Primary total hip replacement in Hong Kong Chinese - A review of 647 hips
Chiu KY, Ng TP, Poon KC, Ho WY, Yau WP
Department of Orthopaedic Surgery, The University of Hong Kong, Queen Mary Hospital, Hong Kong.
We reviewed 647 primary total hip replacements in Chinese patients. The average age was 52.9 years (?5.8 years). The main indication was avascular necrosis (45.6% of hips). Revisions were carried out in 12.8% of hips. Kaplan-Meier survival analysis was performed. The predicted cumulative survival for all hips was 98.1% at 5 years, 87.0% at 10 years, 54.2% at 15 years, and 33.5% at 20 years. For patients who were 50 years old and above, the predicted cumulative survival at 10 years was 91.6% for cemented and 81.8% for cementless prostheses. For patients who were younger than 50 years old, the predicted cumulative survival at 10 years was 87.3% for cemented and 81.2% for cementless prostheses. For the younger patients, survival of cementless prostheses was not better at 10 years.
香港華人全髖關節置換手術 — 647例分析
A huge number of articles on various aspects of total hip replacement have been reported in the literature. However, there was not much information about the demographic data and the pattern of underlying diseases leading to total hip replacements in Chinese population. It has been assumed over the years that these were probably different from those in Caucasians. While the most common indication for total hip replacement was osteoarthritis in Caucasians, this disease was uncommon in Chinese.6 Hoaglund et al studied the racial variations of total hip replacement in San Francisco, and reported a much lower rate in Asians, which was about 10% the rate of the white population.5 The age standardised rate of total hip replacement for primary osteoarthritis was 43 per 100,000 in the white population, while it was 1.3 per 100,000 population in Chinese. Other than this paper, we could not find other articles that looked specifically at the demographic data and indications for total hip replacement in Chinese patients.
The long-term results of total hip replacement in Chinese were also unknown. When being asked by the patients how long their prosthetic hips were going to last, at best one could quote figures reported in the literature for the Caucasian patients. However, the Caucasian experience did not necessarily apply in Chinese. Firstly, the demographic data and pattern of hip diseases could be very different. Secondly, there were significant osteometric differences between the proximal femora in Asians and Caucasians.2 Prosthesis developed according to Caucasian anatomy might not work the same way in Asians.
In this study, we analysed the demographic data and the underlying hip diseases that led to 647 primary total hip replacements in Hong Kong Chinese. We then looked at the effects of sex, age, hip disease and whether cement was used, on the survival of the total hip replacements.
PATIENTS AND METHODS
All Chinese patients who attended a special clinic in Queen Mary Hospital after the primary total hip replacement were reviewed. The operations were performed from 1972 to 1997 in Queen Mary Hospital, Duchess of Kent Children Hospital (before 1997), Grantham Hospital (before 1996), and Nethersole Hospital (before 1992). Non-Chinese patient and revision of failed total hip replacement were excluded. The sex, age, hip disease, type of prosthesis and follow-up duration were documented.
There were 647 hips in 494 patients, 153 patients had bilateral replacements. About the sex distribution, 50.2 % (325 hips) were done in male patients and 49.8% (322 hips) were done in female patients. The mean age at the time of the operation was 52.9 years (SD 15.8, ranged 17.4-87.0 years).
The diseases that led to total hip replacements were avascular necrosis in 295 hips (45.6%), post-traumatic conditions in 101 hips (15.6%), ankylosing spondylitis in 86 hips (13.3%), primary osteoarthritis in 66 hips (10.2%), and rheumatoid arthritis in 32 hips (3.3%).
Concerning the prostheses, 312 (48.2%) were cemented, 331 (51.2%) were cementless, and only four (0.7%) were hybrid. For the cemented prostheses, 285 (91.3%) were Charnley types of prosthesis, the rest were McKee-Farrar, Trapezoidal 28 and curve-stem Muller prostheses. For the cementless prosthesis, there were 103 PCA (Howmedica), 77 AML (Depuy) and 132 Osteonic HA-coated (Stryker) prostheses.
The average follow-up for all the hips was 6.5 years (SD 4.9, ranged 0.5-25.9 years). The average follow-up for cemented hips was 8.5 years (SD 5.7, ranged 0.5-25.9 years), and it was 4.6 years (SD 3.1, ranged 0.5-16.2 years) for cementless hips.
All records were examined for the need of revision or removal. The reason and the time that the latter occurred were determined. Revision was defined as taking out part or whole of the previous total hip replacement, and then replacing with new components. The revision rates were calculated, and comparison of different factors was performed with t-test or chi-square test. Kaplan-Meier survival analysis was performed to predict the cumulative rate of success for the total hip replacements, and the log rank test was used to compare the effects of different parameters on the survival. Statistical significance was defined as p value of less than 0.05.
Out of these 647 hips, 83 hips (12.8%) were revised on an average of 10.5 years (?.9 years) after the primary operation. Two hips (0.3%) were removed for deep infection. Thus, 562 hips (86.9%) were still surviving, and the average follow-up of this group was 5.9 years (?.7 years).
The gender did not affect the revision rate. Thirty-eight of the 325 hips (11.7%) in males, and 45 of the 322 hips (14.0%) in females were revised. Younger patients had higher revision rate. The average age at operation was 40.8 years (?5.6 years) for the revised group, and it was 54.7 years (?5.0 years) for the patients who did not need revision (p < 0.001). With respect to the hip diseases, 37 of the 295 hips (12.5%) with avascular necrosis, 16 of the 101 hips (15.8%) with post-traumatic arthritis, 16 of the 86 hips with ankylosing spondylitis (18.6%), 6 of the 66 hips with osteoarthritis (9.1%), and 5 of the 32 hips (15.6%) with rheumatoid arthritis were revised. About the use of prosthesis, 64 of the 312 (20.2%) cemented hips were revised, and 19 of the 331 cementless hips (5.7%) were revised. The difference was statistically significant (p < 0.001).
Some of the figures above had to be interpreted with care. For instance, the low revision rate for cementless total hip replacement might be explained by the shorter follow-up. The follow-up period for cemented prosthesis was 8.6 years (?.7 years), and was significantly longer than 4.6 years (?.1 years) of cementless prosthesis (p < 0.001). When one was interested in the length of time that elapsed before an event such as revision occurred, survival analysis was very useful.
Kaplan-Meier survival analysis was performed for 645 hips, excluding the two hips removed for deep infection. The survival plot was depicted in figure 1. At 5 years, the predicted cumulative survival was 98.1%. It became 87.0% at 10 years, 54.2% at 15 years, and 33.5% at 20 years. The mean survival time for all hips was 17.1 years (SE 0.7, 95% Confidence Interval 15.7, 18.5).
To study the effect of patients' age, we divided all the hips into two groups. In one group, the patients' age was below 50 years at the time of the operation, with 40.8% of hips in this group. In another group, the patients' age was 50 and above, 59.2% of hips were in this group. The Kaplan-Meier survival plots of the two groups were depicted together in figure 2. For the young age group, the predicted cumulative survival was 98.1% at 5 years, 85.0% at 10 years, 43.5% at 15 years and 23.6% at 20 years. For the old age group, the predicted cumulative survival was 98.0% at 5 years, 88.8% at 10 years, 71.5% at 15 years and 53.9% at 20 years. The difference was statistically significant (log rank test, p = 0.008).
The effect of prosthesis was then analysed. The survival up to 10 years were plotted (Fig. 3), since there were few cementless hips with follow-up more than 10 years. For cemented prostheses, the predicted cumulative survival was 97.7% at 5 years, and 90.0% at 10 years. For cementless prostheses, the predicted cumulative survival was 98.3% at 5 years, and 81.3% at 10 years. The difference was not statistically significant (p = 0.146). It was interesting to note that cementless hips were better initially, but the failures increased after 5 to 6 years. The results of cemented hips at 15 years were also calculated, and the predicted cumulative survival dropped to 55.6%.
Comparison of cemented and cementless prostheses was not fair without considering the effect of age. The mean age at operation for cementless hips was 48.3 years (?3.1 years), and it was 57.8 years (?7.0 years) for cemented hips (p < 0.001). It was therefore important to evaluate the survival of cemented and cementless prostheses according to different age groups.
For the young age group, the predicted cumulative survival was 87.3% at 10 years for cemented prostheses, and 81.2% for cementless prostheses. For the old age group, the predicted cumulative survival was 91.6% at 10 years for cemented prosthesis, and 81.8% for cementless prostheses. The difference between the survival of prostheses in young and old age groups, adjusted for the type of prosthesis, was significant (log rank test, p = 0.012). The difference between the survival of cementless and cemented prostheses, adjusted for the patients' age at operation, did not reach statistical significance (log rank test, p = 0.094). Cemented prostheses in old age group produced the best survival at 10 years, and the survival at 15 years for this particular group was 73.5%.
The sex and the underlying hip disease did not affect the survival of the hip prosthesis.
To study the patients' demographics and the underlying diseases leading to total hip replacements in the Caucasian population, one of the most important sources was The Swedish National Hip Arthroplasty Registry.7 The latter documented 134,056 primary total hip replacements from 1978 to 1994. The population of Sweden was 8.62 million, about 40 % more than that of Hong Kong. About 8,000 total hip replacements were performed each year in Sweden. There was no published data on the annual rate of total hip replacement in Hong Kong, but we estimated that it was less than 10% of the number in Sweden. With respect to the age of patient, the mean age of 24,491 Swedish patients from 1992 to 1994 was 69.9 years (?0.6 years). For our Chinese patients, the mean age was 52.9 years (?5.8 years). The difference was statistically significant (p < 0.001). About the pattern of the hip problems in the Swedish study, 78% were primary osteoarthritis, and avascular necrosis was very rare. For our Chinese patients, 45.6% of total hip replacements were for avascular necrosis, whereas only 10.2% were for osteoarthritis. This was in accordance with the reports on the results of specific hip systems in Chinese patients.3,4 Although the prognosis after total hip replacement for avascular necrosis was believed to be worse when compared with other diagnoses, such relationship could not be established in our Chinese patients.
In the Swedish Registry, majority of the hips (96%) were cemented. The survival of cemented hips performed between 1978 and 1983 for osteoarthritis was 76.8% at 15 years, and the cumulative survival of cemented hips performed between 1984 and 1989 for osteoarthritis was 91.9% at 10 years. The two time periods were separately analysed, since a change of the surgical techniques occurred. We did not go into the details of analysing the surgical and cementing techniques for our Chinese patients. In the Swedish Registry, many cemented hip systems were used and evaluated, and their survivals were compared to that of Charnley prosthesis. We did not analyse the results of different hip systems, but over 90% of our cemented hips were Charnley prostheses. To look at the survival of all cemented hips, our 10-year survival was 90.0% and the 15-year survival was 55.6%. This looked rather poor when compared with the Swedish data. However, one should note that the patients' demographics and underlying disease were not the same when interpreting such differences. For our Chinese patients who were 50 years old and above, the survival for cemented hips was 91.6% at 10 years and 73.5% at 15 years. The latter was comparable to the Swedish figures.
To use cementless hip in young patient was considered to be a major improvement. However, the results of cementless hips were not satisfactory in the Swedish study. The survival at 10 years for cementless hips performed between 1984 and 1989 for osteoarthritis was 72.8%. In the present study, the 10-year survival for all cementless hips was 81.3%. After adjusting for the patient's age at operation, we did not find a significant difference between the survival of cemented and cementless prostheses, at least in the first 10 years. Looking at the survival plots (Fig. 3) closely, we found cementless hips appeared to be better in the first 5 years, but failures increased afterward. Cemented hips were not as well initially, and might be attributed to the technical difficulties in achieving good cementation and primitive cementing techniques 10 to 20 years ago. Perhaps with modern cementing technique, cemented hips may perform equally well as cementless hips.7 The deterioration of cementless hip survival with time could be explained by the accelerated polyethylene worn in the thinner liner of cementless cups. Debris disease started to manifest at 5 to 7 years after the index operations. Another possibility was the poor design of specific cementless hip(s). We did not analyse the results of different systems, since the follow-up was still short for some. Since there were relatively few cementless hips with follow-up more than 10 years, we could not predict the survival of cementless hips at 15 years. Longer follow-up is needed to tell whether difference exists between cemented and cementless hips in long run.
The use of survival analysis in the context of total hip replacements has been well accepted.1 Whether one should use revision operation or radiological loosening as the end-point was debatable. Using revision as the end-point would probably underestimate the failure rate. On the other hand, using radiological loosening as the end-point might be difficult since it was not easy to decide the exact time when it occurred. Even when revision was used as the end-point, controversies still existed. While some papers included revision for all reasons, others just counted revision for aseptic loosening. The magnitude of revision operation also varied. It could be a simple exchange of worn polyethylene liner, or a major reconstruction for massive osteolysis in cementless hips. It could be an isolated cup revision, or a day-long surgery with exchange of both components in cemented hips. It is therefore important for one to understand the assumptions and limitations of survival analysis when they read a paper using this statistical method in evaluating the results.
One could argue that the data presented in this paper did not represent the overall situation in Hong Kong. The only solution is to have a territory wide registry same as the Swedish one. Before it comes true, we recommend our fellow orthopaedic surgeons to interpret the results of total hip replacements reported in the western literature with care.
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6. Hoaglund FT, Yau ACMC, Wong WL. Osteoarthritis of the hip and other joints in Southern Chinese in Hong Kong. J Bone Joint Surg 1973;55A:545-57.
7. Malchau H, Herberts P. Prognosis of total hip replacement. Surgical and cementing techniques in THR - A revision-risk study of 134,056 primary operation. Presented at the 63rd Annual Meeting of American Academy of Orthopaedic Surgeons, Feb 22-26, 1996, Atlanta, USA.
CHIU Peter Kwong-Yuen, FRCSEd, FHKAM (Orth Surg), Associate Professor and Chief of Division of Joint Replacement Surgery, Department of Orthopaedic Surgery, The University of Hong Kong, Queen Mary Hospital, Hong Kong.
NG Lawrence Tze-Pui, MBChB, FRCSEd, Medical Officer, Department of Orthopaedics and Traumatology, Queen Mary Hospital, Hong Kong.
POON Alex Kai-Chung, MBChB, FRCSEd, Medical Officer, Department of Orthopaedics and Traumatology, Pamela Youde Nethersole Eastern Hospital, Hong Kong.
HO Kenneth Wai-Yip, MBBS, FRCSEd, Medical Officer, Department of Orthopaedics and Traumatology, Queen Mary Hospital, Hong Kong
YAU Peter Wai-Pan, MBBS, FRCSEd, Medical Officer, Department of Orthopaedics and Traumatology, Queen Mary Hospital, Hong Kong.