Políticas del Sector

The third aim of the study, and the final one which could be applied to the control group, was to calculate the scale of change in health-related quality of life in patients who have undergone joint replacement surgery, and to elucidate the functions in which the greatest improvements occur. Table 3.3 (page 76) summarizes the various health-related quality of life scores at each stage of the process, and gives a breakdown of the Rosser-Kind ratings into sex/operation site subgroups. As can be seen in the table, there was a marked improvement in the health-related quality of life scores between the preoperative and three month postoperative interviews. For the control group as a whole, the QALY's gained ranged from 0.028 (0.11057/4) to 0.041 (0.16527/4), depending on which estimates are used. Of the 44 patients, the derived estimates showed that 39 improved their rating scores after the three month period, 1 patient's score showed no change, 1 patient's score deteriorated and 3 patients failed to turn up for their follow-up interviews. The respective figures based on the subject's estimates were 36, 2, 3 and 3.

When the data is broken down into hip and knee subgroups, it is immediately noticeable that the improvements in health-related quality of life in the patients who had hip replacements lie in a very narrow range whichever estimates are used. These improvements convert into 0.034-0.036 QALY’s gained over the three month period. For the patients who had knee replacements however, the improvements vary between 0.021-0.048 QALY’s gained depending on the source and stage of estimation. This is the result of the underestimation of the retrospective scores by the knee subgroup, which was highlighted above. When the data is broken down between the sexes, it is evident that the greatest improvements in health-related quality of life were amongst the female patients. However, this may be because the female subgroup had a lower average prospective rating. At the postoperative stage, the differences between the sexes were not significant. Once again, the divergences in health-related quality of life improvements for each of the sexes were largely the result of the underestimation of the retrospective scores by the knee subgroup.

3.331 Control Group: Cost per QALY Gained

To illustrate the differences between the prospective and retrospective rating scores of the hip and knee subgroups, the Cost per QALY gained was calculated for hip and knee joint replacement surgery, using both sets of rating scores as the basis for estimation.

(a) Hips

Figure 3.16 (page 72) illustrates the exercise for hip replacement surgery. The joint survival period resulting from this type of surgery was assumed to

be 10 years. This estimate lies at the lower range of the results calculated by Kilgus et al. (1991). The derived estimates from the questionnaires were used as the basis of the health-related quality of life information, and the cost of a hip replacement was assumed to be £4,426 (Tayside Health Board, April 1991 prices).

Fig 3.16: Control Group: Difference in Cost per QALY (£)

The figure demonstrates that, when a joint survival period of 10 years is assumed, using the two sets of rating scores interchangeably has very little effect on the final Cost per QALY estimate for hip replacement surgery. Indeed, the curves are so close, they are almost indistinguishable. The differences in the Costs per QALY vary between £12 (£3,269 - £3,281) when a discount rate of 0 percent is applied and £19 (£5,320 - £5,339) when a discount rate of 10 percent is applied.

(b) Knees

Figure 3.17 (page 73) illustrates the same exercise for knee replacement surgery. Once again, the survival period of a knee replacement is assumed to

be 10 years [Bowman et al. (1991)], and the derived estimates from the questionnaires are used as the basis of the health-related quality of life information. The cost of a knee replacement is assumed to be £5,302 (Tayside Health Board, April 1991 prices).

Fig. 3.17: Control Group: Difference in Cost per QALY (£) for knee replacement surgery when prospective and

The diagram demonstrates quite clearly that there are large differences in the Cost per QALY estimate for knee replacement surgery when prospective and retrospective rating scores are used as the basis for estimating health- related quality of life improvements. Assuming a 0 percent discount rate and a joint survival period of 10 years, the Cost per QALY for knee replacement surgery is £5,531 when prospective rating scores are used as the basis for estimating health-related quality of life improvements, and £3,208 when retrospective rating scores are used as the basis (a difference of £2,323). Assuming a 10 percent discount rate, the respective estimates are £9,002 and £5,221 (a difference of £3,781).

3.332 Control Group: Change in Quality of Life for Individual Functions

Appendices 7-11 summarize the change in rating scores for individual questions between the preoperative 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 preoperative and postoperative stages. Since we are dealing with interval rather than continuous variables, the chisquare test is used to test the null hypothesis that no improvement in health-related quality of life occur after the operation. Appendix 7 summarizes the results of the whole control group; Appendices 8 and 9 summarize the results of the hip and knee subgroups respectively, and Appendices 10 and 11 summarize the results of the male and female subgroups respectively.

The appendices illustrate significant improvements in the ability to undertake everyday functions. There was an extremely significant reduction in pain (less than the 0.001 level) in every operation site and sex subgroup. In addition, there were significant improvements (at the 0.05 level) in every subgroup 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 functions in which the. improvements were not significant (greater than the 0.1 level) were largely ones in which the subjects already had a high rating prior to their operations (dependence on others for activities of daily living, ability to bathe, ability to dress, ability to cook, assistance in the home and confinement to a chair). The only exceptions were the insignificant improvements in the ability to work and participation in sports. This is hardly surprising, since most patients were elderly and were not employed or active participants in sport prior to their operations. The conclusion here must be that future health status measurements of patients

who have undergone hip and knee joint replacement surgery need not include these functions in their studies, but rather should concentrate on measuring changes within areas where our study has shown significant improvements (pain, sleeping, walking, bending knees, climbing stairs, sitting down on and getting up off chairs).

Table 3.3 - Control Group: Summary of Rosser-Kind Rating Scores for the Sex and Operation Site Subgroups at the Preoperative, Postoperative and Retrospective Stages Overall Mean RKR Mean RKR for Males (n=19) Mean RKR for Females (n=25) Mean RKR for Hips (n=23) Mean RKR for Knees (n=21) SUBPRERKR 0.8475 0.9009 0.8038 0.8267 0.8704 MYPRERKR 0.8368 0.8823 0.8022 0.8246 0.8502 SUBPORKR 0.95807 0.95840 0.95783 0.96220 0.95257 MYPORKR 0.95345 0.95445 0.95255 0.95950 0.94606 SUBRERKR 0.7928 . 0.8605 0.7419 0.8173 0.7601 MYRERKR 0.8046 0.8643 0.7506 0.8241 0.7808 SUBPORKR- SUBPRERKR 0.11057 0.0575 0.15403 0.1355 0.08217 MYPORKR- MYPRERKR 0.11665 0.07215 0.15035 0.1349 0.09586 SUBPORKR- SUBRERKR 0.16527 0.0979 0.21593 0.1449 0.19247 MYPORKR- MYRERKR 0.14885 0.09015 0.20195 0.1354 0.16526 SUBPRERKR- SUBRERKR 0.0547 0.0404 0.0619 0.0094 0.1103 MYPRERKR- MYRERKR 0.0322 0.018 0.0516 0.0005 0.0694 Abbreviations :

MYPRERKR : Derived preoperative Rosser-Kind rating score MYPORKR : Derived postoperative Rosser-Kind rating score

MYRERKR : Derived retrospective Rosser-Kind rating score

RKR : Rosser-Kind rating score

SUBPRERKR : Subject's preoperative Rosser-Kind rating score SUBPORKR : Subject's postoperative Rosser-Kind rating score SUBRERKR : Subject's retrospective Rosser-Kind rating score