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Biomedical subjects

M A Ritter

Publications and source records attributed to M A Ritter.

At least 109 records · Page 6Linked to original sources
PubMed1996

Femoral head size: variation among manufacturers.

Nine manufacturers were contacted for their specific femoral head diameters of the 22 mm, 28 mm, and 32 mm femoral components. The 22 mm heads averaged .869 in. (+/- .005) and 100% were within 1 standard deviation; however, the standard deviation was large. The 28 mm heads averaged 1.101 in. (+/- .002), and 89% were within 1 standard deviation. The 32 mm heads averaged 1.258 in. (+/- .002), and 78% were within 1 standard deviation. It seems that when a 28 mm or 32 mm femoral head is used, different femoral and acetabular components by different manufacturers can be intermixed. However, when changing a 22 mm femoral head, the manufacturer should possibly be notified and an attempt to use the same manufacturer is preferable.

Hip Prosthesis↗
PubMed1996

Assessment of potential doubling time (Tpot), argyrophilic nucleolar organizer regions (AgNOR), and proliferating cell nuclear antigen (PCNA) as predictors of therapy response in canine non-Hodgkin's lymphoma.

The predictive potential of several proliferation indices for therapeutic outcome was investigated in 55 dogs with spontaneously occurring non-Hodgkin's lymphoma (NHL). Indices included potential doubling time (Tpot), argyrophilic nucleolar organizer region (AgNOR) frequency, and proliferating cell nuclear antigen labeling index (PCNA-LI). All tumors were of intermediate- or high-grade histology as assessed by the Working Formulation, and all dogs presented with disease of advanced clinical stage. All tumors were treated with an identical chemotherapeutic protocol. Tpot determination by a bromodeoxyuridine (BrdU) delayed-biopsy technique was readily applied in the dog. AgNOR frequency and PCNA-LI were easily obtained from archival, formalin-fixed, paraffin-embedded canine tissues. When accounting for all other prognostic variables by employing multivariate analysis, Tpot (p=0.017), and AgNOR frequency (p=0.021), but not PCNA-LI, were predictive of first remission duration. AgNOR frequency (p=0.033) was also predictive of survival time, and the predictive potential of Tpot approached significance (p=0.076). We conclude that Tpot and AgNOR frequency can be used as predictors of outcome in dogs with NHL, and spontaneous NHL in the dog may have significant potential as a model for further characterization of the association between tumor cell kinetics and chemoresponsiveness.

Animals↗
PubMed1996

Catastrophic failure of a conforming type of total knee replacement: a case report.

A case study is presented to illustrate the concept of femoral component failure secondary to polyethylene wear in a 67 year old man, 13 years after he had conforming type total knee replacements. This case illustrates the theory that this observed problem may be a leading cause of failure in conforming and nonconforming total knee replacements in the future.

Aged↗
PubMed1995

A rationale for fractionation for slowly proliferating tumors such as prostatic adenocarcinoma.

PURPOSE: The incidence of carcinoma of the prostate has recently begun to exceed that of carcinoma of the lung in males in the United States. Although survival and local tumor control after treatment are good for early stages, improvements are being sought for more locally advanced stages. Dose escalation might be of benefit and might be accomplished using "three-dimensional" conformal radiotherapy or hyperfractionation. Because carcinoma of the prostate is known to be a generally slowly growing tumor, there may be more scope for extreme hyperfractionation, even with prolongation to allow for the extra number of very small fractions. This article explores only the hyperfractionation approach, and only theoretically, to investigate when treatments might become too hyperfractionated. METHODS AND MATERIALS: The major problem was what to assume for proliferation rates in human adenocarcinomas. A literature search yielded labeling indices (S-phase proportions) often averaging about 1%, but spreading up to 6% or more in individual cases. These data are reviewed, and three bands of rate of loss of local control were chosen for the subsequent calculations: 0.5%, 1%, and 2% loss of local control per week of prolongation. Calculations were done using the linear-quadratic model for a series of doses per fraction of 1.2, 1.0, 0.8, and 0.6 Gy, given twice a day (b.i.d.) in 7, 9, 12, and 17 weeks, respectively. They were compared with a "standard" 36 fractions of 2 Gy = 72 Gy in 7 weeks. Total doses for equal late effects were calculated assuming a late alpha/beta of 3 Gy; the tumor Biologically Effective Doses were calculated assuming tumor alpha/beta values of 30, 10, and 5 Gy. The possible increases of local tumor control were estimated assuming a gamma-37 slope of 2% (per percent increase in total tumor dose). RESULTS: Graphs are presented of the estimated local control as a function of dose per fraction (and overall time), for advanced tumors (starting at 30% LC) and for less advanced tumors (starting at 70%). The largest increase is always for the change from 2 Gy once a day (q.d.) to 1.2 Gy b.i.d. Further changes of local control with hyperfractionation depend upon tumor proliferation rate and on the shape of the tumor cell survival curve. The largest gains are for the more advanced tumors. CONCLUSIONS: There is no great encouragement to proceed to more hyperfractionated and prolonged schedules than 1.2-1.0 Gy b.i.d. in 7-9 weeks. We await developments that might more reliably enable potential doubling time and cell survival curve shapes to be routinely determined for individual tumors, before further hyperfractionation might be considered. In the absence of tumor kinetic measurements, we might consider low grade tumors to be the ones to select for prolonged fractionation, whereas high grade tumors would be more suitable for 1.2 Gy b.i.d. with no prolongation, or for dose escalation using conventional fraction sizes and conformal radiotherapy.

Adenocarcinoma↗
PubMed1995

Effects of cimetidine on pharmacokinetics and pharmacodynamics of losartan, an AT1-selective non-peptide angiotensin II receptor antagonist.

This was a 2-period randomized, crossover study in 8 healthy males to determine the effects of cimetidine (400 mg q.i.d. for 6 days) on the pharmacokinetics and pharmacodynamic effects of the angiotensin II receptor antagonist, losartan (100 mg). Cimetidine increased the AUC for losartan 18% without affecting the AUC for E-3174, the active metabolite of losartan. The increase in plasma renin activity following losartan was not affected by cimetidine (maximum mean increases 12.6 and 12.1 ng Ang I.ml-1.h-1 without and with cimetidine, respectively). These results indicate that cimetidine does not appear to alter the pharmacokinetics or pharmacodynamics of losartan to a clinically significant extent.

Adult↗
PubMed1995

Comparative outcomes of total joint arthroplasty.

A prospective pre- and postoperative general health/quality-of-life factor comparison, using the Rand SF-36 Health Status Questionnaire (TyPE Specification, Quality Quest [Health Outcomes Institute, Minneapolis, MN]), was carried out on a consecutive series of patients with diagnosed osteoarthritis undergoing total hip and knee arthroplasty between March 1991 and March 1994. Study groups consisted of 85 total hip arthroplasty patients, 93 total knee arthroplasty patients, and 65 single-stage bilateral total knee arthroplasty patients, all treated at the same specialty hospital, under the care of three senior orthopaedic surgeons. The average patient age was 69 years. Significant improvements in quality-of-life measures including physical functioning, social functioning, role functioning/physical problem, role functioning/emotional problem, mental health, energy/fatigue, pain, and change in health were noted in all hip and knee arthroplasty patients 6 months, 1 year, and 2 years after surgery (P < .05). There appeared to be no significant differences in quality-of-life measures between hip and knee arthroplasty patients. Results therefore indicate that total hip and knee arthroplasty significantly improve the functional status and quality of life among patients suffering from osteoarthritis.

Activities of Daily Living↗
PubMed1995

Single-stage, bilateral, cementless total hip arthroplasty.

Single-stage, bilateral, cementless total hip arthroplasties were performed in 92 patients (184 arthroplasties) between March 1984 and December 1989. The clinical and radiographic findings were retrospectively evaluated, and the effects of weight bearing on the clinical and radiographic outcomes of the patients' prostheses were assessed. With a follow-up period ranging from 24 to 77 months (average, 44 months), the postoperative Harris hip scores averaged 94.6. Radiographic assessment at the most recent follow-up examination showed that 70% of the femoral components were optimally fixed, 26% were stable, and 4% had failed. Ninety-six percent of the acetabular components were optimally fixed. There were six acetabular component failures. These results indicate that single-stage, bilateral, cementless total hip arthroplasty can be performed without compromise to either hip if initial fit is achieved in both the metaphyseal and diaphyseal portions of the femur. Moreover, weight bearing did not adversely affect the initial stability and possible bone ingrowth, further implicating initial rigid fixation as paramount among the factors influencing the amount of ingrowth into the prosthesis.

Bone Cements↗
PubMed1995

Rush rod fixation of supracondylar fractures above total knee arthroplasties.

The authors report on 22 displaced supracondylar femur fractures and total knee arthroplasties treated with Rush rod (Berivon, Meridian, MI) fixation. The average age at the time of total knee arthroplasty was 67 years. Fractures occurred at an average of 5 years after surgery. In only five cases was notch in the anterior cortex noted. The follow-up period averaged 7 years. There were no nonunions. All knees healed between 3 and 4 months after surgery. Postoperative flexion averaged 108 degrees (preoperative average, 102 degrees). Only two knees demonstrated a flexion contracture before surgery (5 degrees-10 degrees), and both had flexion contractures after surgery as well (each 10 degrees). All other knees achieved full extension. The average alignment prior to fracture was 7 degrees of anatomic valgus. At the most recent follow-up evaluation this averaged 10 degrees with two knees in 15 degrees of valgus. The only complications noted were two intraoperative technical errors. No postoperative complications occurred. For supracondylar fractures above a total knee arthroplasty, the authors suggest closed reduction, Rush supracondylar rod fixation, early range of motion, and protected weight bearing until fracture healing. In all cases, an extensive surgical procedure was not required.

Aged↗
PubMed1995

Survivorship analysis of acetabular revision in medial, lateral, and global primary osteoarthritis.

Acetabular revision rates after cemented total hip arthroplasty vary from series to series in the literature. Little attention has been paid to the type of primary osteoarthritis in these previous series. We studied 782 cemented total hips in 671 patients with an average follow up of 7.5 years. Acetabular revision rates were analyzed in medial, lateral, and global primary osteoarthritis using survivorship analysis. Medial osteoarthritis was associated with a higher acetabular revision rate when compared to lateral osteoarthritis (P = .015). No differences were noted in acetabular revision rates when the preoperative diagnosis was medial vs global or lateral vs global primary osteoarthritis (P = .18 and P = .45, respectively). According to this study, a preoperative diagnosis of medial primary osteoarthritis should be added to a list of several factors associated with increased cemented acetabular failure, especially in the Charnley prosthesis.

Acetabulum↗
PubMed1995

Efficacy and safety of enoxaparin versus unfractionated heparin for prevention of deep venous thrombosis after elective knee arthroplasty. Enoxaparin Clinical Trial Group.

This study was a randomized, parallel-group, open-label clinical trial comparing the efficacy and safety of Enoxaparin, a low-molecular-weight heparin, and unfractionated heparin to prevent deep venous thrombosis after elective total knee arthroplasty. Four hundred fifty-three patients were randomized and received study medications. The primary efficacy evaluation was unilateral contrast venography done at the end of study or earlier if clinically indicated. The primary safety outcome was the incidence of bleeding episodes. Patients were assigned to 1 of 2 postoperative treatment groups: Enoxaparin 30 mg subcutaneous every 12 hours (228 patients), or unfractionated heparin 5000 units subcutaneous every 8 hours (225 patients). The incidence of proximal and distal deep venous thrombosis in the Enoxaparin group was 24.6% (56/228), and in the heparin group 34.2% (77/225). Three major hemorrhagic episodes were observed in each treatment group. Two cases of pulmonary embolism occurred in patients receiving heparin (1 fatal); no cases occurred in patients receiving Enoxaparin. This study showed that Enoxaparin administered postoperatively 30 mg every 12 hours is more effective and as safe as unfractionated heparin prophylaxis to prevent deep venous thrombosis in patients having elective total knee arthroplasty.

Aged↗
PubMed1995

Flat-on-flat, nonconstrained, compression molded polyethylene total knee replacement.

Flat-on-flat, posterior cruciate ligament-sparing total knee prostheses recently have shown problems of wear, loosening, and multiple design changes. Two thousand one Anatomical Graduated Components total knee arthroplasties with compression molded, nonmodular polyethylene tibial components were done between 1983 and 1991 at 3 institutions. All knees were evaluated clinically and radiographically every 2 to 3 years; 71 knees were seen in followup > 10 years. There were 8 failures secondary to revision (5 tibial failures; 2 secondary to metalosis from patellar polyethylene dissociation; and 3 femoral failures) resulting in a 98% survival rate at 10 years. The tibial design was flat-on-flat with a compression molded polyethylene that the authors believe is the primary reason for its success.

Adult↗
PubMed1995

The cemented acetabular component of a total hip replacement. All polyethylene versus metal backing.

The increasing use of a cementless acetabular component with a total hip replacement requires the need for metal backing, but metal backing with cement in the author's use has been less than optimal. The intention, therefore, was to evaluate all cemented acetabular components, with and without metal backing, used by the author, to offer a standard by which other acetabular components can be compared. From 1969 to 1983, 238 Charnley, 141 Mueller, 555 T-28, 100 Miami Orthopaedic Surgical Clinic total hip replacements with cemented all-polyethylene acetabula, and 134 Miami Orthopaedic Surgical Clinic total hip replacements with a cemented metal-backed acetabula were performed and followed from 1 to 22 years. The cemented acetabular component failure rates for the Charnley, T-28, and all-polyethylene Miami Orthopaedic Surgical Clinic were 14%, 10%, and 9%, respectively. There was a 20% failure rate in the Mueller and metal-backed Miami Orthopaedic Surgical Clinic acetabular components. The Charnley (p < 0.0001), T-28 (p < 0.0001), all-polyethylene Miami Orthopaedic Surgical Clinic (p < 0.0001), and Mueller (p < 0.012) total hip replacements demonstrated statistically improved survival rates as compared with the metal-backed Miami Orthopaedic Surgical Clinic acetabular components. The Charnley (p < 0.0001) and T-28 (p < 0.0003) sockets survived statistically better than the Mueller sockets.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabulum↗