Two-Stage Revision

Chapter Synopsis

Articulating, antibiotic-impregnated spacers are useful devices in the treatment of infected total knee arthroplasties (TKAs). By reducing the articular surface friction and providing improved knee stability, the prosthesis with antibiotic-loaded acrylic cement (PROSTALAC) facilitates early mobility and discharge from the hospital. It promotes a higher level of activity for the patient, preserves motion through the knee, and improves quadriceps strength before definitive reimplantation. Local delivery of antibiotics can be tailored to the infecting organism by adding customized doses of antibiotics to the bone cement before the spacer is manufactured in the operating room.

Important Points

• Use of heat-stable antibiotic powder is based on the known or suspected organisms, and it is applied at a minimum dose of 4 g of antibiotic per 40 g of cement. For most organisms, we use vancomycin (1.5 g per 40 g of cement) with tobramycin (3.6 g per 40 g of cement).

• Bone stock is preserved whenever possible, but all infected and devitalized tissue must be débrided. Bone loss is preferred to leaving infected tissue in situ.

• The size of the PROSTALAC system is customized to create a stable, well-aligned knee that aids rehabilitation and subsequent reconstruction. Asymmetric defects are augmented with extra antibiotic-loaded cement.

• Patients should be encouraged to move and to work on quadriceps strengthening. We encourage range-of-motion exercises and allow weight bearing as tolerated depending on the quality and quantity of remaining host bone.

Clinical/Surgical Pearls

• Increasing the amount of antibiotic in the cement increases the curing time.

• Combining two antibiotics in the cement increases the overall elution rate.

• After the implants have been sized, manufacturing the spacer on the back table while débridement and irrigation are being completed increases surgical efficiency.

Clinical/Surgical Pitfalls

• The PROSTALAC components should not be removed from the molds until they are completely set. They will not release properly and may be damaged if removed too early.

• The molds are lubricated with sterile mineral oil to prevent the cement sticking to them.

Equipment

Placement of the PROSTALAC system requires the following equipment:

• General or regional anesthesia as appropriate

• Standard supine positioning and an available tourniquet

• Instruments to facilitate implant removal, including specialized knee extraction osteotomes, a Gigli saw, and an angled punch or femoral and tibial component extractors

• Soft tissue débridement and pulse lavage systems

• Palacos acrylic bone cement with gentamicin (three 40-g batches: one for the femoral component, one for the tibial component, and one to secure the spacer and fill minor defects)

• Antibiotic powder: vancomycin (1.5g per 40 g of cement) with tobramycin (3.6 g per 40 g of cement)

• Sterile mineral oil

• Metal femoral condylar runners and polyethylene tibial skids ( Figs. 33A.2 and 33A.3 )

  
  

• Femoral and tibial molds ( Figs. 33A.4 to 33A.6 )

  
  
  

Examination and Imaging

Patients should be assessed for deformity and range of motion (ROM). An effusion or boggy swelling suggests synovitis. Careful attention should be paid to previous incisions and scars, especially recently healed lesions or actively draining sinuses. Vascular and neurologic assessments should be completed.

Anteroposterior, lateral, and skyline plain radiographs should be obtained, and old radiographs are useful for comparison. They are assessed for lysis, implant migration, and likely bone defects. The extent of cement within the femoral and tibial canals should be accounted for in the preoperative plan for removal.

Anatomy and Approaches

When presented with multiple previous surgical scars, the surgeon should try to use the most lateral incision. Transverse scars should be crossed with a perpendicular incision. Incisions should be planned to débride areas where an open wound or sinus exists. If there are concerns about soft tissue viability or about obtaining closure, particularly over the proximal tibia, the opinion of a plastic surgeon should be sought preoperatively. It is always best to achieve stable soft tissues at the first stage rather than wait until the second stage. Having healthy soft tissues at the time of reimplantation reduces the risk of recurrent infection.

A medial parapatellar approach is most commonly used, although lateral approaches have been described. Débriding the synovium from the suprapatellar pouch and then reestablishing the medial and lateral gutters can facilitate exposure and removal of potentially infected tissue. Eversion of the patella is neither required nor recommended. Remnants of the lateral patellofemoral ligament or scar in that area should be released, and the patella should be subluxated laterally instead of everted. After the liner is removed, a medial release is performed, and the tibia is externally rotated to assist in the subluxation of the patella. This protects the extensor mechanism, and extensile maneuvers are rarely required unless the medullary canal of the tibia needs exposure to remove hardware or cement. In that case, a tibial tubercle osteotomy (TTO) or other extensile maneuver (e.g., rectus snip, quadriceps turndown) is performed in keeping with the indications for these techniques.

Surgical Procedure

Step 7. Tibial Component Thickness

The thickness of the tibial component is established from the trial tibial insert. The tibial mold also allows alteration of the thickness of the tibial component in 2-mm increments based on the size of the trial tibial liner. For example, a 12-mm trial liner requires a 12-mm tibial PROSTALAC implant ( Fig. 33A.7 ; see Fig. 33A.6 ).

Step 8. Loading Cement in Molds

Antibiotic-loaded cement is then packed into the appropriate molds that have been lubricated with sterile mineral oil ( Fig. 33A.8 ; see Figs. 33A.4 and 33A.5 ). Curing time is substantially lengthened by the addition of antibiotic.