Arthroscopic Anterior Cruciate Ligament (ACL) Reconstruction (Hamstring Graft)

The anterior cruciate ligament (ACL) is one of the most commonly injured knee ligaments. Generally, the incidence of ACL injury is higher in people who participate in high-risk sports, such as basketball, football, skiing, and soccer. About half of the ACL injuries occur in combination with damage to the meniscus, articular cartilage, or other ligaments. Patients may also have bone bruises of beneath the cartilage surface, which may be seen on a MRI scan and may indicate injury to the overlying articular cartilage.

Anterior cruciate ligament (ACL) reconstruction is a surgical procedure that replaces the injured ACL with a substitute tissue graft, and A/Prof Woodgate prefers to use the hamstring tendons.

The anterior cruciate ligament is one of the four major ligaments of the knee that connects the femur (thigh bone) to the tibia (shin bone) and aids in stabilising the knee joint. The ACL prevents excessive forward movement of the tibia in relation to the femur, as well as limits rotational movements of the knee.

A tear of this ligament can make you feel as though your knee is unreliable and will not permit you to move or even hold you up. Anterior cruciate ligament reconstruction is surgery to reconstruct the torn ligament of your knee with a tissue graft.

Causes

An ACL injury most commonly occurs during sports that involve twisting or overextending your knee, particularly if there is an associated load to the knee. An ACL can be injured in a number of ways:

Sudden directional change
Slowing down while running
Landing from a jump incorrectly
Direct blow to the side of your knee, such as during a football tackle.

Several studies have shown that female athletes have a higher incidence of ACL injury than male athletes in certain sports, and it has been proposed that this is due to differences in physical conditioning, muscular strength, and neuromuscular control. Other hypothesized theories of this gender-related difference in ACL injury rates include pelvis and lower extremity (leg) alignment, increased ligamentous laxity, and the effects of oestrogen on ligament properties.

Symptoms

When the ACL is injured, a loud "pop" sound may be heard and you may feel the knee buckle. Within hours of injury, the knee may swell due to bleeding from vessels within the torn ligament. You may notice that the knee feels unstable or unreliable and seems to give way, especially when trying to change direction on the knee. Patients may also report a loss of full range of motion, pain or tenderness along the joint line and discomfort while walking.

Diagnosis

Most ACL injuries can be diagnosed with a thorough history, physical examination of the knee, and diagnostic tests such as X-rays, MRI scans and arthroscopy. X-rays may be needed to rule out any associated fractures. A specific examination test (Lachman test) will demonstrate increased forward movement of the tibia and a soft or mushy endpoint in an ACL injured knee compared to a healthy knee. The pivot shift test is another test to assess an ACL tear. During this test, if the ACL is torn, the tibia will move forward when the knee is completely straight and as the knee bends past 30° the tibia moves back into correct place in relation to the femur.

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Natural History

The natural history of an ACL injury without surgical intervention varies from patient to patient and depends on the patient's activity level, degree of injury and instability symptoms.

The prognosis for a partially torn ACL is often favourable, with the recovery and rehabilitation period usually at least 3 months, though some patients with partial ACL tears may still have instability symptoms.

Complete ACL ruptures have a much less favourable outcome without surgery. After a complete ACL tear, some patients are unable to participate in cutting or pivoting-type sports, though there are some rare individuals who can participate in sports without any symptoms of instability. This variability is related to the severity of the original knee injury, as well as the physical demands of the patient.

About half of ACL injuries occur in combination with damage to the meniscus, articular cartilage or other ligaments. The "unhappy triad," frequently seen in football players and skiers, consists of injuries to the ACL, the MCL, and the medial meniscus. Secondary damage to these other knee structures may occur in patients who have repeated episodes of instability due to ACL injury. With chronic instability, a large majority of patients will have meniscus damage when reassessed 10 or more years after the initial injury. Similarly, the prevalence of articular cartilage lesions increases in patients who have a 10-year-old ACL deficiency.

Surgical Treatment

ACL tears are not usually repaired using suture to sew it back together, because repaired ACLs have generally been shown to fail over time. Therefore, the torn ACL is generally replaced by a substitute tendon graft, with options including:

Hamstring tendon autograft (autograft comes from the patient)
Patellar tendon autograft
Quadriceps tendon autograft
Allograft (taken from a cadaver) patellar tendon, Achilles tendon, semitendinosus, gracilis, or posterior tibialis tendon.

In young children or adolescents with ACL tears, early ACL reconstruction creates a possible risk of growth plate injury, leading to bone growth irregularities or problems. ACL surgery may need to be delayed until the child is closer to skeletal maturity, or a modified ACL surgery technique is used to decrease the risk of growth plate injury.

In cases of combined injuries, surgical treatment generally produces better outcomes. As many as half of meniscus tears may be repairable and may heal better if the repair is done in combination with the ACL reconstruction.

Surgical Procedure (Hamstring Tendons)

Before any surgical treatment, the patient is usually sent to physiotherapy. Patients who have a stiff, swollen knee lacking full range of motion at the time of ACL surgery may have significant problems regaining motion after surgery. It usually takes at least three or more weeks from the time of injury to regain full range of motion. Associated ligament injuries may need a brace and time to heal prior to ACL surgery.

The semitendinosus hamstring tendon on the inner side of the knee is used in creating the hamstring tendon autograft for ACL reconstruction, usually combined with an additional tendon, the gracilis, which is attached below the knee in the same area. This creates a four-strand tendon graft (once they 2 tendons are folded). Proponents of the hamstring graft technique claim there are fewer problems associated with harvesting of the graft compared to the patellar tendon autograft including:

Fewer problems with anterior knee pain or kneecap pain after surgery
Less postoperative stiffness problems
Smaller incision
Faster recovery

The goal of ACL reconstruction surgery is to tighten the knee and restore its stability.

The procedure is performed under general anaesthesia. Two small cuts about 5mm long are made for the portals of the arthroscope used for assistance with the procedure. An arthroscope, a tube with a small video camera on the end, is inserted through one incision to see the inside of the knee joint. Along with the arthroscope, a sterile solution is pumped into the joint to expand it enabling the surgeon to have a clear view and space to work inside the joint. The knee is bent at right angles and the hamstring tendons felt on the upper inner tibia region. A small incision is made over the hamstring tendon attachment to the tibia and the two tendons (semitendinosus and gracilis) are stripped off the muscle and the graft is prepared separately. The torn ACL stump will be removed and the path for the new ACL graft is prepared. Small holes are drilled into the femur and tibia using alignment guides and arthroscopic assistance. The holes form tunnels to accept the new graft. Then the graft is pulled through the predrilled holes in the tibia and femur. The new tendon is then fixed into the bone with screws and or pins/staples to hold it into place while the ligament heals into the bone. Before the surgery is complete, the graft is assessed to make sure it has good tension, verify that the knee has full range of motion and no impingement occurs during range of motion. The incisions are then closed with sutures and sterile pressure dressings are applied.

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Post-Operative Care

Following the surgery, rehabilitation begins immediately. Much of the success of ACL reconstructive surgery depends on the patient's dedication to rigorous physical therapy. The physiotherapist will teach you specific exercises to be performed to strengthen the leg and restore knee movement. Competitive sports are avoided for 5 to 6 months. This allows time for the new graft to incorporate into the knee joint, and to allow time to regain full knee range of motion, muscle strength, endurance, and restoration of full functional use of the leg. The patient's sense of balance and control of the leg must also be restored through exercises designed to improve neuromuscular control. This usually takes 4 to 6 months.

Risks and Complications

Possible risks and complications associated with ACL reconstruction using hamstring grafts include:

Numbness
Infection – incidence is very low
Bleeding - Rare risks include bleeding from acute injury to the popliteal artery
Blood clots (Deep vein thrombosis)
Nerve and blood vessel damage
Failure of the graft
Loosening of the graft – due to re-rupture or stretching of the reconstructed ligament
Decreased range of motion
Crepitus (crackling or grating feeling of the kneecap)
Pain in the knee
Repeat injury to the graft.
Growth plate injury - In young children or adolescents with ACL tears, early ACL reconstruction creates a possible risk of growth plate injury, leading to bone growth problems. The ACL surgery can be delayed until the child is closer to reaching skeletal maturity. Alternatively, the technique of ACL reconstruction may be modified to decrease the risk of growth plate injury.
Extensor mechanism failure - Rupture of the patellar tendon (patellar tendon autograft) or patella fracture (patellar tendon or quadriceps tendon autografts) may occur due to weakening at the site of graft harvest.
Kneecap pain. - Postoperative anterior knee pain is especially common after patellar tendon autograft ACL reconstruction. The incidence of pain behind the kneecap varies greatly in studies, whereas the incidence of kneeling pain is often higher after patellar tendon autograft ACL reconstruction.
Viral transmission - Allografts specifically are associated with risk of viral transmission, including HIV and Hepatitis C, despite careful screening and processing. The chance of obtaining a bone allograft from an HIV-infected donor is calculated to be less than 1 in a million.

Other Surgical Choices

Patellar Tendon Autograft

The middle third of the patellar tendon of the patient, along with a bone plug from the tibia (shinbone) and the patella (kneecap) is used in the patellar tendon autograft. It may be recommended for high-demand athletes and patients whose jobs do not require a significant amount of kneeling.

In studies comparing outcomes of patellar tendon and hamstring autograft ACL reconstruction, the rate of graft failure was lower in the patellar tendon group. In addition, most studies show equal or better outcomes in terms of postoperative tests for knee laxity (Lachman's, anterior drawer and instrumented tests) when this graft is compared to others. However, patellar tendon autografts have a greater incidence of postoperative patellofemoral pain (pain behind the kneecap) complaints and other problems.

The pitfalls of the patellar tendon autograft are:

Postoperative pain behind the kneecap
Pain with kneeling
Slightly increased risk of postoperative stiffness
Low risk of patella fracture.

Quadriceps Tendon Autograft

The quadriceps tendon autograft may be used for patients who have already failed ACL reconstruction. The middle third of the patient's quadriceps tendon and a bone plug from the upper end of the patella (kneecap) are used. This yields a larger graft for taller and heavier patients. As there is a bone plug on one side only, the fixation is not as solid as for the patellar tendon graft. There is a high association with postoperative anterior knee pain and a low risk of patella fracture. Patients may find the incision is not cosmetically appealing.

Allografts

Allografts are grafts taken from cadavers. These grafts are also used for patients who have failed ACL reconstruction before and in surgery to repair or reconstruct more than one knee ligament. Advantages of using allograft tissue include elimination of pain caused by obtaining the graft from the patient, decreased surgery time and smaller incisions. The patellar tendon allograft allows for strong bony fixation in the tibial and femoral bone tunnels with screws.

However, allografts are associated with a risk of infection, including viral transmission (HIV and Hepatitis C), despite careful screening and processing. Several deaths linked to bacterial infection from allograft tissue (due to improper procurement and sterilization techniques) have led to improvements in allograft tissue testing and processing techniques. There have also been conflicting results in research studies as to whether allografts are slightly more susceptible to graft elongation (stretching), which may lead to increased laxity during testing. Some published literature may point to a higher failure rate with the use of allografts for ACL reconstruction. Higher failure rates for allografts have been reported in young, active patients returning to high-demand sporting activities after ACL reconstruction, compared with autografts. The reason for this higher failure rate is unclear. It may be due to graft material properties (sterilization processes used, graft donor age, storage of the graft), or it could possibly be due to an ill-advised earlier return to sport by the athlete because of a faster perceived physiologic recovery, when the graft is not biologically ready to be loaded and stressed during sporting activities.