The level of the constraint is matched to the design characteristics of the retained femoral component.
A tibial stem is typically used in revision situations. Its length depends on the specific system selected. Cemented or cementless stem fixation can be used.
Supplemental metaphyseal fixation
The surgeon may consider using supplemental metaphyseal fixation of the tibial component with a cone or sleeve.
Metaphyseal fixation enhances the support of the tibial component.
Different surgical techniques are involved with the use of a cone or a sleeve.
Compensation for bone loss
The surgeon should have tibial augments and wedges available to compensate for bone loss in the proximal tibia.
3. Patient preparation
The patient is placed in the supine position. A radiolucent table may facilitate intraoperative fluoroscopy if required.
4. Surgical approach
This procedure requires an adequate visualization of the knee joint. The most commonly used is a midline skin incision followed by a medial parapatellar arthrotomy. A proximal and distal extension may be necessary to achieve sufficient visualization and soft tissue releases.
Tibial component removal
The tibial fracture should be stabilized with provisional fixation prior to the component removal.
Care should be taken to avoid excessive bone removal and/or fracture propagation when the component is removed.
Tibial component removal is performed using a combination of a small oscillating saw and the cement osteotomes on the undersurface of the tibial tray.
Cement in the tibial metaphysis around the keel of the tray is removed using cement osteotomes and cement hooks.
Preparation of the tibia
The tibial canal is prepared using reamers of increasing size.
The depth of the reaming is determined by the length of the selected stem.
The diameter of the stem is determined by the reamer diameter which achieves cortical contact with the diaphyseal bone. One should allow for at least 2 mm of cement mantle around the stem if cement fixation is used.
If cementless stem fixation is selected, line to line fit of the reamer to the final stem diameter is used.
Using the reamer and the intramedullary tibial cutting jig, the upper tibia is recut to establish the proper coronal and sagittal alignment.
If there is bone deficiency due to fracture fragmentation, additional bone cuts may be required to remove the fragments and to accommodate the use of augments or wedges under the tibial tray.
If a metaphyseal cone or a sleeve is to be used, further preparation of the tibial metaphysis is performed with the appropriate instruments.
The trial tibial component is assembled, and a trial reduction is performed.
Gap balancing and knee stability assessment are performed using the appropriate thickness of the trial polyethylene insert. The goal is to achieve symmetrical flexion and extension gaps. This is performed using tension spreaders or gap sizing blocks.
Patella tracking is carefully assessed to ensure no instability or impingement throughout the entire range of knee motion.
7. Component insertion
Bone preparation for cementing
The tibial bone surface and canal are lavaged to remove any debris. The bone surface is dried before proceeding.
The cement restrictor is inserted into the tibial canal to allow for a 1 cm cement mantle between the stem tip and the restrictor.
Supplemental tibial metaphyseal fixation
If supplemental tibial metaphyseal fixation is selected, the cone is inserted first.
If a sleeve is selected, the sleeve is impacted on the tibial component and inserted as a monobloc implant.
Cement is mixed using standard techniques and is injected into the canal with retrograde filling and pressurization, using a cement gun.
Insertion of tibial component
The tibial component (including any augment or wedge), is seated with rotational alignment to the tibial tubercle.
8. Final reduction
The polyethylene bearing type is selected to match the specific design characteristics of the retained femoral component. The thickness of the bearing insert is determined by gap balancing and stability examination.
If patellar tracking is not ideal, a lateral retinacular release and medial imbrication can be performed.
The patient can be mobilized with full weight-bearing and active range of motion immediately after surgery.