Anterior Cruciate Ligament Tear: Rationale and Indications for Anatomic ACL Reconstruction

Abstract

Reconstruction of the anterior cruciate ligament (ACL) is one of the most frequently performed operations in orthopaedic sports medicine [17]. Traditionally, treatment for complete ACL tears has long been a conventional single-bundle (SB) reconstruction [13, 19]. Short-term results for SB reconstructions have been relatively good, with improvement in subjective knee instability and the ability to return to sports [25]. However, in a subset of patients, subjective knee instability persists, and they remain unable to return to prior activity. With SB reconstruction, good to excellent results are only achieved in 60 % of patients and less than 50 % returns to playing sport at their preinjury level [5, 7]. Moreover, long-term results suggest that the rate in which osteoarthritic (OA) changes occur is not reduced by SB reconstruction as compared to nonoperated knees [10, 15, 26]. Multiple studies have shown that the native biomechanical properties of the knee cannot be fully restored by nonanatomic SB reconstruction [8, 40] and that this may be a cause of cartilage thinning [3, 37].

Appendix: ACL Reconstruction: An Individualized Surgery

Case 1

A 22-year-old male, who is 6′ 4″ tall and weighs 345 lb, sustained an injury to the left knee while he was going up for a rebound when playing basketball 1 month ago. He heard a “pop” at the time of injury and had complaints of persistent pain and giving way ever since. Physical examination revealed a grade 1 Lachman test with soft end points and negative pivot-shift test. Measurements with a KT-1000 arthrometer (MEDmetric, San Diego, CA) revealed a side-to-side difference of 2 mm with a 30 lb anterior force and the knee in 30^o of flexion. Subsequent MRI showed a ruptured ACL and bone bruising of the lateral femoral condyle. Measurement of the ACL tibial insertion site on sagittal MRI was 18 mm in length (Fig. 21.20).

Fig. 21.20

Case 1. The length of tibial insertion site is 18 mm on sagittal MRI

Two months after injury, we performed ACL reconstruction surgery. During evaluation under anesthesia, the injured knee showed a grade 2 Lachman test with a soft end point, a grade 1 anterior drawer test and a grade 2 pivot-shift test. Arthroscopic evaluation showed a complete AM and PL bundle tear with proximal attachment and no meniscus tear or chondral lesions. Intraoperative arthroscopic measurements with a ruler revealed a tibial insertion site length of 17 mm and midwidth of 10 mm. The femoral insertion site was 16 mm in length and measured 8 mm at midwidth. The intercondylar notch was 11 mm wide at the base, 10 mm wide at midwidth, 6 mm wide at the apex, and 22 mm high (Fig. 21.21).

Fig. 21.21

Case 1. Intra-articular measurements of the ACL insertion site and intercondylar notch. Shown are the tibial insertion site (a, b), the intercondylar notch (c), and the femoral insertion site (d, e)

Case 2

The second case is a 14 year-old female who sustained a twisting injury of her left knee while playing football in gym class. She is 5′ 6″ tall and weighs 110 lb. The office exam demonstrated an anterior unstable left knee with a grade 2 Lachman test with soft end points, a grade 2 pivot-shift test, and 3 mm of side-to-side difference on KT-1000 arthrometer measurements. The MRI revealed a complete intrasubstance tear without meniscal or chondral pathology. The ACL tibial insertion site on sagittal MRI was 17 mm in length (Fig. 21.22). The physes were nearly closed, as evaluated on MRI and X-rays.

Fig. 21.22

Case 2. The length of tibial insertion site is 17 mm on sagittal MRI

Five weeks after injury, we performed ACL reconstruction surgery. Physical examination findings were consistent under anesthesia as compared to preoperative evaluation at office visit. Arthroscopic evaluation showed a complete AM and PL bundle tear with proximal attachment without chondral, cartilage, or meniscal lesions. Intrao­perative arthroscopic measurements revealed 18 mm tibial insertion site length and 10 mm midwidth. The femoral insertion site was 13 mm in length and 9 mm at midwidth. The intercondylar notch was 17 mm wide at the base, 14 mm wide in the middle, 10 mm wide at the apex, and 21 mm high (Fig. 21.23).

Fig. 21.23

Case 2. Intra-articular measurements of the ACL insertion site and intercondylar notch. Shown are the tibial insertion site (a, b), the intercondylar notch (c), and the femoral insertion site (d, e)

Comments About Cases 1 and 2

The anatomical ACL reconstruction concept is based on the morphological characters of each patient and individualizing each surgical procedure accordingly. If the length of tibial insertion site is less than 14 mm arthroscopically, we consider SB reconstruction. Other relative indications for SB reconstruction are open physes, severe bone bruising, a narrow notch, severe arthritic changes, or multiple ligamentous injuries. If the length of tibial insertion site is more than 18 mm, we consider DB reconstruction to fill the native ACL insertion site with graft sufficiently. For patients with a tibial insertion site between 14 and 18 mm, either SB or DB reconstruction can be performed. In these cases, the eventual decision may be guided by cofactors such as femoral insertion morphology, notch size, or complicating injuries.

In Case 1, the tibial insertion site length was 17 mm, and either SB or DB technique can be employed. However, the width of the intercondylar notch was only 11 mm at the base, making a DB procedure technically complicated with the added risk of damaging cartilage on the medial femoral condyle or potentially penetrating the posterior wall of the lateral femoral condyle. Additionally, it is difficult to create both femoral tunnels anatomically. Specifically, the AM insertion site may be hard to reach with a drill. Drilling transtibially may not reach the native insertion site, while drilling through the AMP, the medial condyle may damage. Therefore, we chose for an anatomic SB reconstruction with a transportal technique (Fig. 21.24a).

Fig. 21.24

Femoral tunnel positioning in Case 1 (a) and Case 2 (b) respectively

For the second case, however, the tibial insertion length was 18 mm – which seemed rather large for her height – and she had a 17 mm wide clearance at the base of the intercondylar notch. For these reasons, she was eligible for an anatomic DB reconstruction (Fig. 21.24b). Because of her small stature, her hamstring tendons did not provide enough graft to construct two bundles. Therefore, we used an (peroneus longus tendon) allograft for PL bundle and the harvested hamstring autograft for the AM bundle. In this case, the sizable insertion site and notch allowed for a DB reconstruction. Moreover, a SB procedure would have not reconstructed the same percentage of native ACL insertion site (also due to the small graft).

These cases clearly illustrate that body habitus is not always correlated to actual knee anatomy and that objective measurements may greatly vary between individuals.

1.1 Conclusion

Anatomic ACL reconstruction is the functional restoration of the ACL to its native dimensions, collagen orientation, and insertion sites, and one of the goals of surgery is to restore the native insertion as completely as possible. In order to achieve this goal, surgeons should strive toward individualizing each surgery with respect to the patient’s anatomy. Preceding cases hopefully provide some insight in the considerations a surgeon should make before deciding on the actual procedure. All patients are different and so are their treatment options. For patients with tibial insertion sites between 14 and 18 mm, it can be particularly difficult to decide on the best treatment. Systematically reviewing the possibilities and boundaries in these cases should provide some guidance in the decision-making process.