The hip joint allows us to remain mobile and is one of the most important joints within the body. It is a ball and socket synovial joint with the ball of the femur slotting into the hip joint. The physiology of the joint means that it is very stable yet offers a great deal of flexibility and is a major component in the locomotor system.
A healthy joint works when the articular surface of the femoral head sits firmly in the joint and sitting against the articular cartilage of the acetabular fossa. Common conditions such as osteoarthritis (see below) occur where there is degradation of the articular cartilage of the acetabular fossa which results in the head of the femur connecting directly with the pelvic bone.
Pelvic girdle: The pelvis is formed from the fusion of 3 separate bones in that of the Illium, Pubis and Ischium. It is designed to protect the abdominal organs and absorbs shock from the lower limbs.
Femur: This the longest bone in the body and forms the top part of the leg. It is also the insertion point for many of the muscles affecting the hip joint, with the head of the femur inserting into the acetabulum of the pelvis.
Surrounding muscles: there are 4 main muscles surrounding the hip joint which connect to the femur in that Flexors (lliopsoas), Extensors (Gluteals), Abductors (Gluteus Medius) and the Adductors (Adductor longus/brevis).
Stability of the hip joint
The hip is an extremely stable joint, a key requirement for overall mobility and has an extensive range of motion, and helped by the deep acetabulum, joint capsule an associated ligaments and muscles. In flexion there is a 125 – 135 degree range of motion with 20 to 30 degrees in extension. In abduction (away from midline) there is a 40 – 45 degree level of flexibility and 30 degrees in adduction (towards midline). There is also a 40 degree range of motion for both internal and external rotation.
Osteoarthritis is a degenerative condition resulting in the degradation of cartilage within a joint and leading to bone on bone contact which can be painful and ultimately compromises the mobility of a patient. Hip osteoarthritis is the second most common form of OA diagnosed, with 9.5 million sufferers in EMEA, of which the UK has the second highest figure of 2.12 million people having been diagnosed.
Typically the onset of OA will eventually lead to a hip replacement, with 100 to 200 replacements taking place for every 100,000 people. The condition is more prevalent in females (66%) than males (33%) with the average age of those diagnosed around 70 years. Statistics do show however that the age of diagnosis is gradually getting lower, though the biggest issue faced is that surgeons are reluctant to operate on younger patients to avoid to need for subsequent surgery in the future, since hip replacements are only designed to last 10-15 years.
50% of those diagnosed are between the ages of 60 and 75, which is why there is an increasing market non-surgical treatments in the form or painkillers, physiotherapy and bracing of which the latter two focus primarily on changing the physiology of the patients walk to reduce the bone on bone contact in the hip.
As with all forms of osteoarthritis the main important thing is diagnosis so that treatment can begin and the degradation of cartilage can be managed in an attempt to delay the need for surgery whilst maintaining a patient’s mobility.