Journal of Orthopaedics

Purpose: To evaluate short-term efficacy of sandwich-type liner used in revision hip arthroplasty cases.

Materials and Methods:In the span of period from 1999 to 2009, we performed 128 cases of revision hip arthroplasty using sandwich-type liners and continued to follow up after the surgery for minimum 2 years in 103 cases of 97 patients, which were included in our study. We evaluated clinical Harris hip score and some radiologic categories.

In clinical evaluation, the average Harris hip score increased from 58.8 to 86.8. In radiological evaluation, the change of acetabular inclination by more than 10 ° was observed in 4 cases. There was 1 case of osteolysis around the femoral prosthesis and subsidence of stem by more than 5mm. The overall results were basically satisfactory. However, postoperative complications were observed in 17 cases including 5 cases of non-union of greater trochanter, 4 cases of recurrent dislocation, 3 cases of heterotopic ossification, 3 cases of periprosthetic fracture, 1 case of liner breakage and 1 cases of infection.

Compared with the results of primary hip arthroplasty, the clinical and radiological results observed in the subject cases of revision hip arthroplasty using sandwich-type liner were generally satisfactory although not superior.

There have been a number of studies on the replacement arthroplasty using artificial joint focusing on a variety of topics including surgical techniques, instrumental design and the choices of articular surface materials. However, wear of articular liner and prosthetic dissociation are still the greatest causes of the failure of arthroplasty, and these problems led to a numerous undertakings to develop new articular liners. Ceramic-on-ceramic liner, in particular, was first developed in France in 1970 by Pierre Boutin1) and used ever since, for example, by Griss in 1973 and by Mittlemier in 1974 in Germany. Some problems were identified at the early stage, but it has been continuously improved. Recent studies reported successful results of the use of ceramic liners for more than 10 years. With high wear resistance and stable biocompatibility, ceramic liner has become a popular material for articular prosthesis that offers solution to the osteolysis problem of polyethylene caused by abrading particles2,3). Despite benefits of ceramic liner, it is relatively ineffective in shock absorption because of its high stiffness and can cause loosening of the acetabular cup that may lead to the damage in femoral head and the liner4,5). Boutin et al1,6) reported that their postoperative follow-up observation for 15 years of the use of ceramic liner revealed 12.5% occurrence rate of loosening, which they suggested was caused by a lack of shock absorption capacity of the ceramic liner which, in turn, is related to its high stiffness6), Such problem is related to the ineffective dispersion of impacts over the articular surface. In order to solve this problem, a concept of sandwich-type liner with low stiffness was introduced. This type of liner consists of alumina ceramic liner coupled with polyethylene shell and presents both high resistance against wear and effective load dispersion capability. This new concept was first introduced in 1993 by Lima-Lto (Udin, Italy) and was later commercialized by Ceramtec. This sandwich ceramic liner can effectively disperse dynamic load and minimize micro-vibration and contact load on articular surface. There have been several studies that reported successful results from primary hip arthroplasty using sandwich-type liners showing improvement in wear resistance and decreased acetabular osteolysis7,8). However, there are few cases of clinical studies in which sandwich liners were used for revision hip arthroplasty. Therefore, we analyzed in this study the short-term results of revision hip arthroplasty using sandwich-type liners.

We have performed hip arthroplasty using artificial ceramic-on-ceramic hip joints in approximately 1,500 cases including 172 cases of revision arthroplasty. Among these revision hip arthroplasty cases, we used sandwich liners in 128 cases. Finally, 103 cases in 97 patients where we could perform follow-up observation for minimum 2 years (average 48.3 months, 24 ~ 124 months) were included in the analytical study. The reasons that required revision arthroplasty in the subject cases of this study were; loosening of acetabular cup or femur (72 cases), infection (10 cases), wear of polyethylene liner (10 cases), recurrent dislocation (7 cases), periprosthetic fracture (3 cases) and ceramic breakage (1 case) (Table 1). Among these subject cases, structural bone graft was given

due to severe periprosthetic bone defect around the acetabular cup in 32 cases including 8 cases in which metallic Kerboul plates were used to stabilize implanted bone grafts. For metallic Kerboul plate, Müller-type liners manufactured by Lima-Lto were used together with cement for immobilization of the liner. Except for these 8 cases, 46~62mm SPH cups manufactured by Lima-Lto were used in all the rest of the subject cases. The exterior of the SPH cup was made of titanium alloy, coated with porous lining to induce bone growth, and was designed to be able to fix the hip acetabular cup with three screws. The liners were of A(40.4mm), B(43.4mm), C(44.4mm), D(48.4mm) and E(54.4mm) type cups according to their sizes and D cup liners were most used in our revision arthroplasty. In the cases where periprosthetic bone loss is significant, we performed structural allograft of distal femur on this location and fixed it with one or two screws to enhance stability.

Causal Complication (Before)

	Cases (Percentage)
Loosening	72 (69.9%)
Infection	10 (9.7%)
Polyethylen wear	10 (9.7%)
Recurrent dislocation	7 (6.80%)
Periprosthetic fracture	3 (2.91%)
Liner fracture	1 (0.97%)
Total	103 (100%)

Table 1. Causal complications existing before the revision arthroplasty using sandwich-type ceramic-on-ceramic liner.

Preoperative Harris hip score was evaluated for all subject patients and changes were monitored through re-evaluation during follow-up observation period. Postoperative questionnaire was also used during the follow-up observation period to investigate the incidents of squeaking sounds that typically occurs from ceramic-on-ceramic joint during joints movements. For radiological examination, radiographs taken immediately after the surgery and during the follow-up observation period were compared to measure the changes in the inclination of the acetabular cup, osteolysis around the acetabular cup and around femoral prosthesis, and the subsidence of the femoral prosthesis. The inclination of acetabular cup was measured as the angle between the connecting line of bilateral ischial tuberosities and the connecting line of top and bottom of acetabular cup, and the resulting value of more than 10 degrees was rated as being significant. Using DeLee & Charnley’s classification, the occurrence of osteolysis around acetabular cup was determined when radiolucency could be observed in more than 2 mm around acetabular cup, while the occurrence of periprosthetic osteolysis around femoral prosthesis was determined by using Gruen’s classification when continuous radiolucency could be observed in more than 2 mm around femoral prosthesis. The extent of postoperative prosthetic subsidence was evaluated by measuring the distance between the great trochanter of femur and the shoulder of femoral prosthesis and significance of subsidence was determined when the measurement value exceeded 5 mm. All patients were subjected to preoperative evaluation of Harris hip score as well as radiographic evaluation which was repeated 3, 6, and 12 months after the surgery followed by annual evaluation thereafter.

Clinical Results
The Harris hip score, evaluated as a clinical observation, improved from 58.8 point in average (23 ~ 91 points) before the surgery to average 86.8 points (66 ~ 100 points) during follow-up observation period, indicating satisfactory improvement. Postoperative complications were observed in 17 cases (16.5%) in which non-union of the greater trochanter of femur was observed in 5 cases and recurrent dislocation was observed in 4 cases, forming the most frequent complications, followed by 3 cases of femoral periprosthetic fracture and 1 case of breakage in sandwich liner (Fig. 1). No case of chip fracture of liner and femoral periprosthetic fracture during surgery was reported. Additionally, there were 3 cases of heterotopic ossification and 1 case of infection (Table 2). In 6 cases, revision arthroplasty had to be repeated after the surgery including 4 cases of revision arthroplasty of acetabular cup due to migration of the cup and 1 case each of acetabular wall fracture, recurrent dislocation. Revision femoral prosthesis replacement was performed in 1 case due to osteolysis. Replacement of liner was performed in 1 case. Postoperative squeaking sounds from ceramic joint was observed in 3 out of 103 cases in which noise occurred while walking in 2 cases and while lifting a leg in 1 case. The cases of the repeated revision hip arthroplasty during the period from the first revision hip arthroplasty using sandwich-type liner until the last follow-up observation were used for the analysis of Kaplan-Meier survival curve which resulted in the survival rate of 93.0% until the last follow-up observation (Fig.2).

Complication (After)	Cases (percentage)
Non-union of greater trochanter	5 (4.9%)
Recurrent dislocation	4 (3.9%)
Heterotopic ossification	3 (2.9%)
Periprosthetic fracture	3 (2.9%)
Liner breakage	1 (1.0%)
Infection	1 (1.0%)
Total	17 / 103 (16.5%)

Table 2. Complications observed after the revision arthroplasty using sandwich-type ceramic-on-ceramic liner

Radiological Results
The angle between the connecting line of bilateral ischial tuberosities and the connecting line of top and bottom of acetabular cup, which was measured for radiological evaluation, was 42.8° in average (27° ~ 62°) immediately after the surgery and 43.1° in average (4° ~ 79°) after the follow-up period, indicating no significant difference. However, migration of cup by more than 10° was observed in 4 cases (3.9%) of which 2 cases were related to early osteolysis around acetabular cup, 1 case to the fracture of acetabular wall and 1 case to recurrent hip dislocation. Revision hip arthroplasty was repeated in all 4 cases (Fig. 3). Osteolysis around acetabular cup was evaluated using DeLee & Charnley’s classification9) and in no case radiolucency could be observed around acetabular cup during follow-up observation. Periprosthetic osteolysis around femoral prosthesis was evaluated using Gruen’s classification and radiolucency in more than continuous 2 mm around femoral prosthesis could be observed in 2 cases (1.9%). Radiolucency in more than 4 mm was not observed in any case. Zone 1 and zone 7, which are close to the femoral prosthesis, were the locations of radiolucency, one case showing occurrence in zone 1 only and the other in both zone 1 and zone 7. Subsidence of femoral prosthesis by more than 5 mm was observed in 1 case (1%) but it did not correspond with the extent of periprosthetic osteolysis (Fig.4).

Ceramic has been known to be extremely inert and excellent in hardness and hydrophilic property, compared with other materials. Since alumina ceramic is neither soluble in water nor decomposable, it is extremely stable both biodynamically and thermodynamically and is an excellent biocompatible material11). However, it has several setbacks due to its high stiffness which ironically is also its beneficial attribute. Unlike polyethylene, the main cause of loosening and failure of artificial joint made from ceramic material is not wear but its inferiority in shock absorption capability due to high stiffness. Other factors such as improper positioning of acetabular cup and defective design can also contribute to the inability of dispersing the weight to prevent loosening12-14). While ceramic is very stiff, it is also very brittle, making it vulnerable to impact which can cause it to break if shock is not properly absorbed. In order to maximize the benefits of ceramic and compensate weaknesses, the sandwich-type liner was developed. This type of liner consists of ceramic layers that form the surface of the joint and a polyethylene layer that covers the backside of ceramic layer to effectively disperse and absorb shock. Since the polyethylene layer can absorb the shock load, occurrence of periprosthetic osteolysis can be reduced and damage of liner can be prevented when the soft parts around liner collides with metallic femoral prosthesis. Also, ocurrence of ceramic chip fracture during operation using ceramic liner can be prevented and liner can easily be inserted to the acetabular cup by striking.
Although no incidence of the breakage of ceramic head occurred in the subjects of this study, breakage of sandwich liner occurred in 1 case (0.97%) without specific traumatic event 33 months after the surgery. Stephen et al also reported 1 case of liner breakage in 1 case out of 194 cases of alumina ceramic-ceramic joint during follow-up observation period of average 4.3 years15) and argued that this result did not show significant difference from the results of Heck et al from their study in which incidence of liner breakage were observed in 45 cases (0.45%) out of 10,000 cases of using polyethylene liner16). Bizot et al reported 1 case (0.43%) of damage in the soft part around liner out of 234 cases of using ceramic liner, during minimum 5 years of follow-up observation17) while Bierbaum et al reported no case of the damage of ceramic part in 514 cases using ceramic-ceramic joint, during 48 of follow-up18). Hwang et al reported 1 case (1.3%) of liner damage out of 75 cases of using sandwich-type liner, during average 34.3 months of follow-up observation19) and Ravasi et al reported that there was no case of liner damage in 56 cases primary arthroplasty, during 5 years of follow-up7). While many researchers anticipate in their study that ceramic material would be more prone to breakage because of its inferiority in shock absorption and high brittleness, the currently popular third-generation ceramic material (Biolox Forte®) has more improved strength than previous first-generation ceramic materials and more recent fourth-generation ceramic material (Biolox delta®) has even high stiffness and breakage resistance as well as twice as much crush strength as the third-generation material. There has been no study ever performed on long-term use of sandwich-type liner, but the clinical analysis of the results of numerous previous studies on short-term use indicate that approximately 1 % of breakage occurred, showing no significant difference from the results of our study7,8,20). Theoretically, breakage in the lower layer of the liner occurs as the result of collision between hard part of femoral prosthesis and polyethylene part that covers ceramic part underneath the liner during external rotation movement of hip and the breakage in the upper layer of the liner occurs due to collision with femoral head and concentration of force on the liner. Liner is particularly vulnerable to breakage when the inclination of acetabular cup is large subjecting the upper part of the liner under the concentrated force. In this study, the breakage of liner occurred in the soft part around the upper layer of the liner and the patient complained about friction noise but without pain. The patient had severe bone defect of acetabular cup before the revision arthroplasty, so distal femoral allograft was performed and fixed with screws, then an acetabular cup was fixed firmly over it. The inclination of the acetabular cup was 48° immediately after the surgery and it was increased to 51° when the patient was admitted to hospital to receive revision arthroplasty. The position of the acetabular cup is important for effective dispersion of load over the acetabular cup and femoral head. The possible inclination of the acetabular cup fixed at below 45° is recommended. As the inclination of the acetabular cup is smaller, the load on the soft part around the liner becomes less and, therefore, can reduce the risk of breakage in the surrounding soft part and the extent of loosening 21,22). In this study, the inclination of acetabular cup immediately after the surgery of greater than 45° was observed in 36 cases (35.0%). It is because it was not easy to fix the inclination of the acetabular cup within an appropriate range as compare with the cases of primary hip arthroplasty since, in many cases, bone graft had to be performed in various ways during revision arthroplasty to fill the space of bone defect that existed over a large area around acetabular cup. Nevertheless, neither the extent of liner breakage nor the frequency of the occurrence of osteolysis around acetabular cup showed any significant difference from the results of primary arthroplasty in this study23,24).
Sharkey et al reported that osteolysis around acetabular cup was observed in 7 cases (18%) out of 39 cases of hip arthroplasty using polyethylene, during the follow-up observation period of average 69 months and suggested that these osteolysis were mainly caused by polyethylene wear. However, manifestation of osteolysis has decreased considerably since ceramic-ceramic articular surface were used instead. Yoo et al reported that use of ceramic-ceramic articulation resulted in radiolucency around acetabular cup during 68 months of follow-up period in 10% of total 100 cases of primary hip arthroplasty, but no migration of acetabular cup occurred nor periprosthetic radiolucency was observed around femoral prosthesis25). Stephen et al also reported that no incidence of radiolucency around femoral prosthesis or migration of acetabular cup could be observed during average 4.3 years of follow-up period in total 173 cases of ceramic-ceramic arthroplasty20). Ravasi et al who performed 56 cases of primary hip arthroplasty using sandwich-type ceramic liners reported that there was no manifestation of radiolucency around femoral prosthesis or migration of acetabular cup observed during average 62.4 months of follow-up period7). Although there is no proven method of accurately quantifying the ceramic wear, it is only a tiny fraction (1/8,000) of the wear rate of polyethylene-metal articulation surface. The periprosthetic osteolysis around ceramic-ceramic hip joint is not caused by abrading debris as is in the case of polyethylene, but it is caused by ineffective absorption of shock within the shock load transmission system. In this study, no incidence of osteolysis around acetabular cup was found after revision hip arthroplasty but periprosthetic osteolysis was found around femoral prosthesis in 2 cases. There have been a number of studies on sandwich-type liner used in primary hip arthroplasty, but none of these studies reported osteolysis around acetabular cup although they were short-term studies as our study7,19,20). One may anticipate frequent occurrence of osteolysis around acetabular cup on the ground that stabilizing the prosthesis often could not be done as securely as in primary arthroplasty due to bone defect around acetabular cup and other reasons, and that it is not easy to fix the inserted acetabular cup at an appropriate angle during bone grafting, but, in reality, there was no significant difference. Periprosthetic osteolysis around femoral prosthesis occurred in 2 cases and subsidence of femoral prosthesis occurred in 1 case during follow-up period. It is very likely that these incidence occurred because possibility of femoral osteoporosis is very high as the femur has been shielded by existing femoral prosthesis, and because femoral greater trochanter osteotomy is often performed when femoral prosthesis is removed.

Despite the fact that sandwich-type liner has many beneficial attributes, it is not easy to compare clinical efficacy of ceramic liners due to lack of long-term follow-up observation data. However, no incidence of chip fracture has been reported to have occurred during liner inserting procedure of surgery in our studies which were based on short-term follow-up observation. Furthermore, the results of our study indicate relatively satisfactory results in addressing the problems of osteolysis and liner breakage. Unlike primary arthroplasty, revision hip arthroplasty often requires bone grafting due to severe bone defect around acetabular cup or in femur and often encounters osteoporosis. In such cases, if we consider the use of ceramic-ceramic articulation, there is a high risk of problems including osteolysis and subsidence of prosthesis because ceramic liner is not effective in shock dispersion and absorption. We believe that use of low stiffness, sandwich-type liner in revision arthroplasty would be helpful in solving these problems, but further studies will be necessary involving long-term follow-up observation as long-term data is not available yet.

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