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 underdiagnosed due to the lack of reliable diagnosis using clinical examination and electrophysiologic evaluation. Most fibular nerve compressions may be classified into 2 broad categories: (a) mechanical causes, which occur at fibrous or fibro-osseous tunnels, and (b) dynamic causes related to nerve injury during specific limb positioning. Foot drop resulting from weakness of the dorsiflexor muscles of the foot is a relatively uncommon presentation and closely related to L5 neuropathy caused by a disc herniation. However, we herein describe a rare case of usually painless foot drop triggered by a cyst at the proximal tibiofibular joint compressing the deep fibular nerve. The presence of multilevel disc diseases made the diagnosis more difficult. Foot drop is highly troubling, and health care providers need to broaden their search for the imperative and overlapping causes especially in patients with painless drop foot, and the treatment is variable and should be directed at the specific cause. The magnetic resonance imaging (MRI), including high-resolution and 3D MR neurography, allows detailed assessment of the course and anatomy of peripheral nerves, as well as accurate delineation of surrounding soft-tissue and osseous structures that may contribute to nerve entrapment. Knowledge of normal MRI anatomy of the nerves in the knee and leg is essential for the precise assessment of the presence of peripheral entrapment conditions that may produce painless or painful drop foot. In conclusion, we stress the importance of preoperative anatomic mapping of entrapment neuropathies to minimize neurological complications.Key words: Foot drop, fibular nerve, ganglion cyst, proximal tibiofibular jointFoot drop, fibular nerve, ganglion cyst, proximal tibiofibular joint.