Introduction
Tibial posterolateral impression fractures (tPLF) are common concomitant injuries of an anterior cruciate ligament (ACL) rupture resulting in a loss of osseous support of the posterior horn of the lateral meniscus. It is unknown if the additional treatment of the tPLF presenting a 3mm of tibial depression and 50% of support of the external meniscus posterior horn brings a benefit in the treatment of symptomatic ACL-deficient knees.
Aim
The purpose of this biomechanical study was to compare the effect of different reconstruction states in an ACL-deficient knee with tPLF to the native state on kinematics.
Material And Methods
A 6 degrees of freedom robotic system equipped with a force-torque sensor was used to test 8 unpaired knees in the intact, ACL-deficient, ACL-deficient with tPLF, ACLR with tPLF, ACLR with ALT (modified Lemaire) and tPLF, and ACLR with reconstructed tPLF (reposition and internal fixation with 2 screws). Simulated laxity tests were performed at 0°, 30°, 60°, and 90° knee flexion under constant 50 N axial loading: 89N anterior tibial translation (ATT), 8 Nm valgus rotation (VR), 4 Nm internal (IR) and external rotation (ER). The simulated Pivot-shift (PS) test (89N ATT, 8Nm VR and 4Nm IR) was performed at 0°, 15°, 30°, and 45° of flexion. The primary outcome measures of this force-controlled setup were anterior tibial translation (ATT; in mm) and tibial rotation (in degrees). A two-way repeated-measures ANOVA with post hoc Bonferroni corrections for multiple comparisons was performed to evaluate the effect of different states over different angles. The significance level was set to 0.05.
Results
There was no significant difference in any ACLR state compared to the native state for ATT in 0° to 90°. ACLR with reconstructed tPLF compared to native state presented in 60° a significant increase of IR (p<0.05). ACLR with ALT presented a significant reduction of IR in 30° (p<0.001) and 90° (p<0.05) compared to native state. In the simulated PS the ACLR with reconstructed tPLF showed a significant higher ATT compared to native state in 15° to 45° (p<0.05). In comparison, the ACLR with ALT showed no significant differences to the native state in 0° to 45°. ACLR with reconstructed tPLF did not show a significant IR difference to the native state in the PS in 0° and 30°. ACLR with ALT presented a significant reduction of IR in PS compared to the native state in 15° to 45° (p<0.01). The ER was significantly reduced in 0° in the ACLR with ALT compared to native state (p<0.05). No reconstructed state showed a significant VR difference in PS compared to the native state.
Conclusion
ACLR with additional reduction and fixation of the tPLF in ACL-deficient knees with low-grade tPLF provides only incomplete restitution of knee kinematics, especially for anterior translation in the simulated pivot-shift test. ACLR with ALT restores more native anterior translation, including the simulated pivot-shift test. However, it carries the risk of an overall over-constrainment in rotation, especially internal rotation, compared with native knee kinematics.