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An ACL reconstruction is one of the most common surgical procedures in orthopaedic surgey. Although only 10% of grafts fail, this is still a large number of cases. There can be many reasons for an ACL reconstruction failure.
The most common reason for an ACL graft to fail is due to technical issues with the original surgery. An ACL reconstruction is very technical and it is well recognized that surgeons who perform more of these procedures have improved outcomes. However, the majority of ACL reconstructions performed in the United States are performed by surgeons who perform ten (10) or less each year. For that reason, misplaced graft reconstruction tunnels are still a very common cause of an ACL reconstruction failure. This can be due to placement being too posterior on the tibia, which results in a central graft that does not control rotation, or too anterior placement on the femur, which can result in the graft stretching out as knee flexion returns.
CT scan of a failed ACL reconstruction demonstrating the wide diameter of the previous ACL tibial reconstruction tunnel. In some patients, these tunnels will become larger than when they were originally reamed, especially for hamstring autografts or cadaver allografts. If they are larger than 12 to 14 mm in diameter, or are in a position where an anatomic positioning of the ACL reconstruction graft would break into the previously malpositioned tunnel, then a two-staged surgery would be recommended. This would involve bone grafting of the tunnels and, once the tunnels heal in approximately four to six months, to proceed with a revision ACL reconstruction in the correct anatomic position.
The second most common cause of ACL reconstruction failure is due to untreated secondary instabilities. This could include a posterolateral corner injury, a meniscal root detachment, or a lack of the posterior horn of the medial meniscus. It is well recognized that a deficiency of these areas, and other areas to include an unrecognized PCL injury, medial knee injury, alignment issues in patients who have arthritis and other issues, are also common causes of ACL reconstruction failures. For this reason, the work-up for an ACL revision surgery must include evaluation of the secondary restraints of the knee and the integrity of the posterior horn of the medial meniscus.
Traumatic reinjuries also can occur, but in general are not felt to be the most common cause of ACL graft failure. In this circumstance, an athlete sustains a reinjury to their knee with the ACL graft being torn. While less common, athletes in this circumstance may have improved overall outcomes with an ACL revision surgery
Another important issue to evaluate for ACL reconstruction graft failures from ACL knee surgery is biologic issues. Literature has reported that patients who are less than 25 years of age have a much higher risk of ACL graft failure with an allograft reconstruction. In addition, a small number of patients may have their own grafts not completely heal and tear over time. Reasons for early allograft failure could include an immune response and lack of graft incorporation, a too early return back to high level activities prior to graft incorporation or issues with the graft itself to include unrecognized tearing within the graft or use of irradiation to sterilize the graft (which has been shown to increase the risk of graft failure).
Thus, the work-up for ACL revision surgery has to include an evaluation of biology, evaluation of the patients alignment and their secondary restraints, a careful assessment of the posterior horn of the medial meniscus and also an evaluation of the previous reconstruction tunnel placement and size. Soft tissue ACL reconstruction grafts often cause graft reconstruction tunnel enlargement over time and a careful assessment for this must be performed.
When all factors have been evaluated, an assessment can then be made if a one stage or two stage reconstructions are necessary. There are certain times when trying to perform a one stage ACL reconstruction may significantly increase the risk of failure of the revision graft. Possible treatment scenarios include patients undergoing an autograft or allograft revision reconstruction, either as a first stage or as a second stage surgery after bone grafting the tunnels first and/or a combined proximal tibial osteotomy. Concurrent procedures with the revision ACL reconstruction could include meniscal repairs, meniscal transplants, posterolateral corner or medial knee reconstructions.
It is very rare that the evaluation of a failed ACL reconstruction graft is easy. There is usually a reason why the graft failed and a very careful assessment must be performed including long leg alignment x-rays, possible varus/valgus stress x-rays, a Rosenberg view to look at joint space narrowing and an MRI scan to look at the location, size and position of the previous ACL reconstruction graft tunnels as well as the status of the meniscus and articular cartilage of the joint.
A very thorough physical exam is necessary but these secondary studies are often required to choose the best plan of treatment for a revision ACL reconstruction. In general, the success rates in the literature for ACL revision surgery are approximately 75%. A very careful assessment of the cause of the graft failure is necessary to try to maximize an individual patient’s outcome with an ACL revision surgery.
The rehabilitation program for a revision ACL surgery needs to progress slower than those for a primary (first time) ACL reconstruction. In most patients, we keep them on crutches but with full weight bearing to minimize stress on the ACL graft. The timing of advancement of the specific rehabilitation exercises is generally slowed down by about 50% and a return to full activities is rarely allowed prior to 9 months after surgery.