Chondrolabral Damage in the Natural Hip Joint

Previously, the labrum was considered the non-functional rim of the acetabulum of the hip joint and was resected when damaged or causing pain. However, there is increasing evidence suggesting the labrum plays a vital role in the healthy functioning of the hip. Contact stresses in acetabular articular cartilage can increase by 92% when the labrum has been removed. Underlying structural abnormalities such as femoroacetabular impingement (FAI) increase the risk of labral tearing. Labral tearing can lead to loss in mobility, joint degeneration and is often found in degenerative conditions like osteoarthritis. Although there has been some success in managing symptoms caused by labral tears, the long-term outcomes are poorly understood and there is little underpinning evidence of the best surgical strategy. There is a growing need for understanding the structure and function of the labrum and how it can become damaged in relation to structural abnormalities. In this thesis, an electromechanical hip simulator was used to simulate physiological joint loads and motions to simulate chondrolabral damage in porcine natural hip joints in an effort to better understand the damage mechanisms. Unloaded and loaded porcine acetabulae were investigated by altering the mechanical loading environment in terms of the axial load, the orientation of joint components, test duration, alignment, and motion. By first running some preliminary tests, it was identified how the simulation model could be applied to induce labral tearing and chondral delamination primarily through increased axial loading and a torsional motion applied on the joint to damage the articular cartilage. The tissues were subsequently characterised macroscopically and microscopically using histological examination and novel non- linear imaging methods to analyse changes to the structure in particular with collagen fibres present in the tissue to determine the effects of damage on the structure. The simulation model was developed with the potential for assessing early interventions, to aid in the management of labral tearing and associated chondral injuries. Multimodal multiphoton revealed preliminary insight into the mechanical disruption of collagen fibres through applied loading. It was noted that collagen fibres align with the direction of the tear and these fibres could be visualised and traced through the application of polarised-second harmonic imaging. In the future, this work can contribute to the understanding of chondrolabral damage and how surgeons may consider the fibre arrangement to restore mechanical function to the labrum.