Total Knee Arthroplasty Indications

Total knee arthroplasty is one of the most successful orthopaedic procedures, giving reliable pain relief and functional improvement for end-stage knee arthritis. Appropriate patient selection is critical to the outcome, because up to 15-20% of patients remain dissatisfied despite technically successful surgery.

History. Modern TKA has evolved significantly since the 1970s. Constrained designs, improved polyethylene and standardised surgical technique have produced excellent long-term survivorship, and the current focus is on optimising patient selection and managing expectations.

Burden. Knee osteoarthritis affects approximately 250 million people worldwide and is a leading cause of disability in older adults. Demand for TKA continues to rise globally with ageing populations and increasing obesity, and high-volume registries report annual primary TKA numbers in the hundreds of thousands:

• USA - over 670,000 per year
• UK - roughly 100,000 per year, through the NJR
• Australia - around 65,000 per year, through the AOANJRR

Primary osteoarthritis accounts for around 95% of procedures across registries.

Approach. The medial parapatellar approach is the most common and the standard for most primary TKA, with good, extensile exposure. The other approaches:

• Subvastus - less quadriceps disruption, in selected patients
• Midvastus - a compromise approach
• Lateral - valgus deformity, where it gives better lateral access

Implant decisions. Cruciate-retaining versus posterior-stabilised, cemented versus uncemented, and whether to resurface the patella. Patient factors drive each choice: deformity severity guides constraint, bone quality affects the choice of fixation, and ligament integrity affects the implant type.

The indication. TKA is indicated for end-stage knee arthritis with failed conservative management, characterised by:

• Significant symptoms (pain, stiffness) affecting quality of life
• Functional limitation (walking distance, stairs, activities of daily living), documented
• Night pain and rest pain, which are particularly indicative of advanced disease requiring surgery
• Radiographic OA (joint space narrowing, osteophytes, subchondral sclerosis) that correlates with the symptoms
• Failure of at least 3-6 months of conservative care

The conditions. Beyond primary osteoarthritis, the indications include rheumatoid arthritis, post-traumatic arthritis, osteonecrosis and crystalline arthropathy. Each requires individualised assessment.

Risk is not eligibility. Patients older than 55 with unilateral disease, who are non-obese, motivated and realistic in their expectations, carry lower average risk. Patients younger than 55 (revision risk), the morbidly obese, smokers, those with poorly controlled comorbidities and those with workers' compensation claims carry higher average risk. These profiles describe risk, and every "optimal candidate" description on this page is a statement about average risk rather than an eligibility rule: NICE NG226 states explicitly that age, sex, BMI and comorbidity must not by themselves be used to refuse referral.

Absolute contraindications. Active infection of the knee or elsewhere in the body is an absolute contraindication, and remote infections (UTI, dental abscess, skin infection) must be treated before elective arthroplasty. Severe peripheral vascular disease with ischaemia risk makes TKA dangerous; vascular surgery consultation is required if pulses are absent or the ABI is abnormal. Neuropathic arthropathy (Charcot joint) results in rapid prosthesis failure through abnormal loading and bone destruction, and a patient medically unfit for major surgery completes the list.

Relative contraindications. The relative contraindications are morbid obesity (BMI over 40), poorly controlled diabetes, immunocompromise, active smoking, unrealistic expectations and extreme youth. Obesity and youth are taken up under special populations, and diabetes under optimisation.

Osteoarthritis. Primary osteoarthritis is a disease of articular cartilage: progressive loss of hyaline cartilage, subchondral bone change, osteophyte formation and synovial inflammation. The process is irreversible once bone-on-bone contact occurs.

Inflammatory arthritis. Rheumatoid arthritis and other inflammatory conditions cause synovial hypertrophy with pannus formation, leading to cartilage destruction, bone erosion and ligamentous instability. Medical management with DMARDs has reduced, but not eliminated, the need for TKA.

Secondary causes. Post-traumatic arthritis after tibial plateau fractures, ligament injuries or meniscectomy represents a significant proportion of younger TKA patients. Osteonecrosis, crystal arthropathies and haemophilic arthropathy are less common causes.

Kellgren-Lawrence. The most widely used grading system for the severity of knee osteoarthritis, applied to weight-bearing radiographs.

ICRS cartilage classification. Used primarily for arthroscopic assessment of cartilage damage, it complements the radiographic grade.

The grade is not the indication. Clinical-radiographic correlation is essential. Some patients with severe radiographic OA have minimal symptoms, while others with mild changes have significant pain, so the indication for TKA is failed conservative management of symptomatic arthritis, not radiographic severity alone.

Imaging. Weight-bearing AP, lateral and skyline radiographs, with long-leg alignment films if there is deformity. MRI is rarely needed, unless there is diagnostic uncertainty.

Bloods and baseline tests. FBC, UEC, LFTs and coagulation; HbA1c in diabetics; albumin for nutritional status; vitamin D for bone health, with a target greater than 75 nmol/L; and CRP and ESR if infection is suspected. An ECG for cardiac assessment should show no acute changes.

Suspected infection. Aspirate for cell count and culture, with WBC greater than 1700 and PMN greater than 65% as the thresholds, alongside a persistently elevated CRP.

Inflammatory arthritis. Rheumatology review, with perioperative DMARD management.

Diabetes. Target HbA1c less than 8% and perioperative glucose less than 10 mmol/L. Poor control increases surgical site infection risk threefold.

Cardiovascular. A recent MI (under 6 weeks) or unstable angina requires cardiology clearance. Beta-blockers should be continued perioperatively.

Nutrition. Albumin less than 35 g/L and a lymphocyte count less than 1500 are associated with wound complications.

Modifiable risk factors. Smoking cessation for a minimum of 4 weeks before surgery, weight-loss programmes for a BMI greater than 35, and dental clearance to exclude occult sources of infection. Optimisation significantly reduces perioperative complications.

Before attributing pain to arthritis and proceeding to TKA, exclude the mimics and confirm clinical-radiographic correlation. A painful knee in an older adult is not always intra-articular OA, and referred or extra-articular pain will not improve after arthroplasty.

The trial. A minimum of 3-6 months of non-operative treatment comes before surgery is considered: weight loss, physiotherapy, activity modification, analgesia (paracetamol, NSAIDs), walking aids, bracing and intra-articular injections (corticosteroid, hyaluronic acid).

When it has failed. Conservative management is considered failed when adequate trials of multiple modalities over 3-6 months have not given sufficient pain relief or functional improvement.

Timing. Operate neither too early, while conservative care is still working, nor too late, once deformity has set in.

The pathway. The decision runs in three steps:

1. Confirm the diagnosis - radiographic OA with symptom correlation, and other causes (infection, referred pain) excluded
2. Conservative trial - a minimum of 3-6 months of weight loss, physiotherapy, analgesia and injections
3. Patient selection - assess the contraindications and optimise the modifiable risk factors, over a variable period; TKA follows if conservative care has failed, once the patient is optimised

Alternatives. Consider these before TKA:

• Unicompartmental arthroplasty - isolated single-compartment disease with the ACL intact
• High tibial osteotomy - the young, active patient with medial OA
• Patellofemoral arthroplasty - isolated patellofemoral disease

Infection risk. Infection risk is increased by a BMI greater than 40, diabetes with an HbA1c of 8% or more, smoking, malnutrition and immunosuppression. Glycaemic control, smoking cessation, weight optimisation and nutritional status are the modifiable factors.

The first six weeks. Full weight-bearing with a walker or crutches, DVT prophylaxis for 2-6 weeks, physiotherapy for range of motion and strength, and wound care. Walking is protected, and the goal is a range of 0-90°.

Six to twelve weeks. The patient progresses to independent walking and returns to sedentary activities, physiotherapy continues, and the goal is full extension.

Three to six months. Light activities, with a range of 0-120°.

Long term. Low-impact sports (walking, swimming, golf) are recommended and high-impact activities avoided: no running or jumping, and no contact sports. The activity modification is lifelong.

Follow-up. Review at 6 weeks, 3 months and 1 year, then annually, with serial radiographs for loosening. The patient reports any new pain or swelling.

Survivorship. The figures are all-cause survival with revision as the endpoint, so an unrevised painful knee counts as a survivor:

• Approximately 95% at 10 years
• Approximately 90% at 15 years
• 82% at 25 years - pooled registry data from 14 registries (Evans, Lancet 2019, carded below)

The registries (AOANJRR, NJR, AJRR) agree on a 10-year cumulative revision of around 4-6% for primary TKA, and younger age and male sex are consistent risk factors for revision.

Satisfaction and function. Approximately 81% of patients are satisfied overall; in Bourne's 1703 knees, 19% were dissatisfied despite technically sound surgery. Pain relief, at 90% or more, is the most reliable outcome. Return to sport is variable and limited to low-impact activity.

Prognostic factors. Outcomes are better in patients over 55, the non-obese, those with realistic expectations and those with primary OA. They are worse in young patients (through higher revision), and with morbid obesity, inflammatory arthritis and unrealistic expectations.

Global Epidemiology

Knee OA affects an estimated 250 million people worldwide and is among the leading global causes of years lived with disability. Primary OA accounts for around 95% of TKAs across all major registries. Procedure volumes are rising fastest in ageing, higher-income populations, driven by demographics and obesity.

Side-by-Side Guideline Comparison

Registry Evidence

National joint registries (NJR for England/Wales, AJRR in the US, AOANJRR in Australia, SHAR/Swedish, Norwegian, NZJR) consistently show 10-year primary TKA revision of around 4-6% and pooled 25-year survival around 82% (Evans, Lancet 2019). Younger age and male sex are reproducible revision risk factors. Registries also benchmark implant and fixation performance and flag outlier devices.

High- vs Limited-Resource Practice Variation

• High-resource settings: prehabilitation clinics, dedicated arthroplasty pathways, enhanced recovery, robotic/PSI options, day-case TKA in selected patients, and registry surveillance.
• Limited-resource settings: longer waiting times allow disease to progress to severe deformity; implant and revision capacity is constrained, so case selection is more conservative and durable, lower-cost cemented implants are favoured. Access and affordability, not indication, are the dominant limiting factors.

Related pages: Knee Osteoarthritis is the disease this operation treats and carries the natural history and the non-operative evidence that must fail before the indication exists, with Osteoarthritis Pathophysiology for why cartilage loss produces pain that correlates so poorly with the Kellgren-Lawrence grade; Unicompartmental Knee Arthroplasty is the main alternative when disease is confined to one compartment and is the reason compartmental assessment belongs in the indication, not just the plan; Articular Cartilage Injuries and Cartilage Healing and Repair cover the joint-preserving options that come first in the young knee this page counsels rather than excludes; TKA Alignment Philosophies and TKA Alignment Options take over once the decision to operate is made; Revision TKA is the consequence the age discussion is really about, and TKA Aseptic Loosening is the commonest reason a knee reaches it; Periprosthetic Joint Infection and TKA Complications: Infection are the deep infection the HbA1c threshold is invoked against but was never shown to predict; TKA Complications: Instability, TKA Stiffness and TKA Patellar Complications are the failure modes behind the one-in-five dissatisfaction rate; Smoking Cessation for the one relative contraindication that is fully reversible before surgery; and Venous Thromboembolism for the prophylaxis that consent must cover.

Young patients (under 55). Higher activity demands and longer life expectancy bring a higher lifetime revision risk: revision rates of 15-20% at 15 years, against 5-10% in older patients. Counsel rather than exclude. Set realistic expectations about activity limitations, consider the alternative procedures (osteotomy, UKA), and discuss how likely future revision surgery is.

Elderly patients (over 80). Perioperative medical risk is higher, with higher cardiac and pulmonary complication rates, yet pain relief is excellent, as is functional improvement despite comorbidities. Medical optimisation is essential, and single-stage bilateral TKA is generally avoided.

Morbid obesity. A BMI over 40 increases surgical site infection 2-3 fold, elevates DVT and PE risk and raises implant loosening rates. Weight-loss programmes are beneficial, but surgery is not contraindicated.

The Bourne (2010) cross-sectional study of 1703 primary TKAs found that unmet expectations were by far the strongest predictor of dissatisfaction, about a tenfold increase in risk and a larger effect than pain, function scores or complications. Yet expectation assessment is often informal and rushed. Structured expectation work is a core part of appropriate patient selection, not an afterthought.

Eliciting expectations. Ask specifically what the patient hopes to achieve (pain relief, walking distance, stairs, return to work, sport or kneeling) rather than accepting a vague "get back to normal". Validated instruments exist to structure this, such as the Hospital for Special Surgery Knee Replacement Expectations Survey (HSS-KRES), which quantifies the number and type of expectations a patient holds.

Fulfilment decides satisfaction. Satisfaction depends on whether expectations are met, not on the absolute outcome score. Two patients with identical objective results can differ in satisfaction according to what they expected.

The unrealistic expectations to correct are these:

• Complete elimination of all pain and a "forgotten", entirely normal knee. TKA reliably reduces pain and improves function, but it is a resurfacing procedure, not restoration of a native joint
• Return to high-impact sport or heavy manual labour without restriction
• Comfortable kneeling, which remains difficult or uncomfortable for a large proportion of patients long-term and must be discussed explicitly before surgery
• Rapid recovery. Meaningful functional gains and the pain plateau typically continue to evolve over the first postoperative year

Aligning them. Use structured preoperative education, decision aids and shared decision-making to correct misconceptions, then document the agreed, realistic goals. Screen for the psychological and pain-sensitisation drivers of poor outcome (covered in Knee Osteoarthritis) and involve them in counselling. Managing expectations is the single most powerful modifiable lever on postoperative satisfaction.

Many candidates for TKA have symptomatic bilateral disease, which forces a distinct selection decision: should both knees be replaced under one anaesthetic (simultaneous) or as two separate operations (staged)?

Simultaneous. A single anaesthetic, one hospital admission, one rehabilitation episode, faster overall recovery of both limbs and lower total cost. The price is a higher risk of cardiopulmonary complications and blood transfusion, and several studies report increased perioperative mortality compared with staged surgery.

Staged. Spreading the physiological insult across two events allows recovery and reassessment between operations, at the cost of a second anaesthetic, a second admission and a longer total treatment course. The interval is individualised to allow adequate recovery before the second procedure.

Selection. Because the added risk falls on the cardiopulmonary system, simultaneous surgery is generally reserved for younger, fitter patients (typically ASA grade one or two) without significant cardiac or pulmonary disease, with careful shared decision-making and informed consent about the higher perioperative risk. Older patients and those with meaningful comorbidity are better served by a staged approach, or by treating the more symptomatic knee first.

• BMI thresholds: Many units historically applied a hard BMI cut-off (often 40) for elective TKA. The evidence (Dowsey 2010) shows higher complications and smaller functional gains in the morbidly obese, but absolute benefit remains substantial, and guidelines (NICE) explicitly reject refusing surgery on BMI alone. The debate is optimisation and shared decision-making versus rationing.
• Timing — too early vs too late: The MEDIC RCT (Skou 2015) shows structured non-surgical care helps many "surgery-eligible" patients, supporting a genuine conservative trial; yet excessive delay risks fixed deformity, muscle wasting and worse outcomes. There is no universally agreed minimum trial duration; 3-6 months is pragmatic, not evidence-mandated.
• The persistently dissatisfied 15-20%: Roughly one in five patients are dissatisfied despite technically sound surgery (Bourne 2010), driven largely by unmet expectations and central pain sensitisation rather than implant or technique. Selecting and counselling these patients remains unsolved.
• Age limits: Younger patients gain function but face higher lifetime revision risk; older patients carry higher perioperative medical risk but excellent pain relief. Chronological age alone is a poor selection criterion.
• Bilateral simultaneous vs staged TKA: Simultaneous bilateral reduces total hospital time and a second anaesthetic but carries higher cardiopulmonary and transfusion risk; patient selection is debated.
• Robotic and patient-specific instrumentation: Improve alignment precision but have not yet shown consistent long-term survivorship or satisfaction benefit to justify routine use everywhere — a cost-versus-value question, especially in limited-resource settings.