Anteroposterior and rotational movement of femur during knee flexion

This study was designed to analyze anteroposterior and rotational movement of femoral condyles during knee flexion from 15 degrees to 90 degrees using magnetic resonance imaging. After a pilot study, scans were made in 10 healthy male Japanese volunteers. When centers of the circular profiles of posterior femoral condyles were used as reference points, the medial and lateral femoral condyles displaced posteriorly 1.9 +/- 0.8 mm and 2.3 +/- 0.5 mm, respectively (mean +/- standard error). Duplicate examinations on two separate occasions revealed the accuracy of this procedure was in the range of 1 to 2 mm. These results have confirmed that femoral rollback occurs in the unloaded normal knee during flexion from 15 degrees to 90 degrees, but its magnitude is small (2 mm). The results obtained in this in vivo measurement of anteroposterior movement of the femoral condyles have relevance for total knee replacement design.

Atrial arrhythmia after surgical closure of atrial septal defects in adults

BACKGROUND

Atrial flutter and atrial fibrillation are causes of morbidity in adults with an atrial septal defect. In this study, we attempted to identify risk factors for atrial flutter and fibrillation both before and after the surgical closure of an atrial septal defect.

METHODS

We searched for preoperative and postoperative atrial flutter or fibrillation in 213 adult patients (82 men and 131 women) who underwent surgical closure of atrial septal defects because of symptoms, a substantial left-to-right shunt (ratio of pulmonary to systemic blood flow, >1.5:1), or both at Toronto Hospital between 1986 and 1997.

RESULTS

Forty patients (19 percent) had sustained atrial flutter or fibrillation before surgery. As compared with the patients who did not have atrial flutter or fibrillation before surgery, those who did were older (59+/-11 vs. 37+/-13 years, P<0.001) and had higher mean pulmonary arterial pressures (25.0+/-9.7 vs. 19.7+/-8.2 mm Hg, P=0.001). There were no perioperative deaths. After a mean follow-up period of 3.8+/-2.5 years, 24 of the 40 patients (60 percent) continued to have atrial flutter or fibrillation. The mean age of these patients was greater than that of the 16 who converted to sinus rhythm (P=0.02). New-onset atrial flutter or atrial fibrillation was more likely to have developed at follow-up in patients who were older than 40 years at the time of surgery than in those who were 40 or younger (5 of 67 vs. 0 of 106, P=0.008). Late events (those occurring more than one month after surgery) included stroke in six patients (all but one with atrial flutter or fibrillation, one of whom died) and death from noncardiac causes in two patients. Multivariate analysis showed that older age (>40 years) at the time of surgery (P=0.001), the presence of preoperative atrial flutter or fibrillation (P<0.001), and the presence of postoperative atrial flutter or fibrillation or junctional rhythm (P=0.02) were predictive of late postoperative atrial flutter or fibrillation.

CONCLUSIONS

The risk of atrial flutter or atrial fibrillation in adults with atrial septal defects is related to the age at the time of surgical repair and the pulmonary arterial pressure. To reduce the morbidity associated with atrial flutter and fibrillation, the timely closure of atrial septal defects is warranted.

The natural history of tibial radiolucent lines in a proximally cemented stemmed total knee arthroplasty

A total of 207 tibial components in total knee arthroplasty (TKA) have been reviewed at a maximum of 10 years after replacement. Twelve knees developed aseptic femoral loosening and were reviewed separately from the remaining 195. All tibial components were fixed with cement confined to the proximal surface of the implant combined with an uncemented stem. In the 195 TKAs with well-fixed femoral components and (presumably) low wear, 15% of tibiae developed early-onset, nonprogressive partial radiolucent lines (RLLs), typically in relation to preoperative sclerosis. Tibial component vertical migration was measured in 36 components: no migration was detected over the course of 5 years whether or not an RLL was present. There was no case of tibial osteolysis, no tibial component was revised for aseptic loosening, and no implant was radiologically loose. In 12 knees, the femoral component loosened with subsidence exposing peripheral bone that caused severe HDP wear. Tibial RLLs were present in 9, and osteolysis was present in 11 (although the tibial component was actually loose in only 1). This material has been used to study 1) the natural history of RLLs in cemented TKA and 2) the outcome of using cement confined to the proximal part of the tibial interface. We conclude that in low-wear prostheses RLLs are due to a failure to inject cement into sclerotic bone. Such lines are nonprogressive and do not affect fixation. In the presence of severe wear, however, they may provide a portal for the entry of debris into the interface causing progression of the RLL and lysis. Proximal cement plus an uncemented stem furnishes adequate tibial fixation, provided that the HDP wear rate is low.

Antioxidant BO-653 and human macrophage-mediated LDL oxidation

Oxidation of LDL is now widely accepted to be involved in atherogenesis. The aim of this study was to examine the effect of BO-653, a strong radical scavenger and antioxidant, on oxidation of LDL by human macrophages in vitro. Fifty microg/ml LDL protein was incubated with macrophages in Ham's F10 medium, supplemented with additional Fe2+, for up to 48 h. Then the medium was analysed by LDL agarose gel electrophoresis, the thiobarbituric acid assay and gas chromatography. In the absence of added exogenous antioxidants, after 24h LDL oxidation produced 30.48 nmoles MDA equivalents/mg LDL protein and a relative electrophoretic mobility of 4.74. Linoleic acid (18:2), arachidonic acid (20:4) and cholesterol were depleted and 7beta-hydroxycholesterol was generated. BO-653 completely inhibited this cell-mediated oxidation of LDL in concentrations as low as 5 microM, being more effective than either alpha-tocopherol or probucol, which completely inhibited oxidation at 200 and 80 microM and only partially at 80 and 8 microM, respectively. This inhibition of cell-mediated LDL oxidation was not due to toxicity, as alpha-tocopherol, probucol and BO-653 were not toxic for the macrophages at the concentrations tested. Eighty microM alpha-tocopherol, 8 microM probucol and 5 microM BO-653 significantly reduced the toxicity to the oxidising culture caused by LDL oxidation. The results show that in this system BO-653 is a more effective antioxidant than alpha-tocopherol or probucol.

Review of the biological response to a novel bone cement containing poly(ethyl methacrylate) and n-butyl methacrylate

This review describes work published independently elsewhere in which the biological reactions to poly(ethyl methacrylate) n-butyl methacrylate (PEMBMA) have been studied. This material has been compared throughout with conventional poly(methyl methacrylate) (PMMA). Butyl methacrylate monomer used in PEMBMA was slightly less toxic than methyl methacrylate monomer used in PMMA when injected intraperitoneally in mice. No differences in cardiorespiratory effects were found between n-butyl and methyl monomer infused intravenously into anaesthetized rabbits. The tissue reaction to the beaded polymers of poly(methyl methacrylate) and poly(ethyl methacrylate) implanted subcutaneously was identical. The surface appearance of the two materials differed significantly when viewed by scanning electron microscopy, showing a series of elevations resembling tightly packed spheres in the case of PMMA, but a smooth surface with only occasional smooth elevations in the case of PEMBMA. Intramuscular implantation showed more fibrous tissue and tissue damage in relation to PMMA cured in situ compared with PEMBMA and there was more bone necrosis and a thicker fibrous tissue layer adjacent to PMMA than PEMBMA when cured intraosseously.

Can a total knee replacement prosthesis be made entirely of polymers?

We have prospectively studied 63 total knee replacements (TKR) in which the femoral component was polyacetal, and 138 TKRs in which the femoral component was conventional cobalt chrome. The tibial and patellar components were of ultrahigh molecular weight polyethylene (UHMWPE). Patients were followed-up for at least 10 years. In the polyacetal group, a number of patients have died or have been revised, for reasons unrelated to the presence of polyacetal. There were no instances of femoral component fracture, nor failure by wear. One postmortem specimen, retrieved at 9 years after surgery, showed no measurable polyacetal wear and negligible HDP wear. The histology of tissue in contact with polyacetal was indistinguishable from that adjacent to polymethyl methacrylate and UHMWPE in the same knee. We believe that polyacetal could be used for the femoral component of a TKR and that a further trial should be undertaken.

Finite element analysis of the implanted proximal tibia: a relationship between the initial cancellous bone stresses and implant migration

The cancellous bone stresses within the implanted proximal tibia were examined using a three-dimensional anatomical finite element model. Three versions of a proximal tibial prosthesis were examined: an all polyethylene press-fit design; a metal backed, stemmed press-fit design and a (horizontally) cemented metal backed, stemmed design. All three designs had published migration and survivorship data. The objectives of the study were (i) to compare the stresses generated by each of the tibial components, (ii) examine the influence of the resected surface morphology and (iii) compare the initial cancellous bone stresses with the published migration and survivorship data. The all polyethylene prosthesis generated the highest cancellous bone stresses. Addition of a metal backing and a stem reduced the stresses, but the cemented device produced the lowest cancellous bone stresses. The surface morphology had a significant effect on the cancellous bone stresses generated by press-fit prostheses. As the bone-prosthesis contact area decreased, the peak cancellous bone stresses increased by as much as 243%. The surface morphology had no effect on the cancellous bone stresses generated by the cemented implant. Good correlation was found between the predicted cancellous bone stresses and the migration and survivorship data, with the implant generating the highest cancellous bone stresses migrating the most and having the poorest survival rates at 5 year. The results support the hypothesis that the progressive failure of cancellous bone is a mechanism of implant migration regardless of the method of fixation and the implantation site.

Leakage associated with load fatigue-induced preliminary failure of full crowns placed over three different post and core systems

Thirty-six maxillary central incisors were endodontically treated and restored with a post and core and cast crown. Three different post and core systems were evaluated. Restored teeth were fatigue-loaded until preliminary failure of the casting occurred as detected by a strain gauge bonded across the lingual margin of the cast crown. After preliminary failure, fatigue loading was continued for 100,000 load cycles with the crown margin exposed to basic fuschin dye. Teeth were then immersed in dye for 24 h, sectioned, and evaluated for leakage. There was no significant difference in the number of load cycles required to cause preliminary failure among the three post and core systems. Leakage occurred in all three groups, with no significant difference between groups. The occurrence of preliminary failure is clinically undetectable, yet it allows leakage between the restoration and tooth that may extend down the prepared post space.

Cost and value of performance indicators. Results from IBH's (Institute for Behavioral Healthcare) National Leadership Council

Consumer Reports style report cards are becoming commonplace in our industry and will emerge as a necessary component of 21st century behavioral healthcare. As a result, health plans and providers are increasingly required to invest in and maintain an infrastructure for comparative performance measurement and reporting. Policymakers and accrediting agencies must be careful to require reporting about the most cost-effective indicators in order to minimize the extra cost burden imposed upon health plans and providers by this effort. The Institute for Behavioral Healthcare's National Leadership Council evaluated "real life" performance indicators already in use in health plans, facility-based provider settings, community mental health centers, and behavioral group practices. This study shows which performance indicators are most worth measuring and those which are not, and why. Significant implications for policy and accrediting organizations, and for the behavioral healthcare field, are discussed.

Number of polyethylene particles and osteolysis in total joint replacements. A quantitative study using a tissue-digestion method

Our aim was to analyse the influence of the size, shape and number of particles on the pathogenesis of osteolysis. We obtained peri-implant tissues from 18 patients having revision surgery for aseptically loosened Freeman total knee replacements (10), Charnley total hip replacements (3) and Imperial College/London Hospital double-cup surface hip replacements (5). The size and shape of the polyethylene particles were characterised using SEM and their concentration was calculated. The results were analysed with reference to the presence of radiological osteolysis. The concentration of polyethylene particles in 6 areas with osteolysis was significantly higher than that in 12 areas without osteolysis. There were no significant differences between the size and shape of the particles in these two groups. We conclude that the most critical factor in the pathogenesis of osteolysis is the concentration of polyethylene particles accumulated in the tissue.

Wear particulate species and bone loss in failed total joint arthroplasties

The aim of this study was to evaluate the relative contribution of polyethylene, metal, and polymethylmethacrylate (cement) particles to the overall bone loss in aseptic loosening. Twenty-four interface tissues with adjacent bone were obtained during 17 revision total joint arthroplasties (11 hips and six knees). Osteoclasts and macrophages were identified immunohistochemically on the bone surface. The length of the bone surface in contact with these cell types was measured and analyzed with reference to the particulate species present within the fibrous interface. The presence of abundant polyethylene particles significantly increased the proportion of the bone surface in contact with macrophages but did not have a significant influence on that of osteoclasts. Osteoclastic bone resorption was significantly more extensive in the presence of metal particles. In contrast, the presence of cement particles did not have a significant influence on macrophage or osteoclast coverage of the bone surface. These results highlight the significance of polyethylene particles in macrophage recruitment and subsequent osteolysis and suggest a different mechanism of bone loss related to metal, namely mediation through osteoclastic activities. The relative contribution of cement particles was negligible and needs reevaluation in light of evidence provided by others.

Early radiological observations may predict the long-term survival of femoral hip prostheses

We reviewed a consecutive series of 527 uninfected hip replacements in patients resident in the UK which had been implanted from 1981 to 1993. All had the same basic design of femoral prosthesis, but four fixation techniques had been used: two press-fit, one HA-coated and one cemented. Review and radiography were planned prospectively. For assessment the components were retrospectively placed into two groups: those which had failed from two years onwards by aseptic femoral loosening and those in which the femoral component had survived without revision or recommendation for revision. All available radiographs in both groups were measured to determine vertical migration and examined by two observers to agree the presence of radiolucent lines (RLLs), lytic lesions, resorption of the neck, proximal osteopenia and distal intramedullary and distal subperiosteal formation of new bone. We then related the presence or absence of these features and the rate of migration at two years to the outcome with regard to aseptic loosening and determined the predictive value of each of these variables. Migration of > or = 2 mm at two years, the presence of an RLL of 2 mm occupying one-third of any one zone, and subperiosteal formation of new bone at the tip of the stem were predictors of aseptic loosening after two years. There were too few lytic lesions to assess at two years, but at five years a lytic lesion > or = 2 mm also predicted failure. We discuss the use of these variables as predictors of femoral aseptic loosening for groups of hips and for individual hips. We conclude that if a group of about 50 total hip replacements, perhaps with a new design of femoral stem, were studied in this way at two years, a mean migration of < 0.4 mm and an incidence of < 10% of RLLs of 2 mm in any one zone would predict 95% survival at ten years. For an individual prosthesis, migration of < 2 mm and the absence of an RLL of < or = 2 mm at two years predict a 6% chance of revision over approximately ten years. If either 2 mm of migration or an RLL of 2 mm is present, the chances of revision rise to 27%, and if both radiological signs are present they are 50%. If at five years a lytic lesion has developed, whatever the situation at two years, there is approximately a 50% chance of failure in the following five years. Our findings suggest that replacements using a limited number of any new design of femoral prosthesis should be screened radiologically at two years before they are generally introduced. We also suggest that radiographs of individual patients at two years and perhaps at five years should be studied to help to decide whether or not the patient should remain under close review or be discharged from specialist follow-up.

Bone scintigraphic appearance of asymptomatic hydroxyapatite-coated hip arthroplasties

To obtain information about the bone scintigraphic appearance of a hydroxyapatite (HA)-coated proximal femoral implant, this examination was performed on 24 patients with a clinically and radiologically successful femoral implant in hip arthroplasty. The prosthesis had a proximal HA coating for supplementary fixation. The patients' mean age was 50.3 years (range, 28-65 years) at operation. The interval from the operation to the scintigraphy ranged from 6 months to 5.5 years (mean, 2.2 years). Scintigraphy was performed using 99mTc-medronic acid. Quantitative counts were recorded in 4 zones: 3 along the length of the implant (trochanteric region with HA coating, midprosthesis, and distal tip) and 1 below the prosthesis. The results were expressed as ratios using the nonoperated femur as a control value. The results demonstrated that the mean activities in all 4 zones were increased relative to the untreated side. The highest activity was observed in the region around the prosthetic tip, with an elevation of 46% above the control value. This activity showed a significant decline over time. The counts recorded in the trochanteric region, where the implant was coated with HA, were 20% above the control value and similar to those seen in its adjacent noncoated midprosthetic region. In the trochanteric region, however, the activity did not show a decline over the follow-up period.

Radiological and survival comparison of four methods of fixation of a proximal femoral stem

We compared the radiological appearances and survival of four methods of fixation of a femoral stem in 538 hips after follow-up for five or ten years. The fixation groups were: 1) press-fit shot-blasted smooth Ti-A1-V stem; 2) press-fit shot-blasted proximally ridged stem; 3) proximal hydroxyapatite (HA) coating; and 4) cementing. Survival analysis at five to ten years showed better results in the HA-coated (100% at five to six years) and cemented stems (100% at 5 to 6 years) than in the two press-fit groups. There was a higher mean rate of migration in the smooth and ridged Ti-A1-V shot-blasted press-fit groups (0.8 mm/year and 0.6 mm/year, respectively) when compared with the HA-coated and cemented prostheses (both 0.3 mm/year). More radiolucent lines and osteolytic lesions were seen in the press-fit groups than in either the HA-coated or cemented implants, with a trend for a lower incidence of both in the HA compared with the cemented group. Proximal osteopenia increased in the press-fit and cemented prostheses with time, but did not do so in the HA group. There was a higher incidence of resorption of the femoral neck with time in the cemented group than in the other three. We conclude that the HA and the cemented interfaces both provide secure fixation with a trend in favour of HA. The cemented prosthesis meets the suggested National Institutes of Health definition of 'efficacious' at ten years.

The size and shape of particulate polyethylene wear debris in total joint replacements

Osteolysis induced by wear particles has been recognized as one of the major causes of long-term failure in total joint replacements. However, little is currently known about the exact nature of particles, as the particles are too small to be characterized by light microscopy. In this study, ultra-high molecular weight polyethylene (UHMWPE) particles retrieved from ten cases (six cemented and four uncemented) for Freeman type conforming tibiofemoral total knee replacements (TKRs), three Charnley total hip replacements (THRs) and five Imperial College/London Hospital double cup surface hip replacements for aseptic loosening were extracted using a high-performance method with ultracentrifugation and characterized by scanning electron microscopy. The equivalent circle diameter (ECD) of all 18 cases ranged from 0.40 to 1.15 microns (Mean +/- SE = 0.70 +/- 0.05 micron, median = 0.67 micron). The aspect ratio was 1.50 to 2.04 (Mean +/- SE = 1.75 +/- 0.04, median = 1.73), and roundness was 1.24 to 2.34 (Mean +/- SE = 1.61 +/- 0.07, median = 1.65). The numbers of particles were 5.2 x 10(8) to 9.17 x 10(10)/g tissue (Mean +/- SE = 1.42 x 10(10) +/- 5.41 x 10(9)/g tissue, median = 7.04 x 10(9)). The number of polyethylene (PE) particles/g tissue in TKRs was significantly larger than that in THRs (1.04 x 10(10)/g tissue and 2.16 x 10(9)/g tissue respectively, median, p = 0.03, Mann-Whitney U test). Unstable fixation of the tibial PE component might account for the accumulation of a large number of PE particles in the interface tissue.