“The value of using large anterior cruciate ligament reconstruction (ACLR) registries to evaluate patient outcomes, graft function and survivorship, and complications is increasingly being recognized,” said Scott A. Rodeo, MD, moderator of a symposium on large domestic and international ACLR registries held at the 2014 AAOS Annual Meeting.

During the symposium, orthopaedic surgeons explored data from domestic ACLR registries as well as large Scandinavian registries on ACLR patient outcomes, including factors that may put patients at risk for revision ACLR and/or injury to the contralateral ACL. In addition, Dr. Rodeo explored posttraumatic osteoarthritis (OA) in ACLR patients, noting that future ACLR studies and registries may help shed light on OA risk factors in patients who undergo ACLR.

The Kaiser registry
Kaiser Permanente, an integrated healthcare delivery system with 9 million members and more than 12,000 physicians, has maintained an ACLR registry since February 2005, said Gregory Maletis, MD, chief of orthopaedics at Baldwin Park Medical Center in southern California, one of Kaiser’s institutions. Thus far, the registry contains data on 23,653 cases, including more than 22,000 primary ACLRs and approximately 1,700 revision ACLRs.

These procedures, noted Dr. Maletis, have been performed by 330 surgeons at 52 medical centers. Currently, data on 92 percent of all patients who undergo ACLR and/or revision ACLR at a Kaiser institution are captured in the voluntary registry.

“The registry is composed of 63 percent males and 37 percent females, which makes it slightly more male-dominated than some of the Scandinavian registries,” noted Dr. Maletis. “Our current outcomes measures include postoperative infection, deep vein thrombosis/pulmonary embolism, and revisions/reoperations.”

Although the mean patient age is 29 years, approximately 30 percent of female ACLR patients in the registry are teenagers (14–17 years); male registry patients are more evenly distributed across age ranges.

“A registry can help identify regional variations in graft usage,” said Dr. Maletis. “For example, surgeons at Kaiser institutions in the Pacific Northwest and northern California are using allografts more than half of the time. In southern California and other regions within the Kaiser system, allografts are used in about 20 percent to 30 percent of patients.”

According to registry data, 2.8 percent of ACLR patients have undergone revision surgery, while 8.6 percent have undergone an additional surgery, other than for revision or infection. In addition, 2 percent of ACLR patients have undergone contralateral ACLR, while 0.3 percent of ACLR patients have sustained a deep surgical site infection (SSI).

“When we looked at our deep SSI rate, we found no difference between patients who received allografts and those who had patellar tendon autografts, but we did find that patients who received hamstring autografts had an 8 times greater risk of infection compared to the patellar tendon autograft group,” noted Dr. Maletis. “With regard to superficial infections, we found no difference based on graft type; however, increasing body mass index did increase the risk of superficial infection.”

Although the overall infection rate is quite low, noted Dr. Maletis, the registry data on infections serves as a reminder for orthopaedic surgeons to continue to maintain vigilance regarding sterile techniques, especially with hamstring tendons.

When it comes to graft survival, noted Dr. Maletis, patient age seems to be the most critical factor. Graft survival is lowest among patients younger than age 17 and highest among patients 25 years or older.

“We’ve also looked at graft survival by graft type,” said Dr. Maletis. “We found the best survival rates with bone patellar tendon autografts; allografts have the worst graft survival rates.”

Using registry data, Kaiser has developed revision risk calculators for orthopaedic surgeons to use in educating patients about potential risks of undergoing ACLR with various graft types.

“For example, if we used patellar tendon autograft in ACLR on a 15-year-old female patient, the predicted risk of revision would be 2.8 percent within 18 months; however, if we used allograft, the predicted risk of revision would be 6.4 percent,” said Dr. Maletis.

Overall, the registry data has yielded several intriguing findings.

“ACLRs performed with allografts have a 3 times greater risk of revision compared to ACLRs performed with patellar tendon autograft,” said Dr. Maletis. “Hamstring autografts have a 1.8 times greater risk of revision compared to bone-tendon-bone autografts, but the revision risk is slightly higher among females.”

The data also indicate that age is one of the “driving factors” for both revision and the need for contralateral ACLR.

“We have found that revision ACLR is more likely than contralateral ACLR if hamstrings or allograft tendons are used at the index surgery and that contralateral reconstruction is more likely than revision if a patellar tendon autograft is used at the index surgery,” he said.

Finally, he said, the data indicate that revision ACLRs and contralateral ACL tears are not uncommon, and that rehabilitation may be important in helping prevent additional surgeries after ACLR, especially in patients most at risk for revision or contralateral ACL injury.

Swedish National ACL Register
Jon Karlsson, MD, PhD, professor and chief physician in the department of orthopaedics at Goteborg University in Sweden, helped provide an international perspective on ACL registries. According to Dr. Karlsson, data on more than 90 percent of all ACLRs performed in Sweden are recorded in the Swedish National ACL Register. The registry contains data on almost 25,000 unique ACLRs—including 22,000 primary ACLRs and more than 1,400 revision ACLRs.

The Swedish registry captures Knee Injury and Osteoarthritis (KOOS) scores, as well as scores from the EuroQol-5D, a validated measure of general health status. Approximately 70 percent of patients provide these self-reported outcomes prior to surgery, but fewer patients report at 1 year (60 percent), 2 years (50 percent), and 5 years (40 percent).

Those involved with the Swedish registry have found that females are more likely to respond to registry questionnaires, while males 20 years to 25 years are the least likely to submit responses.

Similar to the Kaiser registry, the Swedish registry contains data on more males (60 percent) than females; the mean age of females is 26 years, while the mean age of males is 28 to 29 years.

“In Sweden, about half of all ACL injuries in males are the result of playing soccer, which also accounts for more than one third of ACL injuries in females,” noted Dr. Karlsson.

KOOS scores indicate that revision patients have poorer outcomes at all follow-up points, said Dr. Karlsson. Smokers, who make up 6 percent of patients in the Swedish registry, also have poorer outcomes following ACLR.

“About 54 percent of soccer players return to play at the same or higher level at 1 year,” said Dr. Karlsson. “And yet, among females with pain and cartilage injuries, there’s only a 10 percent return to play.”

The registry data show that female soccer players ages 15 to 18 years account for more than 30 percent of contralateral ACLRs and revision ACLRs performed in the first 5 years after index injury, indicating this patient group is at a higher risk of tearing the contralateral ACL or revision ACLR.

“So, to summarize our findings, we can say that primary ACL reconstruction significantly improves all KOOS subscale scores at 1, 2, and 5 years,” said Dr. Karlsson. “In addition, young patients—especially females—are at major risk for reinjuring their ACL, or injuring the contralateral ACL. Patients who undergo revision ACLR have poorer outcomes than primary ACLR patients, and smokers have worse outcomes than nonsmokers.”

Posttraumatic arthritis
Posttraumatic arthritis can develop in some ACLR patients over the long term, according to Dr. Rodeo, cochief, sports medicine and shoulder service, at the Hospital for Special Surgery, and professor, orthopaedic surgery, at Weill Cornell Medical College.

“The ACL-injured knee is a good model for the development of posttraumatic arthritis,” he said. “We know that varying rates of OA following ACLR have been reported based on various radiologic classification methods.”

Posttraumatic arthritis in ACLR patients, noted Dr. Rodeo, is likely due to both biologic and biomechanical factors.

“Clearly, cartilage and subchondral bone is injured at the time of the index injury, including shear injury to the articular surface,” he explained. “Subchondral bone injury can contribute to long-term degenerative changes. We also know a translational contusion occurs, which provides evidence of transarticular injury.”

The presence of inflammatory mediators released at the time of injury, leading to the production of matrix metalloproteinases, may contribute to arthritis in ACLR patients. Both meniscus injury and subsequent loss of meniscus function may also contribute to posttraumatic arthritis, as can altered cartilage contact mechanics if normal knee kinematics are not fully restored during surgery.

Rehabilitation to restore range of motion may play an important role in lowering the risk of posttraumatic arthritis.

“Residual quadriceps weakness and abnormal proprioception may be factors we need to consider in our rehabilitation,” noted Dr. Rodeo.

In conclusion, although orthopaedic surgeons can reliably stabilize the knee using ACLR, the surgical procedure “does not necessarily change the natural history of posttraumatic OA,” said Dr. Rodeo.

“Understanding the etiologic factors related to the development of posttraumatic arthritis will suggest what we should measure in ACL reconstruction outcomes studies and ACLR registries,” he said.

Disclosure information: Dr. Rodeo—Smith & Nephew, Cayenne; Drs. Maletis and Karlsson—no conflicts.

Jennie McKee is a senior science writer for AAOS Now. She can be reached at mckee@aaos.org