Anterior Cruciate Ligament Tears and Their Treatment: arthroscopic and minimally-invasive surgery for ACL reconstruction

Edited By: Christopher J. Wahl, M.D., Suzanne L. Slaney, PA-C, ATC, MMS
Last updated Friday, October 20, 2006

Figure 3 - Arthroscopic view of a right knee. Several years after a tear, the ACL has almost completely resorbed from the knee.

Figure 4 - Bone-patellar tendon-bone graft. Left, the graft is harvested from the patellar tendon. Middle, the graft has bone 'plugs' at each end. Right, the bone plugs are docked into the femur and tibia. The patellar tendon becomes the ACL (arrow). Diagram courtesy of Smith+Nephew Endoscopy.

Figure 5a - Schematic drawing (top) and intra-operative photograph (bottom) of a prepared quadrupled hamstring autograft.

Figure 5b - Arthroscopic view of a knee after ACL reconstruction of the ACL using a hamstring autograft.

Figure 6 - Schematic diagram of a double-bundle ACL reconstruction. Diagram courtesy of Smith+Nephew Endoscopy.

Considering surgery

Who should consider arthroscopic anterior cruciate ligament (acl) reconstruction?

The ultimate decision to surgically reconstruct the ACL depends greatly on the patient’s post-injury knee stability, ability to carry out activities of daily living, activities and athletic endeavors, and expectations to return to such activities.

• The patient is a young individual or athlete who will be at significant risk for disability and/or further knee injury if normal knee mechanics are not restored
• The episodes of instability are a significant problem for the patient, and inhibit his or her ability to perform the activities of daily living, sporting activities, or job-specific requirements
• The patient has truly exhausted non-operative treatments, like physical therapy, and are still having frequent giving-way episodes, instability, and an inability to perform the usual activities of daily living or walk without assistive devices such as crutches or a brace
• There is concomitant injury to other structures in the knee
• The patient is sufficiently healthy to undergo the procedure
• The patient understands and accepts the risks and alternatives to the procedure
• An appropriate and comprehensive diagnostic evaluation has been performed and the nature of the problem is clear
• The surgeon is experienced and familiar with the techniques and treatments for arthroscopic ACL reconstruction
• The patient is capable and willing to comply with a comprehensive post-operative physical therapy program

What happens without surgery?

For individuals who choose to not have surgery, rehabilitation of the injured knee is frequently recommended. In order to restore as much function as is possible; a rehabilitative treatment program may help to prevent instability and “giving way” episodes.  Rehabilitation will focus on strengthening the muscles around the knee in order to provide better support, control, and stability.

There is nothing inherently dangerous about a mildly unstable knee so long as the patient is able to be adequately braced and willing to use appropriate assistive devices (cane, crutch, or walker) that will prevent falls or further injuries. This may require significant changes in lifestyle and activities to reduce the risk of instability events. For instance, an individual may have to avoid activities such as basketball or soccer and participate in non-impact activities such as biking or swimming for fitness. The goal is for patients to find activities where the knee feels stable and is pain free.

A minority of patients will continue to have instability to the degree that they are unable to walk or put weight on the extremity without it buckling on them.  These persons are best served by surgery to stabilize the knee and restore function.

With or without surgery, a knee that has an ACL injury is at risk to develop osteoarthritis in the knee over time.  Even a perfectly performed surgery cannot restore absolutely ideal knee kinematics.  However, the arthritis usually takes years to develop if the mechanics of the knee are optimized.

Surgical options

Patients should be aware that there are different grafts available for use when reconstructing the ACL. Due to the uniqueness of each knee and injury from person to person it is best to discuss the different possibilities with an appropriately trained orthopaedic surgeon.

What is the difference between ‘repair’ and ‘reconstruction’?

‘Reconstruction’ of the ACL alludes to ‘substituting’ for the ligament by providing a new ligament. In reality, the surgeon creates a soft tissue substitute called a “graft” that reestablishes knee stability and provides a scaffold.  Miraculously, the patient’s body will recognize this graft scaffold, populate it with living cells, and permanently attach it in place.  Over a relatively short time (about 4 to 6 months) this new ‘ligament’ takes on the appearance and function of the normal ACL.  The functional results of ACL reconstruction are predictably excellent, and the overwhelming majority of patients are able to get back to the same or higher degree of athletic activity without pain or instability. Figure 2, Video 2.

Because the tissue graft is really serving as a temporary scaffold, there are many different options. In general, there are 2 categories of grafts:  those that are taken from elsewhere in the patient’s body (called autograft) and tissues that are donated from persons who are organ donors (called allograft).  In addition, there are several different anatomic sources of ‘autograft’ and ‘allograft’.  There is no absolute “right” choice for graft, and the decision is usually based on various patient factors and the surgeon’s preference.  Each has advantages and disadvantages that will be discussed below.

The ‘bone-patellar tendon-bone’ autograft, or “BPTB” is a widely used source for ACL reconstruction.  In general, the surgeon takes the middle 1/3 of the patellar ligament that runs from the bottom of the kneecap (patella) to the front of the tibia.  This graft is ‘harvested’ with bone blocks from the patella and tibia respectively.  These bone blocks can then be secured into bone tunnel ‘sockets’ that are placed at the anatomic location where the ACL originates on the femur (the ‘origin’) and the anatomic location where the ACL ends at the tibia (the ‘insertion’).  BPTB autograft has been used for a long time and has an established track record.  The body heals the bony portions of the graft to bone, and the ligament between serves as the substitute ACL.  Advantages of this graft include its stiffness, strength, and low re-tear rate.  It is also rapidly incorporated into the patient.  Potential disadvantages include temporary or permanent pain at the front of the knee, slight motion losses, and a more difficult/painful early postoperative course. Figure 4.

Five hamstring tendons help to flex the knee. It is possible to use one or two of these tendons, from the inner part of the knee to reconstruct the ACL.  Hamstring autograft has also been in use for a long time and has a very good track record.  There is no bone harvested with the hamstring tendons, and therefore the harvest is easier for the patient with respect to pain.  While the hamstring tendons used are technically stronger than the BPTB construct, the methods to fix the soft tissue graft into the sockets is generally less stiff.  Advantages to hamstring grafts are that they are strong, easy and relatively painless to remove, and do not result in long-term knee pain.  Disadvantages include the fact that the reconstructed ligament may not be quite as stiff, they are slower to incorporate, and there is controversy about whether there may be a slight loss in total hamstring strength after they are harvested.  For many surgeons, this is the graft of choice.  Figure 5a-b. 

A ‘hybrid’ graft is the quadriceps tendon autograft. This graft uses a bone plug from the upper kneecap and some of the tendon soft tissue from the quadriceps (thigh) muscle tendon at the knee.  This graft is not as widely used, but has a very reliable track record.  Advantages are that the quad tendon graft probably results in little long-term knee pain, it is strong, and uses bony healing at one end.  Disadvantages are that it is slightly more painful to harvest in the short term, and may not be as stiff as the BPTB.

Allograft is donated tissue from organ donors.  There are many different sources of donor tendons and ligaments that can be used for ACL reconstruction.  In addition to allograft BPTB and hamstring and quadriceps tendon, other grafts are also used, such as the tibialis anterior and tibialis posterior.  Advantages to allograft is that they do not require the harvest of normal tissues from the patient with the ACL tear, so there is no “donor site” pain.  The grafts are also typically robust and strong.  However, there are theoretical risks of disease transmission from the donated tissue.  Nationally, this risk is about 1:1.5-million for the transmission of HIV, and about 1:470,000 for hepatitis.  The donated allografts DO NOT result in a significant immune response, and the patient does not have to take medication or worry about “rejection”.  Allografts have a slightly higher re-rupture rate than BPTB, hamstring, and quad tendon graft.  They have been commonly used for revision (repeat) ACL reconstructions and the reconstruction of multiple ligaments, however, the predictably good results of allograft use have led many surgeons to use these grafts in primary ACL reconstructions, even in young athletes.

Aside from graft choice, the other major consideration for the patient and surgeon is whether to consider a “double bundle” ACL reconstruction. The native ACL controls both translation of the tibia under the femur in the front/back plane and also the rotation of the tibia.  While the ACL is made of millions of small fibers, these fibers are generally arranged into two major “bundles”.  One bundle is predominantly a translation stabilizer, and the other a rotation stabilizer.  Some surgeons advocate the substitution of both of the separate bundles to control the translation and rotation more completely.  The reason this is important is that the single-bundle ACL reconstructed knee is still prone to develop osteoarthritis over the long term.  It is possible that this is because a single bundle can not restore normal mechanics to the knee.  However, the theoretical advantages to double bundle reconstruction have not been proven in long-term studies.  At our institution, we perform double bundle reconstructions when patients request them, and in special cases that are prone to rotational instability.  Figure 6.

Effectiveness

Urgency

Reconstruction of the ACL is not an emergency. It is actually recommended to wait at least a few weeks after the initial injury to allow the inflammation to decrease and for the patient to regain full knee range of motion.  This will contribute to a more successful return of motion and muscle strength after the surgical procedure.  Except in special cases, it is generally advised to rehabilitate the knee first, to see if instability becomes a true problem before considering ACL reconstruction.  

• Be in optimal health
• Understand and accept the surgical alternatives, options, risks and benefits
• Have considered, discussed and or attempted non-operative measures to treat the problem
• Have undergone a comprehensive examination that includes appropriate diagnostic images such as X-rays and MRIs to define any additional factors contributing to the problem
• Seek out a surgeon who is experienced in arthroscopic surgery and reconstructing the ACL

Risks

The risks of an ACL reconstruction procedure include but are not limited to the following:

• Infection
• Temporary or permanent injury to the nerves and blood vessels around the knee
• Excessive joint stiffness
• Pain
• Scarring
• Immune reactions to donated tissue or suture materials (very low risk)
• Disease transmission from the donated tissue (exceedingly low risk)
• Failure of the reconstructed ligament
• The need for additional surgeries
• Anesthesia

Managing risk

Many of the risks of an ACL reconstruction can be effectively managed if they are promptly identified and treated.

• Infections may require a wash-out of the joint, and rarely removal of the implanted tissue.
• Blood vessel or nerve injuries are rarely caused by the surgical procedure.  Most of theses injuries resolve spontaneously overtime, but occasionally such an injury may require surgical repair.  It is common to have decreased sensation around the incision sites.  This numbness may or may not entirely resolve in time. 
• Excessive stiffness of the joint is rare in the person who is cooperative with the postoperative rehabilitation program, and most of the stiffness will respond to exercises.
• Pain is a likely response after a surgical procedure that can be treated with medications, rest, ice, and compliant rehabilitation.  As healing progresses overtime, the pain will diminish. 
• Individuals scar and heal differently, and it is inevitable that anyone undergoing a surgical procedure will have scars.  To allow for proper healing and therefore less scarring, the patient should follow post-operative instructions provided by their surgeon on how to care for their incisions. 
• The risk of disease transmission from donor tissue is very small, but cannot be disregarded.  All potential donors undergo strict screening that meets the guidelines of the American Association of Tissue Banks and the Food and Drug Administration.  The tissue is thoroughly tested for HIV (risk of contracting HIV through donor tissue is less than 1 in 1.67 million), hepatitis (risk of contracting hepatitis is less than 1 in 470,000), and other infectious diseases.  The transplant is then prepared and processed to prevent the transmission of bacteria and viruses according to United States Federal guidelines.

If a patient has questions or concerns about the “normal” course after surgery, the surgeon should be informed as soon as possible and be available to explain the expected course and outcome.

Surgery for Anterior cruciate ligament - ACL - tear at the University of Washington

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