The ACL is one of the important stabilizing structures of the knee joint and is also the most vulnerable part. Some statistics: the incidence of ACL injuries is about 60 per 10,000 people/year. In the United States, there is one ACL injury in about 3,000 people per year, about 100,000 ACL injuries, and about 50,000 cases undergo surgical reconstruction. There are no detailed statistics in China, but with the popularity and development of mass sports, the number of surgical cases is also increasing year by year, so improving the diagnosis and management of the ACL has become an important issue in orthopedics and sports medicine.
The parenchyma of the ACL is a dense connective tissue that is both elastic and rigid, located within the joint but surrounded by the synovial membrane, and is an intra-articular extra-synovial structure. The blood supply is derived from branches of the middle knee artery. The ligament begins within a semicircular area on the posterior medial aspect of the lateral femoral condyle, travels anteriorly and inferiorly, and ends between the anterior tibia and the intercondylar spine by crossing the intercondylar fossa. It is approximately 30-38 mm in length and 10-12 mm in width. the parenchyma is the thinnest, with an area of 44 and 36 mm2 in men and women, respectively (approximately 7.5 mm and 6.8 mm in diameter, based on a circle), and the stop is approximately 3.5 times larger than the parenchyma. In alignment, there is approximately 90 degrees of external rotation.
The most important function of the ACL is to prevent anterior displacement of the tibia, as well as to limit internal rotation of the tibia, to prevent hyperextension, and to limit internal and external rotation. These effects are present throughout the flexion and extension process. The ACL has adapted to this need and has been structurally divided into several functional units. The anteroinferior bundle starts at the proximal part of the femoral stop and ends at the anteroinferior part of the tibial stop, which plays a greater role in flexion, while the posterior bundle starts at the distal part of the femoral stop and ends at the posterior part of the tibial stop, which plays a greater role in extension.
The ACL has a great tensile strength of about 1700-2400 N and a stiffness of about 242 N/mm, similar to the 10 mm patellar tendon (1784 N and 210 N/mm) and the four-strand N cord tendon (2422 N and 238 N/mm) (Woo). In daily life, the ACL is loaded at 400 to 700 N, but during strenuous exercise, the ACL may be subjected to greater tension, which can lead to rupture. There are statistics that about 70% of injuries are related to sports, especially in some sports with more sharp turns, sharp stops, diagonal cuts, etc. These high-risk sports are mainly soccer, basketball, alpine skiing, rugby, handball, etc. There are other high-risk factors, including being female and the presence of other injuries in the joint.
The site of injury can be the parenchyma, tibial intercondylar spine avulsion and femoral intercondylar spine avulsion (the latter is rare), with parenchymal breaks being the most common. It can be divided into complete and partial tears. It can be a simple ligament injury or a combination of other ligament and structural injuries.
For the management of intercondylar spine avulsion fractures, in principle, fractures with displacement (type II or higher) should be fixed surgically, with arthroscopic fixation, which is less traumatic and has fewer complications. The specific methods are not repeated in this section.
For partial parenchymal laceration injuries, the prognosis is related to the degree of tearing, and it is generally believed that tears over 50% have a chance of becoming total tears in the future of more than 80%, so they are treated as total tears. Tears of less than 50% can be treated conservatively.
For complete tears of the parenchyma, the risk of meniscal and articular cartilage damage is further increased because the majority of the injury cannot form an effective clot and cannot heal, leading to joint instability over time.
Therefore early and correct diagnosis is very important. History and physical examination are of utmost importance. In acute injuries there is a distinct “pop” sound and severe pain, often swelling within a few hours and an inability to walk normally and continue exercising, and swelling often takes at least two weeks to recover. The symptoms of the chronic phase after recovery depend on the level of motion and the compound injury. It often feels like the joint is unable to use force, and it is easy to sprain during sports, especially when preparing to change direction or accelerate, with a feeling of instability, often repeated sprains, and gradually showing signs of meniscal damage and cartilage damage. It is important to let the patient fully relax and check the Lachman test for lack of hard end resistance to confirm the diagnosis; the axial shift test (Pivot
MRI can better reflect the site of the tear and the compound injury and bone contusion, which is typically limited to the lateral aspect of the femoral epicondyle and the posterior lateral aspect of the tibial plateau.
Whether, when, and what to operate after a cruciate ligament rupture, the management of compound injuries, the management of minor patients, and postoperative rehabilitation remain critical, although controversial, and there are some common views.
For simple ACL rupture, activity level, expectation, and schedule are key factors in whether to operate or not. The expectation to return to a high level of motion should be considered as an option for surgery; low-risk, low-need patients may be considered for conservative treatment. In chronic cases, with symptoms of instability, or dealing with a combined injury (e.g., meniscal tear), surgery should be considered. Some athletes, who cannot have surgery due to event scheduling, can be treated conservatively first. The keys to conservative treatment are three: swelling reduction, muscle strengthening and lifestyle or training program changes.
Timing of surgery, most people now advocate surgery when swelling disappears and joint mobility returns to normal, especially when full extension can be achieved and muscle control is good, rather than surgery in the acute phase. The main measures to reduce swelling are ice packs, elevation of the affected limb, quadriceps tensing exercises, and appropriate physical therapy. This is usually 2-6 weeks post-injury to reduce the chance of joint stiffness.
Combined compound injuries, including medial collateral ligament, meniscus, lateral collateral ligament and posterior lateral joint capsule compound structures, N tendon, posterior cruciate ligament, and even neurovascular injuries.
Combined medial collateral ligament injuries are the most common, accounting for 60-80% of compound injuries. Treatment opinions are more controversial, but how to obtain a stable and functional joint is the goal of treatment. First: combined first- and second-degree medial collateral ligament injuries are treated as simple cruciate ligament injuries. Secondly, even if combined with third degree medial collateral ligament injury, the effect of simple conservative treatment is not good, and the ACL should be reconstructed early, and the medial collateral ligament can still obtain satisfactory stability after reconstruction with conservative treatment. However, it is also believed that for third-degree inferior stop tears, the stop should be reconstructed surgically or fixed for a longer period (2-4 weeks). Third, for combined severe medial collateral ligament and posterior capsule tears with significant separation of the severed ends and meniscal avulsion, surgery should be performed to repair the medial structures at the same time. Fourth: In cases of combined lateral collateral ligament and posterior posterolateral structure tears with intact posterior cruciate ligament, the lateral structure often heals unsatisfactorily and requires surgical repair, usually in 7-14 days, along with reconstruction of the cruciate ligament. Fifth, combined posterior cruciate ligament injury, there are four cases: 1) ACL combined with medial collateral ligament and second degree or less posterior cruciate ligament laxity, should be treated conservatively first to restore the stability of the medial and posterior cruciate ligaments, and the ACL will be reconstructed in the future according to the symptoms. 2) ACL combined with medial collateral ligament and third degree or more posterior cruciate ligament laxity, if the medial collateral ligament is torn near the upper stop, first After about 2-4 weeks, the medial collateral ligament will be stabilized and the swelling will subside, and the mobility will reach 0/0/120, and the posterior cruciate ligament will be reconstructed in the subacute stage; if the medial collateral ligament is torn at the inferior stop and rarely causes stiffness, it can be recovered to 0/0/120 in 1-2 weeks, and the posterior cruciate ligament will be reconstructed and the inferior stop of the medial collateral ligament will be reconstructed in parallel. The ACL should be treated conservatively first, and the need for ACL reconstruction should be decided after the mobility is completely restored to normal. 3) ACL combined with lateral structures and posterior cruciate ligament injury of second degree or less, the posterior cruciate ligament does not need to be operated; the swelling should be reduced first, usually in 7-14 days, to restore the range of motion, and the lateral structures should be repaired anatomically, and the cruciate ligament should be reconstructed at the same time. 4) ACL combined with lateral structures and posterior cruciate ligament injury of third degree or more, the most important thing is that the posterior cruciate ligament should be reconstructed. The most important thing is to stabilize the posterior cruciate ligament and the posterolateral structures after short-term preoperative rehabilitation, reconstruction of the posterior cruciate ligament and simultaneous direct anatomic repair of the posterolateral, anterior cruciate ligament stage II before deciding whether to operate or not. Such patients sometimes have a combined common peroneal nerve pull injury that does not require acute phase treatment after separation. In conclusion, for ACL injuries combined with medial collateral ligament injuries, the majority of the medial structures can heal on their own while the ACL is reconstructed in the subacute phase; for injuries combined with lateral structures and posterior posterolateral horn complexes, acute anatomic repair of the lateral structures while reconstructing the ACL; for injuries combined with posterior cruciate ligament injuries, the posterior cruciate is below second degree laxity and is treated conservatively while the ACL is operated in the subacute phase; if the posterior cruciate ligament If the posterior cruciate ligament is more than third degree laxity, the posterior cruciate ligament is reconstructed first and the reconstruction of the anterior cruciate ligament is delayed. Otherwise, it is easy to stiffen.
Combined meniscal injuries are the most frequent type of intra-articular structures. The acute phase is about 30-80%, and the incidence increases year by year with time. And the protection of cartilage by the meniscus is increasingly valued. In fact, the amount of meniscus removal is positively correlated with the degree of joint degeneration, so the meniscus should be preserved to the maximum extent possible, that is to say, it should be sutured as much as possible, and the success rate is higher when performed simultaneously with cruciate ligament reconstruction, which is over 80%. However, as time passes, the chance of suturing the meniscus decreases, so it is advisable to do it as early as possible. If suturing is not possible, partial resection will be considered, and if there is no possibility of preservation, then total resection will be performed. In contrast, there are meniscal injuries that are asymptomatic, such as complete or incomplete stable longitudinal tears with a short radial tear of no more than 1/3 of the width, which can be left untreated. Failure rates are high, up to 50%, with simple suturing of the meniscus without cruciate ligament reconstruction, meaning that a stable knee is very important to guarantee the success of the procedure. Try to reposition the suture even if it is a lifting basket injury. The suture should be thoroughly fresh before suturing, including the surrounding synovial tissue. Vertical red tape sutures from the inside out with non-absorbable sutures are the gold standard. Artificial or allogeneic meniscal transplantation is the future direction of research after partial or complete meniscal resection.
Combined cartilage injury, with a combined rate of about 15-40% in the acute phase, is mainly concentrated in the lateral aspect and closely correlates with MRI manifestations of bone contusion. However, the prognostic impact is not as obvious as that of meniscal injury. The treatment principle is based on the degree and area of injury as in general cartilage injury.
For ACL reconstruction methods, arthroscopic single-incision technique is currently the mainstream. The timing of surgery, as discussed earlier, is to try not to operate in the acute phase. There are currently three main types of grafts: autologous bone-patellar tendon-bone (BPTB), autologous four-strand N-cord tendon (G/ST), and homogeneous allograft tendon. Each has advantages and disadvantages, all have sufficient initial strength, and all achieve satisfactory clinical results, but try to use autologous material to avoid the spread of disease. The position of the osseous tract is also an important factor in the success of the procedure. If the tibial bone tract is too far forward, it will lead to limited extension and impact with the top of the intercondylar fossa of the femur, resulting in failure; if it is too far back, it will become a “suspensory” ligament and will not work. Some people advocate a posterior deviation of 2 mm from normal, with the center point located on the extension line of the free edge of the lateral meniscus, about 7 mm from the posterior cruciate ligament, and slightly inward is preferred. If the femoral osteochondral tract is anterior, flexion is limited and passive flexion leads to ligament tear and failure. Therefore, the femoral tract should be as far back as possible, preferably 1-2 mm from the posterior femoral edge, at about 2 (left) or 10 (right) points. A strong initial fixation strength is also essential for the success of the procedure. Femoral end: BPTP is generally fixed with interface screws, while the four-strand N cord tendon is mostly fixed with buttons or through pins. At the tibial end, interfacial screws are still preferred, while interfacial screws with portal nails or tethered pins or Intrafix provide adequate strength for the four N-cord tendons. The angle of fixation tends to be in the straightened position or 30 degrees, and the ligament tension during fixation is not the more about the better, generally considered to be about 80N.
In recent years, double-bundle reconstruction of the four bony tracts of the ACL has received increasing attention. Theoretically, double-bundle reconstruction provides better control of the rotational function of the knee. In clinical practice, recent results, with some disagreement, have reported no significant difference, while others have reported improved rotational control function. Long-term results need to be further investigated.
Long-term results of artificial ligaments need to be improved. It should be selected with caution.
In immature patients, it is advocated to be conservative first and advise them to change their activity level, use braces and strengthen their muscles. ACL reconstruction should be performed when the bone is mature or near mature. However, for very young patients who are unwilling to change their activity level, have unstable joints and positive axial shift test, conservative treatment is not effective and reconstructive surgery should be considered. However, how to avoid epiphyseal injury is highly controversial. It has been shown that bone blocks or metal fixations across the epiphysis can lead to epiphyseal closure. Therefore the surgical approach is very challenging. Direct suturing does not work well. Extra-articular reconstruction does not work well. Reducing or not damaging the epiphysis is an attempt to achieve good results. The lower end of the patellar tendon or N cord tendon is preserved, passing under the anterior horn of the meniscus and the coronary ligament, or the sulcus, into the joint and fixed in an over the top position, or in a groove avoiding the epiphysis. The tendinous portion of the tendon has also been drilled through the epiphysis and fixed in the over-the-top position with no significant growth effects seen. The size of the bone hole is controversial and as small as possible, about 6 mm, is appropriate. However, it is not clear whether these grafts grow and hypertrophy with growth.
After tendon reconstruction and fixation, healing takes time and is generally considered to be at least 6 weeks for bone bone healing and at least 8 weeks for tendon bone healing, with a further 2 weeks delay for allograft tendons. For patellar tendon grafts, the weakest point is the graft-tract intersection at 3 weeks and is located proximal to the bone mass at 6 weeks; for N cord tendons, the weakest point is the graft-tract intersection at 3 weeks and the tendinous portion within the tract at 6 weeks. The transformation of the intra-articular tendon starts from the surface, at about 3 months, and at about 5 months, the hemo-transportation is all completed, and the healing is complete at about 6 months. However, with allograft tendons, it has been observed that they remain incomplete for about 3 years. These results directly affect the rehabilitation procedure.
Currently, an aggressive rehabilitation program has achieved satisfactory clinical results and reduced the chance of joint adhesions. Postoperative immobilization in the extended position, elevation of the affected limb, or the use of ice packs reduce bleeding and swelling. Hyperextension distraction, and quadriceps exercises should be performed as early as possible. Joint mobility exercises should begin after 2 days and reach 90 degrees for one week, or be limited to 90 degrees for 4 weeks with a combined meniscus suture. Weight bearing should be done as early as possible, but activity should be reduced for one week to minimize bleeding and swelling. Combined meniscal sutures require partial weight bearing after 4 weeks and full weight bearing at 8 weeks. Combined with cartilage injury in the weight-bearing area and microfracture treatment, partial weight-bearing at 4 weeks and full weight-bearing at 8 weeks. full joint mobility is restored at 8-12 weeks. Gradually resume activities, from low speed, low external force, controlled activities to high speed, high external force, uncontrollable activities. Competitive sports activities are required after six months to one year.
Sports activities pose new challenges to sports medicine and orthopedic surgeons, constantly. We believe that with the joint efforts of scientists, doctors and patients, the future of ACL treatment will be better.