Selected Topics in Athletic Training

Efficacy and Validity of Anterior Cruciate Ligament Reconstruction

Greg Harrison
California University of Pennsylvania

Abstract

Basic Anatomy of the Knee, ACL, and Ligament Structure

ACL reconstruction is one of the most abundant types of surgery performed daily. Currently, an estimated 75,000 to 100,000 ACL reconstructions are performed each year in the United States alone.¹ Essentially, the knee is comprised of three bones that make up two joints. The tibiofemoral joint is the meeting place of two important bones in the leg, the femur and tibia. The patellofemoral joint is where the patella, or kneecap rests on top of the tibiofemoral joint. The tibiofemoral joint is in place by ligamentous structures. All joints in our body are held together by bands or sheets of fibrous connective tissue called ligaments. They are able to provide stability to a joint during rest and movement.

The ACL is one of the major stabilizing intracapsular ligaments in the knee joint. This ligament prevents excessive anterior translation of the tibia on the femur, in addition to playing a secondary role of limiting internal rotation of the tibia. The ACL is housed in the intercondylar notch of the femur. The proximal attachment is the posterior medial surface of the lateral femoral condyle, while it attaches distally to the anterior portion of the intercondylar eminence of the tibia.²

Each anterior cruciate ligament consists of two parts, a distinct anteromedial band (AMB) and a main posterolateral part (PLB).³ As the knee moves from extension into flexion, a juxtaposition of the ACL�s attachment site occurs. When the knee is in full extension the PLB is tight; when the knee is fully flexed the AMB is taut. Only recently, laboratory studies have clearly shown that there is an uneven distribution of forces between the anteriomedial and posterolateral bundles of the ACL in response to externally applied loads to the knee.^4-6 With this evidence, researchers and doctors have sought different ways to improve reconstruction of the ACL.

Types of ACL Grafts

A variety of graft sources, such as autografts, allografts, and synthetic grafts, have been used for ACL reconstruction to improve function and kinematics in ACL deficient knees. Despite the abundance of articles published about ACL reconstruction, there is not a consensus on which procedure or graft source is optimal. Each graft has its advantages and disadvantages. The patellar tendon graft closely resembles the ACL because of its length and has a bony attachment point on both the insertion and origin of the tendon, which can allow for bone-to-bone healing. Extensor mechanism pain, patellofemoral crepitation, and loss of extension have been associated with autologous patellar tendon reconstruction.⁷ The hamstring graft is a less invasive surgery for the patient because there is no removal of a piece of bone, so less pain is experienced by the patient. On the contrary, because there is no bone removal on the graft, the fixation of it in the bone tunnel is a problem. As there is no bone to bone healing, a longer period of time is necessary for the graft to become rigid for most patients. Some physicians are skeptical about the autografts because of strength issues that have been reported. However, Anderson⁷ found that harvesting the semitendinosus and gracilis tendons or the middle third of the patellar tendon does not cause a permanent loss of strength in either the hamstring or quadriceps muscles.

The allograft is the least used graft but is refuted in Cohen�s⁸ published study. The main allure of the allograft is the absence of harvest site morbidity. The disadvantages of the allograft are the risk of disease transmission, a weak graft, a longer time to incorporate into the bone tunnels, the graft is not universally available, and is expensive.⁹ Cohen surveyed a total of 1,038 patients that had received ACL surgery in the last five years to find out why they chose the graft, whether they were satisfied with their graft and outcome, whether they would choose another graft, and if so which one. With a return rate of 208 questionnaires, allografts were used in 63.3 percent of patients and autografts in 35.4 percent. The most common factor influencing graft selection was physician recommendation, which was 74.2%. Of the patients, 93% were satisfied with their graft selection and only 12.7 percent would have chosen another graft if in the same situation again. Of these patients, 63.3 percent would change from an autograft to allograft.⁸ Although autographs have been more popular with physicians, according to Cohen�s⁸ research, there has been an unpleasant result using these types of grafts due to the resent advances in allograft harvesting.

Types of ACL Reconstruction

The �gold standard� for ACL reconstruction has been the single bundle for many years. It was only recently that the single bundle technique has been scrutinized with the astonishingly good result of the double bundle technique. There has not been a consensus on which technique is better. The common goal of each technique is to restore biomechanical function of both anteromedial and posterolateral bundles and to provide proper stability. To date, most ACL reconstructions are performed as single bundle reconstructions, from 50,000 to 100,000 per year, thereby making ACL reconstructions the sixth most common orthopedic procedure performed in the United States.¹⁰ This would also make the single bundle technique the �gold standard� for surgeons. Many clinical outcome studies have demonstrated satisfactory stability of the knee joint after a single bundle anterior cruciate ligament reconstruction. In addition, degenerative joint disease may be associated with traditional single bundle ACL reconstructions in as many as 90 percent of cases seen at seven-year follow ups.¹⁰

The single bundle technique is also successful in limiting anterior tibial translation in response to an anterior tibial load but is reportedly insufficient to control a combined rotary load of internal and valgus torque.^{5, 11} Many clinical outcome analyses have demonstrated satisfactory short-term stability of the knee joint after a single bundle anterior cruciate ligament reconstruction. However, long-term clinical studies have reported a high incidence of osteoarthritis and knee pain in the ACL reconstructed knee.^{5, 11} Although high clinical success rates have been reported in the literature, there are also reports of persistent pain and instability in patient follow-up studies.¹² Several authors have reported that up to 30 percent of patients had a second operation within five years of the original surgery. ^3,12,13 For the average person, this surgical technique has been shown to be efficient over the past several years; however to the physically active, newer surgical techniques may be more promising but at a greater cost.

Surgical ACL reconstruction techniques are evaluated by their ability to restore anterior stability of the knee during anterior drawer tests that detect the amount of forward motion the tibia exhibits at the knee. Recently, the ACL reconstruction has also been evaluated under rotational movements.¹² If the surgeon is able to anatomically restore the ACL, research shows that rotational stability will increase because at different degrees of flexion and extension these two bundles (AMB and PLB) become taut. In response to an anterior tibial load, the magnitude of the in situ force in the anteromedial bundle slightly increased with an increasing flexion angle, whereas the force in the posterolateral bundle was larger at lower extension angles and diminished at higher flexion angles. Thus, replication of both bundles during ACL reconstruction appears to be important.⁵ By definition, the in situ force in a knee ligament is the force carried by the ligament in response to a given load applied to the knee while the knee (and ligament) remains intact. The in situ force within a ligament characterizes the role that the ligament is playing in resisting an external load applied to the intact knee.⁵ Throughout the literature, the double bundle is stated to have better results due to the surgery�s ability to reproduce both bundles giving the knee better rotational stability and anterior stability. This is supported in Yagi�s⁵ study. He aimed to see if an anatomic two-bundle reconstruction restored knee kinematics more closely to normal than single-bundle reconstruction. His end results found the anatomical, a two-bundle reconstruction technique compared closely to that of an intact ACL in anterior translation, in situ force, and combined rotary forces. The single bundle technique was found to be the least effective when comparing the two. Either technique is not capable of restoring the ACL to its original state, but the anatomical technique proves to restore kinematics more closely to normal than does the single bundle reconstruction.

Tunnel Position

The angle at which the tunnel is positioned is crucial because of the forces that the ligament is going to endure. In earlier years of ACL reconstruction, the tunnel position was that of a more vertical graft. This would allow the rotational forces to twist the graft because of the angle at which it was placed. Dr. Emond, a team physician for California University of Pennsylvania as well as an Orthopedic surgeon in Belle Vernon, Pennsylvania, has concluded that by putting the ACL graft vertically, patients were reporting a twist and pivot symptom (personal communication). Surgeons are now starting to put the grafts at about 60� left of the vertical on a left knee and the opposite for a right knee. By doing this, the graft is able to control the pivot a little better.¹³ The surgeons recreated the AM bundle that does not control the pivot forces but rather the anterior posterior forces. So now surgeons are looking at putting the graft for a single bundle technique at more of a �blended� position between the anteromedial and posterolateral anatomic grafts.

Summary

The medical staff, including the athletic trainer, is responsible for providing the best and appropriate care to the athlete. The athletic trainer needs to be able to understand the ACL research and guide the athlete in the right direction. The single bundle technique is successful in limiting anterior tibial translation, but has been reported as insufficient to control a combined rotary load. By replicating both bundles of the ACL, the double bundle technique restores knee kinematics and provides better stability in anterior translation as well as rotary forces. To the average person, the single bundle is sufficient, but to the physically active, young, female athlete, the double bundle might be more suitable.

References