Introduction
The 20th and 21st centuries are a landmark epoch in the evolution of the field of medicine including the discovery and advancement of the hip replacement technique. Hip replacement stands out as a great breakthrough in the treatment of hip complications that can no longer respond to other normal therapy.
When the hip deteriorates, it leads to complications and pain during movement of the legs thus making walking a painful affair. This scenario is attributed to the wearing out of the hip joints, which are usually made up of cartilage tissues that provide a smooth ball joint effect during movement.
The wearing out of the cartilage tissue due to such complications like arthritis has been cited as the major cause of damage to the hip joint leading to need for hip replacement.
Hip replacement also happens in case of an accident and the femur is damaged close to the hip in a way that it cannot be repaired. Metal on metal hip replacement was hailed as a success when it was invented, but it has recently come under criticism due to failures and side effects that have been reported on persons using the procedure.
Materials and Design
There are “different types of hip implants in the market and all of them are meant to perform the same function” (Ziaee et al. 2007, p.304). The difference that makes implants different from one another is the material used to manufacture the implant coupled with how it is attached to the body of the patient.
All the implants made so far have been found to be good enough in serving their purpose though they have differences that tend to inform their choice.
Metal on metal hip prosthesis involves the use of a metal ball as the femoral head, which is connected to a metallic femoral stem running along the thighbone and joined at the hip with a metal cup known as the acetabular component, which is attached to the hip to make up the complete metal on metal hip joint.
This condition is usually referred to as a complete hip replacement because the whole hip joint, which is a ball and socket will be made up by the metal. There is also metal on metal resurfacing whereby the ball joint is simply resurfaced and a metal cap is fitted on it to give the worn out joint a new ball. The “acetabular component is also replaced with a metallic socket” (Issa 2013, p.6).
Another type of the implant is the metal on polyethylene type of hip replacement and it involves the use of a replaced metal ball joint at the end of the femur and a plastic acetabular, or can have the socket lined with plastic.
There is also a ceramic material on metal hip replacement prosthesis, which has been hailed as a better solution to the problems posed by metal on metal hip prosthesis for it is resistant to the wear and tear associated with metal and polyethylene joint replacements.
There is also ceramic on ceramic joint replacements well as ceramic on polyethylene replacements. When polyethylene is used in most cases, it is used as the acetabular component to make up the socket.
Source: Samelco et al. 2013, p.5.
Clinical and Safety Efficacy
Implants like other medical procedures are meant to provide a medical solution that will better the condition of the patients by alleviating them from their present day problems and making them feel better. However, this achievement does not come without a hitch because like all artificial solutions, implants also have their own manifested complications that cannot be avoided once they have been applied.
The same situation applies to metal-to-metal hip prosthesis and they have received positive reviews as well as negative reviews. So far, metal-to-metal hip prosthesis has been found to have clinical efficacy and that is why it has been applied as a solution to the hip joint problem.
One of the biggest problems that have bedeviled this type of implant is the rate of failure that has been recorded immediately after the patients have had the implants.
Metal-to-metal hip implants have recorded an up to 5% failure within the first six years of the operation being performed (p.1). This problem has been attributed to metal debris that is formed during the friction between the metallic ball joint and socket.
In their research to establish hypoxia related effects in patients who have undergone this procedure, Samelco et al. 2013 found that too much exposure coming from the metal debris like Cobalt-chromium-molybdenum alloy leads to the development of other infections to the patient thus making the implant unsafe.
The metal-to-metal implants have been found to produce debris that leads to inflammation and tissue damage (Samelco et al. 2013). The researcher’s conclusion found that the debris produced was responsible for creating a hypoxic environment, which in turn led to the inflammation of tissues. This condition further led to the implanted joints coming off due to bone deterioration.
Inabo (2006) presents findings about Candida infections in medical implants. Under these findings, metal-to-metal hip implants are named as one of the implants that are susceptible to Candida infection.
The reason for the high rate of Candida infections is the long hours a patient takes on the operating table when the prosthesis is being fixed. However, this occurrence is not exclusive to metal on metal hip replacements only, but to almost all forms of prosthesis replacements.
The metal on metal hip prosthesis became popular due to its long life advantage as other prosthesis would either be susceptible to breaking or wearing out thus requiring the patient to undergo further operations to replace the replacement. According to a research by Ziaee et al. (2007), the metal on metal hip joint prosthesis has a side effect on the fetus being carried by a pregnant mother who has this kind of hip implant.
The metals used to make the prosthesis, in this case an alloy that includes cobalt and chromium, usually releases metal ions that get absorbed in the blood and can be transported through the mother’s placenta to the fetus.
The absorption of this kind of minerals by the unborn baby leads to mineral imbalances in the developing fetus leading to deformity of the fetus before and after birth. Therefore, the side effects that are found in the use of metal on metal implants are proving to be medically negative than the said solutions they provide.
Ziaee et al. (2007) further report that the solubility of the metal ions of chromium and cobalt makes them easy to transport through body fluids and can be found when tests are made on blood and urine of the patient. The use of metal for both the ball and socket makes it almost inevitable for this problem to occur for hip joint is the focal point of movement by legs thus there must be friction when it occurs.
The debris that is usually produced in this case is so fine that it is easily absorbable in the body fluids and further transported to other parts of the body. Ziaee et al. (2007) note that, whereas cobalt and chromium are essential trace elements needed by the body, excessive administration of cobalt can lead to the development of diseases like goiter and to some extent cardiomyopathy.
When metal on metal hip implants were adopted for use in the medical practice, the researchers were confident that the alloys used would be strong enough to resist the wear and tear that is being experienced at the time. Caution has been laid on the use of this form of hip replacement with many governments tightening the application of the procedure.
Though the metal on metal hip implant has come under a lot of criticism and caution, it has been widely recommended for younger people because it is an implant that is supposed to last a lifetime. At the same time, its strength allows a younger person to continue engaging in exerting activities at all times without a problem.
Initially, hip implants or commonly referred to as replacements were meant for older people who needed them when their bones could no longer hold due to age related medical problems. However, with new discoveries, even young people can be accorded the service if recommended by the doctors.
One of the biggest side effects of introducing foreign bodies into the human body has been the risk of developing cancerous cells by the recipient of such a service. The carcinogenic potential of the chromium and cobalt has led to many researchers asking the question if the debris from these two metals can lead to the development of cancer.
Lalmohammed et al. (2013) conducted one of these researches with a group of other scientists who came out to investigate the risk of cancer from metal on metal implants as compared to other implants. On the positive side, Lalmohamed et al. (2013) found that there is no evidence to show so far that the metal debris from the chromium and cobalt alloys can lead to the development of cancerous cells.
The research indicates that the metal on metal hip replacement has a lower cancer risk on patients as compared to other procedures that use different materials. Lalmohammed et al. (2013) note, “The risk of cancer increased over time in both THR patients and referent subjects….
Patients on MoM hip devices remained constant …” (p. 4). Therefore, the only conclusion that can come out of this finding is that the metal on metal hip device is a better choice when it comes to running the risk of someone developing cancer.
Other types of implants tend to increase the risk of developing cancer with time, which thus makes patients with those types of implants to be highly susceptible to cancer. This aspect though does not rule out the risk factors of cancer from this type of hip transplant because as the researchers put it, there is a need to develop a highly dependable database that will bring all factors together in order to make the research conclusive.
According to Deborah Cohen, an investigative writer with the British Medical Journal, the use of metal on metal implants has been controversial for a long time. Cohen (2012) poses the question, “why are patients still exposed to the harm of metal implant failures identified in 1975?” (p. 4).
According to Cohen (2012), a drive by the companies manufacturing these implants to achieve commercial success has overridden the concerns to observe patients safety because the same problems that were identified a long time ago are still being observed to date.
Cohen (2012) notes that the conventional total hip replacement should be made up of a metal head, which will be inserted into a polyethylene cup. However, this replacement does not last long because it tends to wear out sooner than the metal on metal implant thus cannot work well with young people (p. 4).
Young people using this type of implant would need to undertake revision surgery to replace the worn out part, which is the plastic cup. Ideally, this mode is meant for older people who are not very active. Cohen (2012) further finds that manufacturers of the metal on metal hip implants have engaged in unethical practices, which have led to many cases of malfunctioning metal on metal implants on patients.
Manufacturers have been found to circumvent the ethical considerations of the industry by secretly tweaking designs of the implants when complains were raised. The ideal situation required is that manufacturers should alert patients and regulators of their concern.
Consequently, “the regulators in both Europe and the United States failed to identify the design changes and the consequences they would have on patients” (Cohen 2012, p.3). This failure by the entire system has put at risk patients who have undergone this procedure because there is no fallback position to their problems.
Although metal-to-metal hip implants have been receiving a lot of criticism, its outcomes have been viewed as better compared to other forms of implants. Issa et al. (2013) posit that the metal on metal resurfacing comes out as a better solution than other orthroplasty procedures (p. 1).
The researchers found that the metal on metal hip resurfacing offers superior retention of biomechanical characteristics that should be found in a normal hip joint than other orthroplasty procedures. The challenge of surgeons has been the achievement of precision in the fixing of the implants.
In most cases, patients have tended to feel or to find out that the legs that have undergone the procedure tend to be longer than the other leg. Therefore, the achievement of greater biomechanical characteristics as provided by metal on metal hip resurfacing is a great success.
Hip resurfacing tends to reduce many dangers that face patients who have had hip implants as they have recorded lower dislocation rates together with higher femoral bone preservation. The research further records the success rate of this procedure to be at around 94% with easier revision surgeries being recorded.
Metal on metal hip resurfacing though still faces the same problem of metal alloys deposition and just like all metal on metal implants, it ends up producing debris that ends up in the patients system. The challenge that this debris deposits problem poses is the lack of long-term records that have been developed to offer a background study on the problem, thus leaving the researchers in a no man’s land.
Cohen (2012) laments, “Little knowledge on the transportation, distribution and excretion of metal ions has not helped the cause.” (p. 2). This assertion holds because the toxic threshold of the metals being deposited in the body has not been determined and thus poses a risk to the continuous use of these implants by patients.
The success of the implants depends on several factors that have to be observed when the whole procedure is being undertaken. There has to be collaboration between the doctor fixing the implant and the manufacturers of the device so that the doctor finds a perfect fix. Each patient has his/her unique characteristics that have to be noted so that the correct placement and implantation is made.
According to Marker et al. (2010), the component positioning of the implant has a great effect on the success of the implant. Therefore, precision of all the components in play should be observed and achieved at the highest level.
Conclusion
The use of the metal on metal hip replacement is slowly becoming a failure according to the many negative reviews that this type of hip replacement is getting. Although the metal on metal prosthesis is the best for young people who have a longer life to live as well as activities to engage in, the lack of a solution for the debris produced during movement is a worry to medical practitioners.
At the same time, the lack of knowledge on the threshold amount from the alloy debris that can be said to be dangerous also leaves the medical practitioners groping in the darkness about the possible future side effects.
Reference List
Cohen, D 2012, ‘How Safe are Metal on Metal hip Implants’, British Medical Journal, vol. 344 no.1, pp. 1-7.
Inabo, H 2006, ‘The Significance of Candida Infections of Medical Implants’, Science Research and Essay, vol. 1 no.1, pp. 8-10.
Issa, K, Palich, A., Tatevossian, T, Kapadia, B, Naziri, Q & Mont, M 2013, ‘The outcomes of hip resurfacing compared to standard primary total hip arthoplasty in men’, BMC Musculoskeletal Disorders, vol.14 no.161, pp. 1-7.
Lalmohammed, A, MacGregor, A, Uries, F, Leufkens, H & Staa, T 2013, ‘Patterns of risk of cancer in patients with metal on metal hip replacement versus other bearing surface types: a record linkage study between a prospective joint registry and general practice electronic health records in England’, PLOS One, vol. 8 no.7, pp. 1-7.
Marker, D, Zywiel, M, Jason, A, Thorsten, S & Mont, M 2010, ‘Are component positioning and prosthesis size associated with hip resurfacing failure’, BMC Musculoskeletal Disorders, vol. 11 no.1, pp. 227-233.
Samelco, L, Caicedo, M, Lim, S, Della-Valle, C, Jacobs, J & Hallab, N 2013, ‘Cobalt alloy implant debris induce hif-1 hypoxia associated responses: a mechanism for metal specific orthopedic implant failure’, PLOS One, vol.8 no.6, pp. 1-7.
Ziaee, H, Daniels, J, Datta, K, Blunt, S & McMinn 2007, ‘Transplacental transfer of cobalt and chromium in patients with metal on metal hip orthroplasty’, The Journal of Bone Joint Surgery, vol. 89 no.3, pp. 301-305.