What is the best diagnostic test for a patellar fracture?

From the Guidelines

The best diagnostic test for a patellar fracture is a plain radiograph (X-ray) of the knee, which should include anteroposterior (AP), lateral, and patellofemoral views. This recommendation is based on the American College of Radiology (ACR) Appropriateness Criteria for acute trauma to the knee, which suggests that radiographs should be the initial imaging modality for evaluating acute knee trauma, including suspected patellar fractures 1. The patellofemoral view is particularly useful for evaluating the patella and detecting fractures or subluxation/dislocation 1.

Key Points to Consider

• Radiographs are readily available, cost-effective, and can identify most patellar fractures with high sensitivity.
• The lateral view is important for demonstrating the fracture pattern and displacement.
• If X-rays are negative but clinical suspicion remains high, advanced imaging such as computed tomography (CT) may be warranted for detecting occult fractures or better characterizing complex fracture patterns 1.
• Magnetic resonance imaging (MRI) might be considered when there is suspicion of associated soft tissue injuries, particularly to the extensor mechanism 1.
• Physical examination findings that should prompt imaging include inability to perform a straight leg raise, knee effusion, and tenderness over the patella.

Imaging Modalities

• X-ray: initial imaging modality for evaluating acute knee trauma, including suspected patellar fractures.
• CT: may be used to detect occult fractures or better characterize complex fracture patterns.
• MRI: may be used to evaluate associated soft tissue injuries, particularly to the extensor mechanism.

Clinical Considerations

• Early and accurate diagnosis is essential because proper treatment depends on fracture type and displacement, with surgical intervention often required for displaced fractures to restore knee extensor function.
• Clinical judgment and common sense should supersede clinical guidelines in any case scenario 1.

From the Research

Diagnostic Tests for Patellar Fracture

• The best diagnostic test for a patellar fracture can vary depending on the type and severity of the fracture, as well as the clinical presentation of the patient 2.
• High-quality radiographs are often sufficient for detecting most fractures around the knee, including patellar fractures 2.
• However, some fractures may have subtle findings and require additional imaging modalities, such as computed tomography (CT) or magnetic resonance imaging (MRI) 2, 3, 4.
• CT scans can provide more detailed information about the fracture pattern and extent of displacement, which can be useful for surgical planning 4, 5.
• MRI can be useful for evaluating soft-tissue injuries, such as medial patellofemoral ligament (MPFL) tears, which are common in patellar dislocations 3, 6.
• Three-dimensional CT scans have been shown to improve the interrater reliability of the AO/OTA classification of patellar fractures, which can aid in treatment planning 5.

Specific Fracture Patterns

• Vertical patellar fractures are often nondisplaced and can be best evaluated with sunrise or Merchant views on radiographs 2.
• Avulsion fractures from the proximal or distal poles of the patella can be evaluated with lateral views, while osteochondral fractures can be evaluated with sunrise or internal oblique views 2.
• CT scans can help identify distinctive fracture patterns, such as severely comminuted distal pole fractures, which can be unappreciated on plain radiographs 4.
• Three-dimensional CT scans can provide detailed information about the size and location of osteochondral fragments, which can aid in treatment planning 6.

Imaging Modalities

• Radiographs are often the initial imaging modality of choice for evaluating patellar fractures, but may not provide sufficient information for surgical planning 2, 3.
• CT scans can provide more detailed information about the fracture pattern and extent of displacement, but may not be necessary for all patients 4, 5.
• MRI can be useful for evaluating soft-tissue injuries, but may not be necessary for all patients 3, 6.
• The choice of imaging modality will depend on the specific clinical presentation and treatment goals of the patient 2, 3, 4, 5, 6.