Nerves of the lower limb Flashcards
What are the dermatomes of the lower limb?
L1: inguinal region
L2: upper lateral thigh
L3: lower lateral thigh
L4: medial leg + medial great toe
L5: anterolateral leg + foot, dorsal toes 2-4
S1: lateral margin of the sole of the foot + heel
S2: leg + posterior thigh
S3-4: medial buttock, inter gluteal cleft + perineum
How is the deep tendon reflex of the patellar tendon tested and what is the nerve root?
Patient to sit on edge of couch.
Strike the patellar tendon (ligament) with a knee hammer.
Expect brisk extension of the knee joint
Simultaneous contraction of the quadriceps should be palpated on the anterior surface of the thigh.
Repeat on the opposite side + compare responses.
Main nerve root is L4.
How is the deep tendon reflex of the ankle jerk tested and what is the nerve root?
Patient to sit on edge of couch.
Strike the calcaneal tendon (Achilles) with a knee hammer while holding the foot (slightly dorsiflexed) with the other hand.
Expect: plantar flexion of the ankle joint
Repeat test on opposite side + compare responses.
Main nerve root is S1.
What are the surface markings of the sciatic nerve?
Palpate posterior superior iliac spine (PSIS), ischial tuberosity + greater trochanter.
Nerve leave greater sciatic notch + enters gluteal region at midpoint between PSIS + ischial tuberosity
Forms a downwards curve to pass into the thigh + around the midpoint between greater trochanter + ischial tuberosity reaches popliteal fossa behind knee
How would you test the motor component of the sciatic nerve?
Supplies posterior compartment of thigh: hamstring muscles (semitendinosus, semimembranosus, biceps femoris) + part of adductor magnus.
Patient to lie prone with the legs flexed ~30 degrees.
Ask the patient to flex the knee further .
Apply firm pressure over the distal part of the leg to resist further flexion. With the other hand, palpate the back of the mid thigh for the contraction of the hamstrings.
How would you test the motor component of the gluteal nerve?
Innervates gluteus maximus: extension of hip joint
Patient to lie prone with knees flexed to 90 degrees (to relax hamstrings)
Patient to lift (extend) their thigh off the couch.
Apply pressure at the distal end of the posterior thigh to resist the extension. With the other hand, palpate the buttock for the contraction of the muscle.
Also innervates the gluteus medius + minimus: hip abduction.
Patient to lie on 1 side with both limbs fully extended.
Patient to lift uppermost limb upward away from the couch.
Apply downward pressure to resist the abduction of the thigh. With the other hand, palpate the gluteus medius for contraction.
How would you test the motor component of the femoral nerve?
Innervates quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius): extension of the knee joint.
Patient to sit with knees over edge of couch
Patient to extend their knee .
Apply firm pressure over the distal part of the leg to resist extension.
With the other hand, palpate the front of the mid-thigh for the contraction of the quadriceps.
How would you test the motor component of the obturator nerve?
Innervates adductor group of muscles (longus, magnus, brevis) + obturator externus: adduction of the hip joint.
Patient to lie supine with both limbs fully extended.
Test leg passively abducted to 45 degrees.
Ask patient to adduct forcefully.
Apply force to resist the adduction of the thigh.
With the other hand, palpate the medial aspect of the thigh for contraction of the adductors.
How would you test the motor component of the deep peroneal nerve?
Innervates tibialis anterior, extensor hallucis longus + extensor digitorum longus: dorsiflexion (extension) of the foot.
Patient to lie on couch with lower limb fully extended.
Patient to dorsiflex their foot.
Place the palmar surface of your hand across the dorsum of toes to resist the action.
The tendons of the muscles can be seen and felt.
How would you test the motor component of the superficial peroneal nerve?
Innervates peroneus longus + brevis muscles: foot eversion.
Ask patient to turn foot outward + plantar flex (eversion) while grasping the forefoot to oppose the movement.
Why is the sciatic nerve easily damaged and what does this cause?
The peroneal branch wraps around the back of the knee, leaving it vulnerable to injury
Causes foot drop
