The hip joint is a ball and socket type joint. The ball consists of the head of the femur bone and this sits snugly in the acetabulum (socket) of the pelvis.
The surfaces of the head of the femur and acetabulum that articulate with each other are covered in articular cartilage. Arthritis is the result of these surfaces being worn away.
The hip is surrounded by a relatively loose capsule that allows the joint to move throughout a wide arc. Arthritis often causes the capsule to thicken and contract and this contributes to the stiffness that you may experience.
The glenoid labrum is a thickened ring of cartilage that is attached firmly to the acetabulum and acts to deepen the socket.
Powerful muscles surround the hip joint. The iliopsoas muscle allows you to bend the hip forward whilst the powerful gluteals allow you to bring it back. The adductors bring the leg in from the side and the abductors bring the leg out to the side. The abductors also have an important role in stabilizing the pelvis when you are walking.
Basic hip bony anatomy
Basic hip muscular insertions
Pain is the main presenting symptom of the majority of people presenting with hip pathology. Usually the pain is located towards the groin but occasionally people present with buttock pain or lateral hip pain. Often the pain is activity related but night pain is also common with hip problems. Sometimes the pain radiates down the leg but hip pathology will rarely go below the knee. Remarkably, some patients can present purely with knee pain even though the source is their hip problem and this is known as referred pain.
Sometimes you might notice difficulty with activities that require a moderate amount of hip flexion such as putting on your shoes / socks or cutting your toe nails. Also activities like getting into / out of a car or even getting up from a chair can be hard.
This is the most common form of arthritis and refers to the progressive loss of cartilage from the surface of joints and is characterized by the development of bony spurs and cysts in response.
This refers to arthritis that develops due to a previous trauma. For example if you previously had a fracture of the acetabulum, you may be at risk of arthritis in the future.
This is a group of disorders that occur when the body's own immune system starts to attack its own tissues. The most well known of these is rheumatoid arthritis but the group also includes psoriatic arthritis, ankylosing arthritis, SLE and inflammatory bowel disease.
In contrast to osteoarthritis, joint swelling and inflammation are usually the predominant symptoms and usually these are worse in the morning time.
When the blood supply to the femoral head is interrupted the bone effectively dies and with time begins to collapse. It can be caused by steroids, alcohol, sickle cell disease, radiotherapy or a multitude of other causes but in reality most are "idiopathic" where the cause remains unknown.
When avascular necrosis is suspected, an MRI will help to confirm the diagnosis and this is important as early intervention can potentially prevent progression of the collapse.
The ring of fibrocartilage around the acetabulum, the labrum can tear in response in trauma in a similar manner to torn cartilage in the knee. Often patients are predisposed to this due to structural abnormalities in either the acetabulum or femoral neck or both. This process is known as femero-acetabular impingement.
Pelvis x-ray demonstrating osteoarthritis in the right hip
Iliopsoas bursitis / tendinitis
The iliopsoas is a powerful hip flexor that runs down from the lumbar sine and pelvis and across the front of the hip joint to insert on the lesser trochanter. A large sac or bursa lies between the hip capsule and the iliopsoas tendon and when inflamed causes iliopsoas bursitis. The tendon itself may also get inflamed from an acute injury or overuse causing a tendinitis.
This refers to inflammation of the small fluid-filled pouch that sits over the greater trochanter. Bursae sit where muscles or tendons move over a bony prominence and act to reduce friction.
In reality, many cases of trochanteric bursitis are actually due to tears at the insertion of the gluteal muscles similar to rotator cuff tears in the shoulder. They should be suspected when steroid injections do not produce lasting relief and are usually diagnosed on MRI. Significant tears that remain symptomatic may be treated either arthroscopically or with a small open repair.
This is usually a burning type of pain down the outside of the thigh due to compression of the lateral cutaneous nerve of the thigh as it passes under the inguinal ligament.