Surgery (St Vincent's) - Theses

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Type: Masters Research thesis × Start date: 2017 × Author: Miles, Oliver Joseph ×

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    Characterisation of sensory corpuscles, vasculature and collagen in the injured scapho-lunate ligament
    Miles, Oliver Joseph ( 2022)
    Background: The scapho-lunate ligament (SLL) is a ligament spanning between the scaphoid and lunate bones of the carpus. It has a well-established role in ligamentous restraint of intercarpal motion and maintenance of carpal alignment under axial load. The SLL also has a role as a sensory organ. Sensory mechanoreceptors are located within the ligament. These receptors are responsible for the afferent input to the reflex arc of extrinsic forearm muscular contraction that provides additional dynamic stability to the wrist joint. The SLL is the most frequently injured ligament within the wrist[1]. Complete disruption of the SLL causes carpal instability and malalignment[2], which eventually leads to osteoarthritis of the wrist. When the ligament is torn, surgical treatment options include reconstruction of the ligament with procedures that usually use tendon grafts or transfers that act as a replacement for critical portions of the damaged ligament complex. These techniques may be able to replicate the static restraint of the SLL, however, they fall short of producing an innervated construct that is capable of co-ordinating neuromuscular reflexes. In search of improved reconstructive surgical options, the ligamentous stump of the damaged SLL has been postulated to be a source of native cells that may drive the process of ligamentisation, the process of transformation of the reconstructed ligament created from alternative tissue such as tendon or synthetic construct, to the histological and functional phenotype of a true ligament. This phenomenon has been investigated in knee ligament reconstruction, with anterior cruciate ligament (ACL) remnant preservation being a popular technique used in ACL reconstruction. Methods: This study aims to investigate the structural and cellular makeup of injured SLLs and compare them to the known structure of normal SLLs to estimate the regenerative potential of the residual SLL stump and its value in developing innervated constructs. Injured SLLs were collected from voluntary human subjects at the time of SLL reconstruction or limited wrist fusion, where the ligament remnants would otherwise be discarded. These specimens were formalin fixed and paraffin embedded for histological analysis and immunostaining was performed to identify the vascular and neural structures of the SLL as well as to determine its collagen constitution. Results: Fifteen ligaments were harvested from subjects at surgery after SLL injury ranging from 39 days to 20 years from time of injury. Eleven ligaments were harvested less than one year after injury and four ligaments were harvested two years or more after injury. A total of 66 mechanoreceptors were identified, 50 in the 11 specimens harvested less than one year following injury. Nine of these 11 specimens within one year contained mechanoreceptors, 54% of which resided in the volar subunit, 20% in the dorsal subunit and 26% in the proximal subunit. Two of the four specimens harvested two years or later from injury contained mechanoreceptors, all of which were located in the dorsal subunit. Blood vessels were found in 13 of the 15 samples. Mean vessel density for all specimens was 1.3%, with the highest average density being 1.8% for the volar subunit. The vessel density in the volar subunit decreased with time after injury, with vessel density of 2.5% seen in specimens less than three months post injury, and vessel density of 0.03% in those specimens that were more than three months post injury. The mean collagen I density was 45.6% of the ligament area for all specimens, with the highest average in the dorsal subunit (53% of the ligament area). Collagen I density did not vary significantly within the first two years of injury. Collagen III density varied significantly with time since injury, with average density of 47% of ligament area in specimens less than three months after injury and and 31% in those specimens that were harvested greater than three months after injury. This decline in Collagen III density after three months was most prominent in the volar subunit. Collagen I:III ratio reflected the pattern of change seen in the collagen III profile. Conclusion: Mechanoreceptors were reliably located in the SLL, particularly in the volar subunit of specimens harvested less than one year after injury. Vessel density in the volar subunits was reliably associated with the mechanoreceptor distribution, as was collagen III distribution in the volar subunit in the initial three months post injury. Scapholunate ligaments demonstrate favourable histological findings that warrant further research into remnant inclusion techniques in earlier injuries, particularly incorporating the volar subunit.