An ACL injury is one of the most traumatic injuries an athlete can suffer. ACL reconstruction involves a painful surgery, many months of physical therapy, and often 9 to 12 months or more before she returns to play. Add to those realities the possibility of retearing the ACL graft or tearing the contralateral ACL (the intact ACL in the opposite knee), and these injuries affect athletes physically and psychologically.
Just how likely are these second knee injuries, though? And what are the risk factors for those injuries? Does the graft type matter? What about the age of the patient? Or his or her race?
Gregory B. Maletis, MD and others recently published data from the Kaiser Permanente ACLR registry, which collected data from patients who underwent surgery between February 1, 2005 and September 30, 2012. Their study, published online in the American Journal of Sports Medicine in December 2014, included 17,436 cases from 259 surgeons at 49 hospitals.
Before I share their findings about the risk factors for revision ACL surgery or contralateral ACL surgery, it’s worth noting the overall survival data for the primary ACL reconstructions. The authors found that the ACL grafts survived in 95.1% of the cases. The contralateral ACL remained uninjured in 95.8%.
Still, when you’re looking at a sample of over 17,000 cases, even 3% or 4% means quite a few reinjuries of the graft or the opposite ACL. When the authors looked specifically at revision ACL reconstructions, they found certain factors increased the risk:
• Use of allografts and hamstring autografts in the primary ACL surgery increased the risk for needing a revision ACL surgery on that side compared to the use of patellar tendon autograft.
• Males had a higher risk for revision ACL reconstruction.
• Young patients had a higher risk for revision surgery. In fact, the risk for a second surgery on that knee dropped 8% for each year increase in age.
• When looking at race, blacks proved to have a lower risk of revision ACL compared to whites.
The study also offers insight on the risk for tearing the opposite knee’s ACL:
• Patellar tendon autografts had a higher risk of contralateral ACL surgery.
• Females had a higher risk for these injuries than male patients.
• Younger patients also had a higher risk for later contralateral ACL reconstruction.
An important aspect of this study is its sheer sample size. To truly tell if one type of graft has a higher rate of failure than another, researchers need more than 50 or 100 patients. This study has data from over 17,000 ACL cases.
Maletis GB, Inacio MCS, Funahashi TT. Risk factors associated with revision and contralateral anterior cruciate ligament reconstructions in the Kaiser Permanente ACLR registry. American Journal of Sports Medicine. Published online before print December 29, 2014.