HISTOCHEMICAL STUDIES OF THE DEVELOPMENT OF THE HUMAN HIP JOINT

Abstract

Hip joints from 30 human fetuses removed by Caesarean section were examined. These fetuses ranged in crown-rump length from 20 to 121 mm, corresponding to a menstrual age of from 7 1/2-16 weeks. The following histochemical staining methods were used: (1) Meta-chromatic staining with azure A. (2) Staining with Alcian blue-PAS. (3) Staining with periodic acid-Schiff (PAS). (4) In addition, the author tried a new combination of stains, Alcian blue-van Gieson in order to visualize amorphous ground substance and collagenous fibers in the same section. Prior to the formation of the joint cavity, fairly large amounts of acid mucopolysaccharides, especially chondroitin sulphate A and C, accumulate in the 3 layered interzone or blastemal disc which is present at the site of the joint and which consists of 2 chondrogenous layers and an intermediate layer. The function of these substances is discussed, in particular their possible relation to the early fetal movements in the extremities. The formation of the joint cavity, which occurs between 34 and 42 mm c. r. length takes place as follows: The intermediate layer of the interzone is incorporated from both sides into the 2 chondrogenous layers which in turn become incorporated into the respective cartilages. The joint cavity has now been formed, and the cartilages adjoin by relatively smooth surfaces. The cavity formation takes place in an annular rim, limited on 1 side by the head of the femur and on the other side by the glenoid labrum and the future facies lunata. In the middle of the articular anlage, the joint cavity is interrupted by the ligamentum teres and its wide communication with the tissue in the acetabular fossa. At the outset the cavity reaches peripherally only to the tip of the labrum and centrally not to the position between the head and the ligamentum teres or between the latter and the tissue in the acetabular fossa. In later stages it spreads peripherally beyond the neck of the femur and centrally to surround the ligamentum teres. The cavity formation is not preceded by any sign of cellular degeneration. The ligamentum teres is laid down in the blastemal disc in which it is distinct at 25 mm. It contains large quantities of acid mucopolysaccharides, and between 31 and 34 mm collagenous fibers. The ligament does not become vascularized until a crown-rump length of 61 mm. At 25 mm the glenoid labrum is apparent as the peripheral part of the skeletal blastemal tissue of the acetabulum, containing even at this early stage large amounts of acid mucopolysaccharides and at 31-34 mm collagenous fibers in the peripheral areas. The labrum also becomes vascularized at approximately the 61 mm stage. The joint capsule appears to be formed as a condensation peripherally in the interzone, in direct continuation of the perichondria of the adjacent cartilages. Simultaneously with its vascularization (around the 25 mm stage), the tissue of the acetabular fossa undergoes pronounced changes in the course of its transformation into synovial tissue. According to the present findings, the vascularization which appears in the cartilaginous eplphyses appears to be in the form of active ingrowth caused by chondrolysis. At no stage can the acetabulum be said to be flat. From the earliest stages it extends, together with the labrum, beyond the equator of the head of the femur.