Patellar Grind Test: What It Is, How to Perform, and Interpret Results

How do you do a grind test?

The patellar grind test, also known as Clarke's sign or the patellar compression test, is a clinical assessment used to evaluate the integrity of the patellofemoral joint and identify potential sources of anterior knee pain, often indicating issues like patellofemoral pain syndrome or chondromalacia patellae.

What is the Patellar Grind Test?

The patellar grind test is a simple orthopedic maneuver designed to provoke symptoms within the patellofemoral joint. It involves compressing the patella (kneecap) against the trochlear groove of the femur (thigh bone) while the quadriceps muscle attempts to contract. This action increases the pressure and friction within the joint, helping to reveal underlying issues such as cartilage degeneration, roughening of the articular surfaces, or improper patellar tracking. A positive test typically elicits pain or a grinding sensation (crepitus) beneath the patella.

When is the Patellar Grind Test Performed?

This test is commonly performed when an individual presents with symptoms of anterior knee pain, particularly pain that is exacerbated by activities involving knee flexion and extension under load, such as:

• Climbing or descending stairs
• Running, especially downhill
• Squatting or lunging
• Prolonged sitting with bent knees ("theater sign")

It helps clinicians screen for conditions like:

• Patellofemoral Pain Syndrome (PFPS): Often referred to as "runner's knee," characterized by pain around or behind the kneecap.
• Chondromalacia Patellae: Softening and breakdown of the cartilage on the underside of the patella.
• Patellar Instability: Though less direct, poor tracking can contribute to positive findings.

Who Should Perform This Test?

While the principles of the test can be understood by fitness enthusiasts or student kinesiologists, it is crucial to understand its context:

• Self-Assessment: Individuals can attempt a modified, gentle version to gauge initial symptoms, but this should not be used for diagnosis. Overly aggressive self-testing can exacerbate existing conditions.
• Professional Assessment: The definitive performance and interpretation of the patellar grind test should be conducted by a qualified healthcare professional, such as a physical therapist, orthopedic surgeon, or sports medicine physician. They can integrate the findings with a comprehensive history, physical examination, and potentially imaging studies to arrive at an accurate diagnosis and treatment plan.

Step-by-Step Guide to Performing the Patellar Grind Test

This guide outlines the most common variation of the patellar grind test (Clarke's Sign).

Preparation:

• Patient Position: The individual lies supine (on their back) on an examination table or firm surface, with the involved knee fully extended and relaxed. The quadriceps muscles should be completely relaxed.
• Examiner Position: The examiner stands beside the involved leg, facing the patient's knee.

Execution:

1. Patellar Displacement: Place the web space of your hand (between thumb and index finger) just superior to the patella. Gently but firmly push the patella inferiorly (towards the foot) into the trochlear groove of the femur. The goal is to seat the patella firmly against the underlying femoral condyles.
2. Quadriceps Contraction Request: While maintaining the inferior pressure on the patella, instruct the patient to gently and gradually contract their quadriceps muscle. They should try to push their kneecap upwards towards their hip, as if trying to lift their foot slightly off the table (without actually lifting it).
3. Resistance and Observation: Continue to apply downward pressure on the patella, resisting its upward movement as the patient attempts to contract their quadriceps. Observe the patient's reaction and listen for any sounds.

Observation:

• Positive Test: The test is considered positive if the patient experiences pain under the patella or reports a grinding, creaking, or crunching sensation (crepitus) during the quadriceps contraction against resistance.
• Negative Test: The test is negative if the patient can contract their quadriceps without pain or crepitus.

Interpreting the Results

The results of the patellar grind test provide valuable information but should always be considered within a broader clinical context.

• Positive Test (Pain/Crepitus):
  • Indication: Suggests irritation or pathology within the patellofemoral joint. This could be due to roughening of the articular cartilage (chondromalacia), poor patellar tracking causing abnormal friction, or inflammation.
  • Significance: It supports a diagnosis of patellofemoral pain syndrome but is not solely diagnostic. Further evaluation is necessary to determine the specific cause and severity.
• Negative Test (No Pain/Crepitus):
  • Indication: Suggests that the patellofemoral joint may not be the primary source of the anterior knee pain, or that the condition is not severe enough to be provoked by this specific maneuver.
  • Significance: While reassuring, a negative test does not entirely rule out patellofemoral issues, as other tests or activities might still provoke symptoms.

Understanding the Underlying Mechanics

The patellar grind test directly assesses the interaction between the patella and the femur.

• Patellofemoral Joint: This joint is critical for efficient knee extension. The patella acts as a fulcrum, increasing the mechanical advantage of the quadriceps muscle.
• Cartilage Health: Both the underside of the patella and the trochlear groove of the femur are covered with smooth articular cartilage, which allows for frictionless movement. When this cartilage is damaged, softened, or uneven, the increased compression and friction during the test can lead to pain and crepitus.
• Patellar Tracking: If the patella does not track smoothly within the trochlear groove (e.g., due to muscle imbalances, anatomical variations), it can lead to areas of increased pressure and irritation, which the grind test can highlight.

Important Considerations and Limitations

• Not a Definitive Diagnosis: The patellar grind test is a provocative test, meaning it aims to provoke symptoms. A positive result indicates a problem but doesn't definitively diagnose a specific condition. It must be combined with a thorough history, other physical tests (e.g., Q-angle assessment, muscle strength tests), and potentially imaging.
• Potential for Discomfort: The test is designed to elicit pain if a problem exists. It should be performed gently and stopped immediately if severe pain occurs.
• False Positives/Negatives: Some individuals may experience crepitus without pain, which isn't necessarily pathological. Conversely, some with patellofemoral issues might not exhibit a positive grind test if their condition is mild or if other factors are at play.
• Seek Professional Advice: If you experience persistent anterior knee pain, a positive grind test, or any concerns about your knee health, consult a healthcare professional for an accurate diagnosis and personalized treatment plan. Self-treating based solely on this test is not recommended.

Conclusion

The patellar grind test is a valuable, albeit non-definitive, tool in the assessment of anterior knee pain and patellofemoral joint dysfunction. By understanding how to perform it correctly and interpret its results within a broader clinical context, fitness professionals and individuals can gain insights into potential issues. However, it is paramount to remember that this test is a screening measure, and professional medical evaluation is essential for accurate diagnosis and effective management of knee conditions.