Solute Transport of Negatively Charged Contrast Agents Across Articular Surface of Injured Cartilage.

Solute transport through the extracellular matrix (ECM) is crucial to chondrocyte metabolism. Cartilage injury affects solute transport in cartilage due to alterations in ECM structure and solute-matrix interactions. Therefore, cartilage injury may be detected by using contrast agent-based clinical imaging. In the present study, effects of mechanical injury on transport of negatively charged contrast agents in cartilage were characterized. Using cartilage plugs injured by mechanical compression protocol, effective partition coefficients and diffusion fluxes of iodine- and gadolinium-based contrast agents were measured using high resolution microCT imaging. For all contrast agents studied, effective diffusion fluxes increased significantly, particularly at early times during the diffusion process (38 and 33% increase after 4 min, P < 0.05 for iodine and Gd-DTPA; and 76% increase after 10 min for diatrizoate, P < 0.05). Effective partition coefficients were unaffected in mechanically injured cartilage. Mechanical injury reduced PG content and collagen integrity in cartilage superficial zone. This study suggests that alterations in contrast agent diffusion flux, a non-equilibrium transport parameter, provides a more sensitive indicator for assessment of cartilage matrix integrity than partition coefficient and the equilibrium distribution of solute. These findings may help in developing clinical methods of contrast agent-based imaging to detect cartilage injury.

Modeling accident occurrence at signalized tee intersections with special emphasis on excess zeros.

In implementing effective remedial treatments at hazardous intersections, it often is necessary to identify the geometric and traffic factors that lead to accident occurrence. However, one particular problem frequently encountered in accident studies is how to distinguish virtually safe intersections with little likelihood of accident occurrence from those that have happened to have no accident due to the random process. To deal with this problem, the "excess" records of zero accident, the zero-inflated negative binomial was used to assign the probability to the accident outcome. Accident data at 104 signalized tee intersections in Singapore over a period of 9 years were employed for model development. The model indicates that uncontrolled left-turn slip road, permissive right-turn phase, existence of a horizontal curve, short sight distances, large number of signal phases, total approach volume, and left-turn volume may increase accident occurrence. On the other hand, right-turn channelization, acceleration section on the left-turn lane, median railings, and more than 5% approach gradient may reduce accident occurrence. Moreover, there is a trend of reducing accidents over the years.

The effects of therapeutic doses of irradiation on experimental bone graft incorporation over a porous-coated segmental defect endoprosthesis.

The incorporation of autogeneic bone graft into a porous coated segmental endoprosthesis after high-dose irradiation was studied in dogs. A mid-diaphyseal defect was surgically created and then reconstructed with a porous-coated segmental endoprosthesis in 16 dogs. Autogeneic bone grafts were placed over the porous-coated regions of the endoprosthesis and at the endoprosthesis-bone junctions to achieve extracortical fixation. In eight dogs, the reconstructed femora were treated with a time-equivalent dose of 5500 cGy, delivered over a five-week period, beginning three weeks after surgery. In eight dogs, which served as the control group, the reconstructed femora were not irradiated. Dogs were killed 12 weeks after surgery, and the reconstructed femora were evaluated clinically, roentgenographically, mechanically, and histologically. Extracortical bone formation and bone ingrowth into the porous-coated segmental endoprosthesis were significantly inhibited by high-dose irradiation. Nonirradiated reconstructed femora had higher maximum torque at the implant-bone junction than irradiated femora. Nonirradiated femora had significantly greater bone ingrowth within the porous space than irradiated femora. Intracortically, irradiated femora had greater unlabeled bone and less porosity as well as more new bone than nonirradiated femora at 12 weeks postsurgery. Extracortically, irradiated femora had greater original cortical bone and less porosity as well as more new bone than nonirradiated femora at 12 weeks postsurgery. Mineral apposition was less in the irradiated femora from the initiation of radiotherapy to the time of killing five weeks after cessation of irradiation.

Roentgenographic and mechanical performance of centrifuged cement in a simulated total hip arthroplasty model.

Roentgenographic analysis showed that centrifugation significantly reduced the gross and regional porosity of the cement compared with hand-mixed controls in a simulated total hip arthroplasty model. Static failure test of the prosthetic system demonstrated that the centrifuged cement had significantly greater strength than the hand-mixed cement. Under low-cycle fatigue tests of the same composite models, there was a trend for the centrifuged cement to be stronger than the hand-mixed specimens, although statistically it was not significant. Thus, centrifugation can reduce porosity and significantly improve the static strength of cement in a simulated in vitro total hip replacement model. When cement is used, any possible improvement in the physical properties of bone cement should be considered.

The effect of centrifugation on the mechanical properties of cement. An in vitro total hip-arthroplasty model.

An in vitro total hip-arthroplasty model was evaluated to determine if centrifugation of bone cement results in greater static strength and low-cycle fatigue strength than hand-mixing. The static-failure test of the stem, cement, and simulated bone composite demonstrated that the centrifuged cement had significantly greater static strength than the hand-mixed cement. However, under low-cycle fatigue tests on the same composite models, the centrifuged and hand-mixed specimens were not significantly different.

Metastatic diaphyseal fractures of the shaft of the humerus. The structural strength evaluation of a new method of treatment with a segmental defect prosthesis.

The surgical treatment of extensive metastatic diaphyseal lesions of the humerus with pathologic fractures is difficult. Patients with failed internal fixation often have large segments of bone loss. Rigid fixation often is not possible in these cases. Four patients were treated with a titanium segmental defect (SD) prosthesis with good clinical results. A comparative in vitro analysis of fixation with the SD prosthesis, a Rush rod, and a dynamic compression plate (DCP) augmented with methylmethacrylate was performed. The SD prosthesis performed better than the Rush rod and DCP in both the nondestructive four-point bending test and the destructive torsional test. The reconstructed humeri using the SD prosthesis had a torsional strength approaching that of an intact specimen. Hence, the SD prosthesis is a useful adjunct device in treating patients with extensive destructive lesions of the humerus secondary to metastatic disease and hematologic malignancies and in patients with malignant diseases who have had failed attempts at internal fixation.