Studies of hip impingement diagnosis

Abstract

Hip impingement is a hip associated abnormality which develops among young and middle-aged individuals. It reduces the activity of those affected and if it is not detected at early stage, it can result in osteoarthritis. In this thesis a reliable framework for studying impingement detection is developed. Current clinical methods in detecting hip impingement involve measuring three angles, first the patient’s leg being flexed until maximum angle, second patient’s leg being flexed until 90° then adducted until maximum angle, and third patient’s leg being flexed until 90° afterwards internally rotated until the maximum angle also known as FADIR (Flexion, adduction in 90° flexion and internal rotation in 90° flexion) test. This is a manual method and relies heavily on surgeons experience and even pain tolerance of the patient and the method is prone to error. The use of computational programmes are known to be more accurate and reliable as the kinematic of contact can easily be studied using the digitised bones of the hip joint assuming that the impingement is determined by bone to bone contact kinematics. Current impingement studies assume that the kinematics of hip joint can be studied by assuming the centre of rotation is fixed for hip joint. For highly conforming joints this assumption is acceptable but for cases where conformity is poor the presence of soft tissue and soft tissue loading becomes very important. The important need in orthopaedics field is to develop a model without too much simplification. In this thesis for the first time the complete computational model of hip with soft tissue has been used to detect the impingement in a specific patient. The effect of centre of rotation and soft tissue are considered on impingement detection. In this study the femur, acetabulum, cartilage and ligaments of specific patients were modelled in MIMICs (Materialise' Interactive Medical Image Control System) using both MRI and CT scan. 3D hip models with and without soft tissues of normal hip, hip with impingement and hip with impingement after reshaping were modelled. The hip models were meshed in 3-Matic. The hip models were imported to Abaqus and boundary conditions were applied. Impingement zone and impingement angle was detected in Abaqus. Different centre of rotation was applied to consider the effect of centre of rotation to detect impingement. Experimental studies were set up to validate the hip models. Mocap, Wiimote, MotionNode and goniometer were used together at the same time to measure the flexion, adduction and internal rotation in 90⁰ of flexion in twenty two healthy volunteers. Validity and reliability of all of the methods were calculated. It is the first time that reliability and validity of Wiimote and MotionNode are considered to be used in medical application. Our results show that the model with soft tissue is closer to the experimental results. It shows that the soft tissue in hip model affects hip impingement angle and hip biomechanics. This finding also shows that, if the boundary condition is closer to the real hip, then the results of computer-aided program will be more reliable.