A higher patella after reconstruction might be to blame by shifting the load onto cartilage, Australian researchers say.
Changes in the movement of the knee after anterior-cruciate-ligament (ACL) reconstruction may lead to early onset knee osteoarthritis by changing the position of the patella, new research suggests.
Australian researchers say gait measurements showed that the position of the patella when walking was “considerably higher” in participants who had ACL reconstruction compared to controls.
A high‐riding patella in the ACLR participants was due to a longer patellar tendon, and may contribute to knee osteoarthritis by moving the load to cartilage, they said.
“The patella articulated higher (by 7.6mm) on the femoral trochlea in both the ACLR and contralateral knees compared to the healthy knee, due primarily to a longer patellar tendon (by 8.9mm),” the researchers said in the Journal of Orthopaedic Research.
“A higher riding patella may contribute to the development of patellofemoral OA by shifting the load‐bearing areas on the femoral trochlea to regions of cartilage unaccustomed to load and leaving previously loaded regions underloaded.”
The researchers measured the patellofemoral and tibiofemoral joint motion of 15 young adult participants while they were walking on level ground and on a 10-degree downhill slope, and compared the results to the healthy knees of 10 participants who had not been injured.
The ACLR participants were physically active and took part in competitive sports at least once a week, while those in the control group were mainly sedentary.
“Significant differences were observed in all three sagittal‐plane movements of the patella relative to the femur for both the ACLR and contralateral knees compared to the healthy knee in both activities,” the researchers said.
“Mean superior translation of the patella was greater in the ACLR knee and contralateral knee compared to the healthy knee in both activities, indicating an elevated position of the patella in both knees of the ACLR participants.”
Dr Marcus Pandy, co-author and University of Melbourne chair of mechanical and biomedical engineering, said: “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.”
The researchers said previous MRI studies had shown that knee cartilage degeneration could occur within six months after ALC reconstruction.
The researchers noted that the controls were drawn from a pool of college students who did not engage in sport, but said previous studies had found patellar tendon lengths to be similar in athletes and non‐athletes.
The ACL participants were also an average 6cm taller, but the researchers said a post-hoc analysis including body weight and height found that knee type still significantly affected patellar tendon length.
