Carpet lesion is a term for focal chondral delamination, where articular cartilage is peeled off the subchondral bone plate as a result of shearing forces. It is a frequent finding on hip arthroscopy and is associated with femoroacetabular impingement 1,2, particularly cam morphology 6.
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Terminology
The carpet lesion was given its name by its arthroscopic appearance, where it was compared to an undulating carpet also known as carpet phenomenon or wave sign 1,3.
Clinical presentation
Usually, patients present with pain.
Pathology
Chondral delaminations and carpet lesions are due to excessive shear forces, usually parallel to the articular surface 1,4. The delamination occurs at the junction of the deep, non-calcified and calcified cartilage 1,4,7.
Location
The carpet lesion is typically found on the acetabular side of the hip joint, located anterosuperiorly, sometimes with extension into the labrum 1. They are often found immediately adjacent to labral lesions 6.
Radiographic features
MRI
The presence of fluid between the articular cartilage and the subchondral bone plate is indicative, however, the diagnosis is challenging because often cartilage shows normal thickness and contours, and in joints like the hip the detection of fluid accumulation is often limited, without applying traction 1.
MR signal characteristics
T2FS: hyperintense
IMFS: hyperintense
CT / MR arthrography
Full-thickness fissure with undermining contrast alongside the bone-cartilage interface but no detachment 1, some authors 6 apply a 'two-slice rule". On MR arthrography, acetabular chondral delamination is best seen on sagittal T1FS or PDFS sequences 6.
Treatment and prognosis
Treatment depends more on the location but includes direct technical fixation 2 or chondral debridement and joint lavage with potentially further following restorative therapy 2. Cartilage delamination can progress to full thickness chondral loss and intra-articular bodies 6.
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