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Cartilage thickening in the left (ipsilateral) knee and no change in cartilage thickness in the right (contralateral) knee
10%
433/4537
Cartilage thinning in both knees
6%
293/4537
Cartilage thinning in the left (ipsilateral) knee and no change in cartilage thickness in the right (contralateral) knee
51%
2297/4537
Cartilage thinning in the left (ipsilateral) knee and increased cartilage thickness in the right (contralateral) knee
31%
1424/4537
Increased cartilage thickness in both knees
0%
22/4537
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After a period of off-loading, the off-loaded limb will experience cartilage thinning. The contralateral limb will not demonstrate any cartilage changes. Physiologic loading of cartilage increases proteoglycan synthesis and cell proliferation and is chondroprotective. Joint immobilization leads to cartilage thinning, tissue softening, and reduced proteoglycan content, leading to cartilage erosion. Joint overuse leads to cartilage damage (in vitro only). Hinterwimmer et al. examined cartilage atrophy after partial load bearing using quantitative MRI. They found cartilage thinning in all knee compartments (greatest thinning, medial tibia; least thinning, patella). There was no change in cartilage morphology in the contralateral knee. Sun reviewed the relationship between mechanical loading and cartilage degeneration. In OA, cartilage breakdown occurs at the articular surface, and is then fueled by synovial proteases and cytokines. In RA, synovial cells and macrophages are the source of degradative enzymes and incite cartilage destruction. Milward-Sadler et al. examined mRNA levels following mechanical stimulation in normal and osteoarthritic chondrocytes. Normal chondrocytes showed increased aggrecan mRNA and decreased matrix metalloproteinase 3 (MMP-3) mRNA after stimulation. This chondroprotective response was absent in osteoarthritic chondrocytes. Illustration A shows pro- and anti-inflammatory mechanisms of mechanical loading on chondrocytes. Underloading and overloading induce cartilage damage through pathways involving the upregulation of MMPs and ADAMTSs (ADAMTS, a disintegrin and metalloproteinase with thrombospondin motifs, or aggrecanase). Physiological loading blocks these increases. Incorrect Answers: Answer 1: Cartilage THINNING (not thickening) will occur on the offloaded limb (left). Answers 2 and 5: There will be a difference in cartilage thickness between knees as a result of different weightbearing status on both lower extremities. Answer 4: Noticeable cartilage hypertrophy does not occur on the uninjured limb.
1.9
(32)
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