Contemporary alumina and alumina-ceramic bearing articulations are harder, scratch-resistant, and more hydrophilic than other bearing couples, resulting in reduced wear and reduction of particle load to the surrounding tissue. In addition, alumina is biocompatible and precludes concerns over metal ion release.2 Therefore, it has advantages as a bearing choice for younger and more active patients, provided there is no risk of fracture.
First- and second-generation ceramics had fracture rates as much as 13% and 5%, respectively.2 The current, or third-generation, ceramic, which is manufactured using hot isostatic pressing with small grain size, provides improved mechanical strength. The fracture rate with third-generation ceramics is 0% to 0.004%.2,16
We have implanted the ABC® alumina insert (Stryker Orthopaedics, Mahwah, NJ) in 580 patients using a modified two-incision minimally invasive technique and encountered three cases of liner fracture, a rate higher than we expected.
A 45-year-old man, who weighed 93 kg, was operated on in June 2004 using a two-incision minimally invasive THA17 for avascular necrosis of the left hip. A 52-mm Secur-Fit™ (Stryker) acetabular component with a 32-mm alumina-ceramic insert (ABC®) and a femoral cone prosthesis (Zimmer, Inc, Winterthur, Switzerland) (Size 19) with a 32-mm ceramic head were used. The liner was inserted using a liner inserter and gently tapped twice with an impactor. No prosthetic impingement was seen intra-operatively. The lateral opening angle of the acetabular component, as measured on a postoperative radiograph, was 41° and the angle of anteversion was 19.6°. The patient recovered uneventfully after surgery and the arthroplasty functioned well for 23 months. He presented to us with a history of a fall in the bathroom followed by hip pain and a clicking sound. Physical examination showed a positive Patrick test with 120° flexion, 35° abduction, 15° adduction, 5° internal rotation, and 40° external rotation. Crepitus was felt on movements of the left hip. Radiographs showed a fracture of the ceramic liner into multiple fragments (Fig 1A). Revision surgery was performed. The ceramic liner was broken into tiny pieces. Acetabular and femoral components were well fixed. The ceramic head was discolored as a result of contact with the acetabular shell. We observed tiny scratches on the trunnion of the femoral component that we believed were caused by broken ceramic fragments. The joint was débrided of all the ceramic fragments and a thorough synovectomy was performed. A Metasul® liner (Centerpulse Orthopedics Inc, Austin, TX) was cemented into the acetabular component and the ceramic head was replaced with a 28-mm metal head (Fig 1B). The patient was doing well 8 months after surgery with no pain or limp and had resumed full activities.
A 46-year-old man, who weighed 64 kg, was operated on in February 2005 using a two-incision minimally invasive THA for avascular necrosis of the right hip. A 48-mm Secur-Fit™ acetabular cup with a 28-mm ABC® liner and a femoral cone prosthesis (Size 15) with a 28-mm BIOLOX® head (CeramTec AG, Plochingen, Germany) were used. The acetabular component was implanted in 34° abduction and 17.4° anteversion. His arthroplasty had been functioning well for 15 months, when he suddenly heard a clicking sound in his right hip while he was walking. Hip pain started 1 week after the clicking. He had no history of trauma and his occupation did not involve heavy work. On physical examination, there was tenderness in the groin and 100° flexion, 30° abduction, 10° adduction, 5° internal rotation, and 20° external rotation. Movements were painful in all planes. Radiographs showed a fracture of the ceramic liner. At revision surgery, the ceramic liner was broken into multiple pieces (Fig 2A). The femoral and acetabular components were well fixed. Extensive synovectomy was performed to remove ceramic fragments. A Metasul® liner was cemented into the well-fixed acetabular component (Fig 3). The ceramic head was replaced with a 28-mm cobalt-chromium head. At the 1-year followup, the patient was doing well with no pain or limp and had no activity restrictions.
A 44-year-old man, who weighed 70 kg, was operated on in 2004 using a two-incision minimally invasive THA for avascular necrosis of the right femoral head. A 54-mm Secur-Fit® acetabular cup with a 32-mm ABC® insert and a femoral cone prosthesis (Size 22) with a 32-mm BIOLOX® head were used. The acetabular component was implanted in 35° abduction and 11° anteversion. Three years after surgery, he noted a clicking sound and mild discomfort in the right hip. On physical examination, his gait and hip range of motion were normal and painless. The radiographs revealed signs of ceramic liner fracture. During revision surgery, we found the liner broken in its peripheral portion (Fig 2B). The central portion of the liner was so firmly fixed to the acetabular shell that it had to be broken into pieces for removal. Femoral and acetabular components were well fixed. There was no sign of impingement on the neck of the femoral component or the edge of the acetabular component. Liner cementation using a Metasul® liner was performed after thorough débridement and synovectomy. The ceramic head was replaced with a 28-mm cobalt-chromium head. The patient was doing well 9 months after surgery with no pain or limp and had resumed full activities.
The erratic performance of the earlier alumina-ceramic material was largely because of a combination of poor prosthetic design, component issues such as component malalignment, and material issues such as large alumina-ceramic grain size.4 As a result of hot isostatic pressing, the current, or third-generation, ceramic has a grain size of 1.8 μm as compared with 4.2 μm in the first generation and 3.2 μm in the second generation. Corresponding to the grain size, the burst strength increased from 46 kN in 1984 to 65 kN in 1995.2 During manufacturing, proof testing is performed to validate the mechanical properties, and laser etching rather than mechanical engraving is used to prevent stress risers. All modern components are subjected to a burst strength examination before sterilization and shipping.3 This has reduced the fracture rate of third-generation ceramic articulation to four per 100,000.2 Also, the alumina-ceramic bearings now are used with femoral stems and acetabular components that have a successful track record for fixation. This combined improvement provides great promise for prolonged fixation of implants, particularly in young and more active patients. Unfortunately, that promise was not fulfilled for three of our patients.
The ABC® system was introduced in 1996 in the United States for clinical trial.3 The cup has a peripheral self-locking design with a peripheral radius 1 mm greater than the radius of the dome of the socket. The liner sits in the acetabular shell at a 19°-angle and its high taper height provides better support to the liner (Fig 4). The ceramic liner is slightly recessed in its metal shell to protect the liner from neck impingement (Fig 5). D'Antonio et al4 did not encounter any ceramic fracture or ceramic bearing failure at an average followup of 5 years. However, they reported chipping of nine ceramic liners during insertion. The problem of insert chipping was believed caused by the impaction of a liner not seated completely within the rim of the shell. This problem is ostensibly solved by introduction of the Trident® design (Stryker), which has a metal-backed alumina liner.4 Other investigators reported one case of ceramic liner fracture among 194 hips using the BIOLOX® Forte XLW bearing (CeramTec).10
Several factors contribute to ceramic liner fracture. Trauma, high activity level, and obesity may cause fracture by increasing the load across the joint surface.9 Mechanical properties and liner design have been modified as discussed above and are less likely responsible for fracture of a so-called third-generation liner. Liner malposition and incomplete sitting can result in chipping and subsequent fracture.9 Suboptimal placement of the acetabular shell could be one of the reasons, as vertical cup placement can enhance edge loading, whereas horizontal placement results in impingement between the liner and the neck.5,11,15 Impingement also can result from insufficient oscillation angle, which is related to the head diameter and the geometry of the neck of the femur and of the acetabularcomponent.19 However, in all three of our patients, components were placed in what we judged as an acceptable position and we believed there was little likelihood for impingement because of a recessed ceramic liner (Fig 5).
We are not sure of the cause of ceramic liner fracture in our patients. The first patient was slightly overweight and he had a history of falling, but there are examples of substantial trauma to the hip showing either fracture of the acetabulum or of the femur without any disturbance of the modern alumina material.13 Recently, one report attributed ceramic liner fracture in the nonWestern population to such activities as squatting, kneeling, and sitting crossed leg, which can result in impingement and liner fracture.9 The practice of squatting and sitting in a Buddhist position is an essential part of the Asian lifestyle. In our opinion, this might have caused edge loading and/or stress concentration in the peripheral portion of the liner resulting from hyperflexion and wide abduction. This was evident in the third case, in which the liner was broken only in the peripheral portion. We believe the crack originated initially in the periphery of the liner and then propagated to the center, resulting in complete breakage.
Controversy exists regarding the treatment of ceramic liner fractures. Third-body wear resulting from the presence of ceramic particles may be unavoidable even after meticulous débridement. This makes soft bearings such as polyethylene or cross-linked polyethylene vulnerable to wear by retained ceramic particles. Therefore, hard-on-hard bearings such as ceramic-on-ceramic or metal-on-metal are advisable. Theoretically it is desirable to use another ceramic liner because it would be more resistant to the roughening by retained ceramic particles. However, an unrecognized defect on the acetabular shell may lead to fracture of the newly implanted ceramic liner. Subsequent liner fracture also can create medicolegal problems for the surgeon. Some authors recommend removal of all the components and use of an alumina-on-alumina or ceramic-on-polyethylene bearing to avoid third-body wear and damage to the metal by ceramic particles.8 We believe removal of well-fixed components can be a complicated procedure with increased blood loss and damage to the bone stock. We have obtained good results with metal-on-metal articulation by cementation of a metal-inlay polyethylene liner in cases of polyethylene liner wear and osteolysis without loosening of the acetabular component.18 In biomechanical tests, the cemented-liner construct has a similar fixation strength as that of a locking mechanism.11,18 There are reports regarding cementation of conventional polyethylene liners in a metal shell.6,14 How ever, only a thin polyethylene liner can be contained in the shell when the existing metal shell is small, and we believe it may lead to early failure. In addition, insertion of a polyethylene liner carries a risk of subsequent osteolysis and aseptic loosening. Therefore, the use of a metal-inlay polyethylene liner is theoretically a better choice for long-term survival. Use of metal-on-metal articulation after ceramic-bearing fracture also has been supported by others.1,7 We obtained satisfactory short-term results in these three patients by cementing a metal-inlay polyethylene liner in the existing acetabular shell.
Ceramic liner fracture is still an unsolved problem for arthroplasty surgeons. Newer designs are introduced to minimize this risk. One such design, the sandwich cup (polyethylene-ceramic composite liner), had an unacceptably higher rate of fractures.5,8,12 A ceramic liner with a titanium sleeve appears promising in this context, but its long-term performance is a matter of speculation. Cementation of a metal- inlay polyethylene liner after débridement may be a good option for revisions after ceramic fracture.
We thank Sung Hwa Park and Ju Kwon Park, MD, for assistance with data collection and manuscript preparation.
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