REIDER PART 2
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Chaptf.r 9_Lumbar Spine 355

examiner feels a contraction transmitted through the semitendinosus tendon or actually sees slight flexion of the knee take place.

Achilles' Tendon Reflex (S1). The Achilles tendon reflex represents the SI nerve root. This reflex may be elicited in the patient who is seated with the legs dangling comfortably off the end or side of the examination table. The examiner gently dorsiflexes the foot to place the Achilles tendon under tension, and then strikes the Achilles about 3 cm above the calcaneus using the fiat end of the reflex hammer (Fig. 9-24A).

In most paticnts, this action produces a visiblc twitch of the ankle into plantar flexion. As with other deep tendon reflexes, a unilateral decrease in the magnitude of or disappearance of the Achilles reflex suggests a lower motor neuron lesion. The most common cause of this picture is a herniated L5-S1 disk impinging the ipsilateral SI nerve root. Bilateral hyperreflexia suggests the possi-bility of an upper motor neuron lesion.

If the examiner experiences difficulty in eliciting the Achilles tendon reflex, the use of reinforcement tech-niques is often helpful. A convenient method for rein-forcing the Achilles tendon reflex is to ask the patient to kneel on the examination table with the feet projecting a few inches past the end or side (see Fig. 9-24B). The examiner then strikes cach Achilles in tum as already described. This techniąue brings out the Achilles tendon reflex in the vast majority of individuals.

Pathologic Reflexes

If undue briskness of the Achilles or the patellar tendon reflexes leads the examiner to suspect the presence of an upper motor neuron lesion, the provocative tests for ankle clonus and the Babiński sign should be carried out. The details of these procedures arc described in Chapter 8, Cervical and Thoracic Spine. It is important to remember that the spinał cord usually ends at the inferior mar gin of the LI vertebra. Distal to this level, the nerve roots that constitute the cauda eąuina function very much like peripheral nerves. Thus, for an upper motor neuron picture to occur, a lesion must typically be situ-ated at the LI level or higher.

Nerve Tension Tests

An important component of the lumbar spine examina-tion is to determine whether evidence of nerve root com-pression exists. Nerve root compression is usually considcred probable whcn strctching the peripheral nerve associated with the nerve root in question reproduces pain in the distribution of that nerve. The most important peripheral nerves deriving from the lumbar and the sacral nerve roots are the femoral and the sciatic nerves. The femoral nerve runs down the anteromedial aspect of the thigh and is formed by the L2, L3, and L4 nerve roots. The sciatic nerve runs down the posterior thigh and is formed by the L4, L5, SI, S2, and S3 nerve roots.

Straight-Leg Raising Test

The straight-leg raising test is the most well-known nerve tension test for the lumbar spine. The test is per-formed with the patient lying in a comfortable supine position with the head and pclvis fiat. While fuli knee extension is maintained, one of the patient s feet is slowly lifted off the table. The limb is progressively elevated until

Figurę 9-24. A, Achilles’tendon reflex (SI nerve root). B, Reinforcement technique.