Correct Positions for Patella X-rays: Knee Imaging

Patellar X-ray

I have undergone three X-rays of my patella.
The first was taken while lying down with my knee hanging down, the second while lying face down with my knee elevated, and the third while sitting on the bed with my knee bent.
In the first two instances, different doctors indicated that the patella was not dislocated.
However, in the third instance, the doctor stated that the patella was laterally displaced.
What is the correct position for taking a patella X-ray?

Bai Yun, 30~39 year old female. Ask Date: 2003/12/03

Dr. Shi Qiming reply Orthopedics

Dear Mr.
Baiyun,
Regarding the X-ray examination of the patella, the positioning during the examination depends on the purpose of the assessment.
If the goal is to check for fractures, only anteroposterior and lateral views are necessary.
However, if the aim is to evaluate for any dislocation of the patella relative to the femoral condyle, the X-ray should be taken with the knee fully flexed to diagnose any lateral displacement of the patella.
If you have any further questions, please feel free to visit our outpatient clinic for additional evaluation.
Orthopedics, Dr.
Wang Zikang
12/4/03

Reply Date: 2003/12/03

More Info

When it comes to obtaining accurate X-ray images of the patella (kneecap), the positioning of the patient is crucial. The patella's alignment and any potential subluxation or dislocation can be effectively evaluated through specific imaging techniques. Understanding the correct positions for patella X-rays can help ensure that the images obtained are diagnostic and can guide appropriate treatment.

Correct Positions for Patella X-rays
1. Standard Views: Typically, two standard views are taken for patella X-rays: the anteroposterior (AP) view and the lateral view. The AP view is taken with the patient standing or sitting, while the lateral view is taken with the knee flexed at approximately 30 degrees.

2. Anteroposterior (AP) View: In this position, the patient can either stand or sit with the knee fully extended. The X-ray beam is directed perpendicular to the film, capturing the patella in its natural position against the femur. This view is essential for assessing the overall alignment of the knee joint.

3. Lateral View: For this view, the patient typically lies on their side or sits with the knee flexed at about 30 degrees. This position allows for a clear view of the patella's relationship to the femur and can help identify any lateral subluxation or dislocation. The knee should be flexed to ensure that the patella is not obscured by the femoral condyles.

4. Merchant View: This is a specialized view where the patient is positioned supine with the knees flexed at 45 degrees, and the X-ray beam is angled downwards. This view is particularly useful for evaluating patellar tracking and any potential patellar instability.

Importance of Positioning
The discrepancies in your previous X-ray results may stem from the different positions used during imaging. For instance, if the knee was not adequately flexed during the lateral view, it could lead to an inaccurate assessment of patellar alignment. Conversely, if the knee was flexed too much or not enough, it could also obscure the true position of the patella.

Clinical Implications
Patellar lateral subluxation can lead to various complications, including patellofemoral pain syndrome, osteoarthritis, and chondromalacia patellae. Accurate imaging is essential for diagnosing these conditions and determining the best course of treatment, which may include physical therapy, bracing, or surgical intervention.

Recommendations
If you have concerns about the accuracy of your X-ray results or the positioning used during your imaging, it is advisable to discuss this with your healthcare provider. They may recommend repeat imaging with specific positioning to ensure a comprehensive evaluation of your knee joint.

Additional Resources
For further information on knee imaging and patellar conditions, you may refer to reputable medical websites such as:
- American Academy of Orthopaedic Surgeons (AAOS): [www.aaos.org](http://www.aaos.org)
- RadiologyInfo.org: [www.radiologyinfo.org](http://www.radiologyinfo.org)
These resources provide valuable insights into knee anatomy, imaging techniques, and potential treatment options for patellar conditions. Always consult with your healthcare provider for personalized medical advice and treatment plans.

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