Clarke's Test: Purpose, Performance, and Clinical Significance

What is the Clarke's test for?

The Clarke's test, also known as the patellar grind test or patellar compression test, is a clinical orthopedic examination used primarily to assess for patellofemoral pain syndrome (PFPS) and related conditions involving irritation or degeneration of the articular cartilage on the undersurface of the patella.

Purpose of the Clarke's Test

The primary purpose of the Clarke's test is to evaluate the integrity and function of the patellofemoral joint, specifically looking for signs of patellar irritation or pain. It aims to reproduce symptoms associated with increased pressure or abnormal tracking of the patella (kneecap) against the femoral trochlear groove during quadriceps contraction. A positive test often suggests conditions such as:

• Patellofemoral Pain Syndrome (PFPS): A common overuse injury characterized by pain around or behind the kneecap.
• Chondromalacia Patellae: Softening and breakdown of the cartilage on the underside of the patella.
• Patellar Mal-tracking: When the patella does not move smoothly within the femoral groove during knee flexion and extension.

Anatomical and Biomechanical Basis

The Clarke's test works by increasing the compressive forces between the patella and the femur. Understanding the underlying anatomy and biomechanics is crucial:

• Patellofemoral Joint: This joint is formed by the patella (a sesamoid bone embedded within the quadriceps tendon) and the trochlear groove of the femur. Its primary role is to increase the mechanical advantage of the quadriceps muscle.
• Articular Cartilage: Both the posterior surface of the patella and the trochlear groove are covered with articular cartilage, a smooth, low-friction tissue designed to facilitate effortless gliding during knee movement.
• Quadriceps Muscle: When the quadriceps contracts, it pulls the patella superiorly, causing it to glide within the trochlear groove.
• Mechanism of Pain: In conditions like PFPS or chondromalacia, the articular cartilage may be irritated, softened, or damaged. When the patella is manually compressed against the femur and the quadriceps contracts, this maneuver increases the pressure on the compromised cartilage, potentially eliciting pain. Abnormal patellar tracking can also contribute to uneven pressure distribution and pain.

How to Perform the Clarke's Test

The Clarke's test is typically performed with the patient in a supine (lying on their back) position.

1. Patient Positioning: The patient lies supine with the involved knee extended and relaxed.
2. Examiner Hand Placement: The examiner places the web space of their hand (between the thumb and index finger) just superior to the patella, cupping its superior pole. This position allows the examiner to apply downward and slightly inferior pressure on the patella, essentially "seating" it firmly within the trochlear groove.
3. Instruction to Patient: The examiner then instructs the patient to gently and gradually contract their quadriceps muscle, as if they are trying to straighten their leg or lift their heel off the table.
4. Observation and Palpation: While the patient attempts to contract the quadriceps, the examiner observes for any signs of pain, apprehension, or the inability to sustain the contraction. The examiner may also feel for crepitus (a grinding or popping sensation) under the patella.

Interpreting the Results

The interpretation of the Clarke's test relies on the patient's symptomatic response:

• Positive Test: A positive Clarke's test is indicated if the patient experiences pain under or behind the patella during the quadriceps contraction, and/or if they are unable to complete or sustain the quadriceps contraction due to pain. The pain should be localized to the patellofemoral joint.
• Negative Test: A negative test occurs if the patient can contract their quadriceps without experiencing pain or significant discomfort under the patella.

It's important to differentiate pain from general quadriceps weakness or discomfort from the examiner's pressure alone. The pain must be specific to the patellofemoral joint during the contraction.

Clinical Significance and Limitations

While widely known, the Clarke's test is part of a broader clinical assessment and has specific considerations:

• Diagnostic Value: The Clarke's test is considered a provocative test, meaning it aims to reproduce symptoms. While a positive test suggests patellofemoral irritation, it is not diagnostic of chondromalacia patellae or PFPS on its own. It should be used in conjunction with other objective measures, a thorough patient history, and observation of functional movements.
• Sensitivity and Specificity: Research on the test's diagnostic accuracy (sensitivity and specificity) is varied, with some studies showing low to moderate reliability. This means it may not always identify all individuals with PFPS (low sensitivity) or may produce false positives in individuals without the condition (low specificity).
• Patient Discomfort: The test can be uncomfortable or painful for some individuals, even those without significant patellofemoral pathology, if performed too aggressively. Care should be taken to apply gentle pressure and instruct the patient to contract gradually.
• Other Causes of Pain: Patellofemoral pain can stem from various sources, including patellar tendinopathy, fat pad impingement, or plica syndrome. The Clarke's test primarily isolates compressive forces on the articular cartilage, but its results must be considered within the context of the entire knee examination.

Related Conditions and Management

If the Clarke's test is positive, it warrants further investigation to determine the underlying cause of the patellofemoral pain. Common conditions associated with a positive test include:

• Patellofemoral Pain Syndrome (PFPS): Often multifactorial, involving muscle imbalances (e.g., quadriceps weakness, hip abductor/external rotator weakness), biomechanical issues (e.g., pronated feet), overuse, or poor training techniques.
• Chondromalacia Patellae: While the test can suggest this, definitive diagnosis requires imaging (MRI) or arthroscopy.

Management typically involves:

• Activity Modification: Reducing activities that aggravate pain.
• Rehabilitation Exercises: Strengthening the quadriceps (especially VMO), gluteal muscles (abductors and external rotators), and core stabilizers.
• Flexibility Training: Addressing tightness in hamstrings, quadriceps, and IT band.
• Biomechanical Correction: Addressing foot mechanics with orthotics if necessary.
• Pain Management: Modalities such as ice, NSAIDs, or taping.

Conclusion

The Clarke's test serves as a valuable clinical tool for fitness professionals, physical therapists, and medical practitioners to screen for patellofemoral joint irritation. While a positive result indicates the presence of pain under patellar compression, it is crucial to interpret it within a comprehensive orthopedic assessment. Understanding the anatomical basis and limitations of the test allows for more accurate clinical reasoning and guides appropriate referral or management strategies for individuals experiencing anterior knee pain.