Did you know that on this day 120 years ago, the very first x-ray machine was displayed by Professor Henry L. Smith in North Carolina? I thought I'd steal the spotlight and jump all over this opportunity to give you a crash course in hip and pelvis x-rays. You could call it "Hip x-rays for dummies" or just what my consultant explained to me on my last visit!
In order to diagnose hip dysplasia, usually hip and pelvis x-rays are used alongside the clinical signs and symptoms a patient has. MRI scans can be helpful later on in determining if there is any labral pathology and to see the overall quality of the joint. CT scans can also be used with a 3D reconstruction using computer software,
and this helps in seeing the entire 3D shape of the joint. But what really needs to be seen is the morphology of the hip joint (the shape of the bones), as with a dysplastic hip, that is where the problem lies, so specialist usually use just an x-ray to begin with. Take a look at the comparison below.
You can see that the first of these x-rays is of a normal hip and the second one is dysplastic. But what exact markers are used to determine this? Using the pictures below, there are 3 things that are taken into account (some of this is also taken from West & Sutherland, 2011):
1) The Centre-Edge angle (CE angle). Imagine a vertical line drawn up from the centre of the femoral head, and a second one to the edge of the acetabulum, (shown in white on the diagram). The angle between these is the CE angle and should be roughly 25°-30°. Anything less than 25° means the hip is dysplastic. In a severe case it could even be in minus figures.
2) The weight-bearing zone (shown by the black line). In a normal hip this can be marked by a horizontal line, which means the load is taken adequately through the hip socket. In a dysplastic hip this line is sloped, so that load is taken through the edge of the acetabulum. Eventually this will begin to damage the labrum at the edge of the acetabulum (known as acetabular rim syndrome), and then eventually the underlying cartilage.
3) How much of the femoral head is contained inside the hip socket. This you can see by looking at the faint grey line sloping across the middle of the femoral head on the x-ray, indicating the edge of the hip socket. Most of the femoral head should be inside the socket.
So there you have it. A crash course in the basics of how orthpaedics diagnose hip dysplasia!
"But why," I hear you say, "Why does it then take so many years for some to gain a diagnosis of adult dysplasia, when all they need is an x-ray?!" Johan Witt, a highly regarded consultant specialising in young adult hip problems, broached this subject in a recent paper. He and some colleagues conducted a study at a conference of orthopaedic consultants who treated a variety of hip pathologies. He asked attendees to state what their diagnosis and advice would be for a number of different x-rays of hip dysplasia and FAI and there was a huge amount of subjectivity found when comparing answers. However, it was found that this subjectivity decreased and the answers became more accurate amongst those who saw and treated a higher volume of patients with these young adult hip conditions. The surmise is therefore that those who treat higher volumes of young adults with hip problems are more able to accurately diagnose a hip pathology such as dysplasia, and to better advise those patients on treatment options available to them. Sadly, these experienced hip consultants are few and far between and I believe this to be part of the difficulty in gaining this diagnosis.
Malviya, A., Raza, A. & Witt, J. D. (2016) Reliability in the diagnosis of femoroacetabular impingement and dysplasia among hip surgeons: role of surgeon volume and experience, Hip International, Vol. 26 (3)
West, S. & Sutherland, D. (2011) A guide for adults with hip dysplasia: A patients guide. Australia: Sutherland Studios.
