Ganglion Cyst at the Proximal Tibiofibular Joint in a Patient with Painless Foot Drop

Entrapment neuropathies of the fibular nerve and its branches are often underdiagnoseddue to the lack of reliable diagnosis using clinical examination and electrophysiologicevaluation. Most fibular nerve compressions may be classified into 2 broad categories:(a) mechanical causes, which occur at fibrous or fibro-osseous tunnels, and (b) dynamiccauses related to nerve injury during specific limb positioning. Foot drop resulting fromweakness of the dorsiflexor muscles of the foot is a relatively uncommon presentationand closely related to L5 neuropathy caused by a disc herniation. However, we hereindescribe a rare case of usually painless foot drop triggered by a cyst at the proximaltibiofibular joint compressing the deep fibular nerve. The presence of multilevel discdiseases made the diagnosis more difficult. Foot drop is highly troubling, and healthcare providers need to broaden their search for the imperative and overlapping causesespecially in patients with painless drop foot, and the treatment is variable and shouldbe directed at the specific cause. The magnetic resonance imaging (MRI), includinghigh-resolution and 3D MR neurography, allows detailed assessment of the course andanatomy of peripheral nerves, as well as accurate delineation of surrounding soft-tissueand osseous structures that may contribute to nerve entrapment. Knowledge of normalMRI anatomy of the nerves in the knee and leg is essential for the precise assessment ofthe presence of peripheral entrapment conditions that may produce painless or painfuldrop foot. In conclusion, we stress the importance of preoperative anatomic mapping ofentrapment neuropathies to minimize neurological complications.Key words: Foot drop, fibular nerve, ganglion cyst, proximal tibiofibular joint