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Seven to 10 Years Followup of an Anatomic Hip Prosthesis: An International Study

Herrera, Antonio*; Canales, Vicente*; Anderson, John; García-Araujo, Carlos; Murcia-Mazón, Antonio§; Tonino, Alphons, J

Clinical Orthopaedics and Related Research: June 2004 - Volume 423 - Issue - p 129-137
doi: 10.1097/01.blo.0000128973.73132.0b
SECTION II: ORIGINAL ARTICLES
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Hypothetically, hydroxyapatite-coated anatomic-shaped femoral stems and hemispheric acetabular cups should improve biologic fixation of the implant and strength transmission to the bone, improving unsatisfactory results of the first cementless hip prosthesis focused on the stress-shielding phenomenon at the femur and failure of the threaded acetabular cups. A consecutive series of 312 patients who had primary Anatomique Benoist Giraud hip prostheses unilaterally implanted were followed up. We analyzed the clinical and radiographic results and report the outcomes 7–10 years after implantation. Two hundred thirty-two patients were assessed at 7–10 years. The survival rate for the implant was 96.8%; 77.2% of patients had no pain, 72.4% maintained total mobility, and 62.9% were able to walk without restrictions. However, radiologic assessment shows that problems improved but did not disappear. More than 55% of femurs had signs of proximal stress-shielding develop. More important, substantial polyethylene wear was observed in at least 62% of the acetabular inserts at 7–10 years followup.

From the *Department of Orthopaedic Surgery, University Hospital “Miguel Servet”, Zaragoza, Spain; †South Cleveland General Hospital, Middlesbrough, England; ‡Department of Orthopaedic Surgery, Hospital “La Princesa”, Madrid, Spain; §Department of Orthopaedic Surgery, Hospital “De Cabueñes”, Gijón, Spain; and the Department of Orthopaedics, De Wever Hospital, Heerlen, The Netherlands.

Received: October 18, 2002

Revised: March 24, 2003; July 16, 2003

Accepted: July 21, 2003

The study was supported by Stryker Howmedica Osteonics.

Correspondence to: A. Herrera, MD, Servicio de Cirugía Ortopédica, Hospital Universitario “Miguel Servet”, Paseo de Isabel La Católica 1-3, 50009 Zaragoza, Spain. Phone: 34 976 76 56 64; Fax: 34 976 76 56 52; E-mail: aherrerar@wanadoo.es.

Cemented hip prostheses have been implanted with satisfying results since the 1960s.7,8 However, the relatively frequent onset of pain and disability, secondary to loosening at the prosthesis-cement or cement-bone interfaces26,28,36 has impaired long-term outcomes, particularly in young patients.

The first cementless designs, characterized by straight and very stiff distally fixed cementless stems, had serious stress-shielding phenomenons.30,34 Threaded acetabular cups also failed after 4–5 years.30,34 To avoid these problems new fixation systems were developed,15,16 and new models were designed. New hemispheric press-fit acetabular cups and new anatomic-shaped femoral stems transmitted load in the metaphyseal area, theoretically reducing the stress-shielding effect. However, this effect did not disappear, although it became weaker.20,44 A new step to improve proximal fixation of the femoral stem consisted of using HA coating on its metaphyseal part to facilitate bone ongrowth.1,19,21

Another problem detected in cemented prostheses was the appearance of osteolysis secondary to inflammatory reactions against polyethylene (PE) and cement particles.29,36 The problem of osteolysis has not disappeared with new cementless implants,37 although now its origin is PE wear. This probably is the most serious threat to implant survival according to Harris who stated, “the problem is osteolysis”.23

A prospective international study evaluated the midterm followup results of an anatomic proximal hydroxyapatite (HA)-coated stem and hemispheric HA-coated cup hip prosthesis. The aim of the study was to monitor the clinical and radiographic outcome of patients implanted with the ABG system. The early, 2-year, and 5-year results have been published,48,49 and the 7- to 10-year results are presented here. Although HA-coated implants have been investigated for more than a decade, only a few midterm results are published.4,14 At first, our hypothesis was that we would have a lower percentage of stress-shielding with a new anatomic proximal HA-coated design of stem. We also thought that with using a HA-coated system to facilitate bone ongrowth, we would have a lower incidence of migration of PE particles and osteolysis.

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MATERIALS AND METHODS

The objective of this study was to confirm the safety and efficacy of the ABG HA-coated total hip prosthesis (Howmedica Europe, Staines, England). Safety was assessed by recording the nature and incidence of any postoperative complication. Efficacy was assessed by evaluating postoperative pain, ROM, and functional and mechanical results. In addition, radiographs were taken at each postoperative evaluation to assess the status of implant and bone response. For logistic reasons, five of the original 10 institutions ended their participation, which left five institutions in three European countries, with a variable number of patients from each institution (Table 1). A common prospective protocol was followed in all institutions. All patients gave consent to participate in the study.

Table 1

Table 1

The operations were done between January 1990 and December 1991. Three hundred twelve patients were included in the study, with only 30 lost to followup at 7–10 years. Taking deaths into account (50 patients), this gave a compliance rate of 91%. The average followup was 8.5 years, with a minimum of 6.9 years and a maximum of 10.4 years.

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Implant System

The ABG prosthesis used in this study was designed by a group of French surgeons. The anatomic stem is made of Ti6A14V, with its proximal third HA-coated to promote proximal osseointegration, and therefore only proximal stress transfer. The macro-relief scaled surface on the proximal third was designed to encourage transmission of vertical loading from implant to bone, and to reduce dependence on friction at the HA surface. There is an area of transmission between the coated metaphysis and the noncoated diaphysis of the stem to prevent chipping of the HA during insertion. To obtain proximal rotational stability, regardless of diaphysis fill, there is 7° anteversion in the stem’s metaphyseal portion and 5° anteversion of the neck, giving 12° anteversion in the coronal plane. The stem is not polished distally but has a grit-blasted surface and tapers very slightly distally to transmit compression forces to the bone. The acetabular component is a hemispheric, totally HA-coated exact-fit cup with 12 holes where the surgeon can insert one or more spikes or screws.

The HA coating was applied with a vacuum plasma-spray torch on a sublayer of pure Ti, which improves adhesion of HA to the implant. This coating had chemical purity greater than 99.99%, crystallographic composition of 98–99% HA with a maximum porosity of 2%, the mechanical shear resistance was 62 Mpa, and the thickness was 60 ± 10 μm.2

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Patient Assessment

The patients included in this study were evaluated preoperatively, (demographics, diagnosis), perioperatively (surgical approach, size of the implants, beginning of mobilization and weightbearing, and overall result when discharged), and postoperatively (including need for revision surgery and, in some patients, date of death), establishing assessments at 3 and 6 months and annually thereafter until a maximum of 10 years or revision surgery.

All patients with the original prosthesis in situ were evaluated clinically and radiographically. The Merle D’Aubigne and Postel scoring system,39 was used for preoperative and postoperative examinations, measuring pain, mobility, and function with a maximum score for each of six. The difficulty of reduction also was recorded because it was considered to be indicative of muscle tension.

For radiologic examination AP and lateral projections of the lower pelvis were taken. The degree of osteoporosis was recorded preoperatively using a modified Singh index,15 and ectopic bone formation was evaluated according to the method of Brooker et al.3 Detailed analyses were done to assess changes of the position of the implants and of the host bone. The femur was evaluated using the Gruen zones,22 and the acetabulum using the DeLee and Charnley zones.12 Femoral cancellous densification was identified by an increase in bone mineral content anywhere between the implant and femoral cortex. Cortical thickening was identified by an increase in the outer diameter of the cortex at the proximal point of hypertrophy, whereas cortical densification was shown by an increase in bone mineral content anywhere in the cortex. Bone resorption was defined as a visible loss of trabecular bone density, cortical softening, or thinning. Reactive line formation was indicated by a thin radiopaque layer of bone seen parallel, and in close proximity to the implant and covering at least 50% of the zone length. Radiolucency was defined as a radiolucent zone anywhere around the implant, with no relationship to any radiopaque area, at least 2 mm wide, and covering at least 30% of any zone. A cyst was defined as a scalloped erosion greater than 2 mm diameter at the prosthesis interface.

Wear was analyzed by some participating investigators in a crude manner by measuring the displacement of the center of the femoral head from the center of the acetabular cup using a ruler on the radiographs.

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Statistics

For survival analysis using the Kaplan-Meier method,6 failure was defined as reoperation involving the revision of any component for any cause. Survivorship curves with corresponding confidence intervals were generated with failure defined according to three end points: (1) revision of any component; (2) revision of the acetabular component; and (3) revision of the femoral component.

Other statistical analysis has proved difficult because of the sample mix and, perhaps the differing assessment techniques used by the investigators in this multicenter study. The chi square test was used to compare two categorical variables, applying Fisher’s exact test when necessary (samples smaller than five cases). Both tests were considered significant if p < 0.05 (95% confidence level).

To compare categorical and continuous or ratio variables, normal distribution of continuous variables was monitored. If it was distributed normally (which was confirmed by doing calculations and boxplot diagrams to compare the mean, 5% trimmed mean, and medians in the distribution and doing the Kolmogorov-Smirnov test), the t test was applied. When the sample size was too small for a t test the equality of the variances was assessed using Levene’s test with an adjusted value for degrees of freedom.

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RESULTS

The total number of implants included in the study was 312 in 312 patients, distributed between five institutions in Europe (Table 1). Patients have a followup of 7–10 years. A common study protocol was used in all institutions, and all the patients gave consent to participate in this study. Unfortunately, information about some variables was not recorded in some patients. The mean age of the patients at the time of implantation was 65.5 years (range, 25–86 years), with a distribution of 130 men (41.7%) and 182 women (58.3%). The surgically treated hip was the right in 161 patients (51.6%) and the left in 151 patients (48.4%); however, although all patients included in the study had unilateral implantation, there were 94 patients (30.1%) with bilateral indications for hip surgery. The most frequent indication for a total hip prosthesis was primary osteoarthritis (OA) (73.7%), followed by osteonecrosis (ON) (12.8%). In 131 patients (42%) no other joints were involved. Preoperative bone density was graded poor for 23 patients (7.4%), fair for 136 patients (43.6%), and good for 150 patients (48.1%), and in three patients (1%), the information was not recorded. The surgical approaches used were lateral in 164 patients (52.6%), posterolateral in 111 patients (35.6%), and anterolateral in 36 patients (11.5%), and in one patient (0.32%), the information was not recorded. Reaming for the acetabular component was strictly subchondral in 123 patients (39.4%), cancellous in 40 patients (12.8%), and subchondral and cancellous in 148 patients (47.4%), and in one patient (0.32%), the information was not recorded. Acetabular bone grafting was used in 85 patients (27.2%). Reduction was easy in 173 patients (55.4%), fair in 132 patients (42.3%), and difficult in six patients (1.9%), and in one patient (0.32%), the information was not recorded.

Femoral stems Number 4 and Number 5 (58.3%) were used in most cases. In 52 cases (16.7%) the stems were smaller, and in 27 (8.7%) larger, than planned. The diameter of the acetabular cup sizes between 50- to 58-mm diameter were used in most cases (82%), with fixation using spikes in 263 cases (84.3%), screws in 12 (3.8%), and spikes and screws in 36 (11.5%), and in one patient (0.32%), the information was not recorded.

For articulation standard inserts were used in 99 patients (31.7%). Hooded inserts were placed anteriorly in 39 patients (12.5%), anterosuperiorly in nine (2.9%), posteriorly in 32 (10.3%), posterosuperiorly in 41 (13.1%), and superiorly in 91 (29,2%), with information of one patient missing. Zirconia femoral heads were used in 161 patients (51.5%) and CoCr femoral heads were used in 150 (48.1%), with a diameter of 28 mm in most cases (98.4%) and with a neck length of −5 mm in 59 (18.9%), −3 mm in 100 (32.1%), 0 mm in 121 (38.8%), and +5 mm in 31 (9.9%). Information about the last two variables was missing in one patient.

The survival rates for stems and cups (Kaplan-Meier) were excellent with this system at 99.13% for stems, 96.85% for cups, and 96.85% for the system after 9 years. Only seven patients had revision surgery, five of them because of cup loosening (2.2%) associated with PE wear and two because of severe PE wear and cyst formation behind the cup (0.9%); another patient needs revision surgery (eight patients; 3.4%).

The clinical and radiographic results of 232 patients were collected and analyzed 7–10 years after implantation (mean followup, 8.5 years; range, 6.9–10.4 years), although unfortunately information about some variables was not recorded for some of them. Of the original 312 patients, 50 died before the 7-year followup and 30 were lost to followup. Most patients had neither clinical (215 = 92.7%) nor mechanical (220 = 94.8%) complications.

Clinically, there was no measurable difference in leg length in 176 patients (75.9%) and the overall results were very satisfactory: excellent in 151 patients (65.1%), good in 47 patients (20.3%), satisfactory in 23 patients (9.9%), fair in seven patients (3.0%), and poor in three patients (1.3%), and in one patient (0.43%), the information was not recorded. The mean Merle D’Aubigné and Postel score improved from 4 preoperatively to 16.7 (range, 9–18) at 7–10 years followup, with 119 patients (51.7%) evaluated as having a score of 18. Pain score analysis showed that 179 patients (77.2%) had no pain, 168 patients (72.4%) maintained total mobility, and 146 patients (62.9%) were able to walk unrestricted. One hundred fifty-nine patients (68.5%) were able to participate in outdoor activities and only two patients (0.9%) needed assistance for all activities. Fifty-two patients (22.4%) had some pain. The pain was located in the groin while walking in 24 patients (46.2%), in the anterior thigh in 22 patients (42.3%), in the lateral thigh in 19 patients (36.5%), and in the groin on standing in 10 patients (19.2%). The average flexion was 101.9°, the average extension was 4.3°, the average abduction was 32.7°, and the average adduction was 22.7°, the average internal rotation was 18.9°, and the average external rotation was 27.3°.

Radiographic results were of concern because we found some unexpected problems: more than 55% of patients had stress-shielding phenomenons develop in the proximal femur, more than 62% had high rates of PE wear, and more than 17% had osteolytic lesions develop. Stem position was adequate in 185 patients (79.7%), with 23 in varus (9.9%) and 16 in valgus (6.9%), and in eight patients (3.44%), the information was not recorded. In the lateral view, 205 stems (88.4%) were centered with no cortical contact, seven (3%) had anterior contact, and five (2.2%) had posterior contact, and in 15 patients (6.5%), the information was not recorded. The radiographic findings showed a Brooker ectopic ossification of Grade 0 or 1 in 188 patients (81%) and Grade 3 in 15 patients (6.5%). However, femoral bone reaction to the stem (Tables 2–5) is of concern because more than ½ of the patients had a stress-shielding phenomenon. Tip sclerosis in Gruen Zone 4 was seen in 74 patients (31.9%) in the AP view and in 67 patients (28.9%) in the lateral view. Distal stem migration was detected in only three patients (1.3%).

Table 2

Table 2

Table 3

Table 3

Table 4

Table 4

Table 5

Table 5

Acetabular bone reaction to the implant (Table 6), categorized according to the DeLee and Charnley zones, was good. Normal bone was present at a level of approximately 80% in all zones. Cysts were identified in less than 6% of all patients in any zone and radiolucent lines were almost absent (< 1.3%) during the observation period. Polyethylene wear was observed in 144 patients (62.1%). Of the 114 patients with quantitative data available, an average PE wear of 1.83 mm was measured. Average cup inclination was 47° (range, 18°-75°) with an upper cup position for 15 patients (6.5%), normal for 205 patients (88.4%), and lower for two patients (0.9%), and in 10 patients (4.3%), the information was not recorded. A change in cup orientation was seen in only three patients (1.3%), all of whom subsequently had revision surgery because of cup loosening.

Table 6

Table 6

The cross-correlation analysis showed few statistically significant correlations between the variables. Significant correlation was seen between previous hepatic disease and osteolysis in Zone 2 (p = 0.045) and Zone 3 (p = 0.045) of the cup. There also was a correlation between gender and cystic lesions in femoral Zone 6 (AP view; p = 0.011). There were more cysts in men but the sample was very small (five men). The correlation of bone resorption with stem parameters is shown in Table 7. The analysis of PE wear showed a significant correlation between zirconia femoral heads (chi square with one-degree-of-freedom = 10.597), hooded and posteriorly placed inserts (chi square with one-degree-of-freedom = 4.863), and radiolucent lines in femoral Zones 1A (AP view; p = 0.003), 1B (AP view; p = 0.020), and 1C (lateral view; p = 0.008). There were more radiolucent lines when there was no PE wear. There also was a significant relationship between number of screws used for fixation of the cup and acetabular cup osteolysis in Zone 1 (chi square with two-degrees-of-freedom = 6.041).

Table 7

Table 7

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DISCUSSION

As we hypothesized in the Introduction, the anatomic shape of the femoral stem and the HA coating on its metaphyseal part and on the back of the acetabular cup should improve fixation of both components to the bone; theoretically, this would avoid, or at least diminish, the stress shielding phenomenon and the progression of PE particles between the bone and the implants. Although we consider our clinical outcomes to be very satisfactory, the radiographic assessment shows some issues of concern: frequent phenomena of stress-shielding and osteolytic lesions by PE particles were seen in more patients than expected, equaling those obtained with either nonanatomic38 or HA-coated4,9,10 implants.

The mean Merle D’Aubigné and Postel score was 16.7 (51.7% of patients evaluated as having a score of 18) after 8.5 years mean followup. The overall results at this time were considered excellent or good in 85.4% of patients. We only had five cases of loosening and two cases of migration; these seven complicated cases were revised. The two early revisions within 2 years followup were done because of severe pain in one patient, although revision subsequently was considered a mistake, and dislocation in another patient where the stem and cup were replaced. Another patient with severe osteolytic lesions is waiting for revision surgery at this time.

The survival rate for the ABG system was excellent, at greater than 96% after an observation of 8.5 years. This result compares favorably with any published single center or multicenter study on the success rate of cemented or cementless hip implants with this time.5,11,17,33,40 The survival rate for the ABG acetabular cup (96.8%), although lower than that obtained for the femoral stem (98.71%), also can be considered excellent and similar to other porous-coated cups.35 However, we found stem fixation more reliable than that of the acetabular cup, which correlates with similar findings from other authors.9,10

However, the radiographic outcomes show that bone response to implants was not as we would have hoped in an implant of this design. We observed a femoral stress-shielding phenomenon in more than half of the patients (Fig 1), a higher incidence than reported by other authors with stems fixed distally38,41,46 or proximally, but smaller than incidences reported with HA-coated implants.4,9,10 Stress-shielding is shown by progressive bone resorption proximally (Zones 2–6 and 1–7 in the AP and lateral views) and progressive cancellous densification (Fig 1), cortical densification (Fig 1), and cortical thickening (Fig 1) distally (Zones 2–6 and 3–5), in AP and lateral views (Table 2). In comparison with the published 5- to 7-year results48 of this prosthesis, the percentage of cancellous densifications did not increase for Gruen Zones 2 and 6, but it did increase substantially for Gruen Zone 3 (from 22.7% to 51.9%) and for Gruen Zone 5 (from 23.3% to 55.8%). The percentage of reactive line formation at the tip of the stem diminished from 41.7% at 3 years followup to 36.3% at 5 years and to 22.4% at a mean followup of 8.5 years (Fig 1). This is a well-known bone response mechanism to cementless implants,11,13,17,18,27 which was shown to be progressive in other anatomic devices.31 We consider this phenomenon to be a progressive loading transfer from proximal to distal stem-bone interface zones, with a consecutive proximal weakening. Although it can be attributable to several causes, the analysis of the possible causes of this phenomenon showed only a statistically significant correlation between femoral stem size and bone resorption in Zone 7A (AP view) and between position of the femoral stem (in AP view) and femoral bone resorption. We have seen that 97.2% of patients with correctly sized stems have bone resorption whereas bone resorption is present in only 20% of the patients with undersized stems (p < 0.05). We interpret this issue as an excess of distal load transmission by big stems, which is counteracted better if there is more cancellous bone between the stem and the cortical bone. However the AP view clearly shows there is more resorption in unloaded medial zones: 64% of cases with stems in varus and 75% with stems in valgus in Zone 7A (p = 0.023), and 48% of cases with stems in varus and 68.8% with stems in valgus in Zone 7B (p = 0.022), although this is less obvious when observing the lateral view.

Fig 1.

Fig 1.

However, we do not think that these stem misalignments suffice to explain this phenomenon of proximal bone resorption, because it also is seen in well-positioned stems. We think it can be explained by other factors such as preoperative bone density,42,46 a decrease in blood supply to the trochanteric areas during surgery,32,43 and differences in femoral shape. Some patients have a funnel-shaped proximal end of the femur. In these patients the stem tends to fit into the shaft top, leaving the metaphyseal areas unloaded, which atrophy progressively. We expect that this problem was resolved with the modifications made to the stem in 1997. This will be ascertained from a similar followup comparative study.

Acetabular bone response to the implant was good. Bone resorption was observed in only 15 patients (6.5%) at Zone 3, in 32 patients (13.8%) at Zone 2, and in 35 patients (15.1%) at Zone 1.

We maintain the hypothesis that migration of PE wear particles is responsible for decreasing bone density35 and osteolysis through bone resorption in the acetabulum and femur.40,50 Numerous cystic lesions were found in Zones 1A (15.6%) and 7 (17.7%) on the AP and lateral (13.4% in one: 11.3% in seven) views (Fig 2), although in a smaller percentage than that found by other authors reviewing cases with diverse types of stems.4,10,25 In the acetabulum cystic lesions (Fig 3) were found in Zones 2 (4.3%) and 1 (6%) more frequently than in Zone 3 (3.9%), although the differences were minimal. Tonino et al50 described the histopathologic nature of these cysts, which are filled with granulomatous tissue and PE debris,5 in a histopathologic study of retrieved ABG cups. In their study, a statistically significant correlation was seen between the number of screws and periacetabular cup osteolysis in Zone 1. We think screws facilitate PE particle progression, especially in areas of maximum load transfer. However, there must be sensitivity to PE, because there are patients with considerable PE wear and little osteolysis, and other patients with enormous cystic lesions. We do not know how hepatic diseases affect sensitivity to PE, although both factors had a statistically significant correlation in our study.

Fig 2.

Fig 2.

Fig 3.

Fig 3.

The problem of most concern arising from the study is PE wear (Fig 3), which was detected in 144 patients (62.1%). Although this is of concern, it is not unexpected in the light of experience with all first generation PE. However it also must be borne in mind that even with low PE wear rates, the appearance of eccentricity of the head in the cup from wear will be detectable after 7–10 years. There were noticeable differences between the results from the different institutions. Quantitative assessment was recorded for 114 patients whose average wear was 0.22-mm per year, higher than that reported by Charnley7 (0.10–0.19 mm per year) with cemented prostheses, but similar or smaller than others with cementless systems.24 However, no sophisticated measurement technique was used and the measurements all were rounded up to the nearest millimeter.

On analyzing possible causes for this accelerated wear, the only statistically significant correlation seen was with the posterior position of the hooded PE insert: we detected PE wear in 77.2% of patients with posterior hooded PE inserts and in 61.1% of patients without posterior hooded inserts (p = 0.05). This correlation already was known and the cause of the accelerated wearing is repeated contact between the stem neck and prominent PE. There probably also is a second mechanism resulting from this contact: the dragging movement of the femoral head over the interior surface of the insert. However, there was no correlation between PE wear and other factors such as cup inclination, cup diameter, size of the femoral stem, diameter of the femoral head, and body weight. There are other potential contributory factors to this problem that were not assessed during this study including anteversion of the acetabular component, rotation center offset and height, and muscle tension. However, we think the main problem is the quality of PE after the damage caused during the sterilization process. We hope that this problem has been resolved with the new PE Duration® and with the new sterilization process by gamma irradiation in vacuum. Sterilization by gamma irradiation damages PE.45 The immediate consequence of accelerated PE wear is osteolysis, which is becoming more evident as our study progresses, in accordance with other investigators.37,47 Many of the patients with progressive osteolysis will need revision surgery in the short-term.

Ectopic ossifications were seen in only 15 patients (6.5%), whereas this was found to be more frequent in patients with other hip prostheses.51 However, these findings have not been related to pain or restricted mobility.

After 7–10 years followup we are satisfied with the survival and clinical outcomes of this anatomic cementless system, which shows improvements on results obtained with cemented and cementless nonanatomic systems and compares favorably with published results. This satisfaction is shared by most patients who have almost normal and complete activity levels. However, the radiographic findings raise some questions regarding the future clinical performance of this implant. More than 50% of femurs had signs of proximal stress-shielding induced bone resorption. It has not been possible to distinguish if this is attributable to more distal stress transfer than anticipated or if it is a reaction to ongoing PE wear. Substantial PE wear also was observed in at least 62% of the patients which seems to be higher than normal, and in numerous cases there were serious granulomatous lesions in the femoral and periacetabular bones. Therefore, PE wear and its associated osteolysis seem to be a limiting factor particularly for young and active patients.

We expect that these issues have been resolved successfully with the modifications made to the femoral stem and acetabular cup (no-holes version) and the new PE with irradiation sterilization in inert gas and annealing. However, younger patients should receive implants with a more wear-resistant bearing material such as ceramic-on-ceramic.

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Acknowledgments

We thank Dr. Panisello Sebastiá and Dr. García-Dihinx Checa for scientific contributions in the study, and Dr. Peguero Bona, Dr. Martínez Martín, and Dr. Herrero Barcos for collaboration.

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