Bob's ACL WWWBoard
Re: Causes of failed ACL reconstruction
Posted By: SueBW <sbwestin@csmref.org>
Date: Sunday, 7 December 2003, at 9:17 a.m.
In Response To: Causes of failed Cadaver? (Libby)
Libby,
There are many possible causes for failure of an ACL allograft (cadaver) reconstruction. Some are easier to detect than others, and these include surgeon error which is evident through misplaced tunnels (femoral, tibial or both). Misplaced tunnels can be determined via a quick glance by an experienced and well-trained surgeon at standard anteroposterior (AP) and lateral x-rays. Sometimes MRI films can provide more information, especially in regard to the size of the tunnels. In our studies of failed ACL reconstructions and revision procedures, surgeon error unfortunately was found in at least 50% of the cases.
Other surgeon error factors include inadequate fixation of the allograft to the femur or tibia. This is usually not a factor, especially if you had a patellar tendon allograft with interference screw fixation on both graft ends. However, if you had an Achilles tendon or hamstring tendon allograft (which do not have bone on the graft ends) then fixation could be an issue.
Some patients inherently have "soft bone" (osteopenia) on the tibia and this can also be a cause for early graft stretching and failure.
Another cause of failure is poor healing of the collagenous portion of the allograft. All ACL grafts, whether allograft or autograft, go through a process of ligamentization whereby the graft "becomes' a new ligament. This process involves the body's own cells invading the graft, laying down collagen in the correct manner and orientation, and healing over a lengthy period of time. Scientists believe that it takes approximately 1 year for autografts to complete this process and about 2 years for allografts to do the same.
Yet another factor for failure is untreated ligament deficiency of other ligaments in the knee, including the lateral collateral ligament, posterolateral ligamentous complex, and medial collateral ligament. Also, untreated varus malalignment (bowed legs) can cause an ACL graft to fail.
Rejection of allografts is in fact a rare occurrence. In cases of rejection, the signs are apparent within a few days of the operation and the graft must be removed on an urgent basis.
Our studies have demonstrated that allografts have a high failure rate (30%) in knees with chronic ACL-deficiency. In other words, patients who waited several months (or years) before having the reconstruction after their original injury had poorer results than those who had the operation within a few months. The failure rates for the latter group (acute ACL injury) were similar to those of autografts; about 7% which is quite acceptable.
We also found that many patients who experienced ACL graft failure actually had multiple factors that probably contributed to the problem. I suggest you seek other opinions from experienced surgeons about your knee problems - if it is related to surgeon error, your surgeon probably won't recognize it. Finally, if you do require a revision ACL reconstruction, the best graft choices are either your own patellar tendon or your own quadriceps tendon. Studies have documented that these tendons provide the best success rates for revision operations. Allografts have poor track records with revision procedures and should only be used if autogenous tissue is not available.
I hope this information has been helpful.
SueBW
