Roentgenographic Demonstration of the True Articular Space

Abstract

IT is essential to realize that the articular space, as commonly referred to by most roentgenologists, is a misnomer, inasmuch as this designated space roentgenologically represents that portion of the joint which is relatively radiolucent, and corresponds to the distance between the osseous ends of the apposing surfaces. This comprises, in the diarthroses or freely movable articulations, the contiguous osseous surfaces covered by articular cartilage, and connected by ligaments lined with synovial membrane. This joint may be divided by an articular disc or meniscus, the periphery of which is continuous with the fibrous capsule, and its free surfaces likewise covered by synovial membrane. This potential space, intervening and enclosed by synovial membrane, is the true articular space; and changes in width, according to varying stress and strain. There is normally a slight amount of synovial fluid contained in this space, the presence of which probably tends to make the roentgenographic visualization of this space difficult. Prior to the work of Dittmar (1), it had been erroneously considered that this true articular space was never roentgenologically demonstrable under normal conditions. Dittmar demonstrated this space without artificial filling, in the knee joints of children, and stated that this was occasionally noted in normal knee joints in children but never in adults, unless there was concomitant pathologic involvement. It is this latter statement which we wish to correct or modify, for we have been fortunate in demonstrating the true articular space in children, adolescents, and adults, in cases in which no history of trauma or disease was elicited. It is our conviction that, under optimum and coincidental conditions, this space is visible under normal conditions, with improved technic and if attention is focussed upon this phenomenon. To attest for the latter statement, since recognizing the first reported case of articular visualization, we were surprised at the number of cases presenting this appearance when particular stress was apportioned to this region, and search made for the entity. In the main, we were unable to duplicate the excellent results in the visualization of the semilunar cartilage of the knee, as outlined by Dittmar, who recommends special technic. This consists of obtaining the ordinary anteroposterior projection of both knee joint regions and, additionally, with the knees in position of passively induced valgus. This method is of especial importance in examination of children's knees, inasmuch as a fair percentage present normally visualized articular spaces in the medial aspect of the articulations. Thus by comparing the two knee joints, one can determine the variance in size of the medially situated triangular shadow projecting into the space medio-laterally. This shadow is the medial semilunar cartilage cross-section viewed in situ, and any definable alteration of its normal shape can readily be noted.