The Journal of Arthroplasty Vol. 14 No. 4 1999

The Charnley Versus the Spectron Hip Prosthesis

Clinical Evaluation of a Randomized, Prospective Study of 2 Different Hip Implants

G/Sran Garellick, MD, PhD, Henrik Malchau, MD, PhD, and Peter Herberts, MD, PhD

A b s t r a c t : Prospective, randomized studies must be performed when new surgical techniques or implants are evaluated. In this study, a new implant system was compared with the Charnley prosthesis, which over the years has been the most used hip implant in Sweden. Between 1985 and i989, 410 hips were randomized to t reatment with a Chamley or a Spectron total hip arthroplasty: 206 Chamley and 204 Spectron prostheses were implanted. The patients were operated on by a standard- ized procedure using a contemporary cementing technique. The patients were followed prospectively by an independent observer after l, 3, 5 to 6, and l0 years. Harris Hip Score and patient satisfaction were recorded in the outcome evaluation. A total of 144 patients with 164 hips were deceased, and 15 patients (8 Charnley and 7 Spectron) have required a revision. Nine hips were revised because of aseptic loosening (5 Charnley stems and 4 Spectron metal-backed cups). The Charnley stem as well as the metal-backed Spectron cup had a higher risk for revision because of aseptic loosening. The Chamley ogee cup and the Spectron stein have performed remarkably well with no revision of these components. Seven Chamley prostheses dislocated, but no dislocation was recorded in the Spectron group. Survivorship calculations with a mean follow-up of 10 years revealed an overall i i - y e a r survivorship of 94.5% _+ 3.4% (Charnley, 93.2% + 5.8%; Spectron, 95.9% +-_ 3.0%). The clinical outcome did not differ between the 2 systems. The overall results in this old population, using a contemporary surgical technique, illustrate that cemented hip arthroplasty is an excellent t reatment alternative for elderly patients. K e y words: hip prosthesis, cemented, Charnley, Spectron.

M a n y i m p l a n t s h a v e b e e n i n t r o d u c e d s ince C h a r n - l ey i n t r o d u c e d the l o w - f r i c t i o n a r th rop las ty , b u t f ew p rospec t ive , r a n d o m i z e d s tudies h a v e b e e n p u b - l i shed desc r ib ing the l o n g - t e r m resu l t s [1 -3] . A

From the Department of Orthopaedics, Institute of Surgical Sciences, Sahlgrenska University Hospital, GiSteborg University, Gb'teborg, Sweden.

Submitted April 28, 1997; accepted May 14, 1998. Reprint requests: GSran Garellick, MD, PhD, Department of

Orthopaedics, Institute of Surgical Sciences, Sahlgrenska Univer- sity Hospital, Gateborg University, S-413 45 G6teborg, Sweden.

Copyright © 1999 by Churchill Livingstone ® 0883-5403/99/1404-0002510.00/0

s t u d y us ing a c o n t e m p o r a r y c e m e n t i n g t e c h n i q u e a n d 2 d i f fe ren t i m p l a n t s was i n i t i a t ed at Sah lg ren -

ska U n ive r s i t y Hosp i t a l in 1985. The a i m of t he

s tudy was to e v a l u a t e t he i n f l uence of p ro s th e t i c

des ign o n ea r ly a n d l o n g - t e r m cl inical a n d rad io -

g raph ic o u t c o m e s . O u r h y p o t h e s i s was t ha t t he a d v a n t a g e s c l a i m e d t h e o r e t i c a l l y for a m e t a l - b a c k e d cup {4-6] a n d a co l l a red s t em [7-9] p r o v i d e d b y one of t he devices m i g h t be r e v e a l e d clinically, for e x a m p l e , b y survival . This ar t ic le r epor t s t he cl inical o u t c o m e .

407

408 The Journal of Arthroplasty Vol. 14 No. 4 June 1999

Material and Methods

Implant Systems

Hips were randomized to a Charnley (DePuy, Leeds, UK previously Thackery Ltd., Leeds, UK) or a Spectron prosthesis (Smith & Nephew Inc., Mem- phis, TN previously Richards Inc., Memphis, TN). The Charnley prosthesis is a minicollared (some- times claimed to be collarless) stainless steel implant with a head diameter of 22.2 mm. The medial length of the stem used in this study was 112 mm. The all-polyethylene, flanged ogee cup was used. The Spectron prosthesis, made of chrome-cobalt , is collared and was used in its monoblock version with a head diameter of 32 mm and a medial stem length of 130 ram. The cup was metal backed (Fig. 1).

Patients

A total of 410 primary total hip arthroplasties (THAs) (206 Charnley and 204 Spectron) were performed on 372 patients. All patients receiving a cemented primary THA between September 1, 1985, and May 31, 1989, were recruited to the study. The allocation by a random number table was kept in a sealed envelope until the morning of the operation. For bilateral replacements, the second hip was also randomized. The patients were preopera t ive ly classified into clinical categories according to Charn- ley [10]. Randomizat ion resulted in a similar distri- but ion of diagnosis, age, gender, and Charnley clinical category in the 2 groups (Table 1). A total of 144 patients (164 hips) died during the study.

(A) Fig. 1. The (A) Charnley and the (B) Spectron prosthe- ses,

Surgical Procedure

All patients were operated on in a laminar airflow box, in a supine position, and through an anterolat- eral and transgluteal approach. In the Chamley group, the procedure was performed by a modifica- tion of Charnley's technique [ 10], wi thout trochan- teric os teotomy or use of a rotatory reamer. The old inst rumentat ion with only 1 (not oversized) femo- ral broach was employed, and the acetabulum was hand- reamed after a pilot hole was drilled. The Spectron arthroplasties were performed as recom- mended in the surgical technique [11], including a more m o d e r n i n s t rumen ta t i on wi th several broaches, which were oversized to permit a cement mantle of minimal 1- to 2-ram thickness. A calcar reamer was used, and the acetabulum was reamed by incremental power-dr iven reamers.

In the acetabular preparation, part of the subchon- dral plate was left intact, 5 to 8 5-ram holes were drilled, and cement pressurization was applied through a silicone diaphragm. The femoral cement- ing technique for both prostheses used a brush, high pulsatile lavage, adrenaline swab, distal polyethyl- ene cement restrictor, retrograde cement filling, and proximal seal for pressurization. In 375 hips, Sim- plex cement was used, and 35 hips received Palacos with gentamicin (Schering-Plough, Heist, Belgium).

Outcome Evaluation

All patients were observed prospectively, with clinical (and radiographic) examinat ion preopera- tively and postoperatively after 1, 3, 5 to 6, and 10 years performed by an independent observer. Pa- tients with major radiolucencies or unexplained pain were followed yearly. Through the identifica- tion number assigned to all persons living perma- nent ly in Sweden and the national databases, we have been able to trace all patients. Two patients (3 hips) were lost to follow-up: 1 patient (2 hips) refused to at tend examination, and 1 patient emi- grated to Finland. The study group has been checked for patients who died (via the Population Register of Sweden [12]) or who have been revised (via the local registry and the National Hip Arthroplasty Registry [13,14]) 4 times annually.

The clinical results were evaluated by reference to the Harris Hip Score [15]. In addition, patient satisfaction was classified (satisfied, uncertain, or dissatisfied), and complications were recorded.

Statistical Methods

All statistical calculations were done on a per- sonal computer using SPSS for Windows 95 (Ver-

T a b l e 1. P a t i e n t D a t a

Charnley Spectron Demographic Data (n = 206) (n = 204)

Gender Female 70 % 64 % Male 30% 36%

Age Mean value 70 y 71 y Range 41-85 y 40-86 y

Diagnoses Osteoarthrosis 57 % 63 % Rheumatoid arthritis 18 % 17 % Hip fracture 19 % 15 % Miscellaneous 6% 5%

Clinical category Category A 42 % 37 % Category B 23% 29% Category C 35% 34%

sion 7.5, SPSS, Chicago, IL). Survivorship was ana- lyzed according to Kaplan-Meier [16]. The 95% confidence limits (1.96 x standard error of the mean) are indicated on the survival curves. The other statistical methods used are indicated in the text. Two-tailed tests were performed.

Results

All patients available (nondeceased and nonre- vised patients) for follow-up were examined after 5 to 6 years. To date, 100 patients have been reviewed at 10 years (Tables 2 and 3) by which time 2 patients (3 hips) were lost to follow-up. Survival analyses have been based on a mean follow-up of 10 years (range, 7.9-11.6 years).

Clinical Follow-up

Preoperatively, the mean Harris Hip Score was 37 (range, 6-75) in the Charnley group and 33 (range, 3-70) in the Spectron group. Mean pain scores were 13 (range, 0-40) and 10 (range, 0-30). Postopera-

T a b l e 2. F o l l o w - u p C h a r n l e y (n = 206)

Fol low- Clinical Deceased Lost to up Time Examin- Patients Fol low- (y) ation (Hips) Revised up

1 1 9 8 7 I - - 3 I83 20 3 - -

5-6 154 45 (47)* 4 1 10t- 52 80 (83)* 8 i

*Some of these patients were operated bilateralIy with 1 Charnley and i Spectron prosthesis.

t Incomple te follow-up.

Charnley Versus Spectron: Clinical • Garellicket al. 409

T a b l e 3. F o l l o w - u p S p e c t r o n (n = 204)

Fol low- Clinical Deceased Lost to up Time Examin- Pat ients Fol low- (y) ation (Hips) Revised up (Hips)

I 1 9 6 5 (6 ) 1 1 3 185 12 (14) 3 1 (2)

5-6 160 35 (38)* 4 1 (2) 10-~ 48 74 (81)* 7 1 (2)

*Some of these patients were operated bilaterally wi th 1 Charnley and 1 Spectron prosthesis.

t Incomple te follow-up.

tively, the Harris Hip and pain scores and the percentage of satisfied patients for the Charnley and Spectron cohorts are shown in Table 4. At no time was there a statistically significant difference be- tween the 2 groups (Fisher's exact test). Trochan- teric pain was the most f requent cause of dissatisfac- tion. Four of the dissatisfied patients had radiographic signs of loose components (according to the criteria of Harris et al. [17] and Hodgkinson et al. [18]). Consequently, most of the dissatisfied patients had stable implants, and the reason for dissatisfaction was not associated with aseptic loosening.

Complications

Of the 410 replacements, 54 (13%) had a major general complication. The mean age at operat ion among the patients who suffered a major postopera- tive complication was 74 years versus 70 years in the group wi thout complications (P < .01, Mann- Whi tney U test). The mean hospital stay for the patients with a major general complication was 20 days (range, 5-75 days) compared to 15 days (range, 3-49 days) for the remainder (P = .001, Mann- Whi tney U test).

T a b l e 4. C l i n i c a l O u t c o m e

Year and Harris Pain Satisfaction Prosthesis Hip Score Score (%)

1 Year Charnley Spectron

3 Years Charnley Spectron

5-6 Years Charnley Spectron

10 Years Charnley Spectron

83 (23-100) 41 (10-44) 92.9 84 (37-100) 42 (10-44) 92.3

86 34-100) 86 44-100)

86 47-100) 87 35-100)

81 46- i00) 82 34-100)

42 (20-44) 95.1 42 (20-44) 94.6

42 (20-44) 90.9 43 (I 0-44) 94.4*

43 (20-44) 92.3 41 (10-44) 89.5*

*Not significant (Fisher's exact test).

410 The Journal of Arthroplasty Vol. 14 No. 4- June 1999

Two patients suffered sciatic (2 Spectron) and 3 patients peroneal pareses (2 Charnley, 1 Spectron). One of the sciatic pareses was permanent at 5 years. Four patients (1%--2 Charnley, 2 Spectron) had a deep infection, 1 early and 3 late. There was no difference in the major complication rate between the 2 groups.

Dislocation

In the Charnley group, 7 dislocations (4 within hospital stay) and 13 snapping hips were recorded. No dislocations or snapping hips were observed in the Spectron group. Two of the 7 hips with dislocat- ing Charnley hips had a malpositioned cup. No malposition was detected in the remainder. Of patients with Charnley prostheses, 13 reported re- current snapping of the hip. Three of these hips were examined by fluoroscopy: The snapping was found to be associated with transient dislocation. (We speculate but cannot prove that all 13 snapping hips were due to spontaneously reducing disloca- tions.)

The difference in the true dislocation rate be- tween the 2 groups (3.4% in the Charnley and 0% in the Spectron group) was significant (P = .015, Fisher's exact test). If patients with subluxation are included, the Charnley rate was 9.7% versus 0% in the Spectron group (P < .001, Fisher's exact test).

Revisions

Fifteen hips (8 Charnley, 7 Spectron) have been revised: 3 for infection, 3 for malpositioned

components, and 9 for aseptic loosening. Five Charnley femoral prostheses (2.4%) and 4 Spectron acetabular components (2%) have been revised for aseptic loosening (Table 5). One Charnley femoral prosthesis and 2 Spectron acetabular prostheses await revision. If these clinically and radiologically loose components are included, the differences in revision for aseptic loosening of cups and stems are significant, the Charnley femoral prosthesis loosen- ing more frequently than the Spectron and the Spectron acetabular prosthesis loosening more fre- quently than the Charnley (P < .03 in each case, Fisher's exact test). Mean time from index operation to revision for aseptic loosening was 75 months (range, 22-126 months).

Survival Analysis

Survival analysis was performed, with revision of I or both components or removal of the implant as the definition of failure. Thus, hips awaiting revi- sion with a radiologic diagnosis of aseptic loosening are not classified as having failed by this definition, whereas hips revised for dislocation or sepsis are classified as failed. The survival rate at 11 years for all hips was 94.5% _+ 3.4% (Fig. 2). Survival for the Charnley prosthesis was 93.2 _+ 5.8% (Fig. 3) and for the Spectronprosthesis 95.9% _+ 3.0% (Fig. 4), a difference that was not significant. Survival rates for the individual components with aseptic loosening as the definition of failure are given in Table 6. Sur- vival of the Charnley femoral prosthesis was less than that of Spectron, but the reverse was true for the acetabulum.

Table 7. Revisions*

No.

Age at Opera-

tion Prosthesis Gender Diagnosis Cause Procedure

Months After

Operation

1 2 3 4 5 6 7 8 9 10 11 12 I3 14 15

74 Charnley Female Arthrosis 66 Spectron Male Arthrosis 68 Spectron Female Hip fracture 70 Charnley Male Arthrosis 65 Spectron Female Arthrosis 69 Chamley Male Arthrosis 40 Spectron Female Avascular necrosis 75 Charnley Female Hip fracture 77 Charnley Female Arthrosis 66 Spectron Female Arthrosis 67 Charnley Male Sequele perthes 76 Spectron Male Sequele dysplasia 66 Spectron Female Arthrosis 62 Chamley Female Hip fracture 61 Charnley Female Arthrosis

Malpositioned cup Infection Malpositioned cup Aseptic loosening Aseptic loosening Infection Infection Stem penetration Aseptic loosening Aseptic loosening Aseptic loosening Aseptic loosening Aseptic loosening Aseptic loosening Aseptic loosening

Cup revision Total revision 2 seans Cup revision Stem revision Cup revision Total removal Total removal Stem revision Stem revision Cup revision Stem revision Cup revision Cup revision Stem revision Stem revision

3 3

i6 22 25 37 38 66 77 82 84 85 87 89

126

*One Chamley stem and 2 Spectron cups on the waiting list for revision because of aseptic loosening.

100

95

90

¢rcent survivors

85 ' 2 . . . . 7 g ' 1 ' 0 ' 0 l 3 4 5 6 9 11

years

number at risk: 410 396 379 370 351 329 303 283 250 189 107 45

Fig. 2. Eleven-year survival rate for all hips with revision or removal as failure endpoint: 94.5% _+ 3.4%. 95% confidence limits and number at risk are shown.

CharnleyVersus Spectron: Clinical • Garellick et al. 411

percent survivors 100

95

90

[ _ _

85 0 I 2 3 4 5 6 9 10 11

years

number at risk: 204 197 190 186 177 167 152 141 130 95 48 25

Fig. 4. Eleven-year survival rate for Spectron hips with revision or removal as failure endpoint: 95.9% -+ 3.0%. 95% confidence limits and number at risk are shown.

D i s c u s s i o n

It is m a n d a t o r y to pe r fo rm prospective and ran- domized studies w h e n n e w surgical techniques or implants are evaluated [ 1,19]. In this study, a new implant system (Spectron) was compared with an accepted reference, the Charnley prosthesis, which over the years has been the most used hip implant in Sweden {13,14]. The clinical results were similar in the 2 compared groups. Traditional scoring sys- tems, however , are not sensitive enough to identify minor differences in outcome. This issue and the variable results obta ined in the different Charnley categories have been discussed in detail in a separate publicat ion {20].

percent survivors 100

95

90

t ~ _ I - - [ _ _ _

]

85 i i i I i i i i i I J

0 1 2 3 4 5 6 7 8 9 10 11

years

numberatrisk: 206 199 189 184 174 162 151 142 120 94 59 20

Fig. 3. Eleven-year survival rate for Charnley hips with revision or removal as failure endpoint: 93.2% -+ 5.8%. 95% confidence limits and number at risk are shown.

Hedlundh et al. [21,22] have publ ished retrospec- tive mul t icenter studies of dislocations after THA. They found a higher rate of early dislocation of Charnley prostheses operated by a posterior (Moore) approach compared to those operated by the origi- nal technique, including t rochanter ic osteotomy. There was, however , no correlat ion be tween surgi- cal approach and late or recurrent dislocation. In a s tudy including 6,062 THAs with ei ther a 32- ram or 22 . 2 -mm head (Lubinus vs Charnley), they found a 2.3 times higher risk for recurrent dislocation if the small head was used and a significantly increased dislocation rate associated with inexper ienced sur- geons and hip fracture as the index diagnosis. All hips in the current study were exposed by a standard- ized lateral, transgluteal approach. Age and diagno- sis were similar in the 2 implant groups. Most of the patients with a manifest or transient dislocation in our study had osteoarthrosis and were operated on by an experienced surgeon. These results speak in favor of the 32-ram head for prevention of dislocation after THA. A biomechanical relationship be tween increased stabil- ity and a large femoral head has been repor ted [23]. Clinical results have not conf i rmed this observat ion

T a b l e 6. S u r v i v o r s h i p A c c o r d i n g to K a p l a n - M e i e r a t 11 Y e a r s

Group S u r v i v a l (%) No.

All r ev i s ions Asep t i c l o o s e n i n g C h a r n l e y - - a l l r ev i s ions C h a r n l e y asep t ic l o o s e n i n g - - c u p C h a r n l e y asep t ic l o o s e n i n g s t e m S p e c t r o n - - a l l r ev i s ions Spec t ron asep t ic l o o s e n i n g - - c u p Spec t ron asep t ic l o o s e n i n g - - s t e m

94.5 -+ 3.4 410 96.0 _+ 3.2 410 93.2 -+ 5.8 206

100 206 94.8 + 5.7 206 95.9 _+ 3.O 204 97.4 ± 2.5 2O4

100 204

412 The Journal of Arthroplasty Vol. 14 No. 4 June 1999

{24-27], but so far no earlier randomized study of this subject has been performed.

Metal-backing was shown by finite-element analy- sis [4,5] to produce a more even distribution of stress in the cement mant le and acetabulum, raising the hope that the rate of late aseptic loosening might be reduced. The biomechanical predictions have not been conf i rmed in mid - t e rm to long- te rm in vivo studies [28-30]. The reason for the inferior results of meta l -backing is probably multifactorial. Part of the cause may be the th inner polyethylene liner, wi th inferior wear properties. Wear be tween the liner and the meta l shell because of poor conformity might increase the a m o u n t of polyethylene debris. In the Spectron group, a 32- ram head was used, which is associated wi th increased vo lumet r ic wear [31,32]. Compared to the Charnley prosthesis wi th the smaller head articulating on a m u c h thicker layer of polyethylene, there are several factors producing a m u c h higher a m o u n t of wear particles.

In vitro studies have shown that a flanged cup is able to create a m u c h higher pressure on setting bone cement and that this pressure is main ta ined th roughou t the polymerizat ion [33]. Hodgkinson et al. [34] and Wroblewski and Siney [35] have shown superior long- te rm radiographic and clinical results wi th the flanged compared to the unf langed compo- nent. Another contr ibuting factor to the difference in cup revisions might be that larger-circumference femoral heads have been shown to create greater frictional torque {36,37] and hence higher stresses on the b o n e - c e m e n t interface.

It is more difficult to explain the difference in s tem revisions, but one possibility is that it is more technically demanding to insert and position the Charnley s tem compared to the longer, collared Spectron stem. Fur thermore , it is more difficult to achieve and reproduce adequate cement mant les a round the Cham l ey s tem w h e n using the original, quite unsophisticated, ins t rumenta t ion , perhaps es- pecially in the absence of t rochanter ic osteotomy. Because the cemen t ing t echn ique was similar th roughou t the present study, our findings suggest that m o d e r n ins t ruments are impor tan t for the optimal fixation of cemented stems. To wha t extent the collared s tem design and quality of the cement mant le contr ibuted to the difference in s tem revi- sion is fur ther discussed in a subsequent article regarding the radiographic results of this trial.

Conclusion

There were no clinical ou tcome differences, mea- sured by Harris Hip Score or pat ient subjective

satisfaction, be tween the 2 systems. The Charnley prosthesis, inserted wi thou t t rochanter ic osteotomy, had a significantly increased rate of dislocation. The revision rate because of aseptic loosening was in- creased for the Charnley s tem and the meta l -backed Spectron cup. The study did not confirm the hypoth- esis of an improved mechanica l stability of a metal- backed cup. We found an increased survival rate for the Spectron stem, and the reason for this is prob- ably multifactorial. The Charnley ogee cup and the Spectron s tem have pe r fo rmed remarkab ly well with no revision of these componen t s after 7 to 1 I years. The overall results, wi th a survival rate of 94.5% after 11 years in this old popula t ion opera ted with con tempora ry technique, illustrate that ce- men t ed hip ar throplasty is an excellent t r ea tment for the elderly pat ient wi th hip disease.

The newly int roduced implant system (Spectron) had a l 1-year survivorship of 95.9% + 3.0% compared to 93.2% _+ 5.8% for the control system (Charnley). The difference is not statistically signifi- cant, and bo th systems mee t the suggested National Institutes of Health [38] definition of efficacy of a hip replacement .

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