Osborne's ligament: Anatomical study with application to better understanding ulnar nerve compression at the elbow.

Objective Almost 70 years ago, Osborne described a fibrous band, Osborne’s ligament, stretching between the humeral and ulnar heads of the flexor carpi ulnaris, which forms the cubital tunnel’s roof. Prior to this account, this ligament had received limited attention in the anatomical literature and had been poorly studied. Therefore, the present anatomical study was performed to better elucidate this structure. Methods thirty adult anatomical donors (60 sides) underwent dissection of the medial aspect of the elbow with a focus on Osborne’s ligament. Identified ligaments were documented, classified, and measured. Additionally, histological evaluation of these structures was performed. Results osborne’s ligaments were identified on 49 sides (81.7%). These were classified as absent (type I; 18.3%), wide and thin and more distally located (type II; 51%), narrow and more proximally located (type III: 39%), coexistent with an anconeus epitrochlearis muscle (type IV; 6%), and absent with only anconeus epitrochlearis muscle (type V; 4.1%). When coexistent with anconeus epitrochlearis muscle (6%), the anconeus epitrochlearis muscle was usually located more proximally, although in some cases, it was in the same plane, especially with larger anconeus epitrochlearis muscles. Conclusions based on our findings, the Osborne’s ligament is not a ligament but is usually made up of aponeurosis/tendon over the proximal flexor carpi ulnaris muscle and can coexist with the anconeus epitrochlearis muscle. This structure comes in various forms, illustrating that this term is not specific to a single structure.Clinical trial number: Not applicable.