internal medicine

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
1970
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
0
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.