Frequently asked questions – concerning hip surgery
· What is the surface treatment on the hip joint?
· Why is the surface replacement of the hips recommended by some doctors?
· What are the advantages of surface replacement?
· What are the disadvantages of surface replacement of the hip?
· The range of joint motion following a cap prosthesis should be greater than that following conventional hip prostheses – is that true?
· Are there differences between the different cap prostheses of the individual manufacturers?
· What should be considered in the after-treatment?
· Under what conditions is surface replacement of the hip joint possible?
· Up to what age is surface replacement possible?
· Should I expect additional costs for the cap prosthesis?
· Is the cap prosthesis a ‘minimally invasive’ operation?
· What is an arthrosis on the hip joint and how does it come about?
· How can the development of arthrosis be influenced positively or slowed down?
· Do so-called cartilage building syringes help?
· Can cartilage transplantation help?
· How long does an artificial hip joint last for?
· What is the procedure in an operation?
· Additional questions to the Joint Centre Berlin
What is the surface treatment on the hip joint?
Actually, osteoarthritis is a cartilage disease, and if the cartilage is lost, the replacement of the cartilage is the treatment of choice. Even if the new methods for cartilage cultivation appear to be promising, the present possibilities are not sufficient to restore the entire load-bearing surface of a joint. Even from when replacement of the hip joint started, attempts have been made to cover the bone with artificial materials. Previously, the methods failed due to the inadequate properties of the artificial surfaces, which were either not stable enough for the high loads or led to high wear with corresponding consequences. The introduction of the metal-metal pairing into the surface replacement of the hip by Derek McMinn proved to be the first reliable medium-term successes. To date, the materials made of cobalt-chromium alloys, which have also been tested in the conventional endoprosthetics of the hip, have kept up with the natural stresses.
Why is the surface replacement of the hips recommended by some doctors?
The long-term connection of living bone with artificial materials is temporally limited for various reasons. Long term, material wear and/or modification processes in the living substance lead to a relaxation of the artificial joints which are used. If the artificial joint then has to take exchanged, the bony bearings of the prosthesis parts are often so severely damaged or altered that the following artificial joint has a poorer long-term outlook. Surface replacement prostheses do not usually lead to extensive changes with a deterioration of the bone structure. As such, during the exchange operation, the conditions of the bony structures are improved to a greater extent than following the failure of prostheses with shafts. This applies both to the surface prostheses of the hip and knee as well as to the so-called short-shaft prostheses or ‘metaphyseal’ prostheses of the hip joint, e.g. the pressure disc prosthesis based on Huggler and Jacob.
What are the advantages of surface replacement?
If it is only the surface that needs to be replaced during the first operation, the adjacent structures of the bone remain functional and anatomically intact. This also applies to the sensitive structures of the joint system, so that the comparatively rapid recovery of the functional capability of the joint can be understood in this way. For operations that are required in earlier ages in life, the preservation of the natural neighbouring structures also has the advantage of preserving intact sections of articulated bones for a standard prosthesis, in the event of a change in the surface joint being necessary.
What are the disadvantages of surface replacement of the hip?
First of all, the long-term results are not yet known. Derek McMinn carried out the first implantations in 1991; the surface replacement of the hip has only been used since about 1996 in greater volumes. Therefore, meaningful 10-year results from in-dependent users are not yet available. In terms of abrasion, mechanical durability over 30 years would be conceivable. However, there are justifiable concerns against the surface replacement of the hip:
In addition to the ‘usual’ risks (thrombosis, embolism, bleeding, nerve damage, inflammation, relaxation, luxation, etc.), the surface prostheses have a few disadvantages which go against uncritical general use:
1. The most frequent special complication is a possible fracture of the femur of the neck (frequency between 0.5% and 1.5% of cases) in the first 10 weeks after the ope-ration. Corresponding relief for this period and careful rehabilitation therefore appears necessary (walking sticks, no weight training, no exercises against resistance or on the long lever).
2. The dying back of the bone under the hip cap (0.5%), which can lead to slipping of the cap within one to two years, is less frequent.
3. Time and again, users are warned of the metallic abrasion caused by the friction in the metal-metal joint. Although the prostheses (as fixed bodies) are stable in the body as such as precious metals , the tiny particles from the abrasion in the body are either absorbed or stored in certain cells or chemically attacked and dissolved, resulting in increased levels of cobalt and chromium in the blood. So far, it has not been possible to safely exclude or prove the suspicion of germ cell damage or a long-term risk, e.g. with regard to the advancement of tumours. However, long-term studies involving metal-metal joints from the 1960s speak against tumour risk as a result of metal ablation through endoprostheses.
4. There are also concerns about possible allergic reactions following metal abrasion. It has not yet been possible to compile unambiguous data (as of 2004), however the risk is very low. Skin tests for an allergy to cobalt or chromium do not suggest possible reactions in the body and as such, are not recommended before an operation. Alternative materials (ceramics) are not available. Materials which are better tolerated, such as titanium, are not stable enough.
The range of joint motion following a cap prosthesis should be greater than that following conventional hip prostheses – is that true?
The hip is a ball joint, in which a ball can move in a roughly hemispherical socket until the neck of the prosthesis strikes against the edge of the socket. This indicates the importance of the relationship between the ball diameter and the femoral neck diameter: If, in the case of a standard prosthesis and a ball (with a diameter of 28 mm) there is a range of motion of approx. 124°, and in the case of a 32 mm diameter ball of 32 mm, a range of movement of approx. 135 °, there is an advantage in having large balls. This is the case if the neck of the standard metallic prosthesis remains as thin as the conventional standard prosthesis. However, the natural and relatively thick femoral neck remains in the case of the cap prosthesis. This means that an early abutment can occur. If the bone is saved in the old socket of the hip joint and the smallest possible socket is used, the smallest possible ball head is used. Then, the range of motion of such a surface joint is only about 90°. With a further motion strike, the femoral neck is struck against the edge of the socket and it is possible that the hip head cap levers out of the joint slightly, which, for example, leads to an uneasy feeling and sometimes, a click in the joint. In short – a surface replacement has a smaller range of motion than a standard prosthesis.
Are there differences between the different cap prostheses of the individual manufacturers?
All surface substitutes are made from cobalt, chromium, and molybdenum alloys with a carbon additive which causes the stability of the material through the formation of carbides. Other important features with regard to long-term stability include roundness (surface irregularities) and the joint gap (radial difference between the socket and cap, ‘clearance’). In particular, the shape and size of the carbides are discussed. To date, there are no reliable data that reliably document the materials of one, or the other manufacturer. Until further notice, the choice of a product depends on the availability of a suitable size for the individual case. In any case, the material must be hard enough (i.e., contain sufficient carbides) and the surface finish must meet certain tolerances.
What should be considered in the after-treatment?
The most important complication is a fracture of the neck of the femur in the first weeks after the operation. Causes include the mechanical weakening of the bone as a result of the necessary operative measures or the fatigue fractures of the bone trabeculae due to the stressing of the femoral neck during the first weeks, during which the muscles overlapping the hip joint
cannot yet compensate the flexion of the femoral neck. All exercises should therefore to be omitted for six weeks , two long under arm rests should be used on longer walks. Driving is not allowed for six weeks due to the lack of coordination. Please discuss the postoperative limitations in detail with the physician providing the treatment.
Under what conditions is surface replacement of the hip joint possible?
The surface replacement only replaces the cartilage. If the bone under the cartilage is substantially damaged in terms of shape or structure, replacement of the surface by means of a cap prosthesis is often no longer possible. In such cases, for example, if there is osteoarthrosis caused by congenital dysplasia, necrosis of the femoral head, or a condition following a separation of the epiphysis, a decision must be taken in the individual case according to the radiograph. Please present your X-ray photos to the operating doctor of your choice. In borderline cases it is often possible to decide whether surface replacement by means of a cap prosthesis is possible or whether alternative prosthesis models have to be used.
Up to what age is surface replacement possible?
As can be seen from the above, the cap prosthesis provides a solution for younger patients who are unlikely to get along with a prosthesis because of long life expectancy. The surface replacement is, so to speak, a ‘preliminary prosthesis’. For older patients, the existing hip prostheses represent excellent and safe implants. However, anyone who wishes a ‘bone-saving’ prosthesis model should have a suitable bone structure because of the specific risks mentioned. Wide scale bone defects or advanced osteoporosis are factors which go against surface replacement. The decision for or against the cap prosthesis should be discussed in detail with the operating doctor.
Should I expect additional costs for the cap prosthesis?
The diagnosis-related groups (DRGs) applicable in Germany set a defined amount of money for the material costs (implants) and the staff costs in the operating room. Cap prostheses are much more expensive than shaft prostheses; furthermore, the staffing costs are higher because of the longer surgery time. Many hospitals therefore reject the use of the cap prostheses at a standard rate for the DRGs and demand additional fees in terms of an ‘elective implant’. Consult the hospital of your choice for information about the additional costs. Private health insurance companies also do not honor the fees for special medical work performed by the doctor (duration of the operation, technical difficulty), so that, depending on the health insurance company, there may be own contributions in the doctor’s invoice.
Is the cap prosthesis a ‘minimally invasive’ operation?
As the femoral head is retained in this method, access to the socket is much more difficult from a technical point of view and the procedure usually requires a longer cut. Even if today, an attempt is made to apply a surface replacement very gently, the skin incision and the intervention in the muscle region are more complex and widespread than in the case of shaft prostheses.
What is an arthrosis on the hip joint and how does it come about?
In addition to the knee joint, the hip joint is one of the joints of human movement that is most frequently affected by arthritis, the excessive wear of the articular cartilage. The causes of this excessive and premature wear of the cartilage and the accompanying pain in the hip joint are numerous. Family-related disposition is the most frequent reason. But also a misalignment of the femoral head (too steep or too shallow: Coxa valga or Coxa vara) can lead to an excessive wear of the articular cartilage on the acetabular cup and femoral head during the course of life. Furthermore, chronic inflammatory diseases, such as rheumatism (correctly: rheumatoid arthritis or pcP = primary chronic polyarthritis), can lead to a destruction of the articular cartilage lasting for many years. Another cause is the destruction of the cartilage or the articular surfaces after injury, so-called posttraumatic arthrosis. Not infrequently, as part of the protection of the affected leg, there is too much strain on adjacent joints and the spine. At the end of a long-standing history of disease, the only effective solution to the problem is the implantation of an artificial hip joint.
How can the development of arthrosis be influenced positively or slowed down?
Even younger people can be affected by pain in the vicinity of hip joints. If there is an in-depth examination and the radiograph associated with it results in a condition-induced misalignment of the femoral head (too steep or too shallow, Coxa valga, or Coxa vara), the correction of this angle by means of an operation can eliminate the pain and slow down the progress of developing arthrosis. Through this, the possible need for an implantation of an artificial hip joint can be eliminated or at least delayed for several years.
Do so-called cartilage building syringes help?
The injection of so-called cartilage building syringes into the affected joint is something which is still highly controversial. To date, independent scientific studies have not shown convincing evidence that it benefits the worn cartilage in any way. Temporary pain relief is often achieved by the anti-inflammatory substances which are also administered in combination, but not by any repairing of the articular cartilage.
Can cartilage transplantation help?
Arthrosis of the hip joint relates to widespread cartilage damage. In such cases, cartilage transplantation alone is impossible because of the size of the surface to be resected. However, unlike the knee joint, it has never been possible to repair minor accident-reated defects to the hip joint by transplanting cartilage. This mainly depends on the unfavorable accessibility and the unfavorable distribution of force at the hip joint.
How long does an artificial hip joint last for?
Average service life of the cement-free implanted implant made of titanium and used by us (CLS shaft, Manufacturer: Centerpulse, RM socket, Manufacturer: Mathys) is over 95% after 15 years. This means that, after a period of 15 years, the hip prosthesis did not have to be replaced because of loosening. In exceptional cases (in very elderly patients, which are dependent on immediate full stress after the operation), we use our own cemented hip shaft, the RR shaft which has been developed by us and manufactured by Merete, Berlin on our behalf.
What is the procedure in an operation?
The patient is usually admitted on the day before the operation. They are visited by the surgeons and the anesthetist, and the procedure is explained again in detail.
The operation on the following day takes approx. 1-1.5 hrs. Physiotherapy starts on the day after surgery. The patient stands up and from the 2nd day after the operation, walking is performed with the crutches. The leg that has been operated on should only be stressed with half the body weight in the first 4 weeks after the operation. This is in order to allow secure healing of the cement-free prosthesis in the bone. In the 5th week the leg that has been operated on can be fully stressed and at the end of the 6th week, the crutches can be dispensed with gradually.
It is self-evident that many questions remain unanswered.
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