gms | German Medical Science

Objective: One of the most important ligaments for providing knee joint stability is the anterior cruciate ligament (ACL). Although providing the primary restraint to anterior translation of the tibia relative to the femur, the ACL also restrains internal tibial rotation, which makes restoration of rotational stability an important goal of ACL reconstruction. We hypothesize that internal rotation, an indicator for joint stability, varies with knee flexion and is altered with regeneration. This study aimed to elucidate the influence of ACL reconstruction on passive rotational stability.

Method: A novel device was developed to achieve an accurate and objective measure of knee-joint rotational stability. The patient foot is fixed to a rotating plate and a 6 DoF force transducer. An axial torque of 2.5 Nm is manually applied to the knee while synchronised fluoroscopic images of the tibia and femur are acquired. 3D surfaces of femur and tibia are then registered to the fluoroscopic images to allow skeletal tibiofemoral axial rotation to be calculated. The injured and healthy contralateral limbs of 13 patients with confirmed ACL injury were measured preoperatively as well as after 3 and 12 months follow-up.

Results and conclusion: Significant differences were found between the injured and the healthy contralateral knees at both flexion angles (Fig 1). At 3 months after reconstruction, a reduction of the internal rotation was seen, although this remained significantly different to the healthy knees at 30° knee flexion. However, after 12 months, a full restoration of the stability was observed for the reconstructed knees compared to the healthy contralaterals.

Although a reduction of the internal rotation was observed after 3 months, the significant difference observed at 30° suggests lack of stability, possibly due to reduced mechanical properties or fixation stability of the graft tissue. It is known that a time window of 6 months is needed to ensure biological remodelling of the reconstructed ACL [1]. After 12 months, this process appears to be completed with improved rotational stability at both flexion angles. Further investigation should focus on parameters that influence the rotational stability and thus alter the risk for ACL re-rupture, especially in patients with concomitant injuries to other passive structures, particularly the collateral ligaments.