Asymmetry in Limb Stiffness, Joint Power, and Joint Work During Landing in Anterior Cruciate Ligament Reconstruction Patients

Abstract

Background: Kinetic and kinematic side-to-side limb asymmetries can increase after anterior cruciate ligament reconstruction (ACLR). Limb stiffness asymmetry has not been previously explored.

Hypothesis: Athletes with ACLR will exhibit greater asymmetry in limb stiffness, peak eccentric joint power, and eccentric joint work compared with asymptomatic controls during landing.

Study design: Case-control study.

Level of evidence: Level 4.

Methods: Forty athletes with 5.9 ± 1.4 months removed from ACLR and 40 asymptomatic athletes completed 7 stop-jumps (SJs) during a single session. Three-dimensional motion capture and ground-reaction force data were collected during landing. Normalized symmetry index values for limb stiffness, peak eccentric joint power, and eccentric joint work of athletes with bone-patellar tendon-bone (BPTB) grafts, athletes with hamstring grafts, and control athletes were compared.

Results: Athletes with ACLR had greater knee power Athletes with ACLR had greater knee power (BPTB, 29.1 ± 17.6; hamstring, 27.3 ± 14.1; Control, 14.2 ± 10.7; P < 0.01) and knee work (BPTB, 35.2 ± 21.5; hamstring, 32.1 ± 18.4; Control, 14.9 ± 10.1; P < 0.01) asymmetries than control athletes. Athletes with BPTB grafts and hamstring grafts both displayed larger knee power and work asymmetries compared with control athletes (P < 0.01 for each comparison), with no differences between graft types (P = 0.90 and P = 0.80, respectively). No between-group differences were found in limb stiffness (BPTB, 16.2 ± 10.8; hamstring, 13.5 ± 9.83; Control, 13.9 ± 9.33; P = 0.63), ankle power (BPTB, 16.5 ± 11.4; hamstring, 14.4 ± 13.0; Control, 18.3 ± 14.0; P = 0.55), ankle work (BPTB, 20.9 ± 13.0; hamstring, 17.4 ± 14.9; Control, 18.4 ± 12.8; P = 0.69), hip power (BPTB, 17.6 ± 12.8; hamstring, 19.5 ± 11.3; Control, 13.3 ± 9.08; P = 0.09), or hip work (BPTB, 17.2 ± 13.9; hamstring, 24.6 ± 14.1; Control, 16.2 ± 11.7; P = 0.06) asymmetries.

Conclusion: Athletes with ACLR use asymmetric landing strategies that favor their nonsurgical limb, resulting in greater knee power and knee work asymmetries compared with controls. No between-group asymmetry differences in limb stiffness, ankle power and work, and hip power and work were found.

Clinical relevance: After 5.9 ± 1.4 months removed from ACLR surgery, athletes favor their nonsurgical limb at the knee, risking further injury. While limb stiffness asymmetry was not different between groups, the groups appeared to modulate limb stiffness differently between limbs to produce similar asymmetry values.

Keywords: ACL; asymmetry; biomechanics; injury prevention; landing; motion analysis; stiffness.

Figure 1.

Modified Helen-Hayes marker set.

Figure 2.

Representative vertical GRF trace during an SJ landing, showing the impact (1) and active (2) vertical force peaks. GRF, ground-reaction force; SJ, stop-jump.

Figure 3.

Three-dimensional renderings of the lower extremities during another SJ landing at the time of peak GRFs in Visual 3D (top-left and top-right), and the GRF-time curves of the right leg produced during this landing. Arrows indicate the GRF vector of the right leg at the 2 different timepoints. Resultant GRF is the magnitude of the GRF vector. Posterior GRF occurs when the direction of the force is opposite to the direction of movement in the anterior-posterior plane. GRFs were normalized to BW (%BW). BW, bodyweight; GRF, ground-reaction force; SJ, stop-jump.

Figure 4.

Internal knee and hip joint moments in the sagittal plane during the landing portrayed in Figure 3. Internal extension moments are positive and flexion moments are negative.

Figure 5.

ACLR and control group average NSI values (%) for limb stiffness, joint powers, and joint works. ACLR, anterior cruciate ligament reconstruction; NSI, normalized symmetry index.

Figure 6.

Limb stiffness (%BW/m) for each limb of the entire ACLR group and the control group, respectively. ACLR, anterior cruciate ligament reconstruction; BW, bodyweight.

Figure 7.

Peak eccentric ankle, knee, and hip joint power (J/[N×s]) for each limb of the entire ACLR group and the control group, respectively. A bar column was included for each limb to display the degree and direction of asymmetry for power at each joint, however, only NSI values were included in the statistical analysis. ACLR, anterior cruciate ligament reconstruction; NSI, normalized symmetry index.

Figure 8.

Eccentric ankle, knee, and hip joint work (Nm) for each limb of the entire ACLR group and the control group, respectively. A bar column was included for each limb to display the degree and direction of asymmetry for work at each joint; however, only NSI values were included in the statistical analysis. ACLR, anterior cruciate ligament reconstruction; NSI, normalized symmetry index.