RECONSTRUCTION 2023, Jan, 08 | 12:00 am

Cementless Fixation

P ITFALLS

  • Osteoporosis

 

Cementless Fixation

 

Indications

  • Tricompartmental arthritis of the knee that has failed nonoperative measures

    Controversies

    • Weight and inflammatory arthritis are not contraindications to cementless fixation.

     

  • Younger patients (65 years), although excellent results have been obtained in patients older than 65 as well

  • Good bone quality

    Examination/Imaging

    Treatment Options

    • Cemented fixation—considered the “gold standard” in older patients.

     

  • Plain radiographs: weight-bearing anteroposterior (AP), lateral, and “sunrise” views, and standing hip-to-ankle alignment radiographs to assess degree of arthritis and bone quality

    Surgical Anatomy

  • The medial and lateral collateral ligaments, patellar tendon, and posterior neurovascular structures are protected at all times during bone cuts with retractors.

  • The posterior cruciate ligament (PCL) can be sacrificed or preserved depending on surgeon preference. If preserved, a ¼-inch osteotome is driven into the tibial plateau just anterior to the PCL to protect it during the tibial cut.

     

    P EARLS

    • Hyperflexion of the knee during tibial preparation allows circumferential exposure to allow for proper sizing.

     

    Positioning

  • Same as for cemented fixation.

     

    Equipment

    • We prefer using a leg holder, which allows “hands-free” positioning of the leg in any degree of flexion/extension/ rotation (Fig. 1).

     

     

    FIGURE 1

     

    197

     

    Cementless Fixation

     

    Portals/Exposures

    • A standard total knee replacement exposure, including minimally invasive techniques, can be used for cementless fixation.

       

      P EARLS

      • During the anterior femoral cut, the saw blade is “sprung” away from the bone to provide a tight AP fit and avoid anterior notching. Avoid chatter against the cutting guide to maintain a precise cut.

         

      • As thermal necrosis of bone occurs at 55° C (93° F), irrigation is used for all saw cuts.

         

      • Bone cuts can be validated using computer navigation if desired to confirm appropriate alignment.

       

    • Our preference for most primary total knee replacements is a subvastus approach.

      Procedure

      Step 1: Femoral Preparation

    • After exposure has been completed, our preference is to cut the femur first. This allows for more space in flexion to cut the tibia.

    • All removed bone is saved for later bone grafting.

    • Cementless fixation requires precision cutting instrumentation and technique.

      Step 2: Tibial Preparation

    • The tibia is cut using either an extra- or an intramedullary alignment guide. Computer navigation can also aid in increasing the precision of the alignment of the tibial cut.

    • The tibia is then sized and broached.

       

      P EARLS

      • Resection of the tibia matching the patient’s natural rotation and posterior slope will improve initial component stability and protect against anterior subsidence (Fig. 2).

         

      • If excellent bone quality is present, either turn the saw blade to expose fresh teeth or use a fresh blade for the tibial cut.

         

      • The cut should be checked for flatness and varus/valgus alignment using a flat instrument (broaching guide). Any rocking will predispose to component loosening.

         

        P ITFALLS

      • Avoid recutting the tibia or performing freehand cuts. This will decrease the precision of the cut and predispose to loosening.

       

      Step 3: Trialing

    • An appropriately sized tibial baseplate trial component is assembled with the appropriate trial liner, replacing the amount of bone resected.

    • The femoral trial component is placed, and the knee is brought through a range of motion to assess the need for soft tissue balancing.

 

 

 

FIGURE 2

 

 

 

198

 

Cementless Fixation

 

A B

FIGURE 3

Step 4: Bone Graft Harvesting and

Application

 

P ITFALLS

  • When placing the tibial trial component, verify that it fits flat against the bone cut without “rocking.”

     

  • Verify that the femoral trial component nicely matches the bone cuts and achieves a tight fit.

 

  • Bone graft is harvested from the center of the underside of the resected tibial bone using a small patellar reamer (Fig. 3A and 3B).

  • The graft is then applied to the tibial surface and to the distal, anterior, and anterior chamfer cuts (Fig. 4).

  • Structural graft can be used to fill any cysts or bony defects.

  • Figure 5 shows that tibial surface after grafting.

     

     

     

    FIGURE 4

     

     

     

    199

     

     

    P EARLS

    • Light pressure with the patellar reamer will prevent harvesting coarse bone graft material.

       

    • A forceps handle can be used to apply the graft to the bone, preferentially to areas of soft bone (laterally for varus knees, medially for valgus knees).

       

    • Cutting block handles can be used like “rolling pins” to spread the graft around and fill any defects.

     

    Cementless Fixation

     

    FIGURE 5

     

    Step 5: Inserting Implants

    • The tibial tray is impacted into place (Fig. 6). Screws (6.5  50-mm bone screws) may be inserted through the tray to augment initial stability (Fig. 7).

    • The polyethylene liner is impacted into the tray.

    • The femoral component is impacted.

      Step 6: Patellar Resurfacing

    • Patellar resurfacing, if desired, is carried out using a measured resection technique. Care is taken to make an even resection medially and laterally as well as superiorly and inferiorly.

       

       

       

      FIGURE 6 FIGURE 7

       

       

       

       

      P EARLS

      • If screw fixation is used, “matchsticks” can be made from the chamfer cuts and inserted into the screw holes to improve fixation (Fig. 8).

         

      • The lateral screw is angled 10° medially. The medial screw is inserted perpendicular to the baseplate.

         

        P ITFALLS

      • When drilling for screw holes, it is critical not to drill deeper than

      ¼ inch. This allows the screws to be inserted using a power screwdriver and to “find” their own course and avoid violating the cortex.

       

      Cementless Fixation

       

      FIGURE 8

       

      200

       

       

      P EARLS

      • Many patients undergoing cementless fixation have minimal arthritic changes on the patella. It is our preference in these patients to simply denervate the patella circumferentially with electrocautery and remove any peripheral osteophytes and not resurface the patella. If the patella is resurfaced, a cemented or cementless patella can be used depending on surgeon preference.

       

  • The medial sagittal ridge is marked prior to resection of the patella and used to center the component in order to medialize the resurfaced patella and improve patellar tracking.

    Postoperative Care and Expected Outcomes

  • All total knee replacement patients (cemented or cementless) are treated the same postoperatively.

  • A continuous passive motion machine is used in the hospital to help minimize postoperative pain and encourage early motion.

  • All patients are allowed to bear weight as tolerated starting on postoperative day 1, but are required to use two crutches for 6 weeks and either a single crutch or a cane for an additional 6 weeks. This is done to minimize swelling and allow for bony integration of cementless implants.