TKA Revision - Femoral Component with Sleeves

Indications. Metaphyseal sleeves reconstruct cavitary and combined bone loss in the distal femur at revision TKA. The principal indications are: - AORI Type 2B femoral defects — metaphyseal bone damage with structural compromise but a cortical rim still present.

• AORI Type 3 femoral defects — metaphyseal deficiency with loss of cortical rim support.
• Aseptic loosening with moderate to severe bone loss (Paprosky Type 2B/3 equivalent).
• Failed primary TKA with progressive osteolysis causing metaphyseal erosion.
• Revision after infection with bone loss from debridement (once infection eradicated).
• Periprosthetic fracture requiring component revision with residual bone defects. Alternative indications include oncologic reconstruction after distal femoral resection (modular sleeve systems), severe coronal plane deformity with asymmetric bone loss requiring joint-line restoration, and failed unicompartmental arthroplasty with significant defects. Contraindications. - Absolute: active infection (stage the reconstruction after eradication), inadequate soft-tissue coverage, a non-functional extensor mechanism (consider hinged prosthesis or fusion), and severe peripheral vascular disease contraindicating tourniquet use.
• Relative: AORI Type 1 or 2A defects (sleeves not required — use augments or primary components), elderly low-demand patients with Type 2B defects (a simpler reconstruction with augments and cement may suffice), severe metaphyseal-diaphyseal mismatch (may require custom components), and extremely poor bone quality (consider longer stems with diaphyseal fixation). Pre-operative assessment. Confirm the diagnosis and exclude infection before planning an aseptic reconstruction. - Clinical: pain (location, severity, rest versus activity), stability (varus-valgus stress at 0 and 20 degrees flexion, anterior drawer, recurvatum), range of motion (flexion contracture and maximum flexion predict exposure difficulty), extensor mechanism (patellar tracking, quadriceps strength, lag), neurovascular status, and skin condition (previous scars, adherence, quality).
• Imaging essential trilogy: AP and lateral weight-bearing radiographs (alignment, bone stock, implant position), full-length standing films (mechanical axis planning), and a CT scan for 3D defect characterisation, cortical thickness and canal geometry. Assess component position, AORI defect type (contained versus uncontained, symmetric versus asymmetric), implant fixation, joint-line height (anatomic is about 40 mm above the fibular head) and patellar height (Insall-Salvati ratio 1.0 to 1.2).
• Laboratory: ESR and CRP (infection screening), synovial fluid cell count, differential and culture if an effusion is present, alpha-defensin if chronic infection is suspected, and routine bloods (FBC, U&E, LFTs, coagulation) for medical optimisation. Equipment. Plan a full revision tray: revision femoral components in multiple sizes, metaphyseal sleeves across a range of diameters and lengths, femoral stems (cemented and uncemented, various diameters and lengths), modular distal and posterior augments, polyethylene inserts (standard and constrained), and trial components; plus extensile-exposure instruments, component-removal tools (osteotomes, Gigli saws, explant tools), cement-removal tools (ultrasonic system, high-speed burr), system-specific sleeve reamers and broaches, flexible reamers, alignment guides, tensioners and trial spacers. Consent specifically for periprosthetic fracture (intra-operative risk 10 to 15 percent), infection (5 to 10 percent in revision surgery), instability (5 to 15 percent), stiffness (15 to 25 percent), neurovascular injury (rare but catastrophic), and the possible need for a constrained or hinged insert if stability cannot be achieved. Setup. Supine on a radiolucent table with a bump under the ipsilateral hip (15 to 20 degrees) to orient the patella anteriorly, the foot of the table flexed to allow 90 degrees of knee flexion, and a lateral post at mid-thigh if valgus stress is needed. High-thigh tourniquet (250 to 300 mmHg, or 100 mmHg above systolic); consider not inflating initially if the component is well-fixed. Chlorhexidine alcohol or povidone-iodine skin preparation of the entire leg, with waterproof draping.

The goal is to gain safe extensile exposure, remove the loose or failed component while preserving every millimetre of remaining bone, classify the cavitary defect, and reconstruct the distal femur with a porous metaphyseal sleeve that transfers load through the metaphysis and sets component rotation — with a stem for alignment rather than primary fixation. The exposure is the foundation of the whole case and is laid out in full as the first steps below (see also the medial parapatellar approach to the knee).

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Closure. Copious irrigation (at least 6 L, dilute povidone-iodine or chlorhexidine), haemostasis with the tourniquet deflated, and a large-bore drain removed at 24 to 48 hours when output is less than 50 mL per 24 hours. Repair the arthrotomy with No. 2 braided absorbable suture. If an extensile exposure was used, repair the quadriceps snip with non-absorbable suture, the V-Y with the tendon advanced distally, and the tibial tubercle osteotomy with cerclage wires or cables. Close the subcutaneous layer (2-0 absorbable, obliterating dead space) and skin (staples or subcuticular), and apply a sterile compressive wool-and-crepe dressing. Post-operative protocol. | Phase | Timing | Milestones | |-------|--------|------------| | Immediate | Day 0 to 2 | Elevate, ice, multimodal analgesia (paracetamol, NSAIDs, opioids), neurovascular checks, drain removal when output is low | | Early mobilisation | Day 1 to 2 | Physiotherapy; touch weight-bearing initially after extensile exposure, weight-bearing as tolerated after a standard exposure; continuous passive motion if stiff | | Wound review | Week 2 | Remove staples, wound check, continue range-of-motion and strengthening therapy | | Radiographic review | Week 6 | Check alignment, component position and absence of fracture; functional assessment | | Ingrowth assessment | Month 3 | Radiographs for radiolucent lines; functional outcomes | | Surveillance | Annually | Long-term monitoring for loosening, wear and instability | Weight-bearing rule. A standard exposure allows immediate weight-bearing as tolerated. After any extensile exposure use protected weight-bearing for 6 weeks to allow healing; after a tibial tubercle osteotomy restrict to touch weight-bearing for 6 weeks, then progressive loading.

Complications.

Epidemiology and the place of sleeves. Across national joint-replacement registries (AOANJRR, the UK NJR, AJRR, and the Swedish and Norwegian registries), aseptic loosening and infection are the leading indications for revision TKA, and a substantial fraction of revisions present with metaphyseal bone loss that primary-style augments and cement cannot reconstruct. Porous-metal metaphyseal fixation — sleeves and cones — was developed to load the remaining metaphyseal shell physiologically and achieve biological ingrowth, supplanting structural allograft for many AORI Type 2B and 3 defects. Registry and single-centre series report high intermediate- and long-term survivorship for femoral sleeves, with intra-operative fracture during impaction the commonest early complication. AORI classification (Anderson Orthopaedic Research Institute). The classification grades the integrity of the metaphyseal bone — the primary load-bearing region — and drives the reconstruction strategy.

Exam points on the AORI system. In Engh and Ammeen's original description, Type 2A denotes a defect of one femoral condyle (or one tibial plateau) and Type 2B denotes defects of both condyles (or both plateaus). In practice 2A defects are managed with augments and 2B/3 defects with metaphyseal sleeves or cones — the clinically important distinction tested in vivas. The surgical distinction between 2B and 3 is the cortical rim: Type 2B retains a partial rim that allows sleeve compression against remaining bone, whereas Type 3 has insufficient rim and needs a longer sleeve bridging to the diaphysis or an allograft-prosthetic composite. A pre-operative CT helps differentiate them. Sleeve design and stem philosophy. Sleeves are porous tantalum or titanium cylinders (about 80 percent porosity) that engage the metaphysis circumferentially and transfer load physiologically through the metaphysis. Femoral sleeves are typically 35 to 45 mm in diameter and come in short (30 to 40 mm), standard (50 to 60 mm) and long (70 to 90 mm) lengths. The historical teaching that the stem provides fixation has given way to the modern metaphyseal-fixation philosophy: the stem provides alignment and rotational stability only, allowing a smaller-diameter stem with less stress shielding. Load transfers through the sleeve-metaphysis interface — the principle that justifies sleeve reconstruction for AORI 2B/3 defects.