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Osteolysis Around Well-Fixed Total Hip Arthroplasty
Key Points
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Osteolytic lesions of the pelvis that progress over a 3- to 6-month period in patients with osseointegrated cementless sockets are an indication for operative treatment. Severe polyethylene wear may justify a lower threshold for treatment because it is optimal to intervene before the time when the head wears through the liner and engages the shell.
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Key factors in determining whether the well-fixed shell can be retained include exchangeability of the liner, extent of osseointegration, position of the socket, and type of fixation surface (i.e., 2-dimensional [ongrowth] vs. 3-dimensional [ingrowth]).
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Indications for operative treatment in cases of femoral osteolysis include progressive lesions, diaphyseal osteolysis, impending fracture, and pain.
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Key factors in determining whether the well-fixed femoral component can be retained include the extent of osseointegration, the location of the lesion, and the exchangeability of the femoral head.
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Although it is clear that implant retention and grafting are appropriate in selected cases, surgeons must have a low threshold for revising the implants if the strict criteria, as outlined in this chapter, are not met.
Aseptic loosening from periprosthetic osteolysis is a common cause of late failure after total hip arthroplasty. In the United States in 2006, 24.7% of 51,345 revision hip procedures were performed for mechanical loosening and bearing surface wear. Although loosening and osteolysis still result in the need for revision surgery, highly cross-linked polyethylene has made a dramatic impact on revision surgery. This impact is best demonstrated in work published from the Australian Joint Registry. At 16 years, the cumulative percentage of revision of primary total hip arthroplasties in patients with conventional polyethylene was 11.7% compared with 6.2% in patients who had highly cross-linked polyethylene. In this chapter, we present a strategy for managing periprosthetic osteolysis in the setting of well-fixed implants.
Osteolysis was first described by Harris et al. in 1976. At the time, it was believed that this was due to “cement disease.” Initially seen around cemented femoral components, osteolysis was later observed around cemented acetabular components that failed because of aseptic loosening. Cementless sockets were then designed to mitigate the failures seen with cemented fixation. Over time, osteolysis was seen around cementless implants as well. It was observed that the processes around cemented and cementless implants were similar histologically. It is now widely accepted that the process of osteolysis is most commonly driven by the biological response to particulate interface wear debris.
The natural history of osteolysis in cemented and cementless fixation is different. In cemented fixation, osteolysis involving the bone-cement interface typically leads to aseptic loosening. Surgical management in this situation consists of a revision of the entire implant and the timing depends on the severity of bone loss and the patient's symptoms. In cementless fixation, osteolysis more commonly involves periprosthetic bone, and the implants may remain osseointegrated, even in the setting of massive bone loss. Revision of the entire implant and bearing exchange with debridement of the osteolytic granuloma and bone grafting are viable options in this setting.
Indications
Patients who develop osteolysis around cemented acetabular components generally present with pain. The radiographic pattern of osteolysis in these patients is usually linear and progresses to involve the entire bone-cement interface. When the entire bone-cement interface is involved, the cup becomes loose. The linear pattern precludes grafting; thus, there is not a prophylactic surgical treatment that is practical. Pain is the indication for operative treatment in these patients. The timing of the intervention should be commensurate with symptoms; many patients with loose cemented sockets report only mild pain that does not warrant surgical intervention immediately.
Indications for the operative treatment of osteolysis around cementless acetabular components are less well-defined. Patients with loose cementless sockets have pain; thus, the indication for revision is straightforward. Controversy exists regarding the timing of operative intervention in cases where the socket remains well-fixed. In these cases, patients often are pain free, and the issue becomes operating on asymptomatic patients. A few small areas of osseointegration can keep cups well-fixed; therefore, patients can remain pain free despite expansile lesions. In general, most experts agree that osteolytic lesions that progress over a 3- to 6-month period are an indication for operative treatment. Severe polyethylene wear may justify a lower threshold for treatment because it is optimal to intervene before the time when the head wears through the liner and engages the shell. Prompt operative treatment is warranted when the head has worn through the liner because this situation will generate metallosis and an intense local inflammatory response from metal and polyethylene debris.
In planning for surgical treatment, it is important to consider that plain radiographs generally underestimate the size of osteolytic lesions. In addition to standard anteroposterior pelvis, anteroposterior hip, and cross-table lateral views, Judet views (45-degree obturator and iliac oblique views) often provide information regarding the extent of involvement of the anterior and posterior columns. Helical (spiral) computed tomography with metal artifact suppression generally provides the most accurate representation of the size and anatomy of osteolytic lesions.
Patients with femoral osteolysis generally remain asymptomatic until an impending fracture or extensive synovitis is present, except when osteolysis is associated with femoral component loosening. As on the acetabular side, the timing for surgical intervention is controversial. Indications for operative treatment in cases of femoral osteolysis include progressive lesions, diaphyseal osteolysis, impending fracture, and pain.
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