Our study demonstrates the poor contribution of MRI for the diagnosis of a medial plica syndrome.
In particular,
the criteria usually described in the literature,
such as a thick long and hypo intense band that covers the anterior surface of the medial femoral condyle are not associated with a medio patellar syndrome.
These results are in according with Boles and al who did not find MR characteristics (width,
thickness,
relation to the trochlear cartilage,
and effusion) significantly predictive of resection [10].
Monabang and al found a significant association when the plica was interposed on more than 5 transverse slices with focal fluid adjacent to the plica [11],
and Jee and al suspected a pathologic medial plica with a criterion of extension beyond the medial end of the patella on axial images [6].
We did not find these results in our cohort.
The result for the floating aspect was unexpected because it is predominant in the control group,
and the length is greater,
supporting the hypothesis that plicae are collapsed and more visible after intra-articular distension.
On the contrary,
floating aspect is rare in the study group.
This data probably explains a large number of plica shown in daily practice explained by a knee pathology generating intra articular effusion,
without being associated with a medio patellar syndrome.
Tendency to patellar chondromalacia in the control group makes us wonder about the pathogenic role of the floating plica on cartilage of these patients.
This assumption could also explain the dissonance between epidemiological and autopsic data,
because the cadaveric phenomena would prevent the visualizing of the medial plica.
Conversely,
intra-articular distension applied during arthroscopy would facilitate its visualization.
Then,
we can ask ourselves about the role of MR arthrography to help diagnosis of a medial plica,
but it remains an invasive procedure for teenagers.
Furthermore,
our study provides epidemiological information on patients suffering of a medial plica syndrome.
This pathology affects teenagers (average age: 14,2 years old),
with a female dominance (Sexe Ratio=3,75),
and with bilateral involvement in 21% of cases (genetic predisposition suspected).
Sport was present in 26% of cases,
triggering trauma in 31%,
crepitus in 5%,
instability in 11%,
pseudo-locking in 47% and quadriceps atrophy in 52%.
In our cohort,
the sensibility of a painful medial cord rolling under the skin was 79% with a specificity of 100 %,
making it a strong diagnosis sign.
There had not any patellar tap.
Complete regression of symptoms was obtained in 74% after arthroscopic resection,
which demonstrates surgery efficiency.
In our work,
several limitations should be taken into account.
The major one comes from the control group that is not fully asymptomatic but presents a pathology generating an intra-articular effusion,
which potentially causes alterations of the plica on MRI images.
Second,
patients and control subjects were not matched individually for age and gender.
Third,
this is a retrospective study with a small population.
Fourth,
all imaging were not performed on the same machine,
and they were not acquired in the same conditions (some were 3D Cube acquisition).
Finally,
despite a blind analysis and a strict analysis of axial T2 Fat-Sat weighted images of the femoro patellar joint,
ligament injury or bone oedema can suggest belonging to the control group.
Others studies with more patients are necessary to confirm this results,
in particular thickness of the medial plica that tends to be greater in the study group.
Paczesny and Kruczynski suggested the aid of dynamic sonography to detect abnormalities of medial plica,
with good sensitivity (90%) and specificity (83%).
Three sonographic criteria were studied: continuous echo sliding over the medial femoral condyle during medial and lateral movement of the patella,
entry of the echo under the patella during medial movement of the patella and pain or discomfort during dynamic sonography [12].
To conclude,
if suspicion of a medial plica syndrome,
MRI is primarily used to eliminate differential diagnosis.
Diagnostic should not be questioned without a long and thick band impinging the femoro-patellar joint.
On the contrary,
a large number of medial plica shown in daily practice are probable incidentalomas revealed by intra-articular effusion.