The Anterior Cruciate Ligament (ACL) is one of the four major ligaments of the human knee. Its name is indicative of its characteristic passage with the posterior cruciate ligament, up to its intersection with the tibia.
The ACL is located in the central part of the joint capsule, outside the synovial cavity. It starts at distal femoral notch bottom, spreads to through the medial wall of the lateral femoral condyle. Thus, the back-side of the femur and the anteromedial part of the tibia are connected and this connection has the function to help the stability of the knee.
Holding up the femur to the tibia and into the knee joint, the ACL is a resistant fabric made of thousands of individual fibers. These fibers, together, form the ligament. Some of these fibers are arranged in bundles of different nature. Usually, a ligament has two bundles of primary fibers. These two beams are positioned close together and can be difficult to distinguish without any medical training.
The Anterior Cruciate Ligament of the knee is a very susceptible to damage structure, especially in sports. According to the American Orthopedic Society (AOS), around 150,000 ACL injuries occur each year in the United States.
The ACL injury occurs primarily during sports activity, but can also occur in various situations, such as dancing, tripping, slipping. Some major trauma, such as automobile and motorcycle accidents can also lead to ACL injury.
A tear of the ACL can be total or partial, depending on the number of fibers that are broken. Treatment of a partial injury will depend on the symptoms the patient presents, pre-surgical physical examination and ACL appearance during surgery. When there is a complete rupture of the ACL, the physician should consider whether the patient should or should not perform the surgery as there are people who do not practice physical exercises that can live with the injury just doing physical therapy.
Plain radiographs, including standing posteroanterior 45 degrees flexed weight bearing, lateral, and Merchant views are obtained. The radiographs allow to measure the width of the intercondylar notch, length of the patellar tendon, tibial slope angle, and width of the patella, which is usually twice the width of the patellar tendon. These measurements are helpful for planning the angle and length of the femoral tunnel and help determine the amount of notchplasty that may be needed to accommodate for the width of the new ACL graft. A MRI scan may be necessary for pre-operative evaluation.
A reconstruction of the ACL can be made with different, each with its own advantages and disadvantages. These include:
To insert the graft in the position of the original ACL, tunnels are made in the tibia and the femur. The graft is then passed through these tunnels to reconstruct the ligament.
With the patient under spinal anesthesia, a pneumatic tourniquet is placed on the thigh root so there is no bleeding during the operation. The surgery begins after a trichotomy and the limb asepsis are performed.
The first step of ACL reconstruction is the removal of the flexor tendons, through a small incision on the inside of the leg just below the knee. After the withdrawal of the graft, the assistant should prepare it to replace the ACL. Tendons are folded in half, forming a new thick and sturdy ligament. Meanwhile, the surgeon begins the arthroscopy, through two small holes on the front of the knee. A camera inside the knee allows studying the lesions previously described. The ACL is evaluated and, if torn, it is resected with the aid of special tweezers and also a shaver. Thus, “opens” a space for the introduction of the graft. Then the rest of the knee is inspected, to assess if other lesions, in the meniscus and the cartilage, should be treated.
The next step is the preparation of the bone tunnels in the tibia and femur. The correct positioning of these tunnels is critical for the success of the surgery. To finish the surgery, the graft is placed within the tunnel and fixed to the bone. Typically, special screws, that may be metallic or absorbable, called interference screws are placed in the tibia. In the femur there are several devices that can be used, including the same interference screws. Other devices include: endobutton, transverse screw and Rigid Fix pin.
After fixing the graft, the physician tests the knee joint, noting whether it has a proper mobility (the flexion and extension are complete) and especially if the knee is stable. The performed cuts are sutured with nylon and occlusive dressings are made. The use of surgical drain is not usual, depending on preference and experience.
Mini arthrotomy is an open surgical procedure, exposing the joint, which can be done where arthroscopic assisted ACL reconstruction is not available.
Why do Anterior Cruciate Ligament reconstructions fail?
ACL reconstruction is a complex process, and although the success rate of ACL reconstruction is generally 85 – 95%, there are times when the reconstruction is unsuccessful. The main causes of ACL reconstruction failure can include:
Failure of an ACL reconstruction is often hard to describe. The patient can have complaints of knee instability, pain, stiffness, or the inability to return to desired activities. Treatment for failed ACL repair is complex and technically challenging, and the results of revision ACL surgery are not as good as an initial ACL reconstruction.
An evaluation for a failed ACL should include a thorough history and physical exam to determine the level of recovery and potential cause of failure. It is critical to repeat x-rays that include the entire leg, an MRI that may require a contrast injection for better detail, and possibly a CT scan or bone scan will often be required to determine causes of failure, other injuries, and plan for potential revision surgery. Issues to consider include injuries to other structures as previously described, but also location and size of the previous tunnels, types of graft material used, and fixation devices used to secure the graft.
Revision Anterior Cruciate Ligament reconstruction is a complex undertaking and is recommended for patients that have instability both subjectively and objectively. The patient must understand that the results of revision ACL reconstructions are not as good as the initial ACL and the goal of the revision is to allow the patient to return to their daily activities, instead of return to competitive athletics. The patient should have realistic goals and understand all of the issues but can be reassured that with the proper evaluation, treatment, and rehabilitation, a successful outcome can be expected in most cases.
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