[Prenatal development of the radial annular ligament]

The prenatal development of the annular ligament of the elbow was studied by investigating 600 microns thick plastinated sections through the elbow joints of nine fetuses with a crown-rump-length (CRL) of 105-360 mm. At 105 mm CRL the annular ligament consists of one layer of circular fibres around the circumference of the radial head. At 130 mm CRL it extends further distally to the radial neck. The postero-lateral region exhibits an arrangement of three layers of fibres of different course. Stages later than the 190 mm stage show in the anterior region external fibres arising from the medial periosteum of the ulna. They pass over the anterior surface of the ulna and blend with fibres arising from the anterior margin of the ulna's radial notch to surround the radial head. At 270 mm the articular capsule can be recognized as a strong homogenous layer of fibres. With all stages investigated the annular ligament consists of circular fibres only near the attachment at the posterior margin of the ulna's radial notch. Anteriorly the annular ligament is narrower than posteriorly. With the later stages of 290, 330 and 360 mm CRL a further differentiation of the annular ligament cannot be recognized. Thus, between 105 mm and 270 mm CRL, the annular ligament develops a more and more complex structure similar to that described for the adult joint. We describe several distinct steps of this differentiation during the fetal period which are not mentioned in the literature yet.