The Journal of Arthroplasty Vol. 11 No. 1 1996
Heterotopic Ossification Incidence in Cemented versus Cementless Total Hip Arthroplasty J a m e s J. P u r t i l l , M D , K e n n e t h
E n g , M S , R i c h a r d H. R o t h m a n ,
a n d W i l l i a m J. H o z a c k , M D
Abstract: To resolve the debate whether cementless total hip arthroplasty (THA) carries an increased risk of heterotopic ossification (HO) as compared with cemented THA, 100 patients undergoing primary cemented THA (both acetabulum and femur) were individually matched to I00 patients undergoing primary cementless THA. Preoperative, 6-week postoperative, and 2-year postoperative radiographs were reviewed for the presence of HO using the Brooker classification. No subject in either group received any postoperative prophylaxis for HO. The matching parameters were age (_+ 10 years), sex, weight (+_ 10 lb.), diagnosis (all were osteoarthritis), Charnley class (A/B), and surgical approach (trochanteric osteotomy or modified Hardinge). The overall incidence of HO was 68% in the cemented group and 65% in the cementless group. The extent of HO (grade III) was significant in 9% of the cemented group and 5% of the cementless group. There was no grade IV HO (bone ankylosis) in either group. Neither the overall incidence nor the incidence of grade III HO was statistically different between the two groups. Patient sex and surgical approach had no interactive effect with type of component fixation on the incidence of HO. Fear of HO should not be a factor in the choice of fixation for THA. Key words: heterotopic bone, ectopic bone, total hip arthroplasty, cemented versus cementless.
HO has b e e n f o u n d to occur at similar, 27-29 increased, 14,26,3° and decreased rates 3 compared with cemented THA. In light of this discrepancy, the relative risk of type of c o m p o n e n t fixation on the d e v e l o p m e n t of IdO needs to be more clearly defined. TWo studies have specifically compared c e m e n t e d and cementless fixation as it relates to the incidence of HO. Unfortunately, they f o u n d contrasting results. 30,3~ In an attempt to eliminate or control for those variables that m a y influence rates of HO, we compared the incidences of HO using m a t c h e d groups and including only those with osteoarthritis receiving no HO prophylaxis. In so doing, we tried to resolve the debate over w h e t h e r cementless THA carries an increased risk of HO as compared with cemented THA.
Heterotopic ossification (HO) is a well-documented complication of cemented total hip arthroplasty (THA). Risk factors have been identified such as h y p e r t r o p h i c osteoarthritis, l-4 ankylosing spondylitis, 4-s male sex, ~,4,9-12 certain surgical approaches,< I3<8 development of HO following a contralateral THA, 1,3 4. 1. 0. .1 9 2 0 and advanced age. 9,2x,22 The distribution of these factors in study populations at least partly accounts for the wide range of incidences (5-90%) reported.l,3,4Al, 12,1
From The Rothman Institute, Philadelphia, Pennsylvania.
Reprint requests: William J. Hozack,MD, The Rothman Institute, 800 Spruce Street, Philadelphia, PA 19107.
HeterotopicOssificationin THA Materials and Methods Subjects In this retrospective matched-pair analysis, a series of I00 patients w h o u n d e r w e n t primary c e m e n t e d THA (both acetabulum and femur) from May 1985 to July 1987 were selected and individually m a t c h e d to 100 patients w h o u n d e r w e n t prim a r y cementless THA (both a c e t a b u l u m and femur) from December 1986 to N o v e m b e r 1990 at one institution. For both c e m e n t e d and cementless groups, inclusion in the study was limited to those with a diagnosis of osteoarthritis with either unilateral arthritis (Charnley class A) 25 or bilateral arthritis with this being the first side operated on (Charnley class B). Patients w i t h o t h e r disabilities impairing ambulation (Charnley class C) were excluded. The matching parameters were age (_+ l0 years), sex, weight (_+ 10 lb.), diagnosis (all were osteoarthritis), Charnley class (A or B), and surgical a p p r o a c h (trochanteric o s t e o t o m y or modified Hardinge). For all patients, hospital charts (specifically, doctor's orders and medication cardex) as well as clinical office charts were reviewed to ensure that no one received prophylaxis for HO in the form of radiation treatments, indomethacin, or other n o n steroidal antiinflammatory medication in the postoperative period. Attention was given to patients' histories to be certain that no prior surgical procedures had b e e n p e r f o r m e d to the hip in question and that there was no history of fracture, post-traumatic arthritis, or other comorbid orthopaedic condition (such as ankylosing spondylitis or Paget's disease). Postoperative complications were recorded.
Components and Operative and Postoperative Regimens The decision to use a c e m e n t e d or u n c e m e n t e d prosthesis was based largely on the standard prosthesis being used at this institution at the time the patient u n d e r w e n t surgery. In the early years of the study, c e m e n t e d hips were used with a gradual transition to cementless technology. All operations were p e r f o r m e d in an ultracleanair enclosure with body isolator systems Surgical approach was t h r o u g h either trochanteric o s t e o t o m y or gluteus medius splitting approach (EIardinge). In the c e m e n t e d group, all patients received the Pennsylvania femoral stem and acetabular components (Biomet, Warsaw, IN). Femoral cementation incorporated the techniques of endosteal curettage,
Purtill et al.
insertion of a distal c e m e n t restrictor, pulsatile lavage, and retrograde injection u n d e r pressure of centrifuged cement. For the acetabulum, the techniques of subchondral bone retention, placement of multiple small anchoring holes, pulsatile lavage, meticulous drying of b o n y surfaces, and pressurization of centrifuged c e m e n t were used. In the cementless group, all patients received the Taperloc femoral c o m p o n e n t and the Universal Cup acetabular c o m p o n e n t (Biomet). For the femoral component, after sequential broaching to a firm, snug fit, the final prosthesis is inserted with firm impaction (no endosteal reaming is required). The acetabular c o m p o n e n t is inserted after reaming the acetabular bed with h e m i s p h e r i c a l reamers. Routinely, at least two t i t a n i u m screws are inserted t h r o u g h the holes of the cup for s u p p l e m e n t a l fixation. Patients in both groups had suction drains, which were r e m o v e d on postoperative day 2. All patients w h o received a c e m e n t e d hip were allowed to weight bear fully using crutches or a walker for 6 weeks, t h e n advance to a cane. All patients w h o received a cementless hip w e r e requested to maintain weight bearing on the limb at only 10% for 6 weeks, at which time they were advanced to a cane. For t h r o m b o e m b o l i s m prophylaxis, a low-dose warfarin protocol was employed in which 10 mg was given on the night of surgery; the dose was t h e n adjusted daily to maintain the p r o t h r o m b i n time b e t w e e n 14 and 16 seconds. Knee-high elastic compressor stockings were w o r n by the patient. All patients were ambulated the day after surgery and encouraged to perform exercises of the calf, thigh, and buttock.
Radiographic Evaluation Anteroposterior radiographs of the pelvis and hip and frog leg lateral radiographs t a k e n before surgery, 6 weeks after surgery, and at 2 years (mean, 2.5 years; range, 1.1-5.4 years) w e r e reviewed for the presence of HO using the Brooker classification 24 (0 = no HO, I = islands of bone within the soft tissues about the hip, II = bone spurs from the pelvis or proximal end of the femur leaving at least 1 cm b e t w e e n the opposing bone surfaces, III= bone spurs with less t h a n i cm b e t w e e n opposing bone surfaces, and IV = bone ankylosis of the hip). Leg holders were e m p l o y e d to accurately position the limb for sequential radiographic review. Data analysis (chi-square, with Yates' correction w h e r e appropriate, and t-tests) was p e r f o r m e d on
The Journal of Arthroplasty Vol. 11 No. 1 January 1996
a n IBM LAN server using the SAS statistical softw a r e package (Cary, NC).
the cementless group. Estimated blood loss was higher in the c e m e n t e d group (811 vs 712 mL m e a n ) , as was the surgical time (2.3 vs 2.0 hours). Postoperative complications for the two groups w e r e similar. Complications a n d s u b s e q u e n t grade of HO developed are listed in Table 2. None of these was associated w i t h an increase in the rate or degree of HO. There was one superficial infection, in the c e m e n t e d group treated with irrigation a n d drainage, w i t h grade III HO. A b r o k e n drain in the same group necessitated a w o u n d exploration; this patient developed grade I HO. There w e r e n o dislocations in either group. The extent of HO in each group is s h o w n in Table 3. Statistical analysis revealed no difference b e t w e e n the two groups (chi-square = 2.708, P > .05). The overall incidence of HO was 6 8 % in the c e m e n t e d group a n d 6 5 % in the u n c e m e n t e d group. The extent of HO (grade III) was significant in 9% of the c e m e n t e d group a n d 5% of the uncem e n t e d group. There w a s no grade IV HO (bone ankylosis of the hip) in either group. Neither the overall incidence n o r the incidence of grade III HO
Results Patient demographics were very similar for b o t h groups and are s u m m a r i z e d in Table 1. In each group there were 69 w o m e n and 31 men. Eighty-eight patients were C h a m l e y class A and 12 were in Charnley class B. The m e a n age was 70.4 years (range, 54-83 years) in the c e m e n t e d group and 72.5 years (range, 58-89 years) in the cemenfless group. The m e a n weight in each group was 151 lb. (range, 100-221 lb. in the c e m e n t e d group, 99-219 lb. in the cementless group) and the m e a n height was 65 inches (range, 55-73 inches in the cemented group, 57-74 inches in the cementless group). Of the demographics, only age showed a statistical difference. Trochanteric o s t e o t o m y was used in 55 patients in each group. Spinal anesthesia was used for 88 patients in the c e m e n t e d group and 96 patients in
T a b l e 1. Patient D e m o g r a p h i c s
Matching variables Age (years) Sex (M/F) Weight (lb.) Preoperative Charnley class (A/B) Surgical approach (Hardinge/trochanteric osteotomy) Other variables Height (inches) Operative time (hours) Estimated blood loss (mL) Anesthesia (spinal/general)
72.5 (58-89) 31/69 151.1 (100-221) 88/12 45•55
70.4 (54-83) 31/69 151.5 (99-219) 88/12 45•55
< .0251 NS NS NS NS
65.0 (55-73) 2.3 (1.3-3.0) 811 (250-4,000) 88/12
65.4 (57-74) 2.0 (1.0-4.0) 712 (200-1,200) 96•4
NS < .0001 < .0289 NS
Values in parentheses are ranges. NS, not significant.
T a b l e 2. Postoperative C o m p l i c a t i o n s No. of Occurrences (Subsequent Grade of Heterotopic Ossification) Cemented
Complication High probability, ventilation-perfusion scan Nonpurulent wound drainage Urinary retention Urinary tract infection Deep vein thrombosis Myocardial infarct Ileus Superficial infection with irrigation and drainage Broken drain with wound exploration Pseudogout in the knees
8 (0=2, I=3, II=2, III=l) 7 (0=2, II=4, III=l) 6 (0=3, I=1, II=l, III=l)
8 (0=5, II=2, III=l) 6 (0=2, II=4) 4 (0=1, I=2, III=l)
3 (0=1, III=2) I (I)
3 (0=1, II=2) 1 (II)
1 1 1 1 1
0 0 0 0 0
(I) (II) (In) (I) (0)
Heterotopic Ossification in THA
Cemented TfIA Cementless THA
Chi-square = 2.708, P = .439.
w a s statistically d i f f e r e n t b e t w e e n t h e t w o g r o u p s . P o w e r a n a l y s i s r e v e a l e d a 9 9 % c h a n c e of d e t e c t i n g a d i f f e r e n c e of 2 5 % o r m o r e (the d i f f e r e n c e in t h e o c c u r r e n c e of g r a d e III/IV HO b e t w e e n c e m e n t e d a n d c e m e n t l e s s f i x a t i o n in o n e study30).
Discussion This a n a l y s i s of HO c o m p a r i n g c e m e n t e d a n d cementless THA using matched groups demons t r a t e d n o d i f f e r e n c e i n t h e i n c i d e n c e of r i O ( o v e r all a n d B r o o k e r g r a d e III/IV). I n a d d i t i o n , p a t i e n t sex a n d surgical a p p r o a c h h a d n o i n t e r a c t i v e effect w i t h t y p e of c o m p o n e n t f i x a t i o n o n t h e i n c i d e n c e o r s e v e r i t y of HO. N o n e of t h e p o s t o p e r a t i v e c o m p l i c a t i o n s e n c o u n t e r e d p r e d i s p o s e d t h e p a t i e n t to t h e d e v e l o p m e n t of HO. A l t h o u g h n o t specifically m a t c h e d for t h e c o m p a r i s o n , m a l e s e x w a s a g a i n s h o w n to b e a signific a n t risk factor for t h e d e v e l o p m e n t of HO. I n a d d i tion, t h e H a r d i n g e a p p r o a c h , w h i c h h a d p r e v i o u s l y b e e n s h o w n to i n c r e a s e t h e r a t e of HO c o m p a r e d w i t h t r o c h a n t e r i c o s t e o t o m y , 13 h a d n o d e t r i m e n t a l effect o n t h e d e v e l o p m e n t of HO i n this series.
Surgical Approach F o r p a t i e n t s u n d e r g o i n g THA u s i n g t h e H a r d i n g e a p p r o a c h , n o d i f f e r e n c e w a s f o u n d in t h e o v e r a l l i n c i d e n c e (67 vs 6 4 % ) o r t h e i n c i d e n c e of g r a d e III/IV HO (4 vs 4 % ) for c e m e n t e d a n d c e m e n t l e s s g r o u p s , r e s p e c t i v e l y . Similarly, p a t i e n t s w h o h a d a t r o c h a n t e r i c o s t e o t o m y s h o w e d n o d i f f e r e n c e in t h e o v e r a l l i n c i d e n c e of HO (69 [ c e m e n t e d ] vs 6 5 % [ c e m e n t l e s s ] ) o r i n c i d e n c e of g r a d e III/IV HO (13 % ] c e m e n t e d ] vs 5 % [ c e m e n t l e s s ] ) (Table 4). If cemented and cementless groups are combined, the surgical approach used did not have a significant effect o n t h e d e v e l o p m e n t of HO ( o v e r a l l o r g r a d e III/IV) (Table 5).
T a b l e 4. Extent of Heterotopic Ossification b y Group a n d Surgical A p p r o a c h
Grade of Heterotopic Ossification
Trochanteric osteotomy Cemented THA Cementless THA Hardinge CementedTHA Cementless THA
17 (30) 19 (35)
20 (36) 13 (24)
11 (20) 20 (36)
7 (13) 3 (5)
38 (69) 36 (65)
15 (33) 16 (36)
13 (29) 14 (3I)
15 (33) 13 (29)
2 (4) 2 (4)
30 (67) 29 (64)
Values represent number (%) of patients.
T a b l e 5. Extent of Heterotopic Ossification b y Surgical A p p r o a c h
Grade of Heterotopic Ossification Hardinge Trochanteric osteotomy
M e n w e r e s i g n i f i c a n t l y m o r e l i k e l y to d e v e l o p HO t h a n w o m e n (81 vs 6 0 % ; c h i - s q u a r e w i t h Yates' c o r r e c t i o n = 7.176, P < .007) as w e l l as to d e v e l o p m o r e s i g n i f i c a n t a m o u n t s of HO ( g r a d e III: 15 vs 4 % ; c h i - s q u a r e w i t h Yates' c o r r e c t i o n = 6.214, P = .013). If, h o w e v e r , m e n a n d w o m e n a r e c o n sidered separately, neither the overall incidence nor t h e i n c i d e n c e of g r a d e III HO w a s d i f f e r e n t b e t w e e n c e m e n t e d a n d c e m e n t l e s s g r o u p s (Table 6).
Grade of Heterotopic Ossification (%) I
Purtill et al.
T a b l e 3. Extent of Heterotopic Ossification b y Group
31 (34) 36 (33)
27 (30) 33 (30)
28 (31) 31 (28)
4 (4) 10 (9)
Chi-square = 1.714, P = .634. Values represent number (%) of patients.
The Journal of Arthroplasty Vol. 11 No. 1 January 1996 T a b l e 6. E x t e n t
of Heterotopic Ossification by Sex and Surgical Approach Grade of Heterotopic Ossification
Men Cemented THA Cementless THA Women Cemented THA Cementless THA
5 (16) 7 (23)
10 (32) 10 (32)
12 (3) 9 (29)
4(13) 5 (16)
26 (84) 24 (77)
28 (41) 27 (39)
17 (25) 23 (33)
24 (35) 14 (20)
0 5 (7)
41 (59) 42 (61)
Values represent number (%) of patients.
The etiology of HO r e m a i n s unclear. A possible source of the ectopic osteoblast a n d its inducing a g e n t is the stromal tissue of the b o n e m a r r o w . 32 Extensive f e m o r a l canal reaming, necessary for initial stability in m a n y u n c e m e n t e d THA systems, could potentially be a source for seeding of these b o n e m a r r o w e l e m e n t s 2 8 In addition, b o n e m a r r o w debris n o r m a l l y sealed in the f e m o r a l canal by c e m e n t in c e m e n t e d THA could escape the m a r r o w cavity a n d e n t e r the periarticular tissue in cementless T H A ) 0 This suggests that t h e r e is the p o t e n t i a l for an increase in HO following c e m e n t less THA. M a l o n e y et al. f o u n d support for this theoretical increase in HO in c o m p a r i n g c e m e n t e d a n d cementless fixation for THA. 30 They d e m o n s t r a t e d a significantly higher incidence and severity of HO using a cementless femoral c o m p o n e n t as opposed to a c e m e n t e d femoral c o m p o n e n t ; however, all patients in this study h a d an u n c e m e n t e d acetabular c o m p o n e n t , so c o m p a r i s o n of purely c e m e n t e d verses cementless fixation is impossible. In addition, patients in the cementless group w e r e significantly y o u n g e r t h a n those in the c e m e n t e d group, a factor that has the potential to affect HO. 9,21,22 In contrast, Duck and Mylod found no significant difference in the incidence of HO comparing individuals u n d e r g o i n g c e m e n t e d or cementless THA, hemiarthroplasty, or surface arthroplasty. 31 They included patients with various preoperative diagnoses (avascular necrosis, osteoarthritis, hip fracture, r h e u m a t o i d arthritis), as well as patients undergoing revision surgery. In addition, half received aspirin for t h r o m b o e m b o l i s m prophylaxis, which m a y decrease HO. 33 Confounding variables m a k e it difficult to draw a strong conclusion from this study. This study was p e r f o r m e d in an a t t e m p t to m o r e clearly d e t e r m i n e the effect of type of c o m p o n e n t fixation on the d e v e l o p m e n t of HO in THA. Limiting the analysis to those with osteoarthritis undergoing p r i m a r y THA w i t h o u t HO prophylaxis a n d m a t c h i n g individual subjects b e t w e e n the t w o
groups w e r e necessary for the following reasons: to h a v e demographically comparable groups, to control for factors possibly affecting the d e v e l o p m e n t of n o (such as age, sex, and diagnosis) by ensuring equal distribution in b o t h groups, and to isolate the variable in question (ie, c e m e n t e d vs cementless c o m p o n e n t fixation) as the only significant difference b e t w e e n the two groups. In contrast to M a l o n e y and colleagues' comparison, 30 all patients in this study received the same type of fixation for b o t h a c e t a b u l u m and femur. A l t h o u g h the groups w e r e statistically different for age in b o t h studies, the difference was small in this one. Duck a n d Mylod's analysis contained patients w i t h r h e u m a t o i d arthritis, a v a s c u l a r necrosis, acute fractures, a n d osteoarthritis u n d e r g o i n g THA, hemiarthroplasty, or surface arthroplasty, as well as revision procedures, w h e r e a s this study included only those with osteoarthritis u n d e r g o i n g p r i m a r y THA. 31 Subjects in this study w e r e carefully r e v i e w e d to be certain that n o n e h a d received nonsteroidal a n t i i n f l a m m a t o r y drugs or radiation for HO prophylaxis, as o p p o s e d to Duck and Mylod's study, in w h i c h half received aspirin after surgery.
Conclusion This retrospective study, carefully controlled for HO risk factors, m o r e clearly compares the effect of the type of c o m p o n e n t fixation as it relates to the HO. This study offered no support for the t h e o r y that cementless fixation for THA increases the risk of HO. Fear of HO should not be a factor in the choice of fixation for THA.
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