The yellow line below corresponds to the alignment of the short pastern bone and the coffin bone. In Figure 3, the alignment is normal. However in Figure 4 the dorsal surface of the coffin bone is not aligned with the short pastern bone. The letter "A" in figure 4 corresponds to the angle of contracture. The contracture occurs in part due to the strong pull of the deep digital flexor tendon that attaches to the bottom of the coffin bone. As the leg bones lengthen and the flexor tendons do not keep up with the growth rate, the coffin bone is pulled resulting in contracture of the joint.