McMurray Test: Principle, Performance, and Clinical Significance

What is the principle of McMurray test?

The McMurray test is a clinical orthopedic examination maneuver designed to detect tears in the menisci of the knee joint by applying specific stresses that can elicit a palpable or audible click, pop, or pain if a meniscal lesion is present.

Understanding the Knee Joint and Menisci

To grasp the principle of the McMurray test, it's essential to understand the basic anatomy of the knee. The knee is a complex hinge joint formed by the articulation of the femur (thigh bone), tibia (shin bone), and patella (kneecap). Between the femoral condyles and the tibial plateau lie two C-shaped fibrocartilaginous structures known as the menisci: the medial meniscus (on the inner side of the knee) and the lateral meniscus (on the outer side).

Key Functions of the Menisci:

• Shock absorption: Distribute forces across the joint.
• Load transmission: Increase the contact area between the femur and tibia.
• Joint stability: Contribute to the overall stability of the knee.
• Lubrication and nutrition: Aid in the health of articular cartilage.

Meniscal tears are common injuries, especially in sports involving twisting or pivoting motions, or due to degenerative changes.

The Core Principle of the McMurray Test

The fundamental principle of the McMurray test is to reproduce the mechanism of impingement or "trapping" of a torn meniscus between the femoral condyle and the tibial plateau, thereby eliciting a diagnostic sign such as pain, a click, or a pop.

This is achieved by strategically combining three key movements:

1. Flexion and Extension: The knee is moved through its range of motion, from full flexion towards extension. This movement guides the menisci.
2. Rotation (Internal and External): The tibia is rotated internally or externally relative to the femur. This rotational stress applies torque to the menisci, pushing specific parts of them into different positions.
3. Valgus or Varus Stress: A gentle abduction (valgus) or adduction (varus) force is applied to the knee. This opens up the joint space on one side, allowing the femoral condyle to press more firmly onto the meniscus on the opposite side.

Mechanism of Action:

• To test the Medial Meniscus: The examiner typically flexes the patient's knee fully, applies a valgus stress (pushing the knee inward, opening the medial joint space), and externally rotates the tibia. As the knee is slowly extended, if a tear is present in the medial meniscus, the femoral condyle can catch, pinch, or trap the torn fragment, causing pain or a characteristic click/pop. This action forces the posterior horn of the medial meniscus forward.
• To test the Lateral Meniscus: The examiner typically flexes the patient's knee fully, applies a varus stress (pushing the knee outward, opening the lateral joint space), and internally rotates the tibia. As the knee is slowly extended, a similar catching or impingement of a torn lateral meniscal fragment can occur, eliciting pain or a click/pop. This action forces the posterior horn of the lateral meniscus forward.

The "click" or "pop" often signifies the torn meniscal fragment being displaced or snapping back into place as the joint surfaces move over it. Pain indicates that the movement is irritating the compromised tissue.

How the Test is Performed (Brief Overview)

While the focus is on principle, a brief understanding of the execution clarifies the concept:

• The patient lies supine (on their back).
• The examiner holds the patient's heel with one hand and places the other hand over the knee joint, palpating the joint line.
• The knee is fully flexed.
• For the medial meniscus, the examiner applies valgus stress and external rotation to the tibia, then slowly extends the knee.
• For the lateral meniscus, the examiner applies varus stress and internal rotation to the tibia, then slowly extends the knee.
• The examiner observes for pain, a palpable click/pop, or a sensation of the joint locking or giving way.

Interpreting Results: A Positive Test

A positive McMurray test is indicated by:

• Audible or palpable click/pop: This is the most classic sign and often suggests a meniscal tear.
• Pain: Localized pain along the joint line during the maneuver.
• Joint locking or giving way: A sensation of the knee catching or momentarily getting stuck.

It's important to note that a positive test is indicative but not definitive. False positives can occur, and some meniscal tears may not elicit a positive response.

Limitations and Clinical Considerations

While the McMurray test is a widely used clinical tool, it has limitations:

• Sensitivity and Specificity: Its diagnostic accuracy varies, with reported sensitivities ranging from 50-70% and specificities from 70-90%. This means it can miss some tears (false negatives) and occasionally indicate a tear when none is present (false positives).
• Acute vs. Chronic Tears: The test may be more sensitive for larger, displaced tears and less sensitive for smaller, stable, or degenerative tears.
• Patient Tolerance: Pain or guarding can limit the ability to perform the test effectively.
• Operator Skill: Proper technique is crucial for accurate results.

Therefore, the McMurray test is typically part of a comprehensive knee examination, alongside other special tests (e.g., Apley's grind test, Thessaly test), patient history, symptom analysis, and often confirmed with imaging studies like Magnetic Resonance Imaging (MRI).

Clinical Significance

The McMurray test remains a valuable component of the clinical assessment of knee pain, particularly when a meniscal injury is suspected. By understanding its underlying principle – the deliberate trapping and stressing of meniscal tissue – clinicians can better interpret findings and guide subsequent diagnostic and treatment decisions, ranging from conservative management to surgical intervention. It helps to differentiate meniscal pathology from other knee conditions.