views, was found to be unexpectedly low (only one case). Although these results are encouraging, a further long-term follow-up of more than 10 years will have to show whether or not comparable results to cemented stems can be realised.

Adult↗
PubMed1996

Uncemented total hip replacement and thigh pain.

We reviewed 145 consecutive patients who had total hip replacements using uncemented CLS Spotorno femoral stems which achieve primary fixation with bony ingrowth which occurs later mainly in the metaphyseal region. The mean age was 54.9 years and average follow up 7.8 years. The Merle d'Aubigne and Harris hip scores were used for evaluation, together with plain radiographs. Current medium term follow up showed a survival rate of 96.7% and a good functional score in more than 90%. Special attention was paid to postoperative thigh pain which occurred in only one patient. These results are encouraging, but a follow up of more than 10 years is required before comparable results to cemented stems can be claimed.

Adult↗
PubMed1996

[Wear behavior of coupled aluminum oxide ceramics-carbon fiber bond as hip acetabulum inlay in a simulated trial].

Hip-simulator studies were carried out to investigate the initial wear between a femoral head made of aluminium oxide ceramic and a CFRP-(carbon fibre-reinforced plastic) inlay in a titanium cup. A load of 2500 N and a frequency of 0.857 Hz were applied. After 200,000 cycles, the centre of the head had moved 9 microns into the liner. After 500,000 cycles, the cup centre had moved inwards by a further micron, and the near radius had increased by 2 microns. After 750,000 cycles the position of the centre of the head remained unchanged, while the mean radius had increased a further 2 microns. After one million cycles any further changes remained below the measuring capability (1 micron) of the system.

Aluminum Oxide↗
PubMed1992

Ten- to 14-year results of a ceramic hip prosthesis.

One hundred total hip arthroplasties with a cementless aluminum oxide socket and ball with different types of cemented metal femoral stems were performed from 1974 to 1979. All were primary implantations. These cases were recently reviewed in a ten- to 14-year follow-up evaluation. Despite extensive laboratory testing of the ceramic material, a significant number of cases resulted in a very unfavorable result such as extensive wear, ball fracture, or migration of the socket. Whereas the patients had died or could no longer be traced in the case of 23 prostheses, there were 25 prostheses that had already been exchanged at the time of review for mechanical reasons (two stem fractures, eight ceramic ball fractures) and for component loosening attributable to wear of the alumina components. The remaining 52 prostheses still in place had good clinical results in 80%. However, roentgenographic evaluation of these prostheses revealed signs of loosening in six femoral components and in three sockets. Migration of more than 5 mm was evident in 24 sockets (46% of surviving prostheses). Although this had caused loosening in only three sockets at the time of review, further migration up to the limits of the acetabular region would be a major reason for future failures.

Adult↗