33
Gap Balancing
The goal of this stage is to have balanced
extension and flexion gaps, with no overlap
in either condyle, (i.e, medial or lateral). The
extension gap will likely look unbalanced when
comparing the medial and lateral space if no
ligament release has been performed for a
deformed knee. The surgeon may choose to
perform ACL release for CR procedure, or ACL
and PCL release for a BCS procedure, and
collateral ligament release to re-collect laxity
information by clicking on the Re-collect Joint
Laxity button, to depict what the joint space will
actually look like in extension. If the surgeon
chooses to perform ligament release after bone
preparation, then the focus should be on the
gap of the looser condyle in extension, as post
implant placement, ligament release would open
up the tighter compartment.
Manipulate the position and orientation of the
implant components in extension such that
the resulting gap on the left (extension - stress
graph) is approximately 2-3 mm above the zero
line (2-3 mm laxity under stress, in the looser
compartment). On the right flexion gap graph
(at 90
º
), the resulting gap should be slightly
increased, and balanced in the medial and
lateral compartment. Balancing the flexion gap
in the medial and lateral compartments can be
performed by rotating the femur component
internally or externally.
Adjustments to femoral component rotation
should be carefully considered relative to prior
parameters such as fit to the bone and anterior
notching.
Confirm that the implant resection is appropriate
for the femur and tibia in extension as well as
flexion. Use the Rotate View button (Button A in
Figure 50) to confirm the anterior transition of the
femur implant to avoid notching and confirm tibia
slope for gap balancing.
Adjustments to femoral flexion should be
carefully considered against prior considerations
regarding anterior fit and alignment to the IM
axis.
Figure 50.
To balance gaps in only extension, manipulate the
superior-inferior positioning of the femur component. To bal-
ance gaps in both flexion and extension, manipulate the tibia
resection level or adjust insert size.
Figure 51.
The final gap graph should reflect an appropriate level of
laxity in the joint, in a tensioned state.
7
Implant Planning - Soft Tissue Balancing
