Procedures for revision ACL surgery are considerably more complicated than the initial cruciate ligament reconstruction. This is because the majority of knees needing revision ACL surgery have compounding problems - joint (articular) cartilage damage, prior meniscectomy, bow leg deformity (varus mal-alignment).
Accordingly, such revision ACL procedures have less favorable results, although in a good proportion of patients it is possible to gain worthwhile improvement in both symptoms and function.
Together with my team of researchers, I have spent nearly three decades studying the causes of failure of knee ligament reconstructions and the outcome of revison operations using a variety of graft materials. Before undertaking revision surgery, our team is careful to look for and fully assess the following:
Existing articular cartilage damage
When I counsel a patient who is considering a revision ACL procedure, but who already has articular cartilage damage, I try to stress with them realistic expectations - a reduction in pain and instability with day-to-day activities, and perhaps a return to light recreational activities. In our 2001 study using bone-patellar tendon-bone autograft (ref 1), we found 58% of patients in this group were able to return to light recreational activities without problems.
If there are any meniscal tears, the patient is advised of our intention to repair any meniscal tear with sutures, as meniscal instability will compromise the new graft.
Loss of secondary ligament restraints
In cases of multiligament damage, there are differences of opinion amongst surgeons as to what graft procedures should be performed and which structures should be simultaneously reconstructed. Our Center observes the patient carefully in the first two weeks after initial injury, and rehabilitation is focused on regaining at least 0-90 degrees of movement. If the knee remains swollen and inflamed we may delay multiligament surgery. If it is undertaken it is with the recognition that rehabilitation is complex and demanding.
As posterolateral corner injuries often involve both ACL and PCL, the issue then arises of whether or not the surgeon should address both ACL and PCL at the same procedure. There is a risk in doing this of developing arthrofibrosis and reduced knee motion, and so the topic remains controversial.
With respect to the other structures, our team has for many years made the point that at least one component - usually the LCL - of the posterolateral corner must be reconstructed with a strong graft material like bone patellar-tendon bone graft, and that this should be an anatomical placement. The popliteus tendon-ligament complex should also be reconstructed.
Bow legs (varus mal-alignment)
Any abnormal movement in the knee caused by damage to the other supporting structures will put extra stress on the graft - this includes bow-leggedness (varus malalignment). We try to determine whether any bow-leggedness is simply a pre-existent anatomical feature not linked to damaged structures, or whether it is a function of -
- damage to the supportive anatomical structures to the back of the knee on the outer side - the so-called 'posterolateral corner'
- damage to the medial meniscus
- bony arthritis and deformity of the medial compartment (inner aspect of the joint)
In our revision cases, we have found up to one-third of patients had lateral, posterolateral or medial ligament deficiency which had probably been there since the initial injury and which should have been addressed with the primary ACL repair.
What we try to do in the clinic is to grade the varus deformity to reflect any associated ligamentous laxity. We use the following grades:
- primary varus - bowing of the leg due to arthritic damage at the tibiofemoral joint but no ligament deficiency or abnormal lateral joint opening.
- double varus - bowing of the leg where lateral collateral ligament damage is demonstrable, with lateral joint opening, in addition to any tibiofemoral arthritic damage.
- triple varus - bowing of the leg where there is deficiciency of the posterolateral structures, with marked lateral joint opening, in addition to the lateral collateral ligament deficiency and any tibiofemoral damage. In these patients we notice a particular stance when standing and bearing weight on the bad leg - the knee bows outwards but also bend backwards (together this is known as 'varus recurvatum'). In these knees it is very important that the damaged structures of the posterolateral corner are repaired.
This can be assessed clinically or with 'stress X-rays', but we can also determine abnormal laxity quite easily during arthroscopy using the 'gap test'. An assistant tries to stress the lateral part of the knee (by attempting to bend the knee sideways while rotating the lower leg inwards - 'varus load') while the surgeon measures how much that part of the joint can be forced open. Normally the gap is about 6 mm but if there is a problem it may open 12 mm or more.
Where varus malalignment is present, a high tibial osteotomy may be needed so that the angular deformity does not continue to put stress on the new graft.
Damage to the posterolateral corner generally occurs at the time of the original injury, and failure to optimise stability here can in itself contribute to the failure of the initial reconstruction procedure. One may suspect posterolateral corner damage if any of these features are present:
- the bow-leggedness is associated with increased joint opening on the lateral (outer side) demonstrable on X-ray or examination (this is the most important important feature)
- there is a thrusting action outwards at the side of the knee while walking ('varus thrust')
- one can elicit rotation of the tibial bone outwards at the posterolateral region.
If no posterolateral corner damage is suspected, then the ACL reconstruction and the high tibial osteotomy can be done at the same time. If, however, it is suspected that there is posterolateral corner damage, then the high tibial osteotomy is done first as a separate procedure and the ACL revision plus posterolateral corner repair done later.
Weakened bone stock
After all the leg has been through, the bone may have become thinned (osteopaenic) and the weakened bone stock means that the bridge between the old tunnel and the new tunnel may collapse. If this is a risk, a second incision may be made at the back of the knee (posterolateral) and a notch made into the bone of the femoral condyle to allow the graft to be positioned anatomically and fixed to the bone with two small screws and a backup suture post.
Pre-op extension deficit
If the patient has a block to full extension prior to the ACL graft revision, this needs to be addressed as a separate issue before continuing with the graft procedure. Lack of full extension may be due to the tibial tunnels being placed too far anterior, or it may be due to the development of a 'cyclops lesion'. If the loss of extension is more than 5 degrees, then I recommend staging the procedure and doing an arthroscopic debridement first. Finally, the extension loss may be due to tight capsular structures at the back of the knee, which may need release before the graft procedure.
Pre-existing bony tunnels
It is critical that the graft is positioned in an anatomical position that most closely reflects the position of the original cruciate ligament. If the surgeon compromises on this the replacement graft, too, is likely to fail. So the surgeon has to ensure that the ligament is properly positioned, and also has to deal with the previous tunnels in both tibia and femur - which tunnels may be wrongly positioned or which may have widened.
If the old tunnel is too wide, the surgeon may chose to bone graft the tunnel or the surgeon may chose to stack two screws ('interference cancellous screws') side by side to hold the graft securely.
If the tunnel in the primary graft procedure was misplaced - usually too anteriorly - a second tunnel may be placed in the correct position but this needs to be done carefully. Leaving the screw in the original tunnel allows some support. When the new tunnel is drilled it needs to be done in a stepwise fashion, drilling into the bone with a narrow gauge drill at first and then slowly increasing the drill size to the correct diameter.
At the time of revision surgery, the notch needs to be carefully examined. There may be -
Secondary notch stenosis
Even after previous notchplasty, with time the side walls of the notch may re-grow and the notch may close up. A second notchplasty may be necessary.
Osteophytes ('spurs') may also grow at the back of the notch, and these may abrade the graft and also interfere with normal joint function. These need to be trimmed off at the time of revision surgery.
- Noyes FR, Barber-Westin, SD. Revision anterior cruciate surgery with use of bone-patellar tendon-bone autogenous grafts. J Bone Joint Surg. 2001;vol;1131-43.