Abstract
The Erlenmeyer flask deformity is a common skeletal modeling deformity, but current classification systems are binary and may restrict its utility as a predictor of associated skeletal conditions. A quantifiable 3-point system of severity classification could improve its predictive potential in disease. Ratios were derived from volumes of regions of interests drawn in 50 Gaucher’s disease patients. ROIs were drawn from the distal physis to 2 cm proximal, 2 cm to 4 cm, and 4 cm to 6 cm. Width was also measured at each of these boundaries. Two readers rated these 100 femurs using a 3-point scale of severity classification. Weighted kappa indicated reliability and one-way analysis of variance characterized ratio differences across the severity scale. Accuracy analyses allowed determination of clinical cutoffs for each ratio. Pearson’s correlations assessed the associations of volume and width with a shape-based concavity metric of the femur. The volume ratio incorporating the metaphyseal region from 0 to 2 cm and the diametaphyseal region at 4–6 cm was most accurate at distinguishing femurs on the 3-point scale. Receiver operating characteristic curves for this ratio indicated areas of 0.95 to distinguish normal and mild femurs and 0.93 to distinguish mild and severe femurs. Volume was moderately associated with the degree of femur concavity. The proposed volume ratio method is an objective, proficient method at distinguishing severities of the Erlenmeyer flask deformity with the potential for automation. This may have application across diseases associated with the deformity and deficient osteoclast-mediated modeling of growing bone.
Highlights
Erlenmeyer flask deformities (EFDs) are well-documented in a multitude of diseases with musculoskeletal involvement, including osteopetrosis, metaphyseal dysplasia, Gaucher’s, Niemann-Pick, and achondroplasia [1,2,3]
Our findings demonstrate that volume ratios incorporating both the metaphysis and a diametaphyseal region can best delineate severities of EFD and tend to be more proficient than width ratios because they account for loss of distal femur concavity
Several clinical cutoffs based on these volume ratios had high receiver operating characteristic (ROC) area under the curve (AUC), suggesting their potential utility among radiologists to accurately classify EFD severity
Summary
Erlenmeyer flask deformities (EFDs) are well-documented in a multitude of diseases with musculoskeletal involvement, including osteopetrosis, metaphyseal dysplasia, Gaucher’s, Niemann-Pick, and achondroplasia [1,2,3]. Skeletal Radiol (2021) 50:361–369 resemblance to the lower portion of an Erlenmeyer flask, the degree of undertubulation varies across patients. A ratio > 0.58 between the width at 4 cm and the width at the physis was reported as being the most robust and accurate differentiator of EFD from non-EFD femurs against radiologist ratings. This differentiation was binary and did not account for the degree of undertubulation
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