This biomechanical study examined the ability of isolated and combined ACL reconstruction and/or lateral monoloop tenodesis to restore intact knee stability in the presence of injuries to the ACL, anterolateral ligament and ITB.
An anterior cruciate ligament (ACL) injury is often combined with injury to the lateral extra-articular structures, which may cause a combined anterior and rotational laxity.
This controlled laboratory study examined the influence on knee laxity after sequentially sectioning the ACL and lateral extra-articular structures. The effects on the laxity of an ACL reconstruction alone, in combination with a lateral monoloop tenodesis, and an isolated monoloop tenodesis without ACL reconstruction were then measured.
Twelve cadaveric left knees were tested in a 6 degrees of freedom rig using an optical tracking system to record the kinematics through 0° to 100° of knee flexion with no load, anterior drawer, posterior drawer, external rotation, internal rotation and combined anterior drawer and internal rotation.
The knees were sequentially tested with an intact ACL, after sectioning ACL, sectioning anterolateral ligament (ALL), taking an iliotibial band (ITB) midportion strip, releasing the deep fibers of the ITB, reconstruction of ACL with hamstrings tendon grafts, lateral monoloop tenodesis combined with an ACL reconstruction, and an isolated lateral monoloop tenodesis without ACL reconstruction. Two-way repeated-measures analyses of variance were used to compare the laxity data across knee states and flexion angles. When differences were found between knee states, paired t tests with Bonferroni correction were performed.
Cutting the ALL significantly increased the anterior laxity only at 20-30° compared to an ACL-deficient knee (p<0.05), and only significantly increased internal rotational laxity at 50° of flexion (p<0.05).
Additional release of the deep ITB significantly increased the anterior laxity at 40-90° (p<0.05) and had a large effect on internal rotational laxity at 20-100° (p<0.01).
After isolated ACL reconstruction, there were no significant differences in anterior drawer compared to the intact knee, however significant differences remained in internal rotation at 30-100° (p<0.01). Also for combined anterior drawer and internal torque significant differences remained, compared to the intact knee in anterior drawer (30-100°) and internal rotation (20-100°) (p<0.05).
Adding a lateral monoloop tenodesis gave a significant decrease in rotational laxity compared to isolated ACL reconstruction at 20-100° (p<0.01). There were no remaining significant differences with either anterior drawer or internal torque compared to the intact knee.
In the presence of the combined injury, isolated lateral monoloop tenodesis allowed abnormal anterior translation to persist across 0 – 100° flexion, and abnormal internal rotation across 30-100°.
This study found that cutting the deep fibers of the ITB caused large increases in tibial internal rotation laxity across the range of knee flexion, while cutting the ALL did not. In case of an ACL deficiency combined with increased rotational laxity caused by cutting both the ALL and deep fibres of the ITB, an ACL reconstruction alone was insufficient to restore normal knee laxity. However, adding a lateral extra-articular ITB ‘monoloop’ tenodesis procedure restored the normal knee laxity.