Estimating Skeletal Maturity by Segmented Linear Modeling of Key AP Knee Radiographic Parameters

Abstract

Background:The recently described Modified Fels knee system allows for accurate skeletal maturity estimation using a single anteroposterior knee radiograph but requires evaluation of 7 parameters. A faster method may have clinical utility in the outpatient setting. Methods: Seven anteroposterior knee radiographic parameters associated with 90% of the final height (an enhanced skeletal maturity standard compared with peak height velocity) were analyzed in 78 children. Segmented linear regression and generalized estimating equation analyses were used to identify the subsets of parameters most important for accurate skeletal maturity estimation for different patient demographics and parameter scores. This process produced abbreviated skeletal maturity systems, which include fewer parameters and are quicker to use. The accuracy of the resulting abbreviated skeletal maturity systems was evaluated and compared with the full 7-parameter Modified Fels knee system and with the Greulich and Pyle (GP) left-hand bone age. Results: A total of 326 left knee radiographs from 41 girls (range, 7 to 15 y) and 37 boys (range, 9 to 17 y) were included. Models generated by segmented regression and generalized estimating equation analysis required fewer parameters (range, 1 to 5 parameters) than the full Modified Fels knee system (7 parameters). Skeletal age estimates produced by segmented regression models were more accurate than GP (P < 0.05) and not significantly different from the full Modified Fels system (P > 0.05). The percentage of outlier estimations (estimations > 1 y off from actual skeletal age) made by segmented regression models was not significantly different from GP (P > 0.05) or the Modified Fels knee system (P > 0.05). Conclusion: An abbreviated version of the Modified Fels knee system estimates skeletal maturity more accurately than the GP system with just 2 to 3 radiographic knee parameters. Clinical Relevance: The abbreviated Modified Fels knee system may allow for rapid skeletal age estimation (~30 s) appropriate for routine outpatient practice.

The Modified Fels and Abbreviated Modified Fels Knee Skeletal-Maturity Systems in the Prediction of Leg-Length Discrepancy

“…The comparable results obtained by the abFels system relative to the mFels system also represent an encouraging finding, as the abFels is estimated to take approximately 30 seconds for analysis 13 . Based on the sex and femoral-capping (FemK) 11 score for any given patient, abFels determines which additional 1 or 2 parameters are highest-yield and excludes the remaining parameters that do not add value at any given skeletal-maturity range.…”

“…The mFels system has been shown to be effective in the prediction of leg length at skeletal maturity, is resistant to rotational variation, and outperforms leg-length predictions based on chronological age 11,12 . In an effort to further streamline this method, the creators of the mFels system also developed an Abbreviated Modified Fels (abFels) system using only 2 or 3 radiographic knee parameters, with potentially similarly effective skeletal maturity estimation 13 .…”

The Reliability of the Modified Fels Knee Skeletal Maturity System

“…abFels requires only 30 seconds to produce an SAE, making it useful even in busy clinical practices. 25 The faster, less taxing (due to fewer XR parameters requiring evaluation) abFels system has made it possible for the authors to rapidly calculate a skeletal age upon first review of a patient's knee radiographs in clinic, before entering the patient's examination room. This abFels system is currently under validation testing using a modern data set.…”

“…The subset of radiographic parameters utilized are selected by the app based on individual patient characteristics. abFels requires only 30 seconds to produce an SAE, making it useful even in busy clinical practices 25 . The faster, less taxing (due to fewer XR parameters requiring evaluation) abFels system has made it possible for the authors to rapidly calculate a skeletal age upon first review of a patient’s knee radiographs in clinic, before entering the patient’s examination room.…”

“…This abFels system is currently under validation testing using a modern data set. 25 The (What's the Skeletal Maturity?) mobile app also allows for evidence-based SAE based on any commonly obtained orthopaedic radiograph: shoulder, elbow, wrist, hand, hip, ankle, or foot XRs.…”