Distal Femoral Replacement
Graham D. Pallante
Rafael J. Sierra
Distal femoral replacement most commonly is used as a salvage procedure in revision total knee arthroplasty (TKA) involving severe bone loss, following oncologic resection, or in supracondylar periprosthetic femur fracture with poor bone quality and loose/malpositioned implants.
Resection of the distal femur involves removal of the collateral ligaments, and constructs are therefore highly constrained designs. Rotating-hinge prostheses usually are preferred to decrease stress transfer to the bone-implant interface.
Distal femoral replacement allows immediate, stable fixation, and thus immediate weight bearing.
Distal femoral replacement may be considered in selected revision TKA in which bone loss cannot be managed with metal augments, sleeves, or cones in isolation.
Uncemented or cemented stems may be used for fixation. Cemented stems are preferred in patients with poor diaphyseal bone or host factors that may limit bony ingrowth potential.
Soft tissue management is important. Often, the soft tissue envelope is deficient. In this scenario, use the smallest possible implant to minimize the need for local or free soft tissue transfer.
Implant design improvements have decreased rates of aseptic loosening. However, distal femoral replacement still incurs elevated risks of infection, periprosthetic fracture, and mechanical failure.
Sterile Instruments and Implants
Routine knee retractors
Small and large oscillating saw
Straight, thin osteotomes
Cement extraction tools, trephines if removing a well-fixed stemmed implant. See Chapter 61 for details regarding implant removal
Pulse lavage with femoral adapter for canal irrigation
Metaphyseal cones, sleeves
Reamers, manual and/or power; straight and/or flexible. Consider the quality of the diaphyseal bone to be reamed and deformity
For cemented stems: cement gun, cement restrictor, vacuum cement mixer
Uncemented stems (with instrumentation)
Cemented stems (with instrumentation)
Nonsterile tourniquet preferred
Standard, midline approach with medial parapatellar arthrotomy is preferred. Considerations should be made for previous skin incisions or soft tissue defects.
Extensile knee approaches such as quadriceps snip or tibial tubercle osteotomy may be required. See Chapter 60 for details.
Obtain previous operative reports and implant records if this is a revision case.
Full-length films preoperatively can aid in the assessment of overall alignment and leg length. Dedicated full-length femur and/or tibia films may also be useful in templating.
Determine femoral resection level, and template based on this. The knee joint line can be used as a guide for femoral length.
Measure the femoral canal diameter to obtain an estimate of stem extension size. This will vary based on whether a cemented or uncemented implant is desired.
Review implant-specific requirements for bony resection, as the femoral resection level may need to be altered to accommodate different implant construct lengths.
Carefully assess the soft tissues. Often, patients have undergone multiple surgeries, and wound closure/healing may be a concern. Skin grafting, local, or free flap coverage may be necessary.
Bone, Implant, and Soft Tissue Techniques
Perform the desired approach to the knee, if necessary, employing an extensile approach to expose the distal femur and proximal tibia. In the revision setting, it is preferable to use the most lateral usable previous incision.
With the knee extended, use a straight-edged ruler or Bovie cord to place a longitudinal line on the anterior cortex of the femur in line with the linea aspera above the level of resection. Next, make a corresponding vertical line on the proximal tibia. These marks will be used to guide implant rotation, which is difficult to judge after distal femoral resection. If either of the femoral condyles are present, they can also be used for reference. Careful attention to rotation is important to avoid patellar maltracking.
Based on preoperative templating, measure and mark the distal femoral resection level before any bony resection or implant removal.
If previous orthopedic hardware is present at the level of planned femoral or tibial osteotomy, remove as necessary, preserving as much host bone as possible (see Chapter 61).
The distal femur is resected/excised first to aid in tibial exposure. Take care to keep the dissection plane against the bone to protect neurovascular structures.
Clear all soft tissue circumferentially around the femur at the level of planned femoral osteotomy.
Assess leg length clinically by comparing the operative and contralateral extremities with the knee extended. If length is preserved, use a ruler to measure the total length of the resection. This distance can be used as a guide when building the implant to calculate the approximate length (Figure 64.1).
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