Discussion about Hip Resurfacing
In public and even by medical colleagues many claims were made which lead to uncertainty of the patients or were meant to advertise or anti-advertise.
In particular frequent complications after the so-called cap protheses or McMinn prostheses, excessive bone loss on the pelvis side and dangerous wear behavior were highlighted.
A large English retrospective analysis came to the conclusion that even without an interaction of age or gender the mortality in hip resurfacing is lower than with standard prostheses of all materials.
The facts are presented here.
As a typical complication after hip resurfacing the femoral neck fracture is named. In fact the neck fracture is essentially a complication of the inexperienced surgeon. All published individual statistics show an increased revision rate due to a femoral neck fracture in the learning phase. An experienced surgeon can minimize this risk by selecting the right surgical technique. This includes, for example, the correct position of the head in order to prevent notching of the femoral neck, a sufficient shortening of the head to cover the prepared parts of the head completely with the cap. The residual risk of postoperative neck fracture is then about 0.5% in context of the risk of fractures in standard hip prostheses (blast of the femur through the inserted shaft).
The special risks associated with large defects in the femoral head or cases of anatomically inadequate situations should be discussed with the surgeon before the operation, and the use of the surface substitute is then weighed out from these points of view.
The original implant and its also successfully used copies are particularly suitable for men. However the smaller sizes used in women are more endangered since they can only function properly with exact positioning to minimize wear, but then can also be just as durable. The average revision rate after 10 years is 10% for women and 5% for men.
A number of other implants on the market were problematic, which were subject to wear more quickly due to their low surface resistance due to modified designs and modified material compositions. When the increased failure rate became known they had to be withdrawn from the market. This was a necessary step, but had a great deal of attention, and left the other implants in bad light.
Bone loss on the pelvis side
The artificial hip socket is generally the biggest problem in time after hip replacement: Cup loosening is more common than stem loosening. Therefore the bone loss in this area should be kept as small as possible in order to obtain sufficient bone for a new cup in the case of possible subsequent revision surgery. With correct choice of implants and implant sizes, bone loss in the pelvis is not greater than in standard prostheses. The size of the cup and the corresponding femoral head are largely identical in size to the sizes before surgery. Only in case of usage of a standard prostheses it is different. There a smaller head is used for the same size of cup in order to reduce the wear and to maintain the polyethylene longer. However this results in an increased risk of dislocation with only a very small up to no risk of dislocation in case of hip resurfacing.
All usable materials are subject to wear, as the natural joint has worn out over the years. Metallic implants such as nails, screws, plates and also endoprostheses have been successfully used in surgery for 60 years. To a very small extent they underlie corrosion in the aggressive milieu of the body. This often lead to an imperceptible but measurable increase in the already existing and vital metal ion concentration in the blood. Many do not know that as humans, we have cobalt and chromium in the body and that we would not be survive without them. In case of joint friction with a metal-metal pairing, metal particles, which are temporarily stored in the body and are “dissolved” in the body in the course of time are released at least in the first year after implantation in order to be excreted via the kidneys at the end. Often the increase of the metal ion concentration is no longer detectable in later course and decreases to normal values. Through the choice of the clearance (avoiding clamping effects) or by means of alternative friction partners (in future perhaps metal on poly in case of small implant sizes), the wear particles are reduced. However physical limits are encountered. A joint with metallic or ceramic friction is only well-lubricated with a fast movement, slow movements or even standstill (standing or sitting) lead to reduce the lubrication film and thus lead to a direct contact of the joint partners with higher friction.
The concentrations of metal ions are very low and are measured in “ppb” ranges (part per billion). In principle the possible increase in metal ion levels is undesirable but also unavoidable.
While relatively high metal ionic levels can be measured after insertion of knee prostheses, this fact has never been discussed in knee prostheses. The hip joints with metal-metal pairing however have been under discussion for 60 years. Country-wide studies for almost 30 years for example have not shown an increase of cancer risk. There has even been evidence that lung cancer is less likely to occur when metal implants are used.
The term McMinn prosthesis
The McMinn prosthesis goes back to the English orthopedic surgeon Dr. Derek McMinn from Birmingham, who has led to a great success starting in the 1990s through the use of proven metal compositions. Previous attempts (example: Wagner cap) were essentially unsuccessful because of material problems. The success attracted other manufacturers to develop their own prostheses and bring them on the market. This was especially important for large companies. Today the term “McMinn prosthesis” is often used incorrectly for implants which only resemble McMinn’s original development and which unfortunately were not so successful due to their fundamental changes. As in case of metal a distinction is not made between the McMinn prosthesis and the non-Mc-Minn prosthesis, but in most cases generalization was made. The original product has been on the market since 1997, for example also in the US.
Although the metal ions are generally undesirable but with correct positioning of the implants they are not dangerous and can not be avoided in the initial phase. The complication rate, the suspicion of bone loss in the pelvis, the metal wear and the specific implant type require a differentiated view.
It has to be noted that most specialists for hip resurfacing know the problems and discuss the advantages and disadvantages with the patients carefully and responsibly. On the other hand, the “reports” published by colleagues in some uncritical media appear to be unsuitable and irresponsible. Apparently they mainly serve a representation at the expense of patients, who wish to receive serious counseling due to there disease, but are disconcerted by this misleading kind of information.
And as a last note: Every doctor is obligated to provide full information about alternative procedures (eg: arthroscopy, hip resurfacing, short stems, cemented or cementless standard prosthesis, or conservative procedures, i.e. no surgery). And every surgeon who performs hip resurfacing has a great experience with standard hip replacement, which he usually performs as his standard procedure. Thats not the case vice versa.