Veterinary Science Collected Works - Theses

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    Functional morphometric analysis of tarsal bones, ligaments including histological examination of fascia with respect to tarsal joint internal alignment and loading biomechanics
    Akbar, Zeeshan ( 2020)
    The tarsus or hock is a complex joint of the hind limb consisting of seven different bones and having various articulations. The tarsal bones are held together in intimate contact through the attachments of soft tissue such as ligaments, tendons and fascia. The tarsal joint is commonly involved in equine hind limb lameness and other pathological problems. Despite suggestions that tarsal conformation is a contributory factor to performance, lameness and orthopedic health, limited studies are available in the literature regarding tarsal bone morphometry, objective radiographic conformation or alignment changes in response to loading of the tarsus in horses, and the role of soft tissue in maintaining the joint stability and range of motion under loading is not known possibly due to insufficient measurable tarsal parameters. In addition to this, faulty conformation and uneven loading of the tarsal bones is believed to result in tarsal pathology, ligamentous ruptures and joint instability of the equine hind limb. The aims of this thesis were 1. To investigate the morphometric and radiographic anatomy of the equine tarsus and develop reliable measurable parameters that can be used to consistently and objectively measure tarsal conformation in horses. 2. To provide baseline data for the developed parameters from tarsal radiographs including the effects of rotations, and inter-rater repeatability. 3. To use developed parameters to assess the change of alignment of the tarsal joint under loading. 4. To investigate the potential role of the tarsal ligaments in the load redistribution within the tarsus, joint stability and range of motion of the tarsal joint. 5. To deduce the potential role of fascia in load redistribution through mechanical connectivity, internal composition (histological) and thickness variation proximal and distal to the tarsus. A pilot study on 10 cadaveric equine hind limbs from 7 adult horses, was used to specify the characteristics and identify reliable landmarks of the bones of the equine tarsal joint to be used for further investigation through radiology to assess the tarsal conformation. “Zero degree Lateromedial” (ZLM) and “Zero degree Dorsoplantar” (ZDP) views were established and 88 measurable parameters with validated anatomical landmarks were developed, including 39 parameters from the ZLM view and 49 parameters from the ZDP views, consisting of individual, as well as correlated angular and ratios parameters to avoid any effects of different tarsal size or magnification effects associated with the radiography technique. LM and DP views were used as the minimum required to gain a 3D appreciation of tarsal bone movements, while a complete investigation would require the inclusion of oblique views as well. Then subsequent studies established: i. baseline data of these parameters from tarsal radiographs. ii. effects of rotations, vertical and horizontal rotations of projection angles of the primary X-ray beam (radiography machine) on the developed tarsal measurements to established acceptable range of rotations. iii. assessment of the inter-rater reliability of the selected parameters. iv. changes in alignment of the tarsal bones under ex vivo loading. v.) Role of soft tissue like ligaments and fascia in loading and joint range of motion (during flexion, extension and incremental load. Increased load on the tarsal joint produced measurable radiographic changes in the alignment and direction of movement of the tarsal bones ex vivo. Six reliable parameters showed the potential to detect changes. Soft tissues such as ligaments were shown to play a significant role in maintaining joint stability and normal range of joint motion. Severing all major tarsal ligaments caused significant changes in tarsal flexion (P < 0.001). Cutting the plantar aspect of the long plantar ligament caused the largest significant change in tarsal extension. Both transverse and longitudinal arrangements of intertarsal ligaments within the tarsus and the arrangement of major tarsal ligaments external to the bones suggest a normal tightly packed alignment of the tarsus allows slight transverse movements of the tarsal bones during loading and prevents over extension and flexion of the tarsal joint, suggesting the existence of more complex mechanisms involving other soft tissue such as fascia that help in maintaining the loading stability and influence the joint range of motion. In consideration of this, this research was then directed towards the broader field of fascial anatomy. Fifteen hind limbs were obtained from adult horses of mixed breeds and an anatomical exploration of fascia by dissection was completed with the purpose being to lay the groundwork for understanding how tension is distributed from the crural region to the distal hindlimb. Characteristics such as relative fascial thickness, attachment points, connectivity and collagen fiber’s orientation, internal composition by histological examination were recorded and described to deduce their potential functional significance. In conclusion, the tarsal bone geomorphometric and loading data, along with information generated on the ligaments and fascia in this study, will allow reliable quantitative assessment of tarsal conformation and eliminate judgmental errors or variation between observers using subjective visual assessment for the tarsus. Locomotory control and the postural stability of the hind limb is largely dependent on the functional integration of different structures which is enabled via the fascial architecture providing mechanical connectivity. Overall, this data will improve our understanding of tarsal loading biomechanics and help in the understanding of the pathogenesis of injury and locomotor dysfunctions. The measurement protocols will require further investigations on large groups of different horse breeds for wider potential usefulness, adaptability and validation. The use of the developed parameters to differentiate between normal conformation and any faulty or pathological conformation will potentially allow investigators to identify possible relationships between morphological measurements and the occurrence of pathology.