Instability is thought to be a clinical classification of LBP that clinicians should be aware of.
| Study title: A literature review of clinical tests for lumbar instability in low back pain: validity and applicability in clinical practice Authors: Ferrari S, Manni T, Bonetti F et al. Publication information: Chiropractic & Manual Therapies 2015; 23: 14-26. |
Instability is thought to be a clinical classification of LBP that clinicians should be aware of. In clinical practice, we often look for and/or encounter ‘functional’ instability, which is thought to be caused by poor function of the muscles of the trunk or insufficient motor control in and around the lumbar spine.
This review assessed the most commonly used clinical tests for instability, including the Prone Instability Test (PIT), the Passive Lumbar Extension (PLE) test, the Aberrant Movements Pattern (AMP), the Posterior Shear Test (PST), the Prone Bridge Test (PBT), the Supine Bridge Test (SBT), and the Active Straight Leg Raise Test (ASLR). Six studies were included, only two of which showed high methodological quality.
Diagnostic accuracy
Two studies investigated the diagnostic accuracy of clinical tests. Kasai et al. looked at a population diagnosed with spinal stenosis, lumbar spondylolisthesis or lumbar degenerative scoliosis, and found that the PLE test was the most accurate clinical test, recommending that it is likely the best test to use clinically. The PLE test is performed with the patient prone. Both lower extremities are then elevated concurrently to a height of about 30 cm from the table while maintaining the knees extended and gently pulling the legs. Pain in the lumbar spine is considered a positive result.
When the individual parts of the AMP were assessed, the Instability Catch Sign (standing patient flexed forward – positive if sudden onset of lumbar pain preventing return to upright position), Painful Catch Sign (supine patient lifts both legs straight up in the air with knees straight – positive if legs fall to table due to lumbar pain when they attempt to lower them), and Apprehension Sign (asking patients if they feel a sensation of lumbar collapse because of sudden pain during ordinary movements) all showed low sensitivity, but good specificity, which suggests the need for caution in the use of these tests. It’s important to note the AMP includes five tests that could be considered as one comprehensive test.
Fritz et al. also found the AMP tests showed low sensitivity and high specificity in a population with chronic LBP. In this group, the PIT showed low to moderate sensitivity and specificity and the PST showed poor sensitivity and specificity. The PIT begins with the patient prone with hips at the edge of the table and legs resting on the floor. The examiner then places downward (posterior to anterior) pressure through each lumbar segment to assess for a level that is hypermobile or painful.
The second part of this test, as it was originally published involves having the patient extend both legs off the floor while repeating the P-A pressure. If pain or hypermobility is reduced, this test is considered positive. The PST is performed with the subject standing with arms crossed over the lower abdomen. The examiner stands at 1 side and places 1 arm around the subject’s abdomen, over the subject’s crossed hands. The heel of the examiner’s opposite hand is placed on the subject’s pelvis for stabilization while the index or middle finger palpates the L5-S1 interspace. The examiner produces a posterior shear force through the subject’s abdomen and an anterior stabilizing force with the opposite hand. The test is repeated at each lumber level. A positive test occurs when symptoms are provoked and is not based on the amount of intersegmental motion detected (8).
Reliability
Five papers looked at test reliability. A single study showed good inter-rater reliability for the PLE. The PIT was assessed in five studies and rated from fair to good for inter-rater reliability. However, once the two studies with the most severe methodological weaknesses were eliminated, that rating went up to moderate to good. The inter-rater reliability of the AMP was assessed in three studies and rated from poor to moderate. Finally, the PST was only investigated by Fritz et al. and showed the worst inter-rater reliability.
Application, conclusions
The PLE test was found to be the most suitable test for detecting lumbar instability, as it shows excellent diagnostic accuracy and good reliability. This recommendation is based on only one study, however.
Further studies are needed to investigate the clinical utility of the PLE and other instability tests for differentiating patients with LBP.
Dr. Shawn Thistle is the founder and CEO of RRS Education (rrseducation.com), which helps busy clinicians integrate current research evidence rationally into practice. He also maintains a practice in Toronto, lectures at CMCC and provides chiropractic medicolegal consulting services. Reach him at: shawn@rrseducation.com
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