Poor outcome of 44 cemented total hip arthroplasties with alumina ceramic heads: Clinical evaluation and retrieval analysis after 10-16 years

We evaluated the long-term results of cemented total hip arthroplasty with alumina ceramic heads in 39 patients (44 hips) from 1981 to 1985. The study comprised 8 men (8 hips) and 31 women (36 hips). Their mean age was 54 (37-76) years and mean weight 52 (34-93) kg. The preoperative diagnoses were osteoarthrosis in 34 patients (38 hips), rheumatoid arthritis in 3 (4 hips) and idiopathic osteonecrosis of the femoral head in 2 (2 hips). The mean duration of follow-up was 13 (10-16) years. At this time, 6 cases had been revised because of aseptic loosening (5 hips showed loosening of both components and 1 acetabular loosening alone). Kaplan-Meier survivorship analysis with radiographic loosening as end-point showed 10-year survival rates of 75% for the acetabular component and 86% for the femoral. The mean linear wear rate of polyethylene was 0.10 mm/year radiographically--i.e., about the same as reported for many metal to polyethylene bearings. 5 alumina ceramic heads were retrieved and showed excellent surface roughness and roundness without scratches. However, debris stuck to the gaps was detected. The debris may act as third-bodies and affect polyethylene wear.     

Poor outcome of 44 cemented total hip arthroplasties with alumina ceramic heads: clinical evaluation and retrieval analysis after 10-16 years.

We evaluated the long-term results of cemented total hip arthroplasty with alumina ceramic heads in 39 patients (44 hips) from 1981 to 1985. The study comprised 8 men (8 hips) and 31 women (36 hips). Their mean age was 54 (37-76) years and mean weight 52 (34-93) kg. The preoperative diagnoses were osteoarthrosis in 34 patients (38 hips), rheumatoid arthritis in 3 (4 hips) and idiopathic osteonecrosis of the femoral head in 2 (2 hips). The mean duration of follow-up was 13 (10-16) years. At this time, 6 cases had been revised because of aseptic loosening (5 hips showed loosening of both components and 1 acetabular loosening alone). Kaplan-Meier survivorship analysis with radiographic loosening as end-point showed 10-year survival rates of 75% for the acetabular component and 86% for the femoral. The mean linear wear rate of polyethylene was 0.10 mm/year radiographically--i.e., about the same as reported for many metal to polyethylene bearings. 5 alumina ceramic heads were retrieved and showed excellent surface roughness and roundness without scratches. However, debris stuck to the gaps was detected. The debris may act as third-bodies and affect polyethylene wear.     

Analysis of survivorship after total hip arthroplasty using a ceramic head

To determine the clinical efficacy of an alumina ceramic head, 119 cemented total hip arthroplasties in 97 patients using an alumina head coupled with ethylene oxide gas sterilized polyethylene were reviewed. Eighty-two patients (101 hips) with greater than 10 years followup were evaluated clinically and radiographically (range, 10-17.6 years), and 97 patients (119 hips) were evaluated for survivorship analysis (range, 0.6-17.6 years). The average functional hip scores according to Merle d'Aubigné and Postel improved from 8.6 preoperatively to 15.0 at the final followup, and 57 patients (64 hips) had no pain. The average polyethylene wear rate was 0.15 mm/year (range, 0.04-0.34 mm/year). Patients with polyethylene wear greater than 3 mm showed significantly higher rates of acetabular loosening. Fifteen-year survival rates (with 95% confidence intervals) with radiographic evidence of aseptic loosening as the end point were 46.8% +/- 13.4% in acetabular components and 91.9% +/- 6.6% in femoral components. Fifteen-year survival rates of hip arthroplasties with revision because of aseptic loosening as the end point were 75.3% +/- 10.2% and 97.9% +/- 3.0%, respectively. Results of the current study suggest that using an alumina head instead of a metal head may not be beneficial when coupled with ethylene oxide gas sterilized polyethylene.     

Alternative bearing surfaces in total hip arthroplasty: zirconia-alumina pairing. Contribution or caveat?

The aim of the present study was to evaluate the zirconia and alumina articulation in total hip arthroplasty in regard to clinical and radiological outcome. This is the first report concerning the clinical application of a hybrid ceramic articulation. Owing to ethical reasons, a limited number of patients was enrolled in the study. Ten consecutive patients with degenerative arthritis were randomly allocated after informed consent to hybrid total hip arthroplasty treatment using an alumina femoral head and an alumina acetabular liner (5 hips), or using a zirconia femoral head and an alumina acetabular liner (5 hips). The median age of patients at index operation was 57.8 years. Current criteria were used for clinical and radiological assessment. The mean follow-up was 5.1 years (5 to 5.3 years). No hip required revision, and no clinical and radiological differences were observed between the two groups of hips. The median preoperative Harris hip score was rated 55.3 points in the control group of hips with alumina head, and 55.6 in the group of hips with zirconia head. The median Harris hip score increased to 94.9 points at the time of follow-up in the control group, and 96 points in the zirconia group. No radiological signs of cup loosening or focal acetabular osteolysis were detected at follow-up. All stems showed stable fixation without radiolucent lines or focal osteolysis. Zirconia femoral heads and alumina acetabular liners have been successfully used in the present series of 5 total hip arthroplasties with a mean follow-up of 5.1 years. Nevertheless, the use of femoral heads made of zirconia in total hip arthroplasties remains an important clinical concern due to the potential genesis of wear microparticles which can lead to progressive osteolysis. Further in-vitro and in-vivo investigations are required to define the value of this alternative bearing surface.     

Efficacy of alumina ceramic heads for cemented total hip arthroplasty.

Fifty-seven cemented total hip arthroplasties (THAs) were reviewed in cases of osteoarthrosis secondary to congenital dysplasia or dislocation. The bearing surface of the prosthesis used in this series consists of a polyethylene acetabular component on an alumina ceramic head. All acetabular components were positioned at the same level as the original acetabulum, and an autologous femoral head graft was performed for 18 hips. The follow-up period ranged from five to eight years, averaging six years two months. The latest survey showed excellent and good results for 53 hips (92.9%). Four acetabular components (7%) and two femoral components (3.5%) showed roentgenographic evidence of loosening. Only one hip (1.8%) had to be treated with revision surgery for femoral component loosening. None of the cases suffered a broken ceramic head. The use of a total hip prosthesis with an alumina ceramic head in THA is likely to lead to excellent results for patients with osteoarthrosis of the hip.     

Alumina ceramic-on-ceramic total hip replacement with a layered acetabular component

A modular layered acetabular component (metal-polyethylene-ceramic) was developed in Japan for use in alumina ceramic-on-ceramic total hip replacement. Between May 1999 and July 2000, we performed 35 alumina ceramic-on-ceramic total hip replacements in 30 consecutive patients, using this layered component and evaluated the clinical and radiological results over a mean follow-up of 5.8 years (5 to 6.5). A total of six hips underwent revision, one for infection, two for dislocation with loosening of the acetabular component, two for alumina liner fractures and one for component dissociation with pelvic osteolysis. There were no fractures of the ceramic heads, and no loosening of the femoral or acetabular component in the unrevised hips was seen at final follow-up. Osteolysis was not observed in any of the unrevised hips. The survivorship analysis at six years after surgery was 83%. The layered acetabular component in our experience, has poor durability because of unexpected mechanical failures including alumina liner fracture and component dissociation.     

Polyethylene sterilized without irradiation in a polished uncemented acetabular component-a clinical and radiographic analysis

Clinical and radiographic analysis of the Reflection uncemented acetabular component was performed. Features of this component include a polished inner shell and ethylene oxide sterilization. Clinical information was available for 158 hips (mean, 4.6 years follow-up). A total of 19 hips have undergone or were recommended revision, 8 for aseptic loosening or wear (5%). Wear analysis was performed for 38 hips with more than 5 years of follow-up (mean, 6.7 years). Osteolysis was present in 20 of these patients. Penetration rate averaged 0.15 mm/y. Patients with uncemented femoral fixation (vs cemented) had a significantly higher penetration rate. Increased volumetric wear was seen with uncemented femoral fixation, thin liners, and ceramic heads. This component demonstrated relatively high penetration and osteolysis rates. Continued surveillance is recommended, particularly for active patients with thin liners.     

Debris from failed ceramic-on-ceramic and ceramic-on-polyethylene hip prostheses

To compare the properties of wear debris between ceramic-on-ceramic and ceramic-on-polyethylene total hip prostheses, particles were isolated and characterized from tissue biopsies obtained at revision arthroplasty or autopsy from two similar uncemented modular hip systems. Group A hips (11 patients; mean, 31 months in vivo) had titanium shells with alumina inserts, alumina femoral heads, and titanium alloy stems. Group B hips (seven patients; mean, 42 months) were the same as Group A but with polyethylene acetabular inserts. Particles were characterized using an electrical resistance particle analyzer, scanning electron microscope, and energy dispersive xray spectroscope. Most of the particles in Group A were ceramic, whereas most of the particles in Group B were polyethylene. Metal particles from the femoral stem and the acetabular shell also were present. If one Group A hip with impingement is excluded, the rate of particle production is significantly lower in the ceramic-on-ceramic group than in the ceramic-on-polyethylene group. With the number of samples available, no significant difference in average size could be detected among the different types of particles or among the groups.     

Polyethylene wear against alumina and zirconia heads in cemented total hip arthroplasty

We compared the polyethylene wear of acetabular sockets articulated with 22.225-mm alumina heads with the polyethylene wear of those articulated with 22.225-mm zirconia heads in cemented total hip arthroplasty during a mean follow-up period of 5.4 years. Using a computer-aided technique, we measured polyethylene wear radiologically in 46 hips with alumina heads and 58 hips with zirconia heads. The preoperative diagnosis in all cases was osteoarthritis. The mean linear wear rate and mean volumetric wear rate of polyethylene sockets against zirconia heads were 0.133 mm/y and 39.8 mm(3)/y, respectively, significantly greater (P < .01) than the wear rates against alumina heads (0.078 mm/y and 24.2 mm(3)/y, respectively). Age at operation, patient body weight as well as height, thickness of polyethylene, and socket abduction angle did not influence the wear rates. We speculate that the excessive polyethylene wear was caused by phase transformation of zirconia, leading to an increase of surface roughness.     

Polyethylene wear and synovitis in total hip arthroplasty: a sonographic study of 48 hips

Forty-six patients (48 hips), operated on with cemented total hip arthroplasty (THA) because of arthrosis, were examined radiographically and sonographically at 10-year follow-up. Polyethylene wear of acetabular cups was measured on conventional non-weight-bearing pelvic radiographs, and the volume of polyethylene debris was calculated. Radiographic signs of loosening were identified. The capsular distance (ie, thickness of the synovium or synovial contents) was measured sonographically. We found a significant correlation between increased volumetric wear and increased capsular distance. Hips with radiographically loose acetabular components had significantly greater volumetric wear and capsular distance than those without signs of acetabular loosening. This relationship was not observed in hips with radiographically loose femoral components. In cemented THA, the volume of polyethylene wear debris and the thickness of the synovium and the synovial contents are related. In the event of radiographic loosening of the acetabular component, they are both increased.     

Preliminary clinical and radiographic results of large ceramic heads on highly cross-linked polyethylene

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.     

Large Metal Heads and Highly Cross-Linked Polyethylene Provide Low Wear and Complications at 5-13 Years

Background

Highly cross-linked polyethylene (XLPE) is reported to have low rates of linear and volumetric wear at 10-14 years. In a prior study, larger (36 and 40 mm) femoral heads were associated with more volumetric wear, but there were only 12 hips with these heads.

Primary total hip arthroplasty with a cementless porous-coated anatomic total hip prosthesis: 10- to 12-year results of prospective and consecutive series.

We performed a prospective study in 108 consecutive patients (116 hips) who were followed for a minimum of 10 years (10-12 years) after primary total hip arthroplasty using an uncemented porous-coated anatomic (PCA) hip prosthesis. The average age of the patients at operation was 48.4 years (range, 19-85 years), and the diagnosis was avascular necrosis of the femoral head in 46 hips, neglected femoral neck fracture in 27, osteoarthrosis secondary to childhood pyogenic arthritis in 24, childhood tuberculous arthritis in 5, and miscellaneous in 14. The average preoperative Harris Hip Score was 55 points, which improved to 87 points at 11 years. Seventy-five hips (65%) were excellent, 11 (9%) were good, and 30 (39%) were poor. The overall rate of revision was 15% (17 of 116 hips). The rate of revision of the femoral component was 11% (13 of 116 hips), and the rate of revision of the acetabular component was 15% (17 of 116 hips). The prevalence of thigh pain was 28% at 11 years. The increase in the incidence of aseptic loosening of the femoral component was found to explain the high incidence of severe thigh pain at 11 years' follow-up. At 11 years, there was femoral osteolysis in 69 hips (59%) and acetabular osteolysis in 65 hips (56%). At 6 years, 20 hips (17%) showed definite wear of the polyethylene liner. At 11 years, 81 hips (70%) showed definite wear of the polyethylene liner. Because the complication rate of the PCA hip prosthesis with respect to loosening, osteolysis, and excessive wear in the polyethylene liner is high, we abandoned the use of this implant.     

Mittelmeier ceramic—ceramic prosthesis after 10 years

The clinical status of 83 Mittelmeier ceramic—ceramic (Mark II) cementless total hip prostheses (Autophor, Osteo AG, Selzach, Switzerland) implanted between 1978 and 1984 was analyzed. Retrieved tissue from the revised hips was studied histologically. The mean patient age was 47.5 years (range, 19–71 years). One or both components of 12 hips were revised (16% at 16 years in the survival study). Eleven acetabular components and seven stems were revised, with three of the sockets fractured. The mean follow-up period for the patients with unrevised hips was 12.3 years. Osseointegration was uncommon in both the cup and stem. Radiographic cup loosening was observed in 53% of hips at 16 years in the survival study, with most having a complete radiolucent line of 2 mm around the cup. Radiographic stem loosening appeared in 15% of hips at 16 years. Fibrous stable fixation was present in 64% of stems. Significant radiographic acetabular wear was not observed in any hip. The Mittelmeier Mark II prosthesis had worse long-term results than reported with cemented or other uncemented prostheses. Although there was no significant acetabular wear, intracellular ceramic wear debris was seen in the retrieved tissues.     

Ceramic-on-polyethylene bearing surfaces in total hip arthroplasty. Seventeen to twenty-one-year results.

BACKGROUND: Polyethylene wear debris, and the resulting inflammatory response leading to osteolysis and loosening, is the primary mode of failure limiting the longevity of total hip replacements. Alternative bearing surfaces, including ceramic-on-polyethylene, have been investigated in an effort to decrease the amount of polyethylene wear debris. The purpose of this study was to evaluate the seventeen to twenty-one-year results of the use of ceramic-on-polyethylene total hip prostheses. METHODS: Sixty-four total hip prostheses were implanted with cement, by one surgeon, in fifty-six patients from 1978 to 1981. The average age at the index arthroplasty was sixty-nine years (range, fifty-one to eighty-four years). The components consisted of a cemented Charnley-Müller stem with a 32-mm modular alumina femoral head and a cemented all-polyethylene acetabular component. All patients who retained the index prosthesis were assessed clinically with use of Harris hip scores and were evaluated radiographically at the time of the latest follow-up. RESULTS: At the time of this latest follow-up, of the original sixty-four implants, eighteen (28%) were still in place and five (8%) had been revised. The remaining forty-one implants were in patients who had died and were functioning well until the patient's death. No patient was lost to follow-up. Of the eighteen hips with an intact prosthesis in the surviving patients, seven had an excellent clinical result; nine, a good result; and two, a fair result. One asymptomatic hip had definite radiographic evidence of femoral loosening. No hip had definite signs of acetabular loosening or evidence of osteolysis. Survivorship analysis revealed that the probability of survival of the prostheses without revision was 95% at five years, 95% at ten years, 89% at fifteen years, and 79% at twenty years. The mean linear and volumetric polyethylene wear rates were 0.034 mm/yr and 28 mm(3)/yr, respectively. There were no fractures of the ceramic heads. CONCLUSIONS: Outstanding long-term clinical and radiographic results were attained despite the use of what are now considered substandard techniques (an inferior stem design, a 32-mm head, and first-generation cementing techniques). The wear rates in this study are lower than previously reported metal-on-polyethylene wear rates and are consistent with the lowest reported in vivo ceramic-on-polyethylene wear rates. These findings support the consideration of ceramic-on-polyethylene bearing surfaces in total hip arthroplasty.     

Precoated femoral component in total hip arthroplasty. Results of 5- to 9-year followup.

One hundred nineteen consecutive primary hybrid total hip arthroplasties with a precoated femoral component were performed by one surgeon in 100 patients and followed up prospectively. Ninety-eight hips in 82 patients (mean age, 67 years) were evaluated clinically and radiographically at a mean of 6.5 years (range, 5-9 years). The hips were evaluated clinically using the Harris hip score, and radiographs were evaluated for femoral cement grade, loosening, and osteolysis. Ninety-five hips remained in place at the most recent followup. Two femoral components were revised for definite loosening, and one well fixed femoral component was removed because of late hematogenous infection. Excluding the three hips that were revised, the clinical result was excellent or good in 79 hips (83%), fair in 12 hips (13%), and poor in four hips (4%). All other femoral components were well fixed. There were defects of the cement mantles (C1 and C2) in 90 hips. No femoral component had a stem and cement radiolucent line. Focal femoral osteolysis was seen in only two hips. One acetabular component was removed at 5 years because of late hematogenous infection. One acetabular component had asymptomatic migration. The remaining 96 acetabular components were well fixed. Focal acetabular osteolysis was present in four hips. The mean linear polyethylene wear rate was 0.06 (+/- 0.05) mm per year. In contrast to other reports of early failure and osteolysis, the use of a precoated femoral component in this study did not adversely affect the fixation of hybrid total hip arthroplasty, with definite failure of only 2% (two of 98) of the femoral components.     

Cementless total hip arthroplasty using a threaded cup and a rectangular tapered stem. Follow-up for ten to 17 years

We carried out a clinical and radiological review of 103 cementless primary hip arthroplasties with a tapered rectangular grit-blasted titanium press-fit femoral component and a threaded conical titanium acetabular component at a mean follow-up of 14.4 years (10.2 to 17.1). The mean Harris hip score at the last follow-up was 89.2 (32 to 100). No early loosening and no fracture of the implant were found. One patient needed revision surgery because of a late deep infection. In 11 hips (10.7%), the reason for revision was progressive wear of the polyethylene liner. Exchange of the acetabular component because of aseptic loosening without detectable liner wear was carried out in three hips (2.9%). After 15 years the survivorship with aseptic loosening as the definition for failure was 95.6% for the acetabular component and 100% for the femoral component.     

Tribological and material analyses of retrieved alumina and zirconia ceramic heads correlated with polyethylene wear after total hip replacement

It has been suggested that the wear of ultra-high molecular weight polyethylene (UHMWPE) in total hip replacement is substantially reduced when the femoral head is ceramic rather than metal. However, studies of alumina and zirconia ceramic femoral heads on the penetration of an UHMWPE liner in vivo have given conflicting results. The purpose of this study was to examine the surface characteristics of 30 alumina and 24 zirconia ceramic femoral heads and to identify any phase transformation in the zirconia heads. We also studied the penetration rate of alumina and zirconia heads into contemporary UHMWPE liners. The alumina heads had been implanted for a mean of 11.3 years (8.1 to 16.2) and zirconia heads for a mean of 9.8 years (7.5 to 15). The mean surface roughness values of the explanted alumina heads (Ra 40.12 nm and Rpm 578.34 nm) were similar to those for the explanted zirconia heads (Ra 36.21 nm and Rpm 607.34 nm). The mean value of the monoclinic phase of two control zirconia heads was 1% (0.8% to 1.5%) and 1.2% (0.9% to 1.3%), respectively. The mean value of the monoclinic phase of 24 explanted zirconia heads was 7.3% (1% to 26%). In the alumina group, the mean linear penetration rate of the UMWPE liner was 0.10 mm/yr (0.09 to 0.12) in hips with low Ra and Rpm values (13.22 nm and 85.91 nm, respectively). The mean linear penetration rate of the UHMWPE liner was 0.13 mm/yr (0.07 to 0.23) in hips with high Ra and Rpm values (198.72 nm and 1329 nm, respectively). This difference was significant (p = 0.041). In the zirconia head group, the mean linear penetration rate of the UHMWPE liner was 0.09 mm/yr (0.07 to 0.14) in hips with low Ra and Rpm values (12.78 nm and 92.99 nm, respectively). The mean linear penetration rate of the UHMWPE liner was 0.12 mm/yr (0.08 to 0.22) in hips with high Ra and Rpm values (199.21 nm and 1381 nm, respectively). This difference was significant (p = 0.039). The explanted zirconia heads which had a minimal phase transformation had similar surface roughness and a similar penetration rate of UHMWPE liner as the explanted alumina head.     

Polyethylene wear in prosthetic hips with loose components

We measured in vivo polyethylene wear of acetabular cups in 74 patients (83 hips) with Charnley total hip arthroplasties (THA), revised because of aseptic loosening of either the acetabular or femoral component. We analyzed conventional pelvic radiographs of 42 THAs before revision due to loose acetabular components alone and 41 THAs before revision due to loose femoral components alone. The THAs were revised after 10 to 26 years. The mean wear-rate in hips with a loose acetabular components was 0.3 mm/y, whereas in hips with a loose femoral components, it was 0.1 mm/y (P=.0001). The mean total linear wear, as measured on the last available radiographs before revision, was 3.4 mm and 1.5 mm, respectively (P=.0001). A significant difference in linear wear between hips with loose cups and loose stems was seen 1 year after surgery: 0.4 mm/y versus 0.3 mm/y, respectively (P=.05).     

Long-term results using the anatomic medullary locking hip prosthesis.

Since the introduction of cementless total hip arthroplasty in the early 1980s, concern has shifted from component loosening toward polyethylene wear and osteolysis. The current review of 223 consecutive unselected Anatomic Medullary Locking femoral and acetabular components extends the followup on a series of patients previously reported on at 5 and 10 years. The purposes are to describe the reasons for revisions and to assess the onset and size of osteolytic lesions, with the hypothesis that osteolysis represents an important cause of loosening. The population included 204 patients (211 hips) with mean followup of 13.9 years (range, 2-18 years). Among them, 122 patients (129 hips) had a minimum 15-year followup. Minimum 2-year radiographs with a mean radiographic followup of 12.2 years (range, 2-18 years) were available for 204 hips (197 patients). Of the entire study group, 39 hips (38 patients) had 44 component revisions, increasing the number of revisions by 24 since this series was reported previously. Twenty-six patients (27 hips) had their first revision surgery more than 10 years after the primary surgery. The most common reason for revision of original components was wear or osteolysis occurring in 22 of the 39 hips (21 of 38 patients). The overall loosening rate was 3.4% (seven of 204) for femoral components and 5.4% (11 of 204) for acetabular components. Twenty-four percent of hips (48 of 204) had evidence of femoral or pelvic osteolytic lesions larger than 1.5 cm2. Femoral osteolysis was not associated with any case of femoral loosening, whereas seven of the 11 loose acetabular components were associated with pelvic lesions larger than 1.5 cm2.