Metaphyseal Fixation: Sleeves and Cones
Brian P. Chalmers
David G. Lewallen
Reestablish metaphyseal support for revision total knee arthroplasty (TKA) implants with ingrowth porous-metal metaphyseal cones or porous-coated metaphyseal sleeves.
Ensure long-term component stability with synergistic hybrid fixation.
Cemented components and stems (cemented or uncemented) to provide immediate stability that promotes subsequent biologic ingrowth of the metaphyseal cone or sleeve.
Porous ingrowth cones or sleeves to achieve bone ingrowth and thus provide long-term stability and diminish stress on cemented interfaces.
Sterile Instruments and Implants
Basic revision TKA retractors
Metaphyseal cones and trials (with implant-specific instrumentation) and/or metaphyseal sleeves and trials (with implant-specific instrumentation)
Revision TKA implant system of surgeon’s choice (with instrumentation) with higher levels of constraint (typically at least a varus-valgus constrained design in those revision TKAs requiring adjunctive metaphyseal fixation)
Standard and metal-cutting burrs
Standard medial parapatellar arthrotomy with a generous medial release on tibial side.
Extensile approaches as necessary—quadriceps snip or tibial tubercle osteotomy.
Obtain the prior operative reports for better knowledge of the current implants and any notations that indicate unique aspects of the patient’s anatomy or intraoperative challenges.
Template a revision TKA implant system for both the femur and the tibia.
Assess likely bone defects (location, size, segmental versus cavitary) to aid in planning benefits of bone graft, sleeves, or cones and potential benefit of any combinations of these to ensure availability at surgery. Remember, radiographs tend to underestimate the extent of bone loss.
Bone, Implant, and Soft Tissue Techniques
Perform the skin incision, medial parapatellar arthrotomy, generous medial release, and medial and lateral gutter release; use an extensile exposure with a quadriceps snip as necessary to safely expose the knee.
Longer incisions and more generous soft tissue releases are the standard.
Carefully remove the polyethylene insert to relax the extensor mechanism and soft tissue tension.
Remove scar tissue to expose the cement interface of the femoral and tibial components circumferentially with electrocautery or a small rongeur.
Minimize host bone removal and/or damage during implant removal: use a saw or pencil-tip burr to divide the cemented interface of the femoral component.
Try to divide all femoral interfaces (anterior and posterior condyles and chamfers).
Thin flexible osteotomes can be useful to ensure as complete a division of cement-implant bond as possible.
Use a square-tip impactor on the anterior flange and a mallet for gentle disimpaction of the femoral component. If unable to disimpact, revisit the above-mentioned steps.
After femoral component removal, hyperflex and externally rotate the leg to expose the tibia. Again, use a saw or pencil-tip burr to divide the cemented interface under the tibial component. Access the underside of the posterior portion of the tray (behind the keel) by using a narrow saw at the posteromedial corner of the tibia and advancing it parallel to the posterior aspect of the tibial cortex from medial to lateral staying under the implant.
The posterolateral corner and the anterolateral aspect just behind the patellar tendon are the most difficult areas to access: try to ensure that a thin osteotome passes underneath as much of the undersurface of component as possible especially in these areas laterally.
Hyperflex the knee and disimpact the tibial component using a narrow square-tip impactor placed under the tray anteromedially or through a vertical slit lateral to the patellar tendon. Ensure that the tibial component clears the posterior condyle of the femur laterally. The biggest risk of iatrogenic bone damage is a posterolateral tibial fracture if that cement-implant interface has not been adequately freed before tibial disimpaction.
If the femoral or tibial component is not freed rather easily with this method, repeat each step from the beginning and try again.
After implant removal, assess bone defects intraoperatively and estimate appropriate size of cone (Figure 63.1) or sleeve (Figure 63.2) that will be necessary.
Clean the cement debris left on the femur and tibia with a high-speed burr or rongeur.
Recut the proximal tibia removing minimal bone to reestablish a neutral mechanical alignment and slope. Some residual defects are usual to minimize bone removal.
Remove some central metaphyseal bone from the femur and tibia (if still present) with a large curette to allow reamer placement. Save this bone for use as autograft.
Sequentially ream the tibial canal to 14 or 15 mm for an intermediate-length cemented stem or until stable reamer with diaphyseal engagement for a longer cementless stem.
Recognize that the dense medial bone of the tibia tends to push tibial reamers and broaches into valgus, and thus a deliberate effort to avoid this should be made particularly when broaching for porous-coated metaphyseal sleeves.
For bone preparation for cone or sleeve placement, leave the final reamer or a trial stem with rod extension in place as an intramedullary guide for broaching/reaming (depending on the instrumentation system) (Figure 63.3).
Sequentially broach (or ream), starting from the smallest size.
Attempt to prepare the bone so as to minimize bone removed while also maximizing cone or sleeve contact on host bone.
Align the tibial cone/sleeve in appropriate rotation, in-line with the medial edge of the tibial tubercle and anterior crest of the tibia (Figure 63.4).
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