Knee Special Tests: Understanding Positive Findings, Ligament, Meniscal, and Patellofemoral Assessments

What is a positive test for the knee?

A positive test for the knee refers to a specific finding during a physical examination or special orthopedic test that indicates the likely presence of injury or dysfunction in a particular knee structure, such as a ligament, meniscus, or patellofemoral joint.

Understanding Knee Assessment

The knee joint, a complex articulation of the femur, tibia, and patella, is frequently subjected to injury due to its weight-bearing and mobility functions. When assessing knee pain or dysfunction, clinicians, physical therapists, and athletic trainers utilize a battery of specialized physical tests. These "special tests" are designed to selectively stress or load specific anatomical structures within and around the knee to elicit a diagnostic response.

General Principles of Special Tests

Special tests are a critical component of a comprehensive physical examination, providing valuable information that guides diagnosis and treatment. They are typically performed after a thorough history taking and initial observation and palpation.

• What is a "Positive Test"? A "positive test" is a specific observable or palpable sign, or a report of pain or apprehension by the patient, that occurs when a particular maneuver is performed. This response suggests the involvement or injury of the structure being targeted by the test. For example, excessive movement during a ligamentous stress test or a distinct click during a meniscal test would be considered positive findings. It's crucial to compare findings to the uninjured contralateral limb whenever possible.

• Importance of Clinical Correlation While a positive test can be highly indicative, it is rarely diagnostic in isolation. The findings from special tests must always be interpreted in the context of the patient's full medical history, symptoms, mechanism of injury, and other physical examination findings. Imaging studies (X-ray, MRI) may be used to confirm a diagnosis suggested by a positive test.

Common Ligamentous Tests

Ligamentous injuries are prevalent in the knee, often resulting from traumatic events. Special tests for ligaments assess the integrity and stability of these crucial connective tissues.

• Anterior Cruciate Ligament (ACL) The ACL is vital for preventing anterior translation of the tibia relative to the femur and controlling rotational stability.

  • Lachman Test: Considered the most sensitive test for ACL integrity.
    • Positive Test: Excessive anterior translation of the tibia on the femur, particularly with a soft or absent "end-feel" (the sensation of resistance at the end of passive range of motion).
  • Anterior Drawer Test:
    • Positive Test: Excessive anterior translation of the tibia on the femur, often indicating a more chronic or complete ACL tear than the Lachman test.

• Posterior Cruciate Ligament (PCL) The PCL prevents posterior translation of the tibia relative to the femur.

  • Posterior Drawer Test:
    • Positive Test: Excessive posterior translation of the tibia on the femur from a neutral position.
  • Posterior Sag Sign (Godfrey's Test):
    • Positive Test: When the patient's hip and knee are flexed to 90 degrees and supported, the tibia sags posteriorly relative to the femur due to gravity, indicating PCL laxity.

• Medial Collateral Ligament (MCL) The MCL resists valgus (knock-knee) forces and prevents excessive gapping on the medial side of the knee.

  • Valgus Stress Test: Performed at both 0 degrees (to assess MCL and other structures) and 30 degrees of knee flexion (to isolate the MCL).
    • Positive Test: Excessive gapping or pain on the medial side of the knee when a valgus force is applied.

• Lateral Collateral Ligament (LCL) The LCL resists varus (bow-legged) forces and prevents excessive gapping on the lateral side of the knee.

  • Varus Stress Test: Performed at both 0 degrees and 30 degrees of knee flexion.
    • Positive Test: Excessive gapping or pain on the lateral side of the knee when a varus force is applied.

Meniscal Tests

The menisci are C-shaped cartilage structures that act as shock absorbers and provide joint stability. Tears can result from twisting injuries.

• McMurray Test:

  • Positive Test: A palpable or audible click, pop, or pain elicited during specific movements (flexion, rotation, and extension of the knee), which can indicate a tear in the medial or lateral meniscus depending on the direction of rotation.

• Apley's Compression Test:

  • Positive Test: Pain elicited or increased during compression of the tibia into the femur while simultaneously rotating the tibia, suggesting a meniscal lesion. Pain with distraction and rotation, conversely, might suggest ligamentous involvement.

Patellofemoral Tests

These tests assess the patella (kneecap) and its articulation with the femur, which is a common source of anterior knee pain.

• Patellar Apprehension Test:

  • Positive Test: The patient expresses apprehension, muscle guarding, or attempts to stop the examiner from dislocating the patella laterally, indicating patellar instability or a history of dislocation.

• Patellar Grind Test (Clarke's Sign):

  • Positive Test: Pain under the patella (retropatellar pain) is elicited when the examiner presses down on the superior pole of the patella while the patient attempts to contract their quadriceps muscle, suggesting patellofemoral pain syndrome or chondromalacia patellae.

Limitations and Next Steps

While invaluable, special tests have inherent limitations, including variable sensitivity (ability to correctly identify those with the condition) and specificity (ability to correctly identify those without the condition). A single positive test may not be definitive, and a negative test does not always rule out an injury. A comprehensive evaluation by a qualified healthcare professional, potentially including advanced imaging like MRI, is often necessary to confirm a diagnosis and formulate an appropriate treatment plan.

Conclusion

Understanding what constitutes a "positive test" for various knee injuries is fundamental for anyone involved in musculoskeletal health. These tests provide crucial insights into the integrity and function of the knee's complex structures. However, their interpretation requires clinical expertise, considering the full context of the patient's presentation to ensure accurate diagnosis and effective management of knee conditions.