© Springer International Publishing Switzerland 2016Piero Volpi (ed.)Arthroscopy and Sport Injuries10.1007/978-3-319-14815-1_41
41. Anterior Cruciate Ligament
Department of sports science and health, Università degli Studi di Roma “Foro Italico”, Piazza L. De Bosis 15, Rome, 00194, Italy
Villa Stuart Sport Clinic, FIFA Medical Center, Via Trionfale 5952, Rome, 00136, Italy
Pier Paolo Mariani (Corresponding author)
KeywordsACLACL reconstructionKneeReturn to playRehabilitation after ACLrSports injuries
The anterior cruciate ligament (ACL) is one of the most commonly disrupted ligaments in the knee of athletes. Most of the injuries happen in a noncontact trauma, when an athlete self-generates great forces or moments at the knee, that applied excessive loading on the ACL. Numerous theories have been proposed to explain what predisposes an athlete to noncontact ACL injury. These theories are classified as anatomic, environmental, hormonal, and neuromuscular . Anatomic factors include an A-shaped intercondylar notch instead of a reverse U-shaped notch that determines impingement of the ACL on the medial border of the lateral femoral condyle in valgus stress and on the roof of the notch in hyperextension. Varus or valgus lower limb alignment adds stress on ACL during sports activities. Muscular discrepancy between extensor and flexor of the knee and knee joint congenital laxity also predispose to ACL rupture. Environmental factors include shoe-surface interface that increases frictional force between foot and ground creating higher-energy forces in the knee during decelerations or in cutting actions. Weather conditions (too hot or cold or raining) may represent another factor of risk. Playing style has a genetic component, but it is influenced by coaching and training and represents a factor of risk. Hormonal factors: women sustain two to eight times more ACL injuries for the same sports than men do. Many studies have tried to demonstrate influence of estrogen, but females’ differences from males in lower limbs alignment, muscle power, and neuromuscular factors interfere with this theory. Neuromuscular factors: the balance between quadriceps and hamstring muscles is crucial to functional knee stability as quadriceps antagonists and hamstring agonists of ACL. Any weakness, increased flexibility, or delayed recruit pattern of hamstrings increases susceptibility to ACL injury.
41.2 Injury Mechanism
ACL rupture may happen for a contact or a noncontact injury. In a contact injury, a direct blow is applied directly on the knee from an opponent player, and it is typical of contact sports such as soccer, rugby, basketball, and American football. In a noncontact ACL injury, the more frequent mechanism, athlete self-generates great forces or moments at the knee that applied excessive loading on the ACL during cutting, decelerations, and landing from a jump. Injury mechanisms are mostly three: valgus-external rotation (VRE), varus-internal rotation (VRI), and hyperextension and tend to occur when the center of gravity of the body is behind the knee and when ground contact with the entire foot occurs . In a report of literature from 1950 through 2007, Shimokochi and Shultz demonstrated noncontact ACL injuries are likely to happen during deceleration and acceleration motions with excessive quadriceps contraction and reduced hamstrings co-contraction at or near full knee extension . Higher ACL loading during the application of a quadriceps force when combined with a knee internal rotation moment compared with an external rotation moment was noted. The ACL loading was also higher when a valgus load was combined with internal rotation as compared with external rotation. However, because the combination of knee valgus and external rotation motions may lead to ACL impingement, these combined motions cannot be excluded from the noncontact ACL injury mechanisms. Further, excessive valgus knee loads applied during weight bearing, decelerating activities also increased ACL loading. Kobayashi et al. analyzed the data of more than 1,700 athletes (838 males and 880 females) with an ACL injury with the aim of confirming the relationship between the ACL injury occurrence and the dynamic alignment of the lower extremity at the time of the injury. The authors referred that at the time of the injury, the number of subjects who had the injury during “competitions” rather than training was the largest (846/1718), accounting for 49.2 % of all the subjects. Noncontact cases were the largest (417/809) than the number of collision cases. The number of the subjects with the alignment of “Knee-in and Toe-out” (VRE) was the largest (793/1,603), followed by “Knee-out and Toe-in” (VRI) and “hyperextension” in this order . Most of the injuries are reported to occur with noncontact mechanisms, such as those involving landing from a jump and sudden deceleration of the body while running, with or without a change in direction. Anterior cruciate ligament injuries often happen when an individual attempts to decelerate the body from a jump or forward running while the knee is in a shallow flexion angle [5–7]. At the time of injury, combined motions such as knee valgus and knee internal-external rotation are often noted. The ACL has been widely known to be loaded with anterior tibial shear forces [8, 9]. Unopposed quadriceps muscle forces produce anterior shear forces, possibly damaging the ACL, especially near full extension [10, 11]. On the other hand, hamstrings co-contraction forces are protective to the ACL, increasing knee stability while the quadriceps are contracting. An ACL injury often occurs when the body is positioned with the weight back on the heel, which may increase the quadriceps contraction force and reduce the efficacy of the hamstrings . Because a combination of knee external rotation and valgus motions may impinge the ACL against the femoral intercondylar notch and because these motions have been often observed during noncontact ACL injury, knee external rotation remains an important consideration for ACL injury . Contact injuries of the ACL are mainly the result of a direct blow applied to the proximal tibia with anterior-posterior direction. Typical examples of this mechanism are front or side tackles in soccer.
The better understanding of etiology and injury mechanisms is at the base for developing a prevention program. Modern literature shows promising results in programs that involve proprioception, strength training, and improved jumping, stopping, and turning techniques.
41.3 Clinical and Diagnostic Examination
Evaluation of the patient starts with the history. An acute ACL tear history is very familiar to the knee surgeon and usually the athlete refers of a “pop” or “crack” with pain in a pivoting movement, often in noncontact type, while playing the sport and also describes the knee as “coming apart” . Mild or marked effusion occurs within 6–12 h after trauma. However, some ACL tears happen with minor trauma, no internal sensation, no or minimal effusion and mild pain, and frequently in emergency room are diagnosed as minimal sprain and lead to chronic instability. An athlete with a chronic ACL history often refers of pain from a meniscal tear or cartilage damage, with minimal instability in pivoting activities and mild effusion after training or competition. However, today, it is very unusual that a top-level athlete could refer of a chronic instability as he is promptly evaluated and treated after trauma by his team physician. It can occur more often after ACL reconstruction if not a good stability is achieved with surgical operation.
Lachman test is considered the most reliable and reproducible method sign of an ACL tear, as it has in acute a sensitivity of 78–99 % . In acute injuries of top-level athletes, with large muscular thigh or hamstrings spasm, the Lachman test is not simple to perform and often is unpredictable unless a firm end point is felt to exclude an ACL tear. We prefer to perform also the prone Lachman test  in which gravity assists the forward movement of the tibia, hip extension stabilizes the femur, and relaxation is enhanced by the contact of quadriceps with the table. The patient is prone, the knee is held 20° or 30° flexed, and the examiner’s hands grasp the tibia; the fingers are positioned in the joint line. Anteroposterior tibiofemoral movement is attempted; its interpretation and the quality of end point are no different from that when the patient is supine.
Pivot shift is a specific but very insensitive test for acute ACL injury in the nonanesthetized patient [15, 16] and also subject to interobserver error, and we use it in operating room under anesthesia in deciding if to perform or not an additional lateral plasty in case of evident positivity.
Valgus, varus, and posterior laxity are also examined in the routine manner.
For instrumented evaluation, we routinely use arthrometer. We have used for many years KT-1000 or 2000 arthrometer, but since the last 3 years, we are using the GNRB (Genurob, Laval, France) that some studies have demonstrated superior intra- and interexaminer reproducibility over the KT-1000 and examiner independency . With arthrometer, it is also possible to suspect an ACL partial tear .
Magnetic resonance imaging (MRI) is an invaluable test to the diagnosis of an ACL injury as it has a specificity of 95 % and a sensibility of 86 % with normal coronal, axial, and sagittal views . We are routinely using the oblique coronal and oblique sagittal images for their improved accuracy . Normal ACL is both distinctly seen and taut, while when acutely injured appears indistinct and lax. MRI is also useful in ruling out other internal derangements detect . Segond’s fracture, visible also in anteroposterior X-ray, reveals avulsion of the anterolateral ligament [22, 23] that in some case needs to be refixed or reconstructed.
41.4 Treatment Strategy
In sports activity that requires cutting, jumping, and pivoting stress, it is mandatory to carry out the reconstruction after an ACL tear. It is well documented in literature that early ligament reconstruction reduces the risk of subsequent meniscal injury, especially in athletic population. Sports activity predisposes early damage of all static structures. Therefore, in ACL tear, surgical treatment is our indication for those athletes who want to continue playing their sports. Natural history of partial ACL tears is quite good over the medium term in the patients that limit their sports activities but functional instability seems to progress with time, especially in athletic population ; therefore, also in the case of ACL partial tear in young athletes, our indication is ACL surgical reconstruction.
In the past, initial concern existed over early reconstruction of ACL injury because of the increased risk for arthrofibrosis, and the surgery was delayed until minimal swelling, good leg control, and full range of motion was achieved. Top-level athletes request early surgery in order to reduce the time of return to play. Moreover, in the presence of associated injuries such as meniscal or collateral ligaments tears, immediate suture repair gives better results than delayed repair. For these reasons, better postoperative pain control and a more aggressive rehabilitative protocol with continuous passive motion, and early muscles exercises, can yield results that are independent of the timing of surgery .
Graft selection is a topic of discussion. The central third of patella tendon (bone-patellar tendon-bone) (BPTB) and the four-strand hamstrings (HS) are the two most commonly used autografts. Some studies show similar results in terms of laxity and functional results between the two grafts, and others show better stability for BPTB but not correlated with functional outcome. Allografts are not as strong as autografts and are not recommended for top-level athletes except in some case of ACL revision surgery. BPTB is our first autograft choice in top-level athletes both in male and in female. The main reason of this choice is the biological fixation, bone to bone, that allows an accelerated protocol of rehabilitation when a prompt return to sport is required.
41.4.4 Surgical Procedure
Surgical treatment of ACL tears has evolved over the past century. Several techniques and methods of fixation have been described, and a detailed description of all procedures is impossible.
The two most commonly used techniques today are anatomical single-bundle ACL reconstruction with HS or BPTB and anatomical double-bundle ACL reconstruction with HS that restore both anteromedial and posterolateral ACL bundle. Double-bundle technique seems to give better restore on rotational stability but in high-level athletes are not rare tears of the reconstructed posterolateral bundle. Our preferred method of ACL reconstruction is a single-bundle reconstruction with transtibial technique and a lateral additional procedure to improve knee stability if needed. Following an initial arthroscopic examination that confirms ACL rupture, the meniscal lesions are searched and treated. When possible, a meniscal suture is always carried out. A vertical central skin incision is made from the center of the patella to the tibial tubercle. The deep fascia is incised and divided to expose the patella tendon that is harvested 10 mm in width with patella (20 mm in length) and tibial (30 mm in length) bone plugs. During the harvesting, the knee is held in flexion so that the tendon fibers are straight due to tension. An oscillating saw is used to make the bone cuts, and in the professional athletes, we perform an oblique cut in order to avoid abnormal stress and the potential risk of patellar fracture. The tibial tunnel is drilled with the knee in full extension using a Howell tibial guide (Arthrotek Inc., Warsaw, IN, USA). An impingement rod is used to avoid the femoral roof to impinge on the graft and notchplasty performed, if necessary, with an abrader. The femoral tunnel is drilled through the tibial tunnel with the knee flexed at 90° on a pin guide located in the center of the anatomical ACL insertion (at 10 o’clock for right knee and 2 o’clock for left knee, 7 mm anterior to the posterior margin of the lateral femoral condyle) . Sometimes it is difficult to reach the anatomical point with the femoral transtibial guide. In this case, after a first pin has positioned with the guide, a second pin is positioned lower, in the right place, with the aid of a cannulated transtibial corrector. Another possibility is to drill the femoral tunnel through the anteromedial portal or by an “Out-In” technique. In this case, a mini lateral skin incision is requested. The graft, armed at the patellar plug with XTendobutton (Smith & Nephew) and at the tibial plug with two sutures, is passed through the tunnels and the button flipped over the lateral femoral cortex. The knee is repeatedly extended and flexed to allow stress relaxation of the graft with the knee flexed at 20° and the graft is tensioned at 80 N and fixed with an absorbable interference screw in the tibial tunnel. In the case of marked anterolateral rotatory instability (Jerk Test 2 or 3+), we are currently using a lateral additional procedure to improve knee stability. Our preferred techniques are the iliotibial band (ITB) extra-articular tenodesis as described by Noyes  or the procedure described by Christel and Djian . In acute cases, if the anterolateral ligament (ALL) is torn, it can be repaired or refixed if an interstitial rupture is present. The anterolateral ligament is an important restraint to internal rotation of the knee, thus preventing the pivot shift phenomenon. The origin of the ALL is situated at the prominence of the lateral femoral epicondyle, slightly anterior to the origin of the lateral collateral ligament, and has an oblique course to the anterolateral aspect of the proximal tibia, with firm attachments to the lateral meniscus, thus enveloping the inferior lateral geniculate artery and vein. Its insertion on the anterolateral tibia is grossly located midway between Gerdy’s tubercle and the tip of the fibular head, definitely separated from the iliotibial band (ITB) . For its reconstruction, we use an isolated strip of ITT (10 × 70 mm) that we fix on the anatomical site of femur through a blind tunnel and interference absorbable screw and with suture anchor or a screw washer on the tibia.
41.5 Rehabilitation After ACL Reconstruction
The importance of a rehabilitation program cannot be underestimated, and although there is no one rehabilitation program proven to be superior to others, the speed and safety with which an athlete returns to play is more dependent upon the rehabilitation program than whether the patient had arthroscopically assisted or two-incision technique, or what type of graft or fixation was used. A clear, logical, responsive, and appropriately aggressive rehabilitation program is the key to returning an athlete to play as quickly and safely as possible. Rehabilitation has undergone a relatively rapid and global evolution over the past years. Traditionally, rehabilitation is divided into three distinct phases based on experimental study performed by Amiel et al.  on biological process of graft implanted into a joint, process called ligamentization. For this reason, after surgery, many rehabilitative protocols have relied on protection of the reconstructed ligament by limiting knee extension and weight bearing. Current rehabilitative programs following ACLr are now more aggressive than those utilized in the past. Presently, we employ two different rehabilitation programs for isolated ACL-reconstructed patients. The accelerated protocol is utilized for professional athletes, whereas recreational patient would follow a slower program, referred to as the regular rehabilitative program. The main difference between the two programs is the rate of progression through the various phases of rehabilitation and the period of time necessary prior to running and return to sports.