Esteemed Professors, Dear Friends, Dear Guests, Today, I am going to talk about “Gap Balancing Method in Total Knee Prosthesis Surgeries.”
With this procedure, our goal is to create a functional knee joint by achieving a symmetrical and balanced flexion-extension range, as well as a proper femoral-tibial component rotation.
Why Gap Balancing Method?
It provides a better stability in the coronal plane. It can be re-applied. It relies on fewer bone markers. With measured cutting method, it is not always possible to achieve a rectangular and balanced flexion gap.
Characteristics of the Gap Balancing Method
Ligament relaxation cut should be done before the femoral rotation bone cuts.
Fixed deformity and extremity axis should be made available before identifying the femoral component rotation.
With this method, it is possible to achieve a functional total knee prosthesis with a better gap balance.
The femoral component rotation is adjusted according to the proximal tibia cut in the vertical direction to the mechanical axis (together with the proper extension balance).
Why Femoral Component Rotation Is Important?
Patella femoral instability
Anterior knee pain
Arthrofibrosis
Flexion gap instability occurs.
Anormal walking pattern
Abrasion and laxation
Pre-Extension “Gap Balancing” Method
This method provides a healthier, repeatable gap balance with a better soft tissue relaxation.
Proximal tibia should be cut 90 degrees.
Distal femur should be cut.
All osteophytes are removed. Extension gap is reviewed. In case of any tension, it should be loosened until balance is achieved.
The same looseness should be achieved on 90 degrees knee flexion.
If the tibial cut is accurate and the gap balance in the extension is good, a rectangular gap will be achieved in the flexion.
Bone Cut: In case of any error in the tibial cut, the femoral rotation will be affected. The bone cuts should be as the length as the implant thickness. Excessive or short cuts create an unconformity in the flexion and extension gaps. If the femoral component is placed in the parallel direction, the varus tibial cut should be inside the rotation. Otherwise, the varus tibial cut should be outside the rotation.
Soft Tissue: In case of any error in the soft tissue balance, the femoral rotation will be affected. That the collaterals are intact and have a good balance is an important component of this method. In case of an YMKL insufficiency, excessive medial flexion gap will occur. It will push the femoral component towards the inside rotation. In case of an LKL-Poplietus complex insufficiency, excessive lateral flexion gap will occur. It will push the femoral component towards the outside rotation. Tibia cut: Tibia should be cut 8-10 millimeters deep, 90 degrees towards the anatomical axis. In case of a YD extension apparent on the
lateral plane, the bone cut should be small (6-8 millimeters on the lateral plane).
Ideal Tibial Size and Rotation: The size should depend on the lateral plane, while the rotation should depend on the medial tibial plane.
Distal Femoral Cut: Protecting the joint line is crucial. The entrance of the femoral (TF and PF joints’ connection line) should not encounter any carving mark. The valgus is cut 5 degrees per the femur anatomical axis. Lateral condyle should be cut 8-10 millimeters. The extra distal cut should not be greater than 1-2 millimeters. The YD on the medial contractile should be loosened. After performing deep MCL on the varus knee, posteriomedial capsule should be reviewed. Thereafter, you may proceed with the surface MCL, pes anserinus and semimembranous tendon.
Flexion Gap and Femoral Rotation: Flexion gap stabilization should be achieved with the bone cuts done for the femoral rotation (i.e. posterior condyle). Thus, a balanced flexion gap is created. This is the most important part of the operation. Because other markers are unavailable. Lateralization: Lateralization is crucial. When we bring the knee to 90 degrees flexion as defined by Ranawat (to reduce Q degree) we must see
the parallel structure as it stands on its own weight. The ideal Patello-Femoral movement minimizes need for lateral loosening. Therefore, the reasons above increases the significance of the lateralization.
Conclusion
Since gap balancing method is less dependant on the bone anatomy, it offers a better flexion gap stability.
The condition of component loosening caused by the undesirable results of anormal kinematics, instability, loss of movement, accelerated component abrasion, or uneven load distribution between the components, thus, become preventable. 17-62% precision rate with 6 degrees of outside rotation – 11 degrees of inside rotation (17 degrees of fallacy) (measured cutting method).
Extension/Flexion gap should be balanced, and the joint line should be protected.
Sufficient proximal tibial cut (8-10 millimeters)
Distal femoral cut (8-10 millimeters)
Pre-extension gap balancing (2-4 millimeters of laxity) (rectangular balanced gap) For flexion; in parallel direction of the tibia cut surface (rectangular balanced gap).