Cementless ceramic hip arthroplasties in patients less than 30 years old

The Journal of Arthroplasty Vol. 11 No. 6 1996

C e m e n t l e s s Ceramic Hip A r t h r o p l a s t i e s in P a t i e n t s Less T h a n 30 Years Old N. Hyder, FRCS Ed, A. B. Nevelos, FRCS, and T. G. Barabas, MBBS

Abstract: Twenty-six cementless ceramic hip arthroplasties were performed in 22

patients with an average age of 24 years (range, 17-30 years) at the time of operation. One patient was lost to follow-up evaluation. Twenty-one patients (25 hips) were reviewed with an average follow-up period of 6.5 years (range, 4-13 years). Two hips had to undergo revision of the ceramic acetabular components because of fractures in the upper part of the cup in both. One further hip was explored because of persistent wound discharge, but a mass of indurated tissue was removed and there was no evidence of deep infection. No organisms were grown from the samples taken during operation. Harris hip scores were good to excellent in 64%, fair in 16%, and poor in 20% of cases. There was no or slight pain in 14 (56%), mild pain in 7 (28%), and moderate pain in 4 (16%) hips. Apart from the two sockets revised, progressive radiolucent lines were seen in five cups (20%) and significant vertical migration was present in nine cups (36%) with an average migration of 1.3 mm/y. In total, acetabular changes were observed in 11 cases (44%). Femoral stem subsidence of between 3 and 6 mm was seen in five cases (20%). The total number of hips showing loosening of one or both components was five (20%). Overall radiographic changes (migration and loosening) in one or both components were present in 13 hips (54%). Key words: total hip, hip arthropIasty, cementless, ceramic.

Hip arthroplasty in y o u n g e r patients is a decision that has to be taken with great care as almost all of these patients will require at least one revision hip surgery during their lifetime. Furthermore, the results in y o u n g e r patients are generally not so good. First, this is due to high demands on these hips, leading to early wear and loosening. Second, because of the primary pathology, these patients often have grossly a b n o r m a l hips, w h i c h makes it impossible to perform a perfect joint arthroplasty. As a result, the abnormal stresses lead to early failure. The results of cemented hip arthroplasties have been s h o w n to be inferior in y o u n g e r patients [1-3]. Bone stock loss is a major issue in

revision arthroplasty. Cement is partly responsible for this [4], but largely this is due to the ukrahighmolecular-weight polyethylene (UHMWP) debris entering into the b o n e - i m p l a n t or b o n e - c e m e n t interfaces. Polymethyl methacrylate and UHMWP debris have repeatedly been s h o w n in the phagocytic macrophages in these osteolytic lesions [5-8]. Cementless arthroplasty has been r e c o m m e n d e d by m a n y authors for y o u n g e r patients in order to encourage n e w bone formation a r o u n d the implant to achieve biologic fixation. Osteolysis does, however, occur even with the cementless implants with UHMWP cups [6]. Alumina ceramic was first used for total hip prostheses by Boutin in 1970 [9]. He implanted c e m e n t e d as well as cementless prostheses. It has since been m o r e widely used. Alumina ceramic has very good wear characteristics and ceramic-on-ceramic articulation has one of the lowest coefficients of friction of any

From Woodlands Orthopaedic Hospital Bradford, West Yorkshire, England. Reprint requests: N. Hyder, 1 St Matthew's Grove, Wilsden, Bradford, West Yorkshire, BD 15 OLE England.

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current articulation. Wear debris is therefore reduced to a m i n i m u m . No wear problems were demonstrated in 255 patients with ceramic endoprostheses by Riska et al. in 1993 [10]. The reported wear rate in explanted ceramic components was 2.6 btm in sockets and 5.4 btm in heads per year [ I l l . This is less than 1/40th of the wear rate of conventional metal on polyethylene. The cementless ceramic-on-ceramic hip arthroplasty (Osteo, Selzach, Switzerland) used in this study was designed by Professor Mittelmeier of Germany. The femoral c o m p o n e n t is made of c o b a l t - c h r o m i u m alloy and has vertical corrugations to provide rotational stability. The interchangeable ceramic head with different neck lengths has a diameter of 32 mm. The alumina ceramic acetabular cup is fully threaded (Autophor, Osteo). None of the components in this original version had any form of coating. Intermediateterm results of these hip arthroplasties in patients w h o were less than 30 years old at the time of operation are presented here.

Materials and Methods Twenty-six cementless ceramic hip arthroplasties were carried out in 22 consecutive patients during a 9-year period (1981-1990). The ages of these patients ranged from 17 to 30 years (average, 24.3 years). Indication for arthroplasty was pain and poor quality of life. Decision to perform arthroplasty was made by one surgeon with the informed consent of the patients or their parents. The primary diagnoses leading to joint destruction were Perthes disease (n = 11), congenital dislocation of the hip (CDH) (n = 4), post-traumatic arthritis (n = 7), idiopathic avascular necrosis (n = 3), and septic arthritis (n = I). All operations were performed by one surgeon (A.B.N.) through an anterolateral approach without osteotomy of the greater trochanter. The acetabulum was reamed to restore its anatomic position, and a fully threaded alumina

T a b l e 1. G r a d i n g for L e v e l s o f A c t i v i t y Level I LeveI 2 Level 3 Level 4 Level 5 Level 6 Level 7

Requires assistance for all activities Independent self-care Indoor activities of daily living Outdoor activities of daily living--sedentary work Low-stress sports (swimming, biking, walking < i mile) light work High-stress sports (jogging, skiing, tennis), moderate manual labor Heavy manual labor (lifting 50-100 lb.)

Data from Wixson et al. [12].

ceramic cup was used in all cases. Acetabular reconstruction was not required in any of our cases. Femoral canal was u n d e r r e a m e d to provide a pressfit fixation. Cancellous milled bone obtained by reaming was used as bone-graft. The largest possible femoral c o m p o n e n t was used with a 32-mm modular alumina ceramic head. Lavage or irrigation was not used in these cases to prevent removal of useful milled autogenous bone. Patients were allowed to walk with crutches bearing only partial weight for 6 weeks and full weight thereafter. Patients were assessed clinically using the modified Harris hip score (total of 100 points). A grading system for level of activity was used as described by Wixson et al. (Table 1) [12]. Serial radiographs were analyzed for presence and progression of radiolucent lines in seven zones along the femoral c o m p o n e n t and three zones along the acetabular cup [13]. Radiographs were also analyzed for migration of acetabular and femoral components [12], radiolucent lines, failure of implants, and heterotopic bone formation.

Results One patient m o v e d from the area and therefore was lost to follow-up evaluation. Twenty-one patients (25 hips) with an average follow-up period of 6.4 years (range, 4-13 years) were reviewed. F o u r t e e n patients (16 hips) had one to five hip operations prior to hip arthroplasty. Details of these hip arthroplasties are given in Table 2. Six patients were involved in sedentary jobs before hip arthroplasty. By occupation, seven patients were m a n u a l workers but were having great difficulty with their jobs because of the disability. Eight patients were u n e m p l o y e d because of their hips. After hip arthroplasty, seven patients w e n t into sedentary occupations, nine patients were involved in m a n u a l work, and five patients were u n e m p l o y e d . The Harris hip score was above 90 in nine hips, above 80 in seven hips, above 70 in four hips, above 60 in two hips, and above 50 in three hips (Table 3). No or slight pain requiring no analgesia was present in 14 hips, mild pain requiring occasional analgesia was present in 7 hips, and moderate pain requiring frequent analgesia was present in 4 hips. S e v e n t e e n patients (20 hips) were pleased with their hips. Three patients (3 hips) felt that the results were not as good as they expected. Two patients (2 hips) were not satisfied with their hip arthroplasties.

Cementless Ceramic Hip Arthroplasty inYoung Patients

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Table 2. Details of the 21 Patients With the Outcome of Their Hip Arthroplasties Follow-up

Patient Age (years) No.*

Sex

Primary Diagnosis

Period

Harris

(years)

Score

Pain

Activity Level

Occupation

1

21

F

CDH

13

81

Slight

4

Clerk

2

30

F

Tr OA

11

72

Mild

4

Secretary

3*L

24

M

Tr OA

9

85

Mild

6

Manual laborer

R

25

M

Tr OA

8

85

Mild

6

4

I9

M

8

93

Slight

5

5*R

22

F

Perthes disease Idio AVN

8

92

None

5

L

22

F

Idio AVN

8

92

None

5

6

21

M

Tr OA

8

97

None

6

Foundary engineer

7

25

F

Tr OA

7

86

Slight

6

Care assistant

8

26

F

Perthes disease

7

92

None

5

Civil s e rva nt

9

24

F

Perthes disease

6

84

Mild

5

Homemaker

I0

27

M

Perthes disease

6

54

Moderate

5

Cab driver

ll*R

26

M

Perthes disease

6

80

None

3

Unemployed

28

M

Perthes disease

4

57

Moderate

3

12

22

M

Perthes disease

5

93

None

5

Taxi driver

13

26

M

Tr OA

5

88

None

5

Factory worker

14

19

F

Chondrolysis

5

93

Slight

5

B a n k clerk

15

25

F

CDH

5

93

Slight

6

Support manager

16" L

27

F

CDH

5

65

Mild

4

Social worker

R

27

F

CDH

5

73

Slight

4

L

Mot or mechanic U ne mpl oye d

Radiographic

Patient's

Analyses

Opinion

Reoperation

Cavitation Pleased femoral s t e m Cup m i g r a t i o n 20 m m / l o o s e No cup m i g r a t i o n / Pleased not loose Stem subsidence 4 m m / n o t loose No l oos e ni ng Pleased No m i g r a t i o n No subsidence Pleased Cup m i g r a t i o n 8 r a m / n o t loose No l o o s e n i n g Pleased No m i g r a t i o n Cup loose II Pleased a nd I I I t No m i g r a t i o n No subsidence No cup m i g r a t i o n / Pleased not loose No subsidence Cup m i g r a t i o n Pleased 4 m m / n o t loose No subsidence Cup m i g r a t i o n Pleased 5 m m / n o t loose No subsidence Cup m i g r a t i o n Not as 10 r a m / n o t loose e xpe c t e d Stem subsidence 4 m m / n o t loose No m i g r a t i o n / PIeased no l o o s e n i n g No subsidence No m i g r a t i o n / Pleased no l o o s e n i n g No subsidence No m i g r a t i o n / Pleased no l o o s e n i n g No subsidence No m i g r a t i o n / Not h a p p y no l o o s e n i n g No subsidence No m i g r a t i o n / Pleased no l o o s e n i n g Stem subsidence 3 m m / n o t loose No m i g r a t i o n / Pleased no l o o s e n i n g No subsidence No m i g r a t i o n / Pleased no l o o s e n i n g No s t e m subsidence Cup m i g r a t i o n Pleased 4 m m / n o t loose Stem subsidence 6 m m / n o t loose Cup loose EII, I I I t Pleased Cup m i g r a t i o n I3 m m No subsidence Cup loose I, II, I I I t Pleased Cup m i g r a t i o n 16 m m No subsidence

--

Cup revised

---

---

--

--

--

--

--

--

--

--

--

Cup revised --

--

--

--

(Table continues)

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The Journal of Arthroplasty Vol. 11 No. 6 September 1996 Table 2. Continued

Patient Age No. (years) Sex

Follow-up Primary Period Harris Diagnosis (years) S c o r e

Pain

Activity L e v e l Occupation

17

17

M

Septic arthritis

5

52

Moderate

4

I8

26

F

Perthes disease

4

93

Slight

5

19

26

M

Perthes disease

4

71

Moderate

5

Perthes disease Tr OA

4

65

Mild

4

4

78

Mild

5

20

26

M

21

28

M

Radiographic Analyses

Unemployed No migration/ no loosening No subsidence Nurse No migration/ no loosening No subsidence Unemployed No migration/ no loosening No stem subsidence Unemployed Cup loose I, II, III No stem subsidence Electrician Cup migration 3 mm/not loose Stem subsidence 3 mm/not loose

Patient's Opinion

Reoperation

Not happy

Excision antibioma

Pleased

--

Not as expected

--

Not as expected Pleased

---

*Patients with both hips done. tGruen's zones. CDEI, congenital dislocation of the hip; Tr OA, traumatic osteoarthritis; Idio AVN, idiopathic avascular necrosis.

Two p a t i e n t s w e r e u s i n g o n e c a n e f u l l - t i m e ; o n e of these p a t i e n t s h a d a b i l a t e r a l h i p a r t h r o p l a s t y for CDH, a n d the o t h e r p a t i e n t h a d o n e hip a r t h r o plasty for P e r t h e s disease. Two f u r t h e r p a t i e n t s u s e d a c a n e for l o n g w a l k s occasionally. All o t h e r patients used no support. U s i n g W i x s o n ' s g r a d i n g for level of activity, 4 p a t i e n t s w e r e p e r f o r m i n g activities of level 6 (highstress sports), 11 p a t i e n t s w e r e t a k i n g part i n level 5 activities (low-stress sports), 5 p a t i e n t s w e r e i n activity level 4 ( o u t d o o r activities of daily living), a n d o n l y 1 p a t i e n t was i n activity level 3 ( i n d o o r activities of daily living). T h i r t e e n p a t i e n t s h a d a slight limp, six p a t i e n t s h a d a m o d e r a t e limp, a n d t w o p a t i e n t s h a d n o l i m p at t h e i r latest f o l l o w - u p e x a m i n a t i o n . T h e r e w e r e n o dislocations a n d n o cases of deep i n f e c t i o n s i n this series.

was i n v o l v e d i n a m o t o r b i k e a c c i d e n t (case 13) (Fig. 1). I n b o t h of these cases, t h e r e w e r e n o signs of l o o s e n i n g a n d o n l y the cup was revised. O n e case was e x p l o r e d b e c a u s e of p e r s i s t e n t w o u n d discharge b u t o n l y a n i n d u r a t e d mass was r e m o v e d a n d t h e r e w e r e n o e v i d e n c e of deep i n f e c t i o n . No organisms were g r o w n from the samples taken d u r i n g o p e r a t i o n . This p a t i e n t ' s original diagnosis was septic arthritis.

Revisions Two hips h a d to be r e v i s e d b e c a u s e of f r a c t u r e of t h e c e r a m i c cup. I n b o t h of these p a t i e n t s , signific a n t t r a u m a was r e s p o n s i b l e for t h e fracture. O n e of t h e s e w a s a p a t i e n t (weight, 96 kg) w h o slipped a n d l a n d e d o n h e r hips (case 2), a n d t h e o t h e r o n e

Table 3. Harris Hip Scores No. of Hips 9 7 4 2 3

Harris Hip Score >90 > 80 > 70 > 60 > 50

Fig. I. Radiograph showing fracture of the acetabular cup following a motorbike accident.

Cementless Ceramic Hip Arthroplasty inYoung Patients

Fig. 2. Postoperative radiograph of the patient who had congenital dislocation of the hip.

Radiographic Assessment Femur. Subsidence of the femoral component was noted in five hips (20%). The range was 3 to 6 ram, with an average subsidence of 0.6 mm/y. None of

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683

these had radiolucent lines suggestive of loosening. Femoral stem cavitation was seen in one patient (Figs. 2, 3) because of aseptic loosening. Although this patient later developed disseminated cancer, there was no evidence of metastatic deposits in the hips. This patient's hip has remained symptom-free. There is an imminent risk of failure of this hip, but revision has not been performed for medical reasons. Acetabulum. Loosening of the cup as judged by the presence of ominous radiolucent lines was seen in five cups (20%). Significant vertical and medial migration of the cup was seen in nine hips (36%) with an average migration of 1.3 mm/y. Sixteen hips • showed no migration of the cup. Some of the cups with significant migration had no radiolucent lines. The above changes were significantly worse in patients with the primary diagnosis of CDH. All of the acetabular cups were either migrating or radiographically loose at the latest follow-up examination. The results in patients with Perthes disease were better than those in the other groups (Table 4). In total, there were five hips (20%) with loosening of one or both components. Overall radiographic changes (migration and loosening) in one or both components were present in I3 hips (52%). Heterotopic bone formation (class IIB-2) [14] was seen in one patient with the primary diagnosis of septic arthritis.

Discussion

Fig. 3. Same patient as in Figure 2, 13 years later, showing acetabular loosening and migration and cavitation of the proximal femur.

The use of m e t h y l methacrylate cement has u n d o u b t e d l y made great contributions to the fixation of implants in joint arthroplasties. Recently, the use of third-generation cementing techniques has further improved the prospects of long-term survival of the femoral components, but there have been continuing problems with the acetabular components, particularly in very y o u n g patients [15-17]. It is generally accepted that the results of hip arthroplasties are comparatively not so good in y o u n g e r patients. Level of activity is partly to blame but the problem is s o m e w h a t fundamental. In most of these patients, the problem starts in their childhood and therefore the hip is often grossly deformed. Small and abnormal femurs, very shallow and sometimes absent acetabuli, markedly shortened legs, and weak abductors are but a few problems that have to be overcome in planning arthroplasty in these patients. Therefore, it is often not possible to position the prosthesis in the perfect place or get a total correction of the leglength discrepancy. This is perhaps the most important factor, which creates abnormal stresses leading to the early aseptic loosening and failure.

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The Journal of Arthroplasty Vol. 11 No. 6 September 1996

Table 4. Radiographic Changes in the Acetabular Cup in 100% of Cases of Congenital Dislocation of the Hip Diagnosis Congenital dislocation of the hip Traumatic osteoarthritis Perthes disease Avascular necrosis/chondrolysis Septic arthritis

Total No. of Hips

Average Follow-up Period (years)

Acetabular Cup Loosening/Migration

Femoral Stem Loosening/Migration

4 7 I0 3 1

7 7.5 5.4 7 5

4 4 2 1 None

2 2 2 None None

Loosening of cemented hip arthroplasty is often associated with considerable bone loss [18-20]. This complication has b e e n referred to as "cement disease" {21]. It is said that rapid initial migration in c e m e n t e d hip arthroplasties is caused by the heat injury to the bone caused by c e m e n t [4]. Bone loss is caused not only by cement but also by the entry of UHMWP wear debris into the b o n e cement interface. These particulate wear debris have repeatedly b e e n s h o w n in the phagocytic macrophages in osteolytic lesions [5-8]. Bone stock loss is a major difficulty in revision arthroplasties of the hip, often requiring impaction b o n e grafts to reconstruct the acetabulum and proximal femur. This makes the task not only technically demanding but also more prone to failure. Cementless hip arthroplasties have b e e n recomm e n d e d by several authors for y o u n g e r patients, as these patients will inevitably require at least one revision during their lifetime. Achieving long-term stable fixation of sockets in particular in cementless implants has caused some problems. Sockets with a porous coating have been s h o w n to have poor bone ingrowth [22]. Fully threaded acetabular cups have been reported to migrate within 1 year of surgery, probably due to prosthetic instability caused by a poor contact b e t w e e n the screw threads and the acetabular bone [23,24]. The use of ceramic heads in hip arthroplasties is n o w well recognized, but its use as the acetabular cup has met with some criticism. There are two reasons for this. First, there is a wide mismatch between the elastic modulus of ceramic and bone leading to migration and loosening. Second, ceramic is brittle, which in the case of the head seems to cause few problems, but the cup, which has several edges and corners, is more likely to fracture. Of the 2,000 ceramic hip arthroplasties in the series by Mittelmeier and Heiser [11], there were five such fractures of the socket and an overall loosening rate of 1.3% was reported. In about 10%, some socket migration were observed radiographically. In our series, we had two fractures of sockets, but both were caused by significant

trauma. The fixation of the threaded ceramic cup was extremely rigid at the time of operation in most cases with adequate acetabuli. In patients with CDH, w h e r e acetabular sockets are inadequate or in a higher position, an attempt was made to fashion the cup in the n o r m a l position. It was possible to implant the cups in positions I and II [25] in all such cases. These cases, however, showed a 100% rate of migration and loosening. Improved results were also reported by Sedel et al. in 1990 with the use of cemented ceramic endoprostheses in y o u n g e r patients [26]. There was 98% survivorship after 10 years. Radiographically, 20 of 71 hips showed signs of loosening or impending failure. Sedel et al. in 1994 reported a survival rate of 89.4% after 10 years using the same prosthesis [27]. Nizard et al. reported a survival rate of 82.5% after 10 years with cemented ceramic prostheses in his series of 187 hip arthroplasties [28]. Survival was better in patients y o u n g e r t h a n 50 years. A cemented alumina ceramic socket was used. Concern was expressed about socket fixation. Although high wear resistance is one of the major attributes of alumina ceramic, Winter et al. reported a high rate of revision and aseptic loosening attributable to wear [29]. M a h o n e y and Dimon reported an unsatisfactory rate of loosening, migration of the socket, and subsidence of the femoral stem with the A u t o p h o r ceramic prosthesis [30]. Migration of the ceramic acetabular socket is a concern raised by m a n y authors [11,27-30]. Unlike the c e m e n t e d sockets or cementless implants with metal backing w h e r e migration is usually seen together with gross loosening and osteolysis, migration in the case of ceramic sockets is not always consistent with loosening, even w h e n progressive. It is often seen w h e n the c o m p o n e n t appears to have firmly consolidated with close b o n e - i m p l a n t contact. It is a continuous remodeling process because of the extreme hardness of alumina ceramic compared with bone. Our results have been comparable to most of the published reports of hip arthroplasties in this age

Cementless Ceramic Hip Arthroplasty inYoung Patients group. Results for cemented hips have been variable. A 24% revision rate was reported by Ballard et al. in 1994 after 11 years of follow-up evaluation in patients less than 50 years of age [17]. A further i 2 % were definitely loose in this series. Dorr et al. in 1983 had 12 revisions of 108 hips after 4.5 years in patients less than 45 years old [31]. Patients in this study with the worst prognosis for success were less than 30 years old. They advocated that results in this age group were so poor that conservative treatments such as osteotomy and arthrodesis have to be seriously considered before performing a total hip arthroplasty. Williams and McCullough in 1993 reported a 43.5% rate of loosening of cemented hip arthroplasties after 5 years of follow-up evaluation in patients with juvenile chronic arthritis [32]. In another series by Chandler et al, in I 9 8 l , the reported rate of loosening was 57% after 5 years of follow-up evaluation {1]. Acetabular loosening occurred more than twice as frequently as femoral stem loosening. Our result of two revisions in 25 hips after 6.5 years compares favorably with most published series. The total loosening in our series was seen in 20%, and overall radiographic changes including migration, subsidence, and loosening were present in 54% of the hips. Using patient criteria, 92% of the hips had a satisfactory outcome. There was only one case with anterior thigh pain in this series as compared with the reported incidence of 12 to 30% [33,34]. We have b e e n pleased with the overall perform a n c e of this hip arthroplasty in this group of patients. Acetabular migration and loosening have b e e n worrisome, but the femoral c o m p o n e n t has so far given us little cause for concern. We are currently using an i m p r o v e d version of this hip arthroplasty, w h i c h has a h y d r o x y a p a t i t e coating on the acetabular c o m p o n e n t s and both p o r o u s and h y d r o x y a p a t i t e coatings on the femoral c o m p o n e n t s .

References 1. Chandler HR Reineck FT, Wixson RL, McCarthy JC: Total hip replacement in patients younger than thirty years old. J Bone Joint Surg 63A: 1426, 1981 2. Joshi AB, Porter ML, Trail IA et al: Long-term results of Charnley low friction arthroplasty in young patients. J Bone Joint Surg 75B:616, 1993 3. Wroblewski BM, Siney PD: Charnley low-friction arthroplasty of the hip: long term results. Clin Orthop 292:191, 1993 4. Mjoberg B: Fixation and loosening of hip prostheses. Acta Orthop Scand 62:500, 1991 5. Maloney WJ, Jasty M, Rosenberg A, Harris WH: Bone lysis in well-fixed cemented femoral components. J Bone Joint Surg 72B:966, 1990

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6. Lennox DW, Schofield BH, McDonald DE Riley LH: A histologic comparison of aseptic loosening of cemented, press-fit and biologic ingrowth prostheses. Clin Orthop 225:171, 1987 7. Goodman SB, Fornasier VL: The effects of bulk versus particulate polymethylmethacrylate on bone. Clin Orthop 232:255, 1988 8. Murray DW, Rushton N: Macrophages stimulate bone resorption when they phagocytose particles. J Bone Joint Surg 72B:988, 1990 9. Boutin P: L'arthroplastie totale de la hanche par prothese en alumine: resultats de 150 cas d'ancrage direct de la piece acetabulaire. Int Orthop 1:87, 1977 10. Riska EB: Ceramic endoprosthesis in total hip artbroplasty. Clin Orthop 297:87, 1993 11. Mittelmeier H, Heisel J: Sixteen-years experience with ceramic hip prostheses. Clin Orthop 282:64, 1992 12. Wixson RL, Stulberg SD, Mehlhoff M: Total hip replacement with cemented, uncemented, and hybrid prostheses. J Bone Joint Surg 73A:257, 1991 13. Gruen TA, McNeice GM, Amstutz HC: "Modes of failure" of cemented stem-type femoral components: a radiographic analysis of loosening. Clin Orthop 141:17, 1979 14. Delee J, Ferrari A, Charnley J: Ectopic bone formation following low friction arthroplasty of the hip. Clin Orthop 121:53, 1976 15. Goetz DD, Smith EJ, Harris WH: The prevalence of femoral osteolysis associated with components inserted with or without cement in total hip replacements: a retrospective matched-pair series. J Bone Joint Surg 76A:1121, 1994 16. Oishi CS, Walker RH, Colwell CW: The femoral component in total hip arthroplasty: six to eight-year follow-up of one hundred consecutive patients after use of a third generation cementing technique. J Bone Joint Surg 76A:1130, 1994 17. Ballard WT, Callaghan JJ, Sullivan PM, Johnston RC: The results of improved cementing technique for total hip arthroplasty in patients less than fifty years old. J Bone Joint Surg 76A:959, 1994 18. Carlsson AS, Gentz C, Linder L: Localised bone resorption in the femur in mechanical failure of cemented total hip arthroplasties. Acta Orthop Scand 54:396, 1983 19. Tallroth K, Eskola A, Santavirta S e t al: Aggressive granulomatous lesions after hip arthroplasty. J Bone Joint Surg 71B:571, 1989 20. Harris WIt, Schiller AL, Scholler JM et al: Extensive localised bone resorption in the femur following total hip replacement. J Bone Joint Surg 58A:612, 1976 21. Jones LC, Hungerford DS: Cement disease. Clin Orthop 225:192, 1987 22. Cook SD, Thomas KA, Haddad RJ: Histologic analysis of retrieved human porous-coated total joint components. Clin Orthop 234:90, 1988 23. Tooke SM, Nugent PG, Chotivichit A et al: Cornparison of in vivo cementless acetabular fixation. Clin Orthop 235:253, 1988 24. Snorrason E Karrholm J: Primary migration of fullythreaded acetabular prostheses: a roentgen stereo-

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25.

26.

27.

28.

29.

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