Intervertebral disc prolapse in the lumbar spine most often affects the L4/L5 and L5/S1 discs. In a man presenting with acute back pain following an episode of lifting a heavy weight, reduced force of which one of the following movements would most suggest an L4/L5rather than an L5/S1 disc lesion? 1. Ankle plantar flexion 2. Eversion of the foot 3. Extension of great toe 4. Inversion of the foot 5. Knee extension Explanation Extension of great toe In the lumbar spine (in contrast to the cervical spine) nerve roots emerge below their respective vertebrae: so the majority of L4/5 disc prolapses would be expected to affect the L5 root and the majority of L5/S1 disc prolapses would affect the S1 nerve root. Although L5 contributes to hip abduction and extension, knee flexion and ankle dorsiflexion, weakness is often minimal because of the contribution of other roots to these movements and tends to be maximal in extension of the toes, particularly the great toe. Ankle plantar flexion Ankle plantar flexion is mediated by S1 and 2, with ankle dorsiflexion by L4/L5. Eversion of the foot Eversion of the foot is mediated by S1. Inversion of the foot Inversion of the foot is mediated by L4 alone. Knee extension Knee extension is mediated primarily by L3/4. 280 Rate this question: 1 2 3 4 A patient presents with pins and needles on the lateral and anterior aspect of his left thigh. On examination, there is no motor deficit. There is no history of trauma. Which of the following is likely to be causing the problem? 1. Lateral cutaneous nerve of the thigh lesion 2. L2 root lesion 3. L3 root lesion 4. Femoral nerve lesion 5. Saphenous nerve lesion Explanation Lateral cutaneous nerve of the thigh lesion The lateral cutaneous nerve of the thigh supplies the antero-lateral aspect of the thigh. It has no motor branches. Meralgia paraesthetica is a condition in which there is irritation of the nerve causing sensory changes in the distribution of the lateral cutaneous nerve of the thigh without any motor changes. L2 root lesion L2 and L3 supply part of the dermatome described, but both have motor branches. L3 root lesion While the L3 nerve root supplies the dermatome, it also has motor branches, therefore if the L3 nerve root were affected weakness could be expected. The main muscle innervated by L3 is the quadriceps femoris. Femoral nerve lesion The femoral nerve supplies the quadriceps muscle therefore a lesion to the femoral nerve would result in weakness of knee extension. Saphenous nerve lesion The saphenous nerve is a terminal cutaneous branch of the femoral nerve. It runs with the saphenous vein to supply an area of skin below the knee on the medial aspect of the leg. Saphenous nerve neuralgia can be seen after varicose vein surgery. Damage can also occur after vein harvest for coronary artery bypass graft (CABG). 297 Rate this question: 1 2 3 A patient presents with a history of back pain that developed 3 months ago when he got up suddenly from a seated position. The pain radiates down the leg to the ankle. On examination he has weakness of the quadriceps, reduced knee jerk reflex and reduced sensation over the patella. Where is the lesion likely to be? 1. Sciatic nerve compression 2. Ilioinguinal nerve 3. L3 nerve root 4. L5 nerve root 5. Compression of the femoral nerve at the inguinal ligament Explanation L3 nerve root The history suggests a prolapsed intervertebral disc. The quadriceps are supplied by the femoral nerve whose root value is L2–L4. The skin over the patella is usually part of the L3 dermatome, and the root value of the knee jerk is L3/L4. Sciatic nerve compression The sciatic nerve innervates the muscles of the posterior compartment of the thigh and the muscles of the leg. It provides sensory innervation for the posterior thigh, the leg and the foot. Ilioinguinal nerve The ilioinguinal nerve supplies a small area of skin on the medial aspect of the upper thigh as well as the scrotum and penis. L5 nerve root Compression of the L5/S1 nerve root produces symptoms of sciatica which would not result in a reduced knee jerk reflex. Compression of the femoral nerve at the inguinal ligament Femoral nerve compression at the level of the inguinal ligament is unlikely, given the history of injury and back pain. 339 Rate this question: 1 A patient complains of sensory deficit halfway down the anterior surface of the thigh. The patient is very disconcerted by their presentation. Which one of the following would cause this sensory deficit? 1. Damage to the sciatic nerve 2. Compression of the ventral roots of L5 to S2 3. Damage to a nerve accompanying the artery in the adductor canal 4. Could be the result of nerve damage during surgical procedures in the femoral sheath 5. Damage to the nerve that innervates the pectineus muscle Explanation Damage to the nerve that innervates the pectineus muscle The anterior surface of the thigh receives its sensory innervation from the femoral nerve so this is the nerve most likely to be injured. The pectineus is supplied by the second, third and fourth lumbar nerves through the femoral nerve. Occasionally, it receives a branch from the obturator nerve. Damage to the sciatic nerve This would result in sciatica in which pain is experienced in the lower back with extension of the pain down the posterior thigh. Compression of the ventral roots of L5 to S2 Compression of the L5–S2 nerve root would result in posterior sciatica symptoms. Damage to a nerve accompanying the artery in the adductor canal The saphenous nerve (a branch of the femoral nerve) can be found in the adductor canal. It has no motor function but provides sensory supply to the medial aspect of the lower half of the leg. Could be the result of nerve damage during surgical procedures in the femoral sheath The femoral branch of the genitofemoral nerve can be damaged within the femoral sheath. This supplies skin around the femoral triangle area. 367 Rate this question: 1 2 3 A young man sustains a skull-base fracture at the middle cranial fossa that injures his right abducens (VI) nerve. Which signs are most likely to be present on clinical examination? 1. There is ptosis on the right side 2. The pupil on the right side is constricted and fails to respond to light 3. The right eyelid is numb 4. The patient is unable to deviate his right eye medially 5. The patient is unable to deviate his right eye laterally Explanation The patient is unable to deviate his right eye laterally The abducens nerve innervates the lateral rectus muscle of the eye exclusively; the sole effect of damage to this nerve is that the patient is unable to abduct (laterally deviate) the eye. There is ptosis on the right side Ptosis would be as a result of damage to the oculomotor nerve. The pupil on the right side is constricted and fails to respond to light The pupillary light reflex is detected by the optic nerve and pupillary constriction is initiated by the oculomotor nerve. The right eyelid is numb The trigeminal nerve is responsible suppling facial sensation including to the right eyelid. The patient is unable to deviate his right eye medially The oculomotor nerve via the medial rectus muscle is responsible for adduction of the eye. 371 Rate this question: 1 2 In performing a lumbar puncture, the operator needs to be familiar with the anatomy involved. There are important structures in the area that can be inadvertently damaged. Which anatomical feature is relevant to this procedure? 1. In the newborn baby, the spinal cord occupies the full length of the dural sac 2. The dural sac in the adult terminates at the lower end of the sacral canal 3. The spinal cord in the normal adult terminates anywhere from opposite the body of T12 to the body of L3; however, the commonest level is at the disc space between L1 and L2 4. The spinal cord in the average male is 12 inches (30 cm) in length 5. The extradural space comprises a thin layer of avascular connective tissue Explanation The spinal cord in the normal adult terminates anywhere from opposite the body of T12 to the body of L3; however, the commonest level is at the disc space between L1 and L2 During a lumbar puncture, a needle most commonly passes through the L3/4 intervertebral space (usually found at the height of the iliac crest) to avoid the spinal cord. In the newborn baby, the spinal cord occupies the full length of the dural sac In the newborn, it terminates at L3. The dural sac in the adult terminates at the lower end of the sacral canal The dural sac in the adult extends to the level of the second sacral segment. The spinal cord in the average male is 12 inches (30 cm) in length The spinal cord in both adult men and women is 18 inches (45 cm) in length. The extradural space comprises a thin layer of avascular connective tissue The spinal extradural space contains loose fat (which allows the ready diffusion of local anaesthetic in an extradural block), together with the extensive vertebral venous plexus of veins. 372 Rate this question: 1 2 3 4 5 A cerebral angiogram is performed on a 37-year-old woman, following a suspected aneurysmal bleed. She presented with reduced GCS and headache without a history of trauma.