They then measured the distance between this line and the lateral border of the patella (a). They also measured the distance between this line and the medial border of the patella (b). BO was calculated as the formula: 100a/(a + b).
Participants had weight-bearing skyline radiography, and the x-rays were read by a rheumatologist who used a four-point scale to grade the presence of osteophytes in the medial and lateral parts of the patella and femur and the joint space narrowing in the medial and lateral parts of the PF joint.
There was a statistically significant association between PLR and both osteophytes and joint space narrowing in the lateral compartment. With increasing PLR, there was an increased risk of lateral joint space narrowing. A similar trend was found between increasing PLR and increasing lateral patellar osteophytosis. There was no significant association between PLR and indices of radiographic PF OA in the medial PF compartment.
SA showed a statistically significant association with medial joint space narrowing and lateral and medial patellar osteophytosis—with increasing SA, there was increased risk of medial joint space narrowing. LPTA showed a statistically significant association with joint space narrowing and osteophytosis of the lateral PF compartment. A more laterally displaced patella was positively associated with increased lateral joint space narrowing and also with lateral patellar osteophytosis. In contrast, lateral patella displacement was negatively associated with medial joint space narrowing—increased medial displacement of the patella was associated with medial joint space narrowing.
The findings suggest that alignment of the patella may be an important factor influencing PF joint degeneration, due to the aberrant distribution of forces with activity. “I think that the important message for clinicians here is that to date, the majority of people really haven't considered problems of malalignment of the patellofemoral joint as important features in patellofemoral osteoarthritis. This study suggests that they're strongly associated,” said Dr. Hunter.
The fact that MRI was performed with the knee placed in a supine position likely means that the findings from this analysis are conservative for measures that could potentially change with weight bearing (LPTA and BO).