TKA Revision - Tibial Component with Cones

• Use the prior midline incision (the most lateral of several scars, to preserve lateral genicular blood supply), and excise any intermediate scar en bloc with the arthrotomy rather than raising a bridge.
• Raise full-thickness flaps only — no subcutaneous beveling — and handle skin gently with skin hooks, never crushing clamps. Skin ischaemia occurs in 8 to 12 percent of revisions.
• Extend proximally to mid-thigh and distally to the tibial tubercle or beyond.

Attempt a standard medial parapatellar arthrotomy first. Release the medial capsule and deep MCL fibres subperiosteally and try to evert the patella with the knee flexed to 90 degrees. If the patella will not evert lateral to the midline without tension, extend the exposure rather than forcing it: - Rectus snip (preferred, lowest complication rate 2 to 3 percent): a 45-degree proximal-lateral incision 2 to 3cm long in the quadriceps tendon from the superomedial patellar pole, preserving the VMO. Repair directly at closure with a figure-of-8 of number-2 FiberWire.

• Tibial tubercle osteotomy (severe stiffness, younger patient): a 5 to 6cm by 1.5cm osteotomy lateral to the tibial crest, cut with a microsagittal saw to 4 to 5mm depth preserving the posterior cortex, cracked with a thin osteotome, and reflected proximally with the patellar tendon. Fix at closure with 2 to 3 bicortical screws or cerclage wires.
• V-Y quadricepsplasty (last resort, ankylosed knee in a low-demand elderly patient): an inverted V with the apex 6 to 8cm proximal to the patella, gaining 3 to 5cm of length. High complication rate (10 to 15 percent disruption); protected weight-bearing for six weeks.

• Disrupt the cement-bone interface with narrow osteotomes; use curved osteotomes posteriorly under direct vision to avoid the popliteal bundle.
• An oscillating saw clears the anterior flange cement; extract the femoral component with a universal extractor.
• Remove all cement with a high-speed burr and ultrasonic device, preserving host bone — do not gouge.

• Flex the knee maximally and elevate the medial and lateral sleeves, preserving the MCL and LCL origins.
• Place bent Hohmann retractors posteromedially and posterolaterally resting on bone, not soft tissue, to protect the popliteal bundle.
• Cut the cement peripherally with a microsagittal saw, then osteotomes at the bone-cement interface working anterior to posterior; a Gigli saw reaches the posterior cement.
• Remove the stem with flexible osteotomes down the canal (cemented) or a slotted extractor (press-fit). Gentle mallet taps only — violent impaction fractures the cortex. Periprosthetic fracture during removal occurs in 5 to 8 percent.

• Clear all cement to bleeding bone (essential for cone osseointegration) using hand tools, burr and ultrasonic removal with pulse lavage between steps.
• Classify the defect by AORI: Type 1 intact metaphysis (no cone), 2A one condyle damaged (augment), 2B both condyles damaged (cone indicated), 3 deficient metaphysis with loss of structural support (cone required).

• Porous tantalum or titanium cone, 80 percent porosity, modulus about 3 GPa (close to bone, low stress-shielding).
• Measure the metaphyseal diameter on CT and choose a cone 2 to 5mm smaller; balance maximising contact against sacrificing healthy bone.

• Begin with the smallest reamer (usually 30 to 35mm) and advance in 2.5mm increments.
• Ream to the bleeding-bone endpoint: punctate bleeding with a firm cortical rim. Non-bleeding sclerotic bone will not osseointegrate.
• Preserve the cortical rim; avoid eccentric reaming that perforates the thin metaphyseal cortex.

• Insert a trial cone 2mm smaller than the planned final size; rotate to optimise contact in asymmetric defects.
• Burr high spots rather than over-reaming (preserves bone). Accept only flush seating or at most 2mm proud — a proud cone has poor contact and will fail.

• Impact the final cone to a stable endpoint, then stress it: it must not rotate under the impactor, subside under axial load, or toggle mediolaterally.
• Fluoroscopy confirms symmetric AP position, correct depth parallel to the joint line, and no occult fracture.
• Target 60 to 70 percent surface contact and no micromotion.

• Pack morselised autograft (reaming debris, preferred) or allograft chips around the cone periphery to fill gaps and enhance ingrowth.
• Keep graft out of the cone-to-baseplate interface, where it would cause instability.

• Trial the baseplate with stem on the cone: rotation aligned to the tibial tubercle, central mediolateral position, no rocking.
• Stem length to bypass the cone by two cortical diameters (100 to 150mm); diameter to fill 80 percent of the isthmus. Use flexible reamers that follow the canal, confirming trajectory fluoroscopically.

• Aim for fixation in at least two of the three Morgan-Jones zones (zone 1 epiphysis via the baseplate, zone 2 metaphysis via the cone, zone 3 diaphysis via the stem), ideally all three.
• The stem shares load with the cone and protects against subsidence if cone ingrowth is incomplete; the load fraction is implant- and construct-dependent rather than fixed.

• Cemented technique (commonest): a thin 1 to 2mm cement mantle on the cone's superior surface, insert the baseplate with stem, hold compression 8 to 10 minutes, remove extruded cement.
• Cementless technique: direct impaction or a central screw through the baseplate into the cone, relying on taper-lock and osseointegration.
• A baseplate-cone gap greater than 2mm causes micromotion and failure — ensure flush contact.

• Trial then cement wedge augments (peripheral, 5 to 20mm) or block augments (central, 5 to 15mm) to the baseplate, avoiding cement at the augment-bone interface.
• Restore the joint line: normally 25mm distal to the medial femoral epicondyle and 10mm distal to the fibular head. Elevation risks patella baja (Insall-Salvati ratio less than 0.8).

• Minimum 10mm polyethylene (highly cross-linked preferred); thicker inserts (12 to 25mm) for laxity or bone loss.
• Choose constraint by ligament status: posterior-stabilised if collaterals intact, constrained condylar (CCK) for 5 to 10mm collateral laxity in extension, rotating hinge for gross instability. Avoid over-constraining.
• Trial and assess stability, balance flexion-extension gaps within 2mm, range of motion to 110 to 120 degrees, and central patellar tracking. Lock the insert, irrigate copiously, and re-check stability.

• Repair the medial arthrotomy with interrupted number-1 Vicryl or PDS; repair a rectus snip with figure-of-8 number-2 FiberWire; fix a tibial tubercle osteotomy with 2 to 3 bicortical screws or cerclage.
• Confirm central patellar tracking and a strong straight-leg-raise against resistance. Close in layers over drains if dead space is a concern, with an occlusive compressive dressing.