Although total hip arthroplasty (THA) is a successful procedure, fretting and corrosion at the taper of the femoral stem are growing concerns.1 There have been sporadic reports about fretting and/or corrosion at the taper after metal-on-polyethylene THA, specifically when a cobalt-chrome (Co-Cr) femoral head is used.2–8 Less is known about how fretting and corrosion at the trunnion differs between ceramic and Co-Cr heads.9–11 Ceramic femoral heads potentially reduce wear debris generated from bearing surfaces,12,13 but ceramic– metal couples would release more metal debris through fretting and corrosion than metal–metal couples. Fretting and corrosion would be greater on the metal–harder ceramic couples for the same amount of micromotion due to differences in elastic moduli and mismatched flexural rigidity. A given load will result in differential material deformation, leading to greater micromotion at the ceramic–metal coupling.9
Although there have been sporadic reports of fretting and corrosion at the trunnion following THA with a metal-on-polyethylene bearing,6,8,14 to the authors' knowledge, no study has compared the prevalence of fretting and corrosion at the trunnion of Co-Cr and zirconia ceramic heads in the same patients. In the current study, the authors sought to determine whether after THA with a Co-Cr or zirconia ceramic femoral head-on-polyethylene bearing (1) fretting and corrosion can occur secondary to metal debris and/or metallic ions at the trunnion of Co-Cr heads vs zirconia ceramic heads and (2) zirconia ceramic heads resulted in less fretting and corrosion than Co-Cr heads.
Materials and Methods
At the authors' institution, 558 patients (818 hips) underwent primary THAs performed by the senior author (Y.-H.K.) between May 1994 and March 2000. Of these 558 patients, 84 patients (168 hips) who underwent isolated revision of the acetabular component from January 2012 to April 2015 for polyethylene wear and osteolysis met the inclusion criteria and were recruited to participate in the study. Patients were excluded if they had unilateral THAs, were older than 50 years at the time of the primary THAs, or had no isolated revision of the acetabular components. The study protocol received institutional review board approval. A detailed informed consent form was signed by each patient. Six patients were lost to follow-up before 2 years postoperatively, leaving 78 patients (156 hips) available for study. The previously reported 10 patients with bilateral THAs were included in the study.15
There were 65 men and 13 women. Mean age was 48 years (SD, 12.7 years; range, 21–49 years) at the time of primary THA. Mean weight was 72 kg (SD, 9.1 kg; range, 56–105 kg), mean height was 170 cm (SD, 9 cm; range, 153–184 cm), and mean body mass index was 28 kg/m2 (SD, 3 kg/m2; range, 27–39 kg/m2). Mean interval between the primary THA and isolated revision of the acetabular component was 16 years (range, 10–18 years). The mean polyethylene wear per year was 0.3±0.1 mm (range, 0.1–0.5 mm) in the zirconia head group and 0.2±0.1 mm (range, 0.05–0.4 mm) in the Co-Cr head group. Polyethylene wear was measured as previously described.16 Mean follow-up after revision of the acetabular component was 4 years (range, 2–5 years). Initially, the presenting symptoms varied among the patients but included groin and anterior thigh pain.
A posterolateral approach was used in all hips for primary THA. All of these primary THAs were performed by the senior author. A cementless Profile stem (titanium alloy) (DePuy, Leeds, United Kingdom) with a zirconia ceramic femoral head (32 mm) was used in 1 hip and a cementless Profile stem with a Co-Cr femoral head (32 mm) was used in the contralateral hip. Taper size was 12/14 mm in both groups. Randomization to treatment with Co-Cr vs zirconia ceramic head was done using a computer-generated study number in a sealed envelope, which was opened in the operating room before skin incision. A cementless Duraloc 100 series (with no screw hole) and 1200 series (with screw holes) acetabular component (DePuy) was used in all hips in both groups. A conventional polyethylene liner made of ram-extruded 415 GUR polyethylene (Ticona GmbH, Frankfurt, Germany) with an inner diameter of 32 mm was used in all hips in both groups. The polyethylene (average thickness, 9 mm) was irradiated in a vacuum and packaged in a vacuum state in both groups.
Before revision surgery, radiographs and computed tomography scans were obtained for all patients. In each case, polyethylene wear and acetabular osteolysis were detected on the radiographs and computed tomography scans. All femoral stems were fixed solidly in both groups. On computed tomography scan, no patient had evidence of abductor muscle deficiency or pseudotumor in the hip joints. Laboratory tests, including erythrocyte sedimentation rate and C-reactive protein level, joint fluid analysis, and culture yielded normal results.
An old posterolateral surgical incision was used in all cases for revision of the acetabular components. A large amount of synovial fluid with polyethylene debris was encountered on entry into the hip joint. A loose acetabular component was removed. Frozen-section analysis, intraoperative cultures, and permanent histological analysis of synovial fluid were performed in all cases.
Polyethylene wear debris and abnormal hypertrophic tissues were removed while a complete synovectomy was performed. In all cases, the Co-Cr or zirconia ceramic femoral head remained securely engaged on the trunnion of the femoral stem. Each modular head was disengaged from the trunnion, and femoral heads were cleaned with a dry lap pad to inspect the fretting and/or corrosion. The surgeon visually inspected the trunnion of the stem and the inner taper of the Co-Cr and zirconia ceramic heads.
Fretting and corrosion at the trunnion of Co-Cr and zirconia ceramic heads were examined using a magnifying lens. Scratching perpendicular to machining lines on the trunnion and/or wearing away of the machining lines were defined as fretting.17 White haziness (indicative of intergranular crevice corrosion), discoloration, and/or blackened debris were defined as corrosion.18 Degree of fretting and corrosion damage at the trunnion of the stem was scored using a previously published 4-point scoring technique.19 A score of 1 indicated minimal fretting or corrosion (fretting on <10% of the surface and no corrosion damage); 2 indicated mild damage (fretting on >10% of the surface and/or corrosion attack confined to 1 or more small areas); 3 indicated moderate damage (fretting >30% and/or aggressive local corrosion attack with corrosion debris); and 4 indicated severe damage (fretting on most [>50%] of the mating surface with severe corrosion attack and abundant corrosion debris). The degree of metal transfer to the inner taper of the ceramic heads was scored using a similar 4-point scoring technique. A score of 1 indicated minimal metal transfer (<10% of the taper surface); 2 indicated metal transfer greater than 10%; 3 indicated metal transfer greater than 30%; and 4 indicated metal transfer greater than 50% of the inner head taper. The scoring plan for the head and stem tapers was developed in collaboration with a consultant biostatistician. Scoring was performed independently by 3 researchers, and their scores were averaged. The intraclass correlation coefficient among the 3 researchers for scoring fretting and corrosion was 0.89 and 0.91, respectively, which was considered excellent.
All acetabular components were revised using a 36-mm alumina delta ceramic liner (CeramTec, Plochingen, Germany). The femoral head was replaced with a new 36-mm alumina delta ceramic head in all hips. A titanium-alloy adapter sleeve (CeramTec) was not inserted over the existing trunnion in any hip in either group.
Patients started to walk on the second postoperative day and progressed to full weight bearing using a walking frame or crutches as comfort permitted. They were advised to use a walking aid for 6 weeks.
Patients were followed at 3 months, 1 year, and 2 or 3 years postoperatively. Harris hip score20 and Western Ontario and McMaster Universities Osteoarthritis Index21 were recorded at each visit. Patient activity level was assessed using the University of California at Los Angeles activity score.22 Radiologic evaluation for radiolucent lines around the acetabular and femoral components, osteolysis, or ceramic fracture was performed at 3 months, 1 year, and 2 or 3 years postoperatively.
To detect an effect size of 0.5, corresponding to an anticipated difference of 5 points in the Harris hip score and standard deviation of 6 points, the authors calculated that 65 patients were required in each group. Anticipating a 10% dropout rate, they aimed for 78 patients in each group. To determine the statistical intraclass correlation between the researchers for scoring the implants, SPSS version 19.0 software (SPSS Inc, Chicago, Illinois) was used. The Shapiro–Wilk test was performed to determine if the fretting and corrosion scores were normally distributed. In all cases, the fretting and corrosion scores did not display a normal distribution. Consequently, the Mann–Whitney U test, a nonparametric statistical hypothesis test that can be used to determine whether 1 of 2 independent sample groups contains significantly larger values, was performed. Fisher's exact test, a statistical significance test used for categorical data when classifying objects in 2 ways, was also conducted. The authors calculated descriptive statistics (mean, standard deviation, and proportion) for continuous study variables. Harris hip score and Western Ontario and McMaster Universities Osteoarthritis Index were analyzed using a paired t test. Radiographic data were compared using a paired t test.
Hypertrophied synovium containing polyethylene wear debris was found in all hips in both groups. No hip in either group had trunnionosis (pseudotumor and abductor muscle damage). On histological analysis of all tissue specimens, no tissue necrosis was revealed in any hip. Remaining viable capsular tissues did not show an area of dense perivascular infiltration of lymphocytes. Intraoperative cultures did not have bacterial or fungal growth for patients in either group.
There were no significant differences between the 2 groups in frequency of observed fretting and corrosion at the trunnion. Evidence of fretting of the trunnion was observed in 63 of 78 hips (81%) in the Co-Cr head group and in 65 of 78 hips (83%) in the zirconia ceramic head group (P=.518). Evidence of corrosion at the trunnion was observed in 3 of 78 hips (4%) in the Co-Cr head group and in 2 of 78 hips (3%) in the zirconia ceramic head group (P=.612). For the Co-Cr head group, the median corrosion score at the trunnion was 1.2±0.8 points. For the zirconia ceramic head group, the median corrosion score at the trunnion was 1.3±0.9 points. Thus, there was no significant difference between the 2 groups (P=.781). For the Co-Cr head group, the median fretting score at the trunnion was 1.4±1.1 points. For the zirconia ceramic head group, the median fretting score at the trunnion was 1.2±1.4 points. Thus, there was no significant difference between the 2 groups (P=.893). Evidence of metal transfer to the inner taper of the femoral head was observed in 6 of 78 hips (8%) in the Co-Cr head group and in 8 of 78 hips (10%) in the zirconia ceramic head group (P=.213). The median metal transfer score was 1.2±0.9 points for the Co-Cr head group vs 1.4±1.1 points for the zirconia ceramic head group (P=.729).
At final follow-up, the mean Harris hip scores (88 vs 90 points), Western Ontario and McMaster Universities Osteoarthritis Index (17 vs 16 points), and University of California at Los Angeles activity scores (7 vs 7 points) were not significantly different between the 2 groups. Most of the revised acetabular components (89% vs 87%) were well fixed at final follow-up.
There have been sporadic reports of trunnionosis associated with fretting and/or corrosion at the trunnion after metal-on-polyethylene THA, specifically when a Co-Cr femoral head is used.6,8,14 This trunnionosis is similar to the deleterious local tissue reactions reported in some patients with metal-on-metal bearing surfaces.2–5 The use of ceramic heads in THA has been advocated on the basis of their superior wear resistance. Furthermore, ceramic femoral heads, which are electrical insulators, would lead to less trunnion corrosion than that previously reported with Co-Cr femoral heads.9,23,24 Less is known about fretting and corrosion at the trunnion of ceramic and Co-Cr heads.9–11 The reported prevalence of trunnionosis in metal-on-polyethylene THA has ranged between 0.25% and 13.3%, owing to fretting and corrosion at the trunnion.25–30 In the current study, the authors determined after THA with a Co-Cr or a zirconia ceramic femoral head-on-polyethylene bearing whether (1) trunnionosis can occur secondary to metal debris from fretting and/or corrosion at the trunnion of Co-Cr heads vs zirconia ceramic heads and (2) zirconia ceramic heads resulted in less trunnionosis than Co-Cr heads.
The current study had some limitations. First, preoperative serum metal ion levels were not measured, and magnetic resonance imaging was not performed to document soft tissue damage. However, histological analysis of the tissue specimens in all patients revealed no evidence of tissue necrosis or perivascular infiltration of lymphocytes. Furthermore, although computed tomography is not comparable to magnetic resonance imaging in documenting soft tissue damage, the authors found that the computed tomography scans were helpful in screening out soft tissue damage. Second, both groups had femoral heads of only 32 mm. Increasing head diameter to 36 or 40 mm may increase stresses at the trunnion and contribute to tribocorrosion and metal ion release. Third, the prevalence of trunnionosis was likely underreported in this cohort, as patients without revision for polyethylene wear and osteolysis were not screened for trunnionosis. Fourth, the low body weight of this group of Korean patients may limit general applicability of the data to other groups of patients. However, although these patients had low body weight, their daily activities, including farming, squatting, and lifting, were vigorous.
The prevalence of trunnionosis in metal-on-polyethylene THA varies, with Hussey and McGrory26 reporting 3.2%, Plummer et al28 reporting 27 patients, Whitehouse et al30 reporting 0.25%, Lash et al27 reporting 11%, Cooper et al25 reporting 1.8%, and White et al29 reporting 13.3%. In the current series, the authors found no trunnionosis due to fretting and/or corrosion at the trunnion in either group. They believe that was because both types of heads had a mild degree of fretting and corrosion.
Hallab et al9 hypothesized that commercially available ceramic head–metal trunnion couples release more metal debris through fretting and/or corrosion than metal head–metal trunnion couples. This was based on the presumption that fretting would be greater on the metal male component when coupled with the harder ceramic female head component for the same amount of micromotion, due to differences in elastic moduli and mismatched flexural rigidity. However, the zirconia ceramic heads did not have greater fretting and/or corrosion than the Co-Cr heads.9 Hallab et al9 offered several possible reasons why the zirconia ceramic head–metal trunnion couples had less fretting and/or corrosion. First, hard-on-soft mechanical interlocking of the ceramic head–metal trunnion contact surfaces could be greater, thereby reducing any potential relative micromotion. Second, the fidelity of interlocking of the ceramic head–metal trunnion could be better preserved over the duration of such long-term fretting testing. Third, the subtle differences in the surface roughness patterns between the 2 types of heads could influence the mechanical interlocking and thus affect fretting. Finally, the micromotion of both modular couples could be the same, but the release of metal from 2 metallic bearing surfaces could disproportionately exceed that of a single surface in the ceramic head–metal trunnion.9
Kurtz et al24 reported that fretting and corrosion scores were lower for the stems in the ceramic head–metal trunnion when compared with the metal head–metal trunnion cohort. Huot Carlson et al10 observed less proximal femoral stem trunnion corrosion for cases with a ceramic–metal trunnion interface as opposed to cases with a metal–metal trunnion interface. In the current series, there was mild fretting and corrosion in the head–trunnion interface in both and no significant differences in fretting and corrosion between the 2 groups. The authors believe that tight taper impaction technique, engagement of the modular trunnion interface in a clean and dry environment, and 32-mm femoral heads all influenced trunnion fretting and corrosion, regardless of whether the femoral head was Co-Cr or ceramic.7,31
In the current series, there was no trunnionosis in the hips with a Co-Cr or a zirconia ceramic head secondary to metal debris resulting from fretting and corrosion. The authors observed only a mild degree of fretting and corrosion at the trunnion of both Co-Cr and zirconia heads. In addition, the severity of fretting and corrosion was not significantly different between the 2 groups.
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