This article provides detailed information on anterior cruciate ligament (ACL) injuries. The following discusses ACL anatomy and the pathophysiology of an ACL tear, as well as treatment options for ACL injuries. ACL tear surgery techniques and rehabilitation, potential complications, and outcomes are also included. This page is intended to assist the patient in making an informed decision about how to manage an ACL injury.

The anterior cruciate ligament (ACL), which is the dense connective tissue that runs through the knee and connects the femur (thigh bone) to the tibia (shin bone), is the most essential of the four ligaments that connect the two. It is one of the most injured ligaments in the knee because it provides structural support during strenuous activity. People who participate in high-risk activities such as football, soccer, basketball, and skiing are more likely to sustain ACL tears.

In essence, the knee is a hinged joint that is held together by the medial collateral (MCL), lateral collateral (LCL), anterior cruciate (ACL) and posterior cruciate (PCL) ligaments. The ACL runs diagonally in the centre of the knee, preventing the tibia from sliding out in front of the femur, along with providing rotational stability to the knee. A layer of articular cartilage covers the weight-bearing surface of the knee. The medial meniscus and lateral meniscus are on either side of the joint, between the cartilage surfaces of the femur and tibia. These menisci function as shock absorbers and work with the cartilage to reduce the stresses between the tibia and femur. That’s why when an individual sustains an ACL tear, they will have difficulty using their knee down to the foot.

About half of all ACL tears occur along with damage to the meniscus, articular cartilage, or other ligaments. In addition, patients may have bruises of the bone beneath the cartilage surface. These bruises may be detected on a magnetic resonance imaging (MRI) scan and may indicate injury to the overlying articular cartilage.

According to studies, non-contact mechanisms such as pivoting, sidestepping techniques, and uncomfortable landings cause the majority of ACL injuries. A lesser percentage is caused by physical contact with another object or player.

In several sports, studies have even indicated that female athletes have a higher rate of ACL tears than male athletes. This is thought to be due to differences in muscular strength, physical conditioning, and neuromuscular control.

Some symptoms that patients experience after an ACL injury include:

• Pain and swelling along the joint
• Knee feeling unstable
• Stiffness and loss of full range of motion
• Discomfort while doing daily activities such as walking, squatting, and kneeling.

During the clinical evaluation, the doctor may conduct X-rays to examine for any possible fractures. A magnetic resonance imaging (MRI) scan may also be conducted to evaluate the ACL and check for any evidence of injury to the other knee ligaments, meniscus cartilage or articular cartilage. Depending on the severity of the tear, an ACL surgery may or may not be required.

On top of performing special tests for identifying meniscus tears and injury to other ligaments of the knee, the physician will usually perform the Lachman’s test to see if the ACL is intact.

If the ACL is torn, the examiner will feel increased forward (upward or anterior) movement of the tibia in relation to the femur. This is especially so when compared to the normal leg. A soft, mushy endpoint will also be felt when this movement ends.

ACL injuries can have various treatments depending on the degree of damage. In Singapore, ACL tear surgery and non-surgical operations can be used to heal and rehabilitate a patient suffering from an ACL tear.

In non-surgical treatment, progressive physical therapy and rehabilitation can restore the knee’s condition close to its pre-injury state. The patient can also be educated on how to prevent instability and be made to use a hinged knee brace. However, many who opt out of ACL surgery may experience secondary injury to the knee because of episodes of instability.

ACL surgery in Singapore is usually advised in the case of mixed injuries, in which the ACL tears in conjunction with other knee problems. For patients with isolated ACL rupture, nonsurgical treatments are likely to be helpful or may be recommended, such as:

• Those with partial tears and no signs of instability
• Those with complete tears and no symptoms of knee instability during low-impact sports, who are willing to give up high-impact sports
• Those who live sedentary or do light manual work
• Children, whose growth plates are still open

Normally, ACL tears are not repaired using suture to sew them back together, because repaired ACLs have mostly been shown to fail over time. As such, the torn ACL is usually replaced by a substitute graft made of a tendon during ACL tear surgery.

• Patellar tendon autograft (autograft comes from the patient)
  In a patellar tendon autograft, the middle third of the patellar tendon of the patient, a bone plug from the shin and the kneecap are used.
  This method is usually recommended for high-demand athletes and patients whose jobs do not require a significant amount of kneeling. Studies comparing the results of the patellar tendon and hamstring autograft ACL reconstruction have shown that the rate of graft failure was lower in the patellar tendon group. Additionally, most studies show equal or better outcomes in terms of postoperative tests for knee laxity (such as Lachman’s, anterior drawer and instrumented tests) when this graft is compared to others. However, there is a greater incidence of postoperative patellofemoral pain (pain behind the kneecap) complaints and other problems with patellar tendon autografts. This means that patellar tendon autograft has drawbacks as well, such as knee soreness, postoperative pain behind the kneecap, slightly higher postoperative stiffness risk, and a low chance of patella fracture.
• Hamstring tendon autograft
  The semitendinosus hamstring tendon on the inner side of the knee is used in creating the hamstring tendon autograft for ACL reconstruction surgery. An additional tendon, the gracilis, which is attached below the knee in the same area, is used by some surgeons. This creates a two- or four-strand tendon graft.
  Advocates of this method claim there are fewer problems associated with harvesting of the graft compared to the patellar tendon autograft such as a faster recovery and smaller incisions needed. Furthermore, there are fewer problems with anterior knee pain or kneecap pain after ACL surgery and fewer postoperative stiffness problems. Since the graft does not have bone plugs, its function may be limited by the strength and type of fixation in the bone tunnels. There have been contradictory results in research studies as to whether hamstring grafts are slightly more prone to graft elongation (stretching), which may cause increased laxity during objective testing. In recent times, some studies have also found decreased hamstring strength in patients post-surgery. There is also certain evidence that patients with intrinsic ligamentous laxity and knee hyperextension of 10 degrees or more may face a higher risk of postoperative hamstring graft laxity on clinical exams. As such, some clinicians suggest the use of patellar tendon autografts for ACL surgery of hypermobile patients instead. Furthermore, since the medial hamstrings frequently provide dynamic support against instability and valgus stress, certain surgeons feel that chronic or residual medial collateral ligament laxity (grade 2 or more) at the time of ACL reconstruction surgery may be a contraindication for use of the patient’s own semitendinosus and gracilis tendons as an ACL graft.
• Quadriceps tendon autograft
  The quadriceps tendon autograft is normally used for patients who have previously failed ACL reconstruction surgery. The middle third of the patient’s quadriceps tendon and a bone plug from the upper end of the knee cap is used. This yields a larger graft for heavier patients.
  However, because there is a bone plug on only one side, the fixation is not as solid as for the patellar tendon graft. As a result, there is a high association between postoperative anterior knee pain and a low risk of a patella fracture. On top of that, patients may find that the incision is not cosmetically appealing.
• Allograft (taken from a cadaver)
  Patellar tendon, Achilles tendon, semitendinosus, gracilis, or posterior tibialis tendon- these grafts are used for patients who have previously failed ACL reconstruction surgery and in surgery to repair or reconstruct more than one knee ligament.
  Some advantages of using allograft tissue include smaller incisions, shorter surgery time and the elimination of pain caused by obtaining the graft from the patient. The patellar tendon allograft allows for strong bony fixation in the tibial and femoral bone tunnels with screws.
  Unfortunately, the downside to allografts is that they are associated with a risk of infection, including viral transmissions such as 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 caused improvements in processing techniques and the testing of allograft tissue. In addition, there are contradictory results from studies as to whether allografts are slightly more prone to graft elongation (stretching), which may cause increased laxity during testing. There are some pieces of published literature that may state that the use of allografts for ACL reconstruction surgery has a higher failure rate. There have been certain reports of higher failure rates for allografts in young, active patients returning to high-impact sporting activities after ACL reconstruction as compared to autografts. However, the exact reason for this higher failure rate is not known. It could possibly be due to graft material properties such as graft donor age, sterilization processes used and storage of the graft. On the other hand, it could also be due to an ill-advised earlier return to sport by the athlete. This could be because of a faster perceived physiologic recovery, when in fact the graft is not biologically ready to be loaded and stressed during sporting activities. Further research in this area is still ongoing.

Physical therapy is usually administered prior to the start of any surgical operation. This is because patients who have a stiff, swollen knee with a limited range of motion at the time of ACL surgery may have trouble regaining motion after the procedure. It normally takes three weeks or more to achieve a complete range of motion after an accident. Other ligament injuries should also be braced and allowed to heal prior to ACL surgery.

The patient, surgeon, and anesthesiologist will next decide on the type of anaesthetic to utilise during the procedure. The patient may benefit from an anaesthetic block of the leg nerves to reduce postoperative pain.

To start off the ACL surgery, the knee is examined to verify that the ACL is torn and also to check for looseness of other knee ligaments that may need to be repaired during ACL surgery or addressed after the operation.

If this physical examination strongly suggests a tear in the ACL, the selected tendon is then either harvested (for an autograft) or thawed (for an allograft). Afterwards, the graft is prepared to the right size for the patient.

Once the graft has been prepared, the surgeon places an arthroscope into the joint. Tiny incisions of one centimetre, called portals, are made in front of the knee. The arthroscope and the instruments are then inserted into the incision for the surgeon to examine the condition of the knee. The meniscus and cartilage injuries are trimmed or repaired and the torn ACL stump is removed.

In the most common method of ACL reconstruction surgery, bone tunnels are drilled into the tibia and femur to position the ACL graft where the torn ACL previously was. Then, a long needle is passed through the tunnel of the tibia, up through the femoral tunnel, and then out through the skin of the thigh. The sutures of the graft are placed through the eye of the needle and the graft is pulled into place up through the tibial tunnel, and then up into the femoral tunnel. This graft is held under tension as it is fixed in position using interference screws, spiked washers, staples or posts. Generally, these devices that are used to hold the graft in place are not removed.

There are variations to this surgical procedure such as the “over-the-top”, “double-bundle” and “two-incision” types of ACL reconstructions. They may be used according to the surgeon’s preference or special circumstances, such as revision ACL reconstruction surgery or open growth plates.

Right before completing the procedure, the surgeon will probe the graft to ensure it has good tension, verify the knee has a full range of motion and conduct tests such as the Lachman’s test to assess graft stability. Finally, the skin is closed and dressings are applied. Depending on the surgeon’s preference, a postoperative brace and cold therapy device may also be used. Normally, patients are able to go home on the same day of surgery.

Pain Management after an ACL Surgery

It is natural to feel some pain after the ACL surgery as this is a normal part of the healing process. The doctor and nurses will help to ease and reduce the pain, which can assist in a speedier recovery.

Typically, medications are prescribed for short-term pain relief after an ACL surgery. There are various types of medications available to help manage pain. They include opioids, local anaesthetics and non-steroidal anti-inflammatory drugs (NSAIDs). A combination of these medicines may be used to improve pain relief and also minimize the need for opioids.

One should be aware that even though opioids are used to help relieve pain after an ACL surgery, they are a narcotic acid and can be addictive. In the U.S., opioid dependency and overdose have even become a critical public health concern. It is thus crucial to use opioids only as instructed by a doctor. The usage of opioids should come to a halt once the pain begins to subside. If the pain has not started to improve within a few days after surgery, one should consult a doctor.

Post ACL Surgery Rehabilitation

An essential part of successful ACL surgery is physical therapy, with exercises starting immediately after the operation. A large portion of the success of ACL reconstructive surgery is dependent on the patient’s commitment to rigorous physical therapy. As there are now new surgical techniques and stronger graft fixation, physical therapy nowadays uses an accelerated course of rehabilitation.

Postoperative course

Within the first 10 to 14 days after the ACL surgery, the wound is kept dry and clean. Early emphasis is placed on regaining the ability to straighten the knees completely and restore quadriceps control.

The knee will be iced consistently to reduce pain and swelling. Depending on the surgeon, a postoperative brace and machine to move the knee through its range of motion may be used. Other than that, the physician also determines the weight-bearing status, which is the use of crutches to keep some or all of the patient’s weight off of the surgical leg, as well as other injuries addressed during surgery.

Rehabilitation

The goals of the rehabilitation of ACL reconstruction surgery include regaining full range of motion of the knee, reducing knee swelling, strengthening the quadriceps and hamstring muscles as well as maintaining mobility of the kneecap.

Only when there is no longer pain or swelling, full knee range of motion has been achieved, and when muscle strength, endurance and functional use of the leg have been fully restored can the patient return to sporting activities.

Over the course of 4 to 6 months, the patient’s sense of balance and control of the leg should also be restored through exercises designed to improve neuromuscular control. Generally, the use of a functional brace when returning to sports is not necessary after successful ACL reconstruction surgery. However, some patients may feel more secure by wearing one.

Rehabilitation and proper resting are essential after an ACL tear surgery. Some of the possible complications post-surgery are as follows:

Infection

Although the incidence of infection after arthroscopic ACL reconstruction surgery is very low, there have been reports of deaths linked to bacterial infection from allograft tissue. This is due to improper procurement and sterilization techniques.

Viral transmission

Allografts, in particular, are linked to risks of viral transmission, including HIV and Hepatitis C. This is in spite of careful screening and processing. However, the chances of getting a bone allograft from an HIV-infected donor is said to be less than 1 in a million.

Numbness and bleeding

There are low risks of bleeding from acute injury to the popliteal artery and weakness paralysis of the leg or foot after an ACL surgery. Although, it is not rare to have numbness of the outer part of the upper leg next to the incision, which may be temporary or permanent.

Blood clots

Even though this is rare post ACL surgery, a blood clot in the veins of the calf or thigh is a potentially life-threatening issue. A blood clot may break off into the bloodstream and travel to the lungs, causing a pulmonary embolism. It could also travel to the brain, leading to a stroke.

Instability

It might be possible for recurrent instability to occur. This may be due to rupture or stretching of the reconstructed ligament or poor surgical technique.

Stiffness

Stiffness is the feeling of difficulty in motion or the apparent loss of range of motion. It is sometimes accompanied by pain or swelling. Some patients have reported a loss of motion or stiffness in the knee after surgery.

Extensor mechanism failure

Rupture of the patellar tendon (patellar tendon autograft) or patella fracture (patellar tendon or quadriceps tendon autografts) may occur because of weakening at the site of graft harvest.

Growth plate injury

This is particularly applicable to young children or adolescents with ACL tears. Early ACL reconstruction creates a possible risk of growth plate injury, which can cause bone growth problems. The ACL surgery can be delayed until the child is closer to skeletal maturity. Alternatively, the technique of ACL reconstruction may be modified to lower the risk of growth plate injury.

Kneecap pain

Lastly, postoperative anterior knee pain is especially common after patellar tendon autograft ACL reconstruction surgery. The incidence of pain behind the kneecap varies widely in studies, while the incidence of kneeling pain is usually found to be higher after patellar tendon autograft ACL reconstruction.