The anterior cruciate ligament (ACL) is a ligament inside the knee that prevents the tibia (shinbone) from sliding forward relative to the thigh bone (femur). It is an important stabilizer in the knee. The ACL can be injured in pivoting sports such as in soccer, when the foot is planted and the knee twists, or in basketball, when landing awkwardly from a jump. It is often seen in skiing injuries, as well. Female athletes are 3 - 9 times more likely to sustain an ACL injury compared to males.
After an ACL injury the knee will swell up and initially be painful. Eventually the pain subsides, but the knee will feel unstable and it may shift or give way during sports or with twisting and turning at the knee.
ACL injuries are diagnosed through clinical examination and magnetic resonance imaging (MRI). MRI is a painless diagnostic tool that provides an extraordinary amount of information in regards to the degree of injury to the ACL (partial tear versus complete), the location of the tear within the ligament and whether there are any other associated injuries in the joint (isolated injury versus complex).
Regardless of age and activity level, the initial treatment after an ACL injury is rest, ice and usually crutches. Unlike the medial collateral ligament (MCL) or posterior cruciate ligament (PCL), tears of the ACL frequently require surgical treatment. ACL tears are treatable using arthroscopy and minimally invasive surgical techniques. Treatment is dependent on the individual’s activity level and symptoms. We will work with you to develop an individualized treatment plan.
In the past, injuries to the ACL prohibited athletes from returning to high impact sports that involve pivoting or "cutting" movements. Today, advanced surgical techniques reliably allow the return to athletic activities and physically demanding labor within six to nine months. The goals of surgically reconstructing the ACL are to:
There are different ways that the ACL can be reconstructed. The surgical success rates for ACL reconstruction at UC San Diego Health System exceed 95 percent.
Anterior Cruciate Ligament (ACL) Tears and Their Treatment: Arthroscopic Minimally Invasive Surgery for ACL Reconstruction
Top Four Things to Know About ACL Reconstruction
- Not every person with an ACL rupture needs to have the ligament reconstructed.
- Post operative physical rehabilitation is a critical and crucial part of the success of the procedure. A team approach between physician and patient almost always leads to successful, satisfying results and a full return to activity. In most cases, the combination of arthroscopic ACL reconstruction and physical therapy will re-establish a functional, comfortable and stable knee that will allow a person to return to normal activities, demanding physical labor and contact/impact sports such as running, soccer, football, basketball and gymnastics.
- There are different options for ACL reconstruction. The major decisions involve the choice of graft (bone-patellar tendon-bone, hamstring, quadriceps, allograft, etc.) and the type of reconstruction (single-bundle or double-bundle). The surgical success rates for ACL reconstruction at UC San Diego Health System exceed 95 percent.
- Seeing a highly trained orthopedic surgeon who handles many injuries of this type is crucial.
Types of ACL Injuries
ACL injuries can be classified by the amount of damage to the ligament (partial or complete disruption). Injury to the ACL is usually a complete disruption, classifying it as a Grade III complete tear.
- Grade I Sprain - There is some stretching and micro-tearing of the ligament, but the ligament is intact and the joint remains stable. These injuries rarely require surgery.
- Grade II Sprain (Partial Disruption) - There is some tearing and separation of the ligament fibers and the ligament is partially disrupted. The joint is moderately unstable. Depending on the activity level of the patient and the degree of instability, these tears may or may not require surgery.
- Grade III Sprain (Complete Disruption) - There is total rupture of the ligament fibers. The ligament is completely disrupted and the joint is unstable. Surgery is usually recommended in young or athletic people who engage in sports that involve cutting or pivoting .
Operative vs. Nonoperative Treatment
In rare cases or in sedentary individuals, there may be a role for non-operative treatment and rehabilitation. Non-operative treatment should be considered in:
- Patients with partial injuries or those with relatively stable knees who can perform their necessary activities of daily living without difficulty
- Patients who were not capable of walking prior to the injury
- Patients who cannot safely undergo surgery
What Happens Without Surgery?
For individuals who choose not to have surgery, rehabilitation of the injured knee is frequently recommended to restore as much function as possible and help prevent instability. Rehabilitation focuses on strengthening the muscles around the knee in order to provide better support, control and stability.
There is nothing inherently dangerous about a mildly unstable knee so long as the patient is able to be adequately braced and is willing to use the appropriate assistive devices (cane, crutch or walker). This may require significant changes in lifestyle and activities to reduce the risk of instability events. For instance, an individual may have to avoid activities such as basketball or soccer and participate in low or non-impact activities such as biking or swimming for fitness. The goal is for patients to find activities where the knee feels stable and is pain-free.
A minority of patients will continue to have instability to the degree that they are unable to walk or put weight on the affected leg without it buckling. These individuals would be best served by undergoing surgery to stabilize the knee and restore function.
Minimally Invasive Surgery To Treat ACL Injury
Who should consider minimally invasive ACL reconstruction?
Arthroscopic ACL reconstruction is considered when:
- The patient is a young individual or athlete who will be at significant risk for disability or further knee injury if normal knee mechanics are not restored.
- The episodes of instability are a significant problem for the patient and inhibit his or her ability to perform activities of daily living, sporting activities or job-specific requirements.
- The patient has exhausted nonoperative treatments such as physical therapy and is still having frequent problems with instability and the knee giving way, and is unable to perform usual activities of daily living or walk without assistive devices, such as crutches or a brace.
- There are injuries to other structures in the knee.
- The patient is sufficiently healthy to undergo the procedure.
- The patient understands and accepts the risks and alternatives to the procedure.
- An appropriate and comprehensive diagnostic evaluation has been performed and the nature of the problem is clear.
- The surgeon is experienced in the techniques and treatments for arthroscopic ACL reconstruction.
- The patient is capable and willing to comply with a comprehensive postoperative physical therapy program
Even if a patient believes his or her knee instability is minimal (they are not having frequent “buckling” episodes), the knee will still incur wear and tear and the joint surfaces will become rougher, which places aditional pressure on the menisci and dames this tissue. An untreated damaged ACL can put pressure on other parts of the knee, damaging the menisci and other ligaments, as these structures compensate for the ACL weakness.
Possible Benefits of Arthroscopic Anterior Cruciate Ligament (ACL) Reconstruction
The ACL is vital for normal knee function and surgical reconstruction can successfully restore this function. The overwhelming majority of our patients who undergo arthroscopic ACL reconstruction to address knee instability have successful results. This success is seen in patients who can participate not only in daily life activities, but also in demanding physical activities, such as competitive sports. As long as the knee is cared for properly and subsequent traumatic injuries are avoided, the benefits of the surgery should be permanent.
Risks of ACL Reconstruction
The risks of an ACL reconstruction procedure include, but are not limited to, the following:
- Temporary or permanent injury to the nerves and blood vessels around the knee
- Excessive joint stiffness
- Immune system reactions to donated tissue or suture materials (very low risk)
- Disease transmission from the donated tissue (extremely low risk)
- Failure of the reconstructed ligament
- Need for additional surgeries
- Anesthesia complications
Our experienced and cautious surgical team uses special techniques to minimize all the above risks. Although adverse events following this surgical procedure are rare, they can occur and cannot be completely eliminated.
What is the difference between ACL repair and reconstruction?
A surgical repair of the ACL refers to affixing the injured ligament back to the tibia or femur from which it has been torn. In rare cases, the ligament may have pulled off of the bone and may have taken a small piece of bone with it. In such cases, the surgeon can suture the ligament or screw the bone back down and restore some, if not all, of the ACL's function.
However, a torn ACL is rarely able to be “repaired” because during most tears, the ligament tears at its midpoint, like a frayed rope. Over time, the ligament may become completely disabled. Even if partially intact, a torn ACL sustains tissue damage and repair of the original ligament has shown to provide relatively poor functional results.
Reconstruction of the ACL involves rebuilding it using a new ligament. The surgeon creates a soft tissue substitute for the ligament, called a graft, that re-establishes knee stability and provides a scaffold. Miraculously, the patient’s body will recognize this graft scaffold, populate it with living cells and permanently attach it in place. Over a relatively short time (about four to six months), this new ligament will take on the appearance and function of the normal ACL. The functional results of ACL reconstruction are predictably excellent, and the overwhelming majority of patients are able to get back to the same or higher degree of athletic activity without pain or instability.
Timing in Reconstructing the ACL
Reconstruction of the ACL is not an emergency. It is actually recommended to wait at least a few weeks after the initial injury to allow the inflammation to decrease and for the patient to regain full range of motion in the knee. This will contribute to a more successful return of motion and muscle strength after the surgical procedure. Additionally, it is best not to wait an extended period of time before undergoing an ACL reconstruction. Since the knee is most likely unstable, it is important to reduce the risk of injury to other knee structures, such as the menisci, collateral ligaments and articular cartilage. A chronically unstable knee can predispose an individual to early arthritis, but it must be noted that arthritis cannot necessarily be avoided by undergoing ACL reconstruction.
ACL Graft Selection
There are two main types of grafts: tissue taken from the patient’s own body (autograft) and donated tissue from organ donors (allograft).
The best type of graft used to reconstruct the ACL depends on a variety of patient factors. There is not one ideal graft that is perfect for every patient. Graft selection should be individualized for each patient based on the advantages and disadvantages of the graft type as well as the patient’s age, lifestyle, activity level and any other associated injuries.
Patellar Tendon Autograft
The bone-patellar tendon-bone autograft, or BPTB, is widely used for ACL reconstruction. The graft is made up of the middle third of the patellar tendon with bone from the top surface of the patella (kneecap) on one end, and bone from the tibia (shinbone) on the other end. BPTB autografts have been used for a long time and have an established track record. The advantages of this type of graft include its ability to reliably restore knee stability, fast incorporation rate and low rate of re-tearing. Potential disadvantages include temporary or permanent pain at the front of the knee, slight loss of motion, a larger incision and more pain immediately after surgery. BPTB is typically recommended for high-level or elite athletes and individuals who have had failed previous ACL reconstructions. Its use should be avoided in patients who have patellar tendonitis, patellofemoral syndrome and individuals who frequently kneel (gardeners, floor installers, plumbers, etc.) or engage in long-distance/repetitive running such as marathoners.
Hamstring Tendon Autograft
Two of the five hamstring tendons (the semitendinosus and the gracilis) are commonly used to reconstruct the ACL. There is no bone harvested with the hamstring tendons, and therefore, the pain immediately after surgery is less in comparison to BPTB autografts. Other advantages to using hamstring autografts include restoring knee stability, a smaller incision and decreased likelihood of long-term knee pain. The disadvantages are that the reconstructed ligament is not as strong as the BPTB graft, there is a slower rate of graft incorporation and healing and a slight loss in hamstring strength when the knee is at its end range of flexion (bending). Hamstring autograft is typically used in younger individuals who are active and in those who do a lot of kneeling. This graft should be avoided in patients who have very flexible joints throughout their body, have an associated MCL sprain.
Quadriceps Tendon Autograft
This graft uses bone from the kneecap and some of the quadriceps (thigh) tendon and has bone on one end and soft tissue on the other end. This graft is not as widely used, but has a very reliable track record. The advantages include less long-term knee pain compared to BPTB, reliable strength and bony healing at one end. The initial pain may be more than with a hamstring autograft, but it's typically less than what is experienced by a BPTB autograft patient.
In addition to BPTB, hamstring and quadriceps allografts, other tendon grafts are also used, such as the Achilles, tibialis anterior and tibialis posterior. An advantages of allografts is the elimination of donor site pain. However, there are theoretical risks of disease transmission from the donated tissue. Nationally, this risk is about 1:1.5 million for HIV transmission and about 1:470,000 for hepatitis transmission. Donated allografts DO NOT result in a significant immune response and patients do not have to take medication to fight rejection. Allografts tend to have residual laxity (looseness) and therefore have a higher re-rupture rate than BPTB, hamstring and quadriceps tendon autografts. Allografts should be avoided in high-activity individuals and are best suited for older, less active patients.
In general, for young competitive and highly active individuals, BPTB is recommended. For young patients who are not involved in competitive sports or older patients who are highly active, hamstring autograft is suggested. For older patients who participate in low-impact activities, hamstring autograft or allograft is typically recommended.
Technical Details of Minimally Invasive ACL Reconstruction
First, three very small (1cm) incisions are made at the front of the knee. Through these small incisions, the arthroscopic camera and specially designed instruments can enter the knee. The knee joint is continuously irrigated with sterile saline, which “inflates” the joint with clear fluid.
The surgeon will maneuver the camera around the entire joint to evaluate all of the important structures in the joint (e.g. ligaments, meniscus, cartilage and bone) and determine if there are any other injuries that may need to be addressed during the surgery. Most often, the surgeon will take photographs and video to help explain to the patient what was found and how it was corrected.
The damaged ACL will then be removed from the knee with small arthroscopic instruments. Sockets or tunnels for the new ACL will be drilled into the tibia (shinbone) and femur (thigh bone). The new ACL graft will then be secured into the two bone tunnels so that it crosses the joint where the injured ligament used to belong.
Length of Surgery
The procedure takes approximately one to two hours to complete. After the procedure, the patient can expect to spend one or two hours in the recovery room and anticipate going home on the same day of surgery.
Recovery from ACL Reconstruction
Patients rarely need to spend the night in the hospital after an ACL reconstruction and can usually plan on going home the same day as the surgery.
Immediately after the surgery, the patient is placed in a hinged brace. This braces allows the patient to bend and straighten their knee. It is typically worn for five to six weeks after surgery. Depending on the surgeon's preference and whether other are procedures performed, the patient can usually put some weight on the operated leg with the help of crutches.
Postoperative physical therapy for a reconstructed ACL is mandatory. The primary objective is to provide a safe environment where the patient can return to normal function without compromising the ACL repair. Rehabilitation takes place in these controlled phases:
Weeks 0 - 2 - The first two weeks of recovery are devoted to achieving successful pain control, allowing the incisions to heal, decreasing swelling and restoring knee motion. Strengthening the muscles in the leg also begins with simple exercises that focus on the quadriceps (thigh) muscles. During this time, the patient will be allowed to bear weight on the operative leg with or without the assistance of crutches. It is imperative that the individual remains in the knee brace while walking.
Weeks 2 - 6 - During this time, physical therapy will focus on preventing muscle atrophy (shrinking), maintaining and increasing range of motion, progressing to full weight bearing without crutches, but while wearing the knee brace and improving muscle control. Patients begin using an exercise bicycle during this time.
Weeks 6 - 12 - In this stage of rehabilitation, the physical therapist will provide exercises that increase muscle strength, stability and endurance. Additionally, the patient will be working on balance and performing exercises on an elliptical machine.
Weeks 12 - 24 - At this stage the patient will be progressing to functional activities. Individuals can expect to be running within15 to 18 weeks and performing agility and cutting movements after 24 weeks.
Read more about physical therapy at our Orthopedic and Sports Medicine Rehabilitation Program.