Abstract
Proper ligament tension in knee flexion within cruciate-retaining (CR) total knee
arthroplasty has long been associated with clinical success; however, traditional
balancing principles have assumed that the distal femoral joint line (DFJL) affects
only extension. The purpose of this study was to determine the effect DFJL may have
on ligament strains and tibiofemoral kinematics of CR knee designs in flexion. A computational
analysis was performed using a musculoskeletal modeling system for two different knee
implants, the high-flex CR (HFCR) and guided-motion CR (GMCR). Tibiofemoral kinematics
and ligament strain were measured at 90-degree knee flexion while the implants' DFJL
was incrementally shifted proximally. Femoral implant position and kinematics were
used to determine the femur's anteroposterior position relative to the tibia. The
change in the femoral medial condyle position relative to the tibia was 0.33 mm and
0.53 mm more anterior per each 1-mm elevation of the DFJL for HFCR and GMCR, respectively.
The change in the lateral condyle position was 0.20 mm more anterior and 0.06 mm more
posterior for HFCR and GMCR, respectively. The strain in the lateral and medial collateral
ligaments changed minimally with elevation of the DFJL. In both implants, strain increased
in the anterior lateral and posterior medial bundles of the posterior collateral ligament
with elevation of the DFJL, whereas strain decreased in the iliotibial band and iliotibial
patellar band. Our findings suggest that DFJL affects ligament tension at 90-degree
knee flexion and therefore flexion balance for CR implants. Elevating the DFJL to
address tight extension space in a CR knee while flexion space is well balanced could
result in increased flexion tension especially when the flexion–extension mismatch
is large. To achieve balanced flexion and extension, the amount of DFJL elevation
may need to be reduced.
Keywords
total knee arthroplasty - cruciate retaining - distal femoral joint line - kinematics
