Patellar fractures after total knee arthroplasty
Patellar fractures (Figure 1) are one of the most common periprosthetic fractures . Their incidence after primary TKA is overall approximately 1% [1, 2], but may be as high as 20% in certain patellar implants . After revision surgery, incidences are roughly twice as high as after primary surgery .
Their etiology is multifactorial. In the minority of cases, the fractures are preceded by a traumatic event [2, 5, 6]. Often, they are asymptomatic [6, 7]. Usually, they emerge within 2 or 3 years after surgery [6, 8]. Broadly speaking, the risk factors can be categorized into patient-related, implant related, and technical.
Patient-related factors are primarily linked to bone quality, bone quantity, and loading of the implant. Besides the obvious osteoporosis and osteopenia linked to aging, they can also be induced by rheumatoid arthritis, which is thus an important risk factor . This is particularly important in the presence of a very thin and eroded patella . Moreover, prosthetic wear and loosening can lead to progressive osteolysis .
Did you know?
Most orthopedic and trauma surgeons are painfully aware of the poor bone quality they often find when operating on patients with rheumatoid arthritis. But why is this so? Clemens Gwinner, head of knee endoprosthetics at the university hospital Charité in Berlin, Germany, explains: “Rheumatoid arthritis is a systemic disease which causes joint inflammation. The inflammatory cytokine release is, amongst other effects, responsible for the increase in osteoclast activity, which ultimately leads to bone degradation.”
Loading of the implant in the presence of correctly aligned components is mainly affected by the patient's weight, activity level [9, 10], and range of motion . Of note, male sex has been identified as a risk factor for periprosthetic patellar fracture by some authors . However, a likely explanation for this otherwise unexplained finding is the higher body weight and higher activity level usually found in men [6, 12]. A high degree of knee flexion has also been shown to be a risk factor . The biomechanical mechanism is, that during active flexion, the stresses in the patellofemoral joint increase gradually as the knee bends. At 45–60° of flexion, the pressures on the proximal part of the patella are the highest. While deep active bending occurs less often with Western lifestyles, it is essential for activities of daily living in many Asian societies.
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- Implant-related factors
- Technical factors
- Indications for nonsurgical treatment
- Indications for surgery and surgical techniques
- Outcomes and conclusions
Additional AO resources on this topic
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- Video: Managing Deformity in Total Knee Arthroplasty
- Video: The Difficult Primary Total Knee Arthroplasty
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This series of articles was created with the support of the following specialists (in alphabetical order):
This issue was written by Elke Rometsch, AO Innovation Translation Center, Clinical Science, Switzerland.
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