When the ACL is torn the most predictable option that allows return to full activities is surgery.  The surgery is an arthroscopic procedure (surgery preformed through small incisions using a camera) and involves replacing the ligament with a tendon graft. 

History of ACL surgery

In the past ACL surgery was performed through a large incision in the front of the knee and the knee was opened up.  The torn ligament was identified and the ends of it were sewn back together.  Afterwards the leg was placed in a cast for 4 to 6 weeks.  Once the cast was removed therapy was started to regain range of motion and to strengthen the muscles that atrophied with the immoblization.  The results from surgical management at that time was about a 50% success rate at 5 years (only 50% of people had a stable knee).

With these poor results orthopedists looked for other methods.  One technique that proved successful was to reconstruct the ACL (replace it) with a tendon graft.  The results of this method turned out to much more successful. 

In the 70’s and 80’s knee surgery was changing from open to arthroscopic surgery.  Instead of opening up the knee a lens was placed in the knee and a surgeon looked through it to visualize the structures inside.  With the improvement in electronics a camera was attached to the lens and the picture was displayed on a video monitor.  Over time the instruments decreased in size and the picture improved and now most knee surgeries are performed this way.

ACL Reconstruction today  (click here to watch a video of the surgical technique)

Today ACL reconstructions are performed arthroscopically.  At the time of surgery the knee is examined to confirm that the ACL is torn.  The knee is then examined arthroscopically and the joint surfaces and the menisci are examined.  If there is a meniscus tear this is treated with either a partial excision or a repair (see meniscal injuries).  The ACL remnant is then removed and a tendon graft is selected.

There are several choices for a graft, there are autografts (tissue taken from the patient) and there are allografts (tissue from a donor, cadaver).   The advantages of an autograft is that it is your own tissue with no risk of disease transmission, and it is populated with live cells.  The disadvantage is the morbidity of the graft harvesting. The most popular autograft tissues are the central third of the patellar tendon, hamstring tendons or a portion of the quadriceps tendon.  Allografts do not have the morbidity of graft harvest but do have the risk of disease transmission, no live cells (dead tissue) and increased cost.  An allograft can add several thousand dollars to the cost of the surgery.  Many times this is paid by your insurance but at times it is not.  My preference for ACL surgery is to use an autograft.

My choice for a tendon graft in ACL surgery are the hamstring tendons.  In the past I exclusively used the central third of the patellar tendon and had great stability results with this however there is some morbidity of harvesting it.  Patients frequently have numbness over their kneecap and have about a 25% risk of anterior knee pain.  Approximately 10 to 12 years ago I started to use the hamstring tendons.  What I noted was the the stability results were similar, however there is a much lower risk of anterior knee pain, numbness, pain after surgery and in the long term the knee feels more normal.  I now have approximately 85 patient who have had a patellar tendon in one knee and a hamstring graft in the other, all but 2 if ever had to do it again would use a hamstring tendon.

At the time of surgery an 2 inch incision is made just below the knee on the medial side.  Two hamstring tendons are harvested (gracilis and the semi-tendinosis) and the tendons are folded in half making a 4 strand graft.  If these tendons are equally tensioned they are approximately 3.5 times stronger than the original ACL.  Approximately 70% of the time the hamstrings will grow back (not quite the same) and if knee flexion strength is evaluated at one year the strength on the operated leg is the same as the other leg.

Two tunnels are drilled in the knee, one in the lower bone and the other in the upper bone.  The graft is then threaded through the tunnels.  The upper portion of the graft is fixed with 2 bioabsorbable pins and the lower portion of the graft is fixed with a bioabsorbable screw and backed up with a metal screw and washer.  Basically the graft is fixed 2 ways in the femur and 2 ways in the tibia.

The day the graft is put in it is at full strength.  Over the next six months the graft will make a transition from a tendon to a ligament.  If the tissue is evaluated at six months it looks more like a ligament than a tendon.  During the time that the graft makes that transition in the first 4 to 8 weeks after surgery the strength in the graft is significantly less.  It is during that time that activities need to be restricted or the graft may stretch out or tear.  At 3 months the graft begins to strengthen and at 5 to 6 months it is strong enough that rotational activities and a gradual return to full activities can be considered.

Click here for ACL surgery video

David M. Oster, M.D.

Telephone  303-214-4500 for appointment

www.davidostermd.com