The hip can be described as ball and socket joint. The ball element is called the femoral head, it is at the end of the thigh bone (femur). The socket is named the acetabulum and this is part of the pelvis. The joint surfaces that move towards each other are coated with a structure called cartilage which is lubricated with fluid; this allows the joint to move with no resistance. Encompassing the hip joint are the capsule, ligaments, muscles, fascia, nerves and blood vessels. There exists a structure referred to as labrum which attaches to the boney rim of the acetabulum which serves to deepen the socket and have a function as a vacuum seal.
Femoral Acetabular Impingement (FAI)
The shape, size and form of the hip joint can fluctuate from individual to individual. This may be from how we are genetically programmed, or how the hip joint develops as we go from youth to adulthood, or other reasons such as trauma or pathology. Listed below, we have tried to simplify the different types of boney differences which can cause impingement, but it is important to understand that there can be various degrees of these and variations.
1.PINCER – This is when the boney rim of the socket (acetabulum) is covering up more of the ball (femoral head) than in the average hip. A specific area of the socket is affected, and this leads to ‘pinching’ of the hip joint structures when the hip joint moves, thus termed impingement. In a number of individuals, there is global overcoverage (involves the entire socket), and this is termed Coxa Profunda.
2.CAM – This phrase refers to a boney bump that is present near the top of the thigh bone (femoral neck). This bump can make the ball of the hip joint less rounded, and and once the hip joint moves, this bump can chafe or catch against the hip joint structures.
3.CAM/PINCER MIXED IMPINGEMENT – Sometimes there might be overcoverage of the socket (pincer/coxa profunda) and additionally, the boney bump (CAM) on the femur.
Hip Dysplasia
This is a problem where the socket is not covering the ball (femoral head), adequately. There are various degrees of this. Measurements named the ‘centre edge angle’ are obtained from the xray to determine how much deficiency of coverage there is. Some patients are given a specific operation by specialist Surgeons known as a peri-acetabular osteotomy (PAO) to help remedy this.
Hip Labral Tears
The fibrocartilagenous labrum which encompasses the socket can at times be torn or become degenerate. There are various categories of this and it can be caused by various reasons including through trauma or hip joint irregularities such as FAI and dysplasia.
If you are affected by any of the injuries described in this article, you should consult your nearest hip physio.
By Louise Grant Physio in North Leeds