Knee Clinic Home

About Dr. Mervyn Cross

Information for patients

Papers online

Presentations online

Other info

Anterior Cruciate Ligament (ACL) Injuries
Gregory Solis MD and Mervyn J Cross OAM MD

What is the ACL?
How is the ACL injured?
What to expect with a torn ACL
Non-Surgical Treatment
Surgical Treatment
Surgical Technique
After Surgery

What Is the Anterior Cruciate Ligament (ACL)?

The Anterior Cruciate Ligament (ACL) is a major ligament within the knee joint.  Ligaments are strong bands of tissue that hold joints together.  The ACL sits in the center of the knee joint and connects the back of the femoral (thigh bone) side with the front of the tibial (shin bone) side Figure 1.  Situated in this position, the ACL primarily prevents the tibia (shin bone) from sliding forward relative to the femur (thigh bone).  It also helps somewhat in side-to-side stability as well as being important in locking the knee in extension (the "screw home" mechanism).

Figure 1


How is the ACL injured?

Most ACL injuries are a result of a twisting motion in the knee.  These most commonly result from sudden twisting on a planted foot while "cutting" or twisting the knee in skiing accidents.  Even in full contact sports such as rugby this injury is not usually the result of impact with another player.

Typical patients hear and/or feel a "pop".  The knee usually swells immediately as a result of bleeding within the joint from the torn tendon ends, but this is not always the case (a small percentage of people do not have the small artery that normally runs inside the tendon).  After a few weeks the pain and swelling can resolve, but people returning to sport may find the knee gives way with sideways movement/cutting and can be very painful.

During the initial injury, the abnormal motion of the joint can damage the disks of cartilage (meniscus) or the cartilage which lines the joint.  If the knee remains unstable additional damage to the joint may occur over time (see Dr. Cross' study).


What can I expect if my ACL is torn?

As mentioned previously, the ACL is an important ligament in maintaining stability in the knee joint.  ACL tears are major injuries to the knee.  Some people are able to cope well without an ACL by learning to avoid activities that cause instability (sudden shift in weight, pivoting, jumping) as well as performing physio to strengthen the knee.

Non-Surgical Treatment

Physio is extremely important after an ACL injury regardless of whether or not you decide to have it repaired.  It is important to strengthen both the quadriceps (muscles on the front of the thigh which straighten the knee) as well as the hamstrings (muscles on the back of the thigh that bend the knee).  Because they tend to pull the tibia backwards, the hamstrings can help prevent the tibia from sliding forward in a knee without an ACL.  Quadriceps strengthening should be done under supervision of a physio as the quadricepts can pull the tibia forward in knees without functional ACL's.  Balancing and proprioception (the body's ability to sense the position of joints and muscles) should also be developed with agility training.   It normally takes 6 months before one would complete physio to the point of being able to participate in sport.  Even then agility sports such as soccer, netball, rugby or volleyball would present a high risk for re-injuring the knee.

Surgical Treatment

In patients who would like to return to competitive sports, or who have episodes of instability or "giving way" of the knee, surgery would generally be recommended.  The purpose of ACL reconstructive surgery is to restore stability to the knee, with a goal of allowing unrestricted activity.  Many patients after ACL reconstruction are able to return to professional/Olympic caliber sport.  For technical reasons, the torn ends of the ACL normally can not be reattached and must be replaced, or reconstructed, with something else.  Typically the patella tendon or the hamstring tendons are used.  Each type has good and bad points.

Patella tendon graft use can occasionally result in some pain around the kneecap and shin especially with kneeling.  In very rare instances fractures of the patella or rupture of the tendon can result.  Hamstring tendon harvest avoids these problems, but the fixation of the graft is not as secure.  ACL reconstructions done with hamstring may not be as secure as done with patella tendon.


Surgical Technique (Using Patella Tendon)

The patella tendon is taken through two small incisions on the front of the knee.  The middle 1/3 of the tendon is taken along with bone blocks where it attaches to the patella and tibia (Figures 2a, 2b).  Screws can be used against these bone blocks to provide very secure fixation. Figure 2c represents the graft after harvest.

Figure 2a
Figure 2b
Figure 2c

After the graft is taken, the arthroscope is used to prepare the joint.  This involves two very small incisions (4-5mm).  Two tunnels are drilled in the bone, one in the femur and one in the tibia (Figure 3a).  The graft is passed through these tunnels (Figure 3b) and secured using interference screws (Figure 3c). Please note that surgical skill is NOT related to artistic abilities  ;-)

Figure 3a
Figure 3b
Figure 3c


After Surgery

Following surgery a good deal of physiotherapy will be needed.  You will need to protect the graft while it heals while also gaining motion in the knee and building up the strength of the muscles.  The natural healing and scarring from surgery can result in stiffness and limited motion in the knee if one does not actively work on motion.  Muscles about the knee get very weak as a result of injury and significant weakness results from surgery.  For proper function of the knee these muscles MUST be restored to normal function.  Following is an outline of our physio progamme.  Times are for guidelines only, some people may take longer to reach goals.

Day 1-14:  You will be in a  knee brace to limit the motion of the knee.  You must keep this on at all times.  You will need crutches to walk.  Hamstring exercises and limited quadriceps exercises will be started.

2-6 Weeks:  Brace is worn for at least 4 weeks.  Can begin removing brace for physio.  Once quadriceps strength is good weight bearing can be increased reducing reliance on crutches (quads MUST be strong enough).  Exercises are increased, stationary bicycle riding can begin.  Only "closed chain" quad exercises are allowed (with pressure on the foot, such as stationary bicycle: check with your physio before doing ANY exercises unless you are specifically told to do them)

6-12 Weeks:   Range of motion should be nearly the same as before surgery.  Functional strengthening can begin.  Normal bicycle can be used.  Depending on muscle strength and proprioception (co-ordination) jogging can begin on flats (NO hills).  Can begin swimming (NO breast stroke kicking motion)

12 Weeks- 5 Months:  Begin agility work, low impact aerobics.  Can progress to flippers in swimming.

5-9 Months:  Begin "open chain" quad exercise (Open chain means without putting pressure down through the foot, such as on a leg extension machine).  Begin sport specific skills and training.  Only return to sport when strength, range of motion and co-ordination are nearly full.  May need to modify sport (i.e.. decrease release strength on ski bindings, train for football in running shoes or short spikes).

The goal of surgery is to restore your level of athleticism.  Most first grade players return to the same level of competition after ACL reconstruction- provided they are properly rehabilitated!



ACL reconstruction is an excellent procedure for restoring stability of the knee and allowing a return to sports and normal activities.  We would expect 85-95% of patients to be significantly improved, which is an extremely good result.  A small percentage of people are not improved or continue to have problems.  With any surgery it is always possible to be made worse, however this is very rare.  Click here for a full list of possible complications from ACL reconstruction and surgery in general.

Return to top

  Surgery for Anterior Cruciate Ligament (ACL) Injuries



Index - Keywords - Pages copyright 2003 content © Australian Knee Clinic
website indexing code ©
Alpha Web Smarts using IP created by Synergy! ©