Augmentation Technique for Anterior Cruciate Ligament Injury

Hiromi Kazusa, MD, Atsuo Nakamae, MD, PhD, Mitsuo Ochi, MD, PhD ^*

Department of Orthopaedic Surgery, Integrated Health Sciences, Institute of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan

E-mail address: ochim@hiroshima-u.ac.jp

Abstract

The augmentation technique for anterior cruciate ligament (ACL) injury has started to receive the attention of orthopedic surgeons because preservation of the ACL remnant may be beneficial in terms of proprioception, biomechanical functions, and vascularization of the graft. This article describes the current indications and surgical techniques of ACL augmentation for patients with continuity of ACL remnant between the tibia and either the femur or posterior cruciate ligament (PCL).

Keywords

• Anterior cruciate ligament (ACL) • Augmentation technique • Partial rupture • Remnant-preserving technique • Double bundle

Key Points

• The anterior cruciate ligament (ACL) augmentation technique has potential advantages in terms of proprioceptive function of the knee, revascularization of the graft, and contribution to knee stability.

• The decision of whether the remaining bundle represents partial rupture or complete rupture of the ACL was made on the basis of physical, magnetic resonance imaging, and arthroscopic findings in a comprehensive manner.

• Single-bundle ACL reconstruction with remnant-preserving technique is performed in cases of partial rupture of the anteromedial (AM) or posterolateral (PL) bundle of the ACL, and double-bundle ACL reconstruction with remnant-preserving technique is done mainly for patients with continuity of the ACL remnant between the tibia and either the femur or posterior cruciate ligament after complete rupture of the ACL.

• The femoral and tibial bone tunnel opening should not be placed at the center of the anatomic attachment of the bundle when using hamstring tendons, because the graft shifts to the anterodistal side in the femoral tunnel opening and to the PL side in the tibial tunnel opening.

• In cases of partial rupture of the AM or PL bundle of the ACL, surgeons should keep in mind that the remaining bundle is not completely intact and it is likely that the biomechanical function of the remaining bundle declines to some extent.

Anterior cruciate ligament (ACL) reconstruction has become a common treatment in orthopedic sports medicine. The normal ACL consists of 2 major functional bundles: the anteromedial (AM) bundle and the posterolateral (PL) bundle. Traditional single-bundle ACL reconstruction has concentrated mainly on the functional restoration of the AM bundle.

Recently, several studies have shown that the central anatomic single-bundle ACL reconstruction can restore normal knee function.¹^–³ With this method, the tibial and femoral tunnels are well placed in the center of their respective ACL footprints. Moreover, interest in double-bundle ACL reconstruction has been growing because of its greater potential to restore knee kinematics.⁴^–⁸ Double-bundle ACL reconstruction can mimic more closely the normal structure of the ACL. Restoration of the biomechanical function is essential in ACL reconstruction. However, biological healing of the graft is vital to the achievement of satisfying clinical results. Accelerated biological healing is necessary not only for early return to sports but also for reliable remodeling of the grafted tendon.

ACL augmentation

Potential Advantages

Arthroscopic examination for ACL reconstruction occasionally demonstrates a relatively thick and abundant ACL remnant. In standard single-bundle or double-bundle ACL reconstruction, the ACL remnant is totally debrided to enable clear visualization of the femoral and tibial bone tunnels. However, recent studies have shown that human ACL remnants contain several types of mechanoreceptors. These mechanoreceptors may provide positive effects on the proprioceptive function of the knee.⁹^–¹² In addition, some studies have shown that the ACL remnants provide some biomechanical stability to the knee.^13,¹⁴ Therefore, ACL reconstruction that preserves the remnant by using the ACL augmentation technique might have several advantages:

1. The ACL remnant may contribute to knee stability and guarantee mechanical strength in the early postoperative period.

2. With respect to the proprioceptive function of the knee, nerve fibers may originate from the preserved ACL remnant and regenerate mechanoreceptors around the augmented graft.

3. The ACL remnant may accelerate cellular proliferation and revascularization of the grafted tendon.

Indications

The ACL remnant often maintains a bridge between the tibia and either the intercondylar notch or posterior cruciate ligament (PCL). Even when the substantial remnant maintains a bridge between the tibia and the intercondylar notch, the femoral attachment of the ACL remnant is often positioned abnormally. These cases represent a complete rupture of the ACL. However, sometimes a partial rupture of the AM or PL bundle of the ACL can be observed. In the authors’ previous studies, the frequency of partial rupture was 10% during 2002 and 2005,¹⁵ and 20% during 2006 and 2008.¹³ In these cases, although rupture of the AM bundle or PL bundle could be seen, the other bundle was well preserved, with an attachment of anatomic femoral origin.

Partial rupture of the AM or PL bundle of the ACL

Previously, the authors performed the ACL augmentation procedure only for cases of partial rupture of the ACL. In these cases, single-bundle reconstruction of the ruptured bundle is desirable to minimize damage to the femoral attachment of the remaining bundle. Therefore, isolated AM bundle or PL bundle rupture is an indication for the single-bundle augmentation technique.

Continuity of the ACL remnant between the tibia and either the femur or PCL after complete rupture of the ACL

In 2008, the authors began performing the ACL augmentation procedure even for patients with continuity of the ACL remnant between the tibia and either the femur or PCL after complete rupture of the ACL. In this complete rupture group, the indication for the procedure comprises cases whose ACL remnant maintains a ligamentous bridge between the tibia and either the intercondylar notch or PCL. Initially, central single-bundle ACL reconstruction with the remnant-preserving technique was performed for patients with a complete rupture. Recently, double-bundle reconstruction with the remnant-preserving technique has been performed to mimic more closely the normal structure of the ACL.

Preoperative and Intraoperative Evaluation

It is sometimes difficult to decide whether the remaining bundle represents a partial or complete rupture of the ACL. The decision was made after thorough consideration of physical, magnetic resonance imaging (MRI), and arthroscopic findings.¹³ Quantitative evaluation of anteroposterior knee laxity can be one indicator for this decision. Partial rupture of the ACL was suspected when the side-to-side difference in the anterior displacement of the tibia was less than about 5 mm and a delayed firm end point was noted. The anterior displacement of the tibia was measured by the KT-2000 knee arthrometer or Kneelax-3 at 30 lb (13.6 kg). MRI also provides important information for evaluation of the femoral attachment of the bundles. However, the final decision was made after arthroscopic confirmation of the status of the injured ACL.

Evaluation by Arthroscopy

Arthroscopic intra-articular inspection was performed through the standard AM portal, anterolateral portal, and the far AM portal. A thorough arthroscopic probing is needed to precisely assess the ACL remnant patterns. Careful probing on the femoral side is important because most ACL ruptures occur in the proximal half. Partial rupture of the ACL was suspected when ligamentous continuous fibers were observed between the tibia and the anatomic femoral insertion of the ACL. Furthermore, arthroscopic examination should be performed in a figure-of-4 position and at various knee-flexion angles to consider the different tension patterns of the 2 bundles.¹⁶^–¹⁹

Classification of the ACL Remnant

The ACL remnant pattern was thoroughly examined to determine the treatment strategy, and was classified (Box 1). Groups 1a and 1b indicate single-bundle reconstruction with the remnant-preserving technique. Groups 1c, 2a, 2b, and 2c indicate double-bundle reconstruction with the remnant-preserving technique. It is important for surgeons to keep in mind that, even in the partial rupture cases, the remaining bundle is invariably not completely intact. It is likely that the biomechanical function of the remaining bundle declines to some extent.

Box 1 Classification of the ACL remnant

Group 1: Partial rupture of the ACL

Group 1a: Partial rupture of the PL bundle

The ligamentous AM bundle of the ACL had an attachment of femoral origin and was well preserved.

Group 1b: Partial rupture of the AM bundle

The ligamentous PL bundle of the ACL had an attachment of femoral origin and was well preserved.

Group 1c: Partial rupture of the ACL but the remaining bundle could not be ascribed to either the AM or PL bundles

Group 2: Complete rupture of the ACL

Group 2a: ACL remnant bridging the PCL and tibia

The normal attachment of the ACL to the intercondylar notch was entirely lost.

Group 2b: ACL remnant bridging the roof of the intercondylar notch and tibia

There were no ligamentous continuous fibers in the normal attachment of the ACL to the femur. Diameter of the remnant was somewhat attenuated.

Group 2c: ACL remnant bridging lateral wall of the intercondylar notch and tibia

Attenuated ACL remnant healed to the lateral wall more arthroscopically anterior than its anatomic origin. There were no ligamentous continuous fibers in the normal attachment of the ACL to the femur.

Group 2d: No substantial ACL remnants bridging the tibia and either the femur or the PCL

Surgical technique

Since 1992, the senior author has performed the ACL augmentation technique when indicated.²⁰ However, the early procedures required 2 incisions at the medial aspect of the proximal tibia and at the lateral femoral condyle, because the grafted tendon was fixed to the femur through the over-the-top route. This early technique had a serious flaw, because it was not a true reconstruction that restored normal ACL anatomy. Therefore, Ochi started to perform the 1-incision technique for ACL augmentation in 1996. Compared with the 2-incision technique, the 1-incision technique is less invasive and enabled reconstruction of the ACL in the anatomic portion. Here the authors introduce the ACL augmentation technique for partial and complete rupture of the ACL.^15,²¹^–²³