Functional testing provides unique insights into the pathomechanics of femoroacetabular impingement and an objective basis for evaluating treatment outcome [electronic resource]
Keywords: Mechanical Engineering

The underlying motivation for this dissertation was the need for a better understanding of the biomechanical factors associated with a clinical problem recently termed Femoroacetabular Impingement (FAI). FAI has been associated with morphologic abnormalities at the hip, resulting in a large number of patients presenting with groin pain, soft tissue damage, and loss of hip motion. Proper diagnosis and treatment for FAI is still debated, and support can be found for conservative, open displacement surgery, as well as arthroscopic techniques. There is a popular belief in the orthopaedic community that FAI is a risk factor for the development of hip osteoarthritis (OA), but the dynamic pathomechanics of FAI and long term outcome for treatment versus non-treatment is still not known. Surgical intervention is gaining in popularity to treat this condition, but current outcome metrics are short-mid term and are either subjective, passive, or static. However, FAI is a condition whose underlying injury mechanism is thought to be dynamic movement. Therefore, the goals of this dissertation were to utilize motion capture techniques to provide an objective analysis of the pathomechanics of FAI and to utilize the FAI kinematic profile as a metric for evaluating surgical outcome and as a potential link to hip osteoarthritis risk. The results of this work provided support for the conclusion that FAI represents a substantial risk factor for OA at the hip where a specific gait profile previously identified as an early biomechanical marker for hip OA was found in untreated patients with FAI. The gait profile was characterized as a "reversal gait profile" where the normal pattern of flexion motion at the hip had an abnormal reversal pattern near the mid stance of gait. The observed "reversal gait pattern" in untreated patients with FAI provided objective support for the idea that FAI is a risk factor for the premature development of hip OA. This work also provided a basis for the objective assessment of treatment for FAI by testing for changes in ambulatory mechanics before and after arthroscopic surgery for FAI. It was found that arthroscopic surgical intervention significantly restored normal hip motion in the FAI group during walking. This was important, since as noted above, the abnormal hip motion during walking is considered a biomechanical marker for hip OA. However arthroscopic surgery did not completely restore normal motion during the more strenuous activities (stair climbing and jogging). While surgery improved the reversal gait profile, there were other kinematic abnormalities, including a general loss of flexion-extension range of motion, a loss of hip adduction, and a loss of internal rotation over the stance phase of walking, stair climbing, and jogging. The abnormal motion observed post-operatively during more strenuous activities indicates a continued underlying joint problem or a learned behavior that was not corrected through surgical intervention and/or rehabilitation. The results of the FAI studies motivated further assessment of the abnormal kinematic profile (reversal gait pattern and reduced hip motions) to gain a better understanding of the causes of the altered motion. Two additional studies were conducted. The first study tested the hypothesis that older healthy subjects will have a greater incidence of the reversal gait pattern. A group of asymptomatic people aged 20-80 were studied and the results indicated an increase in the prevalence of reversal gait pattern in the older age range where there is a substantial increase in the incidence of hip OA. A second study tested a group of patients with documented hamstrings muscle weakness and found the reversal pattern as well as other limited hip kinematics similar to the FAI group. These results suggest muscle weakness as a contributor to the altered kinematics and reversal gait profile and provide pilot data for future studies. Taken together, the results of this dissertation indicate that symptomatic FAI individuals have a distinct kinematic profile that suggests they are on a pathway to hip OA development. Surgical intervention shows promise in terms of restoring normal motion during walking, but continued abnormal motion is still present during more strenuous activities of daily living. The underlying cause of these altered motions could have implications for better understanding the pathomechanics of this condition and for developing more effective treatments. This dissertation provides baseline data to support the use of motion capture as an objective tool for assessing FAI surgical outcome and to support future studies aimed at further characterizing the injury mechanism for FAI.