FPT Chondral lesions about the knee

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Figure 1: Schematic representation of articular cartilage resting on bone (B). The top layer (the lamina splendans) has horizontally aligned collagen molecules, to allow for sliding; the middle zone is oriented vertically, to resist compression. (Modified from https://www.intechopen.com/books/cartilage-tissue-engineering-and-regeneration-techniques/therapeutic-potential-of-articular-cartilage-regeneration-using-tissue-engineering-based-on-multipha)

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Another important biological principle regarding articular cartilage is that mild repetitive loading stimulates proteoglycan production whereas both immobilization and excessive repetitive loading leads to proteoglycan loss.  That is to say, the health of the joint demands that the cartilage must be loaded within its physiological envelope function: too much loading with will cause damage, but too little loading will cause wasting.

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Figure 2: The arrow points at an osteochondral defect of the medial femoral condyle. (from https://radiopaedia.org/cases/osteochondral-defect-2?lang=us)

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CT scanning is perfectly helpful when assessing patellar lesions, as it can more precisely measure the distance between the tibial tuberosity and the trochlear groove. Greater distances signify worse tracking of the patella and may prompt a need for surgical realignment.

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Figure 3: The arrow points at an osteochondral defect of the medial femoral condyle. (from https://radiopaedia.org/articles/osteochondritis-dissecans?lang=us)

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Lab findings are not usually helpful for evaluation of mechanical injuries such as chondral defects. However, inflammatory markers and disease-specific tests can be used to rule out inflammatory disease that may contribute to accelerated disease processes in the joints. Examples include systemic lupus erythematous and rheumatoid arthritis.

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Surgical management is considered in the young patient (<50 years old) who has attempted conservative non-operative treatment with continued long-standing and functionally limiting symptoms, especially those related to a loose chondral fragment. Factors such as lesion size, depth, location, and status of the underlying chondral bone are all considered.  At times, arthroscopy is needed to characterize the size and depth of the lesion (Ffigure 4).

 

Figure 4: The arrow points to a focal femoral condyle lesion seen at arthroscopy. (from https://ars.els-cdn.com/content/image/1-s2.0-S2212628719300490-gr3_lrg.jpg)

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The classic surgical candidate is a young, active patient presenting with acute osteochondral fracture and full-thickness loss of cartilage. Strong contraindications to surgery include inflammatory disease and obesity. Relative contraindications include mechanical issues such as joint laxity, mal-alignment and ligamentous laxity.

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Figure 5: The bone-and-cartilage plugs filling an articular defect are shown in this mini-arthrotomy. (from https://www.oatext.com/cartilage-damage-a-review-of-surgical-repair-options-and-outcomes.php)

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The “plug” technique is limited by the fact that articular cartilage will appear during early growth and development only in response to loadbearing. It is accordingly impossible to harvest cartilage from a non-weight-bearing part of a joint; at best one can hope to harvest from an area that is used sparingly. Accordingly, there may be some donor site morbidity when plugs are harvested.  Also, the radius of curvature of cartilage defect unlikely matches the radius of curvature of the harvested plug precisely.

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