Quadriceps strength and psychological readiness are associated with multiplanar knee kinematics after anterior cruciate ligament reconstruction

Background: Gait asymmetry, negative psychological factors and quadriceps strength deficits are common after anterior cruciate ligament reconstruction (ACLR). Whether quadriceps strength and psychological factors have impacts on multiplanar knee kinematics remains unclear.Research question: What are the relationships of multiplanar knee kinematics during the gait cycle and psychological readiness to quadriceps strength after ACLR?Method: In total, 45 patients were enrolled in this study at 8.3 +/- 1.5 months after ACLR. All patients underwent gait analysis and isokinetic testing. Interlimb differences in the range of motion (ROM) and maximum and initial contact (IC) angles in abduction-adduction, flexion-extension, and internal-external rotation were calculated. The limb symmetry index (LSI) for quadriceps strength was calculated. Psychological readiness was measured using the Anterior Cruciate Ligament Return to Sport After Injury (ACL-RSI) scale. The paired t test analyzed the differences between contralateral and affected limbs in quadriceps and hamstrings strength. Pearson or Spearman correlation was used to assess relationships between the variables of interest.Results: Significant differences between contralateral and affected limbs were observed in isokinetic knee quadriceps strength (P < 0.001) and hamstring strength (P = 0.009). The ACL-RSI score correlated negatively with interlimb differences in the knee flexion angle at IC (r = -0.35, P = 0.02) and ROM in the transverse plane (r = -0.41, P = 0.003). The LSI for quadriceps strength correlated negatively with the peak knee flexion angle (r = -0.37, P = 0.02) and positively with the ACL-RSI score (r = 0.3, P = 0.05).Significance: Greater psychological readiness and quadriceps strength are associated with more symmetrical multiplanar knee kinematics. The improvement of these parameters may aid the recovery of knee kinematics after ACLR, and reduce the rate of reinjury and incidence of posttraumatic osteoarthritis.