Patient safety after partial and total knee replacement
Authors: Justin P Cobb
Journal: The Lancet (2014)

More than 90 000 people in the UK had knee replacements in 2012, according to the National Joint Registry of England and Wales (NJR).1National Joint Registry for EnglandWalesNorthern IrelandNJR 10th annual report 2013. Hemel Hempstead: National Joint Registry, 2013.http://www.njrcentre.org.uk/njrcentre/Portals/0/Documents/England/Reports/10th_annual_report/NJR%2010th%20Annual%20Report%202013%20B.pdfGoogle Scholar The human cost of this expensive surgery is addressed in two articles in The Lancet2Hunt LP Ben-Shlomo Y Clark EM et al.on behalf of the National Joint Registry for England and Wales45-day mortality after 467 779 knee replacements for osteoarthritis from the National Joint Registry for England and Wales: a retrospective observational study.Lancet. 2014; (published online July 8.)http://dx.doi.org/10.1016/S0140-6736(14)60540-7PubMed Google Scholar, 3Liddle AD Judge A Pandit H Murray DW Adverse outcomes after total and unicompartmental knee replacement in 101 330 matched patients: a study of data from the National Joint Registry for England and Wales.Lancet. 2014; (published online July 8.)http://dx.doi.org/10.1016/S0140-6736(14)60419-0PubMed Google Scholar that question conclusions from the NJR, with major consequences for patient safety and the knee replacement industry. The indications for knee replacement remain poorly defined: a patient with a small wear patch seen on MRI is given the same diagnosis as someone whose knee is severely damaged. Both are told they have osteoarthritis. International Classification of Diseases-10 labels osteoarthritis of the knee as gonarthrosis, M17.1, allowing no separation into compartments, and no classification of severity. So, despite being localised to one compartment in most people,4Felson DT Nevitt MC Yang M et al.A new approach yields high rates of radiographic progression in knee osteoarthritis.J Rheumatol. 2008; 35: 2047-2054PubMed Google Scholar because of poor diagnostic criteria, knee osteoarthritis can be validly approached with two different philosophies. Surgeons who deem knee osteoarthritis a disease excise the entire joint, thereby curing the disease and substituting a total knee replacement (TKR). Alternatively, those who deem it to be predictable wear do the smaller operation of partial, or unicompartmental knee replacement (UKR), relining the part that is worn, preserving the rest of the joint surfaces, and, importantly, the anterior cruciate ligament. In TKR, this important structure is routinely excised, which results in reduced ability to walk,5Wiik AV Manning V Strachan RK Amis AA Cobb JP Unicompartmental knee arthroplasty enables near normal gait at higher speeds, unlike total knee arthroplasty.J Arthroplasty. 2013; 28: 176-178Summary Full Text Full Text PDF PubMed Scopus (59) Google Scholar explaining perhaps why TKR is less effective than is total hip replacement,6Ethgen O Bruyere O Richy F Dardennes C Reginster J-Y Health-related quality of life in total hip and total knee arthroplasty. A qualitative and systematic review of the literature.J Bone Joint Surg Am. 2004; 86: 963-974PubMed Google Scholar and why life expectancy might also be affected.7Studenski S Perera S Patel K et al.Gait speed and survival in older adults.JAMA. 2011; 305: 50-58Crossref PubMed Scopus (2976) Google Scholar For patients undergoing either TKR or UKR, if done well, the probability is that this is the last operation that they will need in their lifetime,8Price AJ Svard U A second decade lifetable survival analysis of the Oxford unicompartmental knee arthroplasty.Clin Orthop Relat Res. 2011; 469: 174-179Crossref PubMed Scopus (253) Google Scholar as results from hundreds of thousands of patients now enrolled into national joint registries around the world confirm. Unlike tumour registries, which have strict diagnostic inclusion criteria and use death as an endpoint, joint registries are focused on the outcome of the device: anyone with any amount of joint damage can be admitted, only device-related surgical procedures are reported as failures, and death is counted as a success. Because arthrosis is closely related to ageing, the many patients who have died with no need for revision surgery stretch the use of so-called survivorship statistics when reporting the survival of the implant, not the patient.9Hunt LP Ben-Shlomo Y Clark EM et al.90-day mortality after 409 096 total hip replacements for osteoarthritis, from the National Joint Registry for England and Wales: a retrospective analysis.Lancet. 2013; 382: 1097-1104Summary Full Text Full Text PDF PubMed Scopus (231) Google Scholar The NJR now has more than 500 000 knee replacements registered, making it the world's largest registry, so conclusions from it should have a global impact. Set up to give warning of poorly performing devices, with operations leading to exchange of device as the main focus, the registry is now used to compare TKR with UKR. This focus can lead to perverse results: a joint replacement with a problem that can be fixed, curing the pain and restoring the patient's quality of life, is a failure owing to its revision, whereas a painful joint replacement that cannot be revised, condemning the patient to a lifetime of stiffness and pain, is recorded as a success in registry terms.10Goodfellow J O'Connor J Murray D A critique of revision rate as an outcome measure: re-interpretation of knee joint registry data.J Bone Joint Surg Br. 2010; 92: 1628-1631Crossref PubMed Scopus (132) Google Scholar Thus, TKRs are reported as successful despite the fact that 25% are no better or even worse after surgery.11Noble PC Gordon MJ Weiss JM Reddix RN Conditt MA Mathis KB Does total knee replacement restore normal knee function?.Clin Orthop Relat Res. 2005; 431: 157-165Crossref PubMed Scopus (353) Google Scholar On the basis of revision rates alone, registry data continue to encourage surgeons to concentrate on TKR, and avoid UKR.12Baker PN Petheram T Jameson SS et al.Comparison of patient-reported outcome measures following total and unicondylar knee replacement.J Bone Joint Surg Br. 2012; 94: 919-927Crossref PubMed Scopus (9) Google Scholar, 13Pearse A Hooper G Rothwell A Frampton C Survival and functional outcome after revision of a unicompartmental to a total knee replacement: the New Zealand National Joint Registry.J Bone Joint Surg Br. 2010; 92: 508-512Crossref PubMed Scopus (119) Google Scholar, 14Knutson K Lewold S Robertsson O Lidgren L The Swedish knee arthroplasty register: a nation-wide study of 30,003 knees 1976–1992.Acta Orthop Scand. 1994; 65: 375-386Crossref PubMed Scopus (244) Google Scholar, 15W-Dahl A Robertsson O Lidgren L Miller L Davidson D Graves S Unicompartmental knee arthroplasty in patients aged less than 65: combined data from the Australian and Swedish Knee Registries.Acta Orthop. 2010; 81: 90-94Crossref PubMed Scopus (95) Google Scholar The two Lancet papers look at the patients who have had knee replacements rather than their prostheses. Linda Hunt and colleagues2Hunt LP Ben-Shlomo Y Clark EM et al.on behalf of the National Joint Registry for England and Wales45-day mortality after 467 779 knee replacements for osteoarthritis from the National Joint Registry for England and Wales: a retrospective observational study.Lancet. 2014; (published online July 8.)http://dx.doi.org/10.1016/S0140-6736(14)60540-7PubMed Google Scholar undertook a multivariate analysis of 467 779 cases from the NJR. They linked the national Hospital Episode Statistics (HES) with NJR data, in an observational study assessing 45-day mortality associated with knee arthroplasty to treat osteoarthritis. In their analysis, 1183 patients died within 45 days of surgery during the 8-year study period. Mortality decreased with time; from 0·37% in 2003 to 0·20% in 2011, making knee surgery safer than hip replacement, which they reported on last year.9Hunt LP Ben-Shlomo Y Clark EM et al.90-day mortality after 409 096 total hip replacements for osteoarthritis, from the National Joint Registry for England and Wales: a retrospective analysis.Lancet. 2013; 382: 1097-1104Summary Full Text Full Text PDF PubMed Scopus (231) Google Scholar They did, however, note a substantial difference in risk of perioperative death dependent on the type of procedure: the smaller, cheaper operation of UKR was associated with substantially lower mortality than was TKR (hazard ratio [HR] 0·32, 95% CI 0·19–0·54). Despite this finding, Hunt and colleagues stop short of commending UKR. Perhaps this absent recommendation was to avoid conflict with the stream of registry publications promoting TKR over UKR, with revision as the only indicator of failure.13Pearse A Hooper G Rothwell A Frampton C Survival and functional outcome after revision of a unicompartmental to a total knee replacement: the New Zealand National Joint Registry.J Bone Joint Surg Br. 2010; 92: 508-512Crossref PubMed Scopus (119) Google Scholar, 14Knutson K Lewold S Robertsson O Lidgren L The Swedish knee arthroplasty register: a nation-wide study of 30,003 knees 1976–1992.Acta Orthop Scand. 1994; 65: 375-386Crossref PubMed Scopus (244) Google Scholar, 15W-Dahl A Robertsson O Lidgren L Miller L Davidson D Graves S Unicompartmental knee arthroplasty in patients aged less than 65: combined data from the Australian and Swedish Knee Registries.Acta Orthop. 2010; 81: 90-94Crossref PubMed Scopus (95) Google Scholar, 16Baker P Petheram T Jameson S et al.Comparison of patient-reported outcome measures following total and unicondylar knee replacement.J Bone Joint Surg Br. 2012; 94: 919-927Crossref PubMed Scopus (71) Google Scholar, 17Baker PN Petheram T Avery PJ Gregg PJ Deehan DJ Revision for unexplained pain following unicompartmental and total knee replacement.J Bone Joint Surg Am. 2012; 94: e126Crossref PubMed Scopus (116) Google Scholar Alexander Liddle and colleagues3Liddle AD Judge A Pandit H Murray DW Adverse outcomes after total and unicompartmental knee replacement in 101 330 matched patients: a study of data from the National Joint Registry for England and Wales.Lancet. 2014; (published online July 8.)http://dx.doi.org/10.1016/S0140-6736(14)60419-0PubMed Google Scholar also link HES and NJR data. In addition to mortality, they look at all rates of reoperation, not just revision, and also complications, readmission to hospital, and length of hospital stay. A study group of more than 101 330 matched cases was assembled with propensity score matching to include three TKRs for every UKR (25 334 UKRs were matched to 75 996 TKRs), ensuring the best possible use of data. They report early and late complications separately. Risk of early death after surgery was again significantly lower for UKR than for TKR at all timepoints (30 day: HR 0·23, 95% CI 0·11–0·50; 8 year: 0·85, 0·79–0·92). To avoid one death by 4 years after surgery, the number needed to switch from TKR to UKR is 93, dropping to 62 at 8 years. Death is not only a very firm and clinically important endpoint, but also a surrogate for more common risks of intraoperative complications, stroke, myocardial infarction, thromboembolism, blood transfusion, and admission to critical care—all much more common after TKR than after UKR. Implant-related complications resulting in operations occur later and were substantially more common after UKR (subhazard ratio [SHR] 2·12, 95% CI 1·99–2·26) at 8 years.3Liddle AD Judge A Pandit H Murray DW Adverse outcomes after total and unicompartmental knee replacement in 101 330 matched patients: a study of data from the National Joint Registry for England and Wales.Lancet. 2014; (published online July 8.)http://dx.doi.org/10.1016/S0140-6736(14)60419-0PubMed Google Scholar These problems, which were mainly loosening and implant failure, were usually treated by a primary TKR. When the same problems of loosening or implant failure resulted in reoperation after TKR, they were often treated by larger so-called revision devices involving stems and augments. Infection, which is the most serious and costly local complication, was half as likely after UKR than after TKR in this large analysis (0·50, 0·38–0·66). In neither study was information available about thresholds for reoperation. By combining these datasets with outcome scores and costs, a formal cost-effectiveness analysis shows that UKR is a cost-effective option, despite the revision rate.18Andrews BA, Willis-Owen CA, Aqil A, Cobb JP. A cost-utility analysis of knee arthroplasty using data from three national registries. American Academy of Orthopaedic Surgeons 2014 Annual Meeting Proceedings; New Orleans; March 11–15, 2014.Google Scholar What can be drawn from these two large studies? When measured in terms of risk of perioperative death or serious morbidity, UKR is unequivocally safer than TKR. This simple message should be of great interest to patients and the clinical commissioning groups and insurers who pay for health care. This finding is at odds with the industry-funded NJR that suggests that UKR should be restricted, if not abandoned, for its high revision rate,16Baker P Petheram T Jameson S et al.Comparison of patient-reported outcome measures following total and unicondylar knee replacement.J Bone Joint Surg Br. 2012; 94: 919-927Crossref PubMed Scopus (71) Google Scholar despite improved postoperative scores.1National Joint Registry for EnglandWalesNorthern IrelandNJR 10th annual report 2013. Hemel Hempstead: National Joint Registry, 2013.http://www.njrcentre.org.uk/njrcentre/Portals/0/Documents/England/Reports/10th_annual_report/NJR%2010th%20Annual%20Report%202013%20B.pdfGoogle Scholar Arguments of this sort are not new to surgery. For women with operable breast cancer, for example, lumpectomy and radiotherapy offered substantial advantages, yet were met with fierce resistance from surgeons and centres promoting radical mastectomy. The strategy of radical mastectomy for all malignant breast disease was laid to rest 25 years ago with trial results showing no survival benefit over lumpectomy, despite a substantial reoperation rate for local recurrence in the conservative surgery group.19Fisher B Redmond C Fisher ER et al.Ten-year results of a randomized clinical trial comparing radical mastectomy and total mastectomy with or without radiation.N Engl J Med. 1985; 312: 674-681Crossref PubMed Scopus (1193) Google Scholar A randomised trial of partial versus radical genuectomy (TKR has been described as internal amputation of the knee) reported at 5, 10, and 15 years showed that the smaller operation of UKR was not functionally inferior at any timepoint.20Newman J Pydisetty RV Ackroyd C Unicompartmental or total knee replacement: the 15-year results of a prospective randomised controlled trial.J Bone Joint Surg Br. 2009; 91: 52-57Crossref PubMed Scopus (12) Google Scholar Although in breast cancer survival rightly refers to the patient, and her breast, in the looking-glass of world of implant registries death is a success, and only implant revision counts as a failure. The fairly high mortality in the mainly older population who require knee replacement makes the use of survival statistics challenging when reporting on prostheses, not patients.9Hunt LP Ben-Shlomo Y Clark EM et al.90-day mortality after 409 096 total hip replacements for osteoarthritis, from the National Joint Registry for England and Wales: a retrospective analysis.Lancet. 2013; 382: 1097-1104Summary Full Text Full Text PDF PubMed Scopus (231) Google Scholar So what prevents the smaller, cheaper, and safer operation becoming adopted widely? UKR is a complex operation to learn, yet, in the UK, surgeons and hospitals are paid less for it by private insurers, with NHS reimbursement varying depending on what code is used. Today, many surgeons in the UK have agreed to have their activity and mortality statistics in the public domain as part of the government's focus on patient safety. The NJR goes further though. It reports surgeons to the chief executives of their hospitals, not for excessive mortality, strokes, myocardial infarctions, or infections, but for having a revision rate that is high for TKR, but could be normal for UKR perhaps simply because this small operation is rather easier to fix, if a problem arises. These two papers should provoke a review of knee arthroplasty by policy makers worldwide. Substantial public and private savings are possible: of the 90 000 knee replacements reported in 2012 in England and Wales, only 8% were UKR.1National Joint Registry for EnglandWalesNorthern IrelandNJR 10th annual report 2013. Hemel Hempstead: National Joint Registry, 2013.http://www.njrcentre.org.uk/njrcentre/Portals/0/Documents/England/Reports/10th_annual_report/NJR%2010th%20Annual%20Report%202013%20B.pdfGoogle Scholar If only half of those eligible were offered the more conservative procedure of UKR, the NHS could save an estimated £70 million every year immediately on operative costs alone,18Andrews BA, Willis-Owen CA, Aqil A, Cobb JP. A cost-utility analysis of knee arthroplasty using data from three national registries. American Academy of Orthopaedic Surgeons 2014 Annual Meeting Proceedings; New Orleans; March 11–15, 2014.Google Scholar, 21Willis-Owen CA Brust K Alsop H Miraldo M Cobb JP Unicondylar knee arthroplasty in the UK National Health Service: an analysis of candidacy, outcome and cost efficacy.Knee. 2009; 16: 473-478Summary Full Text Full Text PDF PubMed Scopus (214) Google Scholar and, on the basis of these two papers, there would be 170 fewer postoperative deaths annually, and many hundreds of fewer strokes, myocardial infarctions, and infections. While perverse incentives remain in place, the TKR industry will continue to grow steadily encouraged by statistics based upon revision rates alone. With hundreds of lives and hundreds of millions of pounds at stake every year, a change in knee replacement strategy deserves consideration today, as it did with mastectomy 25 years ago. I am on the design team of a novel knee replacement at MatOrtho, and have received grants from MatOrtho, grants and personal fees from CeramTec, grants and personal fees from Stanmore Implants Worldwide, grants from Biomet, been on the speaker panel for Biomet, received grants from DePuy, been the principal investigator for the MHRA study of a novel hip design at JRI, and am cofounder, director, and minority shareholder of Embody, an Imperial start-up company developing patient-matched instruments for hip and knee arthroplasty. I have a patent on designs for knee implants for robotic implantation, and a patent on an anatomical design of acetabulum and femoral head pending. Adverse outcomes after total and unicompartmental knee replacement in 101 330 matched patients: a study of data from the National Joint Registry for England and WalesIn decisions about which procedure to offer, the higher revision/reoperation rate of UKR than of TKR should be balanced against a lower occurrence of complications, readmission, and mortality, together with known benefits for UKR in terms of postoperative function. If 100 patients receiving TKR received UKR instead, the result would be around one fewer death and three more reoperations in the first 4 years after surgery. Full-Text PDF Open Access45-day mortality after 467 779 knee replacements for osteoarthritis from the National Joint Registry for England and Wales: an observational studyPostoperative mortality after knee replacement has fallen substantially between 2003 and 2011. Efforts to further reduce mortality should concentrate more on older patients, those who are male and those with specific comorbidities, such as myocardial infarction, cerebrovascular disease, liver disease, and renal disease. Full-Text PDF Patient safety after partial and total knee replacementIn his Comment (Oct 18, p 1405) about the controversies in prosthetic surgery for knee osteoarthritis,1 Justin Cobb makes several statements regarding the utility and focus of joint registries in general and specific allegations regarding the probity of the National Joint Registry for England, Wales, and Northern Ireland (NJR). These comments need redress. Full-Text PDF