Abstract
Introduction:
It is generally accepted that ACL instability is a rotational instability, and that ACL injuries result from twisting injuries. The evidence that led to the introduction of double bundle reconstruction, and now wide-spread use of Lateral Extra-Articular Tenodesis (LEAT), to control the supposed rotatory component of ACL laxity is critically reviewed.
Results:
Multiple biomechanical studies trying to quantify the rotational component of ACL laxity/instability are invalid due to constraint of the axis of rotation and/or uncoupling rotation and anterior translation.
The evidence indicates that the centre of rotation of the tibia in ACL laxity and instability is a long way medial to the knee itself. The rotational component of ACL laxity is minor and due to differential medial vs lateral anterior shift, rather than rotation about a pivot point within or even close to the knee.
A review of the literature reveals that the apparent evidence that prompted double bundle reconstructions and now LEAT procedures is based on comparisons with poorly performing ACL reconstruction techniques that fail to control AP laxity (Fu) and/or have poor clinical outcomes (Getgood). If the graft is too vertical it cannot fully control the abnormal AP laxity, which cannot be uncoupled from the rotational component.
It is possible to reconstruct the ACL with a single bundle graft and achieve full restoration of both AP laxity and rotational laxity (Markolf).
Discussion.
Considerable effort has been made to maximize rotational stability when undertaking ACL reconstructions. This was the supposed rationale for double bundle reconstructions, but experience has shown that the outcomes were inadequate, and the procedure has fallen into disrepute. We are now in the midst of a drive to improve outcomes by adding a Lateral Extra-Articular Tenodesis. This is argued to control rotation better than reconstruction of the ACL alone, but the evidence is lacking, and there is a price to be paid in terms of greater morbidity and dissatisfaction. Where should the tunnels be located to maximize restoration of stability with a single bundle reconstruction? The biomechanics and the clinical experience show that the aim should be to reconstruct the antero-medial bundle, not a so-called “anatomic” reconstruction based on the centers of the entire footprints of the native ACL. The graft effectively attaches to bone at the leading edge of each tunnel aperture, so the centre of each tunnel needs to be somewhat offset from the desired attachment site.
Conclusion:
First the nomenclature, then studies on single bundle reconstructions that failed to adequately control AP laxity, and others on biomechanics that were invalid due to constraint of the axis of rotation, have resulted in inappropriate emphasis on additional procedures to control tibial rotation.