The world’s first artificial hip replacement was performed by the German surgeon Gluck in 1891 with a femoral head made of ivory, while the true artificial total hip replacement was probably performed by the British surgeon Phillip Wiles, who used a stainless steel prosthesis and performed six operations. Although these surgeries cannot be called successful, these pioneers made an indelible contribution to modern total hip replacements.
The longevity of the hip prosthesis depends on the bone-prosthesis fixation, the wear rate of the acetabulum-femoral head, the surgeon’s skill and the condition of the patient.
I. Fixation of the prosthesis
The effect of different prosthesis fixation methods is different, and the effect of the same prosthesis fixation method varies for different patients.
1.Bone cement fixation
Modern hip prosthesis is fixed with bone cement in the early stage. Theoretically, bone cement can provide immediate postoperative fixation of the prosthesis, so there is no need to worry about loosening and sinking of the prosthesis in the early postoperative weight-bearing activities.
Early cemented prosthetic fixation has a high failure rate, with a failure rate of up to 40% at 15 years. The reasons for failure are closely related to the cement technique and the design of the prosthesis. Now the bone cement technology has developed to the third generation, i.e., bone surface cleaning, cement vacuum mixing, neutralization, and pressurized infusion. The design of the prosthesis has also changed from sharp and rough in the past to a smooth prosthesis with rounded corners or even conical shape. After a series of improvements, the long-term survival rate of bone cement-fixed prostheses has been greatly improved.
However, the improvement of bone cement technology has only significantly improved the survival rate of the femoral stem prosthesis, whose 15-year survival rate can reach 95%, but has not significantly improved the long-term survival rate of the acetabular prosthesis, whose loosening rate can reach 24% 15 years after surgery, especially the loosening rate is higher in patients under 50 years old. Therefore, most physicians currently believe that cemented acetabular prostheses should only be used in elderly and severely osteoporotic patients. For cemented femoral prosthesis, many doctors also do not advocate using it in young patients under 50 years old because of the difficulty of revision.
2.Non-cemented fixation
Since the early cemented prosthesis had a high rate of loosening, and this loosening was largely caused by fatigue fracture of the bone cement and the activation of macrophages by the debris produced by wear and tear, which resulted in osteolysis, research on non-cemented prosthesis was started in the 1970s.
The current non-cemented prostheses are surface microporous (bone long entry), rough surface (bone long upper), hydroxyapatite coated (covalently bonded), and anatomical intramedullary inlay type. It is well documented that surface microporous acetabulums are significantly better than cemented acetabulums, while the same conclusion cannot be drawn for other types of acetabulums for the time being. The results of non-cemented femoral prostheses are approximately the same as cemented femoral prostheses.
At present, most doctors believe that patients with severe osteoporosis are suitable for cemented prosthesis; for those who are over 70 years old and have a life expectancy of about 15 years, cemented prosthesis can be used; for patients who are under 60 years old and have a life expectancy of 25 years or more, non-cemented or hybrid fixation (cemented acetabulum and non-cemented femoral prosthesis) is suitable. In contrast, for young patients under 50 years of age, most advocate the preference for non-cemented fixation prosthesis.
Second, the acetabular-femoral head material match
A large number of artificial hip joints are currently made by combining a hard metal or ceramic femoral head with an ultra-high polymer polyethylene acetabular cup. Many evidences suggest that the polyethylene particles produced by this combination are the main cause of aseptic loosening of the late prosthesis. Various efforts have been made to address the problem of polyethylene wear. Some people have changed the structure of polyethylene in terms of enhancing its wear resistance and developed highly cross-linked polymer polyethylene materials; on the other hand, people have changed their thinking and simply discarded polyethylene and designed metal-to-metal and ceramic-to-ceramic prostheses, and ceramic-to-metal prostheses are also being experimented with. The wear rate varies considerably when different materials are mated.
One prosthesis that is still in the experimental phase is a metal-to-metal prosthesis with a small concavity on the surface of the femoral head prosthesis, which allows for fluid retention and lubrication. Ceramic-to-metal total hip prostheses are another type of prosthesis in the experimental phase, with an in vitro test wear rate of only 1/2 that of metal-to-metal.
In recent years there have been tremendous advances in ceramic processing and material technology, and ceramic-to-ceramic prostheses are again favored with a linear wear rate of 0,005 mm/year. Further clinical studies have found that ceramic wear debris causes a lower inflammatory response to the body than metal and is particularly suitable for younger patients.
Third, small incision hip joint replacement
While the prosthesis is constantly improving, the surgical technique is also improving. Small incision hip replacement is one of them, and the length of its surgical incision is only 6-10cm.
Its advantages are: small scar, little pain, short hospital stay and quick recovery.
With the development of surgical techniques, instruments and apparatus, small incision hip replacement surgery is now not only about reducing the incision to about 10cm, but also about restoring the original intention, that is, the invasion of soft tissues, especially muscles and fascia, should be small, which is the second level; the deeper requirement is not to invade the muscles, which is the MSS mentioned now, and the anterolateral approach to the hip joint MIS is the representative, and the corresponding special The surgical instruments are constantly being updated.
Due to the restricted visibility of small incision hip replacement surgery, the difficulty of accurate prosthesis placement is greatly increased. To solve this problem, many surgeons are using computerized navigation systems during surgery. The clinical application of surgical robotic arthroplasty has proven its advantages of more accurate prosthesis selection, more perfect femoral medullary cavity filling and more accurate prosthesis placement, which has also gained attention
Fourth, hip joint surface replacement
Artificial total hip replacement is undoubtedly a thorough and durable treatment for femoral head necrosis, acetabular dysplasia, hip osteoarthritis, etc., especially for elderly patients with very good results. However, for young people, total hip replacement has the obvious disadvantage of a high rate of early revision, especially in men who are active and participate in sports after surgery. Hip surface replacements offer unique advantages for this problem.
Hip surface replacement is a reconstructive hip surgery with the advantages of minimal trauma, good postoperative mobility, and preservation of more lateral femoral bone mass. This surgery has been used in clinical practice since the 1950s, and its development history is a rather tortuous process, with its limitations coming more from the prosthesis itself than from the surgical technique. In recent years, with advances in material science and improvements in technical details, clinical applications have gradually increased, with encouraging clinical results.
Unlike total hip replacement, hip surface replacement is characterized by the preservation of the femoral neck, and its adverse effects on the biomechanics of the lower extremity are quite minimal and close to anatomical reconstruction. It is also technically easier and more feasible to perform THA revision in the future than conventional THA because it preserves the structure of the femur itself to the greatest extent possible.
Another feature of the hip surface replacement is the use of a metal-to-metal prosthesis, which reduces debris from wear and tear, as described previously.
A third feature of hip surface replacements is the use of larger diameter femoral heads, usually above 36 mm, approaching the size of the original femoral head. The larger diameter prosthesis improves joint stability and reduces the incidence of dislocation, and the stable joint ensures mobility in all directions.
Of course, the reported follow-up period for the new generation of hip surface replacements is still relatively short, and proof of their stability is yet to be supported by medium- and long-term follow-up results. For young patients with hip disease, surface replacement is a recommended surgical procedure to achieve both pain relief and activity restoration.
V. Problems of artificial hip joint and prospect of solution
The artificial hip joint replacement is very close to the normal joint in terms of solving the patient’s pain and mobility, but the problem that needs to be solved is how to further improve the service life of the prosthesis.
The main problem that needs to be solved to improve the service life of the prosthesis is undoubtedly the debris-induced osteolysis that leads to the loosening of the prosthesis. Ceramic-to-ceramic and metal-to-metal prostheses have greatly reduced debris production, but have not completely eliminated osteolysis. Therefore, we need to conduct further research to find the root cause of osteolysis and prevent it completely.
The progress in surgical treatment of osteolysis is mainly in non-cemented fixed prosthesis. Osteolysis around non-cemented prosthesis is expansive, and patients can have a large range of osteolysis without any symptoms, which can be treated by lesion removal + bone grafting; if loosening of the prosthesis occurs, revision is not controversial.
Efforts are also being made to find non-surgical means of treating osteolysis, mainly by inhibiting the production and transmission of pre-inflammatory signals caused by wear particles, and by research in two directions: antiosteoclast activity. Anti-inflammatory analgesics, hexoketococine and sodium allantoin phosphate have been shown to have an inhibitory effect on periprosthetic osteolysis. However, none of these drugs has yet been approved for clinical use in the treatment of osteolysis.
Antagonist applications of RANK proteins have been found to be the most promising therapeutic tools, the most important of which is OPG, which is currently being tested for the treatment of osteolysis by means of gene therapy for the sustained secretion of OPG protein around the prosthesis.