Magnetic resonance imaging to assess knee cartilage repair tissue after microfracture of chondral defects.

A noninvasive method to assess the repair tissue produced by chondral defect treatment techniques has not been established. The purpose of this study was to evaluate the ability of magnetic resonance imaging (MRI) specialized sequences to predict the presence and quality of repair tissue of knee articular cartilage defects treated by microfracture. Nineteen recreational or high-level athletes underwent standard microfracture technique for 22 traumatic full-thickness chondral defects. Patients subsequently underwent repeat arthroscopy for unrelated knee pathology. Magnetic resonance imaging studies were obtained prior to the second-look arthroscopies and evaluated for the presence of full-thickness articular cartilage defects and for the quality of repair tissue. At arthroscopy, the quality and quantity of the repair tissue was assessed. Twenty-one defects had 100% coverage with repair tissue, whereas 1 defect continued to have areas with full-thickness cartilage loss. Magnetic resonance imaging had sensitivity and specificity of 100% in predicting the presence of a full-thickness lesion after microfracture. In determining whether the repair tissue was of good or poor quality, MRI had a sensitivity of 80% and specificity of 82% using arthroscopy as the standard. Magnetic resonance imaging using specialized sequences proved to be a satisfactory technique for evaluating repair tissue in full-thickness traumatic defects treated by microfracture.

A twisted four-sheeted model for an amyloid fibril.

The formation of amyloid fibers and their deposition in the body is a characteristic of a number of devastating human diseases. Here, we propose a structural model, based on X-ray diffraction data, for the basic structure of an amyloid fibril formed by using the variants of the B1 domain of IgG binding protein G of Streptococcus. The model for the fibril incorporates four beta sheets in a bundle with a diameter of 45 A. Its cross-section, or layer, consists of four strands, one strand from each sheet. Layers stack on top of each other to form the fibril, which has an overall helical twist with a periodicity of about 154 A. Each strand interacts in a parallel fashion with the strands in the layers above and below it, in an infinite beta sheet. Some geometric features of this model and the logic behind it may be applicable for constructing other related cross-beta amyloid fibrils.