ARE THERE FUNCTIONAL BENEFITS TO KEEPING BOTH CRUCIATE LIGAMENTS IN TOTAL KNEE REPLACEMENT? A COMPARATIVE GAIT STUDY

Introduction Preservation of the anterior cruciate ligament (ACL), along with the posterior cruciate ligament, is believed to improve functional outcomes in total knee replacement (TKR). The purpose of this study was to examine gait differences and muscle activation levels between ACL sacrificing (ACL-S) and bicruciate retaining (BCR) TKR subjects during level walking, downhill walking, and stair climbing. Methods Ten ACL-S (Vanguard CR) (69±8 yrs, 28.7±4.7 kg/m2) and eleven BCR (Vanguard XP, Zimmer-Biomet) (63±11 yrs, 31.0±7.6 kg/m2) subjects participated in this IRB approved study. Except for the condition of the ACL, both TKR designs were similar. Subjects were tested 8–14 months post-op in a motion analysis lab using a point cluster marker set and surface electrodes applied to the Vastus Medialis Oblique (VMO), Rectus Femoris (RF), Biceps Femoris (BF) and Semitendinosus (ST). 3D motion and force data and electromyography (EMG) data were collected simultaneously. Subjects were instructed to walk at a comfortable walking speed across a walkway, down a 12.5% downhill slope, and up a staircase. Five trials per activity were collected. Knee kinematics and kinetics were analyzed using BioMove (Stanford, Stanford, CA). The EMG dataset underwent full-wave rectification and was smoothed using a 300ms RMS window. Gait cycle was time normalized to 100%; relative voluntary contraction (RVC) was calculated by dividing the average activation during downhill walking by the maximum EMG value during level walking and multiplying by 100%. Results There were no significant kinematic or kinetic differences between implant groups for level walking (p≥0.19). Both groups walked at 1.1 m/s on average during level and approximately 0.1 m/s slower during downhill walking, with no differences in speed (p= 0.91 and 0.77, respectively). For both ACL-S and BCR groups, gait changes from level to downhill walking were similar. For downhill walking, ACL-S subjects were significantly more variable (p<0.001) over the gait cycle for all measured kinematics and kinetics. During both downhill walking and stair climbing, the ACL-S group showed an external peak abduction moment (Fig. 1) significantly greater than that of the BCR group (p=0.05, 0.01). Also during stair climbing, ACL-S subjects showed trending higher peak knee adduction moments (p=0.14) and a more pronounced internal/external rotation pattern (Fig. 2) than BCR subjects. Since no peak kinematic/kinetic differences between groups during level walking exist, the mean maximum muscle activation from level walking was used for RVC normalization for other activities. On average, BCR subjects had lower maximum RVCs during downhill walking than the ACL-S subjects. Effect sizes were large for RF (d=0.94), ST (d=0.88), and VMO (d=1.21), the latter being borderline significant (p=0.05). Discussion Previous studies on the natural knee have established that the ACL contains mechanoreceptors that improve stability of the knee joint. In this study, BCR subjects show less variable gait measures than subjects with traditional posterior cruciate retaining (ACL-S) TKR, possibly indicating more controlled contact kinematics. In addition, EMG results suggest lower muscle co-contraction during downhill walking, also implying greater knee stability in the BCR group. These results are preliminary and more subjects are needed for definite conclusions.