ACL Tears

The first primary function of the ACL is to prevent excessive anterior movement of the tibia relative to the femur. The ACL works in tandem with the PCL (posterior cruciate ligament) to help control this forward and backward motion. However, the ACL also provides rotational stability during cutting and pivoting while the foot is planted. Thus, the ACL is critical for sports that have sudden changes in direction. Just like any other joint in the body, the static ligaments such as the ACL are dynamically supported by the muscles that cross the knee joint. This includes the quadriceps and hamstring muscles that support the knee.

A tear of the ACL can occur in two primary mechanisms:

Non-contact injuries

1. 1. This commonly occurs during a sudden shift in direction such as a running back trying to quickly decelerate to shake a defender or during an awkward landing such as a volleyball player stretching out to try and hit a ball back.
   2. Non-contact injuries are common in sports that require significant changes in direction and pivoting, such as basketball, soccer, football, and skiing.
   3. In older patients, this can happen with a simple misstep such as missing a step on a sidewalk curb due to age-related changes within the ligament over time.

Contact injuries

Injuries to the ACL can occur from a direct injury such as a motor vehicle accident or a collision.

There are well-known risk factors that can increase the chances of tearing the ACL. These include:

1. Poor landing mechanics after a jump especially if the knee lands in valgus with the tibia rotating outwards (i.e knee collapses inwards and twists outward)
2. Weak hamstrings strength
3. Playing on a fatigued knee where the dynamic control of the knee is lost towards the end of a game
4. Playing on uneven surfaces where the ACL can be suddenly and excessively loaded.

The common symptoms of an ACL tear include

1. The feeling of a sudden pop at the time of the injury, either audible or felt within the knee
2. In addition to the pop that can be felt by the athlete, often the knee gives way and feels unstable as the shin bone slides out in front of the thigh bone. This knee instability is a classic finding of ACL tears.
3. After the injury, patients often have difficulty bearing weight and continuing in the sporting activity
4. Because the ACL has a blood supply from the middle genicular artery, there is often bleeding into the joint (hemarthrosis). As blood is an irritant, patients often have limited range of motion due to the swelling as well as pain within hours of the injury.

ACL tears are diagnosed based on a combination of understanding the patient’s history and symptoms, physical exam, and imaging findings:

Physical exam

1. An acute ACL injury will often have a swollen knee with limited range of motion. However, after the initial swelling subsides, often motion will improve unless there’s another injury in the knee such as a meniscus injury that can be further irritating to the joint
2. Specific exam maneuvers for the ACL include the anterior drawer test which involves bringing the tibia forward on the femur. In an ACL injury, the shin bone will excessively move forward indicating knee instability.
3. Another test includes the Lachman test which similarly bringing the tibia forward on the femur at 30 degrees of knee flexion
4. The pivot shift maneuver tests the rotational stability of the ACL
5. A good exam of the knee will also reveal any associated pathology of the quadriceps tendon, patellar tendon, the other ligaments of the knee, and menisci
6. An exam under anesthesia at the time of surgery helps to reconfirm the diagnosis intraoperatively and also provides useful information on the rotational stability of the ACL.

Imaging studies

1. X-rays are very useful to rule out fractures associated with ACL tears, most often seen during knee dislocations.
2. MRI is the gold standard when an ACL injury is suspected as it both confirms the diagnosis and helps check for associated injuries within the knee such as meniscus, cartilage, and associated ligamentous injuries.
3. A CT scan is not routinely done in the case of an initial ACL injury, but may be useful in revision situations where a surgeon wants to understand the previous ACL surgery done (ex. bone tunnel placement and widening).

Decision making

1. Treating an ACL tear requires several important considerations and is a very important and complex decision
2. We consider the patient’s age, activity level, and personal goals for recovery. This shared decision making is essential to give the patient the best outcome regardless of if surgery is pursued
3. Surgery is not right for every patient and even if surgery is selected, one single graft does not fit every patient. Every patient will have a different recovery and slightly different timelines.

Non-surgical management

1. When we think about non-surgical management, this is suitable when we have a partial tear of the ACL or an ACL tear in lower-demand patients. In our non-pediatric patient population, many patients can have excellent outcomes without having to reconstruct or repair the ACL as long as the dynamic stability around the knee can support the knee during these activities.
2. The overall non-surgical treatment protocol is first to work on reducing the inflammation in the knee and following that with physical therapy to dynamically strengthen the knee. During this process, providing an ACL brace that helps stabilize both anterior/posterior stability and rotational stability is crucial.
3. Surgery is not the best option for every patient because while surgery is a one-day event, the rehabilitation for ACL reconstructions takes at least 6-9 months of dedicated rehabilitation which is not suitable for every patient and not consistent with the goals and demands of every patient.

Surgical management

1. Indications
   • Surgery is most appropriate for patients who are highly active and motivated to undergo the rigorous rehabilitation ahead.
   • Surgery is also recommended to the pediatric population to reduce the risk of further meniscus injury and cartilage injury in the knee as they need a stable knee for the rest of their life.
2. The goal with any ACL surgery is to restore the stability of the knee to return to cutting, pivoting, and high-demand athletic activity. For those patients who are indicated for surgery and are able to faithfully participate in the extended rehabilitation required of them to have a good, successful outcome, surgical options include either an ACL repair or ACL reconstruction.
3. ACL repair is a selective procedure done in very specific tear patterns, such as avulsion patterns where the ligament tear off of the bone, very proximal injuries where the ACL can be brought back to the bone, or in pediatric midsubstance injuries (BEAR procedure). In most cases, however, a reconstruction is a better option compared to an ACL repair to provide a durable new ACL for the patient.
4. While it is beyond the scope of this article to thoroughly discuss all the graft options, graft choices are broken down into autograft and allograft. Autograft involves taking a graft from the patient’s own body, such as the central third of the patellar tendon, the central portion of the distal quadriceps tendon, or the patient’s hamstrings tendon. An allograft is where cadaver donor tissue is taken and fashioned to become the patient’s new ACL.
5. Based on the MRI findings and intraoperative findings, when the arthroscopic camera is inside the knee, ACL reconstruction is often combined with meniscus surgery or cartilage surgery as needed.

Rehabilitation and recovery

1. As has been discussed, proper ACL rehabilitation under supervision of a skilled physical therapist cannot be understated. A well-done ACL surgery with poor rehabilitation will always lead to a poor outcome.
2. While we will not go into the specific details of the rehabilitation, the early focus after ACL surgery is to control swelling and improve range of motion especially in restoring full knee extension. After this, patients slowly improve their strength and near the tail end of the rehabilitation process, patients work on improving plyometrics, agility, and return to sport demands of the knee.
3. It is important to note that the initial strength of the ACL graft slowly decreases over time from the initial ACL surgery so that by 3 months after surgery, the ACL graft is actually the weakest it will be even though the patient often feels good about their knee at this point. After the 3 month mark, the graft begins to go stronger. At around 6-7 months, the graft usually reaches its maximal strength. This is why the rehabilitation process must take so long, because even though the ACL surgery is done on one day, the rehabilitation is a long process for the graft to biologically incorporate well into the bone and joint.
4. With modern techniques and ACL rehabilitation, most patients are able to recover well to achieve an excellent outcome and get back to their desired activities. With patience, consistency, and expert guidance, a torn ACL does not mean the end of an active and healthy lifestyle.