SHORT- AND LONG-TERM EFFECT OF EXERCISE ON HUMAN CARTILAGE

The effects of exercise on hyaline articular cartilage have traditionally been examined in animal models, but due to a lack of accurate, non-invasive technology, little information has been available on human cartilage until recently. Magnetic resonance imaging now permits to analyze cartilage morphology and its composition quantitatively in vivo. This presentation will briefly report the methodological background of quantitative cartilage imaging and will summarize work on short term (deformational behaviour) and long term effects (functional adaptation) of exercise on human articular cartilage. Current findings suggest that human cartilage deforms very little in vivo during physiological activities and recovers from deformation within 90 min after loading. Whereas cartilage deformation appears to become less with increasing age, sex and physical training status do not appear to affect in vivo deformational behaviour. There is now good evidence that cartilage undergoes some type of atrophy (thinning) under reduced loading conditions, such as postoperative immobilization and paraplegia. However, increased loading (as encountered by top athletes) does not appear to be associated with systematically increased average cartilage thickness. Findings in twins suggest a strong genetic contribution to cartilage morphology, and phylogenetic comparisons between animals suggest that the size of the joint area, but not the cartilage thickness, is highly adapted to body weight and loading. Potential reasons for the inability of cartilage thickness to adapt to mechanical stimuli include a lack of evolutionary pressure and a decoupling of mechanical competence and tissue mass

Quantitative Cartilage Imaging in Knee Osteoarthritis

Quantitative measures of cartilage morphology (i.e., thickness) represent potentially powerful surrogate endpoints in osteoarthritis (OA). These can be used to identify risk factors of structural disease progression and can facilitate the clinical efficacy testing of structure modifying drugs in OA. This paper focuses on quantitative imaging of articular cartilage morphology in the knee, and will specifically deal with different cartilage morphology outcome variables and regions of interest, the relative performance and relationship between cartilage morphology measures, reference values for MRI-based knee cartilage morphometry, imaging protocols for measurement of cartilage morphology (including those used in the Osteoarthritis Initiative), sensitivity to change observed in knee OA, spatial patterns of cartilage loss as derived by subregional analysis, comparison of MRI changes with radiographic changes, risk factors of MRI-based cartilage loss in knee OA, the correlation of MRI-based cartilage loss with clinical outcomes, treatment response in knee OA, and future directions of the field

Stress distribution in the trochlear notch

n 16 cadaver humeroulnar joints, the distribution of subchondral mineralisation was assessed by CT osteoabsorptiometry and the position and size of the contact areas by polyether casting under loads of 10 N to 1280 N. Ulnas with separate olecranon and coronoid cartilaginous surfaces showed matching bicentric patterns of mineralisation. Under small loads there were separate contact areas on the olecranon and coronoid surfaces; these areas merged centrally as the load increased. They occupied as little as 9% of the total articular surface at 10 N and up to 73% at 1280 N. Ulnas with continuous cartilaginous surfaces also had density patterns with two maxima but those were less prominent, and in these specimens the separate contact areas merged at lower loads. The findings indicate a physiological incongruity of the articular surfaces which may serve to optimise the distribution of stress

Physiological incongruity of the humero-ulnar joint

Investigations into the distribution of subchondral bone density in the human elbow have suggested that the geometry of the trochlear notch deviates from a perfect fit with the trochlea, and that the load is transmitted ventrally and dorsally rather than through the centre of the humero-ulnar joint. We therefore decided to make a quantitative assessment of the degree of incongruity between the two components in 15 human specimens (age distribution 60 to 93 years) with different types of joint surface. Polyether casts of the joint cavity were prepared under loads of 10,40,160 and 640 N. The thickness of the casts was then measured at 50 predetermined points, and an area distribution of the width of the joint space represented in a two-dimensional template of the trochlear notch. The reproducibility of this procedure was tested by image analysis. At a load of 10 N, only a narrow space was present ventrally and dorsally in the joint, but in the depths of the trochlear notch a width of 0.5 to 1 mm was recorded in the centre, and up to 3 mm at its medial and lateral edges. Specimens with continuous articular cartilage showed a lower degree of incongruity than those with a divided articular surface. As the load was increased to 640 N, however, the original incongruity between the articular surfaces disappeared almost completely. The joint surfaces became more congruous, probably because of the viscoelastic properties of the articular cartilage and the subchondral bone, and the contact areas merged in the centre of the joint. It is suggested that this physiological incongruity brings about an optimal distribution of stress over the articular surface during the transmission of the load, and it may lead to better nourishment of the articular cartilage by providing intermittent mechanical stimulation and circulation of the synovial fluid

Die Verteilung der Knorpeldegeneration an der menschlichen Patella in Beziehung zur individuellen subchondralen Mineralisierung

Nach Arbeiten von Pauwels und Kummer kann die Verteilung der subchondralen Mineralisierung als Parameter der längerfristigen Beanspruchung in den Gelenken gelten. Ausgehend von eigenen Untersuchungen an der Patella zur Verteilung der subchondralen Knochendichte, wurden diese Befunde in der vorliegenden Arbeit den makroskopisch sichtbaren Knorpelschäden gegenübergestellt. Läsionen der lateralen Patellafacette sind Arealen hoher, Schäden der “odd facet” dagegen Arealen geringer subchondraler Mineralisierung zuzuordnen. Die Knorpelschäden der lateralen Facette werden als Folge einer hohen Dauerbeanspruchung und die Schäden der “odd facet” als Ausdruck einer generellen Unterforderung im medialen Gelenkbereich bei seltenen, kurzfristigen Spitzenbelastungen interpretiert