Purpose
The aim of this study was to investigate the pathoanatomic features of patellar instability
by arthroscopically comparing patellofemoral congruence with rotation of the knee
joint and/or electrical stimulation of the quadriceps (ESQ) between knees with and
without patellar instability.
Methods
We retrospectively examined 83 knee joints in 83 patients. The joints were classified
into 2 groups: group 1 comprised those without a history of patellar dislocation and
included 59 patients (25 male and 34 female patients), and group 2 comprised those
with a history of patellar dislocation and included 24 patients (9 male and 15 female
patients). Evaluation of patellofemoral congruence at 30° of flexion of the knee joint
was conducted based on an axial radiograph and arthroscopic findings. The congruence
angle was measured on the radiograph. The position of the patellar central ridge (PPCR)
on the trochlear groove during arthroscopy was measured using still video frames of
knee joints with rotational stress and/or ESQ. Statistical differences in the measurements
between the 2 groups were assessed with the unpaired t test and the area under the receiver operating characteristic curve of each measurement.
Results
There were significant differences (P < .0001) between the 2 groups in the congruence angle on radiographs and PPCR in
knee joints with rotational stress and/or ESQ on arthroscopy. External and internal
rotation of the knee joint caused lateral and medial patellar shift, respectively,
in both groups, but the shift was significantly larger in group 2. ESQ in addition
to rotation caused further patellar shift in group 2 but reduced patellar shift in
group 1. Measurement of PPCR with external rotation of the knee and ESQ was the only
method to show an area under the receiver operating characteristic curve of 1.
Conclusions
There were significant differences in the effects of rotation of the knee joint and/or
ESQ on patellofemoral congruence at 30° of flexion of the knee joint on arthroscopy
between knees with and without patellar instability.
Level of Evidence
Level III, diagnostic study of nonconsecutive patients.
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Article info
Publication history
Published online: January 02, 2014
Accepted:
November 7,
2013
Received:
April 7,
2013
Footnotes
The authors report that they have no conflicts of interest in the authorship and publication of this article.
Identification
Copyright
© 2014 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.
