Abstract
The biology and mechanobiology of joint cavitation have undergone extensive investigation, but we have almost no understanding of the development of joint shape. Joint morphogenesis, the development of shape, has been identified as the ‘least understood aspect of joint formation’ (2005, Birth Defects Res C Embryo Today 75, 237), despite the clinical relevance of shape morphogenesis to postnatal skeletal malformations such as developmental dysplasia of the hip. In this study, we characterise development of early hip joint shape in the embryonic chick using direct capture 3D imaging. Contrary to formerly held assumptions that cavitation precedes morphogenesis in joint development, we have found that the major anatomical features of the adult hip are present at Hamburger Hamilton (HH)32, a full day prior to cavitation of the joint at HH34. We also reveal that the pelvis undergoes significant changes in orientation with respect to the femur, despite the lack of a joint cavity between the rudiments. Furthermore, we have identified the appearance of the ischium and pubis several developmental stages earlier than was previously reported, illustrating the value and importance of direct capture 3D imaging.
Highlights
The biology and mechanobiology of joint cavitation have undergone extensive investigation, but we have very little understanding of joint shape morphogenesis, which has been identified as the ‘least understood aspect of joint formation’ (Pacifici et al 2005)
At the earliest stage examined, HH26, the surface of the proximal femur is indistinguishable from the pelvis
By HH31, the three elements of the pelvis have taken on their characteristic morphologies
Summary
The biology and mechanobiology of joint cavitation have undergone extensive investigation, but we have very little understanding of joint shape morphogenesis, which has been identified as the ‘least understood aspect of joint formation’ (Pacifici et al 2005). The first step of joint formation occurs in the cartilage anlage, where chondrocytes at the presumptive joint site stop proliferating and become compacted to form what is called the interzone. The articular cartilage surfaces and the synovial cavity develop (Pacifici et al 2005). It has been reported that once the cavity has been initiated, the surfaces of the opposing cartilage rudiments undergo gradual shape morphogenesis so that eventually the ends of the two bones form a functioning, friction-minimising contact surface, i.e. a synovial joint (Pacifici et al 2005). No concrete mechanisms directing the development of joint shape have been discovered, despite the clinical significance of this process.
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