Primary Total Knee Arthroplasty - Standard Measured Resection Technique

Indication. Symptomatic end-stage knee osteoarthritis — most often tricompartmental, Kellgren-Lawrence grade 3-4 — that has failed 3-6 months of conservative care (NSAIDs, physiotherapy, intra-articular injections, bracing), with pain, stiffness and functional limitation. Other accepted indications are: - Rheumatoid arthritis / inflammatory arthropathy with advanced joint destruction despite optimal medical management.

• Post-traumatic arthritis with tricompartmental involvement and mechanical symptoms.
• Osteonecrosis (AVN) of the distal femur or proximal tibia with secondary arthritis and collapse. Assess the whole limb, not just the joint. Before committing, plan for the deformity (varus in roughly 80 percent of primary TKAs, valgus in about 20 percent), any fixed flexion contracture, patellar maltracking, and the state of the contralateral hip and ankle — all of which influence exposure, balancing and the eventual mechanical axis. The one technique decision. The page covers the standard measured resection technique, in which cuts are made from fixed bony landmarks and set resection depths. It is the alternative to gap balancing, where cuts are adjusted to create equal tensioned gaps. The two are clinically equivalent (see Background and Evidence), so the choice is driven by surgeon familiarity and reproducibility rather than superiority.

Consent specifically for infection (1-2 percent), venous thromboembolism (DVT 2-4 percent, PE 0.5-1 percent), stiffness and the possible need for manipulation, periprosthetic fracture, instability, common peroneal nerve palsy (especially in severe valgus), and the long-term possibility of aseptic loosening and revision surgery. Setup. Supine with the operative leg free to flex 120° and extend fully; upper-thigh tourniquet inflated to 300mmHg or limb-occlusion-pressure plus 100mmHg (typically 350-400mmHg). A lateral thigh post at hip level and a hip bump give 15-20° of external rotation to ease patellar eversion.

The goal: restore a neutral mechanical axis (HKA 180° plus or minus 3°) with a stable, well-balanced, mobile knee. The exposure is the medial parapatellar approach (the gold standard, used in about 90 percent of primary TKAs), laid out in full as the first steps below and in depth on the medial parapatellar approach to the knee page.

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Rehabilitation | Phase | Timing | Immobilisation / loading | Therapy goals | |-------|--------|--------------------------|---------------| | 1 | Day 0-1 | Compression dressing, TEDS; immediate WBAT with cemented TKA and intact extensor mechanism | Ankle pumps, quadriceps sets, straight-leg raises, active ROM; CPM optional | | 2 | Week 1-2 | Walker to cane | 90° flexion and 0° full extension by 2 weeks; stair climbing with a rail | | 3 | Week 2-6 | Wound check and suture removal at 2 weeks | 120° flexion by 6 weeks; maintain 0° extension; quadriceps strengthening | | 4 | Month 3-12 | Driving cleared at ~6 weeks (right knee: off narcotics, adequate quadriceps control) | ROM plateaus at about 120° flexion; return to low-impact activities; avoid high-impact running and jumping | | 5 | Long-term | Annual review for life | Annual radiographs — progressive radiolucent lines more than 2mm are concerning for loosening | Venous thromboembolism prophylaxis (global named-society practice — agent choice varies by region and risk): LMWH (e.g. enoxaparin 40mg daily) is first choice in many European and UK protocols; a direct oral factor Xa inhibitor (e.g. rivaroxaban 10mg daily, apixaban 2.5mg twice daily) is a NICE NG89 option; low-dose aspirin (75-100mg daily) is endorsed by AAOS and increasingly by registries for standard-risk patients; plus mechanical prophylaxis (intermittent pneumatic compression, graduated compression stockings) and early mobilisation in all. Duration is typically up to 14 days for low-dose aspirin or standard risk and up to 2-5 weeks for pharmacologic anticoagulation, individualised by bleeding and thrombosis risk. The CRISTAL trial (Sidhu et al, JAMA 2022; PMID 35997730) found enoxaparin reduced symptomatic 90-day VTE versus aspirin after hip or knee arthroplasty (1.82 percent versus 3.45 percent) — balance this against bleeding risk. Analgesia is multimodal (acetaminophen, NSAIDs, opioids as needed) with nerve block or periarticular injection, ice and elevation. Complications

Epidemiology and survivorship. Primary TKA is one of the most commonly performed elective orthopaedic procedures worldwide. Osteoarthritis (most often tricompartmental) is the dominant indication; a varus deformity is present in roughly 80 percent of primary TKAs and a valgus deformity in about 20 percent. Counselling draws on widely reported benchmark rates — infection 1-2 percent, symptomatic DVT 2-4 percent and PE 0.5-1 percent, stiffness or arthrofibrosis 5-10 percent, periprosthetic fracture 0.5-2 percent, instability 1-2 percent and common peroneal nerve palsy 0.5-1 percent — and on aseptic loosening of about 5 percent at 10 years and 10 percent at 20 years. National joint registries (UK NJR, American AJRR, Australian AOANJRR, Swedish, Norwegian and New Zealand) underpin these global survival and revision benchmarks. Measured resection - the principle. In the measured-resection technique the femoral and tibial cuts are made from fixed bony landmarks and set resection depths (about 9-10mm from the distal femur and 8-10mm from the least-worn tibial plateau), with femoral rotation referenced from the transepicondylar axis. It is the alternative to gap-balancing, in which the cuts are adjusted to create equal rectangular tensioned gaps; the two philosophies are clinically equivalent (see below), so the choice is driven by surgeon familiarity and reproducibility. Key evidence. Berger (1993) defined the surgical transepicondylar axis and showed the posterior condylar axis internally rotates a mean 3.5° in males and 0.3° in females — the anatomic basis for adding roughly 3° external rotation and for privileging the TEA. Berger (1998) then showed combined internal component rotation correlates directly with the severity of patellofemoral complications. Whiteside and Arima (1995) established the anteroposterior (Whiteside's) axis as a robust independent check, especially in valgus knees with a hypoplastic lateral condyle. Ritter (2011), in 6070 knees, found component-level neutral alignment gave the lowest failure (0.2 percent) and that compensating one malaligned component with another to reach a neutral axis increased failure. Fehring (2001) showed early TKA failure is dominated by infection (38 percent) and instability (27 percent), with cemented aseptic loosening rare (3 percent) — so balancing, infection prevention and reliable cemented fixation are the highest-yield intra-operative priorities. For thromboprophylaxis, the CRISTAL trial (Sidhu, 2022) found enoxaparin reduced symptomatic 90-day VTE versus aspirin (1.82 percent versus 3.45 percent) after hip or knee arthroplasty. Named-society guidance — AAOS (Surgical Management of Osteoarthritis of the Knee, with appropriate-use and VTE-prophylaxis guidance), NICE NG157 (primary joint replacement) and NG89 (VTE prophylaxis) — frames selection and perioperative thromboprophylaxis, with regional detail drawn from the major arthroplasty registries.