The loss of cartilage from the weight bearing or previously traumatized area is usually clearly seen in osteoarthritic joints (Fig. 1.1). This loss is often associated with collapse of neighboring subchondral bone, resulting in a deformed irregular articular surface. Cystic areas due to synovial intrusion into bone are a common finding, especially in the subchondral region of the acetabulum. These areas need to be enucleated prior to cementing the acetabular component. Similarly, the dense subchondral sclerotic areas in the acetabular and tibial pleateau regions need to be aggressively reamed, cut, and drilled to provide a good grip for prosthesis cementation. The removal of the largely avascular sclerotic areas is even more important when uncemented, hydroxyapatite-coated prostheses are used. These are inserted in a tight press-fit fashion and rely on a well-vascularized bone interface to allow porous ingrowth into the component. Osteophytes produced by revascularization of the remaining cartilage and synovial stimulation are located at capsular or tendinous insertions exposed to chronic stretch . Osteophytes are produced in the non-weight-bearing areas of the joint and may be so extensive that movement is restricted. They are relatively softer than the native bone and need to be aggressively trimmed back when the correct size of femoral resurfacing or knee components is being determined. Loose bodies due to fragmentation of the osteochondral surface may also cause painful locking of joints. These can be large, solitary or multiple, free floating or tethered, and are commonly removed at arthroscopy to induce symptomatic relief in the course of arthroplasty.
Osteoarthritis in its advanced stages causes significant destruction and distortion of the capsular ligaments. These in turn lead to deformity, such as flexion contractures seen in the hip and knee, and to malalignment. Correction of this soft tissue imbalance is often the most technically demanding aspect of arthroplasty.
Figure 1.1. Femoral heads, obtained after joint replacement surgery, illustrating the cartilage degradation that occurs during osteoarthritis (OA). (A) Femoral head from a 79-year-old patient with a femoral neck fracture. The cartilage is smooth with no evidence of deterioration. (B) The femoral head from a 69-year-old osteoarthritic patient. Subchondral bone is visible near the weight-bearing regions.
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