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Patella radiography

Patella

Patellar radiography is a fundamental and mandatory diagnostic imaging method used to assess the bony structures of the knee joint. The examination allows for the rapid exclusion of fractures, detection of dislocations, and determination of the stage of osteoarthritis.

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Screening methodRecommended for absolutely all patients for the initial assessment of knee joint structures.
Patient positioningThe standard views are anteroposterior and lateral. An axial view is used specifically for the patella.
Acute traumaThe necessity of radiography is determined strictly according to the Ottawa knee rules (for patients aged 5 and older).
Evidence baseHigh level of recommendation validity (Level of Evidence / Grade of Recommendation: C, 5).
3 min readFor medical studentsUpdated 10.10.2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesPending instructor review

Diagnostic value of the method

Knee radiography, including visualization of the patella, is a mandatory initial instrumental examination method. This type of diagnostic imaging is recommended for all patients without exception. It is the simplest and most accessible screening tool for determining the stage of development of gonarthrosis and its etiological type.

The main purpose of the examination is to evaluate the bony anatomical structures. The radiographs are used to assess:

  • Presence or complete exclusion of fractures.
  • Diagnosis of dislocations and visualization of subluxations of the articular surfaces.
  • Determination of the correct position of the patella.
  • Asymmetry of joint structures.

Projections and special positioning

Standard radiography always involves taking images in two basic projections: anteroposterior (AP) and lateral. However, for a detailed study of the patella and the patellofemoral joint, the protocol is extended:

  • Axial projection: a key additional view. Can be performed with the patient in the supine position.
  • Functional axial projection: performed in a standing position, which makes it possible to assess structural relationships under natural axial load.
  • Flexion view: to assess knee biomechanics, an image is taken with the joint flexed at an angle of exactly 45 degrees.
  • Examination in chronic trauma: in such cases, radiography is also indicated primarily in the standing position.
  • Stress radiography: a specialized technique used at the surgical planning stage.
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Radiological signs of osteoarthritis

When evaluating radiographs, the radiologist actively looks for specific markers of osteoarthritis (OA). Classic imaging signs of this pathology include:

  1. Joint space narrowing — a reliable marker of cartilage thinning.
  2. Subchondral sclerosis — compensatory densification of the bone tissue located beneath the cartilage.
  3. Osteophytes — bone outgrowths forming along the edges of articular surfaces and at ligament attachment sites.
  4. Subchondral bone cysts — characteristic changes in the epiphyses.
  5. Change in the shape of the epiphyses — gross deformation in the late stages of the disease.

Role of radiography in comprehensive examination

Radiography visualizes bones exceptionally well; however, to assess soft tissue structures (integrity of the patellar ligament, quadriceps tendon, cruciate ligaments, and menisci), magnetic resonance imaging (MRI) is additionally recommended for all patients.

It is important to note that laboratory tests (blood and urine tests, and synovial fluid analysis) are not required for the primary diagnosis of osteoarthritis. They are needed exclusively for differential diagnosis with inflammatory pathologies (gout, rheumatoid arthritis, calcium pyrophosphate deposition disease). In non-inflammatory arthrosis, the joint aspirate will be sterile, viscous, crystal-free, and have a leukocyte concentration of less than 2,000/mm³.

Class and exam questions

Does MRI replace radiography in patellar injuries?

No. Radiography is a mandatory starting method for evaluating bones (excluding fractures and dislocations). MRI is used additionally to assess the state of the extensor mechanism and menisci.

What is the best way to visualize the patellofemoral joint?

The optimal additional views are considered to be: the axial projection (in the supine position or standing under load), as well as the view with the knee flexed at a 45-degree angle.

What laboratory tests should be done before an X-ray when arthrosis is suspected?

Blood, urine, and synovial fluid tests are not required for the primary diagnosis of osteoarthritis. They are only needed for differential diagnosis with inflammatory diseases.

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What else to study on this topic

  • Application of the Ottawa knee rules in acute knee trauma.
  • MRI appearance of extensor mechanism injuries (patellar ligament and quadriceps tendon).
  • Specific MRI signs of meniscus tears and parameniscal cyst formation.
  • Differential diagnosis of synovial fluid (inflammatory vs. non-inflammatory nature).
  • Stress radiography in surgical planning.

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