1. Direct: The most common type of insertion. The superficial fibers of the ligament join the fibrous layer of the periosteum, inserting at a 90 degree angle to the surface of the bone. The deep collagen fibers form the bulk of the insertion and transition through four zones as the ligament passes into the bone and blends in with its collagen fibers. The four zones of this transition are: tendon, unmineralized fibrocartilage, mineralized fibrocartilage, and bone. Sharpey's fibers are calcified collagenous anchors within bone that firmly attach the ligament to bone.
2. Indirect (aka oblique insertions): These insertions also have superficial and deep components. The majority of the insertion is composed of superficial fibers that blend in with the fibrous portion of the periosteum. The deep fibers approach cortical bone at an oblique angle and do not undergo well-defined zones of fibrocartilage.
