Morphological features of the posterior oblique ligament of the ulnar collateral ligament of the elbow joint.

The purpose of this basic research study was to clarify the morphological characteristics of the posterior oblique fibers (POL) of the ulnar collateral ligament using a large number of specimens. This study examined 50 arms from 25 Japanese cadavers. Type classification was performed by focusing on the positional relationship between POL morphology and the joint capsule. The morphological features measured were fiber bundle length, width, and thickness. The POL was classified as follows: Type I, the POL's anterior and posterior edges are located on the surface of the joint capsule and can be separated as a single fiber bundle; Type II-a, the POL anterior edge can be separated, but the posterior edge cannot be separated; Type II-b, the POL posterior edge can be separated, but the anterior edge cannot be separated; and Type III, the POL cannot be separated from the joint capsule. Type I was seen in 23 elbows (46%), Type II-a in 6 elbows (12%), Type II-b in 7 elbows (14%), and Type III in 14 elbows (28%). The results of this study suggested that the POL could be classified into an independent type and an unclear type, and the presence of the unclear type was one of the factors that caused morphological variation.