Total Knee Arthroplasty (TKA) — Indications & Outcomes

Total knee arthroplasty (TKA) is among the most commonly performed elective orthopaedic procedures globally, providing reliable pain relief and functional restoration in end-stage knee arthritis. Over 100,000 TKAs are performed annually in the UK (National Joint Registry). Despite the high volume and generally excellent outcomes, TKA is technically demanding, and patient selection, implant design, surgical technique, and rehabilitation all critically influence results. Understanding the indications, implant options, alignment philosophies, and complication management is essential for the orthopaedic surgeon.

• Primary osteoarthritis (OA) is the most common indication, accounting for approximately 85% of cases; other indications include inflammatory arthritis (RA, AS, PsA), post-traumatic arthritis, and AVN of the tibial plateau or femoral condyle
• NJR data: 10-year revision rate for primary TKA approximately 4–5%; >95% survivorship at 10 years for most modern implants; Oxford Knee Score (OKS) is the primary PROM in the UK — 12 questions, 0–48 (48 = best); approximately 80–85% of patients report good to excellent outcomes; approximately 15–20% are dissatisfied with their TKA result — the highest dissatisfaction rate of any major elective orthopaedic procedure; pain and stiffness are the most common reasons for dissatisfaction
• Patient selection, expectation management, and achieving appropriate alignment and soft tissue balance are the most critical factors for a successful outcome; the dissatisfied TKA patient is one of the most challenging problems in arthroplasty surgery

• Indications: end-stage knee OA (tricompartmental or bicompartmental) with severe pain and functional disability failing non-operative treatment; inflammatory arthritis with joint destruction; post-traumatic arthritis; failed HTO or UKA; AVN of the knee; severe coronal deformity (>15° varus/valgus) or flexion contracture not amenable to osteotomy
• Non-operative management should be exhausted: weight management, analgesia (paracetamol, NSAIDs, opioids), physiotherapy, walking aids, corticosteroid injection, hyaluronic acid injection (limited evidence); the decision for surgery should be patient-driven based on disability, not radiological severity alone
• Absolute contraindications: active PJI; active systemic infection; non-functional extensor mechanism (quadriceps/patellar tendon rupture) not repairable; severe peripheral vascular disease precluding wound healing
• Relative contraindications: BMI >40 (higher complication rates, lower functional gain, higher revision rate); active smoking; uncontrolled diabetes; severe osteoporosis; young age (<55 years — higher revision rate due to activity demands and longevity)

• Mechanical alignment (MA): the traditional approach; femoral and tibial cuts are made perpendicular to the mechanical axis of each bone (0° to the mechanical axis); the goal is a neutral mechanical axis (hip-knee-ankle angle of 0°); long-standing leg alignment X-ray is essential; MA produces consistent, reproducible results and is the basis for most registry data and published survival data; the majority of TKAs in the UK use mechanical alignment
• Kinematic alignment (KA): an alternative philosophy in which the femoral and tibial cuts are made to restore the pre-arthritic anatomy of each individual patient — the native distal femoral articular surface angle and proximal tibial slope are recreated; the goal is restoration of the patient`s native joint line and limb alignment rather than a neutral mechanical axis; proponents argue KA produces more natural kinematics and better patient satisfaction; critics argue the long-term survivorship data is immature; growing body of evidence from RCTs and registry studies supports non-inferiority of KA at medium-term follow-up
• Robotic-assisted TKA: rapidly increasing utilisation; improves accuracy of bone cuts and implant positioning relative to planned targets; evidence for improved patient-reported outcomes vs conventional TKA is growing but not yet conclusive; reduces outlier positioning (implants outside the planned alignment zone); higher short-term cost offset by potential long-term revision savings

• Patella resurfacing in TKA: one of the most controversial topics in knee arthroplasty; the UK and most European countries have a high rate of non-resurfacing (patellar button not used); the USA and Australia have a high rate of routine resurfacing; evidence from meta-analyses and RCTs (including the TOPKAT-related work) shows that routine resurfacing reduces the rate of anterior knee pain and re-operation for patellar symptoms compared to non-resurfacing; NICE (2023) recommends considering patellar resurfacing routinely; most UK surgeons currently resurface selectively (damaged patellofemoral cartilage, inflammatory arthritis, obesity, prior patellofemoral surgery)
• Complications of patellar resurfacing: patellar fracture; loosening of the patellar button; patellar maltracking; patellar tendon rupture; residual anterior knee pain despite resurfacing

• Stiffness / reduced ROM: the most common cause of patient dissatisfaction; target ROM post-TKA >90° flexion (ideally >110°); manipulation under anaesthesia (MUA) for stiffness <90° at 6–12 weeks if failing physiotherapy; arthroscopic scar release for established stiffness >3 months; component malposition (flexion gap imbalance, tibial component oversizing) is the most common technical cause
• Peri-prosthetic joint infection (PJI): most serious TKA complication; classified by timing — acute (<3 months), subacute (3 months–2 years), chronic (>2 years); DAIR for acute stable implant PJI within 3–4 weeks of onset of symptoms; two-stage revision for chronic PJI (explant all components, antibiotic spacer for 6 weeks, re-implantation); one-stage revision increasingly used in selected cases at specialist centres; Staph aureus and Staph epidermidis are the most common organisms; the ICM/MSIS criteria define PJI
• Aseptic loosening: most common cause of late revision; tibial component loosening more common than femoral; associated with malalignment, polyethylene wear, osteolysis
• Instability: flexion instability (lax flexion gap) — the most commonly under-recognised cause of TKA dissatisfaction; patients report giving way and difficulty descending stairs; managed with revision to a more constrained implant or liner exchange to a thicker insert
• Peri-prosthetic fracture: supracondylar femoral fracture is most common; Rorabeck classification; management depends on bone stock and implant stability — ORIF for stable implant + adequate bone stock, revision for loose implant
• VTE: DVT and PE; chemical and mechanical prophylaxis mandatory; LMWH for 14 days or rivaroxaban is standard in the UK; TED stockings and early mobilisation

• The dissatisfied TKA patient: approximately 15–20% of TKA patients are dissatisfied; the workup follows a systematic algorithm: (1) exclude PJI (aspiration, serology, cultures — mandatory first step); (2) exclude aseptic loosening or malalignment (weight-bearing X-rays, CT for rotational alignment); (3) assess instability (clinical examination, stress views); (4) assess patellofemoral symptoms (tracking, resurfacing status); (5) exclude referred pain (ipsilateral hip, lumbar spine); (6) consider psychological factors and pre-operative expectations; the most common correctable causes are PJI, component malpositioning (especially rotational), instability, and stiffness
• Tibial component rotation in TKA: the most technically consequential alignment parameter; the tibial component should be externally rotated relative to the tibial tubercle (the tibial tubercle reference, Akagi line); internal rotation of the tibial component causes patellar maltracking, lateral patellar subluxation, anterior knee pain, and instability; CT scan of both components in the problematic TKA is essential to assess rotational alignment — plain X-rays cannot assess rotation reliably
• Flexion gap imbalance: flexion instability occurs when the flexion gap (the space in the knee at 90° flexion) is larger than the extension gap; this results in a knee that feels stable at full extension but unstable in mid-flexion; patients experience giving way descending stairs and sitting-to-standing; initial management is physiotherapy; surgical management involves liner exchange (thicker tibial insert) or revision to a more constrained implant; if the femoral component is too small or too anteriorly positioned, the flexion gap is enlarged and cannot be corrected by liner thickness alone — component revision is required

• NJR: ~5% revision rate at 10 years; OKS 0–48 (48 = best); 15–20% dissatisfaction rate — highest of any major elective orthopaedic procedure
• CR TKA: PCL preserved; PS TKA: PCL sacrificed, cam-post mechanism; PS most widely used; VVC for collateral ligament deficiency; hinged for global instability/salvage
• Mechanical alignment: cuts perpendicular to mechanical axis; neutral hip-knee-ankle axis; traditional gold standard; most NJR data based on MA
• Kinematic alignment: restores native anatomy; improving evidence base; non-inferior at medium term; growing popularity
• PJI workup: aspiration mandatory as first step; DAIR for acute stable (<3–4 weeks); two-stage revision for chronic; Staph aureus + Staph epidermidis most common organisms
• Flexion instability: giving way on stairs/rising; lax flexion gap; liner exchange or revision to constrained implant; commonly under-recognised cause of dissatisfaction
• Patella resurfacing: controversial in UK; NICE (2023) recommends considering routine resurfacing; reduces anterior knee pain and re-operation rate; selectively used by most UK surgeons currently
• Dissatisfied TKA: exclude PJI first (mandatory); then assess malalignment (CT for rotation), instability, patellofemoral symptoms, referred pain; tibial internal rotation = patellar maltracking + anterior knee pain
• Stiffness: MUA for <90° at 6–12 weeks failing physio; arthroscopic release for established stiffness; check component position (flexion gap balance, tibial sizing)
• Peri-prosthetic supracondylar fracture: Rorabeck classification; ORIF for stable implant; revision for loose implant