Conditions of the Lower Leg Quiz

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Which clinical finding is most characteristic of a proximal tibial nerve injury?

A Loss of knee extension due to quadriceps paralysis
B Loss of sensation over the anterior thigh
C Inability to stand on tiptoe due to calf muscle paralysis ✓
D Foot drop with loss of dorsiflexion
E Inability to evert the foot due to fibularis muscle paralysis

The answer is C: Inability to stand on tiptoe due to calf muscle paralysis

Explanation

Why C is correct

See Common Peroneal/Fibular Nerve Injury. Option C is correct because the tibial nerve supplies the posterior compartment of the leg, which holds the main plantarflexors, so a proximal injury causes inability to stand on tiptoe. The tibial nerve is a branch of the sciatic nerve that runs down the back of the leg. It innervates gastrocnemius and soleus (the two big calf muscles that point the foot downwards, which is plantarflexion), tibialis posterior (which inverts the foot), and the long flexors of the toes, and it carries sensation from the sole of the foot. Standing on tiptoe depends on plantarflexion, so this is the classic bedside test. A proximal lesion, for example at the popliteal fossa (the hollow behind the knee), causes weakness of all of these muscles and altered sensation in the sole. The foot also tends to rest in a dorsiflexed, everted position because the muscles on the front and outer side of the leg, supplied by the common fibular nerve, pull unopposed. A memory aid: Tibial = Tiptoes, and fibular = foot-drop.

Supply: the tibial nerve supplies the posterior compartment of the leg.
Muscles: gastrocnemius and soleus are the main plantarflexors.
Sensation: the tibial nerve supplies the skin of the sole.
Bedside test: a proximal injury means the patient cannot stand on tiptoe.

Why the other options are incorrect

A. Loss of knee extension due to quadriceps paralysis: Loss of knee extension from quadriceps paralysis is a femoral nerve problem, because the femoral nerve supplies the quadriceps at the front of the thigh. It would be the answer for a femoral nerve lesion.
B. Loss of sensation over the anterior thigh: Loss of sensation over the anterior thigh is a femoral nerve feature, because the femoral nerve supplies the skin of the front of the thigh. The tibial nerve supplies the sole and the calf region instead. It would be the answer for a femoral nerve injury.
D. Foot drop with loss of dorsiflexion: Foot drop with loss of dorsiflexion comes from a common fibular nerve lesion, because that nerve supplies the muscles that lift the foot. A tibial lesion does the opposite, weakening the muscles that point the foot down. It would be the answer for a fibular nerve injury at the fibular neck.
E. Inability to evert the foot due to fibularis muscle paralysis: Inability to evert the foot from paralysis of the fibularis muscles is a feature of a superficial fibular nerve lesion. The tibial nerve supplies the posterior compartment, not the lateral compartment. It would be the answer for loss of eversion.

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1
What is the definitive treatment for newly diagnosed acute compartment syndrome in a viable limb?
2
A 24-year-old rugby player sustains a blow to the lateral aspect of his knee. He has difficulty dorsiflexing the ankle, causing foot drop, and altered sensation over the anterolateral leg and dorsum of the foot. Which nerve is most likely to be injured?

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