Accuracy of computer-navigated total hip arthroplasty.

Proper acetabular cup orientation is essential in total hip arthroplasty. The purpose of this study was to evaluate the accuracy of a particular imageless computer navigation system in determining cup position. Thirty-nine computer-navigated total hip arthroplasty intraoperative measurements of cup abduction and anteversion were compared with those from follow-up radiographs. Sensitivity, specificity, accuracy, prevalence-adjusted positive value (PPV), and negative predictive value were calculated for both navigation and radiographs. Navigation measurements had high specificity and PPV when assessing cup abduction and anteversion (specificity >90%, PPV >94%). In contrast, the system was not very effective in detecting suboptimal cup position (sensitivity abduction, 50%; anteversion, 33%). Intraoperative navigation readings in the safe zone have high probability of indicating correct placement. However, confirmation of suboptimal cup position intraoperatively requires additional diagnostic methods.

Osteosarcoma cells differentiate into phenotypes from all three dermal layers.

BACKGROUND: Osteosarcomas are the most common solid malignant bone tumors, but little is known of their origin. The embryonal rest hypothesis views cancer cells as arising from committed progenitor stem cells in each tissue. Adult tissue contains primitive stem cells that retain the ability to differentiate across dermal lines, raising the possibility that the stem cell of origin of cancers may be from a more primitive stem cell than a progenitor. QUESTIONS/PURPOSES: Can osteosarcoma cells, when cultured under conditions used for multipotent stem cells, be induced to differentiate into multiple phenotypes, including those of the three different dermal lineages: mesodermal, ectodermal, and endodermal? METHODS: One rat and one human osteosarcoma cell line were cultured and treated with concentrations of 0, 10(-10), 10(-9), 10(-8), 10(-7), and 10(-6) mol/L dexamethasone for 5 weeks. Seventeen phenotypes were assayed either by tissue-specific histochemical stains or antibodies to tissue-specific proteins. Each phenotype was tested across all dexamethasone concentrations for each cell line and each phenotype was tested in three separate experiments with induction by dexamethasone RESULTS: Rat osteosarcoma (ROS) 17/2.8 and human osteosarcoma cell line U-2 show the appearance of cells that have markers for (1) mesodermal phenotypes such as bone, cartilage, skeletal muscle, and endothelial cells, (2) ectodermal phenotypes such as astrocytes, oligodendrocytes, neurons, and keratinocytes, and (3) an endodermal phenotype, hepatocytes. This indicates osteosarcomas are composed, at least in part, of primitive stem cells capable of differentiating into tissues from all three dermal lineages. CLINICAL RELEVANCE: If osteosarcomas arise from primitive stem cells, then treatment of osteosarcomas with exogenous differentiation agents may cause the stem cells to differentiate, thus halting their proliferation and stopping tumor growth.

The tibial sulcus as a reference point for total knee arthroplasty.

Determining the amount of tibial resection is an important aspect of knee arthroplasty. The tibial sulcus is a reference point that should be unaffected by degenerative processes. This study compared the tibial sulcus and plateau height for 50 arthritic knees to 50 normal knees on magnetic resonance imaging. The tibial sulcus measured 17.09 mm in arthritic knees and 17.88 mm in normal knees. Sulcus height differences were not statistically significant. Based on these findings, a tibial cut 12 to 14 mm from the sulcus is recommended as a reference point in arthritic knees. This measuring technique has application in limited incision knee arthroplasty.