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ItemHip joint neuromuscular control and biomechanics in individuals with symptomatic femoroacetabular impingementDiamond, Laura ( 2016)Femoroacetabular impingement (FAI) is recognised as a significant clinical problem among younger active adults. This morphological hip disorder can cause joint stiffness, hip and/or groin pain, and impaired function. Importantly, a link has been proposed between FAI and the future development of hip osteoarthritis. Current treatment often involves arthroscopic surgery; however, there is an overwhelming absence of evidence for its efficacy. It is plausible that non-operative treatments have an important role to play in management of symptomatic FAI. Developing and informing these treatments relies on an objective understanding of the exact nature of the associated physical impairments. This thesis aimed to comprehensively understand the extent of current knowledge and provide new data of the neuromuscular and biomechanical impairments in individuals with symptomatic FAI. Study 1 clarifies the current understanding of physical impairments and activity limitations in individuals with FAI by way of systematic review with consideration of study quality. This review identified 16 studies of level 3b-4 evidence that reported some physical impairments when compared to individuals without FAI. These were mainly in the domain of hip range of motion, particularly in directions of impingement (deep flexion, combined with adduction and internal rotation). Other impairments were suggested during gait, squatting, stair climbing and isometric muscle contractions, though evidence was limited and conflicting. Importantly, surgery for FAI was shown to restore some, but not all, physical impairments. This systematic review identified a need for studies to assess whether hip range of motion and neuromuscular function are compromised in dynamic tasks designed to target positions of impingement in individuals with symptomatic FAI. On the basis of recommendations from Study 1, cross-sectional investigations comparing several biomechanical and neuromuscular factors in individuals with symptomatic FAI, diagnosed by clinical examination and imaging features (n=15), to a matched asymptomatic control group, with no evidence of morphological FAI (n=15) were undertaken. Tri-planar hip kinematics and kinetics during gait were compared between the two groups in Study 2. Individuals with FAI walked with less range of motion in the sagittal plane during a gait cycle, but did not exhibit any other impairments. Less within-group variability was also observed in the FAI group at peak hip adduction angle and peak hip internal rotation angle (directions of impingement) during stance. On the foundation that conservative treatments and rehabilitation protocols following surgery for FAI regularly include hip muscle strengthening, Study 3 compared isometric and isokinetic hip muscle strength and agonist/antagonist ratios between the two groups. Individuals with FAI demonstrated isometric hip abductor muscle weakness, and a strength imbalance in the hip rotators when measured isometrically, but not isokinetically. As no studies have previously explored deep hip muscle function in individuals with symptomatic FAI, Study 4 investigated potential differences in muscle synergies during gait between the two groups. A non-negative matrix factorization algorithm extracted three synergies from the electromyographic patterns of select deep hip muscles, measured using intramuscular electrodes. Between-group comparison indicated the variance accounted for by the muscle synergies was higher in the FAI group than the pain-free controls. This suggests that coordination of deep hip muscles with the anatomical capacity to oppose impingement differed between groups, and importantly, that this difference can be attributed to increased variability in the healthy controls. Participants with FAI exhibited a more homogeneous pattern during the early swing phase of gait that appeared to be consistent with an effort to increase hip joint stability. Given that abnormal hip joint function was not well defined with gait assessment alone, Study 5 compared hip and pelvis biomechanics during two, more provocative, squatting tasks. Findings demonstrated that individuals with symptomatic FAI can squat to a depth comparable to controls, regardless of squatting task design. However, biomechanical alterations were evident at the hip and pelvis when the task was constrained. Decreased variability was once again demonstrated in the FAI group with respect to the transverse plane hip angle during the constrained task. The studies outlined in this thesis identified new neuromuscular and biomechanical impairments in individuals with symptomatic FAI. Taken together, these findings imply that FAI patients have adopted a motor coordination strategy that is consistently similar to each other, a feature that is not observed in healthy pain-free individuals with no pathology. Given the cross-sectional study design, it is not possible to clarify whether the differences precede or follow pathology development. Clinical interventions to restore normal musculoskeletal function around the hip joint may be beneficial, but future research is needed to determine whether these features can be changed and whether this improves outcomes.