The Anterior Cruciate Ligament (ACL)

The anterior cruciate ligament, or ACL is the main stabilizing ligament in the human knee.  Tears or ruptures on this ligament can cause symptoms of instability.  The patient with a complete ACL tear may feel the knee is “giving out” or “buckling” with twisting, turning, or pivoting activities.  These symptoms can arise during sporting activities like football, soccer, basketball or any pivoting action such as stepping off of a curb, turning to talk to someone, or catching your foot in a divot or hole at the park.  Patients are usually symptom free when walking in a straight line and oftentimes can even run in a straight line or on a treadmill after an ACL tear.

No matter how it happens, an ACL tear can be painful. In this post we’ll look at what’s happening inside the knee when the ACL tears and the choices you have when it comes to repairing the ACL.

How ACL Tears Happen

The ACL is a strong, fibrous tissue that connects the femur (thighbone) to the tibia (shinbone). It is one of four main ligaments inside the knee that serves to stabilize the knee joint.

ACL injuries occur when there is a sprain or tear of the ligament. These most often occur in individuals who play sports that involve sudden stops or changes in direction as well as jumping and landing, such as football, basketball, soccer, volleyball, tennis, or skiing.

When the ACL is sprained, the individual may experience pain and an inability to bear weight on the knee. If the ACL is torn, the individual may experience these symptoms along with rapid swelling (blood from the torn ligament), loss of range of motion, and may even hear a pop when the ligament itself tears.

How ACL Tears Are Repaired

Although some people can go back to normal activities with a partial or full ACL tear, it’s not advisable, especially if one plans to continue playing high-impact sports or participating in pivoting activities like hiking, skiing, or snowboarding.. That’s because if the ACL is not repaired, your knee lacks support and other ligaments (PCL, MCL, LCL) and structures (menisci) can begin to sprain or tear.

If surgery is recommended by your doctor, there are multiple ACL repair options, all of which are performed using arthroscopy, a minimally invasive surgical procedure. During an arthroscopy, small incisions are made around the joint for the scope and surgical instruments. The scope is inserted into the knee while saline solution flows through a tube and into the knee to expand the joint and improve visualization. The image is sent to a video monitor from which the surgeon can see inside the joint.

The torn ACL remnant is removed using a small (4-5 mm shaver) and the knee is prepared for reconstruction with a graft. Other structures, such as meniscus tears and cartilage issues are addressed at this time.   Several grafts are available for ACL reconstruction that are harvested from different parts of the knee(autograft), or from a cadaver(allograft).

Allograft

For an allograft procedure, allograft tissue is harvested from a donor. This tissue undergoes special tissue processing to clean and prepare it, and is made up of hamstring tendon that will become your new ACL. During the procedure, the surgeon inserts a surgical instrument into the joint to remove the torn ACL. Next, a guide wire is inserted through the tibia and femur so that the surgeon can use a surgical drill to create a tunnel in the femur and tibia for your new ACL graft. The end of the graft is tied to a loop on the guide wire, allowing the graft to be pulled into place. Last but not least, buttons are placed over the bone ends to secure the graft and over time (6 months) the tendon will incorporate into the navtive bone.  This has an advantage in that nothing needs to be harvested from the patient and early recovery is usually easier than techniques that use the patient’s own tissue.  Healing time is essentially the same, and with newer, anatomic techniques, results with allograft tissue in the appropriate patient are usually excellent.  

Quadriceps Tendon Graft

The quadriceps tendon(tendon above the kneecap) is an excellent and preferred autograft tissue in many patients.  The central ⅓ of the tendon is used and anchored via buttons to the tibia and femur.  Approximately 65 mm of tendon is necessary for an adequate graft length.  Tunnels are drilled in the femur and tibia and the tendon is passed through the tunnels and anchored to bone using ACL Tightrope buttons (Arthrex, Inc.).  The graft is then tensioned on both sides and checked for stability.  Advantages include a very strong, robust graft with excellent healing rates.  Disadvantages include harvest site pain and morbidity with additional healing time in this area and early (1st few weeks) quadricep weakness.

Hamstring Graft

For this procedure, a portion of the hamstring is removed using a specially-designed surgical instrument; this graft will be folded over to increase strength, and both ends will be sutured to facilitate passage through the tunnels and into position. After the torn ACL is removed, a guide wire is inserted through the tibia and femur to drill a new tunnel for the graft. The end of the graft is tied to a loop on the guide wire, and the graft is pulled into place. The surgeon will then use ACL Tightrope buttons (Arthrex, Inc.) to fixate the graft to bone.  The graft is then tensioned on both sides and checked for stability. Advantages include a strong graft with excellent healing rates and excellent cosmesis.  Disadvantages include harvest site pain and morbidity with additional healing time in this area and early (1st few weeks) hamstring pain and weakness.

Bone-Patellar Tendon-Bone Graft

After the torn ACL is removed, the central 1/3 of the patellar tendon is removed. The ends of the tendon are then attached to plugs of bone from your patella and bone to help achor what will become your new ACL. A guide wire is inserted through the tibia and femur to help drill a new tunnel. Once this tunnel is created, the end of the graft is tied to a loop on the guide wire, the graft is pulled into place, and screws are used to secure the plugs of bones into the tunnels. Advantages include excellent healing rates with a very strong graft.  Disadvantages include harvest site pain and morbidity, potential patella fracture, and anterior knee pain.

To better understand your options, you can see visuals of all of these procedures here. 

While ACL tears aren’t fun, they’re not the end of the world!  Knowing your options when it comes to ACL repairs can not only make you more informed, it can help you better understand your doctor’s recommendations for surgery. And once your ACL is reconstructed,  you can return to an active lifestyle within a few months!