Patients who undergo anterior cruciate ligament (ACL) reconstruction surgery to repair torn ligaments may be at an elevated risk of developing early-onset knee arthritis, particularly due to issues related to the kneecap, according to a new study.

Findings show that those who received ACLR surgery had a shift in the positions of their knee bones and joints, causing a change in load on their knees.

The kneecap, or patella, in those who had surgery moved up by 4.4 to 5.6 millimeters more than the other group’s, and this changed the way the knee joint moved. The patella was also pushed forward by 5.4 to 6.3 millimeters more during walking, indicating a change in knee structure that could stress the joint.

The study also noted that the tendon connecting the knee cap to the shinbone was an average of 8.9 millimeters longer in ACLR patients compared to the healthy group.

Among the ACLR participants, nearly half had an abnormally higher knee cap, also known as patella alta, which may put excessive stress on parts of the knee that are not used to handling load.

According to researchers, a higher-riding patella may contribute to the development of knee osteoarthritis by shifting the load-bearing areas between the patella and the femur to regions of cartilage unaccustomed to load and leaving previously loaded regions unloaded.

“If this condition existed prior to the injury, then it may be a predisposing factor for ACL injury,” corresponding author Marcus G. Pandy, of the University of Melbourne in Australia, told The Epoch Times. “Alternatively, if the condition arose as a result of surgery, then it may help to explain the high rate of knee osteoarthritis seen after ACLR.”

The findings suggest that altered knee movements may lead to premature wear and tear on the joint cartilage, contributing to long-term issues such as osteoarthritis. According to Pandy, the key takeaway is that people who have undergone ACLR have an abnormally longer tendon in their knees, causing a higher-than-normal kneecap position.

However, Dr. James Penna, chair of the Department of Orthopaedics and Rehabilitation at Stony Brook Medicine, disagreed that ACLR surgeries could be causing a longer knee tendon.

The angle of the knee upon impact with the ground varies between individuals who have had an ACL injury and those who haven’t, Penna noted.

Researchers of the study raised the question about whether it’s the injury or reconstruction that can lead to elongation of the patellar tendons.

Penna disagreed that the longer tendon in the knee could be caused by the surgery. “It doesn’t, it can’t,” he said. He believes the researchers simply happened to have patients with naturally longer tendons in their sample.

Pandy and team wrote that further research is needed to determine the cause of the longer knee tendon in individuals who have undergone ACLR surgery. The researchers didn’t compare those who received ACLR surgery to those who didn’t—this would be the next step, according to Pandy.

ACL injuries substantially increase arthritis risk, regardless of surgical intervention. Penna pointed out that orthopedic surgeons haven’t yet figured out a way to prevent people from getting arthritis later on.

“We know that ACLR surgery does not prevent knee [osteoarthritis]. One-half of individuals less than 40 years old who have experienced an ACL injury will develop knee osteoarthritis within 8-12 years regardless of the decision to undergo surgery,” Pandy said.

Penna added that the one thing ACL surgeons don’t really tell the world is that everybody who’s torn their ACL is at increased risk for arthritis. He said that bone scans from decades-old studies showed increased activity in the knee joint for years after an ACL injury, indicating ongoing wear and tear—whether or not the patient had surgery.

“Whether or not they were thrilled with their ACL reconstruction, didn’t have ACL reconstruction, or had a terrible outcome,” Penna said, “they had increased bone activity.”