Total hip replacement and resurfacing arthroplasty for end-stage arthritis of the hip

4.1 Clinical effectiveness

4.1.1 The Assessment Group conducted a systematic review of randomised controlled trials (RCTs), published systematic reviews and published registry studies of hip replacement procedures. In addition, the Assessment Group analysed individual patient data from the National Joint Registry (NJR).

4.2 Cost effectiveness

4.3 Consideration of the evidence

4.3.1 The Appraisal Committee reviewed the data available on the clinical and cost effectiveness of THR and hip resurfacing arthroplasty for people with end-stage arthritis of the hip for whom non-surgical management has failed. It considered evidence on the nature of surgery for the treatment of pain and disability, and the value placed on the benefits of THR and resurfacing arthroplasty by people needing surgery. It also took into account the effective use of NHS resources.

4.3.2 The Committee considered the care pathway for people with end-stage arthritis of the hip and the potential place of THR and resurfacing arthroplasty. The Committee discussed the factors that clinicians take into account when deciding whether to offer a THR or resurfacing arthroplasty to individual patients. The Committee heard from the Assessment Group's clinical adviser that the use of resurfacing prostheses has declined over the past few years, noting the Medicines and Healthcare products Regulatory Agency's alerts to recall some resurfacing prostheses and to monitor patients with MoM prostheses. The Committee heard that, after any type of hip replacement, some people need revision surgery to replace the primary prosthesis, and that being younger or more active can increase a person's risk of needing revision surgery. The Committee heard that clinicians take into account a person's risk of needing revision surgery when deciding whether to offer resurfacing arthroplasty or THR, and that clinicians in general consider resurfacing arthroplasty more suitable for younger and more active people. The Committee further heard that clinicians may be more likely to offer resurfacing arthroplasty to men than to women because higher revision rates have been observed in women, which may be associated with women tending to have smaller hips. The Assessment Group's clinical adviser also explained that, because older patients have shorter life expectancies than younger patients, they are less likely to need revision, and that clinicians tend to offer older patients THR. The Committee concluded that both THR and resurfacing arthroplasty are options for treatment of end-stage arthritis of the hip, and that clinicians consider together with patients the factors associated with the risk of revision when choosing the most appropriate procedure.

4.3.3 Having considered which type of prosthesis would be appropriate (THR or resurfacing arthroplasty), the Committee then considered the choice of a given prosthesis, noting that prostheses vary in materials and fixation methods. The Committee heard that the operating surgeon generally chooses the type of prosthesis, taking into consideration those that achieve the recommended standard revision rate as provided by the Orthopaedic Data Evaluation Panel (ODEP). The Committee heard that surgeons need specific training for each class of prosthesis (for example, cemented or cementless THR), but that most orthopaedic surgeons in the UK are trained to use both cemented and cementless prostheses. The Committee further heard that an orthopaedic centre's experience and clinical data for individual prostheses further influence the choice of prosthesis. The Committee noted that the NJR contained data for hip replacements carried out in the NHS and in private practice, but heard that the prostheses used in the 2 healthcare sectors were not expected to differ because the same surgeons work in both the NHS and in private practice. The Committee considered whether surgeons offer cemented prostheses and cementless prostheses to different patients, and heard from the manufacturers and the Assessment Group's clinical adviser that there were no specific groups of patients for whom cemented or cementless prostheses would be specifically indicated. The Assessment Group's clinical adviser explained that a patient's age, sex and activity levels may influence a surgeon's choice of bearing surface for THR. The Committee understood that surgeons tend to choose not only the type but also the brand of hip prosthesis a patient receives, and that this is driven by factors including the surgeon's training, perception of which prostheses perform best, clinical data and experience using different prostheses, among other factors.

4.3.4 The Committee heard from the Assessment Group's clinical adviser that revision surgery is more complex and associated with greater risks than primary THR or resurfacing arthroplasty. It heard from the clinical specialist that patients may need to be referred to a specialist centre for revision surgery. The Committee discussed whether any particular type of THR or resurfacing prosthesis reduced the complexity of subsequent revision surgery, and heard that resurfacing prostheses tended to be easier to replace than THR prostheses, but that the risks associated with surgery to the patients were similar. The Assessment Group's clinical adviser stated that a patient's operative and peri-operative risk depends on why the primary prosthesis failed (for example, infection or fracture) rather than the type of prosthesis, or whether it is cemented or cementless. The Committee recognised that revision surgery is more complicated than primary surgery and concluded that the complexity of the revision surgery is primarily determined by why the primary hip replacement failed.

4.3.5 The Committee considered the clinical evidence available for this appraisal. It noted that the Assessment Group presented evidence from RCTs, systematic reviews, published registry studies and its analysis of data from the NJR, and discussed the relevance of each source to its decision making. The Committee noted the Assessment Group's concerns that the RCTs and systematic reviews it had identified involved small numbers of patients, had relatively short follow-up, reported different outcomes either incompletely or poorly, and were underpowered to detect differences in rates of revision. The Committee accepted that, because of these concerns, it was appropriate that the Assessment Group chose not to meta-analyse the RCTs. The Committee then considered data from registries. It noted that the Assessment Group's retrospective analysis of the NJR provided a record of the revision rates for all types of prostheses used in England and Wales since 2003, and as such provided long-term data generalisable to UK clinical practice. The Committee was aware that, although it is mandatory for NHS organisations to submit data to the NJR, when the registry first started clinicians provided data voluntarily, and that the registry may have missed some procedures that were carried out at the time. The Committee noted that the registry did not provide data on outcomes listed in the scope other than revision, and that it did not provide data on differences in the patient characteristics (for example, activity levels and comorbidities) that might affect both device choice and the risk for revision, causing confounding. The Committee noted the comments received on the appraisal consultation document, stating that there is a problem with an accurate link between the NJR data and Hospital Episode Statistics data, and that data on revision rates from the NJR had not been validated. The Committee concluded that it was appropriate to use both trial and observational data in its decision making, but that uncertainty resulting from the possibility of confounding should be taken into account. The Committee agreed that, although the NJR data had limitations, they are the most comprehensive data reflecting clinical practice in the NHS and therefore the most appropriate for decision making.

4.3.6 The Committee considered the population for whom both procedures are suitable, and the population for whom resurfacing arthroplasty is not suitable. The Committee discussed the Assessment Group's analysis of revision rates of different types of hip replacement in both populations using the NJR data, and whether it had controlled for bias by confounding. The Committee noted that the Assessment Group had controlled for patient age and sex when comparing resurfacing arthroplasty with THR and when comparing different types of THR (in a sensitivity analysis [see section 4.1.23]). The Committee also noted that the Assessment Group's analysis of the NJR in revision after resurfacing arthroplasty compared with THR was consistent with effect measures from RCTs and systematic reviews (see section 4.1.20). The Committee had heard that activity levels influence the choice of whether a person would be offered resurfacing arthroplasty, or which bearing surface of a THR is chosen, and would also affect the rate of wear of a prosthesis (see sections 4.3.2 and 4.3.3), but that the NJR did not contain data on activity. The Committee discussed whether having resurfacing arthroplasty rather than THR would allow people to be more active after their surgery. They heard from the Assessment Group's clinical specialist that observational studies had shown that people were more active after resurfacing arthroplasty than after THR, but were likely to have been more active before resurfacing arthroplasty compared with people who underwent THR, and that 1 RCT showed no difference in activity levels after surgery in people randomised to resurfacing arthroplasty or to THR. The Committee agreed that there was uncertainty around whether the difference in revision rates between THR and resurfacing arthroplasty could just be attributed to risk of failure of the prostheses because it is likely that people who have resurfacing are more active than people who have THR and higher activity may cause accelerated wear of a prosthesis. The Committee also heard that comorbidities may influence which type of prosthesis a patient receives and whether or not a patient is offered revision surgery. The Committee concluded that the Assessment Group's analysis of revision rates was consistent with published systematic reviews of trials, and controlled for some, but not all, potential confounders, notably activity level and comorbidities, and therefore uncertainty remained surrounding the relative revision rates between different types of prostheses.

4.3.7 The Committee considered whether data on revision surgery in the Assessment Group's NJR data set could be considered a proxy for prosthesis failure. The Committee noted that the NJR captured revision rates, but not failure rates of the prostheses, and that some people need revision surgery for pain only (without the prosthesis failing). The Committee further noted that there are people who need a revision because their prosthesis has failed, but who are not fit enough to have surgery or who choose not to have surgery. The Committee appreciated that, in these people, the NJR data on revision rates may underestimate the true failure rate. After consultation on the appraisal consultation document, the Committee further considered revisions that result from prostheses failing and revisions that result from complications during surgery or errors in prosthesis insertion (early revision). The Committee heard from the manufacturers that they expected the proportions of revisions not directly related to device failures to be similar across classes of hip replacement prostheses. The Committee noted a comment received from a manufacturer during consultation stating that early failures associated with dislocation were the fault of the surgeon, but the Committee had no further evidence to support this conclusion. The Committee appreciated that the underlying reason for why a patient needed revision surgery may be difficult to identify and is not routinely recorded in the NJR. In addition, the Committee was told that there is no system that collects data about the prevalence of people living with a failed prosthesis who are unable to, or choose not to, have revision surgery, and no representative data on the proportion of revisions that are a result of failing prostheses. The Committee accepted that, while revision rates may not fully reflect prosthesis failure, revision was an important outcome both from the patient's perspective and in terms of costs and the resources needed.

4.3.8 The Committee considered the approaches to modelling revision rates beyond the maximum 9 years of follow-up in the NJR. It discussed the bathtub model and the log-normal model used by the Assessment Group in its base case, and sensitivity analysis, and the Weibull model used by the manufacturer in its base case. The Committee noted that the bathtub model, which it understood was widely used in manufacturing to describe device failure, assumed that risk of revision would decrease initially and then increase over time, whereas the log-normal and Weibull models assumed an increasing risk of revision over time. The Committee compared the revision rates predicted by all 3 models with data from the Swedish registry, in which people aged between 60 and 75 years who had a hip replacement (resurfacing arthroplasty or THR) were followed up for 19 years. In the population for whom resurfacing was not suitable, the bathtub model predicted longer-term outcomes that fitted the data from the Swedish registry better than the log-normal model. The manufacturer's Weibull model did not fit the Swedish data as well as the Assessment Group's bathtub model did. The Committee noted that there was uncertainty surrounding the generalisability of the Swedish registry data to the UK population, in part because the Swedish registry was initiated earlier than the NJR. The Committee noted that the revision rates in the Swedish registry were higher than the revision rates predicted by the 3 models used to extrapolate data from the NJR. The Committee concluded that, of the 3 models presented to extrapolate revision rates beyond the 9-year follow-up of the NJR, the Assessment Group's bathtub extrapolation was the most plausible.

4.3.9 The Committee examined the economic modelling that had been carried out for the appraisal. The Committee noted that the 2 economic models presented by the Assessment Group and by 1 manufacturer (DePuy Synthes) had similar structures and were based on a model structure that had been used in previous health economic evaluations of hip replacement prostheses. The Committee concluded that the outlined structure of the models adhered to the NICE reference case for economic analysis and was acceptable for the purpose outlined in the scope.

4.3.10 The Committee considered the utility values and the source of the health-related quality-of-life data used by the Assessment Group and the manufacturer. The Committee observed that, in both models, the differences in QALYs gained between the types of hip replacement were very small (see section 4.2.11). The Committee discussed how different types of hip replacement surgery would affect a patient's quality of life. The Committee noted that the Assessment Group's utility values came from PROMs in the NJR and were collected postoperatively, but were not specific to individual types of prosthesis. The Committee noted that, in the manufacturer's model, different types of THR and resurfacing arthroplasty were also associated with the same utility value after surgery. The Committee noted that, in the manufacturer's model, a disutility of 0.145 had been applied after a successful revision. This was to reflect that a patient is unlikely to return to the level of health-related quality of life experienced after the primary surgery, whereas the Assessment Group had assumed that utility after a successful revision would be the same as utility after a successful primary hip replacement. The Committee heard from the Assessment Group's clinical specialist and the manufacturer that, although a successful primary hip replacement would be expected to relieve pain and disability associated with end-stage arthritis of the hip completely, revision surgery was associated with both greater risks and poorer functional outcomes than primary surgery and it was appropriate to apply a disutility value in the post-revision health state, as in the manufacturer's model. The Committee concluded that it was plausible that people who had revision surgery would have a lower quality of life than people who had a successful primary hip replacement. It further concluded that, given the available evidence, it was not possible to determine how use of different types of hip replacement prostheses would affect quality of life.

4.3.11 The Committee discussed the costs of the prostheses. It understood that the Guide to the methods of technology appraisal 2008 recommends using public list prices in the reference-case analysis, but noted that the NHS routinely pays a lower price for hip replacement prostheses because of volume-dependent and locally negotiated discounts. The Committee was aware that the Assessment Group obtained an average of sample list prices from the NHS Supply Chain for multiple manufacturers, and that the manufacturer had presented list prices for its own brands. The Committee also noted that the Assessment Group's prices were higher than the manufacturer's (with some exceptions). The Committee concluded that there was considerable uncertainty surrounding the prices of prostheses.

4.3.12 The Committee considered the base-case economic analyses presented by the Assessment Group and 1 manufacturer. It noted that they generated broadly similar results, that is, THR dominated resurfacing arthroplasty in both the Assessment Group's and manufacturer's base cases, and that resurfacing arthroplasty remained dominated in every sensitivity and subgroup analysis. The Committee also noted that, although the categories of THR differed in the Assessment Group's and manufacturer's analyses, cemented prostheses tended to be the least costly and most effective, but with small incremental differences in costs and QALYs compared with other types of THR. The Committee also noted that, in the analyses of cost effectiveness, the Assessment Group and manufacturer used the average revision rate across category, and that the revision rate was the most important key driver of costs and QALYs in the model. The Committee concluded that THR was more effective and less costly than resurfacing arthroplasty in all analyses, but that the small differences between cemented and cementless THR were associated with uncertainty.

4.3.13 The Committee discussed the approach of comparing the cost effectiveness of categories of THR and resurfacing arthroplasty by category rather than by individual brands. The Committee was aware that devices can differ only slightly and that, within each category, there are multiple brands. The Committee further noted comments received on the appraisal consultation document that not all categories of THR had been investigated by the Assessment Group. The Committee was aware that the Assessment Group had assessed the 5 most frequently used combinations of bearing surface and fixation method in the NJR and considered this to be appropriate. The Committee considered that the Assessment Group and manufacturer had not taken into account the uncertainty related to revision rates of different brands of prostheses within a category. The Committee noted that the Assessment Group had modelled a revision rate of 17.2% for men and women at 10 years for resurfacing arthroplasty, and 12.4% for men only (in current practice resurfacing is predominantly used in men), and that these revision rates were higher than the current NICE standard of 10% or less at 10 years in NICE technology appraisal guidance 2 and NICE technology appraisal guidance 44. However, the Committee noted that 1 manufacturer of resurfacing arthroplasty products had provided evidence that its product had a revision rate lower than the NICE standard. In response to the appraisal consultation document, several consultees emphasised that revision rates vary between different brands of prosthesis within a category. The Committee noted again that making recommendations by revision rate allowed individual brands to be assessed separately. The Committee reiterated that it had considered making recommendations for prosthesis by category based on the average revision rate of multiple brands within a category. However, the Committee chose not to make recommendations by category, having concluded that this would disadvantage individual brands of prostheses with low revision rates, and would give an unfair advantage to individual brands with high revision rates within an overall well-performing category.

4.3.14 The Committee considered whether it was still appropriate to recommend a revision rate for prostheses of 10% or less at 10 years, as recommended in NICE technology appraisal guidance 2 and NICE technology appraisal guidance 44. The Committee noted that the Assessment Group, having analysed and extrapolated data from the NJR for the population for whom both procedures were suitable, had estimated that the 10-year revision rate for resurfacing arthroplasty was worse (higher) than the standard, and that the 10-year revision rates for THR were much better (lower) than 10% at 10 years. Furthermore, the Committee noted that, in the population for whom resurfacing was not suitable, the highest estimate across the 5 categories of THR was less than 5% at 10 years. The Committee agreed that the current standard was too high for both populations, and was aware that prostheses become more cost effective the lower the revision rates. Therefore, it discussed how a new standard could be determined with the data available. The Committee considered that, because all of the categories of THR prostheses for both populations had a predicted revision rate of less than 5% at 10 years, the value reflecting the new standard for THRs should be no higher than 5%. Additionally, it considered that, because the predicted revision rate of THR was less than 5% at 10 years in the population for whom both THR and resurfacing arthroplasty were suitable, the revision rate standard for resurfacing arthroplasty should be the same as that for THRs. The Committee noted that, although the average revision rate was predicted to be 5% or less at 10 years, it was likely that within a category of THR some brands would perform poorly and would not meet this standard. The Committee discussed whether the proposed value should be reduced to even less than 5% to provide a more 'aspirational' standard. However, the Committee acknowledged that limitations in the data available (see section 4.3.6) did not allow it to determine the lowest revision rate that current practice could realistically achieve. The Committee concluded that it was appropriate to recommend that a prosthesis (for either resurfacing arthroplasty or THR) should meet a revision rate of 5% or less at 10 years.

4.3.15 The Committee was aware that NICE technology appraisal guidance makes recommendations on the most cost-effective use of NHS resources but does not specify how to implement the guidance. It was also aware that the NICE Implementation Programme supports health and social care organisations to maximise the uptake and use of evidence and guidance. The Committee was further aware that ODEP, which is independent of NICE, currently provides the NHS with a list of prostheses that do or do not meet the standard for revision rates outlined in NICE technology appraisal guidance 2 and NICE technology appraisal guidance 44, and that there are initiatives to improve collecting and disseminating information on revision rates. The Committee discussed whether, given the current support for implementation available to the NHS, it would be possible to implement guidance in which recommendations depended on prostheses meeting a 5% or less revision rate at 10 years, particularly for brands with less than 10 years of data. The Committee was aware that NICE technology appraisal guidance 2 and NICE technology appraisal guidance 44 considered it reasonable to recommend prostheses with a minimum of 3 years of experience, provided the projected revision rate was consistent with the standard recommended at that time; the Committee considered that this remained appropriate. The Committee noted that the ODEP rating system includes 3 entry revision rate benchmarks assuming a linear relationship between the time since primary hip replacement and the proportion of people who would be expected to have a revision. The Committee agreed that, while other appropriate distributions may exist, the analysis of revision rates presented by the Assessment Group for this appraisal had shown it was reasonable to extrapolate using the bathtub function for prostheses with a follow-up of less than 10 years. Furthermore, the bathtub model accounted for a higher rate of early revisions, which may reflect surgical complications or other factors unrelated to the prosthesis (see sections 4.3.7 and 4.3.8). The Committee preferred the Assessment Group's method of extrapolating revision rates to a linear extrapolation, but was content that ODEP needs to determine the methods with which it estimates revision rates based on the quality of the data provided by the manufacturers and the timing of the reporting of revision rates in clinical practice. The Committee concluded that it would be reasonable to recommend prostheses with less than 10 years of data, provided that the revision rate was, in as much as the shorter term follow‑up data allow, consistent with 5% or less at 10 years and that the recommendation could be implemented within the current support framework provided by ODEP. It also concluded that prostheses currently with at least 3 years of data, which estimate a higher than 5% revision rate at 10 years when projected, should not continue to be offered to patients.

4.3.16 The Committee considered other aspects of how prostheses are currently being rated and noted comments received from ODEP on the appraisal consultation document, in which ODEP clarified that it gave ratings for stem and cup components individually because of the large number of cup and stem components available and their many combinations. The Committee considered whether the revision rate standard of 5% or less at 10 years should apply to each cup and stem component separately. The Committee agreed that total hip replacement or resurfacing arthroplasty can be considered to meet the revision rate standard of 5% or less at 10 years if all components have an ODEP rating consistent with this standard.

4.3.17 The Committee considered the cases in which there may be more than 1 prosthesis suitable for a patient that meets the revision rate standard of 5% or less at 10 years. It was aware that current arrangements of generating ODEP ratings do not provide the NHS with the absolute revision rate for an individual prosthesis but only information on whether or not the standard was achieved, and that this was because ODEP receives revision rates from several registries or published papers each with different volumes of implants making a scientifically robust aggregation difficult. The Committee considered that, if more than 1 prosthesis meets the 5% or less revision rate standard, it would prefer to recommend the most cost-effective prostheses (those with the lowest revision rates) but concluded that, without absolute revision rate data for each hip replacement system, this would not be feasible to implement.

4.3.18 The Committee was aware that, because of uncertainties surrounding the costs of prostheses and the discounts available to the NHS, it was not possible to give an estimate of the mean price paid in the NHS for a given prosthesis. The Committee considered that its recommendations should promote maintaining (at least) the level of discount from prostheses' list prices currently offered to the NHS. The Committee discussed whether, if more than 1 prosthesis meets the 5% or less at 10 years revision rate standard, it should recommend the prosthesis with the lowest acquisition costs. The Committee considered comments received during consultation on the appraisal consultation document. It was aware that the cost of THR and resurfacing arthroplasty included both procedure costs and surgical costs. The Committee noted that the Assessment Group had used published literature to determine surgical costs and had assumed that these would be the same for resurfacing arthroplasty and THR. The Committee also noted that 1 manufacturer (DePuy Synthes) had carried out a costing study to estimate time in surgery and consumables, and that the manufacturer stated that procedure costs differed for resurfacing arthroplasty and for THR, and between various types of THR. The Committee heard from the manufacturers that the cost of a prosthesis may be a small proportion of the tariff paid by the NHS for a hip replacement. The Committee noted that the cost of a prosthesis is included in the fixed NHS tariff. The Committee considered the comments received from consultees on the appraisal consultation document, which stated that the benefits of manufacturer support packages had not been taken into account. However, the Committee concluded that tender costs included training in the use of a prosthesis. The Committee concluded that, although the NHS should be mindful of costs, in situations where multiple prostheses with a revision rate of 5% or less at 10 years are suitable for a patient, it could not currently recommend selecting a prosthesis with the lowest acquisition cost. The Committee further concluded that the recommended standards for revision rate would encourage manufacturers to maintain training programmes to ensure the lowest revision rates possible for their products.

Summary of Appraisal Committee's key conclusions