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International Journal of Rheumatology
Volume 2013 (2013), Article ID 506518, 8 pages
The Utility of Outcome Measures in Total Knee Replacement Surgery
The University of Melbourne, Department of Surgery, Saint Vincent's Hospital, 41 Victoria Parade, Fitzroy, Melbourne, VIC 3065, Australia
Received 9 June 2013; Accepted 15 September 2013
Academic Editor: Lilian Ghandour
Copyright © 2013 Michelle M. Dowsey and Peter F. M. Choong. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Total knee replacement (TKR) is the mainstay of treatment for people with end-stage knee OA among suitably “fit” candidates. As a high cost, high volume procedure with a worldwide demand that continues to grow it has become increasingly popular to measure response to surgery. While the majority who undergo TKR report improvements in pain and function following surgery, a significant proportion of patients report dissatisfaction with surgery as a result of ongoing pain or poor function. Poor outcomes of TKR require care that imposes on already overburdened health systems. Accurate and meaningful capture and interpretation of outcome data are imperative for appropriate patient selection, informing those at risk, and for developing strategies to mitigate the risk of poor results and dissatisfaction. The ways in which TKR outcomes are captured and analysed, the level of follow-up, the types of outcome measures used, and the timing of their application vary considerably within the literature. With this in mind, we reviewed four of the most commonly used joint specific outcome measures in TKR. We report on the utility, strengths, and limitations of the Oxford knee score (OKS), knee injury and osteoarthritis outcome score (KOOS), Western Ontario and McMaster Universities osteoarthritis index (WOMAC), and knee society clinical rating system (KSS).
Total knee replacement is a major surgical procedure that requires multidisciplinary input prior to and after surgery to ensure the best possible outcome. Recovery from surgery is optimized with the inclusion of rehabilitation programs which are tailored to restore mobility and independence . Time to recovery can vary following TKR, and most patients will report substantial gains between 3 and 6 months after surgery [2, 3]. Overall, a continuing pattern of improvement can be observed up to 12 months following surgery [4, 5]. While a majority of patients report improvements in pain and function following total knee replacement [6, 7], a substantial number of individuals do not meet the level of improvement expected at 12 months or more after surgery [8, 9].
A number of individual characteristics are known to influence pain and function after surgery . Individual risk factors which impact on patient outcomes after TKR include age and gender [7, 11, 12], antecedent diagnosis , body mass index [14, 15], ethnicity , psychological distress [13, 17], baseline pain and functional disability [7, 13], comorbidity profile [10, 18], socioeconomic status , and radiographic osteoarthritis severity [7, 20]. Some of these, such as obesity and psychological distress, are potentially modifiable, making accurate and meaningful capture and interpretation of outcome data imperative for both informing those at risk and for developing strategies to mitigate the risk of poor results and dissatisfaction.
Rates of ongoing knee pain and functional impairment following TKR vary considerably in the literature, ranging from 14% to 44% of individuals reporting persistent pain [7, 9, 21, 22] and from 20% to 50% of individual was reporting functional impairment [7, 22, 23] in the first 12 to 24 months following surgery. Of note the way in which data is captured and analysed, the level of follow-up, the types of patient-reported outcome measures (PROMs) used and the timing of their application also vary considerably between these studies. Numerous instruments for measuring the outcomes of TKR exist; however, not all of them contain the necessary attributes of a “good” outcome measure. When selecting which measure to use, consideration should be given to whether the measure is appropriate for use specific to the procedure being assessed. A good outcome measure should be accessible, have demonstrated reliability and validity, place minimal burden on responders, and be responsive to change . High floor and ceiling effects indicate insensitivity for detecting a change of symptoms and the maximum cut-off for floor and/or ceiling effects should be no more than 15% . With this in mind, we reviewed the four most commonly used joint specific outcome measures in TKR and report on their utility, strengths, and limitations.
2. Oxford Knee Score (OKS)
The OKS is a knee joint specific 12-item questionnaire originally developed and validated in 1998 for use in randomised controlled trials in total knee replacement (Table 1) . The OKS has 12 items, 5 for assessing pain and 7 for assessing function. Each item is worth equal weighting (1 to 5) for a total possible score ranging from 12 to 60. A lower score indicates a better outcome. The OKS is freely available at http://phi.uhce.ox.ac.uk/ox_scores.php and widely used in cohort studies and by some joint replacement registries [9, 26, 27]. A scoring manual, list of translations, and licensing information can be found via http://www.isis-innovation.com/outcomes/orthopaedic/oks.html.
The OKS is designed specifically for measuring outcomes in knee replacement. The OKS has also been used to evaluate pharmacological and conservative interventions and other knee surgery procedures in knee osteoarthritis (OA) . Cross-cultural adaptations in Thai, British, Swedish, Portuguese, Dutch, German, Italian, Japanese Chinese, French, and Korean languages have been validated [29, 30]. Given the simplicity and brevity of the questionnaire, higher response rates have been reported than for other PROM’s ; however, this is not always consistent .
Completion and scoring of the OKS is simple; each of 12 questions carries equal weighting (1 to 5) to provide an overall score between 12 and 60 . An updated scoring method is also used, whereby each item is scored between 0 (worst outcome) and 4 (best outcome), to provide an overall score between 0 and 48 . The OKS is patient administered and should take about 5 minutes to complete, and responses are based on symptoms in the preceding 4 weeks. Two missing values are accepted, and where this occurs should be replaced by the mean score for the missing item . The outcome categories for the OKS have been reported based on the following cut points: excellent (>41), good (34–41), fair (27–33), and poor (<27) [32, 33]. However, these categories have not been validated and are neither commonly used nor recommended .
The minimum clinically important difference (MCID) estimates for the OKS as reported by Murray et al.  are between 3 and 5 points. These estimates are based on half the standard deviation of change in OKS scores which Murray et al. report to be is between 6 and 10 points for joint replacement studies. This interpretation is based on a systematic review of health-related quality of life instruments by Norman et al. who concluded that, in most circumstances, the threshold of discrimination for changes in health-related quality of life for chronic diseases appears to be approximately half a standard deviation of the change in outcome score . In a recent study, Judge et al. reported that an 11-point or more absolute change in the OKS at 6 months after TKR discriminated the best between patients’ satisfaction and a 6-month OKS ≥ 30 points identified the highest level of satisfaction . A weak floor effect (7%) has been reported for the OKS prior to TKR ; however, ceiling effects were reported at 6 months, (14%) and 12 months, (22%) following surgery, but this was attributed to patients attaining an optimal outcome rather than a limitation of the OKS .
3. Knee Injury and Osteoarthritis Outcome Score (KOOS)
The KOOS is a knee joint specific questionnaire developed in 1998 originally for the purpose of evaluating short-term and long-term symptoms and functioning in subjects with knee injury and osteoarthritis (Table 1). It was originally validated in patients undergoing anterior cruciate ligament ACL reconstruction . The KOOS is a 42-item survey designed to assess people’s opinions about the difficulties they experience with activity due to problems with their knees. A higher score indicates a better outcome. The questionnaire, scoring instructions, and translations are freely available at http://www.koos.nu/. The KOOS is widely used in younger and/or more active patients with knee injury and knee osteoarthritis .
The KOOS has been validated for measuring outcomes in TKR , ACL reconstruction , and posttraumatic knee OA . The KOOS has also been used to evaluate other OA interventions including minor knee surgery procedures , conservative treatments [42, 43], and nutritional  and pharmacological interventions , and population-based reference data has been published . High response rates have been reported for studies of TKR in the short term: 92% at 6 months and 86% at 12 months . A short-form version (KOOS-PS) which is a 7-item questionnaire derived from the original KOOS has been validated for evaluating physical function in individuals with knee OA undergoing TKR . The KOOS was originally concurrently developed in English and Swedish, and numerous cross-culturally validated and translated versions exist . Translations include Austrian-German, Chinese, Croatian, Czech, Danish, Dutch, Estonian, French, German, Hindi (India), Italian, Japanese, Korean, Latvian, Lithuanian, Norwegian, Persian, Polish, Portuguese, Russian, Singapore English, Slovakian, Slovenian, Spanish (Peru), Spanish (US), Thai, Turkish, and Ukrainian.
Completion of the survey is straightforward; each of the 42 items carries equal weighting (0–4). There are 5 subscales, each measuring a specific outcome: pain (9 items), symptoms (5 items), activities of daily living (17 items), sports and recreation function (5 items), and knee-related quality of life (4 items). Scores for each subscale should be calculated separately and then transformed into a score between 0 and 100 . Scoring instructions and calculators are available at http://www.koos.nu/. The KOOS is patient administered and should take approximately 10–15 minutes to complete, and responses are based on symptoms in the preceding week. The process for managing missing values has been recently (2012) revised (see website), and the mean score for each subscale can be derived from a minimum response of pain (5 of 9 items), symptoms (4 of 5 items), activities of daily living (9 of 17 items), sports and recreation function (3 of 5 items), and knee-related quality of life (2 of 4 items) (http://www.koos.nu/). There are no categorical equivalents, scoring of each outcome should be reported separately, and using an aggregate score is neither recommended nor valid.
The MCID estimates for the KOOS have not been established for patients undergoing TKR. However, the minimal important change (MIC) is currently suggested to be 8–10 according to the website details, while cautioning that there are a number of patients and related factors that may impact on the MIC. Floor and ceiling effects have been reported for studies of TKR in some domains of the KOOS . Preoperatively, the percentage of patients undergoing TKR with the worst possible score have reached 48% for the sports and recreation domain of the KOOS. Ceiling effects at 6 months have also been reported (15% for pain scores and 16% for sports and recreation) and at 12 months (22% for pain scores and 17% for quality of life scores).
4. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)
The WOMAC was initially developed in 1982 and was first validated for the purpose of evaluating response to treatment in patients with hip and knee OA in 1998 (Table 1) . The WOMAC underwent multiple subsequent revisions and refinements between 1996 and 1999 . The WOMAC is a 24-item questionnaire with 3 subscales measuring pain (5 items), stiffness (2 items), and physical function (17 items). A lower score indicates a better outcome. The questionnaire, licensing information, scoring instructions, and translations are available at http://www.womac.org/.
Numerous validation studies have been conducted using the WOMAC . The WOMAC has been validated for measuring outcomes in clinical trials of TKR  and for measuring treatment response of pharmacological interventions for knee OA . It has also been used to evaluate many knee OA interventions, both surgical and conservative . Response rates reaching 90% at 1 year for epidemiological studies in TKR have been reported [55, 56]. A short-form version (WOMAC-SF) which is a 7-item questionnaire derived from the physical function subscale of the WOMAC has been validated for assessing function in knee OA and TKR [57, 58]. The WOMAC is available in more than 80 languages and has been cross-culturally validated in Arabic, Chinese, Dutch, Finnish, German, Hebrew, Italian, Japanese, Korean, Moroccan, Persian, Singapore, Spanish, Swedish, Thai, and Turkish [24, 59].
Completion of the survey is straightforward; each of the 24 items has 5 possible responses for a possible score of 0 to 4 for each response. There are 3 subscales, each measuring a specific outcome: pain (5 items), stiffness (2 items), and physical function (17 items). Alternative versions are available using a visual analogue scale or numeric rating . A total WOMAC score is calculated by summing the items for all 3 subscales, for a total score between 0 and 96 . The WOMAC is patient administered and should take approximately 10 minutes to complete, and responses are based on symptoms in the preceding 48 hours. The method of managing missing values for the WOMAC is a variant of a standard mean imputation method. Scores of the nonmissing items for each case should be added, and the mean value is used for the missing values. However, if the patient has not replied to more than one of the 5 pain or 2 stiffness items or more than 4 of the 17 physical function items, then response for that scale is considered invalid and should not be included in the analyses .
The MCID estimates for the WOMAC as reported by Escobar et al. are 15 points . In addition, Escobar et al. have validated the Outcome Measures in Rheumatology and Osteoarthritis Research Society International (OMERACT-OARSI) set of responder criteria in total joint replacement . Patients are deemed responders or nonresponders based on a combination of absolute and relative changes of pain, function, and global patient’s assessment. The criteria are as follows: (i) an improvement in pain or function ≥ 50% and an absolute change ≥ 20, then the patient is considered a responder, and (ii) if the level of improvement does not reach these criteria but improvement in at least two of the three following criteria, the patient will also be considered a responder, (a) pain ≥ 20% and absolute change ≥ 10, and (b) function ≥ 20% and absolute change ≥ 10, (c) global assessment ≥ 20% and absolute change ≥ 10.
Minimal floor effects for the WOMAC have been reported with the exception of the quality of life subscale which was reported at 14% by Roos and Toksvig-Larsen . Ceiling effects have been reported for TKR at both 6 months; 27% for the pain subscale and 15% for the stiffness subscale and at 12 months; 17% for the quality of life subscale, 30% for the pain subscale, and 27% for the stiffness subscale [39, 63].
5. Knee Society Clinical Rating System (KSS)
The KSS is a knee joint specific questionnaire originally developed and validated in 1989 for use in assessing the outcome of total knee replacement (Table 1) . The KSS has 2 components: a knee rating (0–100 points) and function (0–100 points) worth a total of 200 points. The knee rating is divided into pain (0–50 points) and a knee score which assesses range of motion, stability, and alignment (0–50 points). A higher score indicates a better outcome. The KSS is freely available at http://www.kneesociety.org/web/index.html and widely used in outcome studies for partial and total knee replacement. As a “clinician completed” scoring system aspects of its validity have been questioned by some authors [65–67]. In response to these criticisms, a revised knee society scoring system (2011-KS Score) has recently been developed  and validated  for measuring outcomes in TKR. A scoring manual, list of translations, and licensing information for both the KSS and 2011-KS can be found via http://www.kneesociety.org/web/index.html.
Despite validity issues, the KSS remains one of the most popular questionnaires amongst clinician researchers for measuring outcomes in knee replacement . The KSS includes range of motion and alignment measurements, and this may in part contribute to its popularity. The importance of coronal alignment in TKR in terms of implant survival and functional outcomes has been well established in the literature [70, 71], and knee range of motion is an important marker for many activities of daily living . The KSS has also been used to evaluate outcomes in other orthopaedic procedures such as high tibial osteotomy  and patellofemoral arthroplasty . Linguistically translated versions of the KSS include Spanish  and Portuguese  and for the 2011-KS, Italian, Japanese, Mandarin Chinese, Portuguese, and Spanish. A Dutch version of the 2011-KS has also recently been validated . Despite a “clinician” scoring system, the pain and function subscales of the KSS have been offered to patients to complete with high response rates reported at 12 months or more [7, 78].
Completion and scoring of the KSS are simple; the function subscale (0–100) is based on walking distance (0–50) and ability to climb stairs (0–50) with deductions for use of a gait aid (0–20). The pain subscale is (0–50) and the knee rating (0–50) is based on range of motion (0–25) and knee stability (0–25) with deductions made dependent on the existence and severity of flexion contracture (0–15), extension lag (0–15), and malalignment (0–20) . A negative score is possible and should be converted to zero. A web-based calculator is available at http://www.orthoscores.com/scorepages/knee_society_score.html. Categories for the KSS have been established but not validated . Cut points for each of the 2 subscales are excellent (≥80), good (70–79), fair (60–69), and poor (<60). The KSS is clinician administered and should take less than 10 minutes to complete. The pain and function subscales should take about 5 minutes to complete whether by clinician or patient, and responses are based on symptoms in the preceding 4 weeks. No instruction on managing missing items could be found.
The 2011-KS scoring manual and instructions can be requested via the knee society website above. The 2011-KS expands on the KSS and includes subscales for patient satisfaction (5 items, 0–40 points), expectation (3 items, 0–15 points), and functional activities (19 items, 0–100 points), which is divided into functional activities (5 items, 0–30 points), standard activities (6 items, 0–30 points), advanced activities (5 items, 0–25 points), and discretionary knee activities (3 items 0–15 points) . Satisfaction expectation and function should be reported as separate scores as a composite score is not recommended. The suggested method for managing missing values is to enter dummy values equal to the average of all of the other items in the same domain. This should be limited to instances where fewer than 50% of responses are missing .
The MCID estimates for the KSS and 2011-KS have not been identified for patients undergoing TKR. However, in a study by Jacobs and Christensen, a minimum change of 34.5 points at 3 months in the function subscale of the KSS was established as clinically important . Ceiling effects have been reported for studies of TKR in both the knee (25%) and function (43%) subscales of the original KSS at 12 months . Floor effects did not occur preoperatively and ceiling effects did not occur at 6 months after TKR in a Dutch study validating the KS-2011 .
Total knee replacement remains the mainstay of treatment for people with end-stage knee OA (among suitably “fit” candidates). As a high cost, high volume procedure with a worldwide demand that continues to grow, it is becoming increasingly important to understand the drivers behind response to surgery . Poor outcomes of TKR require care that is an imposition on an already overburdened health system. Not only will there be a demand for ongoing outpatient specialist and community health consultations, persistent use of prescription medication, prolonged requirement for allied health services (physiotherapy and occupational therapy), and the possible need for repeated minor (arthroscopic) and major (revision joint replacement) surgery, these activities potentially deprive or delay other patients with untreated OA from receiving expeditious care.
Numerous instruments for measuring outcomes in TKR have been developed and validated over time  in an attempt to capture response to surgery and predict those who may be at risk of suboptimal results. We have presented a summary of the utility, strengths, and limitations of four of the most commonly used outcome measures for total knee replacement. Generic strengths among the four outcome measures included the relatively minimal burden required to complete each instrument and their design specific to measuring TKR outcomes, whereas ceiling and/or floor effects were a limitation to varying degrees for each of the four outcome measures, with the exception of the 2011-KS which requires further validation studies. No single outcome measure would be suitable for every foreseeable clinical situation or research activity. The individual strengths of each outcome measure may be useful in guiding the decision as to which measure is best suited for use, in any given situation. We noted a number of individual strengths amongst the outcome measures presented in this review.
The OKS is freely available and noted for its simplicity and brevity and appears to be the measure of choice for large data sets and joint registry’s [9, 26, 27]. The KOOS is also freely available and aside from TKR is valuable for measuring outcomes in younger and/or more active patients with knee injury and knee osteoarthritis. The KOOS is also used to measure outcomes following a range of both surgical and conservative interventions of the knee, both surgical and conservative, making it attractive for treatment comparisons [38–45]. WOMAC scores can also be derived from the KOOS. An important aspect of the utility of any outcome measure is the availability of responder definitions and cutoff points and that these are appropriately validated. The WOMAC is currently the only outcome measure that has validated responder definitions and cutoff points specifically for TKR . Having a set of established and validated response criteria makes the WOMAC an excellent option for use in clinical trials that aim to measure response to TKR and other nonsurgical interventions [52, 53]. It also has the most extensive range of translations available. Despite validity issues, the KSS remains one of the most popular rating systems for measuring outcomes in TKR . It is one of the few outcome measures that include assessment of clinical measures that are deemed important in terms of implant survival and functional outcomes [70, 71]. The 2011-KS also includes measures of patient expectation and satisfaction which are emerging as important adjuncts in measuring response to surgery .
While the utility of any one particular outcome measure over another continues to be debated and the number of available instruments continues to increase, we believe that there are 2 key factors that are essential in producing quality outcome data irrespective of the instrument used. Firstly, recording of baseline scores is essential for producing meaningful outcome data. It is well established that better baseline scores correlate with better outcome scores and those with the worst baseline scores demonstrate the greatest amount of improvement . Therefore, at a minimum, data analyses should always be adjusted for baseline when either presenting outcome scores or measuring the change in scores. Finally, individuals who do not respond to surveys report significantly poorer outcomes than those who do . As such establishing a process for data collection that ensures the highest possible response rate such as those used by Bourne et al. will minimise nonresponder bias .
Dr. Dowsey holds an NHMRC early career Australian clinical fellowship (APP1035810).
- C. A. Jones, L. A. Beaupre, D. W. Johnston, and M. E. Suarez-Almazor, “Total joint arthroplasties: current concepts of patient outcomes after surgery,” Clinics in Geriatric Medicine, vol. 21, no. 3, pp. 527–541, 2005.
- R. K. Shields, L. J. Enloe, and K. C. Leo, “Health related quality of life in patients with total hip or knee replacement,” Archives of Physical Medicine and Rehabilitation, vol. 80, no. 5, pp. 572–579, 1999.
- P. Rissanen, S. Aro, H. Sintonen, P. Slätis, and P. Paavolainen, “Quality of life and functional ability in hip and knee replacements: a prospective study,” Quality of Life Research, vol. 5, no. 1, pp. 56–64, 1996.
- N. F. Huang, M. M. Dowsey, E. Ee, J. D. Stoney, S. Babazadeh, and P. F. Choong, “Coronal alignment correlates with outcome after total knee arthroplasty: five-year follow-up of a randomized controlled trial,” Journal of Arthroplasty, vol. 27, no. 9, pp. 1737–1741, 2012.
- A.-. Nilsdotter, S. Toksvig-Larsen, and E. M. Roos, “A 5 year prospective study of patient-relevant outcomes after total knee replacement,” Osteoarthritis and Cartilage, vol. 17, no. 5, pp. 601–606, 2009.
- M. M. Dowsey, D. Liew, J. D. Stoney, and P. F. M. Choong, “The impact of obesity on weight change and outcomes at 12 months in patients undergoing total hip arthroplasty,” Medical Journal of Australia, vol. 193, no. 1, pp. 17–21, 2010.
- M. M. Dowsey, M. Nikpour, P. Dieppe, and P. F. Choong, “Associations between pre-operative radiographic changes and outcomes after total knee joint replacement for osteoarthritis,” Osteoarthritis and Cartilage, vol. 20, no. 10, pp. 1095–1102, 2012.
- H. M. K. Ghomrawi, N. F. Ferrando, L. A. Mandl, H. Do, N. Noor, and A. Gonzalez Della Valle, “How often are patient and surgeon recovery expectations for total joint arthroplasty aligned? Results of a pilot study,” HSS Journal, vol. 7, no. 3, pp. 229–234, 2011.
- V. Wylde, A. W. Blom, S. L. Whitehouse, A. H. Taylor, G. T. Pattison, and G. C. Bannister, “Patient-reported outcomes after total hip and knee arthroplasty. Comparison of midterm results,” Journal of Arthroplasty, vol. 24, no. 2, pp. 210–216, 2009.
- M. M. Dowsey and P. F. M. Choong, Predictors of Pain and Function Following Total Joint Replacement, edited by P. Kinov, Arthoplasty—Update, InTech, Rijeka, Croatia, 2013.
- D. P. Williams, A. J. Price, D. J. Beard et al., “The effects of age on patient-reported outcome measures in total knee replacements,” Bone and Joint Journal, vol. 95, no. 1, pp. 38–44, 2013.
- S. S. Liu, A. Buvanendran, J. P. Rathmell et al., “A cross-sectional survey on prevalence and risk factors for persistent postsurgical pain 1 year after total hip and knee replacement,” Regional Anesthesia and Pain Medicine, vol. 37, no. 4, pp. 415–422, 2012.
- A. Judge, N. K. Arden, C. Cooper et al., “Predictors of outcomes of total knee replacement surgery,” Rheumatology, vol. 51, no. 10, pp. 1804–1813, 2012.
- M. M. Dowsey, D. Liew, J. D. Stoney, and P. F. Choong, “The impact of pre-operative obesity on weight change and outcome in total knee replacement: a prospective study of 529 consecutive patients,” Journal of Bone and Joint Surgery B, vol. 92, no. 4, pp. 513–520, 2010.
- M. J. McElroy, R. Pivec, K. Issa, S. F. Harwin, and M. A. Mont, “The effects of obesity and morbid obesity on outcomes in TKA,” The Journal of Knee Surgery, vol. 26, no. 2, pp. 83–88, 2013.
- M. M. Dowsey, M. L. Broadhead, J. D. Stoney, and P. F. Choong, “Outcomes of total knee arthroplasty in English- versus non-English-speaking patients,” Journal of Orthopaedic Surgery, vol. 17, no. 3, pp. 305–309, 2009.
- M. G. Paulsen, M. M. Dowsey, D. Castle, and P. F. Choong, “Preoperative psychological distress and functional outcome after knee replacement,” Australian and New Zealand Journal of Surgery, vol. 81, no. 10, pp. 681–687, 2011.
- G. A. Hawker, E. M. Badley, C. M. Borkhoff et al., “Which patients are most likely to benefit from total joint arthroplasty?” Arthritis and Rheumatism, vol. 65, no. 5, pp. 1243–1252, 2013.
- N. D. Clement, P. J. Jenkins, D. MacDonald et al., “Socioeconomic status affects the Oxford knee score and short-form 12 score following total knee replacement,” Bone and Joint Journal, vol. 95, no. 1, pp. 52–58, 2013.
- M. M. Dowsey, P. Dieppe, S. Lohmander, D. Castle, D. Liew, and P. F. M. Choong, “The association between radiographic severity and pre-operative function in patients undergoing primary knee replacement for osteoarthritis,” Knee, vol. 19, no. 6, pp. 860–865, 2012.
- T. Czurda, P. Fennema, M. Baumgartner, and P. Ritschl, “The association between component malalignment and post-operative pain following navigation-assisted total knee arthroplasty: results of a cohort/nested case-control study,” Knee Surgery, Sports Traumatology, Arthroscopy, vol. 18, no. 7, pp. 863–869, 2010.
- V. Wylde, S. Hewlett, I. D. Learmonth, and P. Dieppe, “Persistent pain after joint replacement: prevalence, sensory qualities, and postoperative determinants,” Pain, vol. 152, no. 3, pp. 566–572, 2011.
- J. A. Singh, M. O'Byrne, S. Harmsen, and D. Lewallen, “Predictors of moderate-severe functional limitation after primary total knee arthroplasty (TKA): 4701 TKAs at 2-years and 2935 TKAs at 5-years,” Osteoarthritis and Cartilage, vol. 18, no. 4, pp. 515–521, 2010.
- N. J. Collins and E. M. Roos, “Patient-reported outcomes for total hip and knee arthroplasty: commonly used instruments and attributes of a, “good” measure,” Clinics in Geriatric Medicine, vol. 28, no. 3, pp. 367–394, 2012.
- J. Dawson, R. Fitzpatrick, D. Murray, and A. Carr, “Questionnaire on the perceptions of patients about total knee replacement,” The British Editorial Society of Bone and Joint Surgery, vol. 80, no. 1, pp. 63–69, 1998.
- New Zealand Orthopaedic Association, New Zealand Joint Registry 2012, New Zealand Orthopaedic Association, 2013.
- D. P. Williams, C. M. Blakey, S. G. Hadfield, D. W. Murray, A. J. Price, and R. E. Field, “Long-term trends in the Oxford knee score following total knee replacement,” Bone and Joint Journal, vol. 95, no. 1, pp. 45–51, 2013.
- D. W. Murray, R. Fitzpatrick, K. Rogers et al., “The use of the Oxford hip and knee scores,” Journal of Bone and Joint Surgery B, vol. 89, no. 8, pp. 1010–1014, 2007.
- I. S. Eun, O. G. Kim, C. K. Kim, H. S. Lee, and J. S. Lee, “Validation of the Korean version of the Oxford Knee Score in patients undergoing total knee arthroplasty,” Clinical Orthopaedics and Related Research, vol. 471, no. 2, pp. 600–605, 2013.
- J. Y. Jenny and Y. Diesinger, “Validation of a French version of the Oxford knee questionnaire,” Orthopaedics and Traumatology: Surgery and Research, vol. 97, no. 3, pp. 267–271, 2011.
- S. L. Whitehouse, A. W. Blom, A. H. Taylor, G. T. Pattison, and G. C. Bannister, “The Oxford knee score, problems and pitfalls,” Knee, vol. 12, no. 4, pp. 287–291, 2005.
- P. Moonot, G. A. Medalla, D. Matthews, Y. Kalairajah, and R. E. Field, “Correlation between the Oxford knee and American knee society scores at mid-term follow-up,” The Journal of Knee Surgery, vol. 22, no. 3, pp. 226–230, 2009.
- P. B. Pynsent, D. J. Adams, and S. P. Disney, “The Oxford hip and knee outcome questionnaires for arthroplasty,” Journal of Bone and Joint Surgery B, vol. 87, no. 2, pp. 241–248, 2005.
- G. R. Norman, J. A. Sloan, and K. W. Wyrwich, “Interpretation of changes in health-related quality of life the remarkable universality of half a standard deviation,” Medical Care, vol. 41, no. 5, pp. 582–592, 2003.
- A. Judge, N. K. Arden, A. Kiran et al., “Interpretation of patient-reported outcomes for hip and knee replacement surgery: identification of thresholds associated with satisfaction with surgery,” Journal of Bone and Joint Surgery B, vol. 94, no. 3, pp. 412–418, 2012.
- J. Y. Jenny and Y. Diesinger, “The Oxford knee score: compared performance before and after knee replacement,” Orthopaedics and Traumatology: Surgery and Research, vol. 98, no. 4, pp. 409–412, 2012.
- R. G. Marx, E. C. Jones, N. C. Atwan, R. F. Closkey, E. A. Salvati, and T. P. Sculco, “Measuring improvement following total hip and knee arthroplasty using patient-based measures of outcome,” Journal of Bone and Joint Surgery A, vol. 87, no. 9, part 1, pp. 1999–2005, 2005.
- E. M. Roos, H. P. Roos, L. S. Lohmander, C. Ekdahl, and B. D. Beynnon, “Knee injury and osteoarthritis outcome score (KOOS)—development of a self-administered outcome measure,” Journal of Orthopaedic and Sports Physical Therapy, vol. 28, no. 2, pp. 88–96, 1998.
- E. M. Roos and S. Toksvig-Larsen, “Knee injury and osteoarthritis outcome score (KOOS)—validation and comparison to the WOMAC in total knee replacement,” Health and Quality of Life Outcomes, vol. 1, article 17, 2003.
- E. M. Roos, H. P. Roos, and L. S. Lohmander, “WOMAC osteoarthritis index—additional dimensions for use in subjects with post-traumatic osteoarthritis of the knee,” Osteoarthritis and Cartilage, vol. 7, no. 2, pp. 216–221, 1999.
- K. B. Hare, L. S. Lohmander, R. Christensen, and E. M. Roos, “Arthroscopic partial meniscectomy in middle-aged patients with mild or no knee osteoarthritis: a protocol for a double-blind, randomized sham-controlled multi-centre trial,” BMC Musculoskeletal Disorders, vol. 14, article 71, 2013.
- M. Saleki, T. Ahadi, M. Razi, G. R. Raeisi, B. Forough, and M. K. Ali, “Comparison of the effects of acupuncture and isometric exercises on symptom of knee osteoarthritis,” International Journal of Preventive Medicine, vol. 4, supplement 1, pp. S73–S77, 2013.
- G. A. Ghasemi, A. Golkar, and S. M. Marandi, “Effects of hata yoga on knee osteoarthritis,” International Journal of Preventive Medicine, vol. 4, supplement 1, pp. S133–S138, 2013.
- B. F. Riecke, R. Christensen, P. Christensen et al., “Comparing two low-energy diets for the treatment of knee osteoarthritis symptoms in obese patients: a pragmatic randomized clinical trial,” Osteoarthritis and Cartilage, vol. 18, no. 6, pp. 746–754, 2010.
- S. T. Skou, E. M. Roos, M. B. Laursen et al., “Efficacy of multimodal, systematic non-surgical treatment of knee osteoarthritis for patients not eligible for a total knee replacement: a study protocol of a randomised controlled trial,” BMJ Open, vol. 2, no. 6, Article ID e002168, 2012.
- P. T. Paradowski, S. Bergman, A. Sundén-Lundius, L. S. Lohmander, and E. M. Roos, “Knee complaints vary with age and gender in the adult population. Population-based reference data for the knee injury and osteoarthritis outcome score (KOOS),” BMC Musculoskeletal Disorders, vol. 7, article 38, 2006.
- M. A. Peer and J. Lane, “The knee injury and osteoarthritis outcome score (KOOS): a review of its psychometric properties in people undergoing total knee arthroplasty,” Journal of Orthopaedic and Sports Physical Therapy, vol. 43, no. 1, pp. 20–28, 2013.
- A. M. Davis, A. V. Perruccio, M. Canizares et al., “Comparative, validity and responsiveness of the HOOS-PS and KOOS-PS to the WOMAC physical function subscale in total joint replacement for osteoarthritis,” Osteoarthritis and Cartilage, vol. 17, no. 7, pp. 843–847, 2009.
- R. S. Gonçalves, J. Cabri, J. P. Pinheiro, and P. L. Ferreira, “Cross-cultural adaptation and validation of the Portuguese version of the knee injury and osteoarthritis outcome score (KOOS),” Osteoarthritis and Cartilage, vol. 17, no. 9, pp. 1156–1162, 2009.
- N. Bellamy, W. W. Buchanan, C. H. Goldsmith, J. Campbell, and L. W. Stitt, “Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee,” Journal of Rheumatology, vol. 15, no. 12, pp. 1833–1840, 1988.
- N. Bellamy, “WOMAC: a 20-year experiential review of a patient-centered self-reported health status questionnaire,” Journal of Rheumatology, vol. 29, no. 12, pp. 2473–2476, 2002.
- A. Escobar, M. Gonzalez, J. M. Quintana et al., “Patient acceptable symptom state and OMERACT-OARSI set of responder criteria in joint replacement. Identification of cut-off values,” Osteoarthritis and Cartilage, vol. 20, no. 2, pp. 87–92, 2012.
- T. Pham, D. van der Heijde, R. D. Altman et al., “OMERACT-OARSI initiative: osteoarthritis research society international set of responder criteria for osteoarthritis clinical trials revisited,” Osteoarthritis and Cartilage, vol. 12, no. 5, pp. 389–399, 2004.
- N. J. Collins, D. Misra, D. T. Felson, K. M. Crossley, and E. M. Roos, “Measures of knee function: international knee documentation committee (IKDC) subjective knee evaluation form, knee injury and osteoarthritis outcome score (KOOS), knee injury and osteoarthritis outcome score physical function short form (KOOS-PS), knee outcome survey activities of daily living scale (KOS-ADL), lysholm knee scoring scale, Oxford knee score (OKS), Western Ontario and McMaster,” Arthritis Care and Research, vol. 63, supplement 11, pp. S208–S228, 2011.
- I. Papakostidou, Z. H. Dailiana, T. Papapolychroniou, et al., “Factors affecting the quality of life after total knee arthroplasties: a prospective study,” BMC Musculoskeletal Disorders, vol. 13, article 116, 2012.
- V. Wylde, S. Dixon, and A. W. Blom, “The role of preoperative self-efficacy in predicting outcome after total knee replacement,” Musculoskeletal Care, vol. 10, no. 2, pp. 110–118, 2012.
- G. Baron, F. Tubach, P. Ravaud, I. Logeart, and M. Dougados, “Validation of a short form of the Western Ontario and McMaster Universities osteoarthritis Index function subscale in hip and knee osteoarthritis,” Arthritis Care and Research, vol. 57, no. 4, pp. 633–638, 2007.
- S. L. Whitehouse, E. A. Lingard, J. N. Katz, and I. D. Learmonth, “Development and testing of a reduced WOMAC function scale,” Journal of Bone and Joint Surgery B, vol. 85, no. 5, pp. 706–711, 2003.
- H. Nadrian, N. Moghimi, E. Nadrian et al., “Validity and reliability of the Persian versions of WOMAC osteoarthritis index and Lequesne algofunctional index,” Clinical Rheumatology, vol. 31, no. 7, pp. 1097–1102, 2012.
- N. Bellamy, Ed., WOMAC Osteoarthritis Index User Guide, Version 5, 2002.
- ARHP Research Committee, Western Ontario and McMaster Universities Osteoarthritis Index, 2013, http://www.rheumatology.org/Practice/Clinical/Clinicianresearchers/Outcomes_Instrumentation/Western_Ontario_and_McMaster_Universities_Osteoarthritis_Index_(WOMAC)/.
- H. M. K. Ghomrawi, L. A. Mandl, J. Rutledge, M. M. Alexiades, and M. Mazumdar, “Is there a role for expectation maximization imputation in addressing missing data in research using WOMAC questionnaire? Comparison to the standard mean approach and a tutorial,” BMC Musculoskeletal Disorders, vol. 12, article 109, 2011.
- A. Escobar, J. M. Quintana, A. Bilbao, I. Aróstegui, I. Lafuente, and I. Vidaurreta, “Responsiveness and clinically important differences for the WOMAC and SF-36 after total knee replacement,” Osteoarthritis and Cartilage, vol. 15, no. 3, pp. 273–280, 2007.
- J. N. Insall, L. D. Dorr, R. D. Scott, and W. N. Scott, “Rationale of the knee society clinical rating system,” Clinical Orthopaedics and Related Research, no. 248, pp. 13–14, 1989.
- E. Ghanem, I. Pawasarat, A. Lindsay et al., “Limitations of the Knee Society score in evaluating outcomes following revision total knee arthroplasty,” Journal of Bone and Joint Surgery A, vol. 92, no. 14, pp. 2445–2451, 2010.
- E. A. Lingard, J. N. Katz, R. J. Wright, E. A. Wright, and C. B. Sledge, “Validity and responsiveness of the knee society clinical rating system in comparison with the SF-36 and WOMAC,” Journal of Bone and Joint Surgery A, vol. 83, no. 12, pp. 1856–1864, 2001.
- C. M. Bach, M. Nogler, I. E. Steingruber et al., “Scoring systems in total knee arthroplasty,” Clinical Orthopaedics and Related Research, no. 399, pp. 184–196, 2002.
- G. R. Scuderi, R. B. Bourne, P. C. Noble, J. B. Benjamin, J. H. Lonner, and W. N. Scott, “The new knee society knee scoring system,” Clinical Orthopaedics and Related Research, vol. 470, no. 1, pp. 3–19, 2012.
- P. C. Noble, G. R. Scuderi, A. C. Brekke et al., “Development of a new knee society scoring system,” Clinical Orthopaedics and Related Research, vol. 470, no. 1, pp. 20–32, 2012.
- P. F. Choong, M. M. Dowsey, and J. D. Stoney, “Does accurate anatomical alignment result in better function and quality of life? Comparing conventional and computer-assisted total knee arthroplasty,” Journal of Arthroplasty, vol. 24, no. 4, pp. 560–569, 2009.
- M. A. Ritter, K. E. Davis, P. Davis et al., “Preoperative malalignment increases risk of failure after total knee arthroplasty,” Journal of Bone and Joint Surgery, vol. 95, no. 2, pp. 126–131, 2013.
- K. N. Laubenthal, G. L. Smidt, and D. B. Kettelkamp, “A quantitative analysis of knee motion during activities of daily living,” Physical Therapy, vol. 52, no. 1, pp. 34–43, 1972.
- W. H. Jung, C. W. Chun, J. H. Lee, J. H. Ha, J. H. Kim, and J. H. Jeong, “Comparative study of medial opening-wedge high tibial osteotomy using 2 different implants,” Arthroscopy, vol. 29, no. 6, pp. 1063–1071, 2013.
- D. J. Sisto and V. K. Sarin, “Custom patellofemoral arthroplasty of the knee,” Journal of Bone and Joint Surgery, vol. 88, no. 7, pp. 1475–1480, 2006.
- O. Ares, E. Castellet, F. Maculé et al., “Translation and validation of “the knee society clinical rating system” into Spanish,” Knee Surgery, Sports Traumatology, Arthroscopy, 2013.
- A. L. P. Silva, M. K. Demange, R. G. Gobbi, T. F. C. da Silva, J. R. Pécora, and A. T. Croci, “Translation and validation of the knee society score—KSS for Brazilian Portuguese,” Acta Ortopedica Brasileira, vol. 20, no. 1, pp. 25–30, 2012.
- C. van der Straeten, E. Witvrouw, T. Willems, J. Bellemans, and J. Victor, “Translation and validation of the Dutch new knee society scoring system,” Clinical Orthopaedics and Related Research, 2013.
- J. Kim, J. H. Lonner, C. L. Nelson, and P. A. Lotke, “Response bias: effect on outcomes evaluation by mail surveys after total knee arthroplasty,” Journal of Bone and Joint Surgery A, vol. 86, no. 1, pp. 15–21, 2004.
- S. Asif and D. S. Choon, “Midterm results of cemented press fit condylar sigma total knee arthroplasty system,” Journal of Orthopaedic Surgery, vol. 13, no. 3, pp. 280–284, 2005.
- The Knee Society, The 2011 Knee Society Knee Scoring System: Licenced User Manual, 2012, http://www.kneesociety.org/web/2011%20KSS%20User%20Manual_FINAL_12-2012.pdf.
- C. A. Jacobs and C. P. Christensen, “Correlations between knee society function scores and functional force measures,” Clinical Orthopaedics and Related Research, vol. 467, no. 9, pp. 2414–2419, 2009.
- S. E. Na, C. W. Ha, and C. H. Lee, “new high-flexion knee scoring system to eliminate the ceiling effect,” Clinical Orthopaedics and Related Research, vol. 470, no. 2, pp. 584–593, 2012.
- R. B. Bourne, B. M. Chesworth, A. M. Davis, N. N. Mahomed, and K. D. Charron, “Patient satisfaction after total knee arthroplasty: who is satisfied and who is not?” Clinical Orthopaedics and Related Research, vol. 468, no. 1, pp. 57–63, 2010.