Review Question - QID 101672

The clinical and radiographic presentation are consistent for proximal tibiofibular joint cyst with compression of the common peroneal nerve. Numbness on the lateral calf, dorsal foot, and weakness to ankle dorsi-flexion and foot eversion would be the expected physical exam finding.

The common peroneal (fibular) nerve arises from the sciatic nerve at the apex of the popliteal fossa where it passes laterally to the gastrocnemius muscle and then superficially around the head and neck of the fibula. As this nerve wraps around the neck of the fibula, it is very vulnerable to injury. Trauma to the lateral aspect of the leg in addition to fractures of the proximal fibula can injure the common peroneal nerve.

Figure A is an a T2 weighted MRI axial cut of a proximal tibiofibular joint showing a cyst.

Incorrect Answers:
Answer 1: An S1 radiculopathy or tibial nerve injury would lead to an inability to walk on his toes with the heel elevated on the right.
Answer 2: An S1 radiculopathy or tibial nerve injury would lead to a decreased Achilles reflex.
Answer 3: A positive Trendeleberg test is seen with superior gluteal nerve injury. The Trendeleberg test is said to be positive if, when a patient attempts to stand on one leg, the pelvis drops on the side opposite to the standing leg. The muscle weakness causing the pelvic drop is present on the side of the stance leg. These patients will also have a characteristic waddling gait commonly known as the "gluteus medius limp".
Answer 4: A decreased or absent patellar tendon reflex is also known as a Westphal sign. This reflex tests L2-L4 nerves and a decrease in this reflex arc could suggest receptor damage, peripheral nerve disease, or a complete interruption of the impulse transmission through the femoral nerve.