HIP RESURFACING GLOSSARY

Arthroscopy
The use of a telescopic viewing device inserted into a joint via a small incision together with specialised surgical tools, enabling the surgeon to see inside of the joint on a television screen and identify and repair the defect. Also known as orthopaedic endoscopy.

Articular cartilage
Smooth cartilage which protects the inside of the joint.

Clearance
Clearance is the term used to describe the effective gap between the femoral head and acetabular cup in a Metal-on-Metal bearing. It is calculated by subtracting the radius of the femoral head from the radius of the acetabular cup. This difference in radii is used to describe the gap at the equatorial position on the bearing when the femoral head is in contact with the acetabular cup in a polar orientation. Polar bearings operate with a large apparent contact surface area. However the real contact surface area is very small. It is at this point where the articular surfaces interact creating friction and wear.

What is Optimal Clearance?
As well as a value of the difference between head and cup radii, clearance can be expressed as a ratio to head diameter. There is an optimal clearance associated with each head diameter. Although low clearances work well in laboratory conditions, there may be an issue in the clinical environment. Factors such as bone density, implant position and post surgery may all effect the ability of the bearing to generate a fluid film. With low clearances, there is reduced tolerance for correct function in less than perfect implantation or patient conditions. As a Metal-on-Metal bearing is not in continuous motion, it operates in a mixed lubrication regime and its longevity is linked to its ability to generate and sustain a fluid film. Laboratory evidence confirms the BHR generates fluid film lubrication. Small clearances increase friction and may cause micro motion in the cup. This may hamper bony ingrowth resulting in impaired fixation.
The Stribeck Curve is a graphical representation of the measured frictional forces occurring in a bearing. From the shape of the curve, deductions can be made concerning the lubrication operating conditions of the bearing. Results of friction testing of the BHR are shown below in Graph A. The friction tests suggest boundary lubrication pre-testing but at 1 million cycles, a mixed lubrication regime was evident. By 2 million cycles, the classical Stribeck curve had formed indicating a considerable contribution from fluid film, which continued to be evident at 3 millioncycles.

Endoscopy
The use of a telescopic viewing device inserted into a body cavity via a small incision together with specialised surgical tools, enabling the surgeon to see the inside of the body cavity on a television screen and identify and repair the defect.

External fracture fixation
Restoring of fractured limbs to the most anatomically correct alignment through use of constructs or frames which are attached externally to the body.

Hip Arthritis
Arthritis of the hip is a disease which wears away the cartilage between the femoral head and the acetabulum, causing the two bones to scrape against each other, raw bone on raw bone. When this happens, the joint becomes pitted, eroded, and uneven, resulting in pain, stiffness, and instability. In some cases, motion of the leg may be greatly restricted.

Osteoarthritis:
Osteoarthritis is the most common form of arthritis in the Western world. It is degenerative, and although it most often occurs in patients over the age of 50, it can occur at any age, especially if the joint is in some way damaged. It is usually confined to the large weight-bearing joints of the lower extremities, including the hips and knees, but may also affect the spine and upper extremity joints. Patients with osteoarthritis often develop large bone spurs, or osteophytes, around the joint, further limiting motion.

Causes:
Osteoarthritis of the hip is a condition commonly referred to as 'wear and tear' arthritis. Although the degenerative process may accelerate in persons with a previous hip injury, many cases of osteoarthritis occur when the hip simply wears out. Some experts believe there may exist a genetic predisposition in people who develop osteoarthritis of the hip. Abnormalities of the hip due to previous fractures or childhood disorders may also lead to a degenerative hip. Osteoarthritis of the hip is the most common cause for total hip replacement surgery.

Symptoms:
The first and most common symptom of osteoarthritis is pain, usually occurring towards the groin area during weight-bearing activities such as walking.
To decrease hip arthritis pain people usually compensate by limping, which reduces the force across the arthritic hip. Hip osteoarthritis may also result in loss of motion of the hip joint, causing difficulty in doing daily living activities such as putting on socks and shoes. As a result of the cartilage degeneration, the hip loses its flexibility and strength, and may develop bone spurs. As the arthritis worsens, the pain may increase and may become constant, even during non weight-bearing activities.

Human tissue engineered
Tissue grown from a human cell source in the laboratory by simulating growth conditions occurring naturally in the human body.

Intermediate Compression Hip Screw System
A hip fracture reduction system using a plate which is designed for children.

Internal fracture fixation
Restoring of fractured limbs to the most anatomically correct alignment through use of internal implants such as plates, screws and nails.

Intramedullary nail
A nail used in the intramedullary canal which extends along the middle of a long bone like the femur or tibia.

Minimally invasive surgery (MIS)
Surgery not conducted through a large incision which thereby avoids serious tissue damage and long recuperation periods. Also known as 'keyhole surgery'.

Rheumatoid Arthritis
Unlike osteoarthritis which is a 'wear and tear' phenomenon, rheumatoid arthritis is a chronic inflammatory disease that results in joint pain, stiffness, and swelling. The disease process leads to severe, and at times rapid, deterioration of multiple joints, resulting in severe pain and loss of function.

Causes:
Although the exact cause of rheumatoid arthritis is unknown, some experts believe that a virus or bacteria may trigger the disease in people with a genetic predisposition to rheumatoid arthritis. Many doctors think rheumatoid arthritis is an autoimmune disease in which the synovial tissue of the joint has been attacked by the immune system. The onset of rheumatoid arthritis occurs most frequently in middle age and is more common among women.

Symptoms:
The primary symptoms of rheumatoid arthritis are similar to osteoarthritis and include pain, swelling, and the loss of motion. Other symptoms may include loss of appetite, fever, energy loss, anemia, and rheumatoid nodules (lumps of tissue under the skin). People suffering with rheumatoid arthritis commonly experience periods of exacerbation or 'flare up' involving pain and stiffness in multiple joints.

Treatment:
Treatment for pain associated with rheumatoid arthritis may involve medications such as non-steroidal anti-inflammatory drugs (NSAIDs), aspirin, and analgesics.

Supracondylar implant
An implant used above a condyle at the tip of a bone (eg the bottom of the femur, just above the knee joint).

Surgical drive systems
Motorised devices, controlled by the surgeon, that drive the cutting blade.

Tissue repair
The repair of damaged tissue (ie skin, bones, joints and soft tissue) irrespective of whether the damage is induced by trauma, disease or the aging process.