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The two remaining aims of the analysis of the retrospective group data were to estimate the improvements in health-related quality of life in patients who have had hip joint replacements and knee joint replacements, and also to calculate the time period over which the maximum improvements in health-related quality of life are achieved. Table 3.5 (page 90) summarizes the mean Rosser-Kind rating scores at the postoperative and retrospective stages for the entire retrospective group, the operation site and sex subgroups and also the retrospective period subgroups.

It is clear from the table that there were noticeable changes in the health- related quality of life scores for the retrospective group as a whole, and for every subgroup. Nonparametric statistics were used to compare the postoperative health-related quality of life scores of each subgroup because the data was discrete, skewed and indicative of rank order. The medians for each subgroup were as follows: three month hip subgroup (0.95025), one year hip subgroup (0.972), two year hip subgroup (0.972), three month knee subgroup (0.9385) and one year knee subgroup (0.964). The mann-whitney test was used to compare the difference between the sample medians. The medians of the three month and one year hip subgroups were significantly different at the 0.0039 level. The medians of the three month and two year hip subgroups were significantly different at the 0.0014 level. For the one year and two year hip subgroups, the significance level of the difference between the medians was 0.4539. The medians of the three month and one year knee subgroups were significantly different at the 0.005 level.

The average increase in the Rosser-Kind rating score for the 159 patients was between 0.228 and 0.230 (Table 3.5, page 90), depending on the source of estimation, but this figure tells us little since it does not take into account the retrospective periods of estimation. Therefore, it cannot be converted into

average quality adjusted life years gained. Incorporating the time span element allows us to estimate the health-related quality of life improvements at fixed points in time following the operations. The results in Table 3.5 (page 90) are quite interesting. For the knee subgroup, a higher mean Rosser-Kind rating score was calculated for the patients who were interviewed one year following their operations (0.95840-0.96691, depending on the source of estimation) than for the patients who were interviewed three months following their operations (0.8940-0.9161, depending on the source of estimation). If we accept the retrospective estimates as reliable, the average increase in the Rosser-Kind rating scores was between 0.21291 and 0.2395 . (equivalent to 0.21291-0.2395 QALY’s) for the one year retrospective knee subgroup, compared to an average increase of between 0.0933 and 0.1239 (equivalent to 0.023325-0.030975 QALY's) for the three month retrospective knee subgroup. These results suggest that amongst patients who have undergone knee joint replacement surgery, significant improvements in health-related quality of life are achieved between three months and one year following the operation. In addition, the rate of improvement in health- related quality of life suggests that the highest Rosser-Kind rating score is achieved after the first year.

Amongst the 116 patients who were interviewed following their hip replacements, less consistent improvements are noticeable. The mean Rosser- Kind rating scores were 0.94383-0.95180 for the patients who were interviewed three months after their hip replacements, 0.9276-0.9359 for the patients who were interviewed one year after their hip replacements, and 0.95745-0.96493 for the patients who were interviewed two years after their hip replacements. If we accept the retrospective estimates as reliable, the average increase in the Rosser-Kind rating score was between 0.31843 and 0.3514 for the three month retrospective hip subgroup (equivalent to 0.0796-0.08785 QALY's gained). This compares to an average increase in the Rosser-Kind rating score of between

0.2874 and 0.3027 for the one year retrospective hip subgroup (equivalent to 0.2874-0.3027 QALY's gained), and an average increase of between 0.1614 and 0.1677 for the two year retrospective hip subgroup (equivalent to 0.3229-0.3353 QALY's gained before discounting). These results suggest that for patients who have hip replacements, a higher Rosser-Kind rating score is achieved at three months following the operation than at one year following the operation. It was probably the case that the overall one year retrospective hip sample in Table 3.5 (page 90) included a number of patients with abnormally low rating scores (this is supported by the evidence that the mean rating score of the sample was lower than the median). However, the Rosser-Kind rating score starts to increase again beyond the one year period. The rate of increase in the Rosser-Kind rating score between the first and second year following the operations suggests that the highest rating score is achieved after the second year.

When the retrospective estimates are incorporated into our analysis, it is immediately noticeable that the improvements from the retrospective base decline after the first three months. This is the result of the higher retrospective rating scores estimated by the one year and two year subgroups. It may be the case that the one year and two year subgroups overestimated their preoperative health-related quality of life (these groups of patients may have had greater difficulty in recalling their preoperative health status) and, as a result, the true improvements in health-related quality of life have been underestimated. Alternatively, it may be the case that the patients within these two subgroups were less disabled than the patients in the three month hip subgroup. Our analysis of the control group data found the retrospective estimates at three months to be reliable indicators of the preoperative health- related quality of life of patients who have undergone hip replacement surgery. Whether retrospective assessments at one or two years following an operation are reliable indicators of preoperative health-related quality of life

is beyond the scope of this study. However, the analysis in section 3.5 which matches the control and retrospective groups of patients may go some way in explaining our results.

3.421 Retrospective Group: Cost per QALY Gained

To estimate the QALY’s gained over a joint survival period, the health- related quality of life scores for the three month and one year hip and knee retrospective subgroups (using the subjects' estimates) were once again extrapolated over 10 years. Extrapolating the health-related quality of life estimates of the three month hip retrospective subgroup over a 10 year period results in 3.514 QALY’s gained (assuming a 0% discount rate), 2.713 QALY’s gained (assuming a 5% discount rate) and 2.159 QALY’s gained (assuming a 10% discount rate). Extrapolating the health-related quality of life estimates of the one year hip retrospective subgroup over a 10 year period results in 2.874 QALY’s gained (assuming a 0% discount rate), 2.219 QALY’s gained (assuming a 5% discount rate) and 1.766 QALY’s gained (assuming a 10% discount rate). Assuming that the postoperative health-related quality of life score of the three month hip subgroup is achieved immediately after the operation and that the postoperative health-related quality of life score of the one year hip subgroup is achieved immediately after the three month stage results in 3.395 (0% discount rate), 2.621 (5% discount rate) and 2.086 (10% discount rate) QALY’s gained respectively over a 10 year period. If it is assumed that the postoperative health-related quality of life score of the three month hip subgroup is not achieved until the three month stage after the operation and that the postoperative health-related quality of life score of the one year hip subgroup is not achieved until the one year stage after the operation, the extrapolated QALY’s gained are 2.636, 2.035 and 1.619 respectively over 10

years. Finally, if it is assumed that the postoperative health-related quality of life score of the three month hip subgroup is not achieved until the one and a half month stage after the operation and that the postoperative health-related quality of life score of the one year hip subgroup is not achieved until the seven and a half month stage after the operation, the extrapolated QALY's gained are 3.015, 2.328 and 1.853 respectively over 10 years. As a result of these assumptions, our results suggest 1.619-3.514 QALY's gained over a 10 year period. In terms of the Cost per QALY gained from hip replacement surgery, this is equivalent to £2,734-£l,260, using our earlier cost estimate (£4,426, page 72. Amongst the knee patients, extrapolating the health-related quality of life estimates of the one year retrospective subgroup over a 10 year period results in 2.129 QALY's gained (assuming a 0% discount rate), 1.644 (assuming a 5% discount rate) and 1.308 (assuming a 10% discount rate). This translates into a Cost per QALY for knee replacement surgery of £2,490-£4,054, using our earlier cost estimate (£5,302, page 72).

3.422 Retrospective Group: Change in Quality of Life for Individual Functions

Appendices 13-17 summarize the change in rating scores for individual functions between the retrospective and postoperative stages. The scales to each question are listed, as are the number of subjects who fall into each category of each scale at the retrospective and postoperative stages. Once again, the chisquare test is used to test the null hypothesis that no improvements in health-related quality of life occur after the operation. Appendix 13 summarizes the results of the three month hip subgroup, Appendix 14 the results of the one year hip subgroup and Appendix 15 the results of the two year hip subgroup. Appendices 16 and 17 summarize the results of the two knee subgroups.

Significant improvements in the ability to undertake everyday functions are evident in every subgroup. There were significant improvements (at the 0.05 level) in every subgroup in pain reduction, in the ability to sleep without noticeable discomfort, in the ability to walk distances without noticeable discomfort, in the ability to bend knees without noticeable discomfort, in the ability to climb stairs without noticeable discomfort and in the ability to sit down on and get up off chairs without noticeable discomfort. The chisquare values also reveal some interesting trends. There were consistent improvements over the periods of estimation in all categories apart from the ability to bathe, the ability to cook, assistance in the home and confinement to a chair. This can be accounted for, however, by the high preoperative ratings for these functions. As in our discussion of the control group results, our conclusion is that future health status measurement studies of patients who have undergone hip and knee joint replacement surgery should concentrate on measuring changes within the functions most likely to show improvements (pain, sleeping, walking, bending knees, climbing stairs and sitting down on and getting up off chairs).

Table 3.5 - Retrospective Group: Summary of Rosser-Kind Rating Scores for each Retrospective Period and Operation Site Subgroup at the Postoperative and Retrospective Stages of Interview

SUBPORKR MYPORKR SUBRERKR MYRERKR SUBPORKR- SUBRERKR MYPORKR- MYRERKR TOTAL GROUP 0.95282 0.94465 0.7251 0.7156 022772 0.22905 TOTAL HIP GROUP 0.9522 0.94531 0.7102 0.7074 0.2420 0.23791 HIPS: THREE MONTHS 0.95180 0.94383 0.6004 0.6254 0.3514 0.31843 HIPS: ONE YEAR 0.9359 0.9276 0.6485 0.6249 0.2874 03027 HIPS: TWO YEARS 0.96493 0.95745 0.8035 0.7898 0.16143 0.16765 TOTAL KNEE GROUP 0.95435 0.94288 0.7616 0.7375 0.19275 020538 KNEES: THREE MONTHS 0.9161 0.8940 0.7922 0.8007 0.1239 0.0933 KNEES: ONE YEAR 0.96691 0.95840 0.7540 0.7189 021291 02395 TOTAL MALE GROUP 0.97227 0.96868 0.7666 0.7518 020567 0.21688 TOTAL FEMALE GROUP 0.9432 0.9333 0.7046 0.6985 0.2386 02348 Abbreviations :

MYPORKR : Derived mean postoperative Rosser-Kind rating score MYRERKR : Derived mean retrospective Rosser-Kind rating score SUBPORKR : Subjects' mean postoperative Rosser-Kind rating score SUBRERKR : Subjects' mean retrospective Rosser-Kind rating score