JBJS | Progression of Radiolucent Lines Adjacent to the Acetabular Component and Factors Influencing Migration after Charnley Low-Friction Total Hip Arthroplasty*†

The Journal of Bone & Joint Surgery, Volume 79, Issue 9

Articles | September 01, 1997

Progression of Radiolucent Lines Adjacent to the Acetabular Component and Factors Influencing Migration after Charnley Low-Friction Total Hip Arthroplasty*†

EDUARDO GARCÍA-CIMBRELO, M.D., PH.D.‡; VICENTE DIEZ-VAZQUEZ, M.D.§; ROSARIO MADERO, M.S.§; LUIS MUNUERA, M.D., PH.D.§, MADRID, SPAIN

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Investigation performed at the Department of Orthopaedics and the Section of Biostatistics, Hospital "La Paz," Universidad Autónoma de Madrid, Madrid

The Journal of Bone & Joint Surgery. 1997; 79:1373-80

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Abstract

We analyzed the progression of radiolucent lines around the acetabular cup after 452 Charnley low-friction arthroplasties that had been performed in 392 patients between 1971 and 1976. The average duration of follow-up was twenty years (range, eleven to twenty-five years) for the 442 hips (382 patients) that had the original component in place at ten years. The demarcation of the bone-cement interface was classified according to the system of Hodgkinson et al. We sought to determine if there was a relationship between the progression of the radiolucent line and the age, gender, and weight of the patient; the level of activity; the preoperative diagnosis; or the amount of wear of the acetabular cup. The demarcation increased over time in 138 (31 per cent) of the 452 hips. Radiographs made at the time of the latest follow-up showed migration of eleven (5 per cent) of the 233 acetabular cups with no demarcation on the initial postoperative radiograph, eighteen (11 per cent) of the 167 cups with type-1 demarcation, twelve (35 per cent) of the thirty-four cups with type-2 demarcation, and thirteen of the eighteen cups with type-3 demarcation. Preoperative acetabular protrusion, inflammatory arthritis, and severe acetabular dysplasia as well as a previous operation were associated with the extent of the radiolucent line on the most recent radiograph (p = 0.05 for all). A high level of activity and more than two millimeters of wear of the acetabular cup also were related to the progression of the radiolucent line (p = 0.0004 and p < 0.0001, respectively). Kaplan-Meier survivorship analysis demonstrated that the greater the demarcation on the initial postoperative radiograph, the greater the risk of migration (p < 0.0001, Mantel-Cox test).Our data suggest that, after a Charnley low-friction arthroplasty, any cemented cup, even one with the least amount of demarcation (types 0 and 1), can migrate. As the type of the initial postoperative demarcation increases, so does the risk of migration of the cup, particularly when there is loss of the acetabular bone stock.

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Introduction

Introduction | Material and Methods | Results | Discussion | References

Total hip arthroplasty with use of cement continues to be the treatment of choice for severe degeneration of the hip in older and relatively inactive patients. Predominantly, good results have been found as long as twenty years after use of the Charnley prosthesis, despite somewhat obsolete cementing techniques^{11,19,32,36,39,40}. With so-called contemporary cementing techniques, the long-term results probably will be even better^{1,3,14,24,26-28}.

Because an extensive radiolucent line around a cemented cup does not preclude a satisfactory clinical result, migration has been considered the best criterion of loosening of the cup. Nevertheless, most authors have considered a continuous radiolucent line that is at least two millimeters wide in all radiographic zones to be a sign of loosening of the acetabular cup^29,35. However, Hodgkinson et al., in a series of 200 Charnley low-friction arthroplasties that were revised, found that forty-nine (94 per cent) of fifty-two cups with a radiolucent line in all zones were loose, regardless of the thickness of the line¹⁵. Those authors believed that a radiolucent line in all acetabular zones is associated with eventual migration of the cup. Similarly, Schmalzried et al., who analyzed specimens that had been retrieved at autopsy, reported that the extent of the radiolucent line was more important than its thickness³¹.

Relationships have been found between loosening of the acetabular cup and the age of the patient^30,33, male gender²², the preoperative diagnosis^5,9,10,17,22, the position of the cup²², and more than two millimeters of wear of the acetabular cup^10,38. The purpose of the present study was to analyze the progression of radiolucent lines around acetabular cups used in Charnley low-friction arthroplasties. We also evaluated the prognostic importance of a number of variables that have been considered to influence the risk of migration.

*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.

†Read in part at the Annual Meeting of The American Academy of Orthopaedic Surgeons, Atlanta, Georgia, February 22, 1996.

‡Pez Austral 13, 5-A, 28007 Madrid, Spain.

§Hospital "La Paz," Paseo de la Castellana, 261, 28046 Madrid, Spain.

*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.

†Read in part at the Annual Meeting of The American Academy of Orthopaedic Surgeons, Atlanta, Georgia, February 22, 1996.

‡Pez Austral 13, 5-A, 28007 Madrid, Spain.

§Hospital "La Paz," Paseo de la Castellana, 261, 28046 Madrid, Spain.

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TABLE I PROGRESSION OF RADIOGRAPHIC DEMARCATION BETWEEN INITIAL POSTOPERATIVE RADIOGRAPH AND LATEST FOLLOW-UP RADIOGRAPH

*The values are given as the number of cups. All of the changes in demarcation were to a more severe type (p = 0.0001, McNemar test for symmetry).

Initial Postop. Demarcation^15,16	Latest Demarcation*
Type 0	Type 1	Type 2	Type 3	Type 4
Type 0 (n = 233)	170 (73%)	42 (18%)	5 (2%)	5 (2%)	11 (5%)
Type 1 (n = 167)	—	123 (74%)	21 (13%)	5 (3%)	18 (11%)
Type 2 (n = 34)	—	—	16 (47%)	6 (18%)	12 (35%)
Type 3 (n =18)	—	—	—	5	13

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TABLE I PROGRESSION OF RADIOGRAPHIC DEMARCATION BETWEEN INITIAL POSTOPERATIVE RADIOGRAPH AND LATEST FOLLOW-UP RADIOGRAPH

*The values are given as the number of cups. All of the changes in demarcation were to a more severe type (p = 0.0001, McNemar test for symmetry).

Initial Postop. Demarcation^15,16	Latest Demarcation*
Type 0	Type 1	Type 2	Type 3	Type 4
Type 0 (n = 233)	170 (73%)	42 (18%)	5 (2%)	5 (2%)	11 (5%)
Type 1 (n = 167)	—	123 (74%)	21 (13%)	5 (3%)	18 (11%)
Type 2 (n = 34)	—	—	16 (47%)	6 (18%)	12 (35%)
Type 3 (n =18)	—	—	—	5	13

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TABLE II PROGRESSION OF RADIOGRAPHIC DEMARCATION BETWEEN TIME OF APPEARANCE AND LATEST FOLLOW-UP RADIOGRAPH

*At some point during the study.†The values are given as the number of cups. All of the changes in demarcation were to a more severe type (p < 0.0001, McNemar test for symmetry).

	Mean Time to	Latest Demarcation†
Demarcation^15,16*	Appearance of Demarcation	Type 1	Type 2	Type 3	Type 4
	(Mos.)
Type 1 (n = 216)	12.5	165 (76%)	24 (11%)	5 (2%)	22 (10%)
Type 2 (n = 76)	32.1	—	42 (55%)	7 (9%)	27 (36%)
Type 3 (n = 56)	59.4	—	—	21 (38%)	35 (63%)
Type 4 (n = 54)	118.8	—	—	—	54 (100%)

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TABLE II PROGRESSION OF RADIOGRAPHIC DEMARCATION BETWEEN TIME OF APPEARANCE AND LATEST FOLLOW-UP RADIOGRAPH

*At some point during the study.†The values are given as the number of cups. All of the changes in demarcation were to a more severe type (p < 0.0001, McNemar test for symmetry).

	Mean Time to	Latest Demarcation†
Demarcation^15,16*	Appearance of Demarcation	Type 1	Type 2	Type 3	Type 4
	(Mos.)
Type 1 (n = 216)	12.5	165 (76%)	24 (11%)	5 (2%)	22 (10%)
Type 2 (n = 76)	32.1	—	42 (55%)	7 (9%)	27 (36%)
Type 3 (n = 56)	59.4	—	—	21 (38%)	35 (63%)
Type 4 (n = 54)	118.8	—	—	—	54 (100%)

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TABLE III TIME OF APPEARANCE OF RADIOGRAPHIC DEMARCATION

*The values are given as the number of cups.

	When Demarcation Was Seen*
Demarcation^15,16	Within 12 Mos.	After 12 Mos.
Type 1 (n = 165)	129 (78%)	36 (22%)
Type 2 (n = 42)	37 (88%)	5 (12%)
Type 3 (n = 21)	15 (71%)	6 (29%)
Type 4 (n = 54)	43 (80%)	11 (20%)
Total (n = 282)	224 (79%)	58 (21%)

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TABLE III TIME OF APPEARANCE OF RADIOGRAPHIC DEMARCATION

*The values are given as the number of cups.

	When Demarcation Was Seen*
Demarcation^15,16	Within 12 Mos.	After 12 Mos.
Type 1 (n = 165)	129 (78%)	36 (22%)
Type 2 (n = 42)	37 (88%)	5 (12%)
Type 3 (n = 21)	15 (71%)	6 (29%)
Type 4 (n = 54)	43 (80%)	11 (20%)
Total (n = 282)	224 (79%)	58 (21%)

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TABLE IV RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND PREOPERATIVE DIAGNOSIS

* The values are given as the number of cups. The types of demarcation were grouped because of the small numbers in each group.†NS = not significant.‡Progression of the radiolucent line was associated with osteoarthrosis when only patients who had a loss of acetabular bone stock were considered.§Yates corrected chi-square test.

	Latest Demarcation^15,16*
	Types 0	Types 2, 3,
	and 1	and 4	P
Preop. Diagnosis	(N = 335)	(N = 117)	Value†
Osteoarthrosis (n = 143)	115	28	‡
Acetabular dysplasia (grades III and IV⁵) (n = 16)	9	7	0.05§
Inflammatory arthritis (n = 45)	33	12	0.005
Acetabular protrusion (n = 19)	11	8	0.05§
Previous op. (n = 48)	29	19	0.005
Acetabular dysplasia (grades I and II⁵) (n = 51)	36	15	NS
Secondary arthritis (n = 20)	16	4	NS
Avascular necrosis (n = 69)	54	15	NS
Post-traumatic osteoarthrosis (n = 33)	26	7	NS
Other diagnosis (n = 8)	6	2

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TABLE IV RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND PREOPERATIVE DIAGNOSIS

	Latest Demarcation^15,16*
	Types 0	Types 2, 3,
	and 1	and 4	P
Preop. Diagnosis	(N = 335)	(N = 117)	Value†
Osteoarthrosis (n = 143)	115	28	‡
Acetabular dysplasia (grades III and IV⁵) (n = 16)	9	7	0.05§
Inflammatory arthritis (n = 45)	33	12	0.005
Acetabular protrusion (n = 19)	11	8	0.05§
Previous op. (n = 48)	29	19	0.005
Acetabular dysplasia (grades I and II⁵) (n = 51)	36	15	NS
Secondary arthritis (n = 20)	16	4	NS
Avascular necrosis (n = 69)	54	15	NS
Post-traumatic osteoarthrosis (n = 33)	26	7	NS
Other diagnosis (n = 8)	6	2

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TABLE V RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND GENDER, AGE, WEIGHT, LEVEL OF ACTIVITY, AND POSITION OF THE CUP

*The values are given as the number of cups.†Significantly associated with the extent of demarcation (p = 0.0004, chi-square test).

	Latest Demarcation^15,16*
	Type 0	Type 1	Type 2	Type 3	Type 4	Total
Gender
Male	85	88	18	12	23	226
Female	85	77	24	9	31	229
Age < 50 yrs.	51	50	12	6	21	140
Weight > 80 kg	46	41	7	4	14	112
Type-4 (strenuous) activity¹²†	50	23	14	6	5	98
Position of the cup
Horizontal	29	26	8	3	4	70
Vertical	36	36	10	4	13	99
Neutral	105	103	24	14	37	283

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TABLE V RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND GENDER, AGE, WEIGHT, LEVEL OF ACTIVITY, AND POSITION OF THE CUP

*The values are given as the number of cups.†Significantly associated with the extent of demarcation (p = 0.0004, chi-square test).

	Latest Demarcation^15,16*
	Type 0	Type 1	Type 2	Type 3	Type 4	Total
Gender
Male	85	88	18	12	23	226
Female	85	77	24	9	31	229
Age < 50 yrs.	51	50	12	6	21	140
Weight > 80 kg	46	41	7	4	14	112
Type-4 (strenuous) activity¹²†	50	23	14	6	5	98
Position of the cup
Horizontal	29	26	8	3	4	70
Vertical	36	36	10	4	13	99
Neutral	105	103	24	14	37	283

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TABLE VI RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND EXTENT OF WEAR OF THE ACETABULAR CUP

*The values are given as the number of cups.†Significantly associated with the extent of demarcation (p < 0.0001, chi-square test).

	Latest Demarcation^15,16*
Extent of Wear	Type 0	Type 1	Type 2	Type 3	Type 4
<2 mm (n = 315)	120 (38%)	127 (40%)	33 (10%)	14 (4%)	21 (7%)
2 mm (n = 105)	44 (42%)	34 (32%)	7 (7%)	6 (6%)	14 (13%)
>2 mm (n = 32)†	6 (19%)	4 (13%)	2 (6%)	1 (3%)	19 (59%)

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TABLE VI RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND EXTENT OF WEAR OF THE ACETABULAR CUP

*The values are given as the number of cups.†Significantly associated with the extent of demarcation (p < 0.0001, chi-square test).

	Latest Demarcation^15,16*
Extent of Wear	Type 0	Type 1	Type 2	Type 3	Type 4
<2 mm (n = 315)	120 (38%)	127 (40%)	33 (10%)	14 (4%)	21 (7%)
2 mm (n = 105)	44 (42%)	34 (32%)	7 (7%)	6 (6%)	14 (13%)
>2 mm (n = 32)†	6 (19%)	4 (13%)	2 (6%)	1 (3%)	19 (59%)

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FIG1:: Fig. 1 Graph showing the Kaplan-Meier cumulative probability (for the entire series) of an acetabular cup not migrating. The dotted lines indicate the 95 per cent confidence intervals.

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FIG2:: Fig. 2 Graph showing the Kaplan-Meier cumulative probability (for the entire series) of an acetabular cup not becoming radiographically loose (type-3 or type-4 demarcation). The dotted lines indicate the 95 per cent confidence intervals.

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FIG3-A:: Figs. 3-A through 3-D: Graphs showing the Kaplan-Meier cumulative probability of an acetabular cup not migrating according to the type of demarcation on the initial postoperative radiograph. The dotted lines indicate the 95 per cent confidence intervals. Fig. 3-A: Acetabular cups with no (type-0) demarcation.

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FIG3-B:: Fig. 3-B Acetabular cups with type-1 demarcation.

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FIG3-C:: Fig. 3-C Acetabular cups with type-2 demarcation.

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FIG3-D:: Fig. 3-D Acetabular cups with type-3 demarcation.

Material and Methods

Introduction | Material and Methods | Results | Discussion | References

Five hundred and fifty-eight consecutive primary Charnley low-friction arthroplasties of the hip were performed in 485 patients at our institution between March 1, 1971, and December 31, 1976. We excluded 106 hips (ninety-three patients) from the study. Sixty-one (11 per cent) were excluded because the cement was not radiopaque; seventeen (3 per cent), because the patient had been lost to follow-up within ten years after the operation; fifteen (3 per cent), because the patient had died within ten years after the operation; eleven (2 per cent), because of deep infection; and two (less than 1 per cent), because of early revision for malposition of the cup. The remaining 452 hips (392 patients) formed the basis of the study.

Ten hips (ten patients) were revised within ten years after the operation because the cup had migrated. The demarcation of the bone-cement interface on the initial postoperative radiograph involved the lateral one-third of the acetabular component in one hip, involved the lateral and superomedial thirds in three hips, and was complete in six hips. The average duration of follow-up for the remaining 442 hips (382 patients) was twenty years (range, eleven to twenty-five years). Over-all, there were 199 men (51 per cent) and 193 women (49 per cent), the average age of the patients at the time of the operation was fifty-five years (range, eighteen to seventy-eight years), and the average weight was sixty-seven kilograms (range, forty to 100 kilograms). The level of activity of each patient was classified with use of the scale of Gustilo and Burnham¹². According to this classification, type 1 indicates that the patient is sedentary and can walk only indoors; type 2, that the patient can engage in non-stressful activity and can walk for limited distances; type 3, that the patient can participate in moderate activity, including some sports and full-time work or housework; and type 4, that the patient is very active and can participate in vigorous sports activities or perform strenuous manual labor.

The diagnosis at the time of the operation was primary osteoarthrosis for 143 hips (32 per cent), avascular necrosis for sixty-nine (15 per cent), acetabular dysplasia (grade I or II, according to the classification of Crowe et al.⁵) for fifty-one (11 per cent), a previous operation for forty-eight (11 per cent), inflammatory arthritis for forty-five (10 per cent), post-traumatic osteoarthrosis for thirty-three (7 per cent), secondary arthritis for twenty (4 per cent), acetabular protrusion for nineteen (4 per cent), severe acetabular dysplasia (grade III or IV⁵) for sixteen (4 per cent), and other diagnoses for eight (2 per cent). Inflammatory arthritis, acetabular protrusion, severe acetabular dysplasia, or a previous operation weakens the bone and results in loss of the acetabular bone stock.

All of the operations were performed by senior staff surgeons (not necessarily one of us) with use of the same operative technique. The technique consisted of a lateral approach with a trochanteric osteotomy and the insertion of the then-standard Charnley components: a hemispheroid non-flanged acetabular socket made of ultra-high molecular weight polyethylene and a stainless-steel femoral stem with a 22.25-millimeter-diameter head (Thackray, Leeds, England). C.M.W. I radiopaque polymethylmethacrylate cement (C.M.W. Laboratories, Devon, England) was used for fixation. The acetabulum was deepened superiorly, and the eburnated bone in the acetabular roof was removed. A central pilot hole was used to stabilize the reamers, and two additional 12.5-millimeter fixation holes—one in the ilium and one in the ischium—were drilled. Cement was packed into the acetabular cavity with thumb pressure.

Standard anteroposterior radiographs of the pelvis were made for all patients immediately after the operation, at six and twelve months, and annually thereafter. All postoperative and follow-up radiographs were made at our institution according to the same protocol. The patient was positioned supine, with the feet together. The x-ray tube was positioned over the symphysis pubis, one meter from and perpendicular to the table. Variations in magnification were corrected with use of the 22.25-millimeter head of the femoral component as an internal reference. The acetabular angle³⁷ was classified as neutral (40 to 50 degrees), horizontal (less than 40 degrees), or vertical (more than 50 degrees). The distribution of cement around the socket was classified according to the three zones described by DeLee and Charnley⁶.

The presence of a radiolucent line at the bone-cement interface in the different acetabular zones and the amount of wear of the acetabular component were determined on each radiograph and were recorded. Two-dimensional linear wear of the acetabular component was assessed as described by Livermore al.²³. The latest follow-up radiograph was compared with the initial postoperative radiograph, and the cement-prosthesis interface was used to identify the proximal border of the polyethylene. A transparent template was used to locate the center of the femoral head. The precise magnification was calculated from the known dimension of the acetabular cup and from the size of the femoral head as it appeared radiographically. A compass and a pair of calipers were used to locate and measure the greatest amount of wear.

Any radiolucent line at the bone-cement interface adjacent to the acetabular component, the so-called radiographic demarcation, was classified according to the system of Hodgkinson et al.^15,16. The demarcation, regardless of the thickness of the radiolucent line, was categorized as type 0 when there was no demarcation, as type 1 when the line was in zone 1 of DeLee and Charnley⁶, as type 2 when it was in zones 1 and 2, as type 3 when it was in all three zones, and as type 4 when the acetabular cup had migrated. The acetabular component was considered to have migrated when there had been a change of more than three millimeters in the height of the cup, measured from the ipsilateral teardrop, or in the horizontal distance of the cup, measured from the center of the femoral head to the Köhler line¹⁶. The extent of the radiolucent line at the bone-cement interface and the amount of wear of the acetabular component in all of the hips were determined by one of us (V. D.-V.), who had no knowledge of the operative findings.

We attempted to determine if there was a relationship between the extent of the radiolucent line, if present, and gender, an age of less than fifty years, a body weight of more than eighty kilograms, a high level of activity (type 4¹²), the preoperative diagnosis, the postoperative position of the cup, and the amount of polyethylene wear. Kaplan-Meier survivorship analysis²⁰ with 95 per cent confidence intervals⁷ was used to estimate the rates of failure, with migration considered to be the end point for failure, for the different types of demarcation on the initial postoperative radiograph. The results were assessed with the Mantel-Cox test to compare the Kaplan-Meier curves. The level of significance was p < 0.05. The McNemar test for symmetry was used to determine the proportion of acetabular cups that were transferred from one category into another. Yates corrected and chi-square tests also were used.

Results

Introduction | Material and Methods | Results | Discussion | References

The demarcation on the initial postoperative radiograph was classified as type 0 for 233 (52 per cent) of the acetabular components, type 1 for 167 (37 per cent), type 2 for thirty-four (8 per cent), and type 3 for eighteen (4 per cent); no cup had migrated (type-4 demarcation). On the most recent follow-up radiograph, the demarcation was type 0 for 170 (38 per cent) of the acetabular components, type 1 for 165 (37 per cent), type 2 for forty-two (9 per cent), type 3 for twenty-one (5 per cent), and type 4 for fifty-four (12 per cent) (Table I). The demarcation increased over time in 138 (31 per cent) of the 452 hips. Eleven (5 per cent) of the 233 acetabular cups with no (type-0) demarcation on the initial postoperative radiograph had migrated by the time of the most recent radiographic follow-up, an average of 122 months (range, fifty-five to 182 months) postoperatively. Eighteen (11 per cent) of the 167 cups with type-1 demarcation had migrated by an average of 148 months (range, twenty-three to 237 months), twelve (35 per cent) of the thirty-four cups with type-2 demarcation had migrated by an average of 129 months (range, thirty-nine to 221 months), and thirteen of the eighteen cups with type-3 demarcation had migrated by an average of 111 months (range, forty-eight to 179 months). All of the changes in demarcation were to a more severe type (p = 0.0001, McNemar test for symmetry) (Table I). Twenty-two (10 per cent) of the 216 acetabular cups with type-1 demarcation at some time during the study, twenty-seven (36 per cent) of the seventy-six cups with type-2, and thirty-five (63 per cent) of the fifty-six cups with type-3 eventually migrated (Table II). Again, whenever the demarcation changed, it progressed to a higher type (p < 0.0001, McNemar test for symmetry). Type-1 demarcation developed at an average of thirteen months (range, zero to 240 months) after the operation; type-2 demarcation, at an average of thirty-two months (range, zero to 229 months); type-3 demarcation, at an average of fifty-nine months (range, zero to 173 months); and type-4 demarcation, at an average of 119 months (range, twenty-three to 212 months). The radiolucent line developed within twelve months after the operation in 224 (79 per cent) of the 282 hips with evidence of such a line (Table III).

There was a significant relationship between the extent of the radiolucent line on the most recent radiograph and a preoperative diagnosis of acetabular protrusion (p = 0.05), severe (grade-III or IV⁵) acetabular dysplasia (p = 0.05), inflammatory arthritis (p = 0.005), or a previous operation (p = 0.005) (Table IV). Strenuous (type-4) activity (Table V) and more than two millimeters of wear of the acetabular component (Table VI) also were significantly related to the extent of the radiolucent line (p = 0.0004 and p < 0.0001, respectively).

According to the Kaplan-Meier survivorship analysis, the cumulative probability (and 95 per cent confidence interval) of a cup not migrating was 79 ± 9.43 per cent for the entire series at twenty years (Fig. 1). When cups with type-3 or type-4 demarcation were considered to be radiographically loose, the cumulative probability of a cup not being radiographically loose was 67 ± 13.64 per cent for the entire series at twenty years (Fig. 2). The more extensive the demarcation was on the initial postoperative radiograph, the greater the risk of migration (the end point for failure) (p < 0.0001, Mantel-Cox test) (Figs. 3-A, 3-B, 3-C and 3-D).

Discussion

Introduction | Material and Methods | Results | Discussion | References

A loose femoral component is associated with clinical symptoms more often than is a loose cup, even when the cup has migrated^2-4,10,21,25. Although a loose cup rarely causes early notable clinical symptoms, with time movement at the bone-cement junction will cause considerable bone resorption as well as clinical signs and symptoms of failure.

Any demarcation of the bone-cement interface about the acetabular component on the immediate postoperative radiograph must be considered as an important factor affecting the long-term result. The demarcation may be due to poor operative technique¹⁵; it may be the result of failure to remove all of the articular cartilage, particularly at the periphery of the acetabulum, or the result of poor bone-cement apposition during polymerization of the cement^8,34. In previous studies, even minor demarcation in the first year after the operation was associated with radiographic loosening of the cup at ten years in thirty-five (35 per cent) of 100 hips² and forty-three (38 per cent) of 114 hips¹⁵ that had had revision and, in a more recent study by the same authors of the latter study, in forty-four (37 per cent) of 118 hips that had had a primary Charnley arthroplasty¹⁶.

We found that sockets with no demarcation on the initial postoperative radiograph were associated with a good long-term result, but thirteen of the eighteen cups with a complete radiolucent line on the initial postoperative radiograph subsequently migrated, regardless of the thickness of the line. Any radiolucent line that is new or progressive or that was not apparent on the initial radiograph should be considered as important. Our results concur with those of other authors who concluded that the extent of the radiolucent line is more important than its thickness^15,31, and a progression of the line within the first year after the operation is a useful prognostic indicator of late failure of the acetabular cup¹⁶.

Loosening of a cemented acetabular cup occurs by the progressive resorption of bone in three dimensions. However, a radiograph provides only a two-dimensional projection of an object, and this presents difficulties when clinical radiographs are assessed, even under standardized conditions. It is well known that the anteroposterior radiograph underrepresents the presence and extent of radiolucent lines. The addition of an oblique radiograph increases the sensitivity of the anteroposterior radiograph for the detection of the maximum thickness and extent of the radiolucent line adjacent to the socket³¹. The use of different radiographic projections increases the accuracy of detection of radiolucent lines.

A vertical position of the cup postoperatively has been associated with the development of type-3 or type-4 demarcation²², but this association was not found in the present series. Our data indicated that a loss of acetabular bone stock, a high degree of activity, and rapid polyethylene wear predisposed patients to the development of such demarcation.

A loss of acetabular bone stock was a risk factor related to type-2, 3, or 4 demarcation of the acetabular cup in the present series. Thus, patients who had acetabular protrusion or inflammatory arthritis or who had had a previous operation were at risk because of the poor quality of the acetabular bone related to these conditions. The lack of a strong subchondral bone plate or the presence of eburnated bone in the acetabular roof may increase the risk of migration of the cup when the patient has an active lifestyle²². Inoue et al. also considered rheumatoid inflammation to be a contributing factor in the process of loosening of the acetabular component¹⁷. Those authors found rheumatoid nodules and marked lymphoplasmacytic infiltration at the bone-cement interface at the time of revision arthroplasty in patients who had rheumatoid arthritis.

The findings of the present study also confirm that major wear of the acetabular cup is another important factor associated with type-3 or 4 demarcation. A relationship between the depth of polyethylene wear and the prevalence of migration of the cup has been reported^10,38,39. In previous studies, a young age (less than fifty years old), a weight of more than eighty kilograms, and a vertical position of the cup postoperatively have been considered to be related to rapid polyethylene wear¹⁰.

On the basis of our findings, we concluded that all cemented acetabular cups, even those with the least amount of demarcation (types 0 and 1), can migrate after low-friction arthroplasty. Any radiolucent line that develops postoperatively may have a negative implication with regard to the final outcome of the arthroplasty. The more extensive the demarcation on the initial postoperative radiograph, the greater the risk of migration of the cup, particularly when there is a loss of the acetabular bone stock or rapid polyethylene wear.

References

Introduction | Material and Methods | Results | Discussion | References

Ballard, W. T.; Callaghan, J. J.; Sullivan, P. M.; and Johnston, R. C.: The results of improved cementing techniques or total hip arthroplasty in patients less than fifty years old. A ten-year follow-up study. J. Bone and Joint Surg.,76-A: 959-964, July 1994.76-A959 1994

Carlsson, Å. S., and Gentz, C.-F.: Radiographic versus clinical loosening of the acetabular component in noninfected total hip arthroplasty. Clin. Orthop.,185: 145-150, 1984.185145 1984 [PubMed]

Carlsson, Å. S.; Gentz, C.-F.; and Stenport, J.: Fracture of the femoral prosthesis in total hip replacement according to Charnley. Acta Orthop. Scandinavica,48: 650-655, 1977.48650 1977

Carlsson, Å. S.; Lindberg, H. O.; and Sanzén, L.: Loosening of the socket in a 35-mm snap-fit prosthesis and the Charnley hip prosthesis. A roentgenographic evaluation of 321 cases operated upon because of osteoarthritis. Clin. Orthop.,228: 63-68, 1988.22863 1988 [PubMed]

Crowe, J. F.; Mani, V. J.; and Ranawat, C. S.: Total hip replacement in congenital dislocation and dysplasia of the hip. J. Bone and Joint Surg.,61-A: 15-23, Jan. 1979.61-A15 1979

DeLee, J. G., and Charnley, J.: Radiological demarcation of cemented sockets in total hip replacement. Clin. Orthop.,121: 20-32, 1976.12120 1976 [PubMed]

Dorey, F., and Amstutz, H. C.: Survivorship analysis in the evaluation of joint replacement. J. Arthroplasty,1: 63-69, 1986.163 1986 [PubMed]

Eftekhar, N. S., and Nercessian, O.: Incidence and mechanism of failure of cemented acetabular component in total hip arthroplasty. Orthop. Clin. North America,19: 557-566, 1988.19557 1988

Fredin, H.; Sanzén, L.; Sigurdsson, B.; and Unander-Scharin, L.: Total hip arthroplasty in high congenital dislocation. 21 hips with a minimum five-year follow-up. J. Bone and Joint Surg.,73-B(3): 430-433, 1991.73-B(3)430 1991

García-Cimbrelo, E., and Munuera, L.: Early and late loosening of the acetabular cup after low-friction arthroplasty. J. Bone and Joint Surg.,74-A: 1119-1129, Sept. 1992.74-A1119 1992

Garellick, G.; Herberts, P.; Strömberg, C.; and Malchau, H.: Long-term results of Charnley arthroplasty. A 12-16-year follow-up study. J. Arthroplasty,9: 333-340, 1994.9333 1994 [PubMed]

Gustilo, R. B., and Burnham, W. H.: Long-term results of total hip arthroplasty in young patients. In The Hip. Proceedings of the Tenth Open Scientific Meeting of The Hip Society, pp. 27-33. St. Louis, C. V. Mosby, 1982.

Harris, W. H., and McGann, W. A.: Loosening of the femoral component after use of the medullary-plug cementing technique. Follow-up note with a minimum five-year follow-up. J. Bone and Joint Surg.,68-A: 1064-1066, Sept. 1986.68-A1064 1986

Harris, W. H.; McCarthy, J. C., Jr.; and O'Neill, D. A.: Femoral component loosening using contemporary techniques of femoral cement fixation. J. Bone and Joint Surg.,64-A: 1063-1067, Sept. 1982.64-A1063 1982

Hodgkinson, J. P.; Shelley, P.; and Wroblewski, B. M.: The correlation between the roentgenographic appearance and operative findings at the bone-cement junction of the socket in Charnley low friction arthroplasties. Clin. Orthop.,228: 105-109, 1988.228105 1988 [PubMed]

Hodgkinson, J. P.; Maskell, A. P.; Paul, A.; and Wroblewski, B. M.: Flanged acetabular components in cemented Charnley hip arthroplasty. Ten-year follow-up of 350 patients. J. Bone and Joint Surg.,75-B(3): 464-467, 1993.75-B(3)464 1993

Inoue, K.; Nishioka, J.; Hukuda, S.; Shichikawa, K.; and Okabe, H.: Rheumatoid nodules at the cement-bone interface in revision arthroplasty of rheumatoid patients. J. Bone and Joint Surg.,75-B(3): 455-458, 1993.75-B(3)455 1993

Johnston, R. C.; Fitzgerald, R. H., Jr.; Harris, W. H.; Poss, R.; Müller, M. E.; and Sledge, C. B.: Clinical and radiographic evaluation of total hip replacement. A standard system of terminology for reporting results. J. Bone and Joint Surg.,72-A: 161-168, Feb. 1990.72-A161 1990

Joshi, A. B.; Porter, M. L.; Trail, I. A.; Hunt, L. P.; Murphy, J. C. M.; and Hardinge, K.: Long-term results of Charnley low-friction arthroplasty in young patients. J. Bone and Joint Surg.,75-B(4): 616-623, 1993.75-B(4)616 1993

Kaplan, E. L., and Meier, P.: Nonparametric estimation from incomplete observations. J. Am. Statist. Assn.,53: 457-481, 1958.53457 1958

Kobayashi, S.; Eftekhar, N. S.; and Terayama, K.: Predisposing factors in fixation failure of femoral prostheses following primary Charnley low friction arthroplasty. A 10-to 20-year followup study. Clin. Orthop.,306: 73-83, 1994.30673 1994 [PubMed]

Kobayashi, S.; Eftekhar, N. S.; Terayama, K.; and Iorio, R.: Risk factors affecting radiological failure of the socket in primary Charnley low friction arthroplasty. A 10- to 20-year followup study. Clin. Orthop.,306: 84-96, 1994.30684 1994 [PubMed]

Livermore, J.; Ilstrup, D.; and Morrey, B.: Effect of femoral head size on wear of the polyethylene acetabular component. J. Bone and Joint Surg.,72-A: 518-528, April 1990.72-A518 1990

Mulroy, R. D., Jr., and Harris, W. H.: The effect of improved cementing techniques on component loosening in total hip replacement. An 11-year radiographic review. J. Bone and Joint Surg.,72-B(5): 757-760, 1990.72-B(5)757 1990

Munuera, L., and García-Cimbrelo, E.: The femoral component in low-friction arthroplasty after ten years. Clin. Orthop.,279: 163-175, 1992.279163 1992 [PubMed]

Oishi, C. S.; Walker, R. H.; and Colwell, C. W., Jr.: The femoral component in total hip arthroplasty. Six to eight-year follow-up on one hundred consecutive patients after use of a third-generation cementing technique. J. Bone and Joint Surg.,76-A: 1130-1136, Aug. 1994.76-A1130 1994

Roberts, D. W.; Poss, R.; and Kelley, K.: Radiographic comparison of cementing techniques in total hip arthroplasty. J. Arthroplasty,1: 241-247, 1986.1241 1986 [PubMed]

Russotti, G. M.; Coventry, B.; and Stauffer, R. N.: Cemented total hip arthroplasty with contemporary techniques. A five-year minimum follow-up study. Clin. Orthop.,235: 141-147, 1988.235141 1988 [PubMed]

Salvati, E. A.; Wilson, P. D., Jr.; Jolley, M. N.; Vakili, F.; Aglietti, P.; and Brown, G. C.: A ten-year follow-up study of our first one hundred consecutive Charnley total hip replacements. J. Bone and Joint Surg.,63-A: 753-767, June 1981.63-A753 1981

Sarmiento, A.; Ebramzadeh, E.; Gogan, W. J.; and McKellop, H. A.: Total hip arthroplasty with cement. A long-term radiographic analysis in patients who are older than fifty and younger than fifty years. J. Bone and Joint Surg.,72-A: 1470-1476, Dec. 1990.72-A1470 1990

Schmalzried, T. P.; Kwong, L. M.; Jasty, M.; Sedlacek, R. C.; Haire, T. C.; O'Connor, D. O.; Bragdon, C. R.; Kabo, J. M.; Malcolm, A. J.; and Harris, W. H.: The mechanism of loosening of cemented acetabular components in total hip arthroplasty. Analysis of specimens retrieved at autopsy. Clin. Orthop.,274: 60-78, 1992.27460 1992 [PubMed]

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Shelley, P., and Wroblewski, B. M.: Socket design and cement pressurisation in the Charnley low-friction arthroplasty. J. Bone and Joint Surg.,70-B(3): 358-363, 1988.70-B(3)358 1988

Stauffer, R. N.: Ten-year follow-up study of total hip replacement. With particular reference to roentgenographic loosening of the components. J. Bone and Joint Surg.,64-A: 983-990, Sept. 1982.64-A983 1982

Sullivan, P. M.; McKenzie, J. R.; Callaghan, J. J.; and Johnston, R. C.: Total hip arthroplasty with cement in patients who are less than fifty years old. A sixteen to twenty-two-year follow-up study. J. Bone and Joint Surg.,76-A: 863-869, June 1994.76-A863 1994

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Wroblewski, B. M.: Direction and rate of socket wear in Charnley low-friction arthroplasty. J. Bone and Joint Surg.,67-B(5): 757-761, 1985.67-B(5)757 1985

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Topics

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FIG1:: Fig. 1 Graph showing the Kaplan-Meier cumulative probability (for the entire series) of an acetabular cup not migrating. The dotted lines indicate the 95 per cent confidence intervals.

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FIG3-B:: Fig. 3-B Acetabular cups with type-1 demarcation.

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FIG3-C:: Fig. 3-C Acetabular cups with type-2 demarcation.

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FIG3-D:: Fig. 3-D Acetabular cups with type-3 demarcation.

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TABLE I PROGRESSION OF RADIOGRAPHIC DEMARCATION BETWEEN INITIAL POSTOPERATIVE RADIOGRAPH AND LATEST FOLLOW-UP RADIOGRAPH

*The values are given as the number of cups. All of the changes in demarcation were to a more severe type (p = 0.0001, McNemar test for symmetry).

Initial Postop. Demarcation^15,16	Latest Demarcation*
Type 0	Type 1	Type 2	Type 3	Type 4
Type 0 (n = 233)	170 (73%)	42 (18%)	5 (2%)	5 (2%)	11 (5%)
Type 1 (n = 167)	—	123 (74%)	21 (13%)	5 (3%)	18 (11%)
Type 2 (n = 34)	—	—	16 (47%)	6 (18%)	12 (35%)
Type 3 (n =18)	—	—	—	5	13

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TABLE I PROGRESSION OF RADIOGRAPHIC DEMARCATION BETWEEN INITIAL POSTOPERATIVE RADIOGRAPH AND LATEST FOLLOW-UP RADIOGRAPH

*The values are given as the number of cups. All of the changes in demarcation were to a more severe type (p = 0.0001, McNemar test for symmetry).

Initial Postop. Demarcation^15,16	Latest Demarcation*
Type 0	Type 1	Type 2	Type 3	Type 4
Type 0 (n = 233)	170 (73%)	42 (18%)	5 (2%)	5 (2%)	11 (5%)
Type 1 (n = 167)	—	123 (74%)	21 (13%)	5 (3%)	18 (11%)
Type 2 (n = 34)	—	—	16 (47%)	6 (18%)	12 (35%)
Type 3 (n =18)	—	—	—	5	13

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TABLE II PROGRESSION OF RADIOGRAPHIC DEMARCATION BETWEEN TIME OF APPEARANCE AND LATEST FOLLOW-UP RADIOGRAPH

*At some point during the study.†The values are given as the number of cups. All of the changes in demarcation were to a more severe type (p < 0.0001, McNemar test for symmetry).

	Mean Time to	Latest Demarcation†
Demarcation^15,16*	Appearance of Demarcation	Type 1	Type 2	Type 3	Type 4
	(Mos.)
Type 1 (n = 216)	12.5	165 (76%)	24 (11%)	5 (2%)	22 (10%)
Type 2 (n = 76)	32.1	—	42 (55%)	7 (9%)	27 (36%)
Type 3 (n = 56)	59.4	—	—	21 (38%)	35 (63%)
Type 4 (n = 54)	118.8	—	—	—	54 (100%)

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TABLE II PROGRESSION OF RADIOGRAPHIC DEMARCATION BETWEEN TIME OF APPEARANCE AND LATEST FOLLOW-UP RADIOGRAPH

*At some point during the study.†The values are given as the number of cups. All of the changes in demarcation were to a more severe type (p < 0.0001, McNemar test for symmetry).

	Mean Time to	Latest Demarcation†
Demarcation^15,16*	Appearance of Demarcation	Type 1	Type 2	Type 3	Type 4
	(Mos.)
Type 1 (n = 216)	12.5	165 (76%)	24 (11%)	5 (2%)	22 (10%)
Type 2 (n = 76)	32.1	—	42 (55%)	7 (9%)	27 (36%)
Type 3 (n = 56)	59.4	—	—	21 (38%)	35 (63%)
Type 4 (n = 54)	118.8	—	—	—	54 (100%)

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TABLE III TIME OF APPEARANCE OF RADIOGRAPHIC DEMARCATION

*The values are given as the number of cups.

	When Demarcation Was Seen*
Demarcation^15,16	Within 12 Mos.	After 12 Mos.
Type 1 (n = 165)	129 (78%)	36 (22%)
Type 2 (n = 42)	37 (88%)	5 (12%)
Type 3 (n = 21)	15 (71%)	6 (29%)
Type 4 (n = 54)	43 (80%)	11 (20%)
Total (n = 282)	224 (79%)	58 (21%)

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TABLE III TIME OF APPEARANCE OF RADIOGRAPHIC DEMARCATION

*The values are given as the number of cups.

	When Demarcation Was Seen*
Demarcation^15,16	Within 12 Mos.	After 12 Mos.
Type 1 (n = 165)	129 (78%)	36 (22%)
Type 2 (n = 42)	37 (88%)	5 (12%)
Type 3 (n = 21)	15 (71%)	6 (29%)
Type 4 (n = 54)	43 (80%)	11 (20%)
Total (n = 282)	224 (79%)	58 (21%)

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TABLE IV RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND PREOPERATIVE DIAGNOSIS

	Latest Demarcation^15,16*
	Types 0	Types 2, 3,
	and 1	and 4	P
Preop. Diagnosis	(N = 335)	(N = 117)	Value†
Osteoarthrosis (n = 143)	115	28	‡
Acetabular dysplasia (grades III and IV⁵) (n = 16)	9	7	0.05§
Inflammatory arthritis (n = 45)	33	12	0.005
Acetabular protrusion (n = 19)	11	8	0.05§
Previous op. (n = 48)	29	19	0.005
Acetabular dysplasia (grades I and II⁵) (n = 51)	36	15	NS
Secondary arthritis (n = 20)	16	4	NS
Avascular necrosis (n = 69)	54	15	NS
Post-traumatic osteoarthrosis (n = 33)	26	7	NS
Other diagnosis (n = 8)	6	2

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TABLE IV RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND PREOPERATIVE DIAGNOSIS

	Latest Demarcation^15,16*
	Types 0	Types 2, 3,
	and 1	and 4	P
Preop. Diagnosis	(N = 335)	(N = 117)	Value†
Osteoarthrosis (n = 143)	115	28	‡
Acetabular dysplasia (grades III and IV⁵) (n = 16)	9	7	0.05§
Inflammatory arthritis (n = 45)	33	12	0.005
Acetabular protrusion (n = 19)	11	8	0.05§
Previous op. (n = 48)	29	19	0.005
Acetabular dysplasia (grades I and II⁵) (n = 51)	36	15	NS
Secondary arthritis (n = 20)	16	4	NS
Avascular necrosis (n = 69)	54	15	NS
Post-traumatic osteoarthrosis (n = 33)	26	7	NS
Other diagnosis (n = 8)	6	2

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TABLE V RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND GENDER, AGE, WEIGHT, LEVEL OF ACTIVITY, AND POSITION OF THE CUP

*The values are given as the number of cups.†Significantly associated with the extent of demarcation (p = 0.0004, chi-square test).

	Latest Demarcation^15,16*
	Type 0	Type 1	Type 2	Type 3	Type 4	Total
Gender
Male	85	88	18	12	23	226
Female	85	77	24	9	31	229
Age < 50 yrs.	51	50	12	6	21	140
Weight > 80 kg	46	41	7	4	14	112
Type-4 (strenuous) activity¹²†	50	23	14	6	5	98
Position of the cup
Horizontal	29	26	8	3	4	70
Vertical	36	36	10	4	13	99
Neutral	105	103	24	14	37	283

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TABLE V RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND GENDER, AGE, WEIGHT, LEVEL OF ACTIVITY, AND POSITION OF THE CUP

*The values are given as the number of cups.†Significantly associated with the extent of demarcation (p = 0.0004, chi-square test).

	Latest Demarcation^15,16*
	Type 0	Type 1	Type 2	Type 3	Type 4	Total
Gender
Male	85	88	18	12	23	226
Female	85	77	24	9	31	229
Age < 50 yrs.	51	50	12	6	21	140
Weight > 80 kg	46	41	7	4	14	112
Type-4 (strenuous) activity¹²†	50	23	14	6	5	98
Position of the cup
Horizontal	29	26	8	3	4	70
Vertical	36	36	10	4	13	99
Neutral	105	103	24	14	37	283

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TABLE VI RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND EXTENT OF WEAR OF THE ACETABULAR CUP

*The values are given as the number of cups.†Significantly associated with the extent of demarcation (p < 0.0001, chi-square test).

	Latest Demarcation^15,16*
Extent of Wear	Type 0	Type 1	Type 2	Type 3	Type 4
<2 mm (n = 315)	120 (38%)	127 (40%)	33 (10%)	14 (4%)	21 (7%)
2 mm (n = 105)	44 (42%)	34 (32%)	7 (7%)	6 (6%)	14 (13%)
>2 mm (n = 32)†	6 (19%)	4 (13%)	2 (6%)	1 (3%)	19 (59%)

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TABLE VI RELATIONSHIP BETWEEN EXTENT OF LATEST RADIOGRAPHIC DEMARCATION AND EXTENT OF WEAR OF THE ACETABULAR CUP

*The values are given as the number of cups.†Significantly associated with the extent of demarcation (p < 0.0001, chi-square test).

	Latest Demarcation^15,16*
Extent of Wear	Type 0	Type 1	Type 2	Type 3	Type 4
<2 mm (n = 315)	120 (38%)	127 (40%)	33 (10%)	14 (4%)	21 (7%)
2 mm (n = 105)	44 (42%)	34 (32%)	7 (7%)	6 (6%)	14 (13%)
>2 mm (n = 32)†	6 (19%)	4 (13%)	2 (6%)	1 (3%)	19 (59%)