Assessment of spinal patients with low back pain(lumbago) and radicular pain in the sciatic nerve distribution(sciatica) should involve thorough spinal ,neurological and lumbar nerve tension examination.
There is little doubt that the most common test performed ,or referred to in spinal examinations is the so called 'straight leg raise test' (SLRT).
Interpretation of the findings and knowledge of the clinical significance of the results is most important.Evans' text( Evans,RC.Illustrated Essentials in Orthopaedic Physical Assessment: St Louis;Missouri; Mosby;1994) reminds all examiners that the lumbar nerve roots have a narrow range of movement during the stretching manoeuvre. The nerve roots are not brought into tension by the SLRT until 35 to 70 degrees of hip flexion.It is important that an examiner be cognisant of this fact.SLR displaces the L4,L5 and S1 spinal nerves by up to 5 mm and stretches them by 2 to 4 % ( Smith et al 1993).
The examiner should remember that plantar flexion is supplied by the Tibial nerve; Foot and Great toe Dorsiflexion by the Deep peroneal nerve and foot eversion by the Superficial peroneal nerve. Differentiaiting between L5 radiculopathy and a Peroneal nerve causation for foot drop can be challenging! I have written an earlier article on how to determine if a foot drop is due to an L5 radiculopathy (spine) or perineal nerve lesion(lateral knee).If there is doubt Neurophysiology is the 'gold standard' differentiator performed and interpreted by a Specialist neurologist, of course.
The SLRT will be positive in hip and sacra-iliac conditions.To differentiate there are many manoeuvres including SLR until leg pain is just experienced then lowering the leg until pain disappears.If mild passive dorsiflexion at the ankle reproduces the leg pain then this suggests lumbar nerve root tension.Ankle dorsiflexion stretches the tibial nerve by about 1-2 cm.This manoeuvre should not induce pain in the lower limb if the initial leg pain on SLRT was due to hip/S-I joint pathology.Another test involves SLR to leg pain then flexion of knee to release the sciatic nerve and supporting the leg on the examiner's shoulder.Then thumb pressure in the popliteal fossa ('popliteal fossa pressure test') results in sudden severe sciatica in a patient with lumbar nerve tension.No pain should result from the popliteal thumb pressure in hip or S-I joint causes for the original pain on SLR testing.The mechanics of stretching of lumbar nerve roots is often utilised in medico-legal testing. Severe leg pain reporting at SLR 20 degrees may be contradicted when the examinee sits on the bed or over end of bed with the knees extended.The same applies to the sciatic nerve stretching test in the sitting position;the so called 'reclamation Test'.The patient sits up on the end of the couch without leaning back and the examiner raises the examinee's calf.If the examinee leans back and /or places hands behind onto the couch as well ,because of leg pain,the test is positive.(Intervertebral Disk Diseases:Causes,Diagnosis,Treatment and Prophylaxis.Jurgen Kraemer).
Lasegue's test is historic of course.Lasegue was said to be the first to observe that patients with sciatica keep the foot in plantar flexion and complain of increased sciatica when it is dorsiflexed(1864).Lasegue's Test consists of hip flexion combined with knee extension causing pain in the back radiating down the leg in a sciatic distribution.In common medical parlance ,the term positive Lasegue's sign is also applied when SLRT is positive, in Anglo-American literature.Forst first described the provocation by these manoeuvres,a student of Charles Lasegue, cited by Finneson 1980.
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