JBJS | Measurement of Polyethylene Wear in Acetabular Components Inserted with and without Cement. A Randomized Trial*

The Journal of Bone & Joint Surgery, Volume 79, Issue 5

Articles | May 01, 1997

Measurement of Polyethylene Wear in Acetabular Components Inserted with and without Cement. A Randomized Trial*

PETER A. DEVANE, M.B., CH.B.†; ERIC J. ROBINSON, M.D.‡; ROBERT B. BOURNE, M.D.‡; CECIL H. RORABECK, M.D.‡; NARESH N. NAYAK, M.D.‡; J. GEOFFREY HORNE, M.B., CH.B.†, LONDON, ONTARIO, CANADA

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Investigation performed at the Department of Orthopaedic Surgery, University Hospital, London

The Journal of Bone & Joint Surgery. 1997; 79:682-89

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Abstract

We measured the three-dimensional wear of polyethylene after total hip arthroplasty with a titanium metal-backed Mallory-Head prosthesis that was inserted with cement in sixty-nine patients (sixty-nine hips) and with a press-fit titanium metal-backed Mallory-Head prosthesis that was inserted without cement in seventy patients (seventy hips). A modular titanium femoral head was used in all of the hips. The patients in the present study were part of a larger double-blind randomized trial comparing the result of total hip arthroplasty performed with cement with that of the same procedure performed without cement in 250 patients. The criterion for inclusion in the study of polyethylene wear was a minimum duration of follow-up of four years, which was met by 148 patients. As adequate radiographs for digitization were not available for nine patients, 139 patients were included in the present study. The age of the patient, the postoperative Harris hip score, the diameter of the femoral head, the thickness of the liner in the polar region of the acetabular component, and the duration of follow-up were similar for the two groups. The mean rate of volumetric wear of the polyethylene was significantly greater in the prostheses that had been inserted without cement than in those that had been inserted with cement (155.1 cubic millimeters per year compared with 98.5 cubic millimeters per year; p = 0.000008). Thirty-four (49 per cent) of the seventy hips in which the prosthesis had been inserted without cement had evidence of osteolysis on radiographs, compared with twelve (17 per cent) of the sixty-nine hips in the other group (p = 0.0002). Osteolysis was associated with an increased rate of polyethylene wear only in the hips in which the prosthesis had been inserted without cement.

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Introduction

Introduction | Materials and Methods | Results | Discussion | References

Osteolysis due to the generation of particles of debris from the surface of a prosthesis is the most common cause of failure of total hip replacements^9,24,36. In the 1970's, polymethylmethacrylate bone cement was believed to be the source of the debris, and particles of polymethylmethacrylate found in areas of osteolysis around either mechanically stable or loose implants was termed cement disease^22,28. In the 1980's, the so-called press-fit prosthesis was developed for insertion without cement and became an alternative to the use of polymethylmethacrylate for fixation of the implant^14,30. Despite good early results with use of press-fit prostheses without cement^15,20, the stability of the implant achieved through ingrowth of bone did not guarantee an end to the generation of particulate debris³. Recently, it has been suggested that particulate disease is a more appropriate term for the concept of so-called cement disease²¹.

The only particulate debris from an in vivo prosthesis that can be measured is that generated from the primary bearing surface (the articulation of the femoral head with the ultra-high molecular weight polyethylene liner)^5,16; the measurement, which is termed linear wear, is an estimation based on the displacement of the femoral head measured on an anteroposterior radiograph²⁹. This two-dimensional measurement is used in a formula in order to calculate the volume of polyethylene debris²³. Recently, a new technique was developed to measure accurately the three-dimensional displacement of the femoral head and the minimum volume of polyethylene wear¹². Application of this technique to the study of metal-backed acetabular components allowed us to analyze various factors believed to influence polyethylene wear¹³. To our knowledge, no study has prospectively compared polyethylene wear associated with two types of prostheses that have a similar design but a different mode of fixation.

The objective of the present study was to compare polyethylene wear after total hip arthroplasty in two prospectively matched groups of patients. In one group, a non-modular metal-backed acetabular component and a femoral stem were both inserted with cement. In the other, a modular press-fit acetabular component and a press-fit femoral stem were inserted without cement. The relationship of radiographic and clinical factors with the rate of polyethylene wear was analyzed for each group.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

†Department of Surgery, Wellington School of Medicine, P.O. Box 7343, Wellington South, New Zealand. E-mail address for Dr. Devane: surgpd@wnmeds.ac.nz.

‡Department of Orthopaedic Surgery, University Hospital, 339 Windermere Road, London, Ontario N6A 5A5, Canada.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

†Department of Surgery, Wellington School of Medicine, P.O. Box 7343, Wellington South, New Zealand. E-mail address for Dr. Devane: surgpd@wnmeds.ac.nz.

‡Department of Orthopaedic Surgery, University Hospital, 339 Windermere Road, London, Ontario N6A 5A5, Canada.

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Fig. 1 Photograph showing a cross section of two fifty-four-millimeter-diameter Mallory-Head acetabular components. The metal backing and the polyethylene liner were, respectively, seven and eight millimeters thick in the component that had been inserted without cement (left) and three and twelve millimeters thick in the component that had been inserted with cement (right).

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Fig. 2 Scattergraph of the polyethylene wear according to the duration of follow-up. The mean volumetric wear for each year is represented by the solid curve and the 95 per cent confidence interval, by the dotted curves.

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Fig. 3 Graph showing the rates of volumetric polyethylene wear according to the presence or absence of osteolysis after total arthroplasty of the hip with and without cement. The association between the rate of polyethylene wear and osteolysis in the hips in which the prosthesis had been inserted without cement was highly significant (asterisk; p = 0.001).

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Fig. 4 Photograph of a retrieved acetabular component that had been inserted with cement, showing discoloration from titanium debris as well as evidence of polyethylene delamination from the metal backing.

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TABLE I DATA ON THE PATIENTS

*The values are expressed as the mean, with the range in parentheses.

	Patients Who Had Prosthesis	Patients Who Had Prosthesis
	Inserted with Cement	Inserted without Cement	All Patients
	(N = 69)	(N = 70)	(N = 139)
Age* (yrs.)	64 (41—76)	64 (41—76)	64 (41—76)
Gender (M/F)	36/33	35/35	71/68
Postoperative Harris hip score* (points)	94 (55—100)	93 (54—100)	94 (54—100)
Duration of follow-up* (yrs.)	4.5 (4.0—5.8)	4.7 (4.0—6.1)	4.6 (4.0—6.1)

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TABLE I DATA ON THE PATIENTS

*The values are expressed as the mean, with the range in parentheses.

	Patients Who Had Prosthesis	Patients Who Had Prosthesis
	Inserted with Cement	Inserted without Cement	All Patients
	(N = 69)	(N = 70)	(N = 139)
Age* (yrs.)	64 (41—76)	64 (41—76)	64 (41—76)
Gender (M/F)	36/33	35/35	71/68
Postoperative Harris hip score* (points)	94 (55—100)	93 (54—100)	94 (54—100)
Duration of follow-up* (yrs.)	4.5 (4.0—5.8)	4.7 (4.0—6.1)	4.6 (4.0—6.1)

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TABLE II RADIOGRAPHIC DATA ON POLYETHYLENE WEAR

*Values are expressed as the mean.

	Prostheses Inserted	Prostheses Inserted
	with Cement*	without Cement*	All Prostheses*
	(N = 69)	(N = 70)	(N = 139)	P Value
Rate of linear wear (mm/yr.)	0.152	0.246	0.199	0.0002
Rate of three-dimensional displacement	0.228	0.358	0.293	0.0000008
of the femoral head (mm/yr.)
Rate of volumetric wear (mm³/yr.)	98.5	155.1	127.0	0.000008

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TABLE II RADIOGRAPHIC DATA ON POLYETHYLENE WEAR

*Values are expressed as the mean.

	Prostheses Inserted	Prostheses Inserted
	with Cement*	without Cement*	All Prostheses*
	(N = 69)	(N = 70)	(N = 139)	P Value
Rate of linear wear (mm/yr.)	0.152	0.246	0.199	0.0002
Rate of three-dimensional displacement	0.228	0.358	0.293	0.0000008
of the femoral head (mm/yr.)
Rate of volumetric wear (mm³/yr.)	98.5	155.1	127.0	0.000008

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TABLE III DATA ON THE ACETABULAR COMPONENTS*

*The values are expressed as the mean, with the range in parentheses.

	Cups Inserted with Cement	Cups Inserted without Cement	All Cups
	(N = 69)	(N = 70)	(N = 139)
Orientation (degrees)
Tilt	47.6 (30—65)	43.4 (24—59)	45.5 (24—65)
Anteversion	11.0 (2—27)	6.6 (-1—27)	8.8 (-1—27)

Diameter of cup (mm)	48.0 (45—57)	53.6 (46—62)	51.1 (45—62)

Thickness of liner at pole (mm)	8.0 (5.8—12.5)	7.7 (4.9—8.9)	7.8 (4.9—12.5)

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TABLE III DATA ON THE ACETABULAR COMPONENTS*

*The values are expressed as the mean, with the range in parentheses.

	Cups Inserted with Cement	Cups Inserted without Cement	All Cups
	(N = 69)	(N = 70)	(N = 139)
Orientation (degrees)
Tilt	47.6 (30—65)	43.4 (24—59)	45.5 (24—65)
Anteversion	11.0 (2—27)	6.6 (-1—27)	8.8 (-1—27)

Diameter of cup (mm)	48.0 (45—57)	53.6 (46—62)	51.1 (45—62)

Thickness of liner at pole (mm)	8.0 (5.8—12.5)	7.7 (4.9—8.9)	7.8 (4.9—12.5)

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

A randomized, double-blind clinical trial comparing total hip arthroplasty with cement and that without cement was performed at the University Hospital, University of Western Ontario, London, Ontario, Canada. The present study was part of that larger trial, which was funded by the Medical Research Council of Canada. From 1987 through 1992, 250 patients were recruited. Patients were eligible for enrollment in the trial if they were less than seventy-five years old and had osteoarthrosis of the hip. They were excluded if they had severe symptomatic osteoarthrosis of either knee or the contralateral hip, had had a previous arthroplasty of the ipsilateral hip at any time or an arthroplasty of the contralateral hip more than five years before, or had had septic arthritis. Patients were not recruited if they had a serious medical illness and were not expected to survive at least five years postoperatively.

All operative procedures were performed by or under the direct supervision of one of the senior two of us (R. B. B. or C. H. R.) with assistance from experienced operating-room personnel. The operating room was equipped with enclosed vertical laminar airflow, and the operating team wore body-exhaust suits. A modified lateral approach to the hip, as described by Hardinge¹⁹, was used in all patients. The patient, after giving informed consent, and the research nurse were blinded with respect to whether the implant was to be inserted with or without cement. The choice of performing the total hip arthroplasty with or without cement was determined with use of random numbers placed in sealed envelopes that were opened in the operating room. An even number signified that the prosthesis was to be inserted with cement and an odd number, without cement. Postoperatively, all of the patients were instructed to avoid bearing weight on the involved limb for six weeks. Clinical assessment of the patients was performed by the research nurse at six weeks, three months, and six months and yearly thereafter.

The Mallory-Head total hip system (Biomet, Warsaw, Indiana) was selected for the present study because of the similarity in the design of the prosthesis for insertion with cement and for insertion without cement. A titanium femoral component with a plasma-sprayed coating was used for insertion without cement, and a smooth titanium femoral component was used for insertion with cement. The implants had no collar, and a modular titanium twenty-eight-millimeter-diameter femoral head was used in all patients. A modular, fenestrated, titanium acetabular component that had a hexagonal locking mechanism and an ultra-high molecular weight polyethylene liner was used for the arthroplasties without cement. Although holes in the periphery of the metal shell allowed use of screws to supplement fixation, none of the components in the present study needed such fixation. In the acetabular component inserted without cement, the polyethylene liner was several millimeters thinner at its rim than at its pole because of the hexagonal locking mechanism (Fig. 1). For the purposes of this study, we used the measurement given by the manufacturer to determine the thickness of the polyethylene at the pole of a prosthesis inserted without cement. A titanium, metal-backed, one-piece (non-modular) acetabular component was used for the arthroplasties with cement. The polyethylene liner was attached to the metal shell of the acetabular component by molding at the time of manufacture. In each patient, the mode of fixation was the same for both the acetabular and the femoral component.

Of the 250 patients recruited for the study by the Medical Research Council, only those who had been followed for forty-eight months or more were selected for our study of the measurement of polyethylene wear. Standardized anteroposterior radiographs with the beam centered on the symphysis pubis and lateral radiographs of the hip were made at each follow-up visit. A detailed description of the standardized radiographic technique has been reported previously^11,12. The size of the acetabular component implanted at the operation was obtained from the medical records of the patient. The thickness of the polyethylene in each cup was calculated from the specifications provided by the manufacturer. As the polyethylene liner in the acetabular components inserted without cement was thinner at the rim than at the pole because of the hexagonal locking mechanism, we calculated the thickness of the liner at the pole of the component. Polyethylene wear was measured with use of a three-dimensional technique in which the initial postoperative and the most recent follow-up radiographs were digitized with a computer by a single observer (E. J. R.). Custom software created a three-dimensional solid model of the prosthesis from which measurements were made. These measurements included the orientation of the acetabular component (tilt and anteversion), the two-dimensional linear wear, the three-dimensional distance and direction of the displacement of the femoral head, and the minimum volume of polyethylene debris¹¹. With use of the three-dimensional technique, the displacement of the femoral head was measured with reference to the cup as seen in the frontal plane¹², whereas the two-dimensional linear wear was measured in the plane of the anteroposterior radiograph. Therefore, the two-dimensional and three-dimensional values for each patient are not comparable. Because the surgeon who digitized the radiographs was aware of the type of prosthesis used in each patient, this part of the study was not blinded.

Evidence of osteolysis was recorded before digitization of the radiographs. For the purpose of this study, osteolysis was defined as a progressive periprosthetic geographic lesion seen on radiographs. Statistical analysis was performed with CSS:Statistica software (Statsoft, Tulsa, Oklahoma). In addition to basic descriptive statistics, the effects of various clinical and radiographic factors on the measurements of polyethylene wear were examined with use of the Student t test for independent continuous samples and with multiple-regression analysis of the relationships between two continuous samples.

Results

Introduction | Materials and Methods | Results | Discussion | References

Of the 250 patients who had been recruited for the larger trial, 148 patients who had been followed for at least forty-eight months were available for assessment. Nine patients were excluded from the present study because the follow-up radiographs were inadequate for proper digitization. One hundred and thirty-nine patients (sixty-nine who had insertion of the prosthesis with cement and seventy who had insertion of the prosthesis without cement) had appropriate radiographs for digitization and were included in our study. There was no substantial difference between the two groups with respect to the mean age of the patient, the mean postoperative Harris hip score, or the mean duration of follow-up (Table I).

All measurements of displacement of the femoral head and wear of the polyethylene were calculated as rates, with the duration of follow-up for each patient taken into account (Table II). The mean rate of linear wear was significantly greater in the group that had the arthroplasty without cement than in the other group (0.246 compared with 0.152 millimeter per year; p = 0.0002). That group also had a significantly greater mean rate of three-dimensional displacement of the femoral head (0.358 compared with 0.228 millimeter per year; p = 0.0000008) and a significantly greater mean rate of volumetric wear of the polyethylene (155.1 compared with 98.5 cubic millimeters per year; p = 0.000008). The over-all volumetric wear of the polyethylene for both groups increased in association with the duration of follow-up (r = 0.241 and p = 0.004) (Fig. 2).

There were slight differences between the two groups with respect to acetabular tilt and anteversion (Table III). No association was found between the orientation of the acetabular component (tilt or anteversion) and the rate of volumetric wear in either group or in the over-all group. Thirty-four (49 per cent) of the seventy hips in which the prosthesis had been inserted without cement showed osteolysis on radiographs, compared with twelve (17 per cent) of the sixty-nine hips in which the prosthesis had been inserted with cement; the difference was significant (p = 0.0002). The most frequent location of osteolysis on the acetabular side was zone 1 of DeLee and Charnley¹⁰ in the hips that had the cemented prosthesis and zone 2 in the hips in which the prosthesis had been inserted without cement. The most common site of osteolysis on the femoral side was zone 7 of Gruen et al.¹⁸ for both groups. In the hips that had the cemented prosthesis, the rate of displacement of the femoral head and the rate of volumetric wear were not associated with osteolysis. In the group in which the prosthesis had been inserted without cement, however, the thirty-four hips that had osteolysis had a greater rate of volumetric wear of the polyethylene than did the thirty-six hips that had no evidence of osteolysis on radiographs (Fig. 3). This association between the rate of polyethylene wear and osteolysis in the hips in which the prosthesis had been inserted without cement was highly significant (p = 0.001). Radiolucent lines were observed adjacent to twenty (29 per cent) of the sixty-nine cemented prostheses and adjacent to none of the seventy prostheses that had been inserted without cement, but no significant association was demonstrated between the presence of radiolucent lines and the displacement of the femoral head (p = 0.89) or the volume of polyethylene debris (p = 0.67). Zones 1 and 3 of the acetabular component were the zones most commonly affected by radiolucent lines. The mean diameter of the acetabular component in the group that had a cemented prosthesis was slightly smaller than that in the other group, but the thickness of the polyethylene liner was similar for both groups because the metal backing in the prosthesis inserted without cement was thicker than that in the prosthesis inserted with cement (Fig. 1 and Table III). In both groups, we noted a trend toward a greater rate of volumetric wear in the liners that were less than eight millimeters thick at the pole (sixty-nine hips), but this trend was not significant with the numbers available (138 cubic millimeters per year for the liners that were less than eight millimeters thick compared with 115 cubic millimeters per year for the thicker liners, p = 0.085).

Two patients (one in each group) had a revision. The first patient was a sixty-four-year-old man who had had a primary total hip replacement with cement for treatment of osteoarthrosis. Forty-eight months later, he had a revision because of a periprosthetic femoral fracture. At the time of the revision operation, the cement mantle had debonded from the femoral component. The acetabular component was mechanically stable despite progressive radiolucent lines in zones 1 and 3 of DeLee and Charnley¹⁰. Macroscopic titanium debris was embedded in the liner, and the polyethylene had evidence of abrasions and early delamination (Fig. 4). Examination of histological specimens showed evidence of intracellular polyethylene and titanium debris. The second patient who had a revision was a forty-seven-year-old man who had had a primary total hip replacement without cement for treatment of osteoarthrosis. Sixty-four months later, the patient had a revision because of increasing pain in the groin, gross evidence of polyethylene wear, and radiographic evidence of osteolysis in zone 7 of Gruen et al.¹⁸. The preoperative workup remained negative for infection. At the revision operation, the acetabular component was loose and polyethylene wear was evident macroscopically. Examination of a histological section demonstrated evidence of intracellular polyethylene debris.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

The objective of our study was to evaluate and compare wear of the polyethylene of the acetabular component after total hip arthroplasty performed with and without cement. Patients were randomized to one group or the other and were blinded with respect to the treatment group for the purpose of providing an unbiased assessment of the outcome of the procedure and the quality of life, the results of which have been reported previously³⁴. The most important function of randomization, which has been well described^17,26,27, is to maximize the likelihood that the patients in each treatment group will have similar prognostic characteristics. In the present study, randomization allowed an unbiased comparison of the polyethylene wear in the two treatment groups.

The three-dimensional technique allowed us to collect data on the displacement of the femoral head and the volume of polyethylene debris in three dimensions. The rate of two-dimensional displacement of the femoral head (the linear wear) is comparable with the values reported in the literature^6,29,35, whereas the rate of three-dimensional displacement of the femoral head is almost twice as high as those values. This finding suggests that two-dimensional methods for assessing displacement of the femoral head underestimate the rate and amount of wear because the displacement of the femoral head is measured only in the plane of the anteroposterior radiograph³⁸. Formulae for calculating volumetric wear are based on a two-dimensional cylindrical tract of wear in the plane of the anteroposterior radiograph, and they have been applied only to acetabular components inserted with cement²⁹. In a recent study of retrieved components, Kabo et al.²³ demonstrated that the pattern of wear is not completely cylindrical, and they concluded that formulae reported previously for the estimation of volumetric wear are inaccurate. In our study, the rate of volumetric wear in the hips that had a cemented prosthesis (98.5 cubic millimeters per year) was similar to the results of other studies of volumetric wear associated with cemented prostheses^4,32,33.

The results of the present study are consistent with those obtained in our original research with the three-dimensional technique, in which we digitized and analyzed a series of radiographs from 141 patients who had a porous-coated anatomic prosthesis (PCA; Howmedica, Rutherford, New Jersey) inserted without cement¹³. In that study, the rate of three-dimensional displacement of the femoral head of the porous-coated anatomic prosthesis was 0.264 millimeter per year and the rate of volumetric wear was eighty cubic millimeters per year. There was a strong association between polyethylene wear debris and evidence of osteolysis on radiographs. The rate of wear of the polyethylene associated with the Mallory-Head prosthesis inserted with cement was slightly higher than that of the porous-coated anatomic prosthesis, but the rate of wear of the polyethylene of the Mallory-Head prosthesis inserted without cement was much greater. As the Mallory-Head prosthesis has a different bearing surface (titanium articulating with polyethylene), the rate of wear of this prosthesis was not comparable with that of the porous-coated anatomic prosthesis (Vitallium articulating with polyethylene). Differences in the design (a curved compared with a straight femoral stem), the porous coating (beads compared with plasma spray), the composition (Vitallium compared with titanium), and the source of the polyethylene also may account for the difference in the rates of wear associated with these two prostheses.

The rate of volumetric polyethylene wear and the prevalence of osteolysis were significantly greater for the Mallory-Head prosthesis inserted without cement than for the Mallory-Head prosthesis inserted with cement (p = 0.000008 and p = 0.0002, respectively); this is a cause for concern. Both prostheses had been produced by the same manufacturer, were composed of titanium, and had a metal-backed acetabular component and a twenty-eight-millimeter femoral head. In addition, they had been selected for implantation in a completely random manner, which eliminated any difference between the groups with respect to age, gender, weight, level of activity, or duration of follow-up. The difference in the design of the two acetabular cups involved the thickness of the polyethylene liner. In the prosthesis inserted without cement, the liner was thinner at its rim and was attached to the metal shell during implantation by a locking mechanism, whereas the liner in the cemented prosthesis was of uniform thickness and was attached to the metal shell at the time of manufacture. Although the thickness of the polyethylene liner at the pole of the component was similar in the two groups, the decreased thickness at the rim of the liner in the acetabular component inserted without cement may have contributed to the increased rate of polyethylene wear in that group. The major difference between the two groups was the method of fixation. Many investigators have reported greater polyethylene wear associated with thinner spacers^1,7,8,25, but we did not find a significant association between the thickness of the liner at the pole and the rate of polyethylene wear in either group. Although high rates of wear of the polyethylene of metal-backed acetabular components have been reported^4,33, to our knowledge the present study is the first to examine the influence of the method of fixation—not only of the metal shell to bone but also of the polyethylene liner to the metal shell—on the rate of polyethylene wear.

The lower prevalence of osteolysis associated with the cemented prostheses may be explained by a biochemical protective effect of the cement at the interface with the bone, but additional investigation is needed. Alternatively, the relatively high prevalence of osteolysis associated with the components inserted without cement may be due to the modular, fenestrated acetabular component with its hexagonal locking mechanism, which is no longer manufactured in North America. Bartel et al.¹ reported that screw-holes, fenestration, and non-conformity of the interface between the polyethylene and the metal shell in an acetabular component may compromise the surface area available for distribution of stress, thus potentiating both the generation of particulate debris from the bearing surface and the deformation of the polyethylene^2,31,37. Particles of debris generated from the outer surface of the polyethylene liner, where it is in contact with the metal shell, cannot be measured from radiographs of intact components. Also, as only two retrieved specimens were available for study, no conclusions could be made about particles of debris generated from that source. The lower rate of polyethylene wear associated with cemented prostheses is more difficult to explain, but it may be due to a cushioning effect of the cement on the acetabular cup, which decreases stress across the primary bearing surface and thus decreases the generation of particulate debris.

Both of the failed prostheses in the present study demonstrated macroscopic and microscopic evidence of progressive polyethylene wear. Although it was not directly responsible for these two failures, particles of debris probably will be a more frequent cause of failure as the patients in the present study are followed.

In summary, application of the three-dimensional technique for the accurate measurement of polyethylene wear in a study population randomized into two treatment groups—patients who had total hip arthroplasty with cement and patients who had the procedure without cement—provided the opportunity for comparison with a minimum bias. Osteolysis was strongly associated with polyethylene wear only in the hips in which the prosthesis had been inserted without cement. Additional studies directly comparing fixation with cement and that without cement are required, but caution should be exercised in the use of prostheses without cement. The findings of the present study challenge the concept that a good early clinical result with a prosthesis inserted without cement leads to a good long-term result.

NOTE: The authors thank Robert M. Hardie, M.D., for his assistance with the statistical analysis for this manuscript.

References

Introduction | Materials and Methods | Results | Discussion | References

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TABLE I DATA ON THE PATIENTS

*The values are expressed as the mean, with the range in parentheses.

	Patients Who Had Prosthesis	Patients Who Had Prosthesis
	Inserted with Cement	Inserted without Cement	All Patients
	(N = 69)	(N = 70)	(N = 139)
Age* (yrs.)	64 (41—76)	64 (41—76)	64 (41—76)
Gender (M/F)	36/33	35/35	71/68
Postoperative Harris hip score* (points)	94 (55—100)	93 (54—100)	94 (54—100)
Duration of follow-up* (yrs.)	4.5 (4.0—5.8)	4.7 (4.0—6.1)	4.6 (4.0—6.1)

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TABLE I DATA ON THE PATIENTS

*The values are expressed as the mean, with the range in parentheses.

	Patients Who Had Prosthesis	Patients Who Had Prosthesis
	Inserted with Cement	Inserted without Cement	All Patients
	(N = 69)	(N = 70)	(N = 139)
Age* (yrs.)	64 (41—76)	64 (41—76)	64 (41—76)
Gender (M/F)	36/33	35/35	71/68
Postoperative Harris hip score* (points)	94 (55—100)	93 (54—100)	94 (54—100)
Duration of follow-up* (yrs.)	4.5 (4.0—5.8)	4.7 (4.0—6.1)	4.6 (4.0—6.1)

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TABLE II RADIOGRAPHIC DATA ON POLYETHYLENE WEAR

*Values are expressed as the mean.

	Prostheses Inserted	Prostheses Inserted
	with Cement*	without Cement*	All Prostheses*
	(N = 69)	(N = 70)	(N = 139)	P Value
Rate of linear wear (mm/yr.)	0.152	0.246	0.199	0.0002
Rate of three-dimensional displacement	0.228	0.358	0.293	0.0000008
of the femoral head (mm/yr.)
Rate of volumetric wear (mm³/yr.)	98.5	155.1	127.0	0.000008

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TABLE II RADIOGRAPHIC DATA ON POLYETHYLENE WEAR

*Values are expressed as the mean.

	Prostheses Inserted	Prostheses Inserted
	with Cement*	without Cement*	All Prostheses*
	(N = 69)	(N = 70)	(N = 139)	P Value
Rate of linear wear (mm/yr.)	0.152	0.246	0.199	0.0002
Rate of three-dimensional displacement	0.228	0.358	0.293	0.0000008
of the femoral head (mm/yr.)
Rate of volumetric wear (mm³/yr.)	98.5	155.1	127.0	0.000008

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TABLE III DATA ON THE ACETABULAR COMPONENTS*

*The values are expressed as the mean, with the range in parentheses.

	Cups Inserted with Cement	Cups Inserted without Cement	All Cups
	(N = 69)	(N = 70)	(N = 139)
Orientation (degrees)
Tilt	47.6 (30—65)	43.4 (24—59)	45.5 (24—65)
Anteversion	11.0 (2—27)	6.6 (-1—27)	8.8 (-1—27)

Diameter of cup (mm)	48.0 (45—57)	53.6 (46—62)	51.1 (45—62)

Thickness of liner at pole (mm)	8.0 (5.8—12.5)	7.7 (4.9—8.9)	7.8 (4.9—12.5)

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TABLE III DATA ON THE ACETABULAR COMPONENTS*

*The values are expressed as the mean, with the range in parentheses.

	Cups Inserted with Cement	Cups Inserted without Cement	All Cups
	(N = 69)	(N = 70)	(N = 139)
Orientation (degrees)
Tilt	47.6 (30—65)	43.4 (24—59)	45.5 (24—65)
Anteversion	11.0 (2—27)	6.6 (-1—27)	8.8 (-1—27)

Diameter of cup (mm)	48.0 (45—57)	53.6 (46—62)	51.1 (45—62)

Thickness of liner at pole (mm)	8.0 (5.8—12.5)	7.7 (4.9—8.9)	7.8 (4.9—12.5)