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Hips Knees and History
From early times the severe disability of hip arthritis had physicians seeking ways to relieve the patient's plight.
Before Charnley's work there had been many attempts to interpose some material between the ends of the bone in osteoarthritis. Most of the work had been done in hip replacements, where materials such as fascia, skin, glass, pyrex and metal were used.
The first attempts date back to the 19th century. In 1885, Ollier described an interpositional arthroplasty, which generated enormous interest among surgeons.
A major contribution was made by Smith-Petersen, who at the suggestion of his dentist used a vitallium mould prosthesis for the acetabulum in 1938. This proved quite successful and was used for many years.
The credit for the first total hip arthroplasty involving both femur and acetabulum goes to Gluck who in the 1890s used a ball and socket design made of ivory. This was held into the bone with a cement made from colophony, pumice and gypsum.
In England in 1951, McKee and Watson-Farrar developed a metal on metal prosthesis, which initially had a 54% success rate. This improved with the use of acrylic cement after the work of Charnley.
The main problem was that the metal tolerances, being less than perfect, often led to a lot of metal wear particles. However, some of these arthroplasties were very successful and are still functioning in patients today, having been carried out in the early 1970s.
He developed the principles of low friction arthroplasty, initially using Teflon. However, Teflon created problems due to microscopic wear particles (see below).
Charnley's research led to major advances in our understanding of the histological response of the body to wear particles.
He also introduced the use of acrylic cement for the fixation of prostheses and was the first to use high-density polyethylene as a bearing material.
Other achievements included significant improvements in aseptic techniques and quality of air in the operating theatre.
The principles Charnley taught are still applicable today. Even though modern hip arthroplasty has seen improvements in the manufacture of the materials, in the shape of implants and in insertion techniques, the basic prosthesis and the general principles are essentially unchanged.
In the mid 1980s an increased incidence of failures began to appear.
A lot of changes had been made in an attempt to prolong the life of prostheses. Many became loose and osteolysis, often with massive resorption, was seen.
Wear particles were to blame and the concept of cement disease arose. It was thought that the cement failed first, leading to joint failure.
While newer cementing techniques were being developed, other research progressed towards the elimination of cement.
Surfaces were developed that allowed rigid biological fixation with bone ingrowth. It was felt that this
would overcome the failures seen more commonly in younger, more active patients.
However, the long-term results do not favour either technique.
Many of the principles learnt from hips have been applied to knee replacements. However, a major difference exists in mechanics of each joint.
The hip, being a ball and socket joint, is intrinsically stable and is driven by the surrounding muscles.
By contrast, the knee joint is dependent on the intra-articular and extra-articular ligaments for its stability. Once there is good stability, the muscles can work efficiently to control the knee joint.
The knee joint is not a simple hinge joint, as we are often led to believe. It is a complex joint involving rolling and gliding movements. It is essential that this be taken into consideration when a replacement joint is designed.
Over the years there have been three broad avenues of development of the knee replacement.
Initially, hinge joints were used. The first were developed by Waldius in 1951, Shiers in 1953 and MacAusland in 1956. Many others then followed.
The problem with these joints was they did not allow for the more complex forces on the joint during normal movement.
Failures were common and early. Also, because there was usually loss of the ligaments and large amount of bone resection, revisions were difficult and often unsuccessful.
A number of surgeons attempted to interpose a material between the joint surfaces both to act as a bearing surface and also to correct leg alignment.
Judet in 1947 used acrylic, and in 1953 McKeever and Macintosh separately used metal spacers.
The unicompartmental arthroplasty developed from these spacers and replaced both the femoral and tibial surfaces on either the medial or lateral side of the joint.
Gunston in 1969 used polyethylene on the tibial side with a metal runner on the femoral side. Even though the metal was semicircular, it was not fixed to the tibia, allowing more normal movement of the knee joint.
Many unicompartmental knees followed and one of the more successful was the Marmor in 1972. However, it was technically difficult to place and fix the prosthesis accurately and this became doubly difficult if there were degenerative changes on the medial and lateral sides.
The total condylar systems then began to appear. These are the forerunners of the modem full knee replacements used in primary procedures.
Credit for the first designs goes to Charles Townley, who has design drawings from the 1940s. However, his prostheses were all metal and had poor wear characteristics.
Many condylar prostheses appeared in the early 1970s. These began to wrap around the front of the femur and incorporate the patellofemoral articulation. None of the previous replacements had addressed this often symptomatic area well.
Development continued during the 1970s and early l980s.
The more recent advances, particularly in the past decade, have been the refinement of the surgical jigs and the more accurate cutting of the bone.
At the same time, there have been improvements in the manufacture of the polyethylene tibial articulation leading to greater durability. The modem plastic inserts are stronger and longer lasting than those of the past.
Some of the condylar prostheses permit movement within the inserts, usually movement of the plastic insert. These allow increased contact area and decreased wearing of the implant.
They are known as mobile bearing prostheses and are the latest development. While there has been interest in these prostheses, to date there is no significant difference in the results demonstrated.