Variation of the proximal insertion of the abductor digiti minimi muscle: correlation with Guyon's canal syndrome? Case report and literature review.

We describe the case of an original insertion and course of the abductor digiti minimi muscle on the medial part of the palmaris longus tendon. The anomalous muscle was only present on the left side. Various studies have reported the frequency of anomalous muscles in approximately 22 to 35% of hands and it was in majority an anomalous abductor digiti minimi muscle. The knowledge of this original insertion is important because it can sometimes be correlated with ulnar nerve compression at Guyon's canal. But Guyon's canal syndrome is less common than carpal tunnel syndrome, and the incidence of ulnar nerve compression in relation with anomalous muscle is approximately 2.9% of cases. It is possible to diagnose the anomalous muscle through ultrasound or MRI. This variation should be taken into consideration by surgeons during surgical procedures for ulnar nerve decompression at Guyon's canal and when performing anteromedial approach to the wrist between flexors tendons and ulnar bundle.