Antithrombin and antithromboplastin activity accompanying IgG myeloma. Report of a case with a severe bleeding tendency.

Four basic coagulation tests, the prothrombin time, thrombin time, partial thromboplastin time, and prothrombin consumption time, were used, with relatively simple modifications, to demonstrate the presence of two circulating anticoagulants in the blood of a patient with IgG myeloma and a severe bleeding tendency.

Characterization of wear in composite material orthopaedic implants. Part II: The implant/bone interface.

Carbon fiber/PEEK polymer (C/PEEK) composite materials are being developed for use as orthopaedic implant materials. Wear is an issue of increasing importance in orthopaedic implants; particulate debris generated by the wearing of biomaterials may be a causal factor leading to osteolysis and implant loosening. Therefore, numerical and experimental studies were completed to characterize the wear of C/PEEK composite materials in comparison to current orthopaedic implant materials. Finite element analyses (FEA) of a composite material hip stem implanted in a femur and loaded at 890 N determined that peak contact stresses will occur at the proximal-medial and distal regions of the implant. These contact stresses were found to be below 1.0 MPa over most of the implant surface; however the peak stress in the proximal-medial region was 1.8 MPa and higher still at the distal portion of the stem. In vivo forces result in contact stress values up to 9.0 MPa. The composite implant exhibited 10-40% lower contact stresses in the distal region compared to a titanium-alloy implant of identical design. Composite material wear samples were slid against porous hydroxylapatite (HA) to simulate the stem/bone interface. An identical series of experiments was run for comparison to a current orthopaedic implant material--Ti6A14V titanium alloy. Two domains of motion were studied; a composite ring-on-HA disc large amplitude sliding wear test; and a composite pin-on-HA disc small amplitude fretting regimen. Nominal contact pressures during testing were 1.4 MPa and 7.6 MPa for sliding and fretting tests, respectively. Fretting and sliding abrasive wear tests resulted in the composite material exhibiting a lower wear rate than the titanium-alloy. The magnitude of the difference was greatly dependent on the contact pressures, sliding amplitudes, and counterface material properties.

Acetabular strains produced by oversized press fit cups.

The purpose of this study was to determine the amount of acetabular deformation that occurs when acetabular components of different sizes are press fit. The change in acetabular volume was calculated for 1- to 3-mm oversized cup diameters with acetabuli ranging from 40 to 80 mm. An axisymmetric finite element model was used to determine the maximum acetabular strain that occurs when oversized cups are inserted in different acetabuli. The highest acetabular strains occur at the cup periphery, indicating that the resultant compressive force between the lateral pelvis and cup enhances press fit stability. In addition, higher maximum strains occur when the same millimeter amount of oversizing is used in a small compared with a large acetabulum. When a constant millimeter increment in cup oversizing is used, there may be a greater risk of pelvic fracture in a small acetabulum and a greater risk of inadequate press fit stability in a large acetabulum. To achieve the same amount of acetabular deformation and magnitude of strain, more oversizing is needed in a large acetabulum and less oversizing is needed in a small acetabulum. These results suggest that 1 mm of oversizing should be used for cups that are less than 52 mm in diameter, 2 mm of oversizing should be used for cups from 52 to 76 mm in diameter, and 3 mm of oversizing should be used for cups that are more than 76 mm in diameter.

Effect of cementless acetabular cup geometry on strain distribution and press-fit stability.

Use of cementless acetabular cups, which are slightly larger than the reamed acetabulum, can provide press-fit stability without screws; however, the ideal cup geometry to maximize stability is not clear. Acetabular strain distribution, deformation, and implant stability were studied using an axisymmetric finite-element model, and mechanical stability was assessed by testing lever-out and extraction forces required to displace different cup geometries from foam bones. The implants tested included four nonhemispheric cup geometries and 1- and 2-mm oversized hemispheric geometries. A nonhemispheric cup that provides a gradual transition from a hemisphere at the dome to a larger peripheral dimension appears to maximize peripheral strains and implant stability without increasing overall acetabular deformation as much as a larger oversized hemispheric cup.

Nucleotide substitutions and small-scale insertion produce size and antigenic variation in group A streptococcal M1 protein.

The presence of M protein on the surface of group A streptococci (GAS) confers the ability of the cell to resist phagocytosis in the absence of type-specific antibodies. It undergoes antigenic variation with more than 80 different serotypes having been defined. We have sequenced the M protein gene (emm1.1) from strain CS190 and present evidence that individual nucleotide substitutions are responsible for sequence variation in the N-terminal non-repeat region of emm1.1 and these substitutions have altered antibody recognition of opsonic epitopes. The N-terminal non-repeat domains of two other closely related strains, 71-155 and 76-088, were found to have sequence identical to emm1.1 with the addition of a 21 bp insert. This study provides the first evidence that nucleotide substitutions and small insertions are responsible for size and antigenic variation in the N-terminal non-repeat domain of the M protein of GAS.