How to Perform a Knee Examination: Step-by-Step Instructions for Medical Students

Introduction to Knee Examination

The knee joint, being one of the most complex joints in the human body, is crucial for everyday activities such as walking, running, and jumping. Understanding how to conduct a thorough knee examination is essential for medical students and healthcare professionals to diagnose various conditions, including ligament injuries, meniscal tears, and arthritis. A well-conducted knee examination provides valuable insights into the underlying pathology and guides further diagnostic and therapeutic steps.

Basic Anatomy of the Knee

Before diving into the examination techniques, it’s important to have a solid understanding of the knee’s anatomy. The knee joint consists of the following structures:

• Bones: The femur (thigh bone), tibia (shin bone), and patella (kneecap).
• Ligaments: These include the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL).
• Menisci: The medial and lateral menisci are crescent-shaped cartilage that act as shock absorbers.
• Muscles and Tendons: The quadriceps and hamstring muscles are key players in knee movement, with their respective tendons attaching to the knee structures.

Preparation for Knee Examination

Patient History

Begin by taking a detailed history, focusing on the following aspects:

• Onset of Symptoms: Determine whether the pain or dysfunction began suddenly or gradually.
• Location of Pain: Ask the patient to pinpoint where the pain is most severe.
• Mechanism of Injury: Inquire about any recent trauma or activities that may have caused the injury.
• Associated Symptoms: Check for swelling, locking, instability, or clicking sensations.
• Previous Medical History: Review any history of knee surgeries, injuries, or systemic diseases like rheumatoid arthritis.

Patient Positioning

The knee examination is typically performed with the patient in the following positions:

1. Standing: To assess alignment and weight-bearing.
2. Supine: With the patient lying on their back, this position allows for detailed palpation and special tests.
3. Sitting: Useful for assessing the quadriceps muscle strength and patellar tracking.

Inspection

Begin the physical examination with a thorough inspection. Observe both knees, noting any visible abnormalities:

• Swelling: Look for signs of effusion or localized swelling.
• Deformities: Check for bowing (varus or valgus deformity) or patellar malalignment.
• Muscle Wasting: Observe the quadriceps and calf muscles for atrophy, which may indicate chronic pathology.
• Skin Changes: Look for scars, bruises, or redness that might suggest underlying inflammation or previous surgery.

Palpation

Palpation is crucial for detecting tenderness, warmth, and structural abnormalities. Perform the following palpation techniques:

1. Patella: Palpate the patella for tenderness, crepitus, and mobility. Assess for patellar tracking by gently moving it medially and laterally.
2. Joint Line: Palpate along the medial and lateral joint lines to detect tenderness, which may indicate meniscal injury.
3. Ligaments: Palpate the medial and lateral collateral ligaments for tenderness or thickening.
4. Tibial Tuberosity: Check for tenderness at the tibial tuberosity, which could indicate Osgood-Schlatter disease in younger patients.

Range of Motion (ROM)

Assess the active and passive range of motion of the knee:

• Flexion: Ask the patient to bend the knee as far as possible. Normal flexion ranges from 0 to 135 degrees.
• Extension: Check if the patient can fully straighten the knee. Full extension should reach 0 degrees.
• Hyperextension: Some patients may exhibit slight hyperextension, which should be noted but is often normal.
• End Feel: Assess the quality of the end feel during passive movement to differentiate between soft tissue and bony restrictions.

Strength Testing

Strength testing is essential to evaluate the integrity of the muscles surrounding the knee:

1. Quadriceps Strength: With the patient sitting, ask them to extend the knee against resistance. Weakness could suggest quadriceps muscle injury or femoral nerve involvement.
2. Hamstring Strength: With the patient in a prone position, ask them to flex the knee against resistance. Weakness may indicate hamstring strain or sciatic nerve involvement.
3. Hip Abductors and Adductors: These muscles indirectly affect knee stability, so it’s important to assess their strength as well.

Special Tests

Several special tests are employed during a knee examination to assess the integrity of specific structures:

1. Lachman Test (ACL Integrity)

• With the patient supine, flex the knee to 20-30 degrees.
• Stabilize the femur with one hand and pull the tibia forward with the other.
• A positive test, indicated by excessive anterior translation of the tibia, suggests an ACL tear.

2. Anterior Drawer Test (ACL Integrity)

• Flex the knee to 90 degrees and sit on the patient’s foot to stabilize it.
• Grasp the tibia just below the joint line and pull it forward.
• A positive test indicates ACL injury.

3. Posterior Drawer Test (PCL Integrity)

• Position the knee similarly to the anterior drawer test.
• Push the tibia posteriorly. A positive test suggests PCL damage.

4. Varus Stress Test (LCL Integrity)

• With the knee in slight flexion, apply a varus (inward) force to the knee while stabilizing the ankle.
• A positive test indicates lateral collateral ligament injury.

5. Valgus Stress Test (MCL Integrity)

• Similar to the varus stress test, but apply a valgus (outward) force to assess the medial collateral ligament.

6. McMurray’s Test (Meniscal Integrity)

• With the patient supine, flex the knee and hip while palpating the joint line.
• Internally and externally rotate the tibia while extending the knee.
• A click or pain suggests a meniscal tear.

7. Apley’s Compression Test (Meniscal Integrity)

• With the patient prone and the knee flexed to 90 degrees, apply downward pressure on the foot while rotating the tibia.
• Pain with rotation indicates a meniscal injury.

Neurological Examination

Don’t forget to include a neurological examination, as nerve involvement can mimic or complicate knee injuries:

1. Reflexes: Test the patellar reflex (L2-L4) to assess the femoral nerve.
2. Sensation: Evaluate sensation in the dermatomal patterns of the lower extremity, focusing on areas supplied by the femoral, sciatic, and peroneal nerves.
3. Motor Function: Assess the motor function of the quadriceps, hamstrings, and calf muscles.

Gait Analysis

A thorough knee examination should also include gait analysis:

• Observe the Patient’s Gait: Look for limping, antalgic gait, or abnormal patterns such as circumduction or foot drop.
• Trendelenburg Test: Ask the patient to stand on one leg and observe for hip drop, which may indicate weakness in the hip abductors affecting knee stability.

Imaging and Further Diagnostic Steps

Based on the findings from the knee examination, further diagnostic tools may be required:

• X-rays: Useful for detecting fractures, osteoarthritis, and bone deformities.
• MRI: The gold standard for evaluating soft tissue injuries, including ligament tears, meniscal injuries, and cartilage damage.
• Ultrasound: Can be used to assess effusions, cysts, and superficial tendon injuries.
• CT Scan: Offers detailed imaging of bony structures and is useful in complex fractures.

Conclusion

Performing a comprehensive knee examination is a fundamental skill for medical students and healthcare professionals. It requires a combination of knowledge, technique, and careful observation. By mastering the steps outlined in this guide, clinicians can accurately diagnose a wide range of knee conditions, leading to better patient outcomes.