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The Big Red One The Reconstruction (Special Edition)


The Big Red One The Reconstruction (Special Edition)

The 100-year anniversary of the 1918 pandemic and the 10-year anniversary of the 2009 H1N1 pandemic are milestones that provide an opportunity to reflect on the groundbreaking work that led to the discovery, sequencing and reconstruction of the 1918 pandemic flu virus. This collaborative effort advanced understanding of the deadliest flu pandemic in modern history and has helped the global public health community prepare for contemporary pandemics, such as 2009 H1N1, as well as future pandemic threats.

This task was undertaken by renowned microbiologist, Dr. Peter Palese and Dr. Adolfo Garcia-Sastre at Mount Sinai School of Medicine in New York City. A plasmid is a small circular DNA strand that can be amplified (or replicated) in the laboratory. Years earlier, Dr. Palese helped pioneer the use of plasmids in reverse genetics to produce viable influenza viruses. The techniques he developed allowed the relationships between the structure and function of viral genes to be studied, and these efforts paved the way for the techniques used to reconstruct the 1918 virus. Once Dr. Palese and his colleagues at Mount Sinai completed creation of the plasmids, they were shipped to CDC so the official process of reconstruction could begin.

For the reconstruction of the 1918 virus, additional rules were created to govern the experiments to be conducted. For example, to prevent mix-ups and cross-contamination, work on the 1918 virus could not take place alongside work on other influenza viruses.

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.

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.

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.

ACL revision surgery is performed when a first-time ACL repair or ACL reconstruction did not work and the surgery has to be redone. Usually, this requires an extensive workup because the results of ACL revisions are nowhere near as successful as the first time around. This usually requires alignment x-rays, lateral knee x-rays to the look at the tibial slope, an MRI to determine the meniscus volume (which can affect the ability of an ACL graft to heal), the presence of meniscal ramp tears or meniscal root tears, and also a combined physical exam and possibly varus or valgus stress x-rays if there is an unrecognized or untreated MCL or posterolateral corner (which includes an LCL (FCL) tear) injury present. In addition, most ACL revisions require a CT scan to look at the placement of the tunnels from the previous ACL reconstruction and to determine the size of the tunnels to determine if a bone graft may be necessary as a first stage surgery to fill in the tunnels when the tunnel is too large to place an ACL graft in for a first stage revision ACL reconstruction.

The most common cause of ACL failure is a technical error in the first surgery. The two most common technical errors are placing the ACL reconstruction graft on the femur too anterior (away from the back wall) or placing the tibial tunnel too posterior (posterior to the anterior horn of the lateral meniscus). In almost every published study, these are the most common causes of an ACL graft failure. Other causes of ACL graft failures include a lack of a medial meniscus, because the medial meniscus is an important stabilizer to preventing the knee from slipping forward in an ACL deficient knee. When there is no medial meniscus, an ACL graft would be at risk for stretching out. Meniscal root tears can also cause an ACL graft to stretch out, and missed, or unrecognized, posterolateral corner or medial collateral ligament (MCL) tears can also cause an ACL graft to stretch out. In addition, patients who have an increased posterior tibial slope are at risk for having ACL grafts stretch out.

ACL surgery can fail, even in the best of circumstances. It is generally felt that a well-done ACL reconstruction has about a 5% chance of failure due to trauma. The most common cause of an ACL graft failure is a technical error with malposition of the original ACL reconstruction tunnels. Other causes of ACL failure include missed or unrecognized concurrent diagnoses, such as meniscal root tears, meniscal ramp tears, posterolateral corner injuries or MCL tears, or the original graft choice.

As with any procedure, there can be technical issues with an ACL reconstruction which can make things more complicated. First, probably the most important thing is to ensure that all injuries that occur with an ACL are concurrently treated to provide the best chance of the ACL graft healing without having it stretch out and become loose. Issues that can occur with an ACL reconstruction surgery include fractures of the lateral femoral condyle, for which we have published peer-reviewed case reports on, breaking out the back wall, or soft bone which hinders fixation. Breaking out the back wall occurs on occasion when the bone is soft, and can be easily addressed by adding an extra incision and tying the sutures over a screw and washer. This should not slow down the rehabilitation program. In addition, when there is poor graft fixation due to soft bone, which is usually on the tibia, a screw and washer back up can be added to give the best chance of having the ACL graft heal. 153554b96e


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