ReviewTotal knee replacement: Is it really an effective procedure for all?
Introduction
Chronic knee pain, most commonly caused by osteoarthritis (OA), is highly prevalent among the general UK population, affecting between 7 and 33% of adults (Table 1). Many non-surgical therapeutic interventions are available to people with chronic knee pain, such as medications, self-management programmes and physiotherapy. However, these interventions have been shown to have only small effect sizes on knee pain [1]. When these conservative treatments fail, patients may be offered surgical interventions, such as osteotomy and arthroscopy, although these procedures also have only limited success in pain reduction [2]. The only intervention that has a large effect size on relieving chronic knee pain is total knee replacement (TKR) [1].
TKR is widely considered as an effective and successful end-stage surgical procedure for relieving chronic knee pain and functional disability, based on results from surgeon-based outcome tools and survivorship analysis [3], [4]. However, it has emerged, through the use of patient-reported outcome measures, that this is not a true representation of the experience of TKR for all patients because there exists a significant number of patients who experience continuing pain and functional disability after TKR [5]. It is clearly important to identify possible causes, such as pre-operative pain sensitisation, that contribute to a failure to benefit from TKR so that these factors could then be addressed with appropriate pre-operative intervention. The aim of this article is to review the evidence that a considerable proportion of people have a poor outcome after TKR and the possible patient factors that could explain this outcome.
Section snippets
Epidemiology of TKR
The incidence of TKR has risen dramatically since its introduction in the 1960's and 1970's. Between 1991 and 2000 the number of primary TKRs performed in the NHS doubled [6] and the increase in the United States was even greater, with the prevalence of primary TKR tripling between 1990 and 2002 [7]. In 2006, over 45,000 TKRs were performed in England and Wales [8]. Dramatic increases in the future incidence of TKR are also expected. In the United States, statistical projections for the number
Outcomes assessment
With the increasing prevalence of TKR, it is imperative that patient outcomes are rigorously assessed using validated tools to determine the success of the procedure from the patient's perspective. Within orthopaedics, outcomes research has evolved to reflect the growing improvements in prosthetic design and surgical technique. Whereas traditionally survivorship analysis was employed to determine the lifespan of orthopaedic implants, early failure of TKR is now a rare complication, with up to
Chronic pain after TKR
Chronic pain is the primary reason for people electing to undergo TKR [17] and therefore pain relief is a key outcome after surgery. Much of the research literature indicates that TKR provides good pain relief. Using the WOMAC pain scale, on which a score of 0 represents maximal pain and 100 represents no pain, mean scores improve from 40–45 pre-operatively [18], [19] to 76 at 6 months [20], 82 at 2 years [19] and 88 at 10 years post-operative [11]. These pain scores could be interpreted as
Activities of daily living
Improvements in functional ability after TKR are also variable. Whereas post-operative mean WOMAC pain scores can reach into the 80s, the mean WOMAC function scores are lower, improving from 43 pre-operatively [19], [20] to 70 at 2 years [19], 78 at 5 years [25] and 79 at 10 years [11]. The restoration of unimpaired functional ability after TKR is rare, with only 33% of people reporting no functional limitations with their replaced knee [11]. Nearly a fifth of TKR patients felt that their
Poor health-related quality of life after TKR
Health-related quality of life (HRQoL), which includes the physical, emotional and social dimensions of life, has been recognised as a wider outcome domain by which to assess TKR success. A review found that joint replacement improves most dimensions of HRQoL, except the social dimension [35]. Although improvements in HRQoL do occur, they are often slower and smaller than those experienced in other outcome domains, such as physical function [36]. Long-term evaluation of TKR found that a quarter
Patient dissatisfaction after TKR
Patient satisfaction with the outcome of TKR is becoming increasingly used as a measure of the patient's perception of TKR success. Satisfaction has been shown to correlate strongly with pain, functional ability, social functioning and mental health [4], [25]. Mean satisfaction scores are generally high after TKR but, as with other domains of outcomes, not all patients score highly. Based on a sample of over 27,000 patients from the Swedish Knee Arthroplasty Register, 8% of patients were
Comparison of patient-reported outcomes after TKR and THR
Advances in surgery have dramatically improved outcomes after TKR over the past decades, although patients are still less willing to undergo TKR than THR in the UK [41]. Although the two surgical interventions could be perceived as very similar procedures, outcomes after TKR and THR vary greatly. In terms of function and pain, THR results in faster and larger improvements than TKR [37], [39]. Reductions in pain and function limitations that are experienced in the first 3 months after THR can
Why do some patients experience a poor outcome after TKR?
Some of the reported pain and functional limitations after TKR will be due to surgical technique and prosthetic design, such as polyethylene wear and loosening [43]. However, when a series of 27 patients underwent an exploration of TKR for severe unexplained pain, only 45% of patients were found to have problems relating to their implants [43]. Therefore, much of the chronic pain and associated disability experienced by patients after TKR is medically unexplained.
Currently very little is known
Conclusion
TKR is undoubtedly an effective procedure for reducing knee pain and physical limitations in some patients, although physical function is not restored to the level of the general population. From the literature, it is evident that there exists a substantial subsection of the TKR population who experience little or no benefit from the operation. Often the poor outcome of these patients is hidden among the reporting of mean pain and function scores. The identification of this subpopulation of
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