The Development of the Interosseous Membrane of the Forearm

Abstract

Aim: The purpose of this research is to study the forearm interosseous membrane (IOM) in embryos and fetal specimens, in order to determine its tissular origin, stage of appearance, and whether there is an early prenatal existence of the fibers and bundles present in adults, such as the central band, the accessory ascendant bundle, and the distal oblique bundle. Materials and Methods: A population of 10 embryos from 7 to 12 weeks (group 1) and 22 fetuses from 12 to 22 weeks (group 2) was studied. Specimens in group 1 were studied by axial sections and histological staining techniques: hematoxylin-eosin, Mallory trichrome stain, and silver stain. The week of appearance of the IOM, as well as the tissue that gave rise to it, was recorded. Specimens in group 2 were studied by anatomical dissections under 6× to 12× magnification and the IOMs were observed by direct and backlighting. The presence of the central band and the oblique ascendant bundle was studied at the proximal membrane. At the distal IOM (distal to the upper limit of the pronator quadratus), the presence of the distal oblique bundle was investigated. Results: We noticed that the IOM developed from the mesenchymal tissue located between the radius and ulna featuring a bridge between both bones at the chondrification stage. This mesenchyma was observed as an extension of the perichondrium of both bones. The mesenchymal bridge withdraws in order to conform to the IOM. We dated this process between the seventh and eighth week (50-56 days). In group 2, we observed the central band fibers. More proximal fibers were noticed earlier, while the distal most were observed in the last weeks. As far as the ascendant oblique bundle, it was seen in the entire group at the posterior surface of the IOM featuring an arrangement similar to the adult. At the distal IOM (distal to the upper pronator quadratus border), we were not able to identify a distal oblique bundle, as in the adult. The distal IOM was thin and displayed just a developing tissue without a distinct organization. Conclusion: The IOM arises from the mesenchymal tissue located between the ulnar and radial perichondrium. This tissue withdraws between the seventh and eighth week, forming the IOM. The gross anatomical features of the proximal fetal IOM are almost the same as in the adult. The central band fibers and the oblique ascendant band were observed. However, the fetal distal IOM did not showed a distal oblique bundle, well developed in most adults. These results might mean that the distal IOM arrangement in the adult is a consequence of the stress-strain forces to which it is subjected during the forearm and wrist movements, while the proximal membrane would follow a preestablished pattern.