Exact rates of periprosthetic fractures are difficult to ascertain, but are estimated to occur in about 3% of primary and revision total knee arthroplasties.17 Fractures occur more commonly in revision arthroplasties due to weakened bone and sue of longer-stem components. They are rarely seen in primary knee arthroplasty except when long-stem components are used. Fractures occur most commonly in the femur, followed by the patella and tibia. The patella may be at particular risk due to under or over resection of bone, alignment and tracking abnormalities, and avascular necrosis.
Patients at higher risk for fracture include elderly women, osteopenic patients, rheumatoid arthritics and neurologic patients.
Osteopenia due to long periods of inactivity secondary to pain and disability predispose to insufficiency fractures after surgery when patients are ambulating more frequently. Long-stemmed prostheses, which place more stress on bone distal to the stem tip, have higher rates of insufficiency fractures. Of course, trauma is a major risk factor for fracture of any bone, however mild trauma results in increased rates of fracture in these patients.
Total knee replacement complicated by spiral fracture of distal femur.
Evolving insufficiency fracture (arrow) of medial epicondyle over 3-month period. Left is July; right is September.
Insufficiency fracture of proximal fibular shaft.
Lateral radiograph of long-stemmed revised prosthesis with insufficiency fracture distally (arrow).