Variability in developmental timings of the knee in young American children as assessed through Pyle and Hoerr’s radiographic atlas

Methods of Assessing Skeletal Maturity When Planning Surgeries About the Knee

Increased participation in youth sports has led to more knee injuries necessitating surgical intervention. Among the youngest athletes, such procedures typically involve physeal-respecting techniques for anterior cruciate ligament reconstruction, medial patellofemoral ligament reconstruction for patellar instability, osteochondritis dissecans fixation, and implant-mediated guided growth procedures. In each case, the choice of appropriate intervention is critically dependent on a patient's skeletal maturity. Compared with chronologic age, skeletal age accounts for individual maturation and is the benchmark for determination of development in orthopaedics. This is historically assessed using the Greulich and Pyle method, in which bone age is determined through comparison of a patient's hand radiograph with the closest standard radiograph from an atlas of American children from the early 1900s. In the setting of knee pathology, obtaining additional imaging requires further radiation and time. Several bone age determination methods exist incorporating radiographic characteristics of the distal femur, proximal tibia, and/or proximal fibula. This study therefore sought to review available methods for determination of skeletal age when planning surgeries about the knee using readily available, routine knee imaging. The review focuses on both radiograph and MRI-based skeletal maturity staging systems that surgeons may use to guide appropriate treatment while describing the strengths and weaknesses of each method.

Development and Validation of a Shorthand Knee MRI Atlas for Bone Age Estimation in the Korean Population

Background

Estimating skeletal maturity is crucial for treating pediatric knee conditions. Recently, a knee bone age atlas based on the magnetic resonance imaging (MRI) data of pediatric and adolescent population in Southern California (the San Diego atlas) was published. However, its accuracy in other populations has not been verified.

Purpose

To (1) validate the San Diego atlas in a South Korean pediatric and adolescent population and (2) create and validate a shorthand knee MRI atlas for bone age estimation tailored to South Korean pediatric and adolescent population (the Korean shorthand atlas).

Study Design

Cohort study (diagnosis); Level of evidence, 2.

Methods

We retrospectively analyzed the data of 695 participants aged ≤18 years with normal knee MRI findings between 2000 and 2019. To create the Korean shorthand atlas, age-specific features based on the San Diego atlas that appeared on the evaluated MRI scans (n = 417) were modified to reduce the standard deviation of age. In a separate data set (n = 278), the accuracy of both the San Diego and the Korean shorthand atlases was validated by comparing the knee bone age with the chronological age and determining the correlation between bone age and chronological age.

Results

In the overall study population, the mean bone age based on the San Diego atlas did not differ from the mean chronological age, and a very strong correlation was observed between them (r S = 0.95). However, the mean bone age based on the San Diego atlas significantly differed from the mean chronological age in female participants aged 7 to 12.9 years (0.6 years younger; P = .003) and in male participants aged 14.0 to 18.0 years (0.4 years older; P = .045). The mean bone age assessed based on the Korean shorthand atlas did not significantly differ from the mean chronological age in any age or sex subgroup and was also very strongly correlated with the mean chronological age (r S = 0.94) in the overall population.

Conclusion

The San Diego atlas was accurate in estimating bone age in Korean pediatric and adolescent population except for certain age ranges. The Korean shorthand atlas was an accurate tool for estimating bone age in the Korean pediatric and adolescent population at any age range.

Pediatric age estimation from radiographs of the knee using deep learning

OBJECTIVES

Age estimation, especially in pediatric patients, is regularly used in different contexts ranging from forensic over medicolegal to clinical applications. A deep neural network has been developed to automatically estimate chronological age from knee radiographs in pediatric patients.

METHODS

In this retrospective study, 3816 radiographs of the knee from pediatric patients from a German population (acquired between January 2008 and December 2018) were collected to train a neural network. The network was trained to predict chronological age from the knee radiographs and was evaluated on an independent validation cohort of 423 radiographs (acquired between January 2019 and December 2020) and on an external validation cohort of 197 radiographs.

RESULTS

The model showed a mean absolute error of 0.86 ± 0.72 years and 0.9 ± 0.71 years on the internal and external validation cohorts, respectively. Separating age classes (< 14 years from ≥ 14 years and < 18 years from ≥ 18 years) showed AUCs between 0.94 and 0.98.

CONCLUSIONS

The chronological age of pediatric patients can be estimated with good accuracy from radiographs of the knee using a deep neural network.

KEY POINTS

• Radiographs of the knee can be used for age estimations in pediatric patients using a standard deep neural network. • The network showed a mean absolute error of 0.86 ± 0.72 years in an internal validation cohort and of 0.9 ± 0.71 years in an external validation cohort. • The network can be used to separate the age classes < 14 years from ≥ 14 years with an AUC of 0.97 and < 18 years from ≥ 18 years with an AUC of 0.94.

Systematic Isolation of Key Parameters for Estimating Skeletal Maturity on Knee Radiographs

BACKGROUND

The ability to estimate skeletal maturity using a knee radiograph would be useful in anterior cruciate ligament (ACL) injuries and limb-length discrepancy in immature patients. Currently, a quick, accurate, and reproducible method is lacking.

METHODS

Serial knee radiographs made 3 years before to 2 years following the chronologic age associated with 90% of final height (an enhanced skeletal maturity gold standard compared with peak height velocity) were analyzed in 78 children. The Pyle and Hoerr (PH) knee method was simplified by developing discrete stages for the distal part of the femur, the proximal part of the tibia, the proximal part of the fibula, and the patella. The Roche-Wainer-Thissen (RWT) knee method was simplified from the 36 original parameters to 14 parameters by removing parameters that were poorly defined, were not relevant to the peripubertal age range, were poorly correlated with 90% final height, or were poorly reliable on a 20-radiograph pilot analysis. We also compared the recently described central peak value (CPV) of the distal part of the femur. The Greulich and Pyle (GP) left-hand bone age was included for comparison.

RESULTS

In this study, 326 left knee radiographs from 41 girls (age range, 7 to 15 years) and 37 boys (age range, 9 to 17 years) were included. Stepwise linear regression showed higher correlation in predicting years from 90% final height using the modified RWT and demographic characteristics (R2 = 0.921) compared with demographic characteristics alone (R2 = 0.840), CPV and demographic characteristics (R2 = 0.866), GP and demographic characteristics (R2 = 0.899), and PH and demographic characteristics (R2 = 0.902). Seven parameters were excluded from the RWT and demographic characteristics model using stepwise linear regression and generalized estimating equations analysis, leaving 7 parameters (2 femoral, 4 tibial, and 1 fibular) in the final model. Compared with RWT and demographic characteristics (R2 = 0.921), there were minimal incremental increases by adding CPV (R2 = 0.921), GP (R2 = 0.925), or PH (R2 = 0.931).

CONCLUSIONS

This large analysis of knee skeletal maturity systems isolated 7 discrete radiographic knee parameters that theoretically outperform the GP bone age in estimating skeletal maturity.

CLINICAL RELEVANCE

We present a modified knee skeletal maturity system that can potentially preclude the need for additional imaging of the hand and wrist in reliably estimating skeletal maturity.

The growth pattern of Neandertals, reconstructed from a juvenile skeleton from El Sidrón (Spain)

Ontogenetic studies help us understand the processes of evolutionary change. Previous studies on Neandertals have focused mainly on dental development and inferred an accelerated pace of general growth. We report on a juvenile partial skeleton (El Sidrón J1) preserving cranio-dental and postcranial remains. We used dental histology to estimate the age at death to be 7.7 years. Maturation of most elements fell within the expected range of modern humans at this age. The exceptions were the atlas and mid-thoracic vertebrae, which remained at the 5- to 6-year stage of development. Furthermore, endocranial features suggest that brain growth was not yet completed. The vertebral maturation pattern and extended brain growth most likely reflect Neandertal physiology and ontogenetic energy constraints rather than any fundamental difference in the overall pace of growth in this extinct human.

The Creation and Validation of a Knee Bone Age Atlas Utilizing MRI

BACKGROUND

In managing many pediatric knee conditions, an accurate bone age assessment may be critical for diagnostic, prognostic, and treatment purposes. The aim of this study was to create an atlas of magnetic resonance imaging (MRI) studies of the knee spanning the pediatric and adolescent years that would enable accurate skeletal age to be assessed, potentially forgoing the need for a left-hand radiograph.

METHODS

We performed a retrospective assessment of 11 to 31 MRIs from male and female patients of each age from 2 to 19 years. Radiographic features specific to the patella, tibia, fibula, and femur were documented with respect to their presence or absence. From these data, age and sex "standards" were established, allowing the creation on an atlas. A separate cohort of MRIs with 2 to 13 patients per age and sex was then used to validate the reliability and reproducibility of the atlas.

RESULTS

In the creation of the atlas, a total of 859 MRIs were reviewed. The patella, tibia, fibula, and femur were noted to undergo a reproducible sequence of skeletal ossification. The patella provided the best age assessment in early childhood. Features specific to the tibia, particularly ossification of the tibial spine and the tibial tubercle, were of particular importance in children between the ages of 6 and 12 years. MRI features of the fibula and femur served a more important role in age assessment later in skeletal maturity. From a separate cohort of 323 MRIs utilized to validate the atlas, a strong correlation between chronologic age and bone age was shown, as was excellent interobserver and intraobserver reliability.

CONCLUSIONS

The predictable ossification pattern of the patella, tibia, fibula, and femur enables accurate bone age calculations to be made from knee MRIs. When treating conditions about the knee that require MRI, obtaining an additional left-hand radiograph for bone age may be unnecessary. This information can be used to potentially avoid additional radiation exposure, impart cost savings, and lead to greater clinic efficiency.