Improved demonstration of cartilage narrowing in the knee joint using standing PA flexed radiographs.

Objective: To compare standing PA flexed (SPAF) knee radiographs of the knees with standing full-extension AP(SAP) radiographs for demonstration of narrowing of the articular cartilage of the knee joint and the presence and size of osteophytes and to determine if sclerosis is a predictor of the severity of joint space narrowing.

Design: 220 knees in 110 consecutive patients visiting the orthopaedic clinic with knee pain and having both SPAF radiographs and SAP radiographs at the same visit were evaluated by a musculoskeletal radiologist for cartilage narrowing in the knee joint using a scale 0-3 with 0= normal and 3= bone on bone. Osteophytes were also graded 0-3 and sclerosis as present or absent.

Patients: The subjects were patients of one of the authors (C.A.J) who ordered both types of radiographs on most of his patients.

Results: In 47% of knees the SPAF radiograph showed narrowing more severe than the SAP radiograph. In 5% the SAP view showed narrowing more severe than the SPAF view. In the medial compartment the SPAF view showed significantly larger osteophytes than the SAP view. The osteophyte size difference was not significant in the lateral compartment. If sclerosis was present on the AP view, there was a greater than 80% chance that the SPAF view would show greater narrowing.

Conclusion: The SPAF radiograph frequently shows more cartilage narrowing in the knee joint than does the SAP view. It is valuable for routine use or when the clinical severity of arthritis in the knee joint seems to be greater than that demonstrated on the AP standing view. Sclerosis on the SAP view makes it especially likely that the SPAF view will show greater cartilage narrowing.