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Tubular metal furniture by Marcel Breuer helped reinvent the wheelchair. Weight-bearing PA view is taken to detect early arthritis.
Disclaimer: As a service to our readers, Harvard Health Publishing provides access to our library of archived content. While the skyline view has been recommended due to more reproducible assessment of the patellofemoral joint space, the lateral view may be easier to acquire and provides different information.
Of the different views, skylines had to be excluded most often because the image of the patellofemoral joint was technically unsatisfactory. As long as at least an anteroposterior view and one image of the patellofemoral joint is obtained (either skyline or lateral), few cases with radiographic disease will be missed.
To detect osteoarthritis in the patellofemoral joint, skyline or lateral views are needed. Furthermore, the lateral view visualizes the posterior aspect of the tibiofemoral joint, an area usually missed on the AP view because of the superior sweep of the posterior femur.
The reproducibility of one feature in one location should not be the sole basis for the selection of images. Rather, the appropriate choice of an image depends, in large part, on its ability to detect disease when disease is present, an especially acute issue in osteoarthritis, given the putative lack of sensitivity of plain radiographs.
Obviously, the optimal detection of abnormalities could be achieved by obtaining all three (or even more) images of each knee, but this is often not practicable. It can be difficult to obtain images of the weight-bearing patellofemoral joint consistently without a highly trained technician.
For clinical evaluation and population studies, it is important to choose views that maximally detect more radiographic OA and yield technically satisfactory films. To determine the sensitivity of different combinations of X ray views for detecting radiographic OA, we evaluated the relative performance of PA, skyline and lateral views in a group of persons with knee OA who had evidence of osteoarthritis on at least one radiographic view, to determine how often OA was missed when only one or two views were obtained and to evaluate which combination of views should be recommended for clinical practice and for studies.
Three X ray views (PA, lateral and skyline) were obtained on both knees for all subjects. The subjects received weight-bearing AP (using the Framingham OA study protocol ) and supine skyline and weight-bearing lateral films using standard technologistselected techniques.
Intrareader reliability for scores of individual radiographic features was high ( = 0.6–0.9). A knee was eligible for inclusion in the analysis of all three X ray views were of acceptable quality and there was a definite osteophyte on any of the views.
A film was defined as unreadable or as technically unsatisfactory when neither osteophytes nor jointspace narrowing could be scored accurately. Occasionally, osteophytes were scored, but not narrowing, and these knees were included for definitions of OA that are osteophytebased.
Because sensitivity may change depending on how one defines X ray OA and several definitions have been proposed, we used the following definitions of symptomatic knee OA: (1) knee symptoms plus a definite osteophyte of grade 1 (0–3 scale); (2) knee symptoms plus a definite osteophyte of grade 2 (0–3 scale); (3) knee symptoms plus either an osteophyte of grade 2 or jointspace narrowing of grade 2 (0–3 scale) with at least one other feature (an osteophyte grade 1, sclerosis or cyst). as a definition of radiographic knee OA incorporating multiple views.
The men had a lower body mass index than the women (Table 1). When OA was defined as symptoms plus a grade2 osteophyte, the two film combinations were also quite similar in sensitivity.
We then used the definition of radiographic disease that defines disease as present when either a moderatesized osteophyte ( grade 2) or grade2 jointspace narrowing plus another radiographic feature (smaller osteophyte, cyst, sclerosis) is present. Using this definition (Table 4), we found similar results, with the sensitivity of AP and skyline views almost identical to the sensitivity of the AP plus lateral combination (each roughly 95%).
Definition of knee OA: symptoms and a large osteophyte (grade 2) Table 5. Characteristics of knees with OA that would be missed in strategies using only two X rayviews.
Table 5. Characteristics of knees with OA that would be missed in strategies using only two X rayviews. Excluding either a skyline or a lateral view in a screening examination and obtaining the other two views will result in 4–7% of OA cases being missed, depending on how one defines X ray OA.
However, for multigenre studies, AP plus lateral views may be the more desirable combination, as it is more likely to be technically satisfactory without intensive technician training, and, in addition, images the posterior compartment of the knee, which is not seen in other views. Indeed, epidemiological studies evaluating risk factors associated with patellofemoral arthritis were all performed using lateral views.
Our findings have implications for both clinical practice and studies of knee osteoarthritis. The main reasons were positioning problems including incorrect flexion of the knee, an abnormally rotated view, and the patellofemoral joint space being cut off the edge of the film.
Results of inquiries among X ray technologists in three X rays suites in Boston suggest that a ‘ knee series' in most locations includes AP and lateral but not skyline films, and that skyline views are obtained infrequently. The technical difficulty of obtaining highquality skyline vs lateral views, the infrequency with which technologists take skyline views and the variability of technique all combine to create problems in quality.
For clinical practice, skyline views may not provide optimal information unless the technologists are specifically trained to take them. Our adoption of a weight-bearing skyline technique provided highquality images, but this method is unfamiliar to almost all X ray technologists.
We cannot address larger questions about the usefulness of radiographs in knee OA. However, if the goal of a clinical referral or of a study is to detect the presence of radiographic OA, a combination of an AP and a lateral view may be preferable to the combination of AP and skyline views for the reasons we have outlined.
The implications of our findings for studies aimed at identifying those with OA include the recommendation, for multigenre studies which involve many X ray technologists, that lateral films may be preferred to skyline films. We are indebted to Sara McLaughlin, Sean Johnson, Karin Mandolin and Ellen Mitchell for coordinating the study and examining the subjects, to Pam McLeod and other outstanding X ray technologists, who took the X rays, to Josh Goldman for coordinating X ray readings, and to the subjects for their time and cooperation.
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