Evidence-Based Physical Therapy Han, Yueh-Chin Graduate Institute of Physical Therapy National Taiwan University 2004/11/1 -- Critical appraisal of diagnosis and screening

Clinical Question  What’s the most reliable method to assess sciatica associate with disc herniation?

Value of the bell test and the hyperextension test for diagnosisin sciatica associated with disc herniation: comparison with Lasègue’s sign and the crossed Lasègue’s sign Poiraudeau S, Foltz V, Drapè JL, Fermanian J, Lefèvre-Colau MM, Mayoux-Benhamou MA. Rheumatology.2001; 40: Citation

Methods

Subjects—Including Criteria  Subjects hospitalized for acute or chronic sciatica  Having lumbosacral and lower limb pain  Associated with or not paraesthesia  With one of the following Radicular pain below knee after an L5 or S1 nerve root dermatome Radicular pain above knee with neurological impairment Neurological impairment: reflex abolition, muscular weakness or sensory defects in the corresponding radicular area)

Subjects—Exclusion Criteria  Back pain without sciatica  Radicular pain in dermatome other than L5 or/and S1  Systemic lumboradicular pain (tumor, infectious or inflammatory disease)  Prior lumbar surgery  Uncontrolled psychiatric disorder

Investigators  E1: rheumatology trainee with 3 years of experience  E2 and E3: full time physicians for 10 and 25 years experience

Radiographic Assessment  For gold standard  E1, E2 and an experienced radiologist analysed blindly and independently at least one of MRI, CT or saccoradiculography  Divided into 2 groups:  Group A: compression of the nerve root by disc herniated  Group B: sciatica without disc herniation or associated with degenerative changes or spinal stenosis  3 readers disagreed, analysed blindly by E3, not obtained majority (3 to 1), exclusion

Physical Examination  Bell test  Pressure applied with thumb between the spinous processes L4 and L5, or L5 and S1 in standing position  Hyperextension test  Trunk mobilized passively and slowly over the full ROM of extension with the knees in extension in standing position  Lasèque’s sign test  Slowly raise passively the affected leg with sciatica with knee in full extension in supine position, stopped with pain  The pain not included the lumbar pain or hamstring stiffness  Clossed Lasèque’s sign test  The same with the LS test but on the contra-lateral leg  Positive: reproduce or exacerbated the usual radicular pain

Clinical Procedure  3 observers examined each patient blindly, independently and unaware of the diagnosis and radiological finding.  E1 was always the first, E2 and E3 was random  Within 12 h  E2 and E3 for reliability

Results

Table 3. Sensitivity, specificity, PPV and NPV of BT, HT, LS and CL for examiners E1, E2 and E3

Table 4. Sensitivity, specificity, PPV and NPV of sign combinations for examiners E1, E2 and E3

Diagnosis Worksheet  Lasèque’s sign test of E1  Simple calculations: Target Disorder (radiography) Totals PositiveNegative Lasèque’s sign test Positivea=33b=22a+b=55 Negativec=10d=13c+d=23 Totalsa+c=43b+d=35a+b+c+d=78

Sample Calculations  Sensitivity = a/(a+c) = 33/43= 77%  Specificity = d/(b+d) = 13/35 = 37%  Likelihood Ratio for a positive test result = LR+ =sens/(1-spec) =77%/63%=1.23  Likelihood Ratio for a negative test result=LR- =(1-sens)/spec =23%/37%=0.65  Positive Predictive Value = a/(a+b) = 33/55 = 60%  Negative Predictive Value = d/(c+d) = 13/23 = 59%  Pre-test Probability (prevalence) = (a+c)/(a+b+c+d) = 43/78 = 56%  Pre-test-odds = prevalence/(1-prevalence) =56%/44% = 1.27  Post-test odds = Pre-test odds x Likelihood Ratio =1.27x1.23=1.56  Post-test Probability = Post-test odds/(Post-test odds + 1) =1.56/2.56=0.60

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