VIDEO TECHNIQUES: Soft Tissue Balancing in a PS TKA
At ICJR’s instructional course on joint replacement surgery at the 9th Congress of the Chinese Association of Orthopaedic Surgeons, Chitranjan S. Ranawat, MD, from Hospital for Special Surgery in New York, discussed and demonstrated his preferred technique for correcting varus deformity when using a posterior stabilized (PS) total knee prosthesis.
- For most primary TKAs, Dr. Ranawat makes a straight incision from the insertion of the patellar ligament to about 2 fingers-width above the superior pole of the patella.
- The medial flap is then undermined below the deep fascia.
- When performing the arthrotomy, Dr. Ranawat leaves tendinous tissue on both sides of the arthrotomy to ensure tendon-to-tendon healing.
- At the distal section of the arthrotomy, the soft tissue is elevated from the bone subperiosteally.
- To obtain good exposure, part of the distal section of the fat pad is removed.
- Both cruciate ligaments are incised.
- The patellofemoral ligament is released, which aids in patellar
- The knee is then hyperflexed and the tibia is shifted forward to allow removal of the lateral meniscus. Special attention is paid to finding and coagulating the inferior lateral genicular artery.
Basic Bone Cuts and Bone Preparation
- The insertion of the posterior cruciate ligament is marked lateral to the tibial spine. Dr. Ranawat uses this mark to align the tibial cutting guide.
- On a varus knee, the depth of the tibial cut is set to remove 8 to 9 mm of bone from the lateral tibial plateau.
- The lateral tibial cortex is marked to guide the sizing and placement of the tibial template. Any bony overhang medially is removed. This helps relieve tension on the medial soft tissues.
- Ranawat measures the thickness of the patella and does the patella bone cut by hand, making sure not to cut below the subchondral plate of the lateral facet, as this would increase the risk of patella fracture.
- The patella construct is measured and compared with the original measurement. The construct can be up to 2 mm thicker than the original patella; any more than that increases the risk of overstuffing the patellofemoral compartment.
- An intramedullary femoral cutting guide is used. In the varus knee, the guide is set at 5° of valgus, and 8 to 9 mm of bone is removed from the distal femur.
- The extension space of the lateral compartment is then evaluated using a spacer block.
- The medial release is performed in extension with a laminar spreader in place. Using electrocautery, the posterior capsule is cut from the lateral side of the posterior cruciate ligament insertion to the posterior margin of the medial collateral ligament.
Femoral Finishing Bone Cuts
- The femur is sized to avoid notching the anterior femur and to restore the posterior offset of the femur. The femoral rotation is set parallel to the proximal tibial bone cut and 18 mm of femoral bone is resected posteriorly.
- The box cutting guide is applied and lateralized to facilitate patellar tracking.
- The tibial finishing guide is placed so it covers the lateral tibial plateau. Dr. Ranawat does not use the tibial tubercle for the tibial alignment. Instead, the alignment rod should align with the center of the tibia.
Trial Components and Evaluation Soft Tissue Balance
- The trial components are put in place and the knee alignment and balancing are evaluated in flexion and extension. The patella should track properly, and the tension of the medial soft tissues is judged through the range of motion.
- If the medial soft tissues are tight and do not allow for 1 to 2 mm of opening in extension, Dr. Ranawat will perform a “pie crust” release of the anterior fibers of the superficial medial collateral ligament.
- A final check of the tension of the medial soft tissues is done after the final components are cemented in place.
- The femoral canal is plugged with a bone graft and the medial meniscus is removed.
- As part of the perioperative pain management, a local anesthetic “cocktail” is injected into the posterior capsule, the medial and lateral soft tissues, the periosteum around the proximal tibia and femoral condyles, and into the soft tissues around the patella.
Cementing the Components
- After cleaning the bone, cement is applied to the bone and the implant. The tibia is cemented first, then the femur. The knee is then extended to apply pressure to the components and express any excess cement.
- Finally, the patella is cemented.
- Before inserting the tibial polyethylene insert, any excess cement is removed.
- After the tibial insert is in place, the knee is again evaluated for balancing, paying special attention to the tightness of the medial soft tissues.
Click on the image above to watch Dr. Ranawat’s presentation.