Use of high-resolution ultrasound in evaluation of the forefoot to differentiate forefoot nerve entrapments.

Forefoot pain can have single or multiple etiologies, and frequently pain is attributed solely to a forefoot nerve entrapment. It is well known that forefoot nerve entrapments, such as Morton's, can be falsely assumed to be the cause of forefoot pain when in fact other factors, such as plantar plate disturbances, are the true cause. Frequently, the cause of the patient's forefoot pain starts as a forefoot nerve entrapment, but then, as a result of treatment with a corticosteroid injection, other pathologies manifest, such as plantar plate rupture. The development of high-resolution, high-frequency ultrasound scanners has opened the door to in-depth examination of peripheral nerves as well as small pericapsular and intracapsular joint structures of the foot and ankle. In the hands of an experienced clinician, ultrasound can play an important role in differentiating nerve lesions and entrapment syndromes from nonneurogenic pain generators, such as tendons, ligaments, fasciae, and joint capsules. The focus of this article is the forefoot, where differentiation of neuroma, neuritis, and capsulitis can be difficult.