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Patella Apprehension Test – Patellar Instability

The Patella Apprehension Test is a clinical examination used to diagnose patellar instability or a history of patellar dislocation at the knee joint.

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The Patella Apprehension Test is a clinical examination used to diagnose patellar instability or a history of patellar dislocation at the knee joint.

What is the Patella Apprehension Test?

The Patella Apprehension Test is a clinical diagnostic procedure used in orthopedic and sports medicine practice to assess patellar instability – that is, the tendency of the kneecap (patella) to dislocate or partially dislocate (sublux). The term “apprehension” refers to the involuntary protective reaction a patient exhibits when the examiner attempts to move the patella in a direction that triggers fear of dislocation. A positive test result is indicated by muscle guarding, pain, or an anxious response from the patient.

Background: The Patella and Its Stability

The patella (kneecap) is a small, triangular bone embedded within the tendon of the quadriceps muscle. It glides along a cartilage-lined groove on the femur (thighbone) known as the trochlea during flexion and extension of the knee. Several anatomical structures – including ligaments, muscles, and bony geometry – maintain the patella in its correct tracking path.

When these stabilizing mechanisms are compromised – due to trauma, anatomical variation, or muscular imbalance – the patella can dislocate (fully) or subluxate (partially), leading to pain, swelling, and functional limitation. Patellar instability is particularly common in young, physically active individuals.

How the Test is Performed

The Patella Apprehension Test is typically performed as follows:

The patient lies relaxed in the supine position (on their back), with the affected knee in full extension or slight flexion (approximately 20–30 degrees).
The examiner gently grasps the patella and applies a lateral (outward) force, pushing the kneecap toward the outside of the knee.
The examiner observes the patient for any apprehension response: involuntary muscle contraction, visible anxiety, pain report, or withdrawal of the limb.
A positive test is considered a clinical indicator of current or previous patellar dislocation or instability.

Some clinicians also perform the test at 90 degrees of knee flexion or assess medial displacement of the patella to obtain additional diagnostic information.

Clinical Significance and Diagnostic Value

A positive Patella Apprehension Test is a strong clinical sign of patellar instability. It is commonly used alongside other tests, including:

J-Sign Test: observation of abnormal lateral patellar tracking during active knee extension
Patellar Tilt Test: assessment of lateral patellar tilt under passive conditions
Mediolateral Glide Test: evaluation of passive patellar mobility in both directions

The sensitivity of the Apprehension Test is reported in the literature at approximately 39–82 %, with higher specificity values. Its diagnostic value is greatest when interpreted in the context of the patient's clinical history and imaging findings.

Indications

The test is indicated in patients presenting with:

Anterior knee pain or generalized knee discomfort
Suspected patellar dislocation following a sports injury or accident
Recurrent episodes of the knee “giving way” or a sense of instability
Post-traumatic knee swelling
Follow-up care after surgical stabilization of the patella

Further Diagnostic Workup

If the test is positive or clinical suspicion of patellar instability is high, imaging studies are typically ordered:

X-ray of the knee: to assess bony anatomy and patellar height (e.g., patella alta)
MRI (Magnetic Resonance Imaging): for detailed visualization of ligaments, cartilage, and soft tissues, especially after acute dislocation
CT (Computed Tomography): to measure the TT-TG distance (tibial tuberosity – trochlear groove), an important parameter for surgical planning

Treatment Options for Patellar Instability

Treatment depends on the severity and underlying cause of the instability and may be conservative or surgical.

Conservative Treatment

Physiotherapy with targeted strengthening of the quadriceps muscle, especially the vastus medialis oblique (VMO)
Knee braces or orthoses for patellar stabilization
Taping techniques (e.g., McConnell taping)
Anti-inflammatory medications for acute pain management

Surgical Treatment

Reconstruction of the medial patellofemoral ligament (MPFL reconstruction) – the most common procedure for recurrent dislocation
Tibial tubercle transfer (TTT) to correct abnormal patellar pull direction
Trochleoplasty for cases involving trochlear dysplasia

References

Smith TO, Davies L, Chester R, Clark A, Donell ST. Clinical outcomes of rehabilitation for patients following lateral patellar dislocation: a systematic review. Physiotherapy. 2010;96(4):269–281.
Netter FH. Atlas of Human Anatomy. 7th edition. Elsevier, 2019.
Petersen W, Ellermann A, Rembitzki IV, et al. Evaluating the effectiveness of conservative treatment for patellofemoral instability. Knee Surg Sports Traumatol Arthrosc. 2016;24(3):843–851.

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