Total Knee Arthroplasty (TKA) — How It Works, Benefits & Recovery — Procedure Guide, Recovery & Risks | MyMedicPlus

Total knee arthroplasty (TKA), commonly referred to as total knee replacement, is one of the most successful and widely performed orthopaedic procedures in modern medicine, with over 700,000 operations performed annually in the United States and nearly 100,000 in the United Kingdom. The procedure replaces the worn articular surfaces of the medial and lateral femoral condyles, tibial plateau, and optionally the patella (kneecap) with precisely machined prosthetic components: a cobalt-chrome femoral component that caps the end of the femur, a tibial baseplate (cobalt-chrome or titanium) with a polyethylene (ultra-high molecular weight polyethylene, UHMWPE) insert, and an optional polyethylene patellar button.

The replacement components reproduce the natural anatomy of the knee, restoring a well-aligned, pain-free joint that moves through a functional range of 0–120 degrees. Modern implant designs include cruciate-retaining (CR) — which preserves the posterior cruciate ligament — and posterior-stabilised (PS) — which substitutes the PCL function with a cam-post mechanism — each with specific indications and performance characteristics.

The vast majority of TKAs are performed for primary osteoarthritis — the progressive wear of joint cartilage — in patients over 60 years of age, though rheumatoid arthritis, post-traumatic arthritis, avascular necrosis, and other conditions also result in joint destruction requiring arthroplasty. Patient satisfaction after TKA exceeds 85% in appropriately selected patients, with implant survival exceeding 95% at 10 years.

Total knee arthroplasty is indicated for patients with end-stage knee arthritis — most commonly osteoarthritis, but also rheumatoid arthritis, psoriatic arthritis, post-traumatic arthritis, and avascular necrosis — causing severe, constant knee pain that significantly limits daily activities (walking, stair climbing, dressing, sleep), and has not responded to an adequate trial of non-surgical management over at least 3–6 months.

Non-surgical management includes: weight loss (each kilogram of body weight reduction reduces knee load by 4 kg); structured physiotherapy focusing on quadriceps and hamstring strengthening and range-of-motion maintenance; walking aids and activity modification; analgesics (paracetamol, topical NSAIDs, oral NSAIDs where tolerated); intra-articular corticosteroid injections (providing 6–12 weeks of relief); and hyaluronic acid injections (viscosupplementation, providing modest benefit in selected patients).

Radiographic criteria supporting surgical decision-making include Kellgren-Lawrence grade 3–4 osteoarthritis (severe joint space narrowing, osteophytes, subchondral sclerosis). The decision for surgery should be based primarily on symptom severity and quality-of-life impact rather than radiographic findings alone. Patients should be medically optimised before surgery — HbA1c below 8.5% in diabetics, BMI ideally below 40, smoking cessation, and optimisation of cardiovascular and respiratory status.

TKA is performed under general anaesthesia or spinal anaesthesia (preferred — associated with lower blood loss, DVT risk, and post-operative pain). A femoral nerve block or adductor canal block is added for post-operative analgesia.

A medial parapatellar or subvastus approach provides access to the knee joint through a 15–20 cm midline skin incision. The knee is flexed; the patella is everted (turned out) or subluxed laterally to expose the joint.

Bone cuts are made with precision guides referencing the femoral and tibial mechanical axis: the distal femur is cut at 5–7 degrees valgus; the proximal tibia is cut perpendicular to the tibial mechanical axis at 0–3 degrees posterior slope; and the posterior femoral condyles are resected to allow flexion space balance. Sizing trials are inserted and range of motion, stability, and component fit confirmed.

Definitive components are cemented in place using polymethylmethacrylate (PMMA) bone cement for the vast majority of cases (cementless components are increasingly used in younger, higher-demand patients with good bone stock). The polyethylene insert is locked into the tibial baseplate and the joint closed in layers. A drain may be placed. Total operative time: 60–90 minutes for primary TKA.

Robotic-assisted TKA (Mako, ROSA platforms) uses pre-operative CT-based planning and intraoperative robotic arm guidance to achieve highly accurate bone cuts and component positioning, potentially improving alignment and reducing outliers — though functional outcome equivalence to conventional TKA is still being established in randomised trials.

Implant survival exceeds 95% at 10 years and approximately 85–90% at 20 years based on national joint registry data from the UK NJR, Australian NJRR, and Swedish Arthroplasty Register — making TKA one of the most durable surgical interventions in medicine. Patient satisfaction rates exceed 85% in appropriately selected patients.

Pain relief is the primary and most reliable outcome: Oxford Knee Score and KOOS (Knee Injury and Osteoarthritis Outcome Score) demonstrate average improvement of 20–30 points from baseline at 12 months, with maintained improvement at 5 and 10 years. Walking distance improves from a mean of 200–400 metres pre-operatively to unlimited walking in the majority of patients. Stair climbing, independent dressing, and car travel — severely limited by arthritis — are all restored to near-normal function.

The procedure demonstrates cost-effectiveness within 2–5 years when compared to continued medical management of severe knee osteoarthritis, accounting for healthcare costs, lost productivity, and social care requirements. Low-impact recreational activities including walking, swimming, cycling, golf, and light doubles tennis are achievable long-term, contributing significantly to patients' quality of life and cardiovascular health. The psychological benefit of independence, reduced analgesic dependence, and restored mobility is consistently reported by patients as among the most meaningful outcomes.

Deep vein thrombosis (DVT) and pulmonary embolism (PE) are the most common serious complications despite pharmacological and mechanical prophylaxis, occurring in approximately 1–3% of patients. Pharmacoprophylaxis options include low molecular weight heparin, aspirin, rivaroxaban, or dabigatran for 14–35 days post-operatively.

Prosthetic joint infection (PJI) is the most devastating complication, occurring in 1–2% of primary TKAs. Early infection (less than 4 weeks) may be treatable by debridement, antibiotics, and implant retention (DAIR); chronic infection requires two-stage revision — removal of all components, antibiotic spacer insertion, and reimplantation after 6–12 weeks of IV antibiotics — with significant morbidity and cost.

Aseptic loosening of the femoral or tibial component is the most common cause of late revision surgery (10–15 years), resulting from polyethylene wear particle-induced osteolysis and bone loss around the implant. Knee stiffness (arthrofibrosis) — defined as flexion less than 90 degrees — requires manipulation under anaesthesia in 1–2% of cases. Nerve injury (peroneal nerve palsy causing foot drop) occurs in approximately 0.5–1%. Wound healing problems, haematoma, and patellar tendon injury are additional concerns. Patellofemoral complications (lateral patellar tilt, fracture, clunk syndrome) occur in 2–4%.

Enhanced recovery after surgery (ERAS) protocols have transformed TKA recovery. Physiotherapy begins within hours of surgery — patients sit in a chair on day 0 and walk with a frame on day 1. Hospital stay is 2–3 days in most ERAS pathways, with some centres performing day-case TKA in selected patients.

A continuous passive motion (CPM) machine — once universal — is no longer routinely used. Instead, physiotherapy focuses on: active range-of-motion exercises (goal of 0–90 degrees by 2 weeks, 0–110 degrees by 6 weeks); quadriceps activation (straight leg raises); early ambulation with crutches or a walking frame; and stair training before discharge.

Multimodal analgesia (paracetamol, NSAIDs, gabapentin, opioids on a weaning schedule, combined with regional nerve block) manages post-operative pain, enabling earlier mobilisation. Ice (cryotherapy) 20 minutes every 2 hours reduces swelling. DVT prophylaxis with low molecular weight heparin and TED stockings is continued for 14–35 days.

Most patients walk independently with crutches by 2 weeks. Driving (left knee or right knee with automatic transmission) resumes at 4–6 weeks. Return to sedentary work at 4–6 weeks; manual work at 3 months. Low-impact activities (swimming, cycling, walking, golf) are recommended; high-impact sports (running, football) are discouraged to protect the polyethylene insert. Full functional recovery and maximum knee flexion are achieved at 6–12 months.