The Journal of Bone and Joint Surgery, Vol 70, Issue 9 1331-1337, Copyright © 1988 by Journal of Bone and Joint Surgery, Inc
Subluxation of the patella. Computed tomography analysis of patellofemoral congruence
M Inoue, K Shino, H Hirose, S Horibe and K Ono
Osaka University Hospital, Department of Orthopaedic Surgery, Osaka University Medical School, Japan.
Fifty patients who had patellar subluxation and thirty control subjects
were examined using axial roentgenograms of the patellofemoral joint that
were made with the knee in 30 and 45 degrees of flexion, as well as
computed tomography scans that were made with the knee in full extension.
The amount of lateral patellar tilt was quantitatively assessed using the
lateral patellofemoral angle, as described by Laurin et al., and the
congruence angle, as described by Merchant et al. In both the control
subjects and the patients, the angle of Laurin et al. changed significantly
when the knee was flexed from full extension to 30 degrees. The difference
between the groups was statistically significant at each angle of flexion
of the knee, and the difference between the groups was most prominent on
the computed tomography scans that were made with the knee in full
extension (p less than 0.001). In the patients, the average congruence
angle (as described by Merchant et al.) was 5 degrees and in the control
subjects, -10 degrees. This indicated that, in our patients, the extent of
the patellar subluxation was less than that in previously reported series,
and, as a result, the sensitivity of the congruence angle in diagnosing
patellar subluxation was only 0.30. In contrast, the sensitivity and
specificity of the computed tomography scans for diagnosing patellar
subluxation were 0.96 and 0.90, respectively--that is, they were higher
than the values that were obtained using any axial roentgenograms. Thus,
our results indicated that patellar subluxation can be detected more
accurately by using computed tomography with the knee in full extension
than by using conventional axial roentgenograms.
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