Knee Replacement — How It Works, Benefits & Recovery — Procedure Guide, Recovery & Risks | MyMedicPlus

Total knee arthroplasty (TKA), commonly called knee replacement, is an orthopaedic surgical procedure that resurfaces the damaged articular surfaces of the knee joint with precisely engineered prosthetic components to restore pain-free function. The native knee joint has three compartments — medial (inner), lateral (outer), and patellofemoral (kneecap) — all of which are resurfaced in a total knee replacement. The implant system consists of a metal femoral component that caps the end of the femur, a metal-backed tibial baseplate fixed into the tibia, and a polyethylene (ultra-high-molecular-weight plastic) insert that articulates between the femoral and tibial components, absorbing load and providing smooth gliding movement. The patella is optionally resurfaced with a polyethylene button in practice that varies by surgeon preference and evidence from randomised trials. Unicompartmental (partial) knee arthroplasty (UKA) replaces only the affected medial or lateral compartment in carefully selected patients whose disease is confined to a single compartment with intact cruciate ligaments and a correctable deformity. TKA is one of the most frequently performed elective surgical procedures globally — over 700,000 TKA procedures are performed in the United States annually, over 100,000 in the UK, and numbers are rising in India and Southeast Asia as life expectancy increases. The procedure reliably transforms quality of life for patients disabled by end-stage knee arthritis, with 90–95% implant survival at 10 years confirmed by national joint registry data from over 30 countries.

Knee replacement is indicated when knee joint disease causes persistent, severe pain and functional limitation that significantly impairs quality of life and fails to respond to adequate non-operative management. The decision is based primarily on functional impairment and symptoms, not patient age or radiological findings alone. Primary indications include: end-stage knee osteoarthritis (the most common indication — degenerative loss of articular cartilage progressing to bone-on-bone contact, typically presenting with medial compartment-predominant disease, varus deformity, and rest pain); rheumatoid and other inflammatory arthropathies affecting the knee (earlier onset, bilateral, often symmetrical); post-traumatic arthritis following tibial plateau fractures, intra-articular distal femur fractures, or complex ligamentous injuries; avascular necrosis of the femoral or tibial condyle from corticosteroid use, alcohol, sickle cell disease, or idiopathic causes; and other structural causes including Paget's disease, gout, and haemophilic arthropathy. The Oxford Knee Score, KOOS (Knee Injury and Osteoarthritis Outcome Score), and plain radiographs (Kellgren-Lawrence grade III–IV) are used to document disease severity. Non-operative management that must be exhausted before surgery includes: weight management (a 10% body weight reduction significantly reduces knee OA symptoms); structured physiotherapy targeting quadriceps strengthening; analgesic medication including paracetamol, NSAIDs, duloxetine; walking aids; knee bracing; and intra-articular corticosteroid injections (up to 4 per year). Hyaluronic acid injections may provide short-term symptom relief. Surgery is typically recommended when pain severely limits ambulation distance, disturbs sleep, prevents basic activities of daily living, and has not responded to these measures over 3–6 months.

Under spinal anaesthesia (the preferred technique — associated with lower blood loss, reduced DVT risk, and avoidance of general anaesthetic complications) or general anaesthesia, the patient is positioned supine on the operating table with a pneumatic tourniquet applied to the thigh to create a bloodless operative field. A midline anterior skin incision is made from 5 cm above to 5 cm below the patella. The medial parapatellar arthrotomy divides the quadriceps tendon and capsule to enter the joint. The patella is everted, exposing the distal femur and proximal tibia. Precise bony resections are performed using cutting guides aligned to restore normal limb alignment — a mechanical axis within 3 degrees of neutral (valgus) between the hip, knee, and ankle centres. The distal femoral cut is made at 6 degrees of valgus to the femoral shaft; tibial resection is perpendicular to the mechanical tibial axis at 3 degrees of posterior slope to optimise flexion range. Trial components are inserted and the knee is taken through a full range of motion to assess alignment, stability, flexion gap, and extension gap — all must be balanced for optimal outcomes. Ligament balancing — releases of the medial or lateral collateral ligament complex — adjusts for pre-existing varus or valgus deformity. Cemented fixation using polymethylmethacrylate (PMMA) acrylic bone cement is the most widely used technique, providing immediate stable fixation. Cementless components with porous ingrowth surfaces are increasingly used, particularly in younger and more active patients. Patellar resurfacing is performed according to surgeon preference and knee anatomy. Robotic-assisted TKA (MAKO, ROSA systems) uses a patient-specific 3D plan and real-time haptic feedback to guide implant positioning with sub-degree accuracy, potentially improving consistency of alignment and soft tissue balance. Arthrotomy closure, layered wound closure with absorbable sutures, and wound dressings complete the procedure. Total operative time is 60–90 minutes.

TKA achieves 90–95% implant survival at 10 years and approximately 80–85% at 20 years, confirmed by over two decades of national joint registry data from the UK NJR, Swedish Knee Arthroplasty Register, Australian Orthopaedic Association National Joint Replacement Registry, and others encompassing millions of procedures. Pain relief is dramatic — over 85% of patients report substantial or complete pain relief, with Oxford Knee Scores improving by an average of 17–22 points post-operatively. Walking distance increases from often less than 100 metres pre-operatively to unlimited ambulation in the majority of patients. Patient satisfaction is approximately 80–85% at 1 year — slightly lower than hip replacement due to the technical complexity of achieving perfect soft-tissue balance, but very high overall. Quality-adjusted life year (QALY) analysis demonstrates TKA to be highly cost-effective, with a cost per QALY well below health technology assessment thresholds. Modern implant designs — posterior-stabilised (PS) versus cruciate-retaining (CR), fixed versus mobile bearing, and various flexion-optimised designs — provide extensive customisation to patient anatomy. Computer-navigated and robotic TKA improves implant positioning accuracy compared with conventional instrumentation, reducing alignment outliers and potentially reducing revision rates — although definitive evidence of improved patient-reported outcomes at 5–10 years is still emerging from ongoing randomised trials.

Venous thromboembolism — deep vein thrombosis (DVT) and pulmonary embolism (PE) — are the most important early systemic complications; extended thromboprophylaxis with low-molecular-weight heparin (enoxaparin) or direct oral anticoagulants (rivaroxaban, apixaban) for 10–35 days post-operatively, combined with mechanical pneumatic compression stockings and early mobilisation, has reduced symptomatic DVT rates to under 1% at specialist centres. Prosthetic joint infection (PJI) is the most devastating complication, occurring in 1–2% of primary TKA; it may require staged revision surgery (implant removal, antibiotic cement spacer, 6–8 weeks of intravenous antibiotics, then reimplantation), with outcomes significantly worse than primary arthroplasty. Modifiable risk factors for PJI including active smoking, poorly controlled diabetes (HbA1c greater than 8%), obesity (BMI over 40), and any active skin or dental infection should be addressed before elective TKA. Knee stiffness — defined as flexion range below 90 degrees at 6–8 weeks — occurs in approximately 5–10% of patients; manipulation under anaesthesia (MUA) performed at 6–8 weeks effectively restores flexion in the majority. Persistent knee pain at 1 year without an identifiable mechanical cause (known as chronic post-TKA pain) affects approximately 15–20% of patients to varying degrees and is the leading cause of patient dissatisfaction; thorough pre-operative expectation management is essential. Aseptic loosening — failure of the cement-bone or cementless ingrowth interface without infection — is the leading cause of late implant failure, contributing to approximately 30–40% of revisions after 10 years. Periprosthetic fracture around the implant occurs in 0.5–1%, typically from low-energy falls in osteoporotic patients. Anterior knee pain (patellofemoral symptoms) affects approximately 5–10% of patients, particularly when the patella is not resurfaced.

Enhanced Recovery After Surgery (ERAS) protocols enable physiotherapy to begin within hours of surgery on the day of the procedure. Patients stand and take their first steps with a walking frame 4–6 hours post-operatively under physiotherapy supervision. Multimodal analgesia — spinal anaesthesia with long-acting bupivacaine, periarticular local anaesthetic injection by the surgeon, regular paracetamol, NSAIDs, and gabapentin — minimises opioid requirements and reduces nausea, facilitating early mobilisation. Hospital discharge occurs at 2–4 days in standard ERAS pathways; selected patients in day-case TKA programmes are discharged the same day. Knee swelling, warmth, and bruising are expected for 2–3 months and are not signs of infection. A graduated home physiotherapy programme — quadriceps strengthening, range of motion exercises, and progressive walking — is essential for optimal outcomes; supervised outpatient physiotherapy at a rehabilitation centre provides additional benefit for patients with slower progress. Full weight-bearing on the operated knee is permitted immediately with a walking aid. Range of motion exercises to achieve 90–100 degrees of flexion within 4–6 weeks are critical to prevent scar contracture. Crutches transition to a walking stick at 2–3 weeks and are discontinued when gait is stable, usually at 4–6 weeks. Driving resumes when the patient can perform an emergency stop without pain — typically 4–6 weeks after right-sided replacement in an automatic vehicle. Return to desk work occurs at 4–6 weeks; manual work at 3–6 months. High-impact activities including running, contact sports, and heavy lifting are generally discouraged to extend implant longevity, though low-impact activities such as swimming, cycling, and golf are encouraged.