Anatomy and Neuroscience - Theses
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ItemThe Clinical Anatomy of the Hallucal Sesamoids and their Attachments( 2021)The hallucal sesamoid bones are essential, but poorly understood, features of the first, or great, toe complex. With the associated structures of the foot, collectively termed the first ray, this complex is essential for optimal foot function. Disorders of this region present symptomatically in a broad range from intermittent discomfort through to a complete inability to walk or weight-bear. Pain in this region may also be enough to interrupt sleep and a range of daily tasks. Given the perceived importance of the hallucal sesamoids to this complex, it is perhaps surprising to discover the anatomy of the hallucal sesamoids, and particularly their interaction with neighbouring tissues, is poorly understood. One major consequence of this is the lack of a clear, consistent anatomical foundation for the diagnosis, treatment (including surgically) and management of these disorders. This thesis will document a series of studies which aim to collectively enhance the anatomical understanding of the hallucal sesamoids and their relations. After exploring the historical context of the hallucal sesamoids, reviewing the current anatomical and clinical literature, and establishing some key concepts about the presence, absence and variability of these bones, a series of detailed studies will be presented. Using a multi-modal approach that includes dissection, 3D modelling, medical imaging and sectional anatomy (macro and micro), the key tissues thought to interact with the hallucal sesamoids will be investigated: the adductor and abductor hallucis muscles, the plantar aponeurosis, the flexor hallucis brevis muscle and a range of highly specialised ligaments. The ligaments include the deep transverse metatarsal and sesamophalangeal, , amongst others, along with interactions with other tissues such as tendon tunnels, plantar plates and joint capsules. Of particular importance when considering the function of these structures is their attachment to skeletal tissues, such as the hallucal sesamoids. There is contention over what tissues are attached to each of the two hallucal sesamoids. These studies provide a detailed, quantified and uniquely visualised account of the attachments to each bone, and to neighbouring structures. This comprehensive account provides a strong basis for the development of more anatomically informed diagnostic approaches and clinical management of disorders of this area. The key findings presented in this thesis include definitive three dimensional mapping of the detailed attachments to each hallucal sesamoid. These dispel common misconceptions that the sesamoids are engulfed by a single tissue, or that they do not have substantial connections to a range of structures. These data strongly demonstrate these sesamoids have multidirectional interactions which maintain their dynamic position through the gait cycle, but are also particularly vulnerable to injury, including iatrogenic injury. In fact, poor post-operative outcomes from surgical treatments in this area may be attributable to a lack of anatomical understanding. Studies demonstrate the intimate relationships between structures often targeted for surgical release and those which must be maintained. These relations, and particularly the innovative three-dimensional visualisations developed from these data, may inform significant advances in first ray health care.