Patellar Apprehension Test

Patellar Apprehension Test (or Fairbank Apprehension Test) is used to test whether the patella is likely to dislocate laterally (Patellar Instability).

See Also: Patellar Instability

How do you perform the Patellar Apprehension Test?

• The patient is supine with the knee extended and the thigh muscles relaxed.
• The examiner attempts to simulate a dislocation (in a manner similar to the apprehension test in anterior instability of the shoulder) by placing both thumbs on the medial aspect of the knee and pressing the patella laterally.
• The patient is then asked to ex the knee.
• Examiner observes patient’s reaction.

The Patellar Apprehension Test is conducted slowly enough so that it can be terminated once the anticipated response is elicited but before causing the patient undue discomfort.

See Also: Patellofemoral Joint

What does a positive Patellar Apprehension Test mean?

Where a patellar dislocation has occurred, the patient will report severe pain and will be apprehensive of another dislocation in extension or, at the latest, in flexion.

This apprehension manifests itself with behavior ranging from verbal expressions of anxiety to an involuntary quadriceps contraction that prevents further knee flexion.

A positive Patellar Apprehension Test indicates laxity of the medial patellar retinaculum, predisposing the patient to patellar subluxations or dislocations

See Also: Patellofemoral Pain Syndrome

Sensitivity & Specificity

A Cohort study by Christopher S Ahmad ¹ found that the patellar apprehension test is an accurate physical examination in assessing Patellar Instability, the Sensitivity & Specificity of this test was:

• Sensitivity: 100 %
• Specificity: 88 %

To improve the specificity of the test by isolating the medial patellofemoral ligament, move the patella distally and laterally.

Notes

True (frank) dislocation of the patella causes it to shift laterally and lock out of place, resulting in obvious gross deformity and spasm of the quadriceps group as it guards the injury (see Acute Patellar Dislocation).

Acute, chronic, or congenital laxity of the medial patellar restraints or abnormal tightness of the lateral retinaculum causes an increased lateral glide of the patella. Subtle patellar subluxations may occur without the patient’s interpretation as such, producing symptoms described as the knee “giving out” during weight bearing.

Patients suffering from chronic patellar instability also produce a positive Patellar Apprehension Test, which should be performed before conducting a valgus stress test.

The patella is most apt to dislocate or subluxate when the maximum tensile strain is placed on the lateral patellar restraints, normally within the range of 20 to 30 degrees of knee flexion, pulling the patella laterally, or after a valgus blow to the knee.

Several factors predispose an individual to patellar subluxations and dislocations, these include:

1. Lateral patellar tracking.
2. increased Q-angle;
3. tight lateral restraints;
4. lax medial restraints;
5. family history of patellar dislocation/subluxation .

Reference

1. Ahmad CS, McCarthy M, Gomez JA, Shubin Stein BE. The moving patellar apprehension test for lateral patellar instability. Am J Sports Med. 2009 Apr;37(4):791-6. doi: 10.1177/0363546508328113. Epub 2009 Feb 3. PMID: 19193601.
2. Luo, ZP, et al: Tensile stress of the lateral patellofemoral ligament during knee motion. Am J Knee Surg, 10:139, 1997.
3. Clinical Tests for the Musculoskeletal System 3rd Edition.
4. Dutton’s Orthopaedic Examination, Evaluation, And Intervention 3rd Edition.
5. Sarvdeep S. Dhatt, Sharad Prabhakar – Handbook of Clinical Examination in Orthopedics.
6. Campbel’s Operative Orthopaedics 12th edition Book.
7. Millers Review of Orthopaedics -7th Edition Book.
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9. Netter’s Orthopaedic Clinical Examination An Evidence-Based Approach 3rd Edition Book