The incidence of a second injury to the anterior cruciate ligament (ACL) within the first 12 months after ACL reconstruction and return to sport in a young, active population has been reported to be 15 times greater than a previously uninjured cohort. Mark V. Paterno, PhD, PT, SCS, ATC, and colleagues wanted to know whether that higher risk continued beyond the first year.

Their research, presented at the 2013 annual meeting of the American Orthopaedic Society for Sports Medicine, shows that the overall rate of another injury within 2 years to the ACL—on the same or the opposite knee—is six times greater among athletes who undergo ACL reconstruction surgery and return to sport than among those who have never had an ACL tear.

“In our study, female athletes demonstrated more than four times greater rate of injury within 24 months after ACL reconstruction than their healthy counterparts. These data highlight the fact that patients who have undergone ACL reconstruction and return to playing sports are at greater risk for injury and should take appropriate precautions to prevent injury,” said Dr. Paterno.

Injured, control groups
Researchers analyzed data from 78 patients (59 female, 19 male) between 10 and 25 years old, whounderwent ACL reconstruction and were ready to return to a pivoting/cutting sport, and 47 healthy, control individuals. Each study participant was followed for injury and athletic exposures (AE) for a 24-month period after returning to play. Incidence rate ratios (IRR) were calculated to compare the rates (per 1,000 AE) of ACL injury in athletes in each group. For the ACL reconstruction group, similar comparisons were conducted for side of injury and by sex.

During the 24 months, 27 of the 125 study participants sustained an ACL injury; 23 injuries occurred in individuals who had undergone ACL reconstruction and 4 occurred in members of the control group.

The overall IRR for athletes who had undergone ACL reconstruction was 1.39/1,000 AE—nearly six times greater than that for healthy control subjects (0.24/1,000 AE).

Within the group of athletes who had undergone ACL reconstruction, researchers noted a trend for female athletes to be two times more likely to sustain an injury on the knee opposite the injured knee. Overall, 29.5 percent of athletes sustained a second ACL injury within 24 months of returning to activity, with 20.5 percent sustaining an opposite leg injury and 9 percent incurring a graft re-tear injury on the same leg. A higher proportion of females (23.7 percent) sustained an opposite leg injury than males (10.5 percent).

“Our study represents the first report of subsequent ACL injury incidence rate focused on 2-year outcomes of young, active patients returning to sport. Even though additional research still needs to be performed to support our findings, our data provide early evidence for re-examining current rehabilitation and return to sport protocols following ACL reconstruction,” said Dr. Paterno.

Dr. Paterno’s coauthors for “Incidence of Second Anterior Cruciate Ligament (ACL) Injury 2 Years after Primary ACL Reconstruction and Return to Sport” include Mitchell Rauh, PhD, PT, MPH, FACSM; Laura C. Schmitt, PhD, PT; Kevin R. Ford, MS; and Timothy E. Hewett, PhD, FACSM.

Disclosure information: Drs. Paterno and Hewett—no conflicts. Drs. Rauh and Schmitt and Mr. Ford—no information.

Mary Ann Porucznik is managing editor of AAOS Now. She can be reached at porucznik@aaos.org

Bottom Line

• Young, active individuals who return to sport after undergoing ACL reconstruction are at high risk for sustaining a second ACL injury—in the same or the opposite knee—as long as 2 years after surgery.
• Female athletes are more than twice as likely to sustain an injury to the opposite knee than male athletes.
• This study supports the need to re-examine current rehabilitation and return to sport protocols after ACL reconstruction.