Patient safety after partial and total knee replacement

More than 90 000 people in the UK had knee replacements in 2012, according to the National Joint Registry of England and Wales (NJR). The human cost of this expensive surgery is addressed in two articles in The Lancet that question conclusions from the NJR, with major consequences for patient safety and the knee replacement industry. The indications for knee replacement remain poorly defi ned: 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 Classifi cation of Diseases-10 labels osteoarthritis of the knee as gonarthrosis, M17.1, allowing no separation into compartments, and no classifi cation of severity. So, despite being localised to one compartment in most people, because of poor diagnostic criteria, knee osteoarthritis can be validly approached with two diff erent 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, explaining perhaps why TKR is less eff ective than is total hip replacement, and why life expectancy might also be aff ected. 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, as results from hundreds of thousands of patients now enrolled into national joint registries around the world confi rm. 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. 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 fi xed, 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 stiff ness and pain, is recorded as a success in registry terms. Thus, TKRs are reported as successful despite the fact that 25% are no better or even worse after surgery. On the basis of revision rates alone, registry data continue to encourage surgeons to concentrate on TKR, and avoid UKR. The two Lancet papers look at the patients who have had knee replacements rather than their prostheses. Linda Hunt and colleagues 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. They did, however, note a substantial diff erence in risk of perioperative death dependent on the type of procedure: the smaller, cheaper operation of 12 Royal College of Paediatrics and Child Health. Mission, vision and values. April 14, 2014. http://www.rcpch.ac.uk/what-we-do/mission-vision-andvalues/mission-vision-and-values (accessed Aug 1, 2014). 13 Johnson O, Bailey SL, Willott C, et al. Global health learning outcomes for medical students in the UK. Lancet 2012; 379: 2033–35. 14 Suchdev PS, Shah A, Derby KS, et al. A proposed model curriculum in global child health for pediatric residents. Acad Pediatr 2012; 12: 229–37. 15 UNICEF. Convention on the Rights of the Child. http://www.unicef.org/crc (accessed Aug 1, 2014). 16 Audcent T, MacDonnell H, Brenner J, Samson L. International child health (ICH) education in Canadian paediatric residency programs. Clin Invest Med 2007; 30 (suppl): S63–64 (abstr).