Purpose: Patients who sustain non-contact (N-CON) anterior cruciate ligament (ACL) injuries may be predisposed to injury due to deficient biomechanics. In contrast, patients who sustain contact (CON) ACL injuries may be injured due to unlucky trauma rather than poor biomechanics. This study compared biomechanics during change of direction movements between patients with CON vs. N-CON ACL injury mechanisms. We hypothesized that patients with CON ACL injury would have better biomechanics (greater shock absorption and less dynamic limb valgus) than patients with N-CON ACL injury.
Methods: 15 patients age 10-18 years with CON ACL injury (4 female; mean age 15.5, SD 2.1) and 94 with N-CON ACL injury (11 female; mean age 15.6, SD 1.9) underwent motion analysis 6-12 months (mean 7.5, SD 1.3) after ACL reconstruction (ACLR). Subjects performed forward-backwards and lateral change of direction tasks. 3D kinematic and kinetic variables reflecting dynamic limb valgus (frontal and transverse plane) and shock absorption (sagittal plane) were compared between patients who had CON and N-CON injury mechanisms using 2-tailed t-tests.
Results: No significant differences were observed between the CON and N-CON groups (Table).
Conclusion: The CON injury group did not have better biomechanics than the N-CON group. This may be due to both groups engaging in similar rehabilitation programs. Alternatively, the CON injury group may have had similar pre-injury biomechanics to the N-CON group but happened to suffer a contact injury. These results suggest that all patients post-ACLR have potentially modifiable risk factors for re-injury and should have their biomechanics evaluated so any deficiencies can be rectified prior to return to sport regardless of injury mechanism.
Table: Comparison of kinematics and kinetics between contact and non-contact ACL injury groups
| | | | | | |
| Deceleration | Lateral Shuffle |
| Non-Contact | Contact | P-value | Non-Contact | Contact | P-value |
| SHOCK ABSORPTION | | | | | | |
| Max hip flexion | 75.3 (15.2) | 76.9 (16.4) | 0.72 | 68.4 (14.6) | 71.9 (13.6) | 0.39 |
| Max knee flexion | 65.2 (14.1) | 68.8 (20.9) | 0.39 | 61.4 (13.1) | 65.2 (13.5) | 0.31 |
| Max ankle dorsiflexion | -5.5 (7.1) | -2.3 (2.2) | 0.12 | 16.0 (7.5) | 18.2 (8.9) | 0.32 |
| Max hip flexion moment | 2.8 (1.5) | 2.5 (0.9) | 0.58 | 2.07 (0.52) | 2.10 (0.63) | 0.89 |
| Max knee flexion moment | 1.3 (0.5) | 1.2 (0.7) | 0.55 | 1.20 (0.50) | 1.25 (0.45) | 0.72 |
| Max ankle dorsiflexion moment | 0.84 (0.22) | 0.82 (0.29) | 0.80 | 1.07 (0.30) | 1.14 (0.55) | 0.52 |
| Energy absorption at hip | 0.66 (0.43) | 0.56 (0.39) | 0.39 | 0.50 (0.26) | 0.45 (0.25) | 0.50 |
| Energy absorption at knee | 0.50 (0.35) | 0.44 (0.38) | 0.52 | 0.38 (0.26) | 0.38 (0.19) | 0.96 |
| Energy absorption at ankle | 0.17 (0.11) | 0.14 (0.06) | 0.25 | 0.41 (0.19) | 0.42 (0.25) | 0.84 |
| DYNAMIC LIMB VALGUS | | | | | | |
| Max hip internal rotation | 7.8 (7.4) | 5.1 (7.8) | 0.19 | 13.7 (8.8) | 9.3 (7.5) | 0.07 |
| Max hip adduction | 1.9 (6.4) | 2.6 (4.5) | 0.70 | -18.3 (8.3) | -17.2 (7.0) | 0.65 |
| Min knee varus | -1.1 (4.8) | -3.8 (6.6) | 0.05 | -2.4 (5.1) | -3.5 (5.4) | 0.44 |
| Min knee varus moment | -0.34 (0.34) | -0.32 (0.32) | 0.82 | -0.85 (0.69) | -0.81 (0.93) | 0.84 |
External moments are reported. Angles are expressed in degrees, moments in N/kg, energy absorption in J/kg.
