Some individuals who have had anterior-cruciate-ligament reconstruction (ACLR), the kind of surgery often performed on athletes’ knees, may develop early-onset knee osteoarthritis. A new study in the Journal of Orthopaedic Research indicates that altered knee joint movement after ACLR could be a contributing factor.

The study used a unique dynamic X-ray imaging system to accurately measure knee joint movement during walking in people who had undergone ACLR surgery and those with healthy knees. Compared with healthy controls, ACLR patients had a higher vertical position of the patella and a higher location of articular contact between the patella and the femur.

A higher riding patella in the ACLR patients was caused by a longer-than-normal patellar tendon, the structure connecting the patella to the tibia. A surprising finding was that a higher riding patella was observed in both the ACLR knee and the uninjured contralateral knee of the ACLR patients.

Investigators suspect that 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.

“We don’t know whether a longer-than-normal patellar tendon that resulted in a higher riding patella existed prior to the ACL injury or resulted from the ACL injury or ACLR surgery. Further research is needed to determine the cause of a longer-than-normal patellar tendon in individuals who have undergone ACLR surgery,” said corresponding author Marcus G. Pandy, Ph.D., MEngSc, of the University of Melbourne, in Australia.