The effect of soft tissue on detecting hip impingement

Hip impingement is a hip associated abnormality and it reduces the
activity of those affected and also it can result in osteoarthritis. Current
clinical methods in detecting hip impingement known as FADIR test. This is
a manual method and relies heavily on surgeons experience 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. All previous work on detecting impingement has ignored the
factor of soft tissue.
In this paper for the first time the complete computational model of hip with
soft tissue has been used to detect the impingement in a specific patient.
In this paper the femur, acetabulum, cartilage and ligaments of specific
patients were modelled in MIMICs 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 imported to detect impingement zone and impingement angle.
Our results show 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.