Painful nerve compression beyond the carpal tunnel: recognizing the lacertus syndrome

The most common nerve compression in the upper extremity is that of carpal tunnel syndrome. Although generally recognized and treated, as much as a 20% failure rate is reported. Recent publications are indicating that one of the sources of persistent median nerve symptoms may be missed proximal median nerve entrapments, of which the lacertus fibrosus represents a principal cause of compression, and rarely other sites such as the flexor superficialis arch or pronator teres. Compression by the lacertus fibrosus is called lacertus syndrome, and as this is a clinically diagnosed entity, only rarely confirmed using electrodiagnostic or imaging studies, it is frequently overlooked. Clinicians regularly treating patients with carpal tunnel syndrome or patients with signs of median nerve neuropathy should be aware of the lacertus fibrosus as a possible compression site. In this review, we will define lacertus syndrome, describe its clinical manifestations and diagnosis, and demonstrate surgical techniques used to treat it.