What is ACL Revision Surgery?
Anterior cruciate ligament (ACL) revision surgery may be required when one tears a previously reconstructed ACL tendon graft. ACL reconstruction surgery has a success rate between 80-90%, but a surgically reconstructed ACL can also tear or fail. There are several reasons why a reconstructed ACL fails. Common reasons are (1) shortcomings in the surgical technique that was utilized which predisposed the reconstructed ACL graft to tear or (2) another traumatic knee injury, similar to the injury that first tore one’s native ACL, that tears the reconstructed ACL tendon graft.
For patients who are once again unstable after tearing their reconstructed ACL and who wish to have once again have a stable knee so that they can resume high level sports once again, a revision ACL reconstruction surgery may be indicated. Dr. Cunningham specializes in ACL and ACL revision surgery at Vail Summit Orthopedics and Neurosurgery. He is an expert at diagnosing and treating failed ACL surgeries for patients in Vail, Summit County, Aspen, and Denver, CO.
Why Does ACL Reconstruction Fail?
Dr. Cunningham sees ACL reconstructions fail for a number of reasons. Failure of an ACL reconstruction is most commonly due to shortcomings in the surgical technique. The most common example of inadequate surgical technique is improperly placed femoral and/or tibial tunnels. In ACL reconstruction surgery, an ACL tendon graft is seated into a bone socket in the femur and into another bone socket in the tibia. Ideally, these bone sockets are placed exactly where the original ACL attached to one’s femur and tibia. Unfortunately, some surgeons use surgical techniques that do not perfectly replicate these ACL attachments sites in the knee and they place their bone sockets outside of these native ACL attachment sites. When an ACL graft is then secured in mal positioned bone sockets, the graft will see unusual biomechanical forces and over time the ACL graft will stretch out and/or tear with minimal trauma.
A second surgical factor that can lead to premature ACL graft failure is using donor tendon (allograft) instead of using one’s own tendon (autograft) to reconstruct a torn ACL. Numerous orthopedic studies have conclusively demonstrated that if one’s ACL is reconstructed with an allograft, that the failure rates are higher, particularly in young people (less than 30 years of age) or in those who do a lot of cutting and pivoting sports (ie. skiing). Using a tendon graft taken from the patient (autograft) and placing the graft perfectly in the knee gives the highest chance of never again tearing one’s ACL. The reason for this is that your body recognizes your tissue as its own and grows it securely into the bone. Autograft tissue also has new blood vessels grow into it and nourish it and strengthen it, whereas allograft tendons are not incorporated into one’s knee as well.
A third cause of an ACL reconstruction failing is not recognizing and addressing laxity in other ligaments that work in conjunction with the ACL to help stabilize the knee. For instance, when one tears their ACL, they commonly also tear their MCL. Although MCL tears can heal without surgery, Dr. Cunningham finds that severe (Grade 3) MCL tears often only partially heal and remain somewhat lax. If the ACL is then reconstructed in surgery and the loose MCL is not also reconstructed, then this persistent laxity in the MCL puts the ACL at higher risk of re-tearing as the ACL is seeing increased forces during cutting and pivoting sports. Similarly, patients can also tear ligaments on the outside of their knee (their LCL and/or posterolateral corner) which do not heal well without surgery, so if these are not addressed then the ACL will likewise see increased forces and can fail prematurely.
Finally, a reconstructed ACL can fail simply by having another bad, twisting fall while playing sports, much like the injury that tore your native ACL. Even a perfectly reconstructed ACL can tear if subjected to severe enough injury forces. However, a well reconstructed ACL using autograft tissue is not more likely to tear than the normal ACL in your other knee unless one returns to cutting and pivoting sports before you have all your strength in the muscles that support the knee and the ACL.
What are Symptoms of a failed ACL Reconstruction?
Patients who have had their ACL reconstructed in the past and who subsequently re-tear their ACL graft commonly complain of:
- A return of knee instability and “not trusting” the knee
- Pain, clicking, and catching in the knee
- Mild or minimal swelling of the knee
- Possible locking of the knee
- A feeling that the knee will hyperextend
- Unable to confidently return to cutting and pivoting sports
How is Revision ACL Reconstruction Performed?
Revision ACL reconstruction is a highly technical procedure. The first step is identifying the cause of failure. A thorough history and physical exam will be conducted by Dr. Cunningham to determine the probable cause of failure. Repeat X-rays and an MRI–and possibly a CT scan to assess tunnel location and tunnel diameter–will be required to determine the cause of failure.
Surgical treatment for a failed ACL is done in either one or two surgeries (stages). If the tunnels or bone sockets are mal positioned or have expanded over time, then a two stage surgery would be required. The initial surgery would consist of removing old hardware, reaming out old graft material from expanded and/or mal positioned tunnels, and then bone grafting these tunnels. Unfortunately, one must then wait 4 months for the bone graft to consolidate before proceeding with definitive ACL reconstruction surgery and any other necessary repairs (ie. meniscus repair, reconstructing other loose ligaments about the knee, etc).
In some cases, Dr. Cunningham can do a revision ACL reconstruction surgery and all other necessary repairs in just one surgery. This requires that the old tunnels are in good position and have not expanded over time or that he can create new, more anatomic tunnels without intersecting the old mal positioned tunnels in the knee. Dr. Cunningham recommends autograft tissue for revising an ACL whenever possible, but allograft tendons are used outside the knee to reconstruct one’s lax MCL or LCL where there is better blood supply.
In some cases, the knee is mal aligned, with the patient being bow-legged (in varus) or knockkneed (in valgus) or having excessive posterior tibial slope. If there is bony malalignment associated with a failed ACL surgery, then an osteotomy may also be required along with ACL revision reconstruction surgery but this is less commonly the case.
What is the Recovery After ACL Revision Surgery?
Recovery for a routine revision ACL reconstruction is similar to the initial ACL reconstruction but the recovery moves a bit slower. It is very important for patients to follow the prescribed rehabilitation plan with one’s physical therapist. Each rehabilitation program will be individualized taking into account what was done in addition to the ACL revision reconstruction (ie. whether other ligaments about the knee were reconstructed or a meniscus was repaired, etc). Typically, patients are held in a hinged brace for the first few weeks with the knee held straight when walking, but the brace can be unlocked or removed to allow for immediate knee range of motion. A full return to sports is not allowed one has regained all strength in the muscles that support the knee. Dr. Cunningham is an ACL revision surgeon at Vail Summit Orthopedics and Neurosurgery. He is an expert at diagnosing and treating failed ACL surgeries for patients in Vail, Summit County, Aspen, and Denver, CO.