ACL reconstruction is a complex process and although the success rate of ACL reconstruction is generally 85-95%, there are times when the reconstruction is unsuccessful. In order to understand the ways ACL reconstruction may not be successful, it helps to have a good understanding of the surgery itself, and the various choices the patient and surgeon is likely to make. [see ACL reconstruction].
Since many factors contribute to a successful reconstruction and rehabilitation, failure of any one of these factors can lead to less than desirable outcomes. When graft failure occurs, it is necessary to perform an ACL revision procedure.

Main Causes of Failure can be listed as:
1. Drill hole placement in a non-anatomic location.
2. Failure of Fixation
3. Graft impingement
4. Intrinsic graft failure
5. Arthrofibrosis
6. Trauma

1. Placement of the graft is the single most difficult aspect of ACL surgery. Tunnels are drilled into both the femur and tibia in order to secure the graft. Precise placement and orientation of these tunnels to achieve the exact anatomic location of the normal ACL are important for success. Slight variations in placement produce abnormal stresses and lengthen the graft. Improper alignment can result in impingement, which can sacrifice the integrity of the graft. It can also result in excessive laxity, or decreased range of motion, both of which produce unsatisfactory results. Experience of the surgeon matters the most. Newer computer guided systems may help less experienced surgeons improve their accuracy.

2. The weakest link in the reconstruction is the point of attachment. The goals of fixation are to achieve sufficient strength and stiffness, and avoid further complications such as inflammatory response or degradation over time. The fixation technique will initially need to secure the graft tissue in place, while the graft incorporates into the bone tissue, which is the ultimate goal of the reconstruction. Of the many options for graft fixation, our preference has been to use bone patellar tendon bone grafts with interference fit screws. Generally, the fixation choice depends primarily on the type of graft material used. With patellar tendon grafts, interference screws, either metal or bioabsorbable, are used to secure the bony attachments on either end. With hamstring tendons, which require securing soft tissue to bone, a variety of methods are used including cross pin, endobutton, screw and post, or belt-buckle staple technique – each can produce favorable results.

3. Graft impingement occurs from entrapment of the graft in the intercondylar notch. This can occur from graft placement, variations in notch shape and size and from graft hypertrophy. If the graft is impinged then wear increases, length can increase, and failure occur. Most commonly decreased range of motion is noted. The treatment involves surgical debridement or graft re-positioning.

4. Intrinsic failure of the graft can occur from graft impingement or trauma. Recent reports have noted a traumatic rupture rate of autogenous ACL reconstruction of 2% and an allograft rupture rate of 15% (references). In the case of allografts a low level of immunologic reaction can weaken the graft and cause early failure as well.

5. Arthrofibrosis occurs in up to 10% of ACL reconstructions. The fibrosis is the formation of scar tissue after injury or surgery leading to decreased range of motion in the knee. This can be diminished by early and full range of motion exercises both before and immediately after surgery. Some people will develop the fibrosis no matter what procedures are followed. Generally arthroscopic surgical debridement with a careful rehabilitation program will result in a successful outcome.

6. Trauma can cause excessive force on the graft during the healing process before it has reached full strength. In addition, significant trauma after the full healing of the graft can cause rupture of the graft similar to it would cause rupture of the original ACL.

Stone Clinic ACL Revision Procedure:

At surgery we generally employ the following steps to revise a failed ACL reconstruction.

First, the patient is prepared for surgery in a sterile manner. Then arthroscopic portals are established to allow for visualization of the procedure and insertion points for the instruments.

The patients knee is then evaluated within the joint, and any scar tissue removed. The patients knee joint is evaluated and scar tissue removed. The old ACL fibers from the failed graft are removed with a shaver and the intercondylar notch cleared of bone and soft tissue.

Precise placement is necessary for a successful revision. If the old hardware is in the way of the ideal tunnel placement it is removed usually under fluoroscopic (x-ray) control. The anatomic insertion site on the femur for the original ACL is identified, and a drill hole is initiated using a gaff to place a rear-entry guide, then drilled from outside in. The hole is cleared out and the edges are chamfered (rounded) to avoid damage to the graft.

Next, the insertion site of the ACL on the tibia, on the tibial plateau, is identified, and a drill hole is initiated using a triangle-guide, again drilling from outside in. The hole is cleared out and the edges chamfered in a similar manner.

The graft tissue, which usually is a bone-patellar-tendon-bone graft, is brought through the now continuous tunnel running from the femur through the knee joint and through the tibia. The tissue is secured in place using 9x20mm screws, which bind the bone blocks at either end into the tunnel.

The knee is finally brought through a full range of motion to visualize for any impingement of the graft, and to ensure proper placement. The instruments are removed and incision sites closed, the joint injected with Marcaine for pain relief, and the patient is able to return home later that day.