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.

Diagnosis of Radicular Quadriceps Weakness

Rainville J, Jouve C, Finno M, Limke J. Comparison of four tests of quadriceps strength in L3 or L4 radiculopathies Spine 2003;28:2466–2471

This study was designed to address the lack of a standard test for quadriceps weakness in patients with L3 or L4 radiculopathy. The authors describe, given the high levels of strength usually seen from a large muscle group like the quadriceps, the low sensitivity of standard manual muscle testing. If quadriceps strength is used to assess for L3 or L4 radiculopathy, a test with low sensitivity is likely to result in substantial false negatives, and missed diagnoses. The goal of the authors was to determine if a clinical test exists with sufficiently high sensitivity to detect this lesion.

Two sets of patients were assessed: the study group included 33 patients with symptomatic, unilateral lumbar radiculopathy, and an MRI or CT that demonstrated displaced or compressed the L3 or L4 nerve roots on the symptomatic side. The control group was made up of 19 patients with MRI or CT confirmation of displacement or compression of L5 or S1 nerve roots. Symptoms of radiculopathy included unilateral leg pain of the groin, thigh, or lower leg, paresthesias involving the thigh, knee, or lower leg, and/or symptoms suggestive of weakness in the affected extremity.

The following tests were chosen to assess quadriceps weakness: single leg sit-to-stand, step-up, knee-flexed MMT and knee-extended MMT. The single leg sit-to-stand test was the most accurate (61%), versus the step-up (27%), and the bent-knee MMT (42%). In those with L3 or L4 radiculopathies, the single leg sit-to-stand revealed all but one subject with decreased quadriceps strength found by the remaining three tests. The sit-to-stand test was normal in all patients with L5 and S1 radiculopathies.

The subjects were also given a modified Lysholm questionnaire, and both groups described a statistically similar level of difficulty with lower extremity strength activities, including sit to stand, knee buckling, and difficulty with sit to stand. This came despite the fact that those with an L5 or S1 lesion had no demonstrable quadriceps weakness. The only subjective question that could be correlated with quadriceps weakness was the use of a step-to gait in ascending and descending stairs. Description of this gait pattern should be a warning to clinicians that quadriceps weakness may be present and should be assessed.

The authors performed intertester studies on 39 of the patients. The Kappa reliability scores for the single-leg sit-to-stand and step-up test were very good, at .85 and .83, respectively. The Kappa for the knee-extended MMT was .08, which is really no better than flipping a coin. Given the low reliability, and the fact that it detected weakness in only 9% of patients with radiculopathy, it appears that the quadriceps may simply be too strong in this position, and there is no reason to include this test as a screen for quadriceps strength. The bent-knee MMT, however, has moderate reliability (K = .66) and found weakness in half of the expected subjects, and as such may be useful for patients with weightbearing restrictions or restrictions at other extremity joints, who cannot perform the other, multijoint tests.

The other day I was in a meeting where we were reviewing the dermatome tests in our lumbar spine template. Remembering this article, we had a discussion about how best to test the quadriceps (and gastroc/soleus, for that matter), as standard manual muscle testing is fairly ineffective, as shown by this study. I didn’t convince them to include the single-leg sit-to-stand test, but I continue to use as my primary screen for quadriceps weakness in this population.