Do We have an Aimer to put the Tibial and Femoral Tunnels in the Same Line to reduce Mechanical Strain in Reconstructed Anterior Cruciate Ligament?

INTRODUCTION

Surgical techniques as well as the use of proper instrumentation augment the long-term results of anterior cruciate ligament (ACL) reconstruction operation. Braiding the strands,¹ saving the ACL remnant,² tibial tunnel independent technique or classical transtibial technique,³ bone tendon or bone tendon bone, single bundle or double bundle or double bundle double tunnel, immobilization period, knee flexion angle during immobilization, early or delayed rehabilitation, and using biological healing promotion are among them.

The native ACL differs from the reconstructed ACL as it has no tunnel and is inserted on the osteochondral tissue of the tibia and femur.⁴

The three-dimensional (3D) orientation of the native ACL is mandatory to perform its function. The reconstructed ACL (ACL graft) is placed in an orientation using tunnels, but still there is no consensus about the technique, which yields anatomic placement. Up to 70 to 80% of failure of ACL reconstruction may involve nonanatomical tunnel placement.⁵

One of the causes would be the postoperative deviation of the femoral and/or tibial insertion of the ACL to one direction (anteriorly, posteriorly, medially, and laterally). As the entry point of tibial and femoral tunnels will be the future insertion of the reconstructed ACL, this deviation will change the 3D orientation of the ACL and affect its physiometry leading to failure of graft tension.

The critical decrease in mechanical properties of the graft was attributed to the properties of the link between the graft at its tunnel entrance site which was found weakest during the early healing stage of the graft and the most affected region of the graft was the tendon–bone interface in intra-articular environment.⁶

Changes of the insertion sites of the graft, outside the tunnel (intra-articular) and inside the tunnel (intraosseous), can be a cause of graft properties alteration because both will dilate as a part of its healing process during the healing period. From the theoretical point of view–the tension between these two parts of the graft is converted into compression force on the osteochondral tissue at the tunnel entrance leading to erosion of the osteochondral tissues at the entry point of the graft; the new insertion will be moved toward the direction of the maximum strain at the tunnel entrance. At the tunnel entrances and during the early healing period, the maximum mechanical strain (tension force) of the graft, at certain knee flexion angle, is received by the osteochondral tissues as a (compression force) on one side of the tunnel entrances according to the direction of the angle between the intra-articular and intraosseous parts of the graft. To avoid this, we have to ensure the straightening of all parts of the graft at knee flexion where maximum strain is expected considering the postoperative individual activities.^7,8

The expected maximum strain (between 10 and 30° of knee flexion) would lead to the erosion of the entry point boundary and deviation of the new insertion of the graft toward the direction of the strain (for the single bundle techniques, the greatest tibial translation is between 20 and 45° of knee flexion). This deviation will modify the ultimate position of the insertion of the new ACL rendering it maloriented and/or loosened. Decrease of the mechanical properties of the graft can be attributed to this deviation (Fig. 1).

Close

Fig. 1:

Angle between the intra and extra part of the graft facing laterally. If deviation occurs in the coronal plan, the new insertion will move more laterally in relation to the primary drilled position and likewise in a sagittal plane where the new insertion will move more posteriorly in relation to the primary drilled position

Export to PPT

Straightening the intraosseous (tibial and femoral) and intra-articular parts of each bundle of the graft eliminates the strain between the graft tissue and the osteochondral tissue at the tunnel entrances.

Though there is no agreement about the exact anatomy of ACL,^9,10 or about the technique of reconstruction,¹¹ the elimination of the angle between the intraosseous and extraosseous parts of the graft at the tunnel entry point in sagittal and coronal planes can be used for all techniques. Factors that affect healing of reconstructed graft of ACL¹² would also have a relation with tunnel widening¹³ and have to be tested.

To create the tunnels to fulfil the above-mentioned conditions, a conception of an aimer can be suggested.

The aimer has four removable sliding guides/sleeves (Fig. 2). Two intra-articular guides/sleeves and two extra-articular for each bone are present. Similar to the conventional aimer positioning technique, first all guides/sleeves are dismounted from the metallic band of the aimer (Fig. 3).

Close

Fig. 2:

Suggested conception of a tunnel aimer that keeps the femoral and tibial tunnel in one axis. All four movable aimers slide on a metallic band to keep all aimers in one line and ensure that the guide wires pass from tibia to femur or from femur to tibia in one line

Export to PPT

Close

Fig. 3:

All guides/sleeves are dismounted from the metallic band of the aimer

Export to PPT

Start by introducing and keeping the first intra-articular guide/sleeve in contact with the footprint of the first bone followed by the second intra-articular guide/sleeve on that of the second bone. Once the appropriate position is selected, the knee flexion angle is maintained while we amount and fix the metallic band on both intra-articular guides/sleeves as well as during extra-articular guides/sleeves mounting for each bone.