Osteolysis = Hystyocytic Response

Wear polyethylene debris from the acetabular liner migrate into the adjacent bone along the surface of the implant, carried through lymphatics, or through interstices in the cement mantle. Once in the adjacent bone, they elicit a macrophage or histiocyte response with formation of foreign-body granulomas and multinucleate giant cells; in turn, these release inflammatory factors triggering bone resorption.

Initially attributed to cement, osteolysis is also seen in non-cemented prosthesis with polyethylene liners. Contrarily, it is not seen in metal-on-metal articulations or ceramic-on-ceramic prothesis.

Aside from coalescing areas of osteolysis, a more linear pattern can appear resulting in loosening.

The volume of particles pumped into the adjacent bone bears a relation to the presence of osteolysis. Therefore, there is a relationship between the volumetric wear (or total loss of acetabular liner volume) and the presence of osteolysis. Indirectly the volumetric wear can be inferred through the linear wear. However, plastic deformation may result in linear wear without true volumetric wear.

CLINICAL ASPECTS:

Acetabular osteolysis tends to be asymptomatic. However, it needs to be monitored because the prosthesis may become loose, and the lytic areas predispose to pathologic fractures.

The linear wear of the acetabular component should be assessed with MDCT, and if there is no evidence of loosening, replacement of the acetabular liner with curettage and grafting of the areas of osteolysis may be considered.

CT-SCAN EVALUATION:


Note the expansile lytic areas with transgression of the pelvic wall. The sclerotic reaction around the lesion denotes a long-standing indolent etiology.

Note the concomitant tremendous linear wear of the acetabular liner on the left figure. On the right, note the atrophy of the abductor musculature, as well as the presence of trochanteric bursitis.