The hip joint is a ' ball and socket' joint that allows movement to occur between the thigh bone (Femur), and the hip bone (Pelvis). The pelvis contains the 'socket' called the acetabulum into which the ball shaped head of the femur fits forming a ball and socket joint which enables the leg to have a wide range of movements.
Thefemoral head and the acetabulum are covered with articular cartilage. This special cartilage allows the normal painless movements that occur in our joints.

With age, injury or disease, this smooth articular cartilage begins to wear off and the bone ends become roughened. When two rough bone surfaces rub against each other it produces pain, swelling and limitation of movements. This is known as Arthritis.

Hip joint replacement surgery involves replacing the Head of the femur (ball) and the acetabulum (socket) with an artificial joint made of metal and plastic. This artificial joint has smooth surfaces which results in reduction of pain and improvement in the range of motion.

A Total hip prosthesis is made up of the following components:

• The acetabular component or cup replaces the acetabulum. The acetabular component can either be made of a metal alloy outer shell which is fitted with a liner made of plastic, metal or ceramic or it can be a single piece plastic component.
• The femoral component replaces the femoral Head. The femoral component consists of the femoral stemmade of metal alloy and the femoral head made of either ceramic or metal alloy which is attached to the stem.

Fixation of the components to the bone is by:

• Cemented THR: both the components are fixed using bone cement
• Uncemented THR: both the components are fixed without use of bone cement
• Hybrid THR: one component is uncemented while the other is cemented

There are many different designs of hip prosthesis available and your surgeon will choose the one considered most suitable for you.  However, the final decision may need to be made during the time of your operation.

There are a number of conditions that can result in a patient having to undergo hip replacement surgery.

• PRIMARY OA: commonly referred to as 'wear and tear arthritis'. Osteoarthritis can occur with no previous history of injury to the hip joint. The hip simply 'wears out'. There may be a genetic tendency in some people that increases their chances of developing osteoarthritis.Very rare in India.
• SECONDARY OA: arthritis develops secondary to an underlying disorder of the hip joint
  • Avascular Necrosis (AVN) - in this condition, the femoral head (ball) loses a portion of its blood supply and actually dies. This leads to collapse of the femoral head and degeneration of the hip joint. Common causes of AVN are alcoholism, long term steroid intake, Gaucher’s disease.
  • Post – traumatic – following a significant injury or dislocation of the hip joint
  • Sequale of paediatric hip disorders like Developmental dysplasia of hip, Perthes disease or SCFE.
• FRACTURE NECK OF FEMUR:
  • Fresh fractures
  • Non-union
  • Complication (AVN, Implant failure, failed Austin Moore replacements)
• INFLAMMATORY ARTHRITIS:
  • Rheumatoid Arthritis
  • Seronegativespondyloarthropathy (ankylosing spondylitis, psoriasis)

Surgery to replace the hip joint is usually recommended when:
1. Pain becomes:
- Severe, unremitting
- Not responding to conservatives means
- Night pain which disturbs sleep
- Affects activities of daily living
2. Restriction of motion
3. Deformities of the joint develop affecting function

The aim of hip replacement surgery is to:

• Relieve your pain.
• Correct any deformity.
• Provide stability to your joint.
• Restore loss of function in your hip.
• Equalise leg length, if possible.
• Improve your quality of life.

• Infection
• Dislocation
• Leg length inequality