Hip replacement is a medical procedure in which the hip joint is replaced by a synthetic implant. It is the most successful, cheapest and safest form of joint replacement surgery. The earliest recorded attempts at hip replacement, which were carried out in Germany, used ivory to replace the femoral head.
Use of artificial hips became more widespread in the 1930s; the artificial joints were made of steel or chrome. They were considered to be better than arthritis but had a number of drawbacks. The main problem was that the articulating surfaces could not be lubricated by the body, leading to wear and loosening and hence the need to replace the joint again (known as revision operations).
Attempts to use teflon produced joints that caused osteolysis and wore out within two years. Another significant problem was infection. Before the advent of antibiotics, surgery on the joints carried a high risk of infection. Even with antibiotic treatments, infection is still a cause for some revision operations. Such infections are not necessarily caused at surgery; they can also be the result of bacteria entering the bloodstream during dental treatment.
The modern artificial joint owes much to the work of John Charnley at the Manchester Royal Infirmary; 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 3 parts – (1) a metal (originally Stainless Steel) femoral component, (2) an Ultra high molecular weight polyethylene acetabular component, both of which were fixed to the bone using (3) special bone cement. The replacement joint, which was known as the Low Friction Arthroplasty, was lubricated with synovial fluid.
The small femoral head (22.25mm) produced wear issues which made it suitable only for sedentary patients, but – on the plus side – a huge reduction in resulting friction led to excellent clinical results. 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).
In 1960 a Burmese orthopaedic surgeon, Dr. San Baw (29 June 1922 – 7 December 1984), pioneered the use of ivory hip prostheses to replace ununited fractures of the neck of femur (‘hip bones’), when he first used an ivory prosthesis to replace the fractured hip bone of an 83 year old Burmese Buddhist nun, Daw Punya. This was done while Dr San Baw was the chief of orthopeadic surgery at Mandalay General Hospital in Manadalay, Burma. Dr San Baw used over 300 ivory hip replacements from the 1960s to 1980s.
He presented a paper entitled ‘Ivory hip replacements for ununited fractures of the neck of femur’ at the conference of the British Orthopeadic Association held in London in September 1969. An 88% success rate was discerned in that Dr San Baw’s patients ranging from the ages of 24 to 87 were able to walk, squat, ride the bicycle and play football a few weeks after their fractured hip bones were replaced with ivory prostheses. Dr San Baw’s use of ivory was, at least in Burma during the 1960s, 1970s and 1980s (before the illicit ivory trade became rampant starting around the early 1990s) cheaper than metal. Moreover, due to the physical, mechanical, chemical, and biological qualities of ivory, it was found that there was a better ‘biological bonding’ of ivory with the human tissues nearby the ivory prostheses. An extract from Dr San Baw’s paper, which he presented at the British Orthopeadic Association’s Conference in 1969, is published in Journal of Bone and Joint Surgery (British edition), February 1970.
In the last decade, several evolutionary improvements have been made in the total hip replacement procedure and prosthesis. Many hip implants are made of a ceramic material rather than polyethylene, which some research indicates dramatically reduces joint wear. Metal-on-metal implants are also gaining popularity. Some implants are joined without cement; the prosthesis is given a porous texture into which bone grows. This has been shown to reduce the need for revision of the acetabular component. Surgeons still frequently use bone cement for the femoral component, however, which has proven very successful after 35 years of clinical experience.
The latest developments are several competing Minimally Invasive Surgery (MIS) approaches, which may result in far less soft tissue damage and a quicker recovery. C.A.O.S (Computer assisted orthopedic surgery) is also being marketed heavily by the implant manufacturers, though its value remains largely unproven.. Computer assisted surgery is said to better navigate prosthetic implantation.
An alternative to total hip replacement (THR) is hip surface replacement (HSR), also referred to as hip resurfacing. With both THR and HSR, a prosthetic socket is pressed into the pelvis. With THR, the end of the femur is amputated, a metal shank is inserted into the femur, and the shank holds a ball which mates with the socket. With resurfacing, the end of the femur is not amputated; the outer surface of the femoral ball is replaced with a cylindrical metal cap. Resurfacing eliminates the common THR problem of the metal shaft loosening from the femur. Resurfacing preserves bone stock if a revision is ever needed. A larger diameter ball and socket more closely mimic the natural joint structure, reducing the risk of dislocation and improving range of motion. There has been no published clinical evidence to show that today’s CoCr metal-on-metal articulating surfaces have the osteolytic effect on bone that earlier polyethylene devices had. Ten year success rates of hip resurfacing from studies in England report success equal to or greater than standard total hip replacement, in age-matched patients. In the United States, the first modern resurfacing device received FDA approval in May 2006, while some 90,000 resurfacings have been performed world-wide.
Patients need to be aware of all surgical options before hip replacement surgery. Hip surgeons have different surgical techniques and surgical outcomes. Currently, there are several different incisions used to access your hip joint. The posterior approach (widely used by the majority of orthopedic surgeons) separates the gluteus maximus muscle in line with the muscle fibers to access the hip joint. Other methods access the hip from the lateral side of the hip joint. In contrast to the posterior approach and lateral approach, the anterior approach uses a natural interval between soft tissue to gain access to the hip joint. Its main disadvantages are that it risks damage to the lateral femoral cutaneous nerve, and it is not widely available to the public because fewer surgeons have been trained in this technique.