Summary

The severity of trochlea dysplasia can be determined by the height of the Pathologic Double Contour (hPDC)

Abstract

Background

Multiple qualitative and quantitative measures have been described to define trochlea dysplasia. The current classifications of trochlea dysplasia (Dejour and Bristol-Oswestry) are based on qualitative variables which rely on the subjective interpretation of the surgeon. The lack of a quantitative value makes it difficult to determine severity of dysplasia and therefore when to treat. Pathologic Double Contour (PDC) sign is an area of convex lateral trochlea which is elevated over the contour of the medial femoral condyle (MFC) on axial views of MRI.
The goal of this study is to determine if the height of the Pathologic Double Contour can determine the severity of disease and guide treatment

Methods

Three cohorts (235 patients) were included in the study.
Cohort 1: 100 patients who had knee surgery for conditions not related with patella instability.
Cohort 2: 73 patients treated of patella instability with either MPFL reconstruction or a combined MPFL reconstruction and tibial tuberosity transfer.
Cohort 3: 62 patients who had severe trochlea dysplasia to warrant a trochleoplasty.
The presence of the Pathologic Double Contour was determined at three specific anatomic locations. When present, the height of the Pathologic Double Contour (hPDC and hPDCr) was measured at its highest point.
A ROC curve analysis was performed using the hPDC and hPDCr guide to determine the severity of trochlear dysplasia needing trochleoplasty.

Results

PDC was seen in 100%, 47.9% and 4% of patients in Cohort 3, 2, 1 respectively (p<0.001). There was statistically significant difference in the height of the PDC of the cohort 2 (mean hPDC= 2.98mm, SD 1.32; mean hPDCr= 3.85, SD 1.972) compared to the cohort 3 (mean hPDC=6.75mm, SD 2.14; mean hPDCr=8.64, SD 2.48), t (92)=-9.073, p<.001).
t (92)=-9.746, p<.001).
On ROC analysis, hPDC of 3.9mm gave a sensitivity of 96.8%, specificity of 97.1% and hPDCr of 5.43mm gave a sensitivity of 96.8%, specificity of 98.3%.

Conclusion

The Pathologic Double Contour height (hPDC and hPDCr) can determine the severity of the trochlea dysplasia and guide treatment.