Total Knee Arthroplasty Indications

Total knee arthroplasty (TKA) is indicated for end-stage knee arthritis with pain and functional limitation refractory to conservative management (minimum 3-6 months trial). Primary osteoarthritis accounts for 95% of TKAs, with Kellgren-Lawrence Grade 3-4 radiographic changes that correlate with clinical symptoms. Absolute contraindications include active infection and severe peripheral vascular disease; relative contraindications include morbid obesity (BMI over 40), poorly controlled diabetes (HbA1c over 8), and unrealistic expectations. Optimal candidates are over 55 years, non-obese, motivated, and have realistic expectations. TKA achieves 95% 10-year survivorship and 85% patient satisfaction when patient selection is appropriate. Night pain and rest pain suggest advanced disease warranting surgical consideration.

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

Historical Perspective

Modern TKA has evolved significantly since the 1970s. The development of constrained designs, improved polyethylene, and standardized surgical techniques has resulted in excellent long-term survivorship. Current focus is on optimizing patient selection and managing expectations.

Epidemiology

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 aging populations and increasing obesity prevalence; high-volume registries report annual primary TKA numbers in the hundreds of thousands (over 670,000 per year in the USA, roughly 100,000 per year in the UK via the NJR, and around 65,000 per year in Australia via the AOANJRR). Primary osteoarthritis accounts for around 95% of procedures across registries.

Osteoarthritis

Primary osteoarthritis is a disease of articular cartilage with progressive loss of hyaline cartilage, subchondral bone changes, 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 following tibial plateau fractures, ligament injuries, or meniscectomy represents a significant proportion of younger TKA patients. Osteonecrosis, crystal arthropathies, and hemophilic arthropathy are less common causes.

Before attributing pain to arthritis and proceeding to TKA, exclude 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.

Algorithm

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When Conservative Fails

Conservative management is considered failed when adequate trials of multiple modalities over 3-6 months fail to provide sufficient pain relief or functional improvement. Night pain and rest pain are particularly indicative of advanced disease requiring surgery.

Young Patients (Under 55)

Younger patients have higher activity demands and longer life expectancy, resulting in:

• Higher revision rates (15-20% at 15 years vs 5-10% in older patients)
• Need for realistic expectations about activity limitations
• Consideration of alternative procedures (osteotomy, UKA)
• Discussion of future revision surgery likelihood

Elderly Patients (Over 80)

Older patients have higher perioperative medical risks but excellent pain relief outcomes. Considerations include:

• Medical optimization essential
• Higher cardiac and pulmonary complication rates
• Excellent functional improvement despite comorbidities
• Single-stage bilateral TKA generally avoided

Morbid Obesity

BMI greater than 40 increases surgical complications:

• Surgical site infection increased 2-3 fold
• DVT and PE risk elevated
• Implant loosening rates higher
• Weight loss programs beneficial but surgery not contraindicated

• 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.

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.