Orthopedics

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Preliminary Clinical and Radiographic Results of Large Ceramic Heads on Highly Cross-Linked Polyethylene

Morteza Meftah, MD; Prouskeh Bruce Ebrahimpour, MD; Chuan He, MD, PHD; Amar S. Ranawat, MD; Chitranjan S. Ranawat, MD

Abstract

Data are limited regarding large ceramic femoral heads with highly cross-linked polyethylene. We hypothesized that large ceramic head articulation with highly cross-linked polyethylene is safe with a low wear rate, comparable to metal-on-highly cross-linked polyethylene.

The study group comprised 63 patients (72 hips) who had undergone total hip replacement (THR) with ceramic-on-highly cross-linked polyethylene between April 2006 and March 2007 with a minimum 2-year follow-up. Postoperative Western Ontario and Mc-Master Universities Arthritis Index (WOMAC) and Hospital for Special Surgery (HSS) scores were used for clinical assessment. Six-week and 2-year radiographs were analyzed by 2 independent observers using Roman 1.70 software. Twenty-six patients (29 hips) had 32-mm and 37 patients (43 hips) had 36-mm Biolox delta ceramic femoral heads (Ceramtec, Plochingen, Germany). Mean patient age was 60.9±8.9 years, and mean follow-up was 2.9±0.5 years. Mean postoperative WOMAC and HSS hip scores were 30.4 and 36.6, respectively. Mean wear at 1 and 2 years postoperatively was 0.06±0.28 and 0.006±0.12 mm/yr for all hips, respectively. Mean wear at 1 and 2 years postoperatively for the 32-mm femoral head was 0.063±0.278 and 0.007±0.126 mm/yr, respectively, and for the 36-mm femoral head was 0.057±0.292 and 0.006±0.118 mm/yr, respectively. No patient had any clinical complications, such as reoperation, infection, fractures, or radiographic evidence of osteolysis or loosening. The early results of THR with large ceramic heads demonstrate high safety and efficacy. Our data with 2-year follow-up show low wear rates, similar to published data for metal-on-highly cross-linked polyethylene.

Drs Meftah, Ebrahimpour, Ranawat (Amar), and Ranawat (Chitranjan) are from Weill Medical College of Cornell University, Hospital for Special Surgery, New York, New York; and Dr He is from Ruijin Hospital, Shanghai Jiao Tong University Medical School, Shanghai, China.

Drs Meftah, Ebrahimpour, He, Ranawat (Amar), and Ranawat (Chitranjan) have no relevant financial relationships to disclose.

Wear and osteolysis are major contributors to limiting the durability of total hip replacement and ultimately leading to failure. 1,2 Efforts to decrease polyethylene wear debris have included cross-linking of polyethylene and the use of alternate bearing surfaces, including ceramic-on-highly cross-linked polyethylene or ceramic-on-ceramic bearings. 3,4 Ceramic bearing surfaces have historically had low wear properties. 4–7 Only a handful of studies have investigated in vivo wear rates of ceramic-on-polyethylene THRs, 3–7 and to our knowledge, none have analyzed wear rates of large ceramic heads on highly cross-linked polyethylene.

The primary goal of our study was to measure the radiographic wear rate of large-diameter alumina matrix composite ceramic femoral heads (Biolox delta; Ceramtec, Plochingen, Germany) on third-generation highly cross-linked polyethylene (Trident X3; Stryker, Mahwah, New Jersey) and to assess its clinical safety and efficacy at minimum 2-year follow-up.

Between April 2006 and March 2007, all patients who had undergone noncemented THR using 32- or 36-mm ceramic femoral heads and highly cross-linked polyethylene liners were identified from a prospective database. Indications for use of a ceramic femoral head were young (aged 55 years or younger) and/or active patients. Exclusion criteria were any major complications such as dislocations, fractures, infections, or any revision or reoperation. Sixty-three patients (72 hips) were included in the study (26 men, 37 women). The majority of the patients were younger than 55 years; however, age was a rough guideline, and patient activity, physiologic age, and choice of implant were also considered. Twenty-nine hips (26 patients) had received a 32-mm femoral head and 43 hips (37 patients) received a 36-mm femoral head. The cup sizes were 50 mm, 54 mm, 65 mm, 58 mm, or 62 mm, and the polyethylene thickness was 5.9 mm, 7.9 mm, 9.4 mm, or 11.2 mm (Table ). All surgeries were performed by 2 surgeons (C.S.R., A.S.R.)…

Abstract

Data are limited regarding large ceramic femoral heads with highly cross-linked polyethylene. We hypothesized that large ceramic head articulation with highly cross-linked polyethylene is safe with a low wear rate, comparable to metal-on-highly cross-linked polyethylene.

The study group comprised 63 patients (72 hips) who had undergone total hip replacement (THR) with ceramic-on-highly cross-linked polyethylene between April 2006 and March 2007 with a minimum 2-year follow-up. Postoperative Western Ontario and Mc-Master Universities Arthritis Index (WOMAC) and Hospital for Special Surgery (HSS) scores were used for clinical assessment. Six-week and 2-year radiographs were analyzed by 2 independent observers using Roman 1.70 software. Twenty-six patients (29 hips) had 32-mm and 37 patients (43 hips) had 36-mm Biolox delta ceramic femoral heads (Ceramtec, Plochingen, Germany). Mean patient age was 60.9±8.9 years, and mean follow-up was 2.9±0.5 years. Mean postoperative WOMAC and HSS hip scores were 30.4 and 36.6, respectively. Mean wear at 1 and 2 years postoperatively was 0.06±0.28 and 0.006±0.12 mm/yr for all hips, respectively. Mean wear at 1 and 2 years postoperatively for the 32-mm femoral head was 0.063±0.278 and 0.007±0.126 mm/yr, respectively, and for the 36-mm femoral head was 0.057±0.292 and 0.006±0.118 mm/yr, respectively. No patient had any clinical complications, such as reoperation, infection, fractures, or radiographic evidence of osteolysis or loosening. The early results of THR with large ceramic heads demonstrate high safety and efficacy. Our data with 2-year follow-up show low wear rates, similar to published data for metal-on-highly cross-linked polyethylene.

Drs Meftah, Ebrahimpour, Ranawat (Amar), and Ranawat (Chitranjan) are from Weill Medical College of Cornell University, Hospital for Special Surgery, New York, New York; and Dr He is from Ruijin Hospital, Shanghai Jiao Tong University Medical School, Shanghai, China.

Drs Meftah, Ebrahimpour, He, Ranawat (Amar), and Ranawat (Chitranjan) have no relevant financial relationships to disclose.

Correspondence should be addressed to: Morteza Meftah, MD, Hospital for Special Surgery, 535 E 70th St, 6th Floor, New York, NY 10021 (meftahm@hss.edu).
Posted Online: June 14, 2011

Wear and osteolysis are major contributors to limiting the durability of total hip replacement and ultimately leading to failure. 1,2 Efforts to decrease polyethylene wear debris have included cross-linking of polyethylene and the use of alternate bearing surfaces, including ceramic-on-highly cross-linked polyethylene or ceramic-on-ceramic bearings. 3,4 Ceramic bearing surfaces have historically had low wear properties. 4–7 Only a handful of studies have investigated in vivo wear rates of ceramic-on-polyethylene THRs, 3–7 and to our knowledge, none have analyzed wear rates of large ceramic heads on highly cross-linked polyethylene.

The primary goal of our study was to measure the radiographic wear rate of large-diameter alumina matrix composite ceramic femoral heads (Biolox delta; Ceramtec, Plochingen, Germany) on third-generation highly cross-linked polyethylene (Trident X3; Stryker, Mahwah, New Jersey) and to assess its clinical safety and efficacy at minimum 2-year follow-up.

Materials and Methods

Between April 2006 and March 2007, all patients who had undergone noncemented THR using 32- or 36-mm ceramic femoral heads and highly cross-linked polyethylene liners were identified from a prospective database. Indications for use of a ceramic femoral head were young (aged 55 years or younger) and/or active patients. Exclusion criteria were any major complications such as dislocations, fractures, infections, or any revision or reoperation. Sixty-three patients (72 hips) were included in the study (26 men, 37 women). The majority of the patients were younger than 55 years; however, age was a rough guideline, and patient activity, physiologic age, and choice of implant were also considered. Twenty-nine hips (26 patients) had received a 32-mm femoral head and 43 hips (37 patients) received a 36-mm femoral head. The cup sizes were 50 mm, 54 mm, 65 mm, 58 mm, or 62 mm, and the polyethylene thickness was 5.9 mm, 7.9 mm, 9.4 mm, or 11.2 mm (Table ). All surgeries were performed by 2 surgeons (C.S.R., A.S.R.) with a similar technique and posterior approach. The implants used included a non-cemented Accolade TMZF femoral stem (Stryker, Mahwah, New Jersey), a Biolox delta femoral head, a Trident PSL solid acetabular shell (Stryker), and a Trident X3 polyethylene acetabular liner (Stryker).

Acetabular Cup Sizes and Polyethylene Thickness

Table 1. Acetabular Cup Sizes and Polyethylene Thickness

Anteroposterior standing pelvis radiographs taken at an average of 6 weeks postoperatively were used as baseline. Repeat pelvic radiographs were performed at 1 and 2 years postoperatively during the follow-up period. Radiographic wear was measured using Roman 1.70 software using the concentric circles technique developed by Livermore et al. 8 All radiographs were analyzed by 2 independent observers. Femoral penetration was calculated at 1- and 2-year postoperative intervals and compared to the baseline 6-week radiographs. The radiographs were also individually assessed by each observer for any evidence of periprosthetic osteolysis or loosening. The cup inclination angle was also measured on latest follow-up images.

Clinical assessments were conducted using the Western Ontario and McMaster Universities Arthritis Index (WOMAC) and Hospital for Special Surgery (HSS) hip scores at final follow-up. Student t test was used to compare the radiographic wear results in the 32- and 36-mm groups at 1- and 2-year postoperative intervals. All descriptive statistics (mean, standard deviation, and mean standard error) and calculations were performed with SPSS 16.0 (SPSS Inc, Chicago, Illinois). Two-tailed P values <.05 were considered statistically significant.

Results

Mean patient age was 60.9±8.9 years (range, 32–78 years), and mean follow-up was 2.9±0.5 years (range, 2–4 years). Mean WOMAC and HSS hip scores at last follow-up were 30.4±8 (range, 24–56) and 36.6±4.7 (range, 20–40), respectively. Mean cup inclination angle was 41° ±3° (range, 35°–52°). There was no radiographic evidence of loosening or osteolysis.

Mean femoral penetration rate at 1 year postoperatively was 0.06±0.28 mm/yr and at 2 years postoperatively was 0.006±0.12 mm/yr for all hips (Table ; Figure ). For the 32-mm femoral head group, mean femoral penetration rates at 1 and 2 years postoperatively were 0.063±0.278 and 0.007±0.126 mm/yr, respectively. For the 36-mm femoral head group, mean femoral penetration rates at 1 and 2 years postoperatively were 0.057±0.292 and 0.006±0.118 mm/yr, respectively (Figure ). There were no significant differences between the 32-mm and 36-mm groups at 1 ( P=.9) or 2 ( P=.97) years postoperatively.

Wear Rates at 1 and 2 Years Postoperatively, Including Negative Results

Table 2. Wear Rates at 1 and 2 Years Postoperatively, Including Negative Results

Wear Rates at 1 (A) and 2 (B) Years Postoperatively. Green Indicates Positive Wear and Red Indicates Negative Wear.

Figure 1:. Wear Rates at 1 (A) and 2 (B) Years Postoperatively. Green Indicates Positive Wear and Red Indicates Negative Wear.

Wear Rates at 1 (A) and 2 (B) Years Postoperatively when Negative Values Are Converted to Zero.

Figure 2:. Wear Rates at 1 (A) and 2 (B) Years Postoperatively when Negative Values Are Converted to Zero.

When the negative values were considered zero, the wear rates at 1 and 2 years postoperatively were 0.12±0.23 and 0.05±0.06 mm/yr, respectively (Table ; Figure ). The wear rates for 32- and 36-mm heads without the negative values at 1 year postoperatively were 0.13±0.22 and 0.12±0.24 mm/yr, respectively, and at 2 years postoperatively were 0.056±0.065 and 0.047±0.06 mm/yr, respectively. There were no significant differences between the 32- and 36-mm groups at 1 ( P=.8) or 2 ( P=.5) years postoperatively.

Wear Rates at 1 and 2 Years Postoperatively, when Negative Results Are Considered Zero

Table 3. Wear Rates at 1 and 2 Years Postoperatively, when Negative Results Are Considered Zero

Wear Rates in 32-mm and 36-mm Femoral Heads at 1 (A) and 2 (B) Years Postoperatively.

Figure 3:. Wear Rates in 32-mm and 36-mm Femoral Heads at 1 (A) and 2 (B) Years Postoperatively.

Discussion

The new generation of ceramic composites and highly cross-linked polyethylene have shown significant wear reduction in simulator studies. 9,10 Several studies have also demonstrated significantly low wear rates of highly cross-linked polyethylene at 5-year follow-up. 11–14 Moreover, some studies have evaluated the effect of femoral head size on wear rates. 8,15 However, there are no published data evaluating wear of large ceramic heads on highly cross-linked poly-ethylene bearings. The goal of this study was to investigate the radiographic wear of large-diameter Biolox delta ceramic on X3 highly cross-linked polyethylene bearing surfaces at a minimum 2-year follow-up.

Biolox delta is an alumina matrix composite that contains zirconium oxide, as well as other nanocompounds rendering the ceramic material more resistant to fracture while maintaining the hardness of pure alumina. 16 The second generation of highly cross-linked polyethylene that has incorporated sequential low-dose gamma irradiation followed by annealing has shown to preserve mechanical strength and resistance to oxidation while reducing wear. 11–14,17 Wear reduction of as much as 97% when compared to conventional ultra-high-molecular-weight polyethylene and 62% when compared to first-generation annealed highly cross-linked polyethylene was seen in 1 study using hip simulator testing. 17–21 Moreover, they have reduced risk of fatigue cracking seen in remelted highly cross-linked polyethylene and in vivo oxidation seen in first-generation annealed highly cross-linked polyethylene. 22 When combining the alumina matrix composite ceramic femoral head with highly cross-linked polyethylene acetabular liner as a bearing surfacing for THR, there is an advantage of hardness, scratch resistance, decreased coefficient of friction compared to other bearings, increased wettability and improved lubrication, and enhanced wear resistance. 23,24

Our results showed lower wear rates than current metal-on-second-generation highly cross-linked polyethylene articulations. 11–14 There was a significant difference between the first- and second-year wear rates when the negative values were considered zero. This phenomenon has been previously reported at the bedding-in period. 25,26 We also noted no significant difference between 32- and 36-mm head sizes at 2-year follow-up. Several clinical studies have shown significant decreases in linear wear rates in ceramic-on-polyethylene articulations compared to metal-on-polyethylene. 19,26 Similarly, wear rates with metal-on-highly cross-linked polyethylene have been in the order of -0.002 to 0.12 mm/yr at a minimum 2- to 6-year follow-up using a computerized edge-detection method and roentgen stereophotogrammetric analysis methods, values that are significantly lower than metal-on-conventional polyethylene. 11,20,23–25

The Roman method to detect the wear of highly cross-linked polyethylene uses a best-fit algorithm to determine a circle with a center from any number of user-determined points. 27 This method was shown to be more precise, easier to use, and less expensive than other computer-based wear analysis such as the Martell method. 25,26,28 The presence of negative wear values may be due to a combination of factors, including the small magnitude of wear, inconsistent radiographic quality, and human error, which have been reported using other methods of wear analysis when analyzing small wear rates (<1 mm). 25,26,29 We report the wear rates including the negative values in 1 scenario, and converting the negative values to zero in the other.

Limitations of this study were a relatively small number of patients and a short duration of follow-up. However, these results are the benchmark for future studies investigating long-term wear rates of these bearing surfaces.

References

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Acetabular Cup Sizes and Polyethylene Thickness

Femoral Head Size Acetabular Cup Size, mm (No. Hips) Polyethylene Thickness, mm (No. Hips)
32 mm 50 (14) 7.9 (22)
52 (8) 9.4 (6)
54 (4) 11.2 (1)
56 (2)
58 (1)
36 mm 50 (1) 5.9 (2)
52 (1) 7.9 (29)
54 (16) 9.4 (11)
56 (13) 11.2 (1)
58 (11)
62 (1)

Wear Rates at 1 and 2 Years Postoperatively, Including Negative Results

Mean Wear Rate, mm/yr
P Value
1 Year 2 Years
All hips 0.06±0.28 0.006±0.12 .13
32-mm femoral head 0.063±0.27 0.007±0.126 .31
36-mm femoral head 0.057±0.29 0.006±0.118 .29

Wear Rates at 1 and 2 Years Postoperatively, when Negative Results Are Considered Zero

Mean Wear Rate, mm/yr
P Value
1 Year 2 Years
All hips 0.12±0.23 0.05±0.06 .013
32-mm femoral head 0.13±0.22 0.056±0.065 .087
36-mm femoral head 0.12±0.24 0.047±0.06 .056

10.3928/01477447-20110427-08

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