The Moving Patellar Apprehension Test for Lateral Patellar Instability.

Ahmad CS, McCarthy M, Gomez JA, Shubin Stein BE.  The Moving Patellar Apprehension Test for Lateral Patellar Instability. Am J Sports Med. 2009 Feb 3. [Epub ahead of print]

This is a diagnostic study looking at a new variation of patellar provocative testing to determine patellar instability.  The test has two phases.  In phase one, the patella is pushed laterally, and the knee is passively moved from full extension to 90° flexion – a positive test involves apprehension by the patient, or contraction of the quadriceps in an attempt to stabilize the patella and prevent lateral dislocation.  In phase two, the patella is pushed medially, and the same movement is performed – with a positive finding, the patient will not report any pain or apprehension.

This test was performed on 51 patients with various knee symptoms, and compared to whether their patella dislocated with a lateral glide under anesthesia.  The test was found to have a sensitivity of 100%, a specificity of 88.4%, a positive predictive value of 89.2%, a negative predictive value of 100%, and an accuracy of 94.1%.  All of these findings are significantly more robust than previous versions of patellar apprehension tests, which usually involve pushing the patella laterally in full extension, at 30° flexion, or some motion between them.  The test picked up every patient whose patella dislocated under anesthesia, and only 3 false positives out of the 26 who did not dislocate.

This study is made more powerful in that they compared patients with dislocation to patients without, making this much better than one in which normal control subjects are used.  Of course, considering the patients were put under anesthesia for this examination, it would have been hard to convince people without knee symptoms to agree, although I suppose they could have used the contralateral knee.  The authors noted that each of the 25 subjects with positive findings who were positive on the gold standard test also felt better with the patella glided medially.  This calls into question the need for phase two, but I agree with the authors that it can be helpful to use this to confirm the diagnosis, especially since it is performed quickly, and there is no reason to expect harm from performing the second phase.  We should remember that the gold standard used in this exam (dislocation under anesthesia) may not be correlated to any specific functional findings, but with this in mind, the moving patellar apprehension test seems to be a significant improvement over the standard tests we learn.