**3.4.8.2 Stripe wear**

198 Recent Advances in Arthroplasty

head options are available to the surgeon. Potential disadvantages of this new bearing articulation include the risk of a ceramic femoral head fracture and its as-yet unknown

The potential advantages of using a ceramic on ceramic articulation for total hip arthroplasty can be quickly summarized as decreased wear and elimination of osteolysis. Osteolysis from wear debris is commonly viewed as the major obstacle blocking the development of a "lifetime" hip replacement. The need to eliminate wear and osteolysis has been magnified by the extension of indications for total hip arthroplasty to younger, more active, healthier patients with long life expectancies. The potential for decreased wear is derived from the tribologic properties inherent to alumina. Alumina can be highly polished. Alumina bearings are also very hard, and this characteristic increases their resistance to scratching. The hardness minimizes third-body wear from entrapped bone, polymethylmethacrylate, or metal debris derived from surgical instruments or component fretting. Alumina has ionic properties and therefore, in combination with body fluids, has better wettability than chrome cobalt. The fluid film that develops on ceramic surfaces decreases frictional drag and adhesive wear. Wear rates for modern ceramic on ceramic articulations have been shown to be as low as 4 µm/year. This low wear rate coupled with less alumina bioreactivity minimizes the likelihood of osteolysis. With currently used implant designs, osteolysis has not been reported with follow-up as long as 18.5 years.

One significant drawback of ceramic materials is their inherently lower strength and toughness under tension and bending, which are the loading modes that favor the initiation and propagation of cracks. One such adverse loading arises from the mismatch at the taper junction between the metal stem and ceramic head. To prevent this from leading to early fracture, the tolerances at the taper are matched and may be manufacturer-specific. The surgical placement of the components may also predispose the ceramic components to high stresses and initiate fracture. For instance, a third body (bone cement or bone fragment) left in the taper interface or impingement of the femoral component on the rim of the ceramic acetabular liner secondary to malpositioning of the components could also initiate ceramic

Improved material processing, smaller grain sizes, fewer impurities, laser etching, and proof testing have greatly diminished the risk of catastrophic in vivo fracture. The risk of ceramic fracture is estimated to have decreased nearly 100-fold in the last two decades. In 1990 the incidence of fracture was approximately 0.8%, and today is likely between 0.004% and 0.010%. Nonetheless, this complication is devastating and still occurs.(Min 2007) Even with proof testing, it is unlikely that failure by fracture will be eliminated. Although theoretically proof testing eliminates weaker components, flawed products that are likely to fail are not always eliminated. Proof testing theoretically is designed to be stringent enough to remove components with manufacturing flaws that are likely to clinically fail. However, the test must be nondestructive and not cause damage to the tested part. No proof test currently available is 100% effective. So, it must be remembered that production errors can and still do occur. In 1998 a manufacturing change resulted in a high fracture rate of ceramic balls.

clinical performance.(D'Antonio 2009)

**3.4.7 Ceramic advantages** 

**3.4.8 Ceramic concerns** 

fracture.(Barrack 2004) **3.4.8.1 Fracture (Fig.12)** 

> Separation of the ball from the socket in patients with a hip arthroplasty may occur during the swing phase of gait or with impingement of the trunnion on the acetabular rim levering the ball from the socket. When this separation occurs, the contact area of the femoral head on the acetabular liner becomes small and stripe wear can result.(Fig.15) Stripe wear is concerning because volumetric wear associated with this phenomenon is high. In one study, stripe wear produced volumetric wear that averaged 1.24 mm3 per million cycles. Equally concerning, a bimodal array of nanometer- and micrometer-sized particles was created with an enhanced profile of bioreactivity. Separation of the ceramic on ceramic hip articulation is

The Bearing Surfaces in Total Hip Arthroplasty – Options, Material Characteristics and Selection 201

The number of femoral head size and neck length options available to the surgeon when using ceramic articulations is limited. In general, for each acetabular component there is only one size liner diameter and paired head girth available. In addition, collared heads are not manufactured, and this significantly reduces the neck length options available. Also, offset and lipped acetabular liners are not produced because they would lead to impingement and chipping. These limitations have caused some experts to speculate that instability and dislocations will be more common when ceramic on ceramic bearings are used. However, clinically this has not proved to be a problem. Impingement of the femoral component trunnion on the ceramic liner edge is also an area of concern. This impingement can lead to chipping of the ceramic liner or notching of the femoral component. A protective metal rim has been added to the ceramic shell liner. Of course, impingement can still occur; however, this protective rim does seem to prevent ceramic damage. Nonetheless, impingement with the protective rim may still cause femoral neck notching and generate metallic debris. The consequences of this type of impingement are unknown; however, the generation of metallosis may theoretically contribute to the problem of noise and squeaking.

The newest generation of Ceramic-on-Ceramic bearings incorporate nanosized, yttriastabilized tetragonal zirconia particles producing an alumina matrix composite. This new

The newest generation of ceramics, incorporating zirconia into the alumina matrix (marketed as Biolox delta by CeramTec, Plochingen, Germany). Nanosized, yttria-stabilized tetragonal zirconia particles improve the mechanical properties by preventing the initiation and propagation of cracks. Oxide additives produce platelet-like crystals that dissipate energy by deflecting cracks. The addition of chromium oxide further increases the strength and toughness by composite hardening. The final product is a mixture of roughly 75% aluminum oxide, 25% zirconia, and less than 1% chromium oxide and strontium oxide. The result is a composite ceramic with improved mechanical properties and reduced wear as shown on scanning electron microscopy (SEM) and a predicted longer lifespan. These improved mechanical properties reduce overall wear rates of 28-mm heads in a hip simulator wear test from 1.84 mm3 per million cycle to 0.16 mm3 per million cycle, comparing alumina-on-alumina versus alumina matrix composite-on-alumina matrix

There are some laboratory and very short-term clinical data to support the use of ceramic femoral heads articulating with metal acetabular components. These appear to produce less stripe wear with edge loading than metal-on-metal implants. It also appears that there is a reduction in metal ions in the patients at 6 months. Though there have been reports of early catastrophic failure if this pairing is reversed and a metal head is articulated with a ceramic

A concern with ceramic femoral heads is brittle catastrophic failure in vivo. Improvements in the quality and manufacturing of Al2O3 have not eliminated this risk. In the past, zirconia

**3.4.10.1 Fabrication and testing of silicon nitride bearings in total hip arthroplasty** 

**3.4.9 Delta ceramic-on-alumina ceramic articulation in primary THA** 

bearing surface provided high survivorship.

composite, respectively. (Lombardi 2010; Hamilton 2010)

**3.4.10 Other advances** 

acetabular component.

**3.4.8.4 Other ceramic concerns** 

most likely to occur in individuals with tissue laxity or excellent range of motion. Also, patients with vigorous lifestyles and those who perform activities that require placing the hip through a provocative range of motion may be prone to impingement and stripe wear.(Walter 2004) For patients with these risk factors, other articulation choices should be considered. Of course, malpositioned components, as with any articulation, increase the risk of impingement. (Park 2006)

### **3.4.8.3 Motion-related noise**

Hard on hard bearings can produce noise that can be disconcerting and annoying enough that revision surgery is requested by the patient. Specifically, with alumina on alumina bearings patients may describe this noise as "squeaking."(Keurentjes 2008) Ranawat and his colleagues reported that 10 of 159 ceramic on ceramic articulations squeaked and that the phenomenon was self-reported by the patient. The squeaking usually occurred in midrange of motion and was generally considered a significant issue of concern for the patient. In a study on patients with COC THAs who had squeaking, ideal cup position was described as 25 degrees ±10 degrees of anteversion and 45 degrees ±10 degrees of inclination. Clearly, these data suggest that squeaking is related to cup position.(Ranawat 2007; Walter 2007) However, conversely, Parvizi and associates reviewed the incidence of squeaking after 1056 ceramic on ceramic total hip arthroplasties. Thirty-three patients reported squeaking. The patients who had a noisy hip were matched against a control group, and cup position for both groups was carefully determined using computed tomography. There was no significant difference in acetabular position between the two groups.(Restrepo 2008) Retrieval of revised noisy ceramic bearings has so far been inconclusive. Noisy retrieved bearings frequently have a small zone of stripe wear and metallic staining, possibly associated with the head subluxing and making contact with the protective metal rim around the ceramic or the acetabular shell. (Taylor 2007) The management of squeaking begins with informed consent. The occurrence of noise in an otherwise well-functioning arthroplasty is very disconcerting to the patient. The patient's perception that the articulation is malfunctioning can prompt litigation which could involve the surgeon. Reassurance is appropriate because there is no evidence at this time that the noise reflects that the articulation is deteriorating. Certainly the patient should avoid provocative activities because this recommendation seems logical. There is empirical evidence that squeaking is related to a "dry" joint, and oral hydration or injection of viscosupplements can alleviate the noise. If a patient presents with a squeaking ceramic hip, first ceramic breakage must be excluded with a computed tomography scan because a broken ceramic insert can cause squeaking and it may not be obvious on plain radiographs. The computed tomography scan also provides an accurate measure of the acetabular component anteversion. If the noise itself is infrequent, and occurs only with a specific activity, then revision surgery may not be necessary. If the noise itself is troubling, if there is gross component malposition, if there is impingement, or if the patient has symptoms of pain, revision surgery should be recommended. The cup and stem need to be carefully inspected to be sure they are correctly positioned and well fixed. Because the trunnion may be damaged, revision to a metal ball and polyethylene socket is best, as metal on metal articulations have also been reported to occasionally make noise. Using a metal on metal articulation, if it also squeaks, would not likely be acceptable to the patient.(Walter 2008)

### **3.4.8.4 Other ceramic concerns**

200 Recent Advances in Arthroplasty

most likely to occur in individuals with tissue laxity or excellent range of motion. Also, patients with vigorous lifestyles and those who perform activities that require placing the hip through a provocative range of motion may be prone to impingement and stripe wear.(Walter 2004) For patients with these risk factors, other articulation choices should be considered. Of course, malpositioned components, as with any articulation, increase the risk

Hard on hard bearings can produce noise that can be disconcerting and annoying enough that revision surgery is requested by the patient. Specifically, with alumina on alumina bearings patients may describe this noise as "squeaking."(Keurentjes 2008) Ranawat and his colleagues reported that 10 of 159 ceramic on ceramic articulations squeaked and that the phenomenon was self-reported by the patient. The squeaking usually occurred in midrange of motion and was generally considered a significant issue of concern for the patient. In a study on patients with COC THAs who had squeaking, ideal cup position was described as 25 degrees ±10 degrees of anteversion and 45 degrees ±10 degrees of inclination. Clearly, these data suggest that squeaking is related to cup position.(Ranawat 2007; Walter 2007) However, conversely, Parvizi and associates reviewed the incidence of squeaking after 1056 ceramic on ceramic total hip arthroplasties. Thirty-three patients reported squeaking. The patients who had a noisy hip were matched against a control group, and cup position for both groups was carefully determined using computed tomography. There was no significant difference in acetabular position between the two groups.(Restrepo 2008) Retrieval of revised noisy ceramic bearings has so far been inconclusive. Noisy retrieved bearings frequently have a small zone of stripe wear and metallic staining, possibly associated with the head subluxing and making contact with the protective metal rim around the ceramic or the acetabular shell. (Taylor 2007) The management of squeaking begins with informed consent. The occurrence of noise in an otherwise well-functioning arthroplasty is very disconcerting to the patient. The patient's perception that the articulation is malfunctioning can prompt litigation which could involve the surgeon. Reassurance is appropriate because there is no evidence at this time that the noise reflects that the articulation is deteriorating. Certainly the patient should avoid provocative activities because this recommendation seems logical. There is empirical evidence that squeaking is related to a "dry" joint, and oral hydration or injection of viscosupplements can alleviate the noise. If a patient presents with a squeaking ceramic hip, first ceramic breakage must be excluded with a computed tomography scan because a broken ceramic insert can cause squeaking and it may not be obvious on plain radiographs. The computed tomography scan also provides an accurate measure of the acetabular component anteversion. If the noise itself is infrequent, and occurs only with a specific activity, then revision surgery may not be necessary. If the noise itself is troubling, if there is gross component malposition, if there is impingement, or if the patient has symptoms of pain, revision surgery should be recommended. The cup and stem need to be carefully inspected to be sure they are correctly positioned and well fixed. Because the trunnion may be damaged, revision to a metal ball and polyethylene socket is best, as metal on metal articulations have also been reported to occasionally make noise. Using a metal on metal articulation, if it also squeaks, would not likely be

of impingement. (Park 2006) **3.4.8.3 Motion-related noise** 

acceptable to the patient.(Walter 2008)

The number of femoral head size and neck length options available to the surgeon when using ceramic articulations is limited. In general, for each acetabular component there is only one size liner diameter and paired head girth available. In addition, collared heads are not manufactured, and this significantly reduces the neck length options available. Also, offset and lipped acetabular liners are not produced because they would lead to impingement and chipping. These limitations have caused some experts to speculate that instability and dislocations will be more common when ceramic on ceramic bearings are used. However, clinically this has not proved to be a problem. Impingement of the femoral component trunnion on the ceramic liner edge is also an area of concern. This impingement can lead to chipping of the ceramic liner or notching of the femoral component. A protective metal rim has been added to the ceramic shell liner. Of course, impingement can still occur; however, this protective rim does seem to prevent ceramic damage. Nonetheless, impingement with the protective rim may still cause femoral neck notching and generate metallic debris. The consequences of this type of impingement are unknown; however, the generation of metallosis may theoretically contribute to the problem of noise and squeaking.
