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Biomedical subjects

Lawrence D Dorr

Publications and source records attributed to Lawrence D Dorr.

14 recordsLinked to original sources
PubMed2003

Measurement of polyethylene wear in total hip arthroplasty--accuracy versus ease of use.

The aim of this study was to compare the accuracy of four different methods for measuring wear using an apparatus that simulates known amounts of three dimensional wear. Wear was measured using the manual methods reported by Charnley, Livermore, Dorr and Wan and the computerized method reported by Devane. Only the method reported by Devane measured the three-dimensional (superior and anterior) wear with a reasonable accuracy, with a mean measurement error of 0.21 mm. With superior wear alone, Charnley's method underestimated the extent of wear by 16.6%, with a mean error of 0.35 mm; Livermore's method estimated wear to within 9.5%, with a mean error of 0.16 mm; Devane's method estimated wear to within 9.5%, with a mean error of 0.15 mm; and Dorr's method underestimated wear by 25.4%, with a mean error of 0.56 mm. Dorr's method was modified as a result of the experimental tests. The clinical application of the new method showed comparable data to that using the Devane method. In conclusion, this new method can be used to estimate the average wear in groups of patients accurately.

Equipment Failure Analysis↗
PubMed2003

Self-inflicted risks of orthopaedic surgery.

The advancements in medicine, including orthopaedic treatment, since 1960 have so greatly improved quality of life that human nature has changed in its social goals. These technological innovations, especially the products created, have resulted in a self-inflicted increase in risk of practice. This risk will not be leveled until society recognizes that it expects that the physician not only be a healer, but able to fulfill the social goals of the patient.

History, 20th Century↗
PubMed2003

The risk of product liability: orthopaedic surgeons can be trapped.

Orthopaedics has become the specialty that it is because of the technologic advancements of medicine in designing successful implants. However, the use of implants introduces a new risk of product failure. The orthopaedic surgeon needs to be aware of the potential consequences of the risks of use of devices in treating patients.

Humans↗
PubMed2003

A biomechanical analysis of polyethylene liner cementation into a fixed metal acetabular shell.

BACKGROUND: A common clinical scenario encountered by an orthopaedic surgeon is a patient with a secure cementless acetabular shell and a failed polyethylene liner. One treatment option is to cement a new liner into the fixed shell. The purpose of this study was to evaluate technical variables to improve the mechanical strength of such cemented liner constructs. METHODS: The contributions of shell texturing, liner texturing, and cement mantle thickness (between the liner and the shell) were evaluated by comparing torsional strength (among nine groups of constructs) and lever-out strength (among eight groups of constructs). RESULTS: Failure almost always occurred at the cement-liner interface. The two exceptions (failure at the shell-cement interface) occurred with a polished, untextured shell with no screw-holes. This finding indicates that if a shell has existing texturing (such as holes), further intraoperative scoring of the shell is unnecessary, but some sort of texturing is necessary to avoid construct failure at the shell-cement interface. Textured liners had significantly (a = 0.05) greater torsional and lever-out strength than untextured liners. The greatest construct strength occurred when liner grooves were oriented so as to oppose the applied loading. A 4-mm-thick cement mantle resulted in slightly greater torsional strength than a 2-mm-thick cement mantle, and a 2-mm-thick cement mantle resulted in considerably greater lever-out strength than a 4-mm-thick cement mantle, but these differences were not significant. CONCLUSIONS: When cementing a liner into a well-fixed shell, a surgeon should ensure that both the shell and the liner are textured, as interdigitation of the cement with the shell and the liner is crucial to the mechanical strength of this construct.

Arthroplasty, Replacement, Hip↗
PubMed2002

Fixation of the millennium: the knee.

Current reports of noncemented fixation for total knee arthroplasty show that fixation of the components is durable for 20 years. Noncemented fixation may be preferable in patients <60 years old. In revision total knee arthroplasty, cemented stems are preferable in patients >70 years old.

Age Factors↗
PubMed2002

Polyethylene liner cementation into fixed acetabular shells.

A patient presenting with a secure cementless acetabular component and with femoral head penetration through the polyethylene liner is a common clinical problem. Cementing a new liner into the fixed shell is one option. We evaluated this option in a clinical series of 17 cases and with a preliminary mechanical study. In the 1 clinical failure (5.9%), the failure occurred at the cement-liner interface. The most important variable in optimizing the mechanical strength of the cemented liner construct was adequate preparation of the cement-liner interface. This approach to treating the patient with a fixed cementless shell and a worn polyethylene liner can provide a durable construct with minimal morbidity.

Aged↗
PubMed2002

Case challenges in knee surgery: what would you do?

In an interactive case presentation session, the faculty discussed management of complex primary and revision knee arthroplasty issues. Principles discussed included: preoperative evaluation of the failed knee arthroplasty, intra-articular versus extra-articular deformity correction, ligamentous balancing, managing the unstable total knee arthroplasty, bone deficiency management, rotational positioning of prosthetic components, selection of articular constraint in the revision knee, and extensor mechanism balancing.

Arthroplasty, Replacement, Knee↗
PubMed2002

Intraoperative monitoring for safety of bilateral total knee replacement.

Cardiopulmonary hemodynamics in 79 consecutive patients who had one-stage bilateral total knee replacements were monitored prospectively with a pulmonary artery catheter. The pulmonary vascular resistance, wedge pressure, pulmonary artery pressure, and systemic vascular resistance were measured before skin incision, 5 to 10 minutes after implanting the first total knee replacement, and after the second knee replacement. The second knee replacement was cancelled in five patients because the pulmonary vascular resistance after the first knee replacement was more than double the baseline, or above 200 dyne/second/cm(5). No patient had clinical symptoms of fat embolism during the postoperative course. Patient predictive factors, or the use of pulse oximetry readings instead of a pulmonary artery catheter, were not predictive of intraoperative elevation of pulmonary vascular resistance. For this reason, the safety of this operation for the patient requires that intraoperative measurement of hemodynamic parameters of embolism be done.

Aged↗
PubMed2002

Contrary view: wear is not an issue.

Wear was not an issue with total knee replacements that had a round-on-round design such as the Total Condylar and the Insall-Burstein prostheses. As long as designs do not try to reproduce normality in kinematics, wear will not be an issue. To date, there are no data that mobile-bearing knee replacements will decrease wear complications as compared with round-on-round fixed designs. Wear is not an issue if the total knee replacement is done with a round-on-round design with a cobalt chrome femoral component, monoblock tibial component, and an all-polyethylene patella, all with cemented fixation.

Arthroplasty, Replacement, Knee↗
PubMed2002

Cementless hemispheric porous-coated sockets implanted with press-fit technique without screws: average ten-year follow-up.

BACKGROUND: Press-fit implantation of a porous-coated hemispheric acetabular component without screws is an option for primary total hip replacement. The purpose of the present study was to evaluate the results of this technique after an average duration of follow-up of ten years to determine if there was any loss of fixation or increase in osteolysis over time. METHODS: From June 1988 to November 1990, 132 primary total hip replacements were performed with a porous-coated socket that was implanted with use of a press-fit technique. Twenty-two hips were excluded because the patient had died or had been lost to follow-up, leaving 110 hips (103 patients) available for inclusion in the study after an average duration of follow-up of 10.2 +/- 1.0 years. The average age of the patients at the time of operation was 60.7 years (range, 23.7 to 86.2 years). Radiographs were evaluated with regard to initial gaps, radiolucent lines, migration, polyethylene wear, and osteolysis. Kaplan-Meier survivorship analysis was performed to calculate the rate of survival of the acetabular component. RESULTS: One hip (0.9%) had revision of the socket because of aseptic loosening, and four hips (4%) had revision of a stable socket. With the numbers available, the presence of gaps on the initial postoperative radiographs was not associated with the occurrence of radiolucent lines (p = 0.039). Pelvic osteolysis was seen in four hips, with an average time to radiographic appearance of six years. Increased wear was directly related to an abduction angle of >40 degrees. The twelve-year survival rate was 99.1% with revision because of failure of fixation of the metal shell as the end point, 95.3% with revision for any reason as the end point, and 79.6% with exchange of the liner as the end point. CONCLUSIONS: The fixation of this press-fit socket did not deteriorate over time and was associated with a low rate of osteolysis. The most common reasons for reoperation were wear and dissociation of the polyethylene insert.

Adult↗