HIP ARTHROPLASTY

Hip arthroplasty, is a surgical procedure in which the hip joint is replaced by a prosthetic implant. Such joint replacement orthopaedic surgery generally is conducted to relieve arthritis pain or fix severe physical joint damage as part of the hip fracture treatment.

PICTURE OF A HIP IMPLANT XRAY


MODERN HIP JOINT

The modern artificial joint owes much to the work of John Charnley at Wrightington Hospital; his work in the field of tribology resulted in a design that completely replaced the other designs by the 1970s. Charnley's design consisted of three parts—

1.)a metal (originally stainless steel) femoral component,
2.)a teflon acetabular component which was replaced by Ultra High Molecular Weight Polyethylene or UHMWPE in 1962, both of which were fixed to the bone using
3.)PMMA (acrylic) bone cement,and/or screws.

The replacement joint, which was known as the Low Friction Arthroplasty, was lubricated with synovial fluid. The small femoral head (7/8" (22.2mm)) was chosen for its decreased wear rate; however, this has relatively poor stability (the larger the head of a replacement the less likely it is to dislocate, but the more wear debris produced due to the increased surface area). For over two decades, the Charnley Low Friction Arthroplasty design was the most used system in the world, far surpassing the other available options (like McKee and Ring). Recently the use of a polished tapered cemented hip replacement (like Exeter) and uncemented hip replacements have become more popular.

COSTS

In a paper published August 14, 2007 in The Japan Times, signed by K. Rogoff, it is mentioned that 250,000 hip replacements are performed in the U.S. each year, for an average cost of $6,000. Surgery costs vary from country to country, with the US typically being among the highest-priced markets, and countries like Thailand, Cuba and Argentina, among the lowest.

COMPLICATIONS

In the short term post-operatively, infection is a major concern. Reported rates are about 1%. Deep infection will often require one or two stage revision surgery with an extended hospital stay and antibiotics. Recurrent dislocation is another indication for revision. The rate is also about 1%.

In the long term, many problems relate to osteolysis from wear debris. An inflammatory process causes bone resorption and subsequent loosening or fracture often requiring revision surgery . Very hard ceramic bearing surfaces are being used in the hope that they will have less wear and less osteolysis with better long term results. Large metal heads are also used for similar reasons, these also have excellent wear characteristics and benefit from a different mode of lubrication. A greater head neck ratio also contributes to stability. These new prostheses do not always have the long term results or reliability of established metal on poly bearings.

INDICATIONS

Total hip replacement is most commonly used to treat joint failure caused by osteoarthritis. Other indications include rheumatoid arthritis, avascular necrosis, traumatic arthritis, protrusio acetabuli certain hip fractures, benign and malignant bone tumors, arthritis associated with Paget's disease, ankylosing spondylitis and juvenile rheumatoid arthritis. The aims of the procedure are pain relief and improvement in hip function. Hip replacement is usually considered only once other therapies, such as pain medications, have failed.

TECHNIQUES

There are several different incisions, defined by their relation to the gluteus medius. The approaches are posterior (Moore), lateral (Hardinge or Liverpool), antero-lateral (Watson-Jones), anterior (Smith-Petersen) and greater trochanter osteotomy. There is no compelling evidence in the literature for any particular approach, but consensus of professional opinion favours either modified anterio-lateral (Hardinge) or posterior approach.

1.)The posterior (Moore) approach accesses the joint through the back, taking piriformis muscle and the short external rotators off the femur. This approach gives excellent access to the acetabulum and preserves the hip abductors. Critics cite a higher dislocation rate although repair of capsule and SERs negates this risk.

2.)The lateral approach is also commonly used for hip replacement. The approach requires elevation of the hip abductors (gluteus medius and gluteus minimus) in order to access the joint. The abductors may be lifted up by osteotomy of the greater trochanter and reapplying it afterwards using cables (as per Charnley), or may be divided at their tendinous portion, or through the functional tendon (as per Hardinge) and repaired using sutures.

3.)The anterolateral approach develops the interval between the tensor fasciae latae and the gluteus medius.

4.)The anterior approach utilises an interval between the sartorius and tensor fascia latae.

The double incision surgery and minimally invasive surgery seeks to reduce soft tissue damage through reducing the size of the incision. However component positioning accuracy is impaired and surgeons using these approaches are advised to use computer guidance systems.

SIDE EFFECTS

A few hip replacement patients suffer chronic pain after the surgery. Usually, X-ray and MRI cannot detect any problem with the hip joint replacement. Doctors do not know the source of the pain, or how to cure it. Generally, it is believed that such pain is caused by nerve damage during the replacement surgery.