The Accuracy of the Physical Examination for the Diagnosis of Midlumbar and Low Lumbar Nerve Root Impingement
Introduction: In this study, researchers were looking at the accuracy of the physical examination in diagnosing lumbar nerve impingement. An accurate physical examination is essential before ordering imaging; a physician should be able to localize the nerve root impingement before MRI to ensure that the imaging lines up with the clinical examination—and not the other way around. This is especially important given the high prevalence of asymptomatic lumbar disc herniations seen on MRI.
This study examined several physical examination tests in relation to MRIs in diagnosing midlumbar nerve root impingement (L2, L3, or L4), low lumbar nerve root impingement (L5 or S1), and level-specific nerve root impingement.
Methods: This was a cross-sectional, prospective recruitment study; participants were 18 years or older, and they had a history of lower extremity radicular pain (in an L2, L3, L4, L5, or SI dermatome—with or without neurological symptoms) for less than 12 weeks (n = 54).
Participants had the following tests done as part of the physical examination:
- Straight leg raise (SLR)/Crossed leg raise (CLR)
- Femoral stretch test (FST)/Crossed femoral stretch test (CFST)
- Knee extensor strength
- Ankle dorsiflexor strength
- Ankle plantarflexor strength
- Great toe extensor strength
- Hip abductor strength
- Sensory testing
- Reflex testing
Participants then had MRI tests done (at minimum: T1- and T2-weighted sagittal and axial MRIs), and those were reviewed by neuroradiologists for the presence of nerve root impingement.
The sensitivities, specificities, and likelihood ratios (LR) were calculated for each individual test and for test combinations. This was done to see how accurate the tests were in predicting nerve root impingement in relation to the MRIs.
Results: An LR ≥ 5.0 means that there were moderate to large changes from pre-test probability to post-test probability of nerve root impingement.
These tests showed an LR ≥ 5.0 for the diagnosis of midlumbar impingement (LR ∞):
- Medial ankle pinprick sensation
- Patellar reflex testing
In combination testing for diagnosing midlumbar impingement, LR ≥ 5.0 was seen by combining FST with either patellar reflex testing (LR 7.0; 95% Confidence Interval [CI] 2.3-21) or with the sit-to-stand test (LR ∞).
Low lumbar impingement diagnosis had the following results: the Achilles reflex test showed an LR ≥ 5.0 (LR 7.1; 95% CI 0.96-53), and LR was not increased with any test combinations.
In diagnosing level-specific impingement, the following tests showed LR ≥ 5.0:
- Anterior thigh sensation at L2 (LR 13; 95% CI 1.8-87)
- FST at L3 (LR 5.7; 95% CI 2.3-4.4)
- Patellar reflex testing at L4 (LR 7.7; 95% CI 1.7-35)
- Medial ankle sensation at L4 (LR ∞)
- CFST at L4 (LR 13; 95% CI 1.8-87)
- Hip abductor strength at L5 (LR 11; 95% CI 1.3-84)
An increase in LR with test combinations was seen at the L4 level only when diagnosing level-specific nerve root impingement.
Conclusions: In diagnosing nerve root impingement—midlumbar impingement, low lumbar impingement, or level-specific—individual physical examination tests may provide the practitioner with information that assists in making an accurate diagnosis.
In the midlumbar region, combinations of physical examination tests can augment nerve root impingement diagnosis accuracy.
As clinicians, we are constantly bombarded with radiographic findings far more impressive than their physical exam counterparts. In this era of abundant imaging, it is easy lose sight of the importance of a discerning clinical exam as an initial diagnostic tool.
In this first paper, Suri et al analyzed a battery of physical exam components and evaluated their efficacy in predicting compressive lesions on MRI imaging. Clinical pearls from this study are:
- The sit-to-stand test is far superior to manual strength testing for quadriceps function.
- The femoral stretch test was the most specific test for midlumbar nerve root impingement
- And not surprisingly, nerve root impingement is a more selective imaging finding than disc herniation.