Factors Influencing Survivorship of the Femoral Component After Primary Low-friction Hip Arthroplasty Seneki Kobayashi,
MD, PhD, and Kazuo
Terayama,
MD, PhD
Abstract: Two hundred sixty-seven consecutive primary low-friction arthroplasties, followed for 5-18 years after surgery, were studied to assess the factors influencing survivorship of the femoral component, using the Kaplan-Meier method. The end point of survivorship was defined radiographically in two ways: incipient failure (subsidence of the femoral component of ->2 mm) and definite failure (progressive change of position). Twenty-two femoral components developed incipient failure, and twelve of these advanced to definite failure. A canal filling ratio of the stem of ->75%, cement extent distal to the stem tip of ->1 cm, use of an intramedullary bone plug, and an exaggerated valgus alignment of the stem correlated positively with survivorship of the femoral component. Calcar resorption and atrophy of the femoral cortex after surgery were associated with aseptic loosening of the femoral component. K e y words: hip prosthesis, Charnley arthroplasty, low-friction arthroplasty, femoral component, survivorship analysis, radiography.
357 consecutive low-friction arthroplasties (LFAs) were performed in 283 patients as a primary intervention. Clinical and radiographic assessments were m a d e every 6 months. In order to include b o t h hips, all standard clinical radiographs were t a k e n at a distance of 1 m from the tube, which was centered on the symphysis pubis of the patient lying in the supine position. Twenty-seven patients (31 LFAs) were excluded from the study because they had been followed at other hospitals. Nine patients (10 LFAs) were excluded due to their deaths before the minim u m 5-year follow-up period was completed. Thirty-seven patients (48 LFAs) were excluded because of lack of follow-up information. One deep infection necessitated implant removal at 2 years. The remaining 267 arthroplasties in 209 patients were followed for an average of 9.2 years (range, 5 - 1 8 years). Patient age at operation ranged from 28 to 75 years (mean, 59 years). The youngest patient was a 28year-old w o m a n with multiple epiphyseal dysplasia. She used a wheelchair because of i n v o l v e m e n t of other joints, and her bilateral LFAs were functioning well without signs of aseptic loosening at 15 years.
Aseptic loosening is the most c o m m o n long-term complication of total hip arthroplasty and continues to play a significant role in its failure. We assessed factors affecting aseptic mechanical loosening of the femoral c o m p o n e n t in low-friction arthroplasty of the hip, using survivorship analysis to determine m e a n s of improving the durability of this procedure.
Materials and Methods Charnley low-friction arthroplasty was introduced to our d e p a r t m e n t in 1972 by the senior author (K.T.) w h o studied and trained with Sir J o h n Charnley at Wrightington Hospital. All cases were performed with the patient in the supine position using the original Charnley technique, including trochanteric osteotomy. 4 From October 1972 to May 1985, From the Department of Orthopaedic Surgery, Shinshu University School of Medicine, Matsumoto, Japan.
Reprint requests: Seneki Kobayashi, MD, PhD, Department of Orthopaedic Surgery, Shinshu University School of Medicine, Asahi 3-1-l, Matsumoto, 390, Japan.
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Two LFAs were performed on patients aged 2 1 - 3 0 years, 5 on patients 3 1 - 4 0 years, 29 on patients 4 1 - 5 0 years, 120 on patients 5 1 - 6 0 years, 92 on patients 6 1 - 7 0 years, and 19 on patients 7 1 - 8 0 years. Twenty-eight LFAs were performed on 24 m e n and 239 on 185 w o m e n . Osteoarthrosis was present in 229 hips (86%; 175 patients), rheumatoid arthritis in I2 hips (4%; 11 patients), and other disorders in 26 hips (I0%; 23 patients). All sockets were made from an identical high-density polyethylene, and the same bone cement of standard viscosity (CMW 1) was used t h r o u g h o u t the series. Factors affecting survivorship of the femoral component were analyzed using the Kaplan-Meier method. ~8 The end points of survivorship were defined radiographically in two ways: incipient failure and definite failure. Subsidence of the femoral component was measured radiographically using the m e t h o d of L o u d o n and Charnley, 22 with 2 m m or more was regarded as incipient failure. 4"~3"~4(Details of this m e t h o d are described in case 1 .) Socket migration was measured using the acetabular teardrop as a reference landmark, and migration of 2 m m or more or rotation of 2 ° or more was taken to be significant. In addition, visual detection of evidence of socket migration on serial radiographs on a large viewing box facilitated judging that the socket had developed incipient failure. Definite failure was indicated by progressive positional changes after develo p m e n t of the incipient failure. Definite failures prompted consideration of surgical revision. The date of radiographic detection of femoral component failure was recorded and used in survivorship calculations. Survivorship of the femoral c o m p o n e n t was assessed in relation to i7 variables: age, sex, etiology, Charnley's categories, obesity index, design of the femoral component, use of an intramedullary plug, calcar cement thickness, alignment of t h e stem, length of the residual femoral neck, canal filling ratio of the stem, cement extent distal to the stem tip, calcar resorption at 5 years, femoral cortical changes at 5 years, socket wear at 5 years, incipient failure of the socket, and definite failure of the socket. Comparative analysis was performed between patients who were less than 60 years old at time of surgery and those w h o were 60 years or older. Comparisons were also made between m e n and w o m e n , between patients with osteoarthrosis and rheumatoid arthritis, between patients in Charnley's category A (unilateral hip disease, otherwise no functional disabilities) and those in category B (bilateral hip disease, otherwise no functional disabilities), and between patients with an obesity index (the percentage of body weight to
standard weight) of less than 120% and those i 2 0 % or more. Femoral components with nonflanged stem designs were used early in the series, and those with dorsal flanges have been routinely used since August 1979, except for narrow femoral canals into which they cannot be inserted. Survivorship of the femoral component was compared between these two designs. Intramedullary plugging techniques were adopted beginning in September 1981 to achieve better intramedullary filling and pressurization during cement polymerization. A plug manufactured from high-molecular-weight polyethylene (designed by Hardinge) was used first, and a technique of b o n y plugging has been used since January 1982, except w h e n good autologous cancellous bone could not be obtained from the proximal femur or resected femoral head. With an intramedullary plug, a vent tube was used during packing viscous cement with two thumbs. Comparison was made among a group of LFAs without intramedullary plugging, a group with plastic plugs, and one with bony plugs. Using previously described methods for radiographic measurement, 2° the following variables were measured on radiographs taken within 1 m o n t h after surgery and were used in survivorship analyses. Survivorship of the femoral c o m p o n e n t was compared between a group with a calcar cement thickness of less than 3 m m and one with a thickness of 3 m m or more; between a group of femoral components with a residual femoral neck of less than 5 m m and one with femoral necks of 5 m m or more; between a group with a canal filling ratio of the stem (the percentage of stem width to intramedullary width at the midpoint of the stem) of less than 75% and one with a ratio of 75% or greater; and b e t w e e n a group of femoral components with cement extent distal to the stem tip (the length from the distal tip of the stem to the level at which cement filled over 80% of the canal) of less than 1 cm and a group with extent of 1 cm or greater. The alignment of the stem was classified as valgus or varus in relation to the axis of the proximal femoral shaft, and stems in a valgus alignment with a cement thickness of more than 1 cm at the calcar were classified as being in an exaggerated valgus alignment. 2 Survivorship of the femoral component was assessed for these three types of alignments. Calcar resorption, cortical changes around the distal tip of the stem, and socket wear were assessed on radiographs obtained after 5 years. Type IIIB (a cavity in the calcar) and IIIC (absorption of the total thick ~ ness of the calcar) changes in the femoral neck 2 were considered calcar resorption, and resorption of 2 m m
Survivorship of Charnley Femoral Prostheses
or more was regarded as significant. Cortical changes around the distal tip of the stem were classified into four categories: normal, atrophy, hypertrophy with normal outline, and external hypertrophy. 6 The external outline of the femoral cortex was examined, and any fusiform h y p e r t r o p h y near the prosthesis tip was classified as external hypertrophy. W h e n there were no changes in the outline of the femur, cortical thickness was evaluated at the level of the prosthesis tip. Variations in cortical thickness of less than 5 % at 5 years as compared with thickness within 1 m o n t h were classified as normal. W h e n cortical thickness had increased or decreased by 5% or more, femurs were classified as either hypertrophic or atrophic with normal outline, respectively. Socket wear was measured using a m e t h o d developed by Charnley and others, 5"7 and wear of 1 m m or more was regarded as significant. Survivorship was compared between groups of femoral c o m p o n e n t s with and without calcar resorption at 5 years, a m o n g those with distinct varieties of femoral cortical changes at 5 years, and between groups of femoral components with and without significant socket w e a r at 5 years. Survivorship of the femoral c o m p o n e n t was also compared between a group of LFAs that developed incipient failure of the acetabular c o m p o n e n t during the observation period and a group that did not and between a group of femoral c o m p o n e n t s with definite failure of the sockets and a group without such failure. A P value of less than .05 was considered significant in every statistical analysis.
Results In our series of 267 LFAs, 24 sockets (9.0%) developed incipient failure, and 14 of these progressed to definite failure. Incipient failure occurred between 0.4 and 12.3 years (mean, 4.9 years) after surgery, and definite failure occurred between 5.0 and 11.8 years (mean, 8.0 years) after surgery. Twenty-two femoral c o m p o n e n t s (8.2%) subsided by 2 m m or m o r e b e t w e e n 1.0 and 5.0 years (mean, 2.7 years) after surgery, and 12 of these progressed to definite failure by 3 . 0 - 7 . 0 years (mean, 4.6 years) after surgery. Combinations of acetabular and femoral comp o n e n t failure were found in three hips: two had sockets with incipient failure and femoral component with definite failure, and in one, both components manifested incipient failure. At the time of this study (June 1990), six revision operations had been performed for definite failure of the acetabular comp o n e n t and five for definite failure of the femoral component. Only those c o m p o n e n t s with definite
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failure were replaced in these revisions, except in one case in which a femoral c o m p o n e n t manifesting definite failure and a socket with incipient failure were replaced. There was no difference in the survivorship of the femoral component, whether incipient failure or definite failure was used as an end point, b e t w e e n the group of patients younger than 60 years of age (141 LFAs) and those 60 years old or older (126 LFAs); between m e n (28 LFAs) and w o m e n (239 LFAs); between osteoarthritic patients (229 LFAs) and rheumatoid patients (12 LFAs); b e t w e e n patients in Charnley's category A ( 124 LFAs) and those in category B (125 LFAs); or between patients with an obesity index of less than 120% (211 LFAs) and those with an index of 120% or m o r e (56 LFAs). No significant difference was observed in the survivorship of the femoral component, considering both incipient and definite failures as end points, b e t w e e n a group of I47 femoral c o m p o n e n t s without flanges and a group of 120 flanged femoral components; between a group of 84 femoral c o m p o n e n t s with a calcar cement thickness of less than 3 m m and a group of 183 c o m p o n e n t s with a cement thickness of 3 m m or more; or between a group of 114 femoral c o m p o nents with residual femoral necks of less than 5 m m and a group of 153 with femoral necks of 5 m m or more. Use of an intramedullary plug did not affect survivorship w h e n incipient failure was the end point but did influence survivorship based u p o n definite failure (Fig. 1). The survivorship of a group of components fixed with b o n y plugs exceeded not only that of a group of 156 c o m p o n e n t s fixed w i t h o u t intramedullary plugging but also that of a group of 30 components with manufactured plastic plugs
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Fig. 1. Survivorship based upon definite failure of the femoral component for three methods of intramedullary plugging. A, no plugs (156 LFAs); B, manufactured plastic plugs (30 LFAs); C, bony plugs (81 LFAs).
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Fig. 2. (A) Survivorship based upon incipient failure of the femoral component for three classes of stem alignment. A, moderate valgus alignment with calcar cement less than 1 cm thick (222 LFAs); B, varus alignment (25 LFAs); C, exaggerated valgus alignment with calcar cement I cm or more thick (20 LFAs). (B) Survivorship based upon definite failure of the femoral component for three classes of stem alignment. A, moderate valgus alignment with calcar cement less than 1 cm thick (222 LFAs); B, varus alignment (25 LFAs); C, exaggerated valgus alignment with calcar cement 1 cm or more thick (20 LFAs).
from the point 5 years and 6 months after surgery on. The difference in the survivorship between components fixed w i t h o u t plugging and those fixed with m a n u f a c t u r e d plugs was not significant. The alignm e n t of the stem influenced survivorship based u p o n either incipient failure or definite failure as an end point. T w e n t y femoral c o m p o n e n t s fixed in the exaggerated valgus alignment developed neither incipient nor definite failure. The survivorship of a group of c o m p o n e n t s fixed in the exaggerated valgus alignm e n t exceeded that of a group of 222 components fixed in the (moderate) valgus alignment with calcar cement of less t h a n 10 m m in thickness after 3 years and 3 m o n t h s and that of a group of 25 components fixed in the varus alignment after 5 years and 3 m o n t h s w h e n incipient failure was used as an end point (Fig. 2A). W h e n survivorship was based u p o n definite failure, the group of c o m p o n e n t s fixed in an exaggerated valgus alignment had survivorship superior to c o m p o n e n t s fixed in varus alignment at 4 years and to that of c o m p o n e n t s fixed in moderate valgus position at 6 years and 4 months and beyond (Fig. 2B). The difference in survivorship based u p o n incipient or definite failure was not significant between the group of c o m p o n e n t s fixed in varus alignm e n t and those in moderate valgus alignment. The canal filling ratio of the stem influenced survivorship based u p o n incipient failure as the end point but not survivorship based u p o n definite failure. The survivorship of 76 stems with canal filling ratios of 75% or m o r e exceeded that of 191 stems with ratios of less t h a n 75% at 4 years and 7 months or m o r e after
surgery (Fig. 3). Cement extent distal to the stem tip only influenced survivorship based u p o n incipient failure as the end point, w h e r e b y 225 femoral components with cement extent of 1 cm or m o r e had survivorship superior to that of 42 c o m p o n e n t s with extent of less t h a n 1 cm b e y o n d 1 year and 8 m o n t h s (Fig. 4). Both calcar resorption and femoral cortical changes at 5 years correlated with snrvivorship based u p o n incipient and/or definite failure of the femoral component. Two h u n d r e d three femoral c o m p o n e n t s with calcar resorption of less t h a n 2 m m at 5 years had survivorship superior to that of 64 c o m p o n e n t s
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Fig. 3. Survivorship based upon incipient failure of the femoral component for 76 femoral components with a canal filling ratio of 75% or greater (dashed line) and 191 with a canal filling ratio of less than 75% (solid line).
Survivorship of Charnley Femoral Prostheses 100-
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Fig. 4. Survivorship based upon incipient failure of the femoral component for 225 femoral components with cement extent distal to the stem tip of 1 cm or more (dashed line) and 42 with cement extent of less than 1 cm (solid line).
with calcar resorption of 2 m m or more after 1 year and 7 months w h e n incipient failure was taken as the end point (Fig. 5A) and after 5 years and five months w h e n definite failure was taken as the end point (Fig. 5B). Survivorship analysis was applied to every combination of survival curves based upon femoral cortical change at 5 years, and significant differences were found between the following: In 21 femoral components with cortical atrophy, survivorship based u p o n incipient failure was significantly inferior to that of 139 components with normal cortex; to 19 components with cortical hypertrophy with normal outlines; and to 88 components with external hypertrophy beyond 2 years and 5 months after surgery. The components with external hyper-
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trophy had superior survivorship to those with norreal cortex b e y o n d 3 years and 2 m o n t h s (Fig. 6A). W h e n survivorship was based u p o n definite failure, femoral components with cortical atrophy were inferior to those with normal cortex b e y o n d 6 years and 5 months; to those with cortical hypertrophy with a normal outline b e y o n d 6 years and 3 months; and to those with external hypertrophy b e y o n d 5 years and 5 months (Fig. 6B). The difference in survivorship was not significant between a group of 239 femoral components with sockets with wear of less than 1 m m at 5 years and a group of 28 femoral c o m p o n e n t s with sockets that developed wear of 1 m m or more within 5 years, whether based u p o n incipient or definite failure of the femoral component. We could not demonstrate any influence of incipient or definite failure of the socket u p o n survivorship of the femoral component, based u p o n either incipient or definite failure of the femoral component.
Case Reports Case 1 A 62 -year-old woman had low-friction arthroplasty for her unilateral osteoarthritic hip (category A). A nonflanged femoral c o m p o n e n t was inserted without an intramedullary plug in a valgus position of 3.5 °. The calcar cement thickness was 7 ram, the canal filling ratio of the stem was 78%, and the cement extent distal to the tip of the stem was - 14 m m (Fig. 7A). Subsidence of the femoral component was measured using the m e t h o d of L o u d o n and Charnley. 22 All measurements were made in a
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Fig. 5. (A) Survivorship based upon incipient failure of the femoral component for 203 femoral components with calcar resorption of less than 2 mm at 5 years (dashed line) and 64 with calcar resorption of 2 mm or more (solid line). (B) Survivorship based upon definite failure of the femoral component for 203 femoral components with calcar resorption of less than 2 mm at 5 years (dashed line) and 64 with calcar resorption of 2 mm or more (solid line).
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Fig. 6. (A) Survivorship based upon incipient failure of the femoral component for four classes of femoral cortical change at 5 years. A, normal (139 LFAs); B, cortical atrophy (21 LFAs); C, cortical hypertrophy with normal outline (19 LFAs); D, external hypertrophy (88 LFAs). (B) Survivorship based upon definite failure of the femoral component for four classes of femoral cortical change at 5 years. A, normal (139 LFAs); B, cortical atrophy (21 LFAs); C, cortical hypertrophy with normal outline (19 LFAs); D, external hypertrophy (88 LFAs).
line of the axis of the distal two-thirds of the stem. Lines perpendicular to the stem axis were d r a w n through the three d a t u m points (Fig. 7): X was tangential to the distal tip of the stem, Y was at the same level of a constant point on the femur where a double wire passed t h r o u g h the lateral femoral cortex, and Z was tangential to the prosthetic head. XZ and XY were m e a s u r e d in the axis line, and from the XZ meas u r e m e n t the radiographic magnification could be calculated because the same m e a s u r e m e n t on the unmagnified prosthesis was k n o w n to be 155 ram. The actual length of XY (corrected for magnification) was 101.0 m m immediately after surgery (Fig. 7A). One year after surgery, it became 106.5 ram, indicating subsidence of 5.5 m m (Fig. 7B). At 14 years, it was 106.8 m m (Fig. 7C). Therefore, this femoral c o m p o n e n t was considered to be stabilized following the d e v e l o p m e n t of subsidence within 1 year after surgery. Case 2
Low-friction arthroplasty was performed for one of the osteoarthritic hips in a 72-year-old m a n (category B). A flanged femoral c o m p o n e n t was placed without intramedullary plugging in a valgus alignm e n t of 2.0 ° with a calcar cement thickness of 10 ram, therefore, this c o m p o n e n t was in exaggerated valgus alignment. Ten years after surgery, the comp o n e n t functioned well without subsidence in spite of an insufficient canal filling ratio (60%) and of a short extent of cement distal to the stem tip (5 ram) (Fig. 8).
Case 3
A 54-year-old woman had low-friction arthroplasty for one of her osteoarthritic hips~ A flanged femoral c o m p o n e n t was placed with a b o n y plug in an exaggerated valgus alignment with a calcar cement thickness of 10 rnm. Canal filling ratio of the stem was 83% and c e m e n t extent distal to the stern tip was 37 m m . A radiograph t a k e n at 7 years was u n r e m a r k a b l e except for cancellous change of the medial femoral neck (Fig. 9). Case 4
A 60-year-old w o m a n with an osteoarthritic hip had low-friction arthroplasty. A nonflanged femoral c o m p o n e n t was cemented w i t h o u t a plug in an alignm e n t of 0 °, which was classified as a valgus alignm e n t in this study. Calcar c e m e n t thickness was 5 m m and cement extent distal to the stem tip was 13 ram. The ratio of cortical thickness to the outer diameter of the f e m u r at the level of the prosthetic tip was 39% (Fig. 10A). At 13 years, there was neither subsidence of the c o m p o n e n t nor d e m a r c a t i o n around the cement. The ratio of cortical thickness at the level of the stem tip became 47% w i t h o u t change in the outline of the f e m u r (Fig. 10B). Thus, the femoral cortex was classified as hypertrophic w i t h normal outline. Case 5
A 62-year-old w o m a n with osteoarthritic hips had low-friction arthroplasty. A nonflanged femoral c o m p o n e n t was inserted w i t h o u t a plug in a valgus
Fig. 7. Radiograph of 62-year-old w o m a n who had a lowfriction arthroplasty performed on her osteoarthric hip (case 1). XY was the distance along the axis of the stem between the constant point on the femur (a drill hole for a double wire in the lateral femoral cortex) and the reference point for the femoral component (the distal tip of the stem). The measurement XZ was used in correction for magnification. (A) Immediately after surgery (XY = 101.0 mm). (B) One year after surgery (XY = 106.5 mm). (C) At 14years (XY = 106.8 mm).
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Fig. 8. Radiograph of a 72-year-old man with osteoarthritic hips taken l0 years after surgery (case 2).
alignment of 1.0 ° with a calcar cement thickness of 5 m m and a cement extent of 14 ram. The canal filling ratio of the stem was 86% (Fig. 11A). At 12 years, the femoral cortex developed into fusiform hypertrophy near the prosthetic tip. There was neither subsidence of the c o m p o n e n t nor demarcation around the cement (Fig. 11B).
Discussion The Kaplan-Meier survivorship m e t h o d accounts for patients with various follow-up periods and those w h o have b e e n lost during the follow-up period or have died during the period of observation. I8 This nonparametric estimation m e t h o d has therefore b e e n applied to long-term follow-up studies of both total hip and knee arthroplasties. 8'9'x9"26"~2It also allows comparison of groups with different follow-up periods. However, the end points must be carefully defined, because differences in definition can affect loosening rates by as m u c h as 2 to 3 times. 3 In this
Fig. 9. Radiograph of a 54-year-old woman with osteoarthritic hips taken 7 years after surgery (case 3).
study, we defined the end point of survivorship of femoral c o m p o n e n t s radiographicaily in two ways: as incipient failure judged by subsidence of 2 m m or more, and as definite failure indicated by progression of the subsidence after d e v e l o p m e n t of incipient failure. Subsidence was m e a s u r e d using the m e t h o d of Loudon and Charnley. xx Merits of this m e t h o d are correction for magnification and minimization of errors resulting from different a m o u n t s of lateral rotation of the femur, as far as all m e a s u r e m e n t s are made in a line parallel to the axis of the stem. 22 As for reproducibility, Loudon and C h a m l e y 22 m e a sured 50 different radiographs twice to assess the accuracy of the m e t h o d and obtained a n average error of 0.04 + 0.38 m m . They decided to exclude all cases where the subsidence was less t h a n 1.6 m m , w h i c h was 4 times the standard deviation derived f r o m this experiment. Although Loudon and Charnley regarded subsidence of 1.6 m m or m o r e as meaningful, we chose 2 m m as the standard of judgment, as h a v e
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Fig. I0. A 60-year-old woman with an osteoarthritic hip (case 4). (A) One month after surgery. (B) At 13 years.
other researchers. 4"13'14 Regarding the acetabulum, since the tear drop was s h o w n not to vary with a slight degree of pelvic obliquity and to be a reliable landmark for m e a s u r e m e n t of socket migration,11'12 it was used in the present study. However, as differences in magnification and in pelvic tilt were not compensated for in the m e a s u r e m e n t of socket migration, failure of the socket was judged synthetically with visual detection of evidence of positional change. Incipient failure of femoral c o m p o n e n t s in this study might be equivalent to the category of "definite loosening," defined by Harris et al. as definite evidence of migration, although they did not define the migration of the component. 15 In our series, 10 femoral c o m p o n e n t s did not manifest a progression in subsidence after development of incipient failure. Charnley noted that subsidence of the femoral comp o n e n t could result in a n e w and final position of stability. 4 Loudon observed a similar p h e n o m e n o n in 15 of 18 femoral c o m p o n e n t s with subsidence and
defined this m o d e as stable subsidence, distinguishing it from progressive subsidence. 21 Therefore, after detection of subsidence in a femoral prosthesis, careful follow-up examinations are necessary to evaluate the m o d e of subsidence prior to considering revision surgery. In regard to factors related to subsidence of femoral components, Griffith et al. reported that patients manifesting subsidence were, on average, 9 kg heavier. ~3 Loudon and Charnley demonstrated a significant reduction in the incidence and degree of subsidence with the use of flanged stems as c o m p a r e d with nonflanged stems. 22 In our series, neither the obesity index nor the flange design of the stem correlated with prosthetic subsidence, although b o t h the canal filling ratio of the stem and the extent of cement distal to the tip of the stem correlated with subsidence. Beckenbaugh and Ilstrup reported that if the stem diameter was less t h a n half the width of the femoral canal at its midposition, the incidence of loosening was 2.5 times higher t h a n if the stem diam-
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Fig. 11. A 62-year-old woman with osteoarthritic hips (case 5). (A) One month after surgery. (B) At 12 years.
eter was greater than this, and that the degree of cement extent past the tip of the stem was inversely related to subsidence. 1 Bony plugs used in conjunction with viscous cement enhanced the longevity of femoral components in this study. Mulroy and Harris reported a marked reduction in the rate of aseptic loosening in i05 femoral components that were cemented with improved techniques, including the use of a plastic medullary plug, a doughy mix of Simplex P, and a collared stem of chrome-cobalt. 23 They proposed that the use of a medullary plug allowed a greater intrusion pressure of cement, better filling, and improved cement-interface strength. Russotti et al. also reported an improvement in the rate of femoral loosening with improved cementing techniques, although they used both plastic and bony plugs. 28 As the use of bony plugs yielded superior survivorship of femoral components in this study as compared not only with rudimentary cementing techniques without plugging but also with the use of plastic plugs, we recommend the use of an autologous bony plug when it is available. Alignment of the stem should be the most impor-
tant factor within the surgeon's control, as it is correlated with both incipient and definite failure of femoral components. Beckenbaugh and Ilstrup demonstrated a correlation between varus alignment and subsidence.1 Bocco et al., in a 2-year follow-up study, found a lower incidence of subsidence to be associated with exaggerated valgus alignment than with varus or moderately valgus alignment. 2 In our series, with 5-18-year follow-up periods, femoral components fixed in exaggerated valgus alignment did not develop incipient or definite failure. This alignment reduces bending moment acting on the femoral prosthesis, reduces stress in the cement on the calcar femorale and in the cement on the distal and lateral side of the stem, and allows a thick cement mantle on the calcar region of the femur. The importance of cement thickness on the calcar femorale has been previously noted. 1,17,24The thin cement in this region is associated with a high risk of fragmentation, particle generation, and prosthetic subsidence with osteolysis. A disadvantage to the exaggerated valgus alignment might be a decrease in the effective offset of the femur, leading to increased joint
Survivorship of Charnley Femoral Prostheses force, which should be compensated for by lateral transplantation of the greater trochanter. 4 Calcar resorption and femoral cortical changes at 5 years correlated with the development of both incipient and definite failure of the femoral c o m p o n e n t in this study. Although most authors believe that calcar resorption is self-limited and not predictive of failures, 4,3°'3~ Loudon demonstrated its association with subsidence. 21 Several investigators have described an age-related increase in femoral medullary canal diameter that occurs naturally in the general population, ~°'27'29'33 Poss et al. showed that the magnitude of canal expansion and cortical thinning in the presence of a cemented femoral prosthesis was similar to that reported from studies of normal agerelated expansion. 25 Hofmann et al. found that the rate of canal expansion of 30 femurs with femoral loosening was twice that of the nonoperated opposite side and 4 times that of the controls. 16 They suggested that some total hip arthroplasty patients might be predisposed to increased endosteal resorption, with consequent loss of structural support and ultimate failure. Although we acknowledge that calcar resorption and cortical atrophy of the femur represent catabolic changes in the femoral cortex that can lead to subsidence, it is unclear w h y these changes occur in some patients and not in others. This is an issue that should be clarified in future studies.
4. 5.
6.
7. 8. 9.
10.
11.
12.
13.
14.
Summary Risk factors for mechanical loosening of femoral components were investigated in this 5 - ] 8-year follow-up study of 2 67 LFAs. Use of the largest possible stem size; proper cement techniques, including distal packing of cement and use of an intramedullary bony plug; and valgus alignment of the stem, allowing a thick cement mantle on the proximal and medial femoral cortex are important factors within the surgeon's control for longevity of low-friction arthroplasties. Calcar resorption and atrophy of the femoral cortex are considered biological factors correlated with aseptic loosening of the femoral component.
References l. Beckenbaugh RD, Ilstrup DM: Total hip arthroplasty: a review of three hundred and thirty-three cases with long follow-up. J Bone Joint Surg 60A:306, 1978 2. Bocco F, Langan P, Charnley J: Changes in the calcar femoris in relation to cement technology in total hip replacement. Clin Orthop 128:287, i977 3. Brand RA, Pedersen DR, Yoder SA: How definition
15.
16.
17.
18.
19.
20.
21. 22.
23.
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of "loosening" affects the incidence of loose total hip reconstructions. Clin Orthop 210:185, 1986 Charnley J: Low friction arthroplasty of the hip: theory and practice. Springer-Verlag, Berlin, 1979 Charnley J, Cupic Z: The nine and ten year results of the low-friction arthroplasty of the hip. Clin Orthop 95:9, 1973 Charnley J, Follacci FM, Hammond BT: The long-term reaction of bone to self-curing acrylic cement. J Bone Joint Surg 50B:822, 1968 Charnley J, Halley DK: Rate of wear in total hip replacement. Clin Orthop 112: I70, 1975 Dobbs HS: Survivorship of total hip replacements. J Bone Joint Surg 62B:168, 1980 Dorey F, Amstutz HC: Survivorship analysis in the evaluation of joint replacement. J Arthroplasty 1:63, 1986 Erickson MF: Aging changes in the medullary cavity of the proximal femur in American blacks and whites. Am J Phys Anthropol 51:563, i979 Gates HS III, Poletti SC, Callaghan J J, McCollum DE: Radiographic measurements in protrusio acetabuli. J Arthroplasty 4:347, 1989 Goodman SB, Adler SJ, Fyhrie DP, Schurman DJ: The acetabular teardrop and its relevance to acetabular migration. Clin Orthop 236:199, 1988 Griffith M J, Seidenstein MK, Williams D, Charnley J: Eight year results of Charnley arthroplasties of the hip with special reference to the behavior of cement. Clin Orthop 137:24, 1978 Hamilton HW, Joyce M: Long-term results of lowfriction arthroplasty performed in a community hospital, including a radiologic review. Clin Orthop 211 : 55, 1986 Harris WH, McCarthy JC, O'Neill DA: Femoral component loosening using contemporary techniques of femoral cement fixation. J Bone Joint Surg 64A: I063, 1982 Hofmann AA, Wyatt RWB, France EP et al: Endosteal bone loss after total hip arthroplasty. Clin Orthop 245: 138, 1989 Huiskes R: Some fundamental aspects of human joint replacement: analyses of stresses and heat conduction in bone-prosthesis structures. Acta Orthop Scand Suppl 185:109, I980 Kaplan EL, Meier P: Nonparametric estimation from incomplete observations. J Am Stat Assoc 53:457, 1958 Kavanagh BF, Ilstrup DM, Fitzgerald RH Jr: Revision total hip arthroplasty. J Bone Joint Surg 67A:517, 1985 Kobayashi S, Terayama K: Radiology of low-friction arthroplasty of the hip: a comparison of socket fixation techniques. J Bone Joint Surg 72B:439, 1990 Loudon JR: Femoral prosthetic subsidence after lowfriction arthroplasty. Clin Orthop 211 : 134, 1986 Loudon JR, Charnley J: Subsidence of the femoral prosthesis in total hip replacement in relation to the design of the stem. J Bone Joint Surg 62B:450, 1980 Mulroy RD Jr, Harris WH: The effect of improved ce-
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24.
25. 26.
27.
28.
The Journal of Arthroplasty Vol. 7 Supplement 1992 menting techniques on component loosening in total hip replacement. J Bone Joint Surg 72B:757, 1990 Noble PC, Tullos HS, Landon GC: The optimum cement mantle for total hip replacement: theory and practice. Instructional Course Lectures 40:145, I 9 9 I Poss R, Staehlin P, Larson M: Femoral expansion in total hip arthroplasty. J Arthroplasty 2:259, 1987 Romness DW, Lewallen DG: Total hip arthroplasty after fracture of the acetabulum: long-term results. J Bone Joint Surg 72B:761, 1990 Ruff CB, Hayes WC: Subperiosteal expansion and cortical remodeling of the h u m a n femur and tibia with aging. Science 217:945, 1982 Russotti GM, Coventry MB, Stauffer RN: Cemented total hip arthroplasty with contemporary techniques: a five-year m i n i m u m follow-up study. Clin Orthop 235:I41, 1988
29. Smith RW, Walker RR: Femoral expansion in aging women: implications for osteoporosis and fractures. Science 145:156, 1964 30. Stauffer RN: Ten-year follow-up study of total hip replacement: with particular reference to roentgenographic loosening of the components. J Bone Joint Surg 64A:983, 1982 31. Sntherland CJ, Wilde AWH, Borden LS, Marks KE: A ten year follow-up of one hundred consecutive Muller curved stem total hip replacement arthroplasties. J Bone Joint Surg 64A:970, 1982 32. Tew M, Waugh W: Estimating the survival time of knee replacements. J Bone Joint Surg 64B:579, 1982 33. Trotter M, Peterson RR: Transverse diameter of the femur: on roentgenograms and on bones. Clin Orthop 52:233, 1967
MD, PhD, and Kazuo
Terayama,
MD, PhD
Abstract: Two hundred sixty-seven consecutive primary low-friction arthroplasties, followed for 5-18 years after surgery, were studied to assess the factors influencing survivorship of the femoral component, using the Kaplan-Meier method. The end point of survivorship was defined radiographically in two ways: incipient failure (subsidence of the femoral component of ->2 mm) and definite failure (progressive change of position). Twenty-two femoral components developed incipient failure, and twelve of these advanced to definite failure. A canal filling ratio of the stem of ->75%, cement extent distal to the stem tip of ->1 cm, use of an intramedullary bone plug, and an exaggerated valgus alignment of the stem correlated positively with survivorship of the femoral component. Calcar resorption and atrophy of the femoral cortex after surgery were associated with aseptic loosening of the femoral component. K e y words: hip prosthesis, Charnley arthroplasty, low-friction arthroplasty, femoral component, survivorship analysis, radiography.
357 consecutive low-friction arthroplasties (LFAs) were performed in 283 patients as a primary intervention. Clinical and radiographic assessments were m a d e every 6 months. In order to include b o t h hips, all standard clinical radiographs were t a k e n at a distance of 1 m from the tube, which was centered on the symphysis pubis of the patient lying in the supine position. Twenty-seven patients (31 LFAs) were excluded from the study because they had been followed at other hospitals. Nine patients (10 LFAs) were excluded due to their deaths before the minim u m 5-year follow-up period was completed. Thirty-seven patients (48 LFAs) were excluded because of lack of follow-up information. One deep infection necessitated implant removal at 2 years. The remaining 267 arthroplasties in 209 patients were followed for an average of 9.2 years (range, 5 - 1 8 years). Patient age at operation ranged from 28 to 75 years (mean, 59 years). The youngest patient was a 28year-old w o m a n with multiple epiphyseal dysplasia. She used a wheelchair because of i n v o l v e m e n t of other joints, and her bilateral LFAs were functioning well without signs of aseptic loosening at 15 years.
Aseptic loosening is the most c o m m o n long-term complication of total hip arthroplasty and continues to play a significant role in its failure. We assessed factors affecting aseptic mechanical loosening of the femoral c o m p o n e n t in low-friction arthroplasty of the hip, using survivorship analysis to determine m e a n s of improving the durability of this procedure.
Materials and Methods Charnley low-friction arthroplasty was introduced to our d e p a r t m e n t in 1972 by the senior author (K.T.) w h o studied and trained with Sir J o h n Charnley at Wrightington Hospital. All cases were performed with the patient in the supine position using the original Charnley technique, including trochanteric osteotomy. 4 From October 1972 to May 1985, From the Department of Orthopaedic Surgery, Shinshu University School of Medicine, Matsumoto, Japan.
Reprint requests: Seneki Kobayashi, MD, PhD, Department of Orthopaedic Surgery, Shinshu University School of Medicine, Asahi 3-1-l, Matsumoto, 390, Japan.
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Two LFAs were performed on patients aged 2 1 - 3 0 years, 5 on patients 3 1 - 4 0 years, 29 on patients 4 1 - 5 0 years, 120 on patients 5 1 - 6 0 years, 92 on patients 6 1 - 7 0 years, and 19 on patients 7 1 - 8 0 years. Twenty-eight LFAs were performed on 24 m e n and 239 on 185 w o m e n . Osteoarthrosis was present in 229 hips (86%; 175 patients), rheumatoid arthritis in I2 hips (4%; 11 patients), and other disorders in 26 hips (I0%; 23 patients). All sockets were made from an identical high-density polyethylene, and the same bone cement of standard viscosity (CMW 1) was used t h r o u g h o u t the series. Factors affecting survivorship of the femoral component were analyzed using the Kaplan-Meier method. ~8 The end points of survivorship were defined radiographically in two ways: incipient failure and definite failure. Subsidence of the femoral component was measured radiographically using the m e t h o d of L o u d o n and Charnley, 22 with 2 m m or more was regarded as incipient failure. 4"~3"~4(Details of this m e t h o d are described in case 1 .) Socket migration was measured using the acetabular teardrop as a reference landmark, and migration of 2 m m or more or rotation of 2 ° or more was taken to be significant. In addition, visual detection of evidence of socket migration on serial radiographs on a large viewing box facilitated judging that the socket had developed incipient failure. Definite failure was indicated by progressive positional changes after develo p m e n t of the incipient failure. Definite failures prompted consideration of surgical revision. The date of radiographic detection of femoral component failure was recorded and used in survivorship calculations. Survivorship of the femoral c o m p o n e n t was assessed in relation to i7 variables: age, sex, etiology, Charnley's categories, obesity index, design of the femoral component, use of an intramedullary plug, calcar cement thickness, alignment of t h e stem, length of the residual femoral neck, canal filling ratio of the stem, cement extent distal to the stem tip, calcar resorption at 5 years, femoral cortical changes at 5 years, socket wear at 5 years, incipient failure of the socket, and definite failure of the socket. Comparative analysis was performed between patients who were less than 60 years old at time of surgery and those w h o were 60 years or older. Comparisons were also made between m e n and w o m e n , between patients with osteoarthrosis and rheumatoid arthritis, between patients in Charnley's category A (unilateral hip disease, otherwise no functional disabilities) and those in category B (bilateral hip disease, otherwise no functional disabilities), and between patients with an obesity index (the percentage of body weight to
standard weight) of less than 120% and those i 2 0 % or more. Femoral components with nonflanged stem designs were used early in the series, and those with dorsal flanges have been routinely used since August 1979, except for narrow femoral canals into which they cannot be inserted. Survivorship of the femoral component was compared between these two designs. Intramedullary plugging techniques were adopted beginning in September 1981 to achieve better intramedullary filling and pressurization during cement polymerization. A plug manufactured from high-molecular-weight polyethylene (designed by Hardinge) was used first, and a technique of b o n y plugging has been used since January 1982, except w h e n good autologous cancellous bone could not be obtained from the proximal femur or resected femoral head. With an intramedullary plug, a vent tube was used during packing viscous cement with two thumbs. Comparison was made among a group of LFAs without intramedullary plugging, a group with plastic plugs, and one with bony plugs. Using previously described methods for radiographic measurement, 2° the following variables were measured on radiographs taken within 1 m o n t h after surgery and were used in survivorship analyses. Survivorship of the femoral c o m p o n e n t was compared between a group with a calcar cement thickness of less than 3 m m and one with a thickness of 3 m m or more; between a group of femoral components with a residual femoral neck of less than 5 m m and one with femoral necks of 5 m m or more; between a group with a canal filling ratio of the stem (the percentage of stem width to intramedullary width at the midpoint of the stem) of less than 75% and one with a ratio of 75% or greater; and b e t w e e n a group of femoral components with cement extent distal to the stem tip (the length from the distal tip of the stem to the level at which cement filled over 80% of the canal) of less than 1 cm and a group with extent of 1 cm or greater. The alignment of the stem was classified as valgus or varus in relation to the axis of the proximal femoral shaft, and stems in a valgus alignment with a cement thickness of more than 1 cm at the calcar were classified as being in an exaggerated valgus alignment. 2 Survivorship of the femoral component was assessed for these three types of alignments. Calcar resorption, cortical changes around the distal tip of the stem, and socket wear were assessed on radiographs obtained after 5 years. Type IIIB (a cavity in the calcar) and IIIC (absorption of the total thick ~ ness of the calcar) changes in the femoral neck 2 were considered calcar resorption, and resorption of 2 m m
Survivorship of Charnley Femoral Prostheses
or more was regarded as significant. Cortical changes around the distal tip of the stem were classified into four categories: normal, atrophy, hypertrophy with normal outline, and external hypertrophy. 6 The external outline of the femoral cortex was examined, and any fusiform h y p e r t r o p h y near the prosthesis tip was classified as external hypertrophy. W h e n there were no changes in the outline of the femur, cortical thickness was evaluated at the level of the prosthesis tip. Variations in cortical thickness of less than 5 % at 5 years as compared with thickness within 1 m o n t h were classified as normal. W h e n cortical thickness had increased or decreased by 5% or more, femurs were classified as either hypertrophic or atrophic with normal outline, respectively. Socket wear was measured using a m e t h o d developed by Charnley and others, 5"7 and wear of 1 m m or more was regarded as significant. Survivorship was compared between groups of femoral c o m p o n e n t s with and without calcar resorption at 5 years, a m o n g those with distinct varieties of femoral cortical changes at 5 years, and between groups of femoral components with and without significant socket w e a r at 5 years. Survivorship of the femoral c o m p o n e n t was also compared between a group of LFAs that developed incipient failure of the acetabular c o m p o n e n t during the observation period and a group that did not and between a group of femoral c o m p o n e n t s with definite failure of the sockets and a group without such failure. A P value of less than .05 was considered significant in every statistical analysis.
Results In our series of 267 LFAs, 24 sockets (9.0%) developed incipient failure, and 14 of these progressed to definite failure. Incipient failure occurred between 0.4 and 12.3 years (mean, 4.9 years) after surgery, and definite failure occurred between 5.0 and 11.8 years (mean, 8.0 years) after surgery. Twenty-two femoral c o m p o n e n t s (8.2%) subsided by 2 m m or m o r e b e t w e e n 1.0 and 5.0 years (mean, 2.7 years) after surgery, and 12 of these progressed to definite failure by 3 . 0 - 7 . 0 years (mean, 4.6 years) after surgery. Combinations of acetabular and femoral comp o n e n t failure were found in three hips: two had sockets with incipient failure and femoral component with definite failure, and in one, both components manifested incipient failure. At the time of this study (June 1990), six revision operations had been performed for definite failure of the acetabular comp o n e n t and five for definite failure of the femoral component. Only those c o m p o n e n t s with definite
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failure were replaced in these revisions, except in one case in which a femoral c o m p o n e n t manifesting definite failure and a socket with incipient failure were replaced. There was no difference in the survivorship of the femoral component, whether incipient failure or definite failure was used as an end point, b e t w e e n the group of patients younger than 60 years of age (141 LFAs) and those 60 years old or older (126 LFAs); between m e n (28 LFAs) and w o m e n (239 LFAs); between osteoarthritic patients (229 LFAs) and rheumatoid patients (12 LFAs); b e t w e e n patients in Charnley's category A ( 124 LFAs) and those in category B (125 LFAs); or between patients with an obesity index of less than 120% (211 LFAs) and those with an index of 120% or m o r e (56 LFAs). No significant difference was observed in the survivorship of the femoral component, considering both incipient and definite failures as end points, b e t w e e n a group of I47 femoral c o m p o n e n t s without flanges and a group of 120 flanged femoral components; between a group of 84 femoral c o m p o n e n t s with a calcar cement thickness of less than 3 m m and a group of 183 c o m p o n e n t s with a cement thickness of 3 m m or more; or between a group of 114 femoral c o m p o nents with residual femoral necks of less than 5 m m and a group of 153 with femoral necks of 5 m m or more. Use of an intramedullary plug did not affect survivorship w h e n incipient failure was the end point but did influence survivorship based u p o n definite failure (Fig. 1). The survivorship of a group of components fixed with b o n y plugs exceeded not only that of a group of 156 c o m p o n e n t s fixed w i t h o u t intramedullary plugging but also that of a group of 30 components with manufactured plastic plugs
I00
A 1
80>
60-
40fl_ 20.
Follow-up (years)
Fig. 1. Survivorship based upon definite failure of the femoral component for three methods of intramedullary plugging. A, no plugs (156 LFAs); B, manufactured plastic plugs (30 LFAs); C, bony plugs (81 LFAs).
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The J o u r n a l of A r t h r o p l a s t y Vol. 7 S u p p l e m e n t 1992
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n
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Fig. 2. (A) Survivorship based upon incipient failure of the femoral component for three classes of stem alignment. A, moderate valgus alignment with calcar cement less than 1 cm thick (222 LFAs); B, varus alignment (25 LFAs); C, exaggerated valgus alignment with calcar cement I cm or more thick (20 LFAs). (B) Survivorship based upon definite failure of the femoral component for three classes of stem alignment. A, moderate valgus alignment with calcar cement less than 1 cm thick (222 LFAs); B, varus alignment (25 LFAs); C, exaggerated valgus alignment with calcar cement 1 cm or more thick (20 LFAs).
from the point 5 years and 6 months after surgery on. The difference in the survivorship between components fixed w i t h o u t plugging and those fixed with m a n u f a c t u r e d plugs was not significant. The alignm e n t of the stem influenced survivorship based u p o n either incipient failure or definite failure as an end point. T w e n t y femoral c o m p o n e n t s fixed in the exaggerated valgus alignment developed neither incipient nor definite failure. The survivorship of a group of c o m p o n e n t s fixed in the exaggerated valgus alignm e n t exceeded that of a group of 222 components fixed in the (moderate) valgus alignment with calcar cement of less t h a n 10 m m in thickness after 3 years and 3 m o n t h s and that of a group of 25 components fixed in the varus alignment after 5 years and 3 m o n t h s w h e n incipient failure was used as an end point (Fig. 2A). W h e n survivorship was based u p o n definite failure, the group of c o m p o n e n t s fixed in an exaggerated valgus alignment had survivorship superior to c o m p o n e n t s fixed in varus alignment at 4 years and to that of c o m p o n e n t s fixed in moderate valgus position at 6 years and 4 months and beyond (Fig. 2B). The difference in survivorship based u p o n incipient or definite failure was not significant between the group of c o m p o n e n t s fixed in varus alignm e n t and those in moderate valgus alignment. The canal filling ratio of the stem influenced survivorship based u p o n incipient failure as the end point but not survivorship based u p o n definite failure. The survivorship of 76 stems with canal filling ratios of 75% or m o r e exceeded that of 191 stems with ratios of less t h a n 75% at 4 years and 7 months or m o r e after
surgery (Fig. 3). Cement extent distal to the stem tip only influenced survivorship based u p o n incipient failure as the end point, w h e r e b y 225 femoral components with cement extent of 1 cm or m o r e had survivorship superior to that of 42 c o m p o n e n t s with extent of less t h a n 1 cm b e y o n d 1 year and 8 m o n t h s (Fig. 4). Both calcar resorption and femoral cortical changes at 5 years correlated with snrvivorship based u p o n incipient and/or definite failure of the femoral component. Two h u n d r e d three femoral c o m p o n e n t s with calcar resorption of less t h a n 2 m m at 5 years had survivorship superior to that of 64 c o m p o n e n t s
1 0 0 ~
............................
?8 o ~ ~ 6
o
~
ffl
~ 40. (3. 20. 0
f0
f5
Follow-up (years)
Fig. 3. Survivorship based upon incipient failure of the femoral component for 76 femoral components with a canal filling ratio of 75% or greater (dashed line) and 191 with a canal filling ratio of less than 75% (solid line).
Survivorship of Charnley Femoral Prostheses 100-
80-
~>
6o.
'~ o
40.
20.
0
(o
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Follow-up (years)
Fig. 4. Survivorship based upon incipient failure of the femoral component for 225 femoral components with cement extent distal to the stem tip of 1 cm or more (dashed line) and 42 with cement extent of less than 1 cm (solid line).
with calcar resorption of 2 m m or more after 1 year and 7 months w h e n incipient failure was taken as the end point (Fig. 5A) and after 5 years and five months w h e n definite failure was taken as the end point (Fig. 5B). Survivorship analysis was applied to every combination of survival curves based upon femoral cortical change at 5 years, and significant differences were found between the following: In 21 femoral components with cortical atrophy, survivorship based u p o n incipient failure was significantly inferior to that of 139 components with normal cortex; to 19 components with cortical hypertrophy with normal outlines; and to 88 components with external hypertrophy beyond 2 years and 5 months after surgery. The components with external hyper-
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331
trophy had superior survivorship to those with norreal cortex b e y o n d 3 years and 2 m o n t h s (Fig. 6A). W h e n survivorship was based u p o n definite failure, femoral components with cortical atrophy were inferior to those with normal cortex b e y o n d 6 years and 5 months; to those with cortical hypertrophy with a normal outline b e y o n d 6 years and 3 months; and to those with external hypertrophy b e y o n d 5 years and 5 months (Fig. 6B). The difference in survivorship was not significant between a group of 239 femoral components with sockets with wear of less than 1 m m at 5 years and a group of 28 femoral c o m p o n e n t s with sockets that developed wear of 1 m m or more within 5 years, whether based u p o n incipient or definite failure of the femoral component. We could not demonstrate any influence of incipient or definite failure of the socket u p o n survivorship of the femoral component, based u p o n either incipient or definite failure of the femoral component.
Case Reports Case 1 A 62 -year-old woman had low-friction arthroplasty for her unilateral osteoarthritic hip (category A). A nonflanged femoral c o m p o n e n t was inserted without an intramedullary plug in a valgus position of 3.5 °. The calcar cement thickness was 7 ram, the canal filling ratio of the stem was 78%, and the cement extent distal to the tip of the stem was - 14 m m (Fig. 7A). Subsidence of the femoral component was measured using the m e t h o d of L o u d o n and Charnley. 22 All measurements were made in a
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;
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A
40-
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Fig. 5. (A) Survivorship based upon incipient failure of the femoral component for 203 femoral components with calcar resorption of less than 2 mm at 5 years (dashed line) and 64 with calcar resorption of 2 mm or more (solid line). (B) Survivorship based upon definite failure of the femoral component for 203 femoral components with calcar resorption of less than 2 mm at 5 years (dashed line) and 64 with calcar resorption of 2 mm or more (solid line).
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The Journal of Arthroplasty Vol. 7 Supplement 1992
100
O A
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._>
C
100.
C
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80"
i
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~ 6oI
a
g
~, 40n
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~ B
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Fig. 6. (A) Survivorship based upon incipient failure of the femoral component for four classes of femoral cortical change at 5 years. A, normal (139 LFAs); B, cortical atrophy (21 LFAs); C, cortical hypertrophy with normal outline (19 LFAs); D, external hypertrophy (88 LFAs). (B) Survivorship based upon definite failure of the femoral component for four classes of femoral cortical change at 5 years. A, normal (139 LFAs); B, cortical atrophy (21 LFAs); C, cortical hypertrophy with normal outline (19 LFAs); D, external hypertrophy (88 LFAs).
line of the axis of the distal two-thirds of the stem. Lines perpendicular to the stem axis were d r a w n through the three d a t u m points (Fig. 7): X was tangential to the distal tip of the stem, Y was at the same level of a constant point on the femur where a double wire passed t h r o u g h the lateral femoral cortex, and Z was tangential to the prosthetic head. XZ and XY were m e a s u r e d in the axis line, and from the XZ meas u r e m e n t the radiographic magnification could be calculated because the same m e a s u r e m e n t on the unmagnified prosthesis was k n o w n to be 155 ram. The actual length of XY (corrected for magnification) was 101.0 m m immediately after surgery (Fig. 7A). One year after surgery, it became 106.5 ram, indicating subsidence of 5.5 m m (Fig. 7B). At 14 years, it was 106.8 m m (Fig. 7C). Therefore, this femoral c o m p o n e n t was considered to be stabilized following the d e v e l o p m e n t of subsidence within 1 year after surgery. Case 2
Low-friction arthroplasty was performed for one of the osteoarthritic hips in a 72-year-old m a n (category B). A flanged femoral c o m p o n e n t was placed without intramedullary plugging in a valgus alignm e n t of 2.0 ° with a calcar cement thickness of 10 ram, therefore, this c o m p o n e n t was in exaggerated valgus alignment. Ten years after surgery, the comp o n e n t functioned well without subsidence in spite of an insufficient canal filling ratio (60%) and of a short extent of cement distal to the stem tip (5 ram) (Fig. 8).
Case 3
A 54-year-old woman had low-friction arthroplasty for one of her osteoarthritic hips~ A flanged femoral c o m p o n e n t was placed with a b o n y plug in an exaggerated valgus alignment with a calcar cement thickness of 10 rnm. Canal filling ratio of the stem was 83% and c e m e n t extent distal to the stern tip was 37 m m . A radiograph t a k e n at 7 years was u n r e m a r k a b l e except for cancellous change of the medial femoral neck (Fig. 9). Case 4
A 60-year-old w o m a n with an osteoarthritic hip had low-friction arthroplasty. A nonflanged femoral c o m p o n e n t was cemented w i t h o u t a plug in an alignm e n t of 0 °, which was classified as a valgus alignm e n t in this study. Calcar c e m e n t thickness was 5 m m and cement extent distal to the stem tip was 13 ram. The ratio of cortical thickness to the outer diameter of the f e m u r at the level of the prosthetic tip was 39% (Fig. 10A). At 13 years, there was neither subsidence of the c o m p o n e n t nor d e m a r c a t i o n around the cement. The ratio of cortical thickness at the level of the stem tip became 47% w i t h o u t change in the outline of the f e m u r (Fig. 10B). Thus, the femoral cortex was classified as hypertrophic w i t h normal outline. Case 5
A 62-year-old w o m a n with osteoarthritic hips had low-friction arthroplasty. A nonflanged femoral c o m p o n e n t was inserted w i t h o u t a plug in a valgus
Fig. 7. Radiograph of 62-year-old w o m a n who had a lowfriction arthroplasty performed on her osteoarthric hip (case 1). XY was the distance along the axis of the stem between the constant point on the femur (a drill hole for a double wire in the lateral femoral cortex) and the reference point for the femoral component (the distal tip of the stem). The measurement XZ was used in correction for magnification. (A) Immediately after surgery (XY = 101.0 mm). (B) One year after surgery (XY = 106.5 mm). (C) At 14years (XY = 106.8 mm).
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Fig. 8. Radiograph of a 72-year-old man with osteoarthritic hips taken l0 years after surgery (case 2).
alignment of 1.0 ° with a calcar cement thickness of 5 m m and a cement extent of 14 ram. The canal filling ratio of the stem was 86% (Fig. 11A). At 12 years, the femoral cortex developed into fusiform hypertrophy near the prosthetic tip. There was neither subsidence of the c o m p o n e n t nor demarcation around the cement (Fig. 11B).
Discussion The Kaplan-Meier survivorship m e t h o d accounts for patients with various follow-up periods and those w h o have b e e n lost during the follow-up period or have died during the period of observation. I8 This nonparametric estimation m e t h o d has therefore b e e n applied to long-term follow-up studies of both total hip and knee arthroplasties. 8'9'x9"26"~2It also allows comparison of groups with different follow-up periods. However, the end points must be carefully defined, because differences in definition can affect loosening rates by as m u c h as 2 to 3 times. 3 In this
Fig. 9. Radiograph of a 54-year-old woman with osteoarthritic hips taken 7 years after surgery (case 3).
study, we defined the end point of survivorship of femoral c o m p o n e n t s radiographicaily in two ways: as incipient failure judged by subsidence of 2 m m or more, and as definite failure indicated by progression of the subsidence after d e v e l o p m e n t of incipient failure. Subsidence was m e a s u r e d using the m e t h o d of Loudon and Charnley. xx Merits of this m e t h o d are correction for magnification and minimization of errors resulting from different a m o u n t s of lateral rotation of the femur, as far as all m e a s u r e m e n t s are made in a line parallel to the axis of the stem. 22 As for reproducibility, Loudon and C h a m l e y 22 m e a sured 50 different radiographs twice to assess the accuracy of the m e t h o d and obtained a n average error of 0.04 + 0.38 m m . They decided to exclude all cases where the subsidence was less t h a n 1.6 m m , w h i c h was 4 times the standard deviation derived f r o m this experiment. Although Loudon and Charnley regarded subsidence of 1.6 m m or m o r e as meaningful, we chose 2 m m as the standard of judgment, as h a v e
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Fig. I0. A 60-year-old woman with an osteoarthritic hip (case 4). (A) One month after surgery. (B) At 13 years.
other researchers. 4"13'14 Regarding the acetabulum, since the tear drop was s h o w n not to vary with a slight degree of pelvic obliquity and to be a reliable landmark for m e a s u r e m e n t of socket migration,11'12 it was used in the present study. However, as differences in magnification and in pelvic tilt were not compensated for in the m e a s u r e m e n t of socket migration, failure of the socket was judged synthetically with visual detection of evidence of positional change. Incipient failure of femoral c o m p o n e n t s in this study might be equivalent to the category of "definite loosening," defined by Harris et al. as definite evidence of migration, although they did not define the migration of the component. 15 In our series, 10 femoral c o m p o n e n t s did not manifest a progression in subsidence after development of incipient failure. Charnley noted that subsidence of the femoral comp o n e n t could result in a n e w and final position of stability. 4 Loudon observed a similar p h e n o m e n o n in 15 of 18 femoral c o m p o n e n t s with subsidence and
defined this m o d e as stable subsidence, distinguishing it from progressive subsidence. 21 Therefore, after detection of subsidence in a femoral prosthesis, careful follow-up examinations are necessary to evaluate the m o d e of subsidence prior to considering revision surgery. In regard to factors related to subsidence of femoral components, Griffith et al. reported that patients manifesting subsidence were, on average, 9 kg heavier. ~3 Loudon and Charnley demonstrated a significant reduction in the incidence and degree of subsidence with the use of flanged stems as c o m p a r e d with nonflanged stems. 22 In our series, neither the obesity index nor the flange design of the stem correlated with prosthetic subsidence, although b o t h the canal filling ratio of the stem and the extent of cement distal to the tip of the stem correlated with subsidence. Beckenbaugh and Ilstrup reported that if the stem diameter was less t h a n half the width of the femoral canal at its midposition, the incidence of loosening was 2.5 times higher t h a n if the stem diam-
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Fig. 11. A 62-year-old woman with osteoarthritic hips (case 5). (A) One month after surgery. (B) At 12 years.
eter was greater than this, and that the degree of cement extent past the tip of the stem was inversely related to subsidence. 1 Bony plugs used in conjunction with viscous cement enhanced the longevity of femoral components in this study. Mulroy and Harris reported a marked reduction in the rate of aseptic loosening in i05 femoral components that were cemented with improved techniques, including the use of a plastic medullary plug, a doughy mix of Simplex P, and a collared stem of chrome-cobalt. 23 They proposed that the use of a medullary plug allowed a greater intrusion pressure of cement, better filling, and improved cement-interface strength. Russotti et al. also reported an improvement in the rate of femoral loosening with improved cementing techniques, although they used both plastic and bony plugs. 28 As the use of bony plugs yielded superior survivorship of femoral components in this study as compared not only with rudimentary cementing techniques without plugging but also with the use of plastic plugs, we recommend the use of an autologous bony plug when it is available. Alignment of the stem should be the most impor-
tant factor within the surgeon's control, as it is correlated with both incipient and definite failure of femoral components. Beckenbaugh and Ilstrup demonstrated a correlation between varus alignment and subsidence.1 Bocco et al., in a 2-year follow-up study, found a lower incidence of subsidence to be associated with exaggerated valgus alignment than with varus or moderately valgus alignment. 2 In our series, with 5-18-year follow-up periods, femoral components fixed in exaggerated valgus alignment did not develop incipient or definite failure. This alignment reduces bending moment acting on the femoral prosthesis, reduces stress in the cement on the calcar femorale and in the cement on the distal and lateral side of the stem, and allows a thick cement mantle on the calcar region of the femur. The importance of cement thickness on the calcar femorale has been previously noted. 1,17,24The thin cement in this region is associated with a high risk of fragmentation, particle generation, and prosthetic subsidence with osteolysis. A disadvantage to the exaggerated valgus alignment might be a decrease in the effective offset of the femur, leading to increased joint
Survivorship of Charnley Femoral Prostheses force, which should be compensated for by lateral transplantation of the greater trochanter. 4 Calcar resorption and femoral cortical changes at 5 years correlated with the development of both incipient and definite failure of the femoral c o m p o n e n t in this study. Although most authors believe that calcar resorption is self-limited and not predictive of failures, 4,3°'3~ Loudon demonstrated its association with subsidence. 21 Several investigators have described an age-related increase in femoral medullary canal diameter that occurs naturally in the general population, ~°'27'29'33 Poss et al. showed that the magnitude of canal expansion and cortical thinning in the presence of a cemented femoral prosthesis was similar to that reported from studies of normal agerelated expansion. 25 Hofmann et al. found that the rate of canal expansion of 30 femurs with femoral loosening was twice that of the nonoperated opposite side and 4 times that of the controls. 16 They suggested that some total hip arthroplasty patients might be predisposed to increased endosteal resorption, with consequent loss of structural support and ultimate failure. Although we acknowledge that calcar resorption and cortical atrophy of the femur represent catabolic changes in the femoral cortex that can lead to subsidence, it is unclear w h y these changes occur in some patients and not in others. This is an issue that should be clarified in future studies.
4. 5.
6.
7. 8. 9.
10.
11.
12.
13.
14.
Summary Risk factors for mechanical loosening of femoral components were investigated in this 5 - ] 8-year follow-up study of 2 67 LFAs. Use of the largest possible stem size; proper cement techniques, including distal packing of cement and use of an intramedullary bony plug; and valgus alignment of the stem, allowing a thick cement mantle on the proximal and medial femoral cortex are important factors within the surgeon's control for longevity of low-friction arthroplasties. Calcar resorption and atrophy of the femoral cortex are considered biological factors correlated with aseptic loosening of the femoral component.
References l. Beckenbaugh RD, Ilstrup DM: Total hip arthroplasty: a review of three hundred and thirty-three cases with long follow-up. J Bone Joint Surg 60A:306, 1978 2. Bocco F, Langan P, Charnley J: Changes in the calcar femoris in relation to cement technology in total hip replacement. Clin Orthop 128:287, i977 3. Brand RA, Pedersen DR, Yoder SA: How definition
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of "loosening" affects the incidence of loose total hip reconstructions. Clin Orthop 210:185, 1986 Charnley J: Low friction arthroplasty of the hip: theory and practice. Springer-Verlag, Berlin, 1979 Charnley J, Cupic Z: The nine and ten year results of the low-friction arthroplasty of the hip. Clin Orthop 95:9, 1973 Charnley J, Follacci FM, Hammond BT: The long-term reaction of bone to self-curing acrylic cement. J Bone Joint Surg 50B:822, 1968 Charnley J, Halley DK: Rate of wear in total hip replacement. Clin Orthop 112: I70, 1975 Dobbs HS: Survivorship of total hip replacements. J Bone Joint Surg 62B:168, 1980 Dorey F, Amstutz HC: Survivorship analysis in the evaluation of joint replacement. J Arthroplasty 1:63, 1986 Erickson MF: Aging changes in the medullary cavity of the proximal femur in American blacks and whites. Am J Phys Anthropol 51:563, i979 Gates HS III, Poletti SC, Callaghan J J, McCollum DE: Radiographic measurements in protrusio acetabuli. J Arthroplasty 4:347, 1989 Goodman SB, Adler SJ, Fyhrie DP, Schurman DJ: The acetabular teardrop and its relevance to acetabular migration. Clin Orthop 236:199, 1988 Griffith M J, Seidenstein MK, Williams D, Charnley J: Eight year results of Charnley arthroplasties of the hip with special reference to the behavior of cement. Clin Orthop 137:24, 1978 Hamilton HW, Joyce M: Long-term results of lowfriction arthroplasty performed in a community hospital, including a radiologic review. Clin Orthop 211 : 55, 1986 Harris WH, McCarthy JC, O'Neill DA: Femoral component loosening using contemporary techniques of femoral cement fixation. J Bone Joint Surg 64A: I063, 1982 Hofmann AA, Wyatt RWB, France EP et al: Endosteal bone loss after total hip arthroplasty. Clin Orthop 245: 138, 1989 Huiskes R: Some fundamental aspects of human joint replacement: analyses of stresses and heat conduction in bone-prosthesis structures. Acta Orthop Scand Suppl 185:109, I980 Kaplan EL, Meier P: Nonparametric estimation from incomplete observations. J Am Stat Assoc 53:457, 1958 Kavanagh BF, Ilstrup DM, Fitzgerald RH Jr: Revision total hip arthroplasty. J Bone Joint Surg 67A:517, 1985 Kobayashi S, Terayama K: Radiology of low-friction arthroplasty of the hip: a comparison of socket fixation techniques. J Bone Joint Surg 72B:439, 1990 Loudon JR: Femoral prosthetic subsidence after lowfriction arthroplasty. Clin Orthop 211 : 134, 1986 Loudon JR, Charnley J: Subsidence of the femoral prosthesis in total hip replacement in relation to the design of the stem. J Bone Joint Surg 62B:450, 1980 Mulroy RD Jr, Harris WH: The effect of improved ce-
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The Journal of Arthroplasty Vol. 7 Supplement 1992 menting techniques on component loosening in total hip replacement. J Bone Joint Surg 72B:757, 1990 Noble PC, Tullos HS, Landon GC: The optimum cement mantle for total hip replacement: theory and practice. Instructional Course Lectures 40:145, I 9 9 I Poss R, Staehlin P, Larson M: Femoral expansion in total hip arthroplasty. J Arthroplasty 2:259, 1987 Romness DW, Lewallen DG: Total hip arthroplasty after fracture of the acetabulum: long-term results. J Bone Joint Surg 72B:761, 1990 Ruff CB, Hayes WC: Subperiosteal expansion and cortical remodeling of the h u m a n femur and tibia with aging. Science 217:945, 1982 Russotti GM, Coventry MB, Stauffer RN: Cemented total hip arthroplasty with contemporary techniques: a five-year m i n i m u m follow-up study. Clin Orthop 235:I41, 1988
29. Smith RW, Walker RR: Femoral expansion in aging women: implications for osteoporosis and fractures. Science 145:156, 1964 30. Stauffer RN: Ten-year follow-up study of total hip replacement: with particular reference to roentgenographic loosening of the components. J Bone Joint Surg 64A:983, 1982 31. Sntherland CJ, Wilde AWH, Borden LS, Marks KE: A ten year follow-up of one hundred consecutive Muller curved stem total hip replacement arthroplasties. J Bone Joint Surg 64A:970, 1982 32. Tew M, Waugh W: Estimating the survival time of knee replacements. J Bone Joint Surg 64B:579, 1982 33. Trotter M, Peterson RR: Transverse diameter of the femur: on roentgenograms and on bones. Clin Orthop 52:233, 1967
