The ACL Injury
What is an ACL Injury?
Anterior cruciate ligament. ACL, injuries are injuries to a ligament that connects the upper leg bone (femur) with the lower leg bone (tibia). An ACL injury may result in the knee occasionally buckling or giving out. An ACL injury can be a partial or complete tear of the ligament, a separation of the ligament from the upper or lower leg bone (avulsion), or a separation of the ligament and part of the bone from the rest of the bone (avulsion fracture). Other parts of the knee can be injured at the same time, including the pads that cushion the knee joints (menisci), another knee ligament, or the tissue that covers the ends of bones (cartilage).
Why are knee injuries so common?
The knee is particularly vulnerable to injury. It is the joint between the two longest bones of the body, and the entire weight of the body is transferred to the foot through the knee. The knee is also more prone to injury because its stability decreases as it bends. The menisci and the ligaments provide less effective support to the bent knee. Typically an ACL injury occurs when the knee is straightened beyond its normal limits (hyperextended), twisted, or bent side to side. This may happen when changing direction rapidly, which, as mentioned above, commonly occurs in sports that require stop-and-go movements. Symptoms of a sudden ACL injury may include feeling or hearing a pop in the knee at the time of injury, pain, swelling, and a feeling that the knee may buckle or give out.
An ACL injury may develop into chronic (long-lasting and recurrent) ACL deficiency, resulting in greater knee looseness, having the knee occasionally give out, and sliding of the bones. This abnormal sliding can lead to premature osteoarthritis.
Here is a little more detail from the AAOS Website
The weight-bearing surface of the knee is covered by a layer of articular cartilage. On either side of the joint, between the cartilage surfaces of the femur and tibia, are the medial meniscus and lateral meniscus. The menisci act as shock absorbers and work with the cartilage to reduce the stresses between the tibia and the femur.
It is estimated that 70 percent of ACL injuries occur through non-contact mechanisms while 30 percent result from direct contact with another player or object. The mechanism of injury is often associated with deceleration coupled with cutting, pivoting or sidestepping maneuvers, awkward landings or "out of control" play. Several studies have shown that female athletes have a higher incidence of ACL injury than male athletes in certain sports. It has been proposed that this is due to differences in physical conditioning, muscular strength, and neuromuscular control. Other hypothesized causes of this gender-related difference in ACL injury rates include pelvis and lower extremity (leg) alignment, increased ligamentous laxity and the effects of estrogen on ligament properties.
Injury Pathology
Immediately after the injury, patients usually experience pain and swelling and the knee feels unstable. Within a few hours after a new ACL injury, patients often have a large amount of knee swelling, a loss of full range of motion, pain or tenderness along the joint line and discomfort while walking.
In addition to performing special tests for identifying meniscus tears and injury to other ligaments of the knee, the physician will often 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 (especially when compared to the normal leg) and a soft, mushy endpoint (because the ACL is torn) when this movement ends.
Another test for ACL injury is the Pivot Shift Test. In this test, if the ACL is torn, the tibia will start forward when the knee is fully straight and then will shift back into the correct position in relation to the femur when the knee is bent past 30 degrees.
Approximately 50 percent of ACL injuries occur in combination with damage to the meniscus, articular cartilage, or other ligaments. Additionally, patients may have bone bruises of the bone beneath the cartilage surface. These may be seen on an MRI and may indicate injury to the overlying articular cartilage.
What does the inside of the knee look like and where is the ACL?
Move your mouse over the highlighted text to see the different structures of the knee. 
The Knee contains Bones, Muscles, Cartilage, Ligaments, as well as nerves, and blood vessels. A fibrous joint capsule made of collagen surrounds the joint and encircles the end of each bone to give the knee stability
Images from The Steadman-Hawkins Clinic
Treatment for ACL injuries depends on the severity of the knee injury and a person's activity level. Treatment includes physical rehabilitation or surgery plus rehabilitation.
Nonoperative treatment:
- May be used because of a patient's age or overall low activity level.
- May be recommended if the overall stability of the knee seems good.
- Involves a treatment program of muscle strengthening, often with the use of a brace to provide stability.
Operative treatment (either arthroscopic or open surgery):
- Uses a strip of tendon, usually taken from the patient's knee (patellar tendon) or hamstring muscle, that is passed through the inside of the joint and secured to the thighbone and shinbone.
- Is followed by an exercise and rehabilitation program to strengthen the muscles and restore full joint mobility.
So lets look at the surgical procedure.
The surgery usually begins with an examination of the patient's knee while the patient is relaxed due the effects of anesthesia. This final examination is used to verify that the ACL is torn and also to check for looseness of other knee ligaments that may need to be repaired during surgery or addressed postoperatively. If the physical exam strongly suggests the ACL is torn, the selected tendon is harvested (for an autograft) or thawed (for an allograft) and the graft is prepared to the correct size for the patient.
The ACL Graft
There are a number of choices available to the orthopedic surgeon in determining how best to reconstruct the torn ACL. They all involve a "graft" using something to substitute for the torn ACL.
Each of the available ACL graft tissue choices requires a unique harvesting technique. Furthermore, there are usually different methods used for fixing the grafts in the bone tunnels, depending on the characteristics and properties of the tissue selected. Because of these differences in graft techniques, the type of surgery chosen is frequently made by the surgeon based on his or her experience and comfort level with the chosen technique.
Typically, an ACL reconstruction takes two to two and a half hours. The anesthesia may be general anesthesia or a spinal anesthesia. General anesthesia allows the individual to be asleep through the entire procedure. Spinal anesthesia involves an injection in the back that numbs only the lower body. A medication is also administered with a spinal anesthesia to keep the individual sedated throughout the procedure.
There are several available operative procedures:
Patellar tendon graft procedure
Since it was popularized in the mid-1980s, the patellar tendon graft has been the "gold standard" choice for ACL reconstruction. This type of ACL replacement uses the middle third of the person's own patella tendon and is referred to as a bone-tendon-bone (BTB) graft.
In this particular technique,
- Two tiny incisions for arthroscopic instruments are usually placed on either side of the patellar tendon.
- A one- to two-inch incision is made over the patellar tendon on the front of the knee and the tendon is exposed. The middle one-third of the patellar tendon is carefully removed, together with two bits of bone on either end (hence it is called a 'bone-tendon-bone graft').
- Two small tunnels are then drilled into the bones on either side of the joint, in the area where the torn ACL normally attaches to the bone, to allow for fixation of the new ligament.
- The patellar tendon graft is then passed into the joint, placed in a position similar to the original ACL, with the bone pieces at each the end of the graft fitting nicely into the tunnels that have been drilled in the bone.
- The new ACL is then secured with a specialized headless screw in each tunnel.
The patellar tendon graft is tightly secured at the time of the surgery. The knee is stable enough to begin motion and weight-bearing as tolerated, as per the surgeon's instructions.
As healing occurs, the bone tunnels fill in to further secure the tendon ends of the graft in a bone-to-bone relationship. This occurs over the next six to eight weeks.
Advantages
- The fixation is very strong
- The patellar tendon replacing the ACL is as strong as the injured ACL (or even stronger).
Disadvantages
- A few people have mild discomfort on the front of the knee, especially when kneeling. This generally settles down within a year. Workers who kneel frequently may need to look at other graft options.
- A normal patellar tendon has been altered. However, this does heal fully again.
The Patellar Tendon Graft
Hamstring graft procedure
Hamstring reconstruction is an alternative to the bone-patellar-bone graft fixation and is growing in popularity. In this procedure, rather than using the patellar tendon, the surgeon uses the patient's own hamstring tendon, either the semitendinosus or gracilis tendons from the same leg.
There are several variations of this technique. Newer hamstring fixation techniques have been developed to match and even exceed the initial pullout strength of the patellar tendon bone procedure described above. Special screws with threads designed not to cut the hamstring tendons are able to fix the tendon within the bone tunnel, as described with the patellar tendon bone technique.
In younger patients who have torn their ACLs but still have growing bones, the hamstring tendon graft is a good choice because there is less chance of damaging the 'growth plates'- the area responsible for growth of the bone.
Advantages
- The hamstring incision is away from the patella, allowing patients to kneel comfortably.
- The patellar tendon is left intact.
Disadvantages
- Soft tissue-to-bone healing occurs at a slower rate than bone-to-bone healing.
- Unlike the patellar tendon, the hamstring tendons do not grow back after graft harvest resulting in a slight loss in hamstring strength (approximately. average of 10%) after recovery. However, most people do not notice this slight decline in strength.
The Hamstring Graft
Allograft procedure
Another option is the use of tissue from a cadaver (a deceased person) called an allograft.
Patellar tendon, hamstring tendon, or Achilles tendon allografts can be used as tissues inserted and fixed with the same techniques that are used for autografts (grafts using the individual's own tissue).
Allografts are a good choice when the patient's own tissue availability is limited. They are useful for complicated ligament reconstructions needing more than one graft (for example, if both anterior and posterior cruciate ligaments need to be replaced) or if both the ACL and patellar tendon are damaged.
Advantages
- No risks, pain, or scars from the donor site
- Operative time is quicker
Disadvantages
- The very low risk of contracting a serious infection from the cadaver tissue. Newer techniques of tissue radiation have minimized this risk.
- National shortage of allografts due to a high demand combined with a low supply of suitable, qualified cadavers.
Meniscus and cartilage injuries are trimmed or repaired and the torn ACL stump is then removed. In the most common ACL reconstruction technique, bone tunnels are drilled into the tibia and the femur to place the ACL graft in almost the same position as the torn ACL. A long needle is then 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 position up through the tibial tunnel and then up into the femoral tunnel. The graft is held under tension as it is fixed in place using interference screws, spiked washers, posts or staples. The devices used to hold the graft in place are generally not removed.
The Tunnel Preparation and Graft Placement
Variations on this surgical technique include the "two-incision", "over-the-top" and the new "Double Bundle" types of ACL reconstructions, which may be used because of the preference of the surgeon or special circumstances (revision ACL reconstruction, open growth plates).
The Two-Incision Technique
The Gold Standard. The two incision ("backdoor") approach has remained the gold standard for ACL reconstruction, because it is the only technique which can reliably position the femoral tunnel at the 10 o'clock (or 2 o'clock) position (which is necessary for anatomic reconstruction); the one incision (transtibial) technique often cannot reliably reproduce this insertion.
The over-the-top Technique
This procedure is a successful and consistent way to stabilize the ACL-deficient knee. It is considered a very reasonable and easily accomplished alternative whenever a "plan B" procedure is required. It is definitely worth consideration whenever an otherwise apparently adequate femoral tunnel placement proves too anterior during ACL graft isometry testing -- when it is tight in flexion and loose in extension. Even though the surgeon may not be experienced with the technique, reliable results can be expected.
In a study comparing the consistency of accurate femoral tunnel placement between the over-the-top procedure and the use of a rear entry guide, the over-the-top procedure proved to be the most reproducible, regardless of the experience of the surgeon. If they are merely passed over the top without any surgical resculpturing as they were originally described, these grafts will tighten significantly in the last few degrees of knee extension and can result in a flexion contracture or eventually loosen. Biomechanical studies have shown that isometry will be achieved with an adequate posterior notchplasty that anteriorizes the back wall of the femoral tunnel by 5 to 6 cm.
The Double Bundle Technique
The double-bundle ACL reconstruction is a relatively new and innovative technique for replacing an injured ACL. It involves using two separate grafts to reconstruct or replace the native ACL, whereas a standard ACL reconstruction uses a single graft. The advantage of the new technique is that it functions much more like the native ligament. Thus, it should allow the patient to have more normal biomechanical function of their knee. This should lead to better function on the field with less chance of further injury to the knee.
The double-bundle ACL reconstruction is a technique that has been utilized widely in Japan with very impressive results. In the United States it is a procedure that has been performed in significant numbers at only a few centers of excellence.
Before the surgery is complete, the surgeon will probe the graft to make sure it has good tension, verify that the knee has full range of motion and perform tests such as the Lachman's test, shown above to assess graft stability. The skin is closed and dressings (and perhaps a postoperative brace and cold therapy device, depending on surgeon preference) are applied. The patient will usually go home on the same day of the surgery.
The Finished Product
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