SAN DIEGO – Structural damage due to osteoarthritis appears to be more common, and more severe, in the patellofemoral joint than in the tibiofemoral joint, making the patellofemoral joint the predominant one affected by knee osteoarthritis, according to findings from a magnetic resonance imaging–based study involving nearly 1,000 people.
It’s important that future research "not only address the tibiofemoral joint, but also the patellofemoral joint," said lead investigator Joshua Stefanik, Ph.D., a research associate in Boston University’s Clinical Epidemiology, Research, and Training Unit, said at the World Congress on Osteoarthritis.
The findings are surprising because "historically, everybody focuses on the tibiofemoral joint. We are probably missing a lot of disease" by relying on radiographs and clinical exams for diagnosis; they aren’t very good at picking up problems in the patellofemoral joint (PFJ), said Dr. David Hunter in an interview.
But even if it does a better job, "I wouldn’t encourage people to do an MRI if they have knee osteoarthritis." The results won’t change clinical management, and if meniscal tears are found, patients may end up in the operating room having an unnecessary meniscectomy, "which doesn’t do them any favors. Typically, the meniscus isn’t the problem." Tears are common and generally asymptomatic, said Dr. Hunter, a professor of medicine at the University of Sydney.
"Once clinicians are better educated about [such] dangers, MRI may be a good way to pick up [PFJ] disease," he said. Patellofemoral braces and PFJ-modifying shoe inserts are among the management options.
The 970 subjects in the study were part of the Framingham (Mass.) Osteoarthritis Study and were recruited from that community without regards to knee pain or osteoarthritis. Their mean age was 63.4 years and mean body mass index was 28.6 kg/m2; 57% were women, and 22% complained of knee pain. Cases of inflammatory arthritis were excluded. One knee was studied in each patient.
Radiographs found tibiofemoral joint (TFJ) damage in 11.9% of subjects, PFJ damage in just 1.4%, and damage in both joints in 5.9%.
The prevalence of PFJ problems was much higher on MRI; 20.4% had PFJ cartilage damage (WORMS [Whole-Organ Magnetic Resonance Imaging Score] greater than or equal to 2); 10.4% TFJ damage; and 44.2% damage in both joints. When both joints were involved, the most severe lesions were usually in the PFJ.
Similarly, 18.6% of subjects had PFJ cartilage damage extending down to bone (WORMS 2.5, greater than or equal to 5); 8% had TFJ damage down to bone; and 7.8% damage down to the bone in both joints.
The team found PFJ bone marrow lesions (WORMS greater than or equal to 1) in 17.9% of subjects; TFJ lesions in 16.5%; and lesions in both joints in 21.8%. Again, the most severe lesions were usually in the PFJ.
Finally, 15.2% of the Framingham subjects had both bone marrow lesions and cartilage damage down to bone in their PFJs, while only 8.8% had both problems in their TFJs; 4.4% had them in both joints.
Patterns were similar for men and women, and in knees with pain. The researchers used 1.5 T MRI with turbo spin-echo, fat-suppressed images in the sagittal, coronal, and axial planes.
The congress was sponsored by the Osteoarthritis Research Society International. Dr. Stefanik and Dr. Hunter reported no financial disclosures. The National Institutes of Health and the Arthritis Foundation funded the work.