Tunnel Convergence Rate in Combined Anteromedial Portal Anterior Cruciate Ligament and Anterolateral Structure Reconstructions Is Influenced by Anterior Cruciate Ligament Knee Flexion Angle, Tunnel Position, and Direction

Purpose

The goal of the present study was to evaluate a potential tunnel convergence in combined anterior cruciate ligament (ACL) reconstruction using the anteromedial portal technique and lateral extra-articular tenodesis (LET).

Methods

Ten fresh frozen femora were dissected and a K-wires were inserted into the middle of the ACL stump, according to an ACL reconstruction at 110° and 140° knee flexion. ACL reconstruction at 120° and 130° was simulated. Seven K-wires with different femoral insertion sites and angulations were drilled into the lateral femoral condyle relative to the lateral epicondyle (E3: 8 mm proximal and 4 mm posterior; E1: 5 mm proximal and 5 mm anterior and E2: over-the-top position). Tunnel conflict rate was evaluated using a measuring arm and a metrology software.

Results

Drilling the femoral ACL tunnel in low knee flexion (110°-120°) significantly (P < .001) reduced the tunnel conflict rate compared to the ACL drilled in high knee flexion (130°-140°). Changing the insertion point from proximal and posterior (E3) to proximal and anterior (E1) showed a reduced tunnel conflict rate from 40 ± 21.2% to 15 ± 26% and no tunnel conflict for an ACL drilled at 110°-130° knee flexion.

Conclusion

A possible tunnel conflict in simultaneous ACL reconstruction using the AMP technique and LET was dependent on ACL knee flexion angle, LET insertion site, and angulation. This posed the dilemma that no generally applicable LET configuration could be recommended to avoid a tunnel conflict. However, it appears that an insertion point located proximal and anterior to the lateral epicondyle results in less tunnel conflicts than an insertion point located proximal and posterior.

Clinical Relevance

An insertion point located proximal and anterior to the lateral epicondyle with a 30° proximal and 30° anterior angulation could reliably avoid a tunnel conflict when the ACL was drilled between 110 and 130° using a low anteromedial portal.

Introduction

Long-term failure rate for anterior cruciate ligament (ACL) reconstruction vary between 0-13%¹ with higher risks for the young population and patients returning to strenuous sports.2, 3, 4 Adequate trauma, surgical error, failure of graft incorporation, and missed posteromedial and posterolateral peripheral injuries are reasons for graft rerupture and unsatisfying outcome.^5,6 It was demonstrated that tunnel malpositioning was the most common technical failure, whereas peripheral injuries only accounted for a small amount of revisions (3%).² However, recent studies increasingly focus on acute and chronic concomitant peripheral injuries.

In the ACL reconstructed knee, unaddressed peripheral lesions may lead to persistent rotatory instabilities^7,8 and abnormal knee kinematics, induce higher graft forces,9, 10, 11 and may, therefore, increase the risk of graft rupture.12, 13, 14 Even though the link between graft rupture and missed anterolateral rotatory instability (ALRI) has not been shown yet, adding a lateral extra-articular tenodesis (LET) to the ACL reconstruction, displayed a much lower revision rate.^15,16 Thus, it seems logical to perform an additional LET in knees presenting ALRI. The biomechanical principle behind this is, routing a strip of the iliotibial tract (ITT) deep into the lateral collateral ligament (LCL) and tethering it to the metaphyseal region of the lateral femur (proximal and posterior to the lateral femoral epicondyle), in order to restrain anterior subluxation of the lateral tibial plateau.

One of these techniques was introduced by Marcel Lemaire,17, 18, 19 who passed the graft through an osseous tunnel under the femoral gastrocnemius attachment. Newer variations of this technique use an interference screw fixation proximal and posterior to the lateral femoral epicondyle.²⁰ However, this is susceptible to a tunnel conflict with the femoral ACL tunnel21, 22, 23, 24 in the anteromedial portal (AMP) technique and may, therefore, result in an early graft failure, especially when using a femoral suspensory fixation with an endobutton. One possibility to avoid this tunnel convergence may be changing the femoral LET insertion point to proximal and anterior to the lateral femoral epicondyle.²⁵ This alternative insertion point may result into similar LET behavior and length change pattern, because of the pulley effect of the lateral epicondyle,²⁶ as long as the strip of the ITT is guided deep into the LCL and inserted proximal to the lateral femoral epicondyle. This has been clinically done in order to avoid a tunnel conflict.²⁵ However, this anterior insertion point has not been evaluated biomechanically yet.

Other possibilities include changing the knee flexion angle, when drilling the ACL, or changing the LET drill angulation. Recent biomechanical studies showed a high tunnel conflict rate at 125° knee flexion,^21,22 but other flexion angles have not been tested yet. The goal of the present study was to evaluate a potential tunnel convergence in combined ACL reconstruction using the AMP technique and LET. It was hypothesized that the tunnel conflict rate is dependent on the knee flexion angle when drilling the ACL. Furthermore, it was hypothesized that an anterior insertion point²⁵ (5 mm proximal and 5 mm anterior instead of 8 mm proximal and 4 mm posterior), a 30° anterior and 30° proximal angulation,²¹ and large knee size will reduce the tunnel conflict rate.