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Cementless total hip arthroplasty in young Chinese patients
The Journal of Arthroplasty Vol. 16 No. 7 2001
Cementless Total Hip Arthroplasty in Young Chinese Patients A Comparison of 2 Different Prostheses K. Y. Chiu, FHKAM (Ortho Surg), W. M. Tang, FHKAM (Ortho Surg), T. P. Ng, FHKAM (Ortho Surg), K. C. Poon, FRCS (Ed), W. Y. Ho, FRCS (Ed), and K. M. Lee, AFRCSE (Ed)
Abstract: Sixty-one primary cementless total hip arthroplasties were performed in 45 Chinese patients ⬍40 years old. There were 27 Anatomic Medullary Locking (AML, Depuy, Warsaw, IN) prostheses and 34 Porous Coated Anatomic (PCA, Howmedica, Rutherford, NJ) prostheses. The average follow-up was 7.6 years (range, 3–11 years). Ten hips (16%) were reoperated; the reason was polyethylene wear with or without osteolysis in 7 hips. Osteolytic lesion was present in 34 hips (56%). The cumulative successful rate at 10 years was 67% using reoperation for any reason as the endpoint. The cumulative successful rate was 98%, however, if revision for aseptic loosening was used as the endpoint. The 2 prostheses did not show significant differences in most parameters except that the PCA hips had significantly more acetabular loosening (P ⫽ .02) and periprosthetic osteolysis (P ⫽ .01). Key words: total hip arthroplasty, cementless, young, Chinese.
Revision is more likely in total hip arthroplasty (THA) in young patients with higher functional demands and longer life expectancy. Early studies of cemented THA in young patients showed high rates of failure [1–5]. Later studies showed improved results with specific prostheses, such as Charnley low-friction arthroplasty [6 –10], or with improved cementing techniques used on the femoral side [11–13]. Loosening of the cemented ace-
tabular component continues to be a problem, however, in this group of patients. To gain more long-lasting fixation of the components in young patients, cementless THA prostheses have been developed. The published reports on cementless THA in young patients comprised white patients [14 –19]. There were no attempts to compare the outcomes of 2 different cementless THA systems in any of these series. The present study reviews and analyzes the results of primary cementless THA in a group of Chinese patients ⬍40 years old. The medium-term outcomes of 2 widely used cementless THA systems were compared.
From the Division of Joint Replacement Surgery, Department of Orthopaedic Surgery, The University of Hong Kong, Queen Mary Hospital, Pokfulam, Hong Kong. Submitted May 18, 2000; accepted April 18, 2001. No benefits or funds were received in support of this study. Reprint requests: K. Y. Chiu, FHKAM (Ortho Surg), Division of Joint Replacement Surgery, Department of Orthopaedic Surgery, The University of Hong Kong, Room 516, Professorial Block, Queen Mary Hospital, Pokfulam, Hong Kong. E-mail: [email protected] Copyright © 2001 by Churchill Livingstone威 0883-5403/01/1607-0008$35.00/0 doi:10.1054/arth.2001.25505
Materials and Methods Between 1987 and 1995, 68 unselected, consecutive THAs were performed in 50 Chinese patients ⬍40 years old at this institution. The prosthesis was inserted without cement in every hip. Five patients
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864 The Journal of Arthroplasty Vol. 16 No. 7 October 2001 were excluded from the present study: 2 had incomplete clinical and radiologic documentation, and 3 were lost to follow-up. This left 61 hips in 45 patients available for evaluation. There were 25 men and 20 women. The mean age was 33 years (SD, 6 years; range, 22– 40 years) at the time of the index operation. The average follow-up was 7.6 years (SD, 2.0 years; range, 3–11 years). The preoperative diagnosis was avascular necrosis in 36 hips, ankylosing spondylitis in 10, rheumatoid arthritis in 4, juvenile chronic arthritis in 4, previous tuberculosis in 2, post-traumatic arthritis in 1, primary osteoarthritis in 1, congenital dislocation in 1, Legg-Calve´-Perthes disease in 1, and poliomyelitis in 1. Assessing preoperative disability according to Charnley [20], 7 hips were in category A (involvement of only 1 hip), 44 hips were in category B (bilateral hip involvement), and 10 hips were in category C (other factor contributed to the failure to achieve normal locomotion). The low number of category A patients was due to the bilaterality of the predominant hip diseases. The patients had high levels of activity after surgery. Using the scale proposed by Gustilo and Burnham [21], no THA was performed in type 1 (sedentary and able to walk occasionally but only indoors) patient. There were 6 type 2 (can engage in nonstressful activity and able to walk but only for a limited distance) patients (13%), 26 type 3 (can perform moderately stressful activities, including some sports and full-time working and home-making) patients (58%), and 13 type 4 (active, engaging in vigorous sports activities or strenuous manual labor) patients (29%). Four surgeons with equivalent experience performed the operations. There was no significant difference between the distributions of the 2 prostheses among the surgeons (P ⫽ .31). The prostheses used were Anatomic Medullary Locking (AML, Depuy, Warsaw, IN) for 27 hips and Porous Coated Anatomic (PCA, Howmedica, Rutherford, NJ) for 34 hips. All the acetabular components were 2-piece, modular designs. Two types of trispiked AML acetabular components were used; 9 AML plus acetabular components were inserted before 1991, and 18 Duraloc acetabular components were inserted thereafter. The hip balls were 28 mm in diameter for the AML hips and 26 mm in diameter for the PCA hips. The sizes of the components used are shown in Table 1. On the acetabular side, 33% of the AML components and 38% of the PCA components were ⬍50 mm in diameter. On the femoral side, 89% of the AML components were ⱕ13.5 mm in diameter, and 79% of the PCA components were size 3 or less. The posterior approach
Table 1. Sizes of the Components Used for the PCA and AML Hips
Acetabular components Femoral components
PCA (n ⫽ 34)
AML (n ⫽ 27)
Size
No. (%)
Size
No. (%)
46–49 mm 52–55 mm ⱖ58 mm
13 (38) 19 (56) 2 (6)
ⱕ50 mm 52–56 mm ⱖ58 mm
9 (33) 14 (52) 4 (8)
Size 1 Size 2 Size 3 Size 4 or larger
2 (6) 9 (26) 16 (47)
ⱕ10.5 mm 12.0 mm 13.5 mm
2 (7) 13 (48) 9 (33)
7 (21)
ⱖ15.0 mm
3 (12)
was used in 44 hips, the transgluteal approach was used in 11 hips, trochanteric osteotomy was used in 2 hips, and the anterolateral approach was used in 4 hips. All patients received prophylactic antibiotics. None of the patients had chemoprophylaxis for thromboembolism or heterotopic ossification. There was no difference in gender (P ⫽ .15), age at the time of the index operation (P ⫽ .28), or preoperative diagnoses (P ⫽ .57) between the AML and PCA hips. The preoperative disability, distribution of the surgical approaches, and activity level after surgery showed no significant difference between the 2 groups. The average follow-up periods were 7.9 years (SD, 2.1 years; range, 3.5–11.5 years) for the PCA hips and 7.3 years (SD, 1.8 years; range, 4.5–11 years) for the AML hips (P ⫽ .28). The patients were assessed using the Harris hip score [22]. The preoperative scores of all hips and the most recent scores of the surviving hips were documented. Standard anteroposterior radiographs of the pelvis and the affected hip were made for all patients, and the serial radiographs were evaluated. The position of the acetabular component was measured using the criteria of Massin et al [23]. The hip center was determined by intersecting 2 lines perpendicular to the midpoints of 2 cords drawn on the rim of the acetabular component. The distance from this point and the teardrop line was recorded as the vertical position, and the distance from Kohler’s line was the horizontal position. The latter was used to assess the amount of any medial protrusion. The Wiberg angle [24] and the opening (abduction) angle of the acetabular component were recorded. Radiologic loosening of the acetabular component was classified according to the criteria of DeLee and Charnley [25] and Hodgkinson et al [26]. An acetabular component was considered to
THA in Young Patients •
be loose if a continuous radiolucent line was evident in all 3 zones or if the acetabular component migrated. Migration of an acetabular component was defined by a change in the opening angle of ⬎8° or a difference in the component position of ⬎3 mm when radiographs were compared [23]. Stress shielding around the femoral component was evaluated using the 2-year radiographs according to the method of Engh and Bobyn [27]. The proximal femur was divided into 4 levels, and each level was divided into medial, lateral, anterior, and posterior sites, giving a total of 16 sites. Bone resorption in a site was considered to be present if the bone appeared darker or thinner compared with the immediate postoperative films. The extent of bone resorption was divided into 4 degrees according to the number of sites involved: none; first degree, if 1 to 4 sites showed resorptive changes; second degree, if 5 to 7 sites showed resorptive changes; and third degree, if ⱖ8 sites showed resorptive changes. Fixation of the femoral component was evaluated according to the criteria described by Engh et al [28]. A femoral component was defined as having fixation by bone ingrowth when there was no subsidence, no reactive line adjacent to the porouscoated portion, endosteal hypertrophy at the distal limit of the porous coating, and proximal bone resorption secondary to stress shielding. For stable fibrous fixation, there was no progressive implant migration, no or minimal proximal atrophy, and no endosteal hypertrophy at the distal limit of the porous coating; there was a nonprogressive reactive line parallel to the porous-coated portion and separated from it by a narrow interval. An unstable femoral component was characterized by progressive component migration, the formation of a distal pedestal at the stem tip, and the presence of reactive lines that tended to diverge from the component surface and progressively widened with time. An osteolytic lesion was defined as a nonlinear radiolucent line of ⬎5 mm. The Judet oblique radiographs were not used, and pelvic osteolysis may have been underestimated [29]. Anteroposterior radiographs were used for this purpose in other reports on cementless THAs in young patients. Heterotopic ossification was graded according to Brooker et al [30]. The polyethylene wear and the wear rate were measured in all hips using the method described by Livermore et al [31]. Survivorship analysis was performed using different endpoints [32]. Endpoints included reoperation for any reason, revision for aseptic loosening, and reoperation for wear with or without osteolysis. Reoperation was advised if the serial radiographs
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showed continuous and rapid linear polyethylene penetration (ⱖ0.5 mm/y for 2 to 3 consecutive years), and wear-through or fracture of the polyethylene liner became a concern. Reoperation was advised if the osteolytic lesion was clearly progressive. Standard errors for the cumulative successful rates and the 95% confidence intervals were calculated [33]. The cumulative successful rates of the acetabular components and femoral components were evaluated separately. The log-rank test was used to compare the effect of the variables on the cumulative survival rates [34].
Results Clinical Results The average preoperative Harris hip score was 42 points (SD, 9 points; range, 23– 60 points). At the latest follow-up, the average Harris hip score for the surviving hips was 93 points (SD, 5 points; range, 76 –99 points). Four patients (4 hips) (7%) complained of pain in the thigh; pain was mild in all cases and did not limit the patients’ activities. There was no significant difference in the preoperative Harris hip score (P ⫽ .10), the Harris hip score at the latest follow-up (P ⫽ .84), and the incidence of thigh pain (P ⫽ .40) between AML and PCA hips. Ten hips (16%) were revised at a mean time of 7 years (SD, 2 years; range, 5–10 years) after the index operation. One hip was revised for aseptic loosening; 7 hips were reoperated for polyethylene wear with osteolysis; 2 hips were revised for late sepsis. The acetabular component alone was revised in 2 hips; the acetabular component and the femoral component were revised in 3 hips; the polyethylene liner and the hip ball were exchanged without changing the metal acetabular component or the femoral component in 5 hips. The reoperation rate did not differ significantly between PCA and AML hips (P ⫽ .53). Radiologic Results For the acetabular components, there was no radiologic demarcation line about 50 of the 61 hips (82%). Three acetabular components had an incomplete radiolucent line, 2 had a complete radiolucent line, and 6 migrated. Seven of 34 PCA acetabular components (21%) and 1 of 27 AML acetabular components (4%) were loose. The difference was statistically significant (P ⫽ .02). The fixation of 39 femoral components (64%) was classified as bone ingrowth. The fixation of 19 femoral components was classified as stable fibrous,
866 The Journal of Arthroplasty Vol. 16 No. 7 October 2001 nents (59%). For the AML hips, osteolytic lesions occurred around 4 acetabular components (15%) and 8 femoral components (30%). All the femoral osteolytic lesions affected Gruen zone 1, zone 7, or both except 1 PCA femoral component that had an osteolytic lesion at zone 2. With regression analysis, the presence of osteolytic lesions was affected by 2 independent variables: the polyethylene penetration rate (P ⫽ .005) and the type of prosthesis (P ⫽ .04). Other variables, including gender, age at operation, body weight, activity level, different surgeons, position, and opening angle of the acetabular component, were not significant. Fig. 1. Survival plots with revision for aseptic loosening (——) and revision for any reason (---) as endpoints (95% confidence intervals shown at yearly intervals).
and 3 femoral components were considered to be unstable. Nineteen of 34 PCA femoral components (56%) and 20 of 27 AML femoral components (74%) were well fixed by bone ingrowth. The difference was not significant (P ⫽ .17). There was no heterotopic ossification in 36 hips (59%). Brooker I heterotopic ossification was found in 21 hips (34%), and Brooker II ossification was found in 4 hips (7%). None of the hips showed Brooker III or IV heterotopic ossification. There was no difference between AML and PCA hips (P ⫽ .97). Bone resorption secondary to stress shielding around the femoral component was not noted in 26 hips (43%). Thirty hips (49%) showed first-degree stress shielding, and 5 hips (8%) showed seconddegree stress shielding. No hip showed third-degree stress shielding. There was no difference between AML and PCA THAs (P ⫽ .68). The average linear penetration rate was ⬍0.1 mm/y in 17 hips (27.9%), 0.1 to 0.2 mm/y in 17 hips (27.9%), and ⬎0.2 mm/y in 27 hips (44.2%). The average linear penetration rate was 0.18 mm/y (SD, 0.17 mm; range, 0 – 0.75 mm) for the PCA hips and 0.20 mm/y (SD, 0.15 mm; range, 0 – 0.67 mm) for the AML hips; the difference was insignificant (P ⫽ .86). We tried to find out whether different surgeons could be responsible. There was no significant correlation with the linear penetration rate, however, after controlling for the prostheses (P ⫽ .53). Osteolytic lesions were found in 34 hips (56%). Ten of 27 AML prostheses (37%) and 24 of 34 PCA prostheses (71%) were affected (P ⫽ .001). The difference was statistically significant. For the PCA hips, osteolytic lesions occurred around 11 acetabular components (32%) and 20 femoral compo-
Survival Analysis Using reoperation for any reason as the endpoint, the cumulative success rates for all the hips were 98% (95% confidence interval [CI], 95–100%) at 5 years and 67% (95% CI, 47– 88%) at 10 years (Fig. 1). There was no difference between PCA and AML hips (Wilcoxon log-rank test; P ⫽ .81). If revision for aseptic loosening was used as the endpoint (failures secondary to sepsis, wear, and osteolysis were excluded), the cumulative success rates were 98% (95% CI, 95–100%) at 5 years and at 10 years (Fig. 1). There was no difference between PCA and AML hips (Wilcoxon log-rank test; P ⫽ .26). If failures resulting from aseptic loosening and sepsis were excluded, and reoperation for wear with or without osteolysis was used as the endpoint, the cumulative survival rate was 100% at the end of 6 years, but it started to decrease at 7 years and became 72% (95% CI, 51–93%) at 10 years (Fig. 2). There was no difference between PCA and AML hips (Wilcoxon log-rank test; P ⫽ .55).
Fig. 2. Survival plot with revision for wear with or without osteolysis as the endpoint (95% confidence intervals shown at yearly intervals).
THA in Young Patients •
Discussion The results of early series on cemented THAs in young patients were not promising. After follow-up of 5 to 10 years, 36% to 69% of hips were revised or had loose components in the radiographs [1–3]. Other studies showed that 9% to 14% of hips were revised for aseptic loosening after only 6 to 8 years [4,5]. More recent series, especially on Charnley low-friction arthroplasty implanted with early cementing techniques, did not concur with such unsatisfactory results [6 –10]. The survival rates of Charnley cemented hips at 20 years were 75% to 88%. In a single-surgeon series, 13% of acetabular components and 2% of femoral components were revised for aseptic loosening after 18 years; the revision rate for aseptic loosening was 19% on the acetabular side and 5% on the femoral side after 20 to 25 years [7,10]. With the use of improved cementing techniques, the revision rate for aseptic loosening of the femoral stem ranged from 0% to 5% after 11 to 13 years [11–13]. Of acetabular components, 36% to 44% were revised or definitely loose on radiographs after 10 to 12 years despite the use of improved cementing techniques [11,12]. Because of concern that young patients will require ⱖ1 revisions for loosening of cemented components, cementless THA has been recommended in this patient group. It was hoped that the biologic fixation achieved with osseointegration at the prosthesis– bone interface would be more durable and
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long-lasting than fixation of components with cement. There were relatively few reports about the results of cementless THAs in young white patients (Table 2). The prostheses being inserted were heterogeneous in some reports and included nonporous ceramic acetabular components, threaded acetabular components, bipolar THAs, and nonporous press-fit femoral components [16,18,19]. When we reviewed the findings of the these reports, we counted only the components that were either porous coated [14 –19] or hydroxyapatite coated [16]. The average follow-up period of these studies were not too long; the longest one was only 8.3 years. From these reports, one could conclude that the objective of using cementless THA to reduce the aseptic loosening rate in young patients was achieved. For young white patients, the chance of having a loose cementless acetabular component ranged from 0% to 11%, and the loosening rates ranged from 0% to 7% for the cementless femoral components after 4 to 8 years. These results were superior to the results being described in the earlier reports of cemented THAs in young patients. Compared with the results with the use of improved cementing techniques, cementless fixation appeared to do better on the acetabular side. Longer follow-up was necessary to determine whether cementless fixation could match the results of femoral components being inserted with improved cementing techniques. In the present series, 13% of the cementless acetabular components and 5% of the cementless
Table 2. Reports on Cementless Total Hip Arthroplasty With Metal–Polyethylene Articulation in Young Patients
Series Mont et al [14], 1993 Piston et al [15], 1994 Capello et al [16], 1997 Dowdy et al [17], 1997 Kronick et al [18], 1997 Fye et al [19], 1998 Present series
No. Patients (Hips)
Mean Age Follow-up Range Period (y) (Range) (y)
Prostheses
Mechanical Failures Thigh Reoperation (%)* Pain Osteolysis for Wear ⫾ (%) (%) Acetabular Femoral Osteolysis (%)
42 (44)
⬍45
4.5 (3–7)
PCA
23
—
2
7
0
30 (35)
21–40
7.5 (5–10)
AML
6
17
6
6
0
133 (152)
16–49
6.4 (5–8.3)
Omnifit-HA†‡
7
33
11
0
5
36 (41)
19–50
5.3 (4–7)
Mallory-Head§
—
29
12
0
2
145 (174)
14–50
8.3 (2–13)
AML/Prodigy†㛳
6
3
2
1
1
52 (66)
⬍50
7.0 (4–12)
Various†
—
3
0
3
0
45 (61)
22–40
7.6 (3–11)
PCA, AML
7
56
13
5
12
*Hip that was revised or pending revision for aseptic loosening or had definite radiographic loosening of a component. †Various components were used; mechanical failure rates were on porous-coated or hydroxyapatite-coated components. ‡Osteonics, Allendale, NJ. §Biomet, Warsaw, IN. 㛳Depuy, Warsaw, IN.
868 The Journal of Arthroplasty Vol. 16 No. 7 October 2001 femoral components inserted in young Chinese patients were considered to be loose after an average follow-up of 7.6 years. The loosening rates of the 2 cementless hip systems were quite different. For AML hips in young Chinese patients, only 4% of the acetabular components and none of the femoral components were loose after an average follow-up of 7.3 years. In the 2 articles that described the outcomes of the AML THA systems in young white patients, the acetabular loosening rate was 2% to 6%, and the femoral loosening rate was 1% to 6% after an average follow-up of 8 years [15,18]. For PCA hips in young Chinese patients, 21% of the acetabular components and 9% of the femoral components were loose after an average follow-up of 7.9 years. Compared with the study reported by Mont et al [14], the aseptic loosening rate of PCA prostheses in young white patients was 2% on the acetabular side and 7% on the femoral side [14]. This difference could be due to the short follow-up of the patients (average 4.5 years). In another article on PCA acetabular components in patients of all ages, 15% showed migration after an average follow-up of ⬍5 years [35]. The loosening rates of cementless total hip prostheses in young Chinese patients were comparable to the reported series on white patients. Although cementless THA had been successful in decreasing the aseptic loosening rate, it created other problems. In young white patients, pain in the thigh affected 6% to 23% of cementless THAs. Most of the pain was mild and did not limit activity. In the current series, only 7% of hips in young Chinese patients had mild thigh pain. Bone resorption in the proximal femur was common after cementless THAs, especially if the femoral component used was extensively porous coated. In the 2 articles on extensively porous-coated THAs in young white patients, 17% to 55% of hips showed significant atrophy of the proximal femur secondary to stress shielding [15,18]. In the present series, significant stress shielding affected 8% of cementless THAs in young Chinese patients. There was no difference between PCA and AML hips. In young white patients, osteolytic lesions were present in 3% to 33% of cementless THAs after 4 to 8 years. In the present series, osteolysis was found in 56% of hips in young Chinese patients after an average follow-up of 7.6 years. If the 2 hip systems were evaluated separately, osteolysis was detected in 37% of AML hips in young Chinese patients after 7.3 years. This rate was higher than the reported rates of 3% to 17% at 8 years with the use of AML prostheses in young white patients [15,18]. For PCA THAs in young Chinese patients, 71% showed
osteolysis after 7.9 years. In the article on the use of PCA prostheses in young white patients reported by Mont et al [14], the presence of osteolytic lesions was not mentioned. In the literature, osteolysis was common after PCA THAs even if older patients were included. Owen et al [36] reviewed 241 PCA THAs in patients ⱕ65 years old. For THAs with follow-up ⬎5 years, 36% showed acetabular osteolysis, and 13% showed femoral osteolysis. Kim et al [37] followed up 116 PCA THAs in 108 patients for an average of 11 years. Despite that only 37 patients were ⬍40 years old, osteolysis was identified in 56% of acetabular components and 59% of femoral components by 11 years. The osteolysis rate of 71% for PCA prostheses in the present report was higher than these reported figures. The occurrence of osteolysis was more common for PCA and AML hips in Chinese patients. One possible explanation was the smaller acetabula in Chinese patients could result in the use of polyethylene that was not thick enough by today’s standard. It was interesting to find out why osteolysis was detected in only 37% of AML THAs, but was found in 71% of PCA THAs in young Chinese patients. This finding could not be explained by the difference in other parameters between the 2 groups. Gender, age at operation, height, weight, preoperative Charnley functional class, preoperative hip disease, preoperative Harris hip score, sizes of the components used, level of activity after the operation, Harris hip score at follow-up, and average length of follow-up did not show any significant differences between the AML and PCA hips. The higher rate of osteolysis after PCA THAs was not because of increased polyethylene wear; the average linear penetration rate was 0.18 mm/y for the PCA THAs and 0.20 mm/y for the AML THAs. It was possible that the polyethylene particles generated at the articulation could be different for the 2 hip systems, or there could be more backside wear in PCA acetabular components. Excessive backside polyethylene damage had been shown with the PCA acetabular components and was attributed to failure of the locking mechanism and incongruent contact between the metal shell and the polyethylene liner [35]. Reoperations for polyethylene wear with or without osteolysis after cementless THAs have been reported [16 –18]. In the present series, 7 of 10 cementless hips that needed reoperation were for polyethylene wear with or without osteolysis (Fig. 3). To avoid catastrophic failures, we advise patients to have exchange of the polyethylene inserts and the hip ball, with or without grafting of the osteolytic lesions, even when there are no symptoms.
THA in Young Patients •
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Fig. 3. A 28-year-old woman suffered from post-traumatic arthritis of the right hip. (A) One year after PCA total hip arthroplasty. (B) Six years later, the hip ball became eccentric, there was cup migration with pelvic osteolysis (small black arrows), and femoral osteolysis with pathologic fracture of the greater trochanter (large white arrow).
Using such criteria, the cumulative survival rates of well-fixed cementless THA prostheses in the present series started to decrease from 7 years onward in a more or less linear manner and became 72% at 10 years. Although cementless THAs resulted in stable and long-lasting fixation, the overall cumulative survival rate at 10 years was not better than cemented THA in young patients.
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870 The Journal of Arthroplasty Vol. 16 No. 7 October 2001
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25.
plasty in young patients using an intramedullary bone block. J Bone Joint Surg Br 80:273, 1998 Mont MA, Maar DC, Krackow KA, et al: Total hip replacement without cement for non-inflammatory osteoarthritis in patients who are less than forty-five years old. J Bone Joint Surg Am 75:740, 1993 Piston RW, Engh CA, de Carvalho PI, Suthers K: Osteonecrosis of the femoral head treated with total hip arthroplasty without cement. J Bone Joint Surg Am 76:202, 1994 Capello WN, D’Antonio JA, Feinberg JR, Manley MT: Hydroxyapatite-coated total hip femoral components in patients less than fifty tears old: clinical and radiographic results after five to eight years of follow-up. J Bone Joint Surg Am 79:1023, 1997 Dowdy PA, Rorabeck CH, Bourne RB: Uncemented total hip arthroplasty in patients 50 years of age or younger. J Arthroplasty 12:853, 1997 Kronick JL, Barba ML, Paprosky WG: Extensively coated femoral components in young patients. Clin Orthop 344:263, 1997 Fye MA, Huo MH, Zatorski LE, Keggi KJ: Total hip arthroplasty performed without cement in patients with femoral head necrosis who are less than 50 years old. J Arthroplasty 13:876, 1998 Charnley J: The long-term results of low-friction arthroplasty of the hip performed as a primary intervention. J Bone Joint Surg Br 54:61, 1972 Gustilo RB, Burnham WH: Long-term results of total hip arthroplasty in young patients. p. 27. In The Hip: Proceedings of the Tenth Open Scientific Meeting of The Hip Society. CV Mosby, St. Louis, 1982 Harris WH: Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. J Bone Joint Surg Am 51:737, 1969 Massin P, Schmidt EA, Engh CA: Evaluation of cementless acetabular component migration. J Arthroplasty 4:245, 1989 Ranawat CS, Zahn MG: Role of bone grafting in correction of protrusio acetabuli by total hip arthroplasty. J Arthroplasty 1:131, 1986 DeLee JG, Charnley J: Radiological demarcation of cemented sockets in total hip replacement. Clin Orthop 121:20, 1976
26. Hodgkinson JP, Shelly P, Wroblewski BM: The correlation between roentgenographic appearance and operative findings at the bone-cement junction of the socket in Charnley low fraction arthroplasties. Clin Orthop 228:105, 1988 27. Engh CA, Bobyn JD: The influence of stem size and extent of porous coating on femoral bone resorption after primary cementless hip arthroplasty. Clin Orthop 231:7, 1988 28. Engh CA, Glassman AH, Suthers KE: The case for porous-coated hip implants: the femoral side. Clin Orthop 261:63, 1990 29. Zimlich RH, Thomas TK: Underestimation of pelvic osteolysis: the value of the iliac oblique radiograph. J Arthroplasty 15:796, 2000 30. Brooker AF, Bowerman JW, Robinson RA, Riley LH Jr: Ectopic ossification following total hip replacement: incidence and a method of classification. J Bone Joint Surg Am 55:1629, 1973 31. Livermore J, Ilstrup D, Morrey B: Effect of femoral head size on wear of the polyethylene acetabular component. J Bone Joint Surg Am 72:518, 1990 32. Dobbs HS: Survivorship of total hip replacements. J Bone Joint Surg Br 62:168, 1980 33. Peto R, Pike MC, Armitage P, et al: Design and analysis of randomized clinical trails, requiring prolonged observation or each patient: II. Analysis and examples. Br J Cancer 35:1, 1977 34. Peto R, Peto J: Asymptotically efficient rank invariant test procedures. J R Statist Soc Series A 135:185, 1972 35. Astison DJ, Saluan P, Stulberg BN, et al: The porouscoated anatomic total hip prosthesis: Failure of the metal-backed acetabular component. J Bone Joint Surg Am 78:755, 1996 36. Owen TD, Moran CG, Smith SR, Pinder IM: Results of uncemented porous-coated anatomic total hip replacement. J Bone Joint Surg Br 76:258, 1994 37. Kim YH, Kim JS, Cho SH: Primary total hip arthroplasty with a cementless porous-coated anatomic total hip prosthesis: 10- to 12-year results of prospective and consecutive series. J Arthroplasty 14:538, 1999
Cementless Total Hip Arthroplasty in Young Chinese Patients A Comparison of 2 Different Prostheses K. Y. Chiu, FHKAM (Ortho Surg), W. M. Tang, FHKAM (Ortho Surg), T. P. Ng, FHKAM (Ortho Surg), K. C. Poon, FRCS (Ed), W. Y. Ho, FRCS (Ed), and K. M. Lee, AFRCSE (Ed)
Abstract: Sixty-one primary cementless total hip arthroplasties were performed in 45 Chinese patients ⬍40 years old. There were 27 Anatomic Medullary Locking (AML, Depuy, Warsaw, IN) prostheses and 34 Porous Coated Anatomic (PCA, Howmedica, Rutherford, NJ) prostheses. The average follow-up was 7.6 years (range, 3–11 years). Ten hips (16%) were reoperated; the reason was polyethylene wear with or without osteolysis in 7 hips. Osteolytic lesion was present in 34 hips (56%). The cumulative successful rate at 10 years was 67% using reoperation for any reason as the endpoint. The cumulative successful rate was 98%, however, if revision for aseptic loosening was used as the endpoint. The 2 prostheses did not show significant differences in most parameters except that the PCA hips had significantly more acetabular loosening (P ⫽ .02) and periprosthetic osteolysis (P ⫽ .01). Key words: total hip arthroplasty, cementless, young, Chinese.
Revision is more likely in total hip arthroplasty (THA) in young patients with higher functional demands and longer life expectancy. Early studies of cemented THA in young patients showed high rates of failure [1–5]. Later studies showed improved results with specific prostheses, such as Charnley low-friction arthroplasty [6 –10], or with improved cementing techniques used on the femoral side [11–13]. Loosening of the cemented ace-
tabular component continues to be a problem, however, in this group of patients. To gain more long-lasting fixation of the components in young patients, cementless THA prostheses have been developed. The published reports on cementless THA in young patients comprised white patients [14 –19]. There were no attempts to compare the outcomes of 2 different cementless THA systems in any of these series. The present study reviews and analyzes the results of primary cementless THA in a group of Chinese patients ⬍40 years old. The medium-term outcomes of 2 widely used cementless THA systems were compared.
From the Division of Joint Replacement Surgery, Department of Orthopaedic Surgery, The University of Hong Kong, Queen Mary Hospital, Pokfulam, Hong Kong. Submitted May 18, 2000; accepted April 18, 2001. No benefits or funds were received in support of this study. Reprint requests: K. Y. Chiu, FHKAM (Ortho Surg), Division of Joint Replacement Surgery, Department of Orthopaedic Surgery, The University of Hong Kong, Room 516, Professorial Block, Queen Mary Hospital, Pokfulam, Hong Kong. E-mail: [email protected] Copyright © 2001 by Churchill Livingstone威 0883-5403/01/1607-0008$35.00/0 doi:10.1054/arth.2001.25505
Materials and Methods Between 1987 and 1995, 68 unselected, consecutive THAs were performed in 50 Chinese patients ⬍40 years old at this institution. The prosthesis was inserted without cement in every hip. Five patients
863
864 The Journal of Arthroplasty Vol. 16 No. 7 October 2001 were excluded from the present study: 2 had incomplete clinical and radiologic documentation, and 3 were lost to follow-up. This left 61 hips in 45 patients available for evaluation. There were 25 men and 20 women. The mean age was 33 years (SD, 6 years; range, 22– 40 years) at the time of the index operation. The average follow-up was 7.6 years (SD, 2.0 years; range, 3–11 years). The preoperative diagnosis was avascular necrosis in 36 hips, ankylosing spondylitis in 10, rheumatoid arthritis in 4, juvenile chronic arthritis in 4, previous tuberculosis in 2, post-traumatic arthritis in 1, primary osteoarthritis in 1, congenital dislocation in 1, Legg-Calve´-Perthes disease in 1, and poliomyelitis in 1. Assessing preoperative disability according to Charnley [20], 7 hips were in category A (involvement of only 1 hip), 44 hips were in category B (bilateral hip involvement), and 10 hips were in category C (other factor contributed to the failure to achieve normal locomotion). The low number of category A patients was due to the bilaterality of the predominant hip diseases. The patients had high levels of activity after surgery. Using the scale proposed by Gustilo and Burnham [21], no THA was performed in type 1 (sedentary and able to walk occasionally but only indoors) patient. There were 6 type 2 (can engage in nonstressful activity and able to walk but only for a limited distance) patients (13%), 26 type 3 (can perform moderately stressful activities, including some sports and full-time working and home-making) patients (58%), and 13 type 4 (active, engaging in vigorous sports activities or strenuous manual labor) patients (29%). Four surgeons with equivalent experience performed the operations. There was no significant difference between the distributions of the 2 prostheses among the surgeons (P ⫽ .31). The prostheses used were Anatomic Medullary Locking (AML, Depuy, Warsaw, IN) for 27 hips and Porous Coated Anatomic (PCA, Howmedica, Rutherford, NJ) for 34 hips. All the acetabular components were 2-piece, modular designs. Two types of trispiked AML acetabular components were used; 9 AML plus acetabular components were inserted before 1991, and 18 Duraloc acetabular components were inserted thereafter. The hip balls were 28 mm in diameter for the AML hips and 26 mm in diameter for the PCA hips. The sizes of the components used are shown in Table 1. On the acetabular side, 33% of the AML components and 38% of the PCA components were ⬍50 mm in diameter. On the femoral side, 89% of the AML components were ⱕ13.5 mm in diameter, and 79% of the PCA components were size 3 or less. The posterior approach
Table 1. Sizes of the Components Used for the PCA and AML Hips
Acetabular components Femoral components
PCA (n ⫽ 34)
AML (n ⫽ 27)
Size
No. (%)
Size
No. (%)
46–49 mm 52–55 mm ⱖ58 mm
13 (38) 19 (56) 2 (6)
ⱕ50 mm 52–56 mm ⱖ58 mm
9 (33) 14 (52) 4 (8)
Size 1 Size 2 Size 3 Size 4 or larger
2 (6) 9 (26) 16 (47)
ⱕ10.5 mm 12.0 mm 13.5 mm
2 (7) 13 (48) 9 (33)
7 (21)
ⱖ15.0 mm
3 (12)
was used in 44 hips, the transgluteal approach was used in 11 hips, trochanteric osteotomy was used in 2 hips, and the anterolateral approach was used in 4 hips. All patients received prophylactic antibiotics. None of the patients had chemoprophylaxis for thromboembolism or heterotopic ossification. There was no difference in gender (P ⫽ .15), age at the time of the index operation (P ⫽ .28), or preoperative diagnoses (P ⫽ .57) between the AML and PCA hips. The preoperative disability, distribution of the surgical approaches, and activity level after surgery showed no significant difference between the 2 groups. The average follow-up periods were 7.9 years (SD, 2.1 years; range, 3.5–11.5 years) for the PCA hips and 7.3 years (SD, 1.8 years; range, 4.5–11 years) for the AML hips (P ⫽ .28). The patients were assessed using the Harris hip score [22]. The preoperative scores of all hips and the most recent scores of the surviving hips were documented. Standard anteroposterior radiographs of the pelvis and the affected hip were made for all patients, and the serial radiographs were evaluated. The position of the acetabular component was measured using the criteria of Massin et al [23]. The hip center was determined by intersecting 2 lines perpendicular to the midpoints of 2 cords drawn on the rim of the acetabular component. The distance from this point and the teardrop line was recorded as the vertical position, and the distance from Kohler’s line was the horizontal position. The latter was used to assess the amount of any medial protrusion. The Wiberg angle [24] and the opening (abduction) angle of the acetabular component were recorded. Radiologic loosening of the acetabular component was classified according to the criteria of DeLee and Charnley [25] and Hodgkinson et al [26]. An acetabular component was considered to
THA in Young Patients •
be loose if a continuous radiolucent line was evident in all 3 zones or if the acetabular component migrated. Migration of an acetabular component was defined by a change in the opening angle of ⬎8° or a difference in the component position of ⬎3 mm when radiographs were compared [23]. Stress shielding around the femoral component was evaluated using the 2-year radiographs according to the method of Engh and Bobyn [27]. The proximal femur was divided into 4 levels, and each level was divided into medial, lateral, anterior, and posterior sites, giving a total of 16 sites. Bone resorption in a site was considered to be present if the bone appeared darker or thinner compared with the immediate postoperative films. The extent of bone resorption was divided into 4 degrees according to the number of sites involved: none; first degree, if 1 to 4 sites showed resorptive changes; second degree, if 5 to 7 sites showed resorptive changes; and third degree, if ⱖ8 sites showed resorptive changes. Fixation of the femoral component was evaluated according to the criteria described by Engh et al [28]. A femoral component was defined as having fixation by bone ingrowth when there was no subsidence, no reactive line adjacent to the porouscoated portion, endosteal hypertrophy at the distal limit of the porous coating, and proximal bone resorption secondary to stress shielding. For stable fibrous fixation, there was no progressive implant migration, no or minimal proximal atrophy, and no endosteal hypertrophy at the distal limit of the porous coating; there was a nonprogressive reactive line parallel to the porous-coated portion and separated from it by a narrow interval. An unstable femoral component was characterized by progressive component migration, the formation of a distal pedestal at the stem tip, and the presence of reactive lines that tended to diverge from the component surface and progressively widened with time. An osteolytic lesion was defined as a nonlinear radiolucent line of ⬎5 mm. The Judet oblique radiographs were not used, and pelvic osteolysis may have been underestimated [29]. Anteroposterior radiographs were used for this purpose in other reports on cementless THAs in young patients. Heterotopic ossification was graded according to Brooker et al [30]. The polyethylene wear and the wear rate were measured in all hips using the method described by Livermore et al [31]. Survivorship analysis was performed using different endpoints [32]. Endpoints included reoperation for any reason, revision for aseptic loosening, and reoperation for wear with or without osteolysis. Reoperation was advised if the serial radiographs
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showed continuous and rapid linear polyethylene penetration (ⱖ0.5 mm/y for 2 to 3 consecutive years), and wear-through or fracture of the polyethylene liner became a concern. Reoperation was advised if the osteolytic lesion was clearly progressive. Standard errors for the cumulative successful rates and the 95% confidence intervals were calculated [33]. The cumulative successful rates of the acetabular components and femoral components were evaluated separately. The log-rank test was used to compare the effect of the variables on the cumulative survival rates [34].
Results Clinical Results The average preoperative Harris hip score was 42 points (SD, 9 points; range, 23– 60 points). At the latest follow-up, the average Harris hip score for the surviving hips was 93 points (SD, 5 points; range, 76 –99 points). Four patients (4 hips) (7%) complained of pain in the thigh; pain was mild in all cases and did not limit the patients’ activities. There was no significant difference in the preoperative Harris hip score (P ⫽ .10), the Harris hip score at the latest follow-up (P ⫽ .84), and the incidence of thigh pain (P ⫽ .40) between AML and PCA hips. Ten hips (16%) were revised at a mean time of 7 years (SD, 2 years; range, 5–10 years) after the index operation. One hip was revised for aseptic loosening; 7 hips were reoperated for polyethylene wear with osteolysis; 2 hips were revised for late sepsis. The acetabular component alone was revised in 2 hips; the acetabular component and the femoral component were revised in 3 hips; the polyethylene liner and the hip ball were exchanged without changing the metal acetabular component or the femoral component in 5 hips. The reoperation rate did not differ significantly between PCA and AML hips (P ⫽ .53). Radiologic Results For the acetabular components, there was no radiologic demarcation line about 50 of the 61 hips (82%). Three acetabular components had an incomplete radiolucent line, 2 had a complete radiolucent line, and 6 migrated. Seven of 34 PCA acetabular components (21%) and 1 of 27 AML acetabular components (4%) were loose. The difference was statistically significant (P ⫽ .02). The fixation of 39 femoral components (64%) was classified as bone ingrowth. The fixation of 19 femoral components was classified as stable fibrous,
866 The Journal of Arthroplasty Vol. 16 No. 7 October 2001 nents (59%). For the AML hips, osteolytic lesions occurred around 4 acetabular components (15%) and 8 femoral components (30%). All the femoral osteolytic lesions affected Gruen zone 1, zone 7, or both except 1 PCA femoral component that had an osteolytic lesion at zone 2. With regression analysis, the presence of osteolytic lesions was affected by 2 independent variables: the polyethylene penetration rate (P ⫽ .005) and the type of prosthesis (P ⫽ .04). Other variables, including gender, age at operation, body weight, activity level, different surgeons, position, and opening angle of the acetabular component, were not significant. Fig. 1. Survival plots with revision for aseptic loosening (——) and revision for any reason (---) as endpoints (95% confidence intervals shown at yearly intervals).
and 3 femoral components were considered to be unstable. Nineteen of 34 PCA femoral components (56%) and 20 of 27 AML femoral components (74%) were well fixed by bone ingrowth. The difference was not significant (P ⫽ .17). There was no heterotopic ossification in 36 hips (59%). Brooker I heterotopic ossification was found in 21 hips (34%), and Brooker II ossification was found in 4 hips (7%). None of the hips showed Brooker III or IV heterotopic ossification. There was no difference between AML and PCA hips (P ⫽ .97). Bone resorption secondary to stress shielding around the femoral component was not noted in 26 hips (43%). Thirty hips (49%) showed first-degree stress shielding, and 5 hips (8%) showed seconddegree stress shielding. No hip showed third-degree stress shielding. There was no difference between AML and PCA THAs (P ⫽ .68). The average linear penetration rate was ⬍0.1 mm/y in 17 hips (27.9%), 0.1 to 0.2 mm/y in 17 hips (27.9%), and ⬎0.2 mm/y in 27 hips (44.2%). The average linear penetration rate was 0.18 mm/y (SD, 0.17 mm; range, 0 – 0.75 mm) for the PCA hips and 0.20 mm/y (SD, 0.15 mm; range, 0 – 0.67 mm) for the AML hips; the difference was insignificant (P ⫽ .86). We tried to find out whether different surgeons could be responsible. There was no significant correlation with the linear penetration rate, however, after controlling for the prostheses (P ⫽ .53). Osteolytic lesions were found in 34 hips (56%). Ten of 27 AML prostheses (37%) and 24 of 34 PCA prostheses (71%) were affected (P ⫽ .001). The difference was statistically significant. For the PCA hips, osteolytic lesions occurred around 11 acetabular components (32%) and 20 femoral compo-
Survival Analysis Using reoperation for any reason as the endpoint, the cumulative success rates for all the hips were 98% (95% confidence interval [CI], 95–100%) at 5 years and 67% (95% CI, 47– 88%) at 10 years (Fig. 1). There was no difference between PCA and AML hips (Wilcoxon log-rank test; P ⫽ .81). If revision for aseptic loosening was used as the endpoint (failures secondary to sepsis, wear, and osteolysis were excluded), the cumulative success rates were 98% (95% CI, 95–100%) at 5 years and at 10 years (Fig. 1). There was no difference between PCA and AML hips (Wilcoxon log-rank test; P ⫽ .26). If failures resulting from aseptic loosening and sepsis were excluded, and reoperation for wear with or without osteolysis was used as the endpoint, the cumulative survival rate was 100% at the end of 6 years, but it started to decrease at 7 years and became 72% (95% CI, 51–93%) at 10 years (Fig. 2). There was no difference between PCA and AML hips (Wilcoxon log-rank test; P ⫽ .55).
Fig. 2. Survival plot with revision for wear with or without osteolysis as the endpoint (95% confidence intervals shown at yearly intervals).
THA in Young Patients •
Discussion The results of early series on cemented THAs in young patients were not promising. After follow-up of 5 to 10 years, 36% to 69% of hips were revised or had loose components in the radiographs [1–3]. Other studies showed that 9% to 14% of hips were revised for aseptic loosening after only 6 to 8 years [4,5]. More recent series, especially on Charnley low-friction arthroplasty implanted with early cementing techniques, did not concur with such unsatisfactory results [6 –10]. The survival rates of Charnley cemented hips at 20 years were 75% to 88%. In a single-surgeon series, 13% of acetabular components and 2% of femoral components were revised for aseptic loosening after 18 years; the revision rate for aseptic loosening was 19% on the acetabular side and 5% on the femoral side after 20 to 25 years [7,10]. With the use of improved cementing techniques, the revision rate for aseptic loosening of the femoral stem ranged from 0% to 5% after 11 to 13 years [11–13]. Of acetabular components, 36% to 44% were revised or definitely loose on radiographs after 10 to 12 years despite the use of improved cementing techniques [11,12]. Because of concern that young patients will require ⱖ1 revisions for loosening of cemented components, cementless THA has been recommended in this patient group. It was hoped that the biologic fixation achieved with osseointegration at the prosthesis– bone interface would be more durable and
Chiu et al.
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long-lasting than fixation of components with cement. There were relatively few reports about the results of cementless THAs in young white patients (Table 2). The prostheses being inserted were heterogeneous in some reports and included nonporous ceramic acetabular components, threaded acetabular components, bipolar THAs, and nonporous press-fit femoral components [16,18,19]. When we reviewed the findings of the these reports, we counted only the components that were either porous coated [14 –19] or hydroxyapatite coated [16]. The average follow-up period of these studies were not too long; the longest one was only 8.3 years. From these reports, one could conclude that the objective of using cementless THA to reduce the aseptic loosening rate in young patients was achieved. For young white patients, the chance of having a loose cementless acetabular component ranged from 0% to 11%, and the loosening rates ranged from 0% to 7% for the cementless femoral components after 4 to 8 years. These results were superior to the results being described in the earlier reports of cemented THAs in young patients. Compared with the results with the use of improved cementing techniques, cementless fixation appeared to do better on the acetabular side. Longer follow-up was necessary to determine whether cementless fixation could match the results of femoral components being inserted with improved cementing techniques. In the present series, 13% of the cementless acetabular components and 5% of the cementless
Table 2. Reports on Cementless Total Hip Arthroplasty With Metal–Polyethylene Articulation in Young Patients
Series Mont et al [14], 1993 Piston et al [15], 1994 Capello et al [16], 1997 Dowdy et al [17], 1997 Kronick et al [18], 1997 Fye et al [19], 1998 Present series
No. Patients (Hips)
Mean Age Follow-up Range Period (y) (Range) (y)
Prostheses
Mechanical Failures Thigh Reoperation (%)* Pain Osteolysis for Wear ⫾ (%) (%) Acetabular Femoral Osteolysis (%)
42 (44)
⬍45
4.5 (3–7)
PCA
23
—
2
7
0
30 (35)
21–40
7.5 (5–10)
AML
6
17
6
6
0
133 (152)
16–49
6.4 (5–8.3)
Omnifit-HA†‡
7
33
11
0
5
36 (41)
19–50
5.3 (4–7)
Mallory-Head§
—
29
12
0
2
145 (174)
14–50
8.3 (2–13)
AML/Prodigy†㛳
6
3
2
1
1
52 (66)
⬍50
7.0 (4–12)
Various†
—
3
0
3
0
45 (61)
22–40
7.6 (3–11)
PCA, AML
7
56
13
5
12
*Hip that was revised or pending revision for aseptic loosening or had definite radiographic loosening of a component. †Various components were used; mechanical failure rates were on porous-coated or hydroxyapatite-coated components. ‡Osteonics, Allendale, NJ. §Biomet, Warsaw, IN. 㛳Depuy, Warsaw, IN.
868 The Journal of Arthroplasty Vol. 16 No. 7 October 2001 femoral components inserted in young Chinese patients were considered to be loose after an average follow-up of 7.6 years. The loosening rates of the 2 cementless hip systems were quite different. For AML hips in young Chinese patients, only 4% of the acetabular components and none of the femoral components were loose after an average follow-up of 7.3 years. In the 2 articles that described the outcomes of the AML THA systems in young white patients, the acetabular loosening rate was 2% to 6%, and the femoral loosening rate was 1% to 6% after an average follow-up of 8 years [15,18]. For PCA hips in young Chinese patients, 21% of the acetabular components and 9% of the femoral components were loose after an average follow-up of 7.9 years. Compared with the study reported by Mont et al [14], the aseptic loosening rate of PCA prostheses in young white patients was 2% on the acetabular side and 7% on the femoral side [14]. This difference could be due to the short follow-up of the patients (average 4.5 years). In another article on PCA acetabular components in patients of all ages, 15% showed migration after an average follow-up of ⬍5 years [35]. The loosening rates of cementless total hip prostheses in young Chinese patients were comparable to the reported series on white patients. Although cementless THA had been successful in decreasing the aseptic loosening rate, it created other problems. In young white patients, pain in the thigh affected 6% to 23% of cementless THAs. Most of the pain was mild and did not limit activity. In the current series, only 7% of hips in young Chinese patients had mild thigh pain. Bone resorption in the proximal femur was common after cementless THAs, especially if the femoral component used was extensively porous coated. In the 2 articles on extensively porous-coated THAs in young white patients, 17% to 55% of hips showed significant atrophy of the proximal femur secondary to stress shielding [15,18]. In the present series, significant stress shielding affected 8% of cementless THAs in young Chinese patients. There was no difference between PCA and AML hips. In young white patients, osteolytic lesions were present in 3% to 33% of cementless THAs after 4 to 8 years. In the present series, osteolysis was found in 56% of hips in young Chinese patients after an average follow-up of 7.6 years. If the 2 hip systems were evaluated separately, osteolysis was detected in 37% of AML hips in young Chinese patients after 7.3 years. This rate was higher than the reported rates of 3% to 17% at 8 years with the use of AML prostheses in young white patients [15,18]. For PCA THAs in young Chinese patients, 71% showed
osteolysis after 7.9 years. In the article on the use of PCA prostheses in young white patients reported by Mont et al [14], the presence of osteolytic lesions was not mentioned. In the literature, osteolysis was common after PCA THAs even if older patients were included. Owen et al [36] reviewed 241 PCA THAs in patients ⱕ65 years old. For THAs with follow-up ⬎5 years, 36% showed acetabular osteolysis, and 13% showed femoral osteolysis. Kim et al [37] followed up 116 PCA THAs in 108 patients for an average of 11 years. Despite that only 37 patients were ⬍40 years old, osteolysis was identified in 56% of acetabular components and 59% of femoral components by 11 years. The osteolysis rate of 71% for PCA prostheses in the present report was higher than these reported figures. The occurrence of osteolysis was more common for PCA and AML hips in Chinese patients. One possible explanation was the smaller acetabula in Chinese patients could result in the use of polyethylene that was not thick enough by today’s standard. It was interesting to find out why osteolysis was detected in only 37% of AML THAs, but was found in 71% of PCA THAs in young Chinese patients. This finding could not be explained by the difference in other parameters between the 2 groups. Gender, age at operation, height, weight, preoperative Charnley functional class, preoperative hip disease, preoperative Harris hip score, sizes of the components used, level of activity after the operation, Harris hip score at follow-up, and average length of follow-up did not show any significant differences between the AML and PCA hips. The higher rate of osteolysis after PCA THAs was not because of increased polyethylene wear; the average linear penetration rate was 0.18 mm/y for the PCA THAs and 0.20 mm/y for the AML THAs. It was possible that the polyethylene particles generated at the articulation could be different for the 2 hip systems, or there could be more backside wear in PCA acetabular components. Excessive backside polyethylene damage had been shown with the PCA acetabular components and was attributed to failure of the locking mechanism and incongruent contact between the metal shell and the polyethylene liner [35]. Reoperations for polyethylene wear with or without osteolysis after cementless THAs have been reported [16 –18]. In the present series, 7 of 10 cementless hips that needed reoperation were for polyethylene wear with or without osteolysis (Fig. 3). To avoid catastrophic failures, we advise patients to have exchange of the polyethylene inserts and the hip ball, with or without grafting of the osteolytic lesions, even when there are no symptoms.
THA in Young Patients •
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Fig. 3. A 28-year-old woman suffered from post-traumatic arthritis of the right hip. (A) One year after PCA total hip arthroplasty. (B) Six years later, the hip ball became eccentric, there was cup migration with pelvic osteolysis (small black arrows), and femoral osteolysis with pathologic fracture of the greater trochanter (large white arrow).
Using such criteria, the cumulative survival rates of well-fixed cementless THA prostheses in the present series started to decrease from 7 years onward in a more or less linear manner and became 72% at 10 years. Although cementless THAs resulted in stable and long-lasting fixation, the overall cumulative survival rate at 10 years was not better than cemented THA in young patients.
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