Radiographic evaluation of charnley cups used in first-time revision

The Journal of Arthroplasty Vol. 18 No. 8 2003

Radiographic Evaluation of Charnley Cups Used in First-Time Revision: Repeated Observations for 7–15 Years Peter Hultmark, MD,† Joakim Ho¨stner, MD,* Peter Herberts, MD, PhD,* and Johan Ka¨rrholm, MD, PhD*

Abstract: The radiographs of 46 consecutive polyethylene cups used in cemented first-time revision of the acetabulum were studied up to a mean of 10.7 years (range, 0.5–16.3 years). Six cups developed loosening, of which 2 were revised. New radiolucent lines appeared mainly up to the 3 years follow-up. Progression of radiolucencies to new regions was noted in 28 (61%) cups. This progression occurred as an increase in extension from the periphery to the central region of the interface, whereas the width only showed minor changes. Our findings indicate that even radiolucent lines with a width ⬍1.0 mm should be given attention because these lines can surround the cup before significant migration (⬎5 mm) is established. True lateral radiographs exposed to visualize the interface add information concerning presence of loosening. According to our opinion, complete radiolucent lines on either the anterior-posterior or lateral view, with a width of 0.3 to 0.5 mm or more, should be regarded as radiographic failure. Key words: revision hip arthroplasty, cup revision, radiographic failure, aseptic loosening, radiolucency. © 2003 Elsevier Inc. All rights reserved.

Radiographic examination is often unsatisfactory to assess prosthesis loosening at an early stage. Inaccurate determination of migration and difficulty to determine presence and extent of radiolucent lines are the main reasons [1–7]. Pellicci and Wilson et al [8] concluded that progressive radiolucent lines

indicate poor prognosis. Schmalzried and Kwong et al [3] and Schmalzried and Maloney et al [4] demonstrated progression of radiolucencies from the periphery to the dome of the cup. Cellular reactions caused by particles in the joint fluid were regarded to be responsible for this process. Hence, the mechanism of late aseptic acetabular loosening was thought to be biologic in its nature, not mechanical. To evaluate this process on conventional radiographs, prospective studies including repeated radiographic examinations are necessary. We have, however, only been able to find one such study of the acetabular component with long-term follow up [9] where this has been done in a consistent way. Our purpose was to study the appearance and progression of radiolucent lines and other radiographic changes in a consecutive series of Charnley cups used in first-time revisions. In this population,

From the *Department of Orthopaedics, Sahlgrenska University Hospital, Go¨teborg, Sweden. †Author is deceased. Submitted January 23, 2001; accepted July 30, 2003. Benefits or funds were received in partial or total support of the research material described in this article from Greta and Einar Asker Foundation, Hjalmar Svensson Research Foundation, Neubergh Research Foundation, and Go¨teborg Medical Association. Reprint requests: Johan Ka¨rrholm, MD, PhD, Department of Orthopaedics, Institute of Surgical Science, Sahlgrenska University Hospital, Go¨teborg University, SE 413 45 Go¨teborg, Sweden. © 2003 Elsevier Inc. All rights reserved. 0883-5403/03/1808-0010$30.00/0 doi:10.1016/S0883-5403(03)00405-4

1005

1006 The Journal of Arthroplasty Vol. 18 No. 8 December 2003 Table 1. Clinical and Radiological Follow-Up Time After Operation y 1 3 5 7 10 13 15

Follow-Up

Did Not Attend

Maximum Interval

Total* Available

Clinical

Radiographic

Deceased

0.5–2 2–4 4–6 6–8 9–11 12–14 14–16

46 45 42 39 31 16 8

45 33 34 26 26 15 6

40 29 27 32 28 15 6

1 3 2 5 3 3 2

Revised

Clinical

Radiographic

1 1 1

1 9 6 8 1 1 0

6 13 12 1 1 1 0

*Excluding deceased and revised patients in the beginning of each follow-up period.

progression of lucent lines could be expected to be more frequent than in a material based on primary cases.

Materials and Methods Between 1982 and 1990, 47 aseptic first-time cemented revisions were done at our hospital using the Charnley cup. One of these patients with postoperative deep infection was excluded, leaving 46 hips to be studied. There were 25 women (27 hips) and 19 men (19 hips). The mean age at the primary total hip arthroplasty (THA) operation was 63 years (range, 22–75 years) and at the revision 69 years (range, 28 – 83 years). Thirty-nine had noninflammatory arthrosis and 7 had rheumatoid arthritis. There were 8 standard, 20 flanged, and 5 Ogee cups inserted with second-generation technique and 2 standard, 2 flanged, and 9 Ogee cups inserted with third-generation technique. Twelve were small (40 mm) and 34 large (43 mm). Further details about this material are presented elsewhere [10]. Radiographic Evaluation A pelvic view centered on the symphysis and anterior-posterior (AP) and lateral projections of the hips were exposed preoperatively and postoperatively. The same projections were used at the 1and 15-year follow-up after the operation. Endpoints for the study were revision, removal, or death. All except 1 patient, who died 2 years after the operation, attended at least 1 follow-up examination (Table 1). The mean radiographic follow-up time was 9.5 years (range, 0.1–16.0 years). An independent observer (P. Hu) evaluated all radiographs. Proximal and distal migration of the acetabular component was measured as the difference in the

vertical distance between the center of the rotation of the hip and the inferior margin of the teardrop. Medial and lateral migration was measured as the difference in the horizontal distance between the inferior margin of the teardrop and the center of the rotation and the horizontal distance between Kohler’s line and the top of the dome of the cup. These measurements also were used to determine the position of the cup on the postoperative radiographs [11]. The inclination of the cup on the AP view was determined using the teardrop line as reference. On the lateral view, we used 2 methods to determine anteversion and retroversion of the cup. In the first method, we used the radiographs exposed with the patient in a supine position with the cassettes placed on the examination table in a horizontal position. The angle between a line perpendicular to the margin of the radiographs and the cup was measured. In the second method, we measured the angle between the anterior cortex of the ischial ramus and the cup (Fig. 1A). The cortical part used is commonly seen on the radiographs as a radiodense line 15- to 30-mm long. The acetabular components were divided on the AP and lateral radiographs into 60° regions (Fig. 1B). Radiolucent lines were regarded to be present if they had a width of ⱖ0.3 mm (excluding the sclerotic demarcation) and occupied ⬎50% of the interface in each region. The width of any radiolucent line was measured as the mean value of 3 to 4 measurements within ⫾10° from the middle of this region. The width of the cement mantle was measured in the middle part of each region. Acetabular loosening was defined as cup migration ⬎5 mm or circumferential radiolucency of ⱖ0.3 mm width on AP or lateral projection or change of inclination ⬎10° on the AP projection. Nine hips (20%) had bone defects of Type I, 25 (54%) Type II, and 12 (26%) Type III, according to

Radiographic Evaluation of Charnley Cups • Hultmark et al.

1007

Fig. 1. (A) Reference lines used to measure cup tilt on the lateral view in relation to ischial ramus (method 2). The bony reference line (arrow) should be parallel with the anterior cortex of the ischial ramus on a minimum distance of approximately 15 mm. (B) The acetabular components were divided on the AP and lateral radiographs into 60° regions, i.e., 1 to 3 and 4 to 6, respectively. The width of any radiolucent line was measured as the mean value within ⫾10° from the middle of each region.

Gustilo and Pasternak [12]. In 8 cases, small amounts of bone chips (allograft or autograft) were used to cover defects. Osteolysis was defined as focal bone resorption with an area of at least 3 ⫻ 3 mm on any projection. The cement mantle was classified into 4 Grades on the AP and lateral radiographs: A, complete cement filling without radiolucency; B, cement-bone radiolucency ⬍50%; C, radiolucency ⱖ50%; and D, defects in the cement mantle. Categories A and B were considered as good or acceptable and C and D as poor cementing. Penetration (wear) of the femoral head was determined according to Livermore, Ilstrup, and Morrey [13]. Measurements were done manually using a digitized slide caliper with 1/100 mm scale. The intraobserver and interobserver variability were evaluated using the postoperative examination and the 1- and 10-year follow-ups. Fifteen cases were randomly selected. The time period between the 2 observations varied between 11 and 14 months. The interobserver variability was studied by 2 comparisons between 3 observers (P. Hu and J.H., P. Hu and J.K.). Two of these observers (1 and 2) did a number of trial cases (not included in this study) together before the final evaluation, whereas observer 3 did not. Nonparametric tests and Cox regression analysis were used. The intraobserver and interobserver agreements were evaluated for the continuous

data using the Intraclass Correlation Coefficient (ICC) [14] and the Coefficient of Repeatability (CR) [15]. The CR represents the smallest change of a parameter, that could be regarded to represent a true change based on the 95% confidence interval.

Results Radiographic Loosening and Revisions At the latest follow-up, 6 of 46 cups were radiographically loose. Five had complete periprosthetic radiolucency on the AP and lateral views, and 1 only on the AP view (Fig. 2). Two loose cups were revised. Furthermore, 1 was revised due to traumatic acetabular fracture. Thirty-one cement mantles were classified as Grade A, 6 as B, 1 as C, and 8 as D. The mean thickness of the cement mantle varied between 4.2 mm and 8.9 mm (range, 0 –30 mm). There were no fractures of the cement mantle. None of the preoperative radiographic variables seemed to influence the risk of subsequent loosening or revision (Cox regression, see Hultmark and Ka¨ rrholm et al. [10]). Cup Position, Migration, Wear, and Osteolysis Two cups migrated 3.4 and 4.1 mm proximally, twelve 1.0 to 3.0 mm, and 32 ⬍1 mm (Table 2). At

1008 The Journal of Arthroplasty Vol. 18 No. 8 December 2003

Fig. 2. Charnley cup inserted after extraction of a loose ICLH cup in a 63-year-old man. Postoperatively a thin radiolucent line is present in region 3 and in region 4 (A, E; AP and lateral view). One year after the operation, radiolucent lines were present in region 1, 3, 4, and 6, respectively (B, F). At the 10-year follow-up, 100% radiolucency was present on AP and lateral view. At the 13- and 15-year follow-up these lines were principally unchanged (C, G) (D, H). There was no proximal migration (0.4 mm) at 13 years. Between 13 and 15, migration of 1.5 mm was measured, suggesting that cup migrated into the radiolucent line. The patient had minimal pain (Harris pain score ⫽ 40). At the 10-year follow-up, an osteolysis appeared in region 1. The lysis gradually increased from 25 mm2 to 80 mm2 at the 15-year follow-up.

the latest follow-up, the 6 cups with 100% radiolucency had migrated a mean of 1.0 mm proximally (range, ⫺1.6 – 4.1 mm) compared with a mean of 0.1 mm (range, ⫺3.5 to 2.7 mm) in the group with components classified as stable (n ⫽ 40). The changes of inclination in the stable and loose groups were 0.3° (⫺4 – 4) and 1.5° (⫺8 – 4; P ⫽ .2). The corresponding values on the lateral view were 0.9° (⫺17–18) and ⫺0.2° (⫺4 – 6; P ⫽ .2) using method 1 and 1.0° (⫺6 – 6), and ⫺0.4° (⫺4 –2; P ⫽ .8) using method 2. The mean wear for the loose and stable cups were 1.1 mm (0.2–2.6, wear rate 0.09 mm/y) and 0.6

mm (range, ⫺0.1–3.4, 0.08 mm/y; P ⫽ .09), respectively. Preoperatively there was only 1 case with osteolysis (area ⫽ 270 mm2). On the follow-up radiographs, only 1 case developed focal osteolysis (Fig. 2). This cup became surrounded by a complete radiolucency at the same time. Radiolucent Lines No radiolucent lines were observed around 13 (28%, AP view) and 22 (48%, lateral view) cups at any of the follow-up occasions. In 11 of these cups,

Radiographic Evaluation of Charnley Cups • Hultmark et al. Table 2. Cup Position and Change of Position at Last Follow-Up (All Cases) Position Mean

Range

Change Mean

Range

AP or pelvic view Teardrop Proximal/distal (mm) 35.3 20–49 0.2 ⫺3.5–4.1 Medial/lateral (mm) 35.6 25–51 ⫺0.3 ⫺4.0–3.0 Ko¨ hler line (mm) ⫺2.5 ⫺18–11 0.1 ⫺2.2–3.6 Inclination (°) 45 32–68 0 ⫺8–4 Lateral view Anteversion/retroversion Edge of film (°) 6 ⫺22–22 1 ⫺17–18 Ischial cortex (°) 121 98–134 1 ⫺6–6

1009

Between the postoperative and the 1-year follow-up, there was an overall increase of radiolucent lines in regions 1 and 4 (P ⫽ .01–.04, Wilcoxon signed rank test). Between 1 and 7 years, an increase was noted in region 3 and 6 (P ⫽ .03 and P ⫽ .05) and, between 7 to 10 years, in region 6 (P ⫽ .05). In 11 patients with a complete follow-up (0, 1, 3, 7, 10, and 13 years), the mean width of the radiolucent lines increased to the latest follow-up in regions 1 and 6 (P ⫽ .05). In the cups, which became radiographically loose, the width increased in all (P ⫽ .03–.05) (Table 5). Intraobserver and Interobserver Variability

there were no radiolucent lines on either view. Eighty-three percent of those lines that were detected appeared on the postoperative radiographs or within 3 years after the operation (Table 3). All lines that progressed to 100% had for the first time been detected during this interval. Progression of postoperative radiolucent lines occurred in 28 (61%) cups (Table 4). This progression followed a biphasic pattern. Up to 3 years the number of regions occupied by a radiolucent line increased mainly because more hips became involved. Later on, the increase was an effect of progression of lines, which already existed. Nonprogressive radiolucent lines appearing after the postoperative examination were always restricted to 1 region. They were usually seen in region 1 (13 cases), but also in regions 3 (1), 4 (1), and 6 (6). When lines subsequently becoming progressive appeared in only 1 region this event did not seem to favor any location (region 1, 3 cases; region 3, 1 case; region 4, 2 cases; and region 6, 2 cases). Progressive lines also appeared in 2 regions simultaneously (regions 1 and 3, 2 cases; regions 4 and 6, 2 cases). When radiolucent lines appeared for the first time, they were discovered only on the AP or lateral view in 28 cups. Three of these progressed, but in no case to 100%. In 14 cups, radiolucent lines appeared simultaneously in at least 2 regions, 1 on the AP, and 1 on the lateral view. Progression of these lucencies was recorded in 8 cups and in 6 of them to 100%. Radiolucent lines were first detected peripherally (regions 1, 3, 4, and 6; Fig. 3). Central lines appeared later except from 1 case, where it was present already postoperatively. They were always first located on the AP view, with (n ⫽ 2) or without simultaneous (n ⫽ 3) appearance on the lateral view.

Overall the best agreement was obtained between observer 1 and 2, who had evaluated a number of cases together and thereafter did their measurement separately. In the individual case change of inclination and migration of the cup had to reach at least 5° (AP view) and 5 mm until these measurements could be regarded as reliable. The measurements of radiolucent width using a calliper could in most instances be done with a certainty of 0.3 to 0.7 mm (CR, Tables 6 – 8). In general, there was an agreement about progression or not into a new region in 70% to 100% of the cases. If present, discrepancies usually corresponded to a change of 1 class (⫾33%). In none of

Table 3. Time From Appearance of New Radiolucent Lines on AP or Lateral View to 100% Lucency Follow-Up Radiolucent Lines AP or lateral view First detected in 1 region Progress to 2 regions Progress to 3 regions First detected in 2 regions Progress to 3 regions Totals without progression AP and lateral First detected in 1 region Progress to 2 regions Progress to 3 regions First detected in 2 regions Progress to 3 regions Totals without progression Regions with new detected lines Patients with new detected lines *9.7 and 12.8 y. †6.2 and 10.2 y. ‡4.5 y. §1.3 y.

0

1

3

5

7

10

11 2 0 9

7 1 0 6

3 2 5

3 0 3

1 0 1

1 0 2

5 2 2* 1 1§ 1 24 17

3 2† 1 0 2 16 8

2 1‡ 0 1 11 5

0 0 0 3 2

1 0 1 3 2

0 1 0 1 4 1

1010 The Journal of Arthroplasty Vol. 18 No. 8 December 2003 Table 4. Extension of Radiolucent Lines (% on AP/Lateral View) in 46 Patients After the Revision Operation and at the Latest Follow-Up Index Operation (%AP/Lateral) Latest Follow-Up 0/0 0/33 33/0 33/33 33/66 66/0 66/33 66/66 100/66 100/100

0/0 (n ⫽ 29) 11‡ 2 6 4 2

0/33 (n ⫽ 3)

33/0 (n ⫽ 7)

33/33 (n ⫽ 6)

33/66 (n ⫽ 0)

2‡ 1

‡

66/33 (n ⫽ 1)

66/66 (n ⫽ 0)

100/66 (n ⫽ 0)

100/100 (n ⫽ 0)

1 1† 1

3‡ 1 1

‡ 1

2 1† 1*

66/0 (n ⫽ 0)

‡

1

‡ ‡ 1*

2*

1†

‡

*Not revised after 13–15 y follow-up. †Revised after 5 and 7.5 y. ‡Unchanged extension.

the cases the disagreement embraced 3 classes (100% vs. no radiolucency).

Discussion Previous studies have shown comparatively low interobserver and intraobserver agreements for radiographic evaluations of both cups [16,17] and stems [6,16,18,19]. The intraobserver agreement usually is better than interobserver agreement [6,19]. In our evaluation, the intraobserver was not as consistent as the interobserver variability, probably because of the long time period between the examinations in the former case. Thus, our data support that any evaluation should not extend over a too long time period. If more than 1 observer is involved, these examiners should reach consensus by evaluating a number of cases together. “Progressive radiolucent lines” is a frequently occurring term in the literature [7,20]. We have not been able to identify any strict definition of this phenomenon. It seems to be an arbitrary expression for an undefined increase in width and length usually based on visual inspection. Identification of progressive radiolucency is important [21], but rarely has been done in a systematic way. Radiolucencies may represent a complete loss of bone bridges between bone and cement (fibrous tissue), a gradual decrease of bone density toward cement (osteoporosis) [5,6] or bone partially bridging the gap [7]. On plain radiographs it is difficult to distinguish between osterporotic demarcation (i.e., cortical osteoporosis, cancellization, and thinning of

trabeculae) from radiolucent lines, which correspond to complete loss of bone bridges between bone and cement. We believe that this is a bigger problem on the femoral side, because stress shielding is more common. A radiolucent line, in our opinion, should be a dark comparatively even and homogeneous line, without bridging trabeculae. It should follow the surface of the cement. In this study and our previous one of femoral stems [22], we only measured the homogeneous darkest part of the line. Inability to separate between local osteoporosis and true radiolucent lines might explain the poor correlation between the latter phenomenon and stem stability in studies of postmortem specimens [5,23]. In an in vivo study, Hodgkinson, Shelly, and Wroblewski [2] however, did find a definite correlation between radiolucency and cup loosening. These authors noted that the extent of demarcation was the most important prognostic sign for future failure. One-mm wide complete radiolucency on the AP view was associated with loosening in all cases. Five of 8 cups with gap ⬍1 mm were found to be loose. In primary THA, DeLee and Charnely [24] noted that radiolucent lines appeared early in cases that developed loosening, in agreement with our findings. Also Marti and Schuller et al [25] and Ranawat and Deshmukh et al [26] and Ranawat, Peters, and Umlas [27] stressed the importance of primary stability consistent with the theory that early migration precedes clinical loosening [28 –30]. Cases with partial lucencies appearing during the postoperative years, which thereafter seem to become stationary, might have shown no or early and de-

Radiographic Evaluation of Charnley Cups • Hultmark et al.

1011

Fig. 3. Revision of a loose Charnley cup using the same type of implant in a 64-year-old woman. A small radiolucent line is present in region 1 (⬍50% of this region) postoperatively (A, E; AP and lateral view). One year after the operation radiolucent lines were present in regions 1, 3, and 6 (B, F). Two years later there were no progressions on the AP view. In region 6 the line became wider and a new line was visible in region 4 (C, G). At 7 years there was no further progression (D, H).

celerating micromovement. The interpretation of the nonprogressive radiolucent lines in the majority of our cases is not quite clear even if low activity in elderly patients is a probable explanation. In primary THA, many studies have reported that the rate of loosening of cemented acetabular components increases after the first 10 years [2,31–34], whereas others could not confirm this observation in primary [26,35–37] or revision THA [25]. Use of different cup designs, too short follow-up, and de-

creasing activity in some of the populations under study might explain this discrepancy. In our study, we could show that the radiolucent lines first appeared peripherally and usually in regions 1 and 4. Thereafter, they occasionally progressed distally and posteriorly and appeared on the opposite side of the cup, in a few instances, to embrace the entire interface. Small inducible displacements and especially tilting of the cup about an axis close to its dome might be of etiologic

1012 The Journal of Arthroplasty Vol. 18 No. 8 December 2003 Table 5. Radiolucent Width in 11 Consecutive Patients Participating in the 0, 1, 3, 7, 10, and 13 Years Follow-Up Region n⫽1

Follow-Up 11 Cases Postoperative 1 3 7 10 13 Last follow-up 6 Failures Last follow-up

n⫽2

2 6 7 8 8 8 8

0.4 (0.4–0.5) 0.4 (0.3–0.5) 0.4 (0.3–0.5) 0.4 (0.3–0.8) 0.5 (0.3–1.2) 0.8 (0.3–2.6) 0.7 (0.3–2.6)

0 0 0 1 2 2 2

6

1.0 (0.3–2.6)

6

-

n⫽3

n⫽4

n⫽5

n⫽6

0.5 0.8 (0.5–1.1) 0.8 (0.5–1.0) 0.7 (0.4–1.0)

2 2 2 3 3 3 4

0.4 (0.3–0.4) 0.5 (0.4–0.6) 0.6 (0.3–0.7) 0.7 (0.3–0.8) 0.7 (0.3–0.9) 0.7 (0.5–1.0) 0.7 (0.4–1.0)

0 2 2 2 3 3 3

0.5 (0.5–0.5) 0.5 (0.5–0.5) 0.6 (0.5–0.8) 0.6 (0.5–0.9) 0.9 (0.5–1.1) 0.9 (0.5–1.1)

0 0 0 0 2 2 2

0.6 (0.6–0.7) 0.6 (0.5–0.6) 0.6 (0.5–0.6)

0 2 2 5 5 5 5

0.4 (0.4–0.5) 0.4 (0.3–0.5) 0.6 (0.3–1.6) 0.8 (0.3–1.6) 0.8 (0.3–1.5) 0.9 (0.3–1.5)

0.7 (0.4–1.0)

6

1.1 (0.3–2.9)

6

1.2 (0.6–2.6)

5

0.7 (0.4–1.0)

6

1.2 (0.7–1.8)

NOTE: Values at the latest follow-up are indicated also for the 6 patients who were radiographically loose (mean, range, n ⫽ number of patients with radiolucent lines in each region).

importance. Tissue fluid and particles might be pumped into the interface destroying vessels and disturbing the balance between bone formation and resorption in the interface [38]. The comparatively high frequency of postoperative lines in region 1 could be explained by difficulties to obtain sufficient cement pressure in this region. Ritter and Zhou et al [39] reported a high risk of loosening if such lines were present. We found that lines located in regions 3, 4, and 6 more often became progressive than those found in the superior region on the AP view [24,40]. The reason for this difference is unknown. Presence of firsttime radiolucency in only 1 region and on only 1 of the views also turned out to be more benign compared with the situation when this phenomenon was observed on both views (progression in 11%

and 57%, respectively). This finding emphasizes the importance of a true lateral of the pelvis, as earlier stated by Harris and Penenberg [41]. Once radiolucent lines appear on both views, the patient should be followed up regularly to facilitate early detection of progression and loosening. DeLee and Charnely [24] reported that lines in region 2 were progressive in 92%, but only in 16% of the cases if located in region 1. If first appearing in region 3, progression was not observed in any of the cases. Hodgkinson, Shelly, and Wroblewski [2] found 19 cups with radiolucencies in region 1 and 2. Eighteen of these were found to be loose. Our study could confirm the negative prognostic value of radiolucent lines in region 2, but contrary to previous studies, these almost exclusively appeared as the final step in a progression from the periphery.

Table 6. Reproducibility of the Measurements in Terms of Intraobserver and Interobserver Variability Observers 1 vs. 1 Type of Measurement Change of inclination (°) AP view tear drop line Lateral edge of film Lateral ischial cortex Migration (mm) Proximal/distal Medial/lateral Width of radiolucent lines† (mm) AP view Lateral

1 vs. 2

1 vs. 3

n

ICC

SD

CR

ICC

SD

CR

ICC

SD

CR

14 24 16

0.45 0.98 0.76

2.3 2.2 4.0

6.5 6.2 11.3

0.66 0.92 0.36

1.8 2.5 4.2

5.1 7.1 11.9

0.43 0.82 0.21

1.9 5.1 4.6

5.4 14.4 13.0

12* 12

0.63 0.61

2.9 2.0

8.2 5.7

0.85 0.72

1.8 1.7

5.1 4.8

0.61 0.41

2.8 2.4

7.9 6.8

0.39 0.48

0.15 0.22

0.4 0.6

0.75 0.75

0.12 0.16

0.3 0.5

0.41 0.29

0.24 0.39

0.5 0.7

121 122

NOTE: The number of observations varies because the observers were free to refrain from evaluation if they thought the film quality was poor. *Proximal/distal and medial/lateral migration was studied in 20 cases by the same observer (1 vs. 1). †Sum of available evaluations 0 to 1 and 1 to 10 y.

Radiographic Evaluation of Charnley Cups • Hultmark et al.

The development of radiolucent lines followed a biphasic pattern. This pattern may mirror the fixation of the cup. In the postoperative phase, a certain number of cups will show more or less pronounced micromovements. These micromovements may result in a biologic reaction at the interface visible as a radiolucent line. This first line might seemingly take up to 2 to 3 years to become visible depending on the frequency of follow-up available. Later on, progression of radiolucent lines will mainly be restricted to implants with continuous migration and/or inducible displacements. This process, which may proceed to obvious clinical loosening, may last for different time periods depending on bone and interface quality, activity level, type of implant, and other factors. Many patients will not live long enough to experience any problems. Most authors have previously used a gap width of 1 [32,42,43] or 2 mm [6,9,41] to identify a radiolucent line, whereas others did not account for this parameter at all [44,45]. Both Hodgkinson, Shelly, and Wroblewski [2] and Mulroy and Harris [46] did not use limits ⬍1 mm. DeLee and Charnley [24] are probably the only authors who accounted for lines ⬍0.5 mm. We rarely found gaps ⬎1 mm even after 10 years follow-up. If we had defined loosening as presence of complete radiolucencies ⬎2 mm, there had been no radiographic failure, not even in the revised cases. If the limit had been 1 mm, only 2 cups could be regarded as loose and not until a later date (3 years, next consecutive examination). Recordings of cup angle change or cement mantle fracture as recommended in a previous study [46] did not improve the sensitivity of our evaluation. Garellick and Malchau et al [47] found no correlation between vertical or horizontal migration ⬎5 mm and other signs of loosening [2] in primary

Table 7. No. of Agreements/Disagreements Based on Detection of Radiolucent Lines With a Width of 0.3 mm or More Observers n Width of radiolucent lines agreement/disagreement Region 1 2 3 4 5 6

1 vs. 1

1 vs. 2

1013

Table 8. No. of Agreements/Disagreements Based on Progression of Radiolucent Lines Into a New Region and the Total Extension of Lines on the AP and Lateral View, Respectively Observers

Type of Measurement/ Evaluation Progression or not to new region Agreement/disagreement Region 1 2 3 4 5 6 Extension of lines no/1/2/3 classes different* AP view Lateral

1 vs. 1

1 vs. 2

1 vs. 2

24/6 30/0 28/2 28/2 30/0 26/4

25/5 30/0 21/7 21/9 29/0 25/4

18/7 25/1 22/4 16/10 25/1 22/5

34/10/1/0 35/7/2/0 18/20/3/0 31/12/1/0 42/2/0/0 19/19/2/0

*No. of observations with complete agreement/1 class difference (e.g., 33% increase or decrease according to observer 1 vs. no change according to observer 2), 2 class differences (e.g., 66% vs. no change), and 3 class differences.

THA operated with the Ogee cup. Neither could Stro¨ mberg and Herberts et al [33] document any correlation between migration of the cup and the development of circumferential radiolucency around the cup. They concluded that migration had no predictive value. The use of methods with higher resolution such as radiostereometry and perhaps also EBRA [29,48] are necessary to detect migration of the cup at an early stage. Radiostereometric analysis studies by Mjo¨ berg and Selvik et al [49] ¨ nnerfa¨ lt [50] found and Franze´ n, Mjo¨ berg, and O that cemented cups with complete radiolucent lines had migrated 0.7 to 1.8 mm within the postoperative 2 years, which is consistent with our observations. Consecutive observations of progression of thin radiolucent lines were an effective method to detect early loosening of cemented cups. In our study, it was superior to measurements of migration when done without any correction of pelvic tilt on plain radiographs.

1 vs. 3

References 40 41 40 40 41 41

37/3 38/3 34/6 31/9 41/0 37/4

37/3 39/2 37/3 33/7 41/0 37/4

27/13 40/1 34/6 28/12 40/1 34/7

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