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Title: The development and anatomy of the sacrum in relation to the ilium and the sacroiliac joint
Author: Yusof, Nurul Asyiqin
Awarding Body: University of Dundee
Current Institution: University of Dundee
Date of Award: 2013
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The juvenile sacrum is a unique bone which starts as approximately 21 separate osseous components at birth. It eventually fuses throughout development into a single mature sacrum at adulthood. Despite the unfused nature of these ossified structures in early life, its location between the axial and lower appendicular skeleton and function in transmitting stresses are undeniably crucial. During gross physical developmental milestones, a child experiences locomotive and postural changes from sitting, to crawling, and then standing and walking especially during the first 8 years of life. Additionally, the pelvis undergoes functional changes where pelvic viscera descend into the pelvic cavity, together with fusion of the ischiopubic ramus before the age of 6 - 8 years, stabilizes the maturing pelvic complex. During this critical period, the body weight is reported to be transferred through the weight-bearing bones and joints related to body posture via the sacrum, through the sacroiliac joint and the innominate. Recent investigations of trabecular bone architecture that reflect the routes of weight transmission were based on Wolff's law and bone functional adaptation theory. This is defined as the bone morphological response to mechanical strains and loading that is influenced by the genetic, nutritional status and general mechanical environment, where this response is reported to be higher during the juvenile period. The advancement of non-invasive, non-destructive imaging techniques has led to extensive research on this subject. However, studies on juvenile skeletal remains are insufficient, especially pertaining to trabecular pattern analysis, and can most probably be attributed to the limited availability of juvenile specimens compared to the adult. Additionally, the constant change in growth of the juvenile age group make it more difficult to study compared to the adult group. This research was divided into three different studies; the first and second studies were conducted on the juvenile sacrum, and the third on the juvenile ilium. The first was a preliminary study using qualitative radiographic analysis of the juvenile sacral microarchitecture, followed by the second study, a detailed trabecular microarchitecture quantification based on the reconstructed micro-CT images of S1 vertebra. The third study was conducted using a different approach, where a photographic image of the pelvic surface of the juvenile ilium was evaluated. Although not directly similar in terms of the methodological approach on both sacrum and ilium due to time constraints and uneven growth of the juvenile ilium, these studies were compared as the two bones meet at the sacroiliac joint. In contrast to the juvenile ilium that showed most of the characteristic features of the adult bone at birth, the study of the juvenile sacrum pose considerable difficulties as it appears as multiple separated bones at birth with different times of fusion, thus providing until now, no available literature on the trabecular pattern of the juvenile human sacrum has been conducted. Thus the current research aims to fill this gap and to highlight the possible route of weight transmission of the juvenile sacrum during the critical developmental years of a child, especially in the first 8 years of life. The result of the qualitative radiographic analysis of the juvenile sacrum revealed consistent and well-defined high intensity patterns of cortical and trabecular bone organisation in the sacrum from birth until late adolescence concentrating at the uppermost and centremost region of the sacrum. These high intensity areas reduce in the more distal sacral vertebra. The auricular area in contrast, largely exhibits low intensity areas suggesting minimal weight passes through this region. Subsequently, the quantification results of the reconstructed micro-CT sacral images revealed high bone volume, thick trabecular bones at the central part of the juvenile S1 vertebra. This region exhibits the most robust and remodeled area, especially at the anteromedial sacral ala, persistently throughout the first 8 years of life, with increasing absolute values for all bone parameters. In contrast, the auricular area representing the sacral part of the sacroiliac joint exhibit a sparse, low bone volume area with very little remodeling activity reflected in this region. The quantification study on the pelvic surface of the juvenile ilium revealed that postauricular growth is always in advance of the auricular surface throughout development. Thus, from the three studies it can be inferred that the body weight that passes from L5 vertebra to S1 is most likely being transferred via the soft tissue structures that are in a close vicinity to the sacroiliac joint. These soft tissue structures are mainly formed by the strong and abundant posterior sacroiliac and interosseous ligaments that bind the post-auricular surfaces of the sacrum with the ilium. In the erect posture, the sacrum is suspended by these posterior ligaments and supported by the anterior sacroiliac ligaments creating constant tensile forces on these soft tissues. The body weight that passed via the S1 vertebra is postulated to be transmitted to the ilium via these ligaments by virtue of these tensile forces. The vertically-oriented sacroiliac joint that previously was suggested to play an important role in transmitting the body weight is not supported in these studies.
Supervisor: Black, Sue Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available