Fibrocartilage in the transverse ligament of the human acetabulum.

Biomechanical experiments on isolated hip joints have suggested that the transverse ligament acts as a bridle for the lunate articular surface of the acetabulum during load bearing, but there are inherent limitations in such studies because the specimens are fixed artificially to testing devices and there are no modifying influences of muscle pull. Further evidence is thus needed to substantiate the theory. Here we argue that if the horns of the lunate surface are forced apart under load, the ligament would straighten and become compressed against the femoral head. It would thus be expected to share some of the features of tendons and ligaments that wrap around bony pulleys and yet previous work has suggested that the transverse ligament is purely fibrous. Transverse ligaments were removed from 8 cadavers (aged 17-39 y) and fixed in 90% methanol. Cryosections were immunolabelled with antibodies against collagens (types I, II, III, VI), glycosaminoglycans (chondroitins 4 and 6 sulphate, dermatan sulphate, keratan sulphate) and proteoglycans (aggrecan, link protein, versican, tenascin). A small sesamoid fibrocartilage was consistently present in the centre of each transverse ligament, near its inner surface at the site where it faced the femoral head. Additionally, a more prominent enthesis fibrocartilage was found at both bony attachments. All fibrocartilage regions, in at least some specimens, labelled for type II collagen, chondroitin 6 sulphate, aggrecan and link protein, molecules more typically associated with articular cartilage. The results suggest that the ligament should be classed as containing a 'moderately cartilaginous' sesamoid fibrocartilage, adapted to withstanding compression. This supports the inferences that can be drawn from previous biomechanical studies. We cannot give any quantitative estimate of the levels of compression experienced. All that can be said is that the ligament occupies an intermediate position in the spectrum of fibrocartilaginous tissues. It is more cartilaginous than some wrap-around tendons at the wrist, but less cartilaginous than certain other wrap-around ligaments, e.g. the transverse ligament of the atlas.

High-resolution MR angiography: results in diseased arteries.

The purpose of this study was to investigate the value of a respiratory-gated three-dimensional (3D) magnetic resonance angiographic technique (MRCA) in identifying coronary arteries in healthy volunteers and patients with proximal coronary artery stenoses and to compare the results of the navigator echo technique in the assessment of coronary artery stenosis with conventional coronary angiography. Twenty healthy volunteers and twenty patients with proximal coronary artery stenosis were examined at 1.5 Teslas with a cardiac-gated and retrospective respiratory-gated 3D gradient echo sequence. Visualization of the main coronary arteries was analyzed after curved MPR-reconstruction in three defined segments. For the assessment of image quality, a grading system including six scores was used to evaluate 400 vessel segments. Detection of coronary artery stenosis was compared with conventional coronary angiography by two blinded readers. In healthy volunteers, an image quality with a score of at least 3 (i.e., completely identified coronary arteries with major luminal irregularities) was found in 55% for the proximal segment, 47% for the middle segment and 20% for the distal coronary artery segment. Respective data for patients were 69% for the proximal segment, 47% for the middle segment and 20% for the distal segment. In contrast to other studies, we compared MRCA and conventional coronary angiography in the assessment of stenoses for all coronary vessels and for selected coronary vessels with high image quality. For the assessment of coronary artery stenoses (n = 53), sensitivity was 73% and specificity was 50% after evaluation of all patients by two blinded readers. A sensitivity of 79% and a specificity of 54% were found for evaluation of coronary vessels with an image quality score of at least 3. With the navigator echo MR technique, a complete 3D visualization of the main coronary arteries is possible in cases with variable image quality, but further experience and improvement of the prospective navigator echo sequence using shorter acquisition times is necessary for reliable assessment of coronary artery stenoses.