Replacement Ceramic Hip Joints

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Replacement Ceramic Hip Joints

1. Executive Summary

Rennib Advanced Ceramics (RAC) Ltd is an advanced ceramics manufacturing company, which provides various ceramic products covering a very wide area. Artificial hip joint will be a very competitive ceramic product for RAC during the next few years.

The clients of the product are patients suffering various hip problems. Artificial hip joint offers patients a good chance to replace their original hip joint with an artificial one.

RAC can provide different types of artificial hip joints to meet the different demands of different customers. Considering the ages of the customers, different choices can be made. Most young patients are suggested to choose a product with ceramic femoral head which has a longer service life and higher cost than alloy products.

Usually, those high performance ceramic femoral heads consist of alumina or zirconia. A better choice is to oxidise the zirconium surface with a metal femoral head inside, which reaches a compromise to provide both high wear resistance and low cost.

Currently, the processing techniques used in making ceramic hip implants are hot isostatic pressing and colloidal processing. New fast sintering techniques, such as 'Spark Plasma' and 'Microwave Sintering' or even fast heating rate furnaces are now available. Since new techniques are not mature enough, most of them remain in the laboratory stage and various problems still exist.

Based on the size of the current hip replacement market, there still exists very large market potential for the reason that the demands of the artificial hip joints have been increasing stably since 2000. The prediction is that the increasing trend will still maintain an upward momentum in the next few years.

RAC will be in an excellent position if the Board members of the company decide to invest more power on researching and developing new techniques to cut the cost of production without the expense of product quality.

RAC's marketing strategy is to keep focusing on the product quality. The patients, for instance, will feel comfortable to choose our product without hesitation for the reason of high product quality. All RAC's artificial hip joints will be strictly tested prior to selling.

2. Ceramic Replacement Hip Joints

British orthopaedist Sir John Charnley is accredited by many as the first person to complete a total hip replacement in 1960, although developments in the practise had been well underway since the early 1900s [1]. Charnley's joint was made up of a metal femoral stem and ball head that attached to the bone using PMMA and this then inserted into a replacement socket joint made from ultra high molecular weight polyethylene, which was also bonded to the existing hip using PMMA [1].

Since Charnley's creation, many other materials have been tried and tested in the production and use for replacement hip joints. The metal on polymer structure of the joint was used for many years but patients often needed repeat operations due to the life span of the metal on polymer joint being too short. The ceramics alumina and zirconia were introduced as potential new materials in the early 1970s and 1980s respectively [1]. This was because they were found to be far more wear resistant and therfore, although more expensive to buy and manufacture, they decreased the likely hood of patients requiring multiple surgeries in their lifetimes.

Currently under consideration is the possible use of non oxide ceramics to be used in replacement joints. Examples of these are silicon carbide or silicon nitride and they are under consideration because of their near immunity to the slow growth of cracks [2]. This property would further increase the life span of a replacement joint if either non oxide were to be used and would create a joint even more superior to one made from alumina or zirconia. The high crack resistance also relates to a higher overall strength, therefore an improved wear resistance of the product over the ceramics currently used. However, due to these non oxide ceramics being harder and more wear resistant, they also become more difficult to process thus making them more expensive to buy and manufacture [2].


Generally, artificial hip joints are utilized in the orthopaedic surgical field. The final buyers are patients suffering from various hip problems including osteoarthritis, rheumatoid arthritis, traumatic arthritis and avascular necrosis [3]. According to King [4], the artificial joints market is valued at about $12.2 billion in 2008, within which hip and knee replacements act as one of the key segments. Considering of the large market demand, a market analysis is essential to evaluate the possible market potential.

3.1. Current Market

In a Datamonitor report of hip and knee replacement market [5], the contribution of the US is nearly 50% of total procedures worldwide and the contribution of Europe is around 30%. This statistics show that the US and Europe are the two largest markets for hip and knee implants on a global scale.

According to the Datamonitor's market data [5], "the 2005 revenues for hip implants in the US were $2 billion and that for Europe was $1.4 billion". Taking the US market for example, the total hip replacement procedures (including hip resurfacing) number was 368,660 in 2005 [5].

Another example is the data of the Australian orthopaedic market. According to a global market research [6], "there were approximately 72,007 joint replacement operations performed".

3.2. Future Growth

A statistical data cited by The New York Times [7] shows that "the number of total hip replacements has risen by almost 80% since 2000".

The number of total US hip replacements have been growing stably since 2000. It is expected that this trend will be a sustainable growth in the next few years.

3.3. International Competitors

The 10 biggest worldwide orthopaedic device manufacturers in 2007 were listed in Table 1 as follow, according to a top companies report [8].

Within Table 1, 7 companies of the top 10 are now manufacturing the artificial hip joints and regard this product as one of their main products to make profits. They are Stryker Corp, DePuy, Zimmer Holdings, Smith & Newphew, Biomet, DJO Incorporated and Wright Medical [8].

Using 2005 US knee replacement market share for reference (the hip replacement market data is difficult to obtain) [5], the main competitors are very obvious as follow.


The three components of an artificial hip joint can each be manufactured from a number of materials. To make a new lining for the hip socket, a cup can be made from polyethylene. However, polythene cups do not have great wear resistance and the constant rubbing of the harder ball inside the softer polymer cup can erode it and leave debris in the joint that can further increase erosion rate. This can result in the replacement joint needing replacing and a patient having to undergo more than one operation in their lifetime. This means that metal or ceramic cups are often used because although more expensive to produce, they offer a longer life and reduce the chance of a repeat operation [9]. The stem that attaches to the existing femur is today made from either titanium or cobalt or chromium based alloys. Finally, the femoral head is usually made of either metal or a ceramic such as alumina or zirconia [9].

If a cobalt-chrome alloy is used to make the femoral head of an artificial hip implant, it can be manufactured by means of grinding and polishing to achieve an accurate spherical shape at a relatively low cost. The problem with an alloy femoral head, though, is that it does not have such good wear resistance when paired with a polyethylene cup. The wear creates more debris, which can make the surface of the head rougher, thus further increasing wear and the likely hood of the patient requiring another replacement joint. The life of a replacement hip can be increased if a ceramic is used. A ceramic femoral head can be produced using the same grinding method but due to it being far harder than the alloy, it is more expensive to manufacture but will offer superior wear resistance to that of the alloy femoral head.

Above images show a machine similar to the one Smith and Nephew use in the production of their femoral heads and a close up of a femoral head and cutting tool.

So, there is a dilemma. Does one cut production costs by using inferior materials, but increase the chance of the components wearing out? Or should superior materials, which increase the production cost but also the product life, be used? Smith and Nephew are a Memphis based firm that manufacturer and supply a range of different joint replacements. They offer hip replacement systems with different femoral heads; cobalt-chrome alloy, alumina or zirconia. Researchers at Smith and Nephew discovered that zirconium could be oxidised to result in a metal with a ceramic (zirconia) surface.  This made them consider, that if they could machine zirconium to the desired dimensions as easily as they could with the cobalt-chrome alloy then they could oxidise it to give the best of both worlds; the cheaper production costs available using a metal but with a hardened and more wear resistant surface of a ceramic. [10]

5. Processing Routes In the Development in Ceramic Artificial Hip Joints

Ceramic hip joints can normally be formed through production of a green compact which is then sintered/hot isostactically pressed using Zirconia(ZrO2) or more commonly Alumina(Al2O3) powder. However in this modern day environment the hip joint has many variables and many variable material combinations such as ceramic/ceramic wear couple or ceramic/polyethene wear couple[11]. Therefore the each component can be processed differently.

Ceramic materials are known to be brittle and susceptible to slow crack growth. In medical use when in the hip joint, one of the main problems is that the ceramic ball undergoes wear and can then fracture. Modern ceramic bearings have much greater properties and reliability compared with previous generations of the same material. Controlling the starting materials such as the purity, and improved manufacturing processes have led to great improvements in both these areas. Current procedures include tightly controlled ceramic processing methods for homogeneous mixing and consolidation of the powders, and processing environments such as clean-room facilities to minimize inclusions and impurities. The first generation of Al2O3 bearings was produced by sintering. Today, hot isostatic pressing is commonly used to guarantee the production of an almost fully dense material with a fine grain size.

The process used by 'Ceram Tec' is used commonly by other manufacturers to create the femoral ball of the hip joint: Firstly a high purity powder of Alumina is used as the product needs to have maximal mechanical properties therefore the purity needs to be high or else the mechanical properties will drop. The powder then undergoes cold isostatic pressing where the powder is enclosed in a bag then submerged in water and pumped to high pressure to compress and shape the powder. This achieves a uniform shape and density to the mould. The mould is then shaped further and then undergoes 'pre-sintering' where the mould is heated up to below final sintering temperature to make handling of it easier. The mould is then machine bored to make the hole for the stem to be inserted into later. After the ball has been bored it is then sintered where it is heated up and the average grain size increases[12]. This leads to increased strength and mechanical properties. After the ball has been sintered it undergoes hot-isostatic pressing where a gas at high temperature(higher than recystallization temperature of material) and high pressure is used to compact the mould[13]. After the hot-isostatic processing the near finished product is laser marked. This is because each individual part needs to be marked and recorded as there is such importance on the product not failing, that if it does they can recognise which batch it came from and may have to stop that batch from being used. Laser marking is a quick process and has reduced surface irregularities that can serve as stress intensifiers. After the laser etching the product goes into the final stage of the process where it ground and polished then undergoes the final inspection. Other variations of the process are used by other manufacturers such as the ball can be pressed, and after densification by sintering and hot isostatic pressing, the bore can be machined. Laser marking can be performed before or after sintering[14].

Another process used is the 'collodial process technique' The colloidal processing concept involves the manipulation and control of the interparticle forces in powder suspensions. The impurities are removed from a stable suspension of the zirconia toughened alumina powder by it being placed in absolute ethanol (99.97%) with diluted zirconium alkoxide being dripped in. After drying under magnetic stirring at 70°C, the powders are thermally treated at 850°C for twohours in order to remove excess. The powder is then attrition milled, as a suspension in alcohol, with 3mm alumina balls for one hour. The powders is then dried and sieved to less than 45µm. They are then cold isostatically pressed to an initial shape. They are then sintered in air at 1550°C for two hours. This leads leading to 98% theoretical density. The samples are cut and polished. The advantages of this technique are that it improves product reliability and it is cheap[15].

5.1 Future Processes

Hot isostatic pressing of Al2O3 ceramics is the most familiar for use in the processing of the many existing ceramics materials[33] Manabe Y, Fujikawa T, Ueda M, Inoue Y. Effect of O2-HIP for oxide ceramics. In: First European ceramic society conference held at Maastricht, Netherlands, 18-23 June 1989.. This technique is still being improved to meet optimal schedules such that the desired mechanical properties and reduced processing costs

New fast sintering techniques, such as 'Spark Plasma' and 'Microwave Sintering' or even fast heating rate furnaces are now available which give the opportunity into processing of ultrafine, fully dense ceramic materials offering alternatives to Y-TZP (Yttria Tetragonal Zirconia Polycrystal) which is a material which offers great abrasions resistance). As these are new techniques and are not in full use some prototype of Alumina have been made from these processes but unfortunately they suffered poor crack resistance.[16]

Improved processing, such as the use of colloidal methods for producing more homogeneous green microstructures, leads to an increase in KI0 (stress intensity factor) and KIC (fracture toughness). The two ways of improving the strength of ceramics are: to decrease the presence and or the size of an impurity, by careful processing and quality control. Secondly, by increasing KIC by alloying or by transforming the ceramic into a composite. Using colloidal processing and consolidation techniques along with optimum sintering and hot isostatic pressing procedures, will produce monolithic ceramics with a homogeneous, dense, fine-grained microstructures which will enhance fracture strength and reliability. Machining is required to produce the smooth surfaces to remove strength-limiting flaws[14].

6.Recommended Ceramic Process Route

The desirable characteristics for materials used as the articulating surfaces in hip replacement are: high strength so that it doesn't break under the strains and stresses the human body will put it under, high elastic modulus, high fracture toughness (to avoid fracturing and needing to be replaced which will mean further invasive surgery) and high fatigue resistance for mechanical reliability and to resist deformation when subjected to the loads in the body. It needs to have high corrosion resistance as it will be moving around in the socket under a load for many years for several hours at a time, high hardness and good surface finish for long-term wear[17].

I would recommend that the process used by 'ceram tec' be used but to start with the colloidal technique to remove all flaws in the powder to reduce risk of failure in the final product. By using the 'ceram tec' process it means that the product is worked using hot isostatic pressing, and it is also sintered. The process is well respected and commonly used across the world at the moment making it reliable. I would recommend using zirconia toughened alumina (ZTA) as oppose to alumina or zirconia on their own are prone to fracture whereas if you use ZTA it increases the toughness. Some alumina-zirconia composites are already being used or developed by companies which have shown improvement in aging resistance as compared to Y-TZP, and excellent crack resistance [18].  This will reduce the risk of 'subcritical crack growth' which is when cracks slowly appear when under strain which is under the threshold of toughness [19]. To make the powder have optimum quality it should undergo the colloidal process as this will mean that the powder purity is extremely high improving mechanical properties and also it will make the powder optimal size for sintering.

When a product is sintered in certain conditions, cracks will grow slowly until it fails and fractures catastrophically. The sintering however does increase density and grain growth which lead to the desired characteristics for the final product [20].

The product will be hot isostatically pressed, which heats the product up above the recrystallisation temperature and compressed again which will remove some of these small cracks therefore removing the risk of failure [21]. It also makes the material more dense which makes the product stronger and tougher [22].

By laser etching the product, it will save time and reduce surface irregularities that can serve as stress intensifiers [19].  Also by marking each component it also means the company is liable for a product if it fails and can then replace the broken product and can then immediately identify any others which may suffer similar fate by recognising which batch it came from.


Considering the patents of the artificial hip joints, the analysis of the major competitors and the market factors, the RAC has a relatively good chance to get into the hip replacements market.

There are many patents which can be found in artificial hip joints field. Some of them are buyable. Obviously, most competitors have their own patents. Big companies, like Zimmer Holdings [23] and Smith & Nephew [24], usually own a research & development system which is the source of researching and developing the patents. To a certain extent, the intellectual properties determine the altitude of the products.

Most competitors gain less than 5% market share according to a manufacturer's estimation [25], though a few big competitors, like Depuy (>20%), Biomet (5-20%) and Zimmer (5-20%), gain more. The market share data may be unreliable because most companies are not willing to give their exact market data, but it still can be gained from some other sources, which should have reference value. From the data it is clearly that no monopoly exists in the artificial hip joint field. Thus, to RAC, there still exist chances to get into the market and to share it.

The published results [25] show that the rate of most revision operations, which cost more and usually have worse functions than the original hip replacements, is approx 10% at ten years. Therefore, long service life and reliable implants are becoming more and more important. If RAC wants to achieve sustainable competitive advantages, the company must start to develop its own technology. According to Murray, Carr and Bulstrode [25], almost no newer implants can transcend the established designs. This is a good chance to RAC because if the company can invest more power on researching while selling the regular products, there could be a chance to establish the company brand over the hip replacing market via introducing newer and better products.

As mentioned previously (see Market Analysis), the total requirements of hip replacements have been increasing stably (see Figure 1). I believe the future growth of the market will also be in a stable increasing. Therefore, RAC does have a good chance to proceed, and which should be taken into consideration by the Board members.


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[10] Artificial Hip Joints: Applying Weapons Expertise to Medical Technology, LLNL (Lawrence Livermore National Laboratory) 1994


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[14] Rahaman, M.N., Yao, A., Bal, B.S., Garino, J.P, Ries, M.D., 2007. Ceramics for Prosthetic Hip and Knee Joint Replacement. Journal of the American Ceramic Society [Online]. 90(7).

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[15] De Aza, A. H., Chevalier, J., Fantozzi, G., Schehl, M., Torrecillas, R. (2002). Crack growth resistance of alumina, zirconia and zirconia toughened alumina ceramics for joint prostheses. Biomaterials [Online]. 23 (3), p937-945. Available at:

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[19] De Aza, A. H., Chevalier, J., Fantozzi, G., Schehl, M., Torrecillas, R. (2002). Crack growth resistance of alumina, zirconia and zirconia toughened alumina ceramics for joint prostheses. Biomaterials [Online]. 23 (3), p937-945. Available at:

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