3-foot standing AP versus 45 degrees PA radiograph for osteoarthritis of the knee

Objective: Flexion and erect standing radiographs were evaluated in the cur rent study to compare their sensitivity in detecting articular cartilage we ar. Design: Prospective cohort study. Setting: A tertiary care hospital outpatient orthopedic clinic. Patients: All patients with osteoarthritis of the knee ages 40 to 75 schedu led for arthroscopic debridement between March 1995 and November 1997 were considered for the current study. Intervention: Radiographs were obtained 1 week preoperatively in both the S -foot standing anteroposterior (AP) and a 45 degrees posteroanterior (PA) f lexion weight-bearing projection. Joint space height was measured with a ru ler in millimeters at the narrowest point of each compartment. All radiogra phs were assessed by two independent observers who were blinded to the arth roscopic findings and clinical symptoms of the subjects. Main Outcome Measures: Prediction accuracy of each radiograph for severe Gr ade IV articular cartilage wear in tibiofemoral compartments. Results: One hundred fifty-two patients with a mean (+/- SD) age of 60.5 +/ - 8.5 years were enrolled in the study. Fifty-one percent were female. Twel ve patients were categorized as having severe lateral compartment articular chondropathy (Grade IV) at the time of arthroscopy, The lateral joint spac e height averaged 1.0 +/- 1.7 mm SD on the 450 PA radiograph compared with 2.7 +/- 1.1 mm SD on the 3-foot standing AP view. Using a cutoff of 2 mm or less, the 45 degrees PA view was much more sensitive (83% versus 42%) at c orrectly detecting the most severe chondropathy. Forty-one patients were cl assified with severe Grade IV medial compartment chondropathy at arthroscop y. There was little difference in the average joint space height measured b y the 45 degrees PA view (1.4 +/- 1.4 mm SD) or the 3-foot standing AP view (1.9 +/- 1.6 mm SD). A number of cutoff measures were evaluated, but no si gnificant advantage could be found for either view in evaluating the medial compartment severity. Conclusions: The bilateral 450 PA is superior for detecting lateral compart ment wear but offers no advantage on the medial side. This view should be c onsidered as the screening radiograph of choice in evaluating osteoarthriti s of the knee.