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H C Amstutz

Publications and source records attributed to H C Amstutz.

At least 19 recordsLinked to original sources
PubMed2002

Polyethylene wear characteristics in vivo and in a knee stimulator.

Validation of a wear simulator requires that the device produce a similar type and amount of wear and particles of a comparable morphology as occurs clinically. Using techniques previously established to compare polyethylene particles from hip simulators to those from retrieved tissues, particles isolated from six revised posterior stabilized knee replacements were characterized and compared to particles generated from the same knee design worn in a knee simulator. The particles produced in the knee simulator were of comparable size but had less variability in their form factor compared to the particles produced in vivo. Comparable wear features were seen on the articulating surfaces in both groups. These results indicate that this knee joint simulator is able to reproduce a baseline type of wear that is similar to that in vivo and should encourage further use of this device to better understand knee component wear and function.

Arthroplasty, Replacement, Knee↗
PubMed2001

Duration of symptoms and outcome of hemiresurfacing for hip osteonecrosis.

Thirty-seven hips with Ficat Stage II, III, or early IV osteonecrosis were treated with hemiresurfacing. The purpose of this study is to analyze specifically the clinical and radiographic results of patients who had hemiresurfacing to refine the indications for the procedure and identify factors substantially affecting clinical outcome and survivorship. At an average followup of 6.5 years, the average University of California Los Angeles hip scores for pain, walking, function, and activity improved significantly from 4.3, 6.0, 5.3, and 4.2 to 8.0, 8.8, 7.9, and 5.8. The overall survivorship was 79%, 59%, and 45% at 5, 10, and 15 years. Eleven hips have been converted: 10 hips for acetabular cartilage wear and one hip for femoral loosening. The average time to conversion was 7.5 years. A longer duration of symptoms before surgery (16.6 months versus 12.1 months) was associated with a worse acetabular cartilage grading and suggested a relationship with a shorter time to conversion, although the difference was not statistically significant at the 5% level. Survivorship is better when preoperative symptoms are present for 1 year or less, possibly because the articular cartilage is healthier. When necessary, conversion to total hip replacement can be done without adverse results.

Adolescent↗
PubMed2000

Relationship between body mass index and activity in hip or knee arthroplasty patients.

The weight of patients has not been demonstrated to have a consistent effect on the rate of polyethylene wear in clinical studies of total joint replacement. For this reason, we analyzed the relationship between quantitative activity, measured with a pedometer, and body mass index, a measure of obesity. Data were acquired for 209 individuals, 22-82 years of age; all were independent community walkers. One hundred and fifty-one had a well functioning total hip or knee replacement. Analysis of variance was used to evaluate the relationship between activity and body mass index, with adjustments for confounding variables. The 58 individuals with no total joint prosthesis averaged 7,781 steps per day, which was higher (p < 0.01) than those with a total hip (5,869 steps per day) or knee (4,597 steps per day) replacement. The subjects with no total joint prosthesis were, however, younger than the patients with a prosthesis (p < 0.01), and the body mass index of the patients with a total knee replacement was higher than that of the patients with a hip replacement and that of the subjects with no prosthesis (p < 0.01). After adjustment for differences in age, gender, and Charnley class, a higher body mass index (greater obesity) was associated with lower activity (p = 0.05). With regard to the rate of polyethylene wear, decreased ambulatory activity may counterbalance increased weight, which could, at least in part, explain why weight has not had a consistent effect on polyethylene wear in clinical studies. Wear is a function of use, not time. The effect of obesity on activity should be considered in radiographic studies of wear and other outcome assessments of total joint replacements.

Adult↗
PubMed2000

Viability of femoral heads treated with resurfacing arthroplasty.

There is a general conception that resurfacing arthroplasty causes femoral head osteonecrosis and subsequent failure of the implant. This study histologically analyzed 25 resurfaced femoral heads up to 12 years postoperatively and found that osteonecrosis was not induced by the procedure.

Arthroplasty, Replacement, Hip↗
PubMed2000

Use of a magnet to retrieve a broken scalpel blade.

The retrieval of metallic foreign bodies, such as screws, drill bits, needles, and scalpel blades, from the surgical wound during orthopaedic surgery is often a time-consuming procedure. The extra time and dissection may result in increased morbidity. We report a case during a hip arthroplasty in which a broken surgical blade could not be located with surgical dissection even with the aid of an image intensifier. The broken blade finally was retrieved with the introduction of a magnet.

Arthroplasty, Replacement, Hip↗
PubMed2000

The John Charnley Award. Wear is a function of use, not time.

Polyethylene wear (linear penetration) in 37 hip replacements was assessed from digital images using a validated two-dimensional, edge detection-based computer algorithm. Patient activity was assessed with a pedometer, a step activity monitor and a simple visual analog scale. Joint use was related to wear at the 90% confidence level. Without three recognized outliers, wear was highly correlated to use. The visual analog scale activity rating was significantly related to wear for the 24 hip replacements with standard polyethylene. Univariate regression analysis indicated that male gender, height, weight (which were both highly correlated to male gender) and hip center of rotation were significantly correlated to wear. Multivariate regression analysis indicated that male gender, femoral off-set, and Hylamer were significantly correlated to wear. Based on the wear and activity data from the 24 hip replacements with standard polyethylene, the average volumetric wear rate per million cycles with a 70 kg patient weight was 30 mm3. This unique in vivo result can be considered a target wear rate for standard polyethylene in hip simulator studies.

Aged↗
PubMed2000

Innovations in design and technology. The story of hip arthroplasty.

The current study reviews the early history of surgeon-initiated trial and error development in hip joint arthroplasty and the subsequent methodological evolution to proper criteria for hypothesis testing using bioengineers and other research scientists. The interplay and relationships to industry, universities, scientific organizations, and the Food and Drug Administration with respect to device development in hip arthroplasty are reviewed. The ethics of and responsibilities to involved parties are outlined, citing the history of many contemporary developments. Examples are provided from the evolution and introduction of unsuccessful innovations, and the problems inherent in the current methodology of the approval process from the Food and Drug Administration using the 5-10K, Investigative Device Exemption, and the Pre-Market Approval protocols. The pros and cons of randomized trials for devices are outlined with the conclusion that they are not appropriate for device introduction. The proper, rational methodology for introduction of new devices is a phased-in clinical trial process after pertinent bench testing. Finally, the ethical dilemmas created by managed care are addressed. Industry involvements of the surgeon-spokesmen are cited.

Device Approval↗
PubMed1999

Lessons learned from loosening of the McKee-Farrar metal-on-metal total hip replacement.

Clinical and radiographic data for 15 McKee-Farrar hip replacements that had failed because of aseptic loosening (4 stem loosening, 9 cup loosening, and 2 loosening of both components) between 0.6 and 21 years (average, 8.3 years) were compared with 15 hips in which the McKee-Farrar total hip replacement has survived between 21 and 26 years. Hips that loosened were biomechanically disadvantaged compared with those that demonstrated long-term survival. Radiographic evaluation demonstrated that in hips that were revised for aseptic femoral loosening, the offset was decreased by a mean of 1.4, whereas it was increased by a mean of 4.9 mm in the surviving hips (P = .04). Further, in hips revised for aseptic loosening, the center of rotation was medialized by a mean of only 1.4 mm, whereas the center of rotation was medialized by a mean of 6.4 mm in the surviving hips (P = .1). Unfavorable biomechanics results in increased joint reaction forces that could contribute to loosening of these prostheses. Five of 6 McKee-Farrar stems revised for aseptic loosening compared with 7 of 15 surviving stems were in varus (P = .1) and, as a result, had cement mantle defects in zones III and VII. Thus, in the McKee-Farrar, similar to what has been seen in hips with metal-on-plastic bearings, curved stems are associated with varus positioning, cement mantle defects, and loosening. Wear of the metal-on-metal articulation does not appear to be the cause of failure in these cases. Wear could not be detected radiographically. At revision surgery, there was no indication of excessive bearing wear or gross metal staining of periprosthetic tissues. Microscopic analysis of tissue sections demonstrated both metal and polymethylmethacrylate particles of variable size and shape. The variability of the particles suggests that they are likely the result of loosening and that they were not generated by bearing surface wear that could cause loosening. Although it is hoped that improvements in the wear resistance of the bearing will increase survivorship, this experience and analysis of the McKee-Farrar total hip replacement illustrates the importance of the implant design, biomechanics of the reconstruction, and role of surgical implantation technique.

Arthroplasty, Replacement, Knee↗
PubMed1999

The role of acetabular component screw holes and/or screws in the development of pelvic osteolysis.

Anecdotal reporting of osteolysis around cementless modular acetabular components with holes through the metal shell and/or iliac fixation screws has raised concern that such designs may generate excessive particulate debris and/or permit direct access of particulate debris to iliac bone. To address this issue, incidence data are reported on 513 total hip replacements from six different single-surgeon series of total hip arthroplasties performed with six different porous ingrowth acetabular components. With follow-up ranging from 40 to 108 months, a total of 45 pelvic osteolytic lesions were observed (8.8 per cent). Pelvic osteolysis was seen nearly as frequently in the ischium and pubis (21 lesions) as it was in the ilium (24 lesions). It was not possible to explain ischial and pubic osteolysis by holes and/or screws through the acetabular component shell. There was no direct correlation between the presence of screw holes or screws and the incidence of pelvic osteolysis. The incidence of pelvic osteolysis around modular components with holes through the shell was 4.5 per cent (14 of 313 hips). The incidence of pelvic osteolysis with solid-shell components was 15.5 per cent (31 of 200). The incidence of pelvic osteolysis around acetabular reconstructions with screws was 2.3 per cent (3 of 133). The incidence of pelvic osteolysis in reconstructions without screws was 11.1 per cent (32 of 380). The incidence of pelvic osteolysis in one-piece acetabular components (polyethylene pre-fixed in the metal shell) was 12.7 per cent (21 of 165) and the incidence of pelvic osteolysis with the modular components was 6.9 per cent (24 of 348). In each comparison, the incidence of pelvic osteolysis was actually lower in the group assumed to be at increased risk. Based on this review there does not appear to be a direct relationship between holes and/or screws through an acetabular component and the development of pelvic osteolysis. The incidence of pelvic osteolysis was associated with larger head diameters and longer follow-up. While screw holes may provide an access channel in specific cases, the present data indicate that the simple elimination of holes through the acetabular shell will not eliminate pelvic osteolysis. Regardless of other acetabular component design features, joint fluid and polyethylene wear particles from the femoral-acetabular articulation can gain access to bone behind an acetabular component via the peripheral implant-bone interface through regions without sufficient contact or tissue ingrowth. The development of pelvic osteolysis is multifactorial and includes the total volumetric wear of polyethylene as well as specific features of the acetabular component design and reconstruction technique.

Adult↗
PubMed1998

Metal wear particle characterization from metal on metal total hip replacements: transmission electron microscopy study of periprosthetic tissues and isolated particles.

The less intense tissue reaction around metal on metal total hip replacements (THRs) compared to metal on polyethylene (PE) THRs may be explained by the differences in the characteristics of metal wear particles. In this study, transmission electron microscopy was used to study metal wear particles that were either in situ in cells or had been extracted from the cells by a new technique based on enzymatic tissue digestion. The tissues were obtained from 13 patients undergoing revision of metal on metal THRs with cobalt-chromium-molybdenum (CoCrMo) bearing couples. Most of the CoCrMo wear particles were smaller than 50 nm (range 6-834 nm) and round to oval in shape with irregular boundaries. This size range is considerably smaller than that reported for PE particles. While even a small volume of metal wear will produce high numbers of particles, the apparently less severe local tissue reaction to metal particles may be due to the possibility that corrosion, dissolution, and dissemination of metal particles may result in fewer local biological effects than the long-term retention of PE particles in the periprosthetic tissues.

Adult↗
PubMed1998

Evolution and future of surface replacement of the hip.

Surface replacement is a bone-conserving alternative to total hip arthroplasty and is a significant development in the evolution of hip arthroplasty. Surface replacement with polyethylene bearings was largely abandoned, primarily because of component aseptic loosening caused by tissue reaction to high-volumetric polyethylene wear. For patients with osteonecrosis and collapse of the femoral head but with preservation of some acetabular articular cartilage, precision fit, hemisurface replacement of the femoral head only has emerged as the treatment of choice. The survivorship of our series of patients, performed in the 1981-84 era (average age, 32 years), has been 85% at 5 years, 67% at 10 years, and 42% at 16 years. In the absence of polyethylene, there has been no loosening. Revisions were for cartilage wear. The procedure is now much improved with instrumentation for non-trochanteric osteotomy approaches and off-the-shelf components in 1-mm increments. For arthritic hips, a new era of surface replacement has emerged. With metal-on-metal bearings, the volumetric wear has been reduced 20-100 times from those with polyethylene, and there is no penalty for the large ball size. The devices are now conservative on the acetabular as well as femoral side. Hybrid or all-cementless fixation is superior to earlier all-cemented devices. In those patients, the results with up to 4 years have been complication-free, with an absence of pain and a return to high functional levels, including participation in sports. Forty patients have received a Conserve Plus with interference fitting of the acetabular component with sintered beads to obtain fixation. Although the follow-up is short, surface replacement with the large ball size is extremely stable, and dislocation is rare.

Adult↗
PubMed1998

Assessing activity in joint replacement patients.

Outcome evaluations of lower extremity joint reconstructions should include an assessment of patient activity. In vivo wear assessments of total joint prostheses should be based on a measure of use, not time in situ or a proxy such as age or gender; however, clinicians lack a simple method to reliably assess the activity of patients with joint replacement. The modern pedometer can be a satisfactory means of quantifying the use of lower extremity joints. The pedometer, however, requires special effort on the part of the physician or evaluator and the patient. Therefore, we compared the quantitative assessment of walking activity of 100 total joint replacement patients, as measured with a pedometer, to the UCLA activity score and a simple visual analog scale that can easily be employed during a routine office evaluation. Both the UCLA activity rating (P = .002) and the visual analog scale rating of the investigator (P = .00001) had a strong correlation with the average steps per day as recorded by the pedometer. There was, however, up to a 15-fold difference in the average steps per day for individual patients with the same UCLA score. The visual analog scale as rated by the patients of their own activity did not have as strong a correlation with the pedometer data (P = .08) as did patient age (P = .049). For practical reasons, the pedometer is probably best reserved for the evaluation of extreme cases of activity (or inactivity). This study indicates that both the UCLA activity rating and the investigator visual analog scale are valid for routine activity assessment in a clinical setting. Adjustments of the UCLA activity score for the frequency and intensity of activity, as can be done with the investigator visual analog scale, increase the accuracy of the activity rating.

Activities of Daily Living↗
PubMed1998

Direct-exchange arthroplasty for the treatment of infection after total hip replacement. An average ten-year follow-up.

Twenty consecutive patients who had a direct-exchange total hip arthroplasty, performed by one surgeon between October 1979 and July 1990, were prospectively followed and data were collected. The most common infecting organism was Staphylococcus epidermidis (nine patients), followed by Streptococcus species and Staphylococcus aureus (five patients each). Three patients (15 per cent) had a draining sinus tract at the time of the operation. The operation and the postoperative management included meticulous débridement, administration of appropriate systemic antibiotic therapy, and use of antibiotic-loaded cement. By an average of 9.9 years (range, 3.5 to 17.1 years) postoperatively, no patient had had recurrence of the infection. Two patients had a revision for aseptic loosening nine and seventeen years after the direct exchange. Although the present series is relatively small, our experience has shown that direct exchange, which is associated with less morbidity and is less expensive than delayed exchange, can be successful in carefully selected patients.

Adult↗