Revision TKA Bone Loss, Cones and Sleeves

Classification should change the operation:

• Type 1 defects can often be filled because the platform remains supportive.
• Type 2A defects need support for one deficient condyle or plateau.
• Type 2B defects usually require broader metaphyseal reconstruction.
• Type 3 defects require a reconstructability decision: cone/sleeve plus stem if salvageable, or hinged/segmental reconstruction if support and ligaments are not salvageable.
• Defect shape decides whether cement, augment, cone or sleeve is mechanically sensible.

Non-operative treatment is usually for patients who are medically unfit, have low functional demand, decline surgery or need temporary optimisation before revision. It is not definitive treatment for progressive loosening with major bone loss in a fit patient.

Options include:

• Activity modification and walking aids.
• Analgesia and management of inflammatory flares.
• Bracing for instability when surgery is not suitable.
• Infection suppression only when advised by the infection team and curative surgery is not appropriate.
• Optimisation of nutrition, glycaemic control, smoking cessation, anaemia, dental/skin sources and vascular status before surgery.

Failure signs include increasing pain, progressive migration, worsening instability, recurrent falls, fracture risk, sinus or systemic infection features.

Small contained defects can be filled because the remaining cortical or cancellous walls provide support.

Options:

• Cement alone for very small contained defects.
• Cement plus screws for contained defects where screws act as rebar.
• Morselised graft for selected contained cavitary defects when biological restoration is useful.
• Standard augments only if fill will not restore a stable platform.

Avoid cement-only reconstruction for large uncontained defects. Cement fills space, but it does not replace missing structural support.

Modular metal augments are useful when peripheral bone is missing but enough metaphyseal support remains.

Choose augments when:

• A femoral condyle or tibial plateau segment is deficient.
• The defect is too large for cement fill.
• Joint line or posterior femoral offset needs restoration.
• Trial components need a stable rectangular platform.

Key decisions:

• Use distal femoral augments to restore extension gap and joint line.
• Use posterior femoral augments to restore posterior offset and flexion gap.
• Use tibial block or wedge augments for plateau deficiency.
• Add a stem when augment size, bone quality or constraint increases interface load.

A cone is an independent porous scaffold placed into a metaphyseal defect. The revision component is then usually cemented into the cone.

Cones are useful when:

• The defect is irregular, cavitary or combined.
• The metaphyseal rim is deficient but the surgeon can prepare a stable host-bone bed.
• The implant position should not be dictated by the shape of the metaphyseal defect.
• A modular scaffold is needed under a tibial tray or femoral component.

Practical cautions:

• Prepare host bone carefully to avoid fracture.
• Obtain stable rim or metaphyseal contact before cementing the implant.
• Trial stems and augments with the cone in place.
• Removing a well-fixed cone at later revision can be difficult.

A metaphyseal sleeve is broached into the metaphysis and locks to the revision implant. It obtains porous ingrowth while being mechanically linked to the component.

Sleeves are useful when:

• Controlled broaching can obtain axial and rotational stability.
• The metaphyseal defect can be shaped without sacrificing excessive host bone.
• Implant system compatibility and offset options allow good component position.
• The surgeon wants a linked metaphyseal fixation construct.

Practical cautions:

• Broaching can fracture weak metaphyseal bone.
• The sleeve can influence final component position.
• Extraction of a well-fixed sleeve in a later revision can be challenging.
• Avoid forcing malrotation or malalignment to match the sleeve and canal.

Segmental replacement is reserved for non-reconstructable bone or combined massive bone and ligament deficiency.

Consider distal femoral replacement or proximal tibial replacement when:

• AORI type 3 loss leaves no reliable metaphyseal or diaphyseal fixation.
• There is major ligament loss requiring a hinge and segmental replacement.
• Periprosthetic fracture, tumour-style bone loss or repeated failed revision makes standard reconstruction unsafe.
• Extensor mechanism and soft-tissue coverage can support the construct.

The tradeoff is a faster mechanical solution with higher infection, extensor mechanism, loosening and re-revision consequences.

Position and setup

• Supine on a radiolucent table if intra-operative imaging may be needed.
• Tourniquet available; use depends on vascular status, surgeon preference and expected duration.
• Prepare the whole limb from groin to foot.
• Have extraction tools, flexible osteotomes, saws, burrs, cables, plates and stems available.
• Confirm availability of augments, cones, sleeves, CCK, hinge, segmental replacement and backup polyethylene sizes.

Exposure

• Use the previous midline incision where possible, respecting skin bridges.
• Develop full-thickness flaps only as much as necessary.
• Standard medial parapatellar arthrotomy is common.
• Extensile exposure options include quadriceps snip, V-Y turndown or tibial tubercle osteotomy.
• Choose extensile exposure early rather than avulsing the patellar tendon during forced eversion.

Component removal

• Obtain cultures if infection is possible or confirmed.
• Remove polyethylene first to improve access.
• Disrupt implant-cement and cement-bone interfaces with thin flexible osteotomes.
• Work circumferentially and preserve host bone.
• Remove cement, membrane and osteolytic debris.
• Protect the collateral insertions, extensor mechanism and posterior neurovascular structures.

Reassess after explant

• Assign AORI grade only after the components are out.
• Identify contained, uncontained, segmental and combined defects.
• Check for fractures, cortical perforation and collateral avulsion.
• Reconfirm whether the planned reconstruction is still adequate.

Tibial reconstruction

• Establish a stable tibial platform perpendicular to the planned mechanical axis.
• Remove only the bone needed to create a flat reference surface.
• Use augments for plateau deficiency.
• Prepare the canal for stem alignment and load sharing.
• Prepare a cone when an independent metaphyseal scaffold is needed.
• Broach a sleeve when metaphyseal bone can accept a controlled implant-linked press-fit.
• Trial tray rotation, coverage, offset and stem fit before final fixation.

Pitfalls:

• Excess tibial resection worsens joint-line elevation.
• Cement-only fill in a large uncontained medial tibial defect risks collapse.
• Canal-driven stem position can malrotate or maltranslate the tray unless offset options are used.

Femoral reconstruction

• Determine distal femoral joint line using epicondyles, adductor tubercle, patellar height and contralateral comparison when available.
• Use distal augments to restore extension gap and joint line.
• Use posterior augments to restore posterior offset and flexion gap.
• Prepare femoral cone or sleeve when condylar/metaphyseal support is inadequate.
• Use offset stems if the canal position would otherwise force malposition.
• Check rotation using transepicondylar axis, posterior condylar remnants, Whiteside line if visible and gap symmetry.

Pitfalls:

• Excess distal femoral bone loss can tempt overstuffing with thick polyethylene instead of restoring distal joint line.
• Posterior offset loss causes flexion instability.
• Malrotation creates patellofemoral pain, stiffness and asymmetric gaps.

Trialling

Test the knee before cementing:

• Extension gap, flexion gap and mid-flexion stability.
• Varus-valgus opening at full extension, 30 degrees and 90 degrees.
• AP stability at 90 degrees.
• Patellar tracking and extensor mechanism tension.
• Limb alignment, rotation, joint line and range of motion.

Final fixation

• Cement strategy depends on stem type and implant system.
• Cement the implant-cone interface when using an independent cone.
• Seat sleeves according to system technique and avoid malrotation.
• Remove excess cement, especially posteriorly.
• Recheck stability after final components are inserted.
• Close over drains selectively and protect soft tissue.