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

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.

Automated Distal Radius and Ulna Skeletal Maturity Grading from Hand Radiographs with an Attention Multi-Task Learning Method

Background: Assessment of skeletal maturity is a common clinical practice to investigate adolescent growth and endocrine disorders. The distal radius and ulna (DRU) maturity classification is a practical and easy-to-use scheme that was designed for adolescent idiopathic scoliosis clinical management and presents high sensitivity in predicting the growth peak and cessation among adolescents. However, time-consuming and error-prone manual assessment limits DRU in clinical application. Methods: In this study, we propose a multi-task learning framework with an attention mechanism for the joint segmentation and classification of the distal radius and ulna in hand X-ray images. The proposed framework consists of two sub-networks: an encoder-decoder structure with attention gates for segmentation and a slight convolutional network for classification. Results: With a transfer learning strategy, the proposed framework improved DRU segmentation and classification over the single task learning counterparts and previously reported methods, achieving an accuracy of 94.3% and 90.8% for radius and ulna maturity grading. Findings: Our automatic DRU assessment platform covers the whole process of growth acceleration and cessation during puberty. Upon incorporation into advanced scoliosis progression prognostic tools, clinical decision making will be potentially improved in the conservative and operative management of scoliosis patients.

Predicting the Probability of Recurrence Based on Individualized Risk Factors After Primary Lateral Patellar Dislocation Treated Nonoperatively

PURPOSE

To develop a comprehensive and effective personalized scoring system on the basis of demographic and clinical characteristics for predicting recurrence probability in patients with primary lateral patellar dislocation (LPD).

METHODS

Participants included 261 primary patients with LPD with 2-year minimum follow-up from our hospital across 2013 to 2020. Demographic and clinical characteristics were collected retrospectively. The backward stepwise method was performed to identify independent predictors and construct a nomogram to predict the probability of recurrence. The predictive performance was assessed by receiver operating characteristic curves, calibration plots, and decision curve analysis.

RESULTS

After variables selection, 6 independent predictors of recurrence (skeletal maturity, trochlear dysplasia, tibial tuberosity-trochlear groove distance, mechanical axis deviation, Insall-Salvati index, and patellar tilt) were enrolled in our model. Validation of this nomogram in both training and validation cohort revealed powerful predictive ability, with an area under the curve of 0.962 and 0.977, respectively. The nomogram also showed great calibration and good clinical practicability.

CONCLUSIONS

Our study presented a nomogram that incorporates 6 independent risk factors (skeletal maturity, trochlear dysplasia, tibial tuberosity-trochlear groove distance, mechanical axis deviation, Insall-Salvati index, and patellar tilt), which can be conveniently used to accurately predicts the risk of recurrence after primary LPD in individual cases.

LEVEL OF EVIDENCE

Level III, retrospective comparative prognostic study.

Optimizing calibration of modern skeletal maturity systems

Purpose

Greulich and Pyle is the most used system to estimate skeletal maturity but has significant drawbacks, prompting the development of newer skeletal maturity systems, such as the modified Fels skeletal maturity systems based on knee radiographs. To create a new skeletal maturity system, an outcome variable, termed a "skeletal maturity standard," must be selected for calibration of the system. Peak height velocity and 90% of final height are both considered reasonable skeletal maturity standards for skeletal maturity system development. We sought to answer two questions: (1) Does a skeletal maturity system developed using 90% of final height estimate skeletal age as well as it would if it was instead developed using peak height velocity? (2) Does a skeletal maturity system developed using 90% of final height perform as well in lower extremity length prediction as it would if it was instead developed using peak height velocity?

Methods

The modified Fels knee skeletal maturity system was recalibrated based on 90% of final height and peak height velocity skeletal maturity standards. These models were applied to 133 serially obtained, peripubertal antero-posterior knee radiographs collected from 38 subjects. Each model was used to estimate the skeletal age of each radiograph. Skeletal age estimates were also used to predict each patient's ultimate femoral and tibial length using the White-Menelaus method.

Results

The skeletal maturity system calibrated with 90% of final height produced more accurate skeletal age estimates than the same skeletal maturity system calibrated with peak height velocity (p < 0.05). The 90% of final height and peak height velocity models made similar femoral and tibial length predictions (p > 0.05).

Conclusion

Using the 90% of final height skeletal maturity standard allows for simpler skeletal maturity system development than peak height velocity with potentially more accuracy.

The Addition of Hand-specific Skeletal Maturity Parameters Does Not Improve Skeletal Maturity Estimation Accuracy of the Modified Fels Wrist System

BACKGROUND

The Modified Fels Wrist system is potentially the most accurate clinically accessible skeletal maturity system utilizing hand or wrist radiographs. During development, parameters distal to the metacarpals were excluded. We attempted to further optimize the Modified Fels wrist system through the inclusion of hand parameters distal to the metacarpals.

METHODS

Forty-three new anteroposterior (AP) hand radiographic parameters were identified from the Fels and Greulich and Pyle (GP) skeletal maturity systems. Twelve parameters were eliminated from further evaluation for poor correlation with skeletal maturity, poor reliability, and lack of relevance in the peripubertal years. In addition to the 8 previously described Modified Fels Wrist parameters, 31 hand radiographic parameters were evaluated on serial peripubertal AP hand radiographs to identify the ones most important for accurately estimating skeletal age. This process produced a "Modified Fels hand-wrist" model; its performance was compared with (1) GP only; (2) Sanders Hand (SH) only; (3) age, sex, and GP; (4) age, sex, and SH; and (5) Modified Fels Wrist system.

RESULTS

Three hundred seventy-two radiographs from 42 girls and 38 boys were included. Of the 39 radiographic parameters that underwent full evaluation, 9 remained in the combined Modified Fels Hand-Wrist system in addition to chronological age and sex. Four parameters are wrist specific, and the remaining 5 are hand specific. The Hand-Wrist system outperformed both GP and SH in estimating skeletal maturity ( P <0.001). When compared with the Modified Fels Wrist system, the Modified Fels Hand-Wrist system performed similarly regarding skeletal maturity estimation (0.36±0.32 vs. 0.34±0.26, P =0.59) but had an increased (worse) rate of outlier predictions >1 year discrepant from true skeletal maturity (4.9% vs. 1.9%, P =0.01).

CONCLUSIONS

The addition of hand parameters to the existing Modified Fels Wrist system did not improve skeletal maturity estimation accuracy and worsened the rate of outlier estimations. When an AP hand-wrist radiograph is available, the existing Modified Fels wrist system is best for skeletal maturity estimation.

LEVEL OF EVIDENCE

Level III.

The Reliability of the Modified Fels Knee Skeletal Maturity System

BACKGROUND

The recently described Modified Fels knee skeletal maturity system (mFels) has proven utility in prediction of ultimate lower extremity length in modern pediatric patients. mFels users evaluate chronological age, sex, and 7 anteroposterior knee radiographic parameters to produce a skeletal age estimate. We developed a free mobile application to minimize the learning curve of mFels radiographic parameter evaluation. We sought to identify the reliability of mFels for new users.

METHODS

Five pediatric orthopaedic surgeons, 5 orthopaedic surgery residents, 3 pediatric orthopaedic nurse practitioners, and 5 medical students completely naïve to mFels each evaluated a set of 20 pediatric anteroposterior knee radiographs with the assistance of the (What's the Skeletal Maturity?) mobile application. They were not provided any guidance beyond the instructions and examples embedded in the app. The results of their radiographic evaluations and skeletal age estimates were compared with those of the mFels app developers.

RESULTS

Averaging across participant groups, inter-rater reliability for each mFels parameter ranged from 0.73 to 0.91. Inter-rater reliability of skeletal age estimates was 0.98. Regardless of group, steady proficiency was reached by the seventh radiograph measured.

CONCLUSIONS

mFels is a reliable means of skeletal maturity evaluation. No special instruction is necessary for first time users at any level to utilize the (What's the Skeletal Maturity?) mobile application, and proficiency in skeletal age estimation is obtained by the seventh radiograph.

LEVEL OF EVIDENCE

Level II.

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

BACKGROUND

The Modified Fels (mFels) and Abbreviated Modified Fels (abFels) knee systems have been recently developed as options for grading skeletal maturity without the need for a separate hand radiograph. We sought to determine the interobserver reliability of these systems and to compare their prediction accuracy with that of the Greulich and Pyle (G-P) atlas in a cohort managed with epiphysiodesis for leg-length discrepancy (LLD).

METHODS

Three reviewers scored 20 knee radiographs using the mFels system, which includes 5 qualitative and 2 quantitative measures as well as a quantitative output. Short leg length (SL), long leg length (LL), and LLD prediction errors at maturity using the White-Menelaus (W-M) method and G-P, mFels, or abFels skeletal age were compared in a cohort of 60 patients managed with epiphysiodesis for LLD.

RESULTS

Intraclass correlation coefficients for the 2 quantitative variables and the quantitative output of the mFels system using 20 knee radiographs ranged from 0.55 to 0.98, and kappa coefficients for the 5 qualitative variables ranged from 0.56 to 1, indicating a reliability range from moderate to excellent. In the epiphysiodesis cohort, G-P skeletal age was on average 0.25 year older than mFels and abFels skeletal ages, most notably in females. The majority of average prediction errors between G-P, mFels, and abFels were <0.5 cm, with the greatest error being for the SL prediction in females, which approached 1 cm. Skeletal-age estimates with the mFels and abFels systems were statistically comparable.

CONCLUSIONS

The mFels skeletal-age system is a reproducible method of determining skeletal age. Prediction errors in mFels and abFels skeletal ages were clinically comparable with those in G-P skeletal ages in this epiphysiodesis cohort. Further work is warranted to optimize and validate the accuracy of mFels and abFels skeletal ages to predict LLD and the impact of epiphysiodesis, particularly in females. Both the mFels and abFels systems are promising means of estimating skeletal age, avoiding additional radiation and health-care expenditure.

LEVEL OF EVIDENCE

Prognostic Level II . See Instructions for Authors for a complete description of levels of evidence.

Correlations Between Eight Comprehensive Skeletal Maturity Systems in a Modern Peripubertal Pediatric Population

BACKGROUND

Several skeletal maturity systems allow for accurate skeletal age assessment from a wide variety of joints. However, discrepancies in estimates have been noted when applying systems concurrently. The aims of our study were to (1) compare the agreement among 8 different skeletal maturity systems in modern pediatric patients and (2) compare these discrepancy trends qbetween modern and historic children.

METHODS

We performed a retrospective (January 2000 to May 2022) query of our picture archiving and communication systems and included peripubertal patients who had at least two radiographs of different anatomic regions obtained ≤3 months apart for 8 systems: (1) proximal humerus ossification system (PHOS), (2) olecranon apophysis ossification staging system (OAOSS), (3) lateral elbow system, (4) modified Fels wrist system, (5) Sanders Hand Classification, (6) optimized oxford hip system, (7) modified Fels knee system, and (8) calcaneal apophysis ossification staging system (CAOSS). Any abnormal (ie, evidence of fracture or congenital deformity) or low-quality radiographs were excluded. These were compared with a cohort from a historic longitudinal study. SEM skeletal age, representing the variance of skeletal age estimates, was calculated for each system and used to compare system precision.

RESULTS

A total of 700 radiographs from 350 modern patients and 954 radiographs from 66 historic patients were evaluated. In the modern cohort, the greatest variance was seen in PHOS (SEM: 0.28 y), Sanders Hand (0.26 y), and CAOSS (0.25 y). The modified Fels knee system demonstrated the smallest variance (0.20 y). For historic children, the PHOS, OAOSS, and CAOSS were the least precise (0.20 y for all). All other systems performed similarly in historic children with lower SEMs (range: 0.18 to 0.19 y). The lateral elbow system was more precise than the OAOSS in both cohorts.

CONCLUSIONS

The precision of skeletal maturity systems varies across anatomic regions. Staged, single-parameter systems (eg, PHOS, Sanders Hand, OAOSS, and CAOSS) may correlate less with other systems than those with more parameters.

LEVEL OF EVIDENCE

Level III-retrospective study.

Medico-legal indicators and cut-offs in different age classes through quantitative analysis of epiphyseal fusion segments on knee CT scans

Scientists are interested in determining age in subadults for several forensic purposes. High- resolution instrumental techniques are being increasingly used for age estimation, driven by the need to minimize errors; in this context, several studies have focused on the knee joint, recognized as a potential site for age examination in late adolescence. We analyzed 200 CT scans performed on Russian subjects (106 males and 94 females) between 13 and 20 years, without growth diseases, endocrine disorders, or osteodystrophy. Each subject underwent two scans, one for each leg. Two indicators were measured for each bone (femur, tibia and fibula): the entire length of the epiphyseal scar and the length of the part/s that is/are fused with metaphysis. Intra class Correlation Coefficient (ICC) was performed to evaluate the intra-operator reproducibility. The ratio between the two lengths was calculated for each bone (FemurR, TibiaR and FibulaR). The first aim was to evaluate a correlation between the ratios of the three bones and the three bones treated as a single parameter (given by the sum of the ratios) versus age. The results showed good correlations in both cases (τ a = 0.74, 0.64, 0.57 and 0.67). The second aim was to estimate the cut-offs derived from the sum of the three ratios respect to four age classes (14-15 years: cut-off ≤ 0.63, 15-16 years: cut-off ≤ 1.19, 16-17 years: cut-off ≥ 0.68 and 17-18 years: cut-off ≥ 1.49. The results from this research encourage further studies of the knee joint as an indicator of legal adult age.

Validation of central peak height method for final adult height predictions on long leg radiographs

Aims

Accurate skeletal age and final adult height prediction methods in paediatric orthopaedics are crucial for determining optimal timing of growth-guiding interventions and minimizing complications in treatments of various conditions. This study aimed to evaluate the accuracy of final adult height predictions using the central peak height (CPH) method with long leg X-rays and four different multiplier tables.

Methods

This study included 31 patients who underwent temporary hemiepiphysiodesis for varus or valgus deformity of the leg between 2014 and 2020. The skeletal age at surgical intervention was evaluated using the CPH method with long leg radiographs. The true final adult height (FHTRUE) was determined when the growth plates were closed. The final height prediction accuracy of four different multiplier tables (1. Bayley and Pinneau; 2. Paley et al; 3. Sanders - Greulich and Pyle (SGP); and 4. Sanders - peak height velocity (PHV)) was then compared using either skeletal age or chronological age.

Results

All final adult height predictions overestimated the FHTRUE, with the SGP multiplier table having the lowest overestimation and lowest absolute deviation when using both chronological age and skeletal age. There were no significant differences in final height prediction accuracy between using skeletal age and chronological age with PHV (p = 0.652) or SGP multiplier tables (p = 0.969). Adult height predictions with chronological age and SGP (r = 0.769; p ≤ 0.001), as well as chronological age and PHV (r = 0.822; p ≤ 0.001), showed higher correlations with FHTRUE than predictions with skeletal age and SGP (r = 0.657; p ≤ 0.001) or skeletal age and PHV (r = 0.707; p ≤ 0.001).

Conclusion

There was no significant improvement in adult height prediction accuracy when using the CPH method compared to chronological age alone. The study concludes that there is no advantage in routinely using the CPH method for skeletal age determination over the simple use of chronological age. The findings highlight the need for more accurate methods to predict final adult height in contemporary patient populations.

Does Skeletal Maturity Predict the Pattern of Tibial Tubercle Avulsion Fracture?

BACKGROUND

Proximal tibial physeal development and closure is thought to relate to tibial tubercle avulsion fracture (TTAF) patterns. Prior work has yet to formally evaluate the relationship between skeletal maturity and fracture pattern.  Using 2 knee radiograph-derived skeletal maturity assessments [growth remaining percentage (GRP) and epiphyseal union stage], we examined their association with TTAF injury patterns using the Ogden and Pandya fracture classifications. We hypothesized that different TTAF injuries would occur during unique periods of skeletal development.

METHODS

Pediatric patients sustaining TTAFs treated at a single institution (2008-2022) were identified using diagnostic and procedural coding. Demographics and injury characteristics were collected. Radiographs were reviewed to assign epiphyseal union stage, Ogden and Pandya classifications and for measurements to calculate GRP. Univariate analyses examined the relationship between injury subgroups, patient demographics, and skeletal maturity assessments.

RESULTS

Inclusion criteria identified 173 patients with a mean age of 14.76 (SD: 1.78) and 2.95% (SD: 4.46%) of growth remaining. The majority of injuries were classified Ogden III/Pandya C. Most (54.9%) were the result of the axial loading mechanism. Ogden groups showed no significant differences across all patient characteristics studied including age and GRP. With the exception of Pandya A fractures, we did not identify a direct relationship between GRP, age, and Pandya groups. Epiphyseal union stage differed for Pandya A and D groups.

CONCLUSIONS

A predictable pattern in TTAF characteristics across skeletal (GRP), epiphyseal union, or chronologic age was not identified in this study. Distal apophyseal avulsions (Ogden I/II and Pandya A/D) occurred across a broad chronologic and skeletal age range. No differences were identified in epiphyseal or posterior extension (Ogden III/IV and Pandya B/C) injuries. Although differences in age and GRP were identified among Pandya As, this is thought to be due to the degree of skeletal immaturity that is a prerequisite for differentiation from Pandya Ds.

LEVEL OF EVIDENCE

Level III-retrospective cohort study.

Applicability of Shoulder, Olecranon, and Wrist-based Skeletal Maturity Estimation Systems to the Modern Pediatric Population

BACKGROUND

The proximal humerus ossification system (PHOS), olecranon apophyseal ossification system (OAOS), and modified Fels wrist skeletal maturity system (mFWS) were recently developed or updated using a historical, mostly White, pediatric population. These upper extremity skeletal maturity systems have demonstrated skeletal age estimation performance superior or equivalent to Greulich and Pyle in historical patients. Their applicability to modern pediatric populations has not yet been evaluated.

METHODS

We reviewed anteroposterior shoulder, lateral elbow, and anteroposterior hand and wrist x-rays of 4 pediatric cohorts: White males, Black males, White females, and Black females. Peripubertal x-rays were evaluated: males 9 to17 years and females 7 to 15 years. Five nonpathologic radiographs for each age and joint were randomly selected from each group. Skeletal age estimates made by each of the 3 skeletal maturity systems were plotted against the chronological age associated with each radiograph and compared between cohorts, and with the historical patients.

RESULTS

Five hundred forty modern radiographs were evaluated (180 shoulders, 180 elbows, and 180 wrists). All radiographic parameters had inter- and intra-rater reliability coefficients at or above 0.79, indicating very good reliability. For PHOS, White males had delayed skeletal age compared with Black males (Δ-0.12 y, P=0.02) and historical males (Δ-0.17 y, P<0.001). Black females were skeletally advanced compared with historical females (Δ0.11 y, P=0.01). For OAOS, White males (Δ-0.31 y, P<0.001) and Black males (Δ-0.24 y, P<0.001) had delayed skeletal age compared with historical males. For mFWS, White males (Δ0.29 y, P=0.024), Black males (Δ0.58 y, P<0.001), and Black females (Δ0.44 y, P<0.001) had advanced skeletal age compared with historical counterparts of the same sex. All other comparisons were not significant (P>0.05).

CONCLUSIONS

The PHOS, OAOS, and mFWS have mild discrepancies in skeletal age estimates when applied to modern pediatric populations depending on the race and sex of the patient.

LEVEL OF EVIDENCE

Level III - retrospective chart review.

Applicability of the Modified Fels and Optimized Oxford Skeletal Maturity Estimation Systems to the Modern Pediatric Population

BACKGROUND

The recently developed modified Fels knee and optimized Oxford hip skeletal maturity systems (SMS) have demonstrated impressive performance compared with the Greulich and Pyle skeletal age atlas when applied to the same historical, mostly white, pediatric population. We sought to determine whether these 2 systems require modification before being used in modern children.

METHODS

We collected knee and hip radiographs between January 2015 and September 2020 from our electronic medical record from 4 groups of children: (1) white males, (2) black males, (3) white females, and (4) black females. Males between 9 and 17 years and females between 7 and 15 years were included. After reliability analyses, 5 nonpathologic radiographs for each age and joint were randomly selected from each group and evaluated with the appropriate SMS. The mean discrepancy between each group's chronological age at the time of radiograph and estimated skeletal age was compared between our modern cohort and the historical Bolton-Brush children. After normality testing, paired t tests or Wilcoxon signed-rank tests were performed, as appropriate. A Bonferroni correction was applied to address multiple testing.

RESULTS

Three hundred sixty modern radiographs were evaluated (180 knees and 180 hips). All 7 modified Fels knee parameters and all 5 optimized Oxford hip parameters had inter and intrarater reliability coefficients ≥0.7, indicating good to very good reliability. For the modified Fels knee SMS, white males (Δ0.74 y, P <0.001), black males (Δ0.69 y, P <0.001), and black females (Δ0.4 y, P =0.04) had advanced skeletal age compared with their historical counterparts of the same sex. No differences were found between historical and modern patients for the optimized Oxford hip SMS. No differences were found for either SMS comparing modern patients along racial lines ( P >0.05 for all).

CONCLUSIONS

Discrepancies in skeletal age estimates made by the modified Fels knee SMS exist between modern pediatric white males, black males, and black females and their historic counterparts. No differences were found when using optimized Oxford hip SMS. Future studies should evaluate how these translate to clinical decision-making.

LEVEL OF EVIDENCE

Level III; retrospective chart review.

The Systematic Isolation of Key Parameters for Estimating Skeletal Maturity on Lateral Elbow Radiographs

BACKGROUND

Skeletal maturity estimation is central in the management of scoliosis and lower-limb deformity. Utilizing demographic characteristics and modern computing, we sought to create a reliable, rapid, and accurate method for measuring skeletal maturity on an elbow radiograph.

METHODS

Utilizing the Bolton-Brush Collection, 4 parameters from the modified Sauvegrain method and 7 novel parameters were screened. Ten parameters were evaluated on serial peripubertal elbow radiographs, using Greulich and Pyle (GP) skeletal age from corresponding hand radiographs as a comparison. Stepwise linear regression and generalized estimating equations were used to identify radiographic and demographic parameters for estimating skeletal maturity based on 90% of final height. The elbow system was compared with GP only; olecranon apophysis only; age, sex, and GP; age, sex, and olecranon apophysis; age, sex, and elbow system with anteroposterior and lateral parameters; age, sex, and elbow system with anteroposterior parameters; and age, sex, and elbow system with lateral parameters.

RESULTS

In this study, 367 radiographs from 77 patients (40 girls and 37 boys) were included. Following stepwise linear regression, 4 radiographic parameters were included in the anteroposterior and lateral elbow system; 3 were included in the anteroposterior elbow system; and 4 were included in the lateral elbow system. The lateral elbow system predicted skeletal maturity with a mean discrepancy of 0.41 year and produced similar mean discrepancies to GP with age and sex (0.42; p = 0.93), and it trended toward better performance than the olecranon apophysis system with age and sex (0.43; p = 0.06). The lateral elbow system had the lowest percent of outlier predictions >1 year discrepant from the skeletal maturity reference (4.6%), although it was only significantly better than the GP-only group (29.4%) and the olecranon apophysis-only group (21.0%) (p < 0.001 for both).

CONCLUSIONS

We systematically developed a lateral elbow system that performed equivalently to GP using 4 simple parameters and trended toward outperforming the olecranon apophysis systems in skeletal maturity estimation. Future clinical validation will be necessary to understand the utility of this system.

CLINICAL RELEVANCE

The lateral elbow system may be a more accurate prediction of skeletal maturity compared with the previously described olecranon apophysis system and can be used to guide the management of many pediatric orthopaedic conditions.

Estimating Skeletal Maturity Using Wrist Radiographs During Preadolescence: The Epiphyseal:Metaphyseal Ratio

BACKGROUND

Although skeletal maturity is most relevant during adolescence, it has utility in treatment of younger patients in some circumstances, such as scoliosis, limb length discrepancy, or endocrinopathies. Currently, a quick, accurate, and reproducible method of estimating skeletal maturity in preadolescents using wrist radiographs is lacking.

METHODS

Serial anteroposterior wrist radiographs taken at historical growth study visits leading up to the chronological age (CA) associated with 90% of the final height (an enhanced skeletal maturity standard as compared with peak height velocity) were analyzed in 102 children. Epiphyseal and metaphyseal widths of 5 physes were evaluated: distal radius, distal ulna, first metacarpal, third metacarpal, and fifth metacarpal. Ulnar styloid height and radial styloid height were also measured, for a total of 7 epiphyseal:metaphyseal radiographic parameters. Greulich and Pyle (GP) bone age was also measured. A combination of stepwise linear regression and generalized estimating equation analyses was used to produce a skeletal maturity estimation model incorporating demographics (CA and sex) and the epiphyseal:metaphyseal ratios significantly correlated with skeletal maturity.

RESULTS

A total of 273 left anteroposterior hand-wrist radiographs from 56 girls (163 radiographs, range 4 to 13 y) and 46 boys (112 radiographs, range 3.8 to 15 y) were included. The demographics+ratios model had better prediction accuracy than GP only and GP with demographics (0.44, 0.87, and 0.47 y mean discrepancy from actual skeletal age, P <0.05 for both comparisons). There was no significant difference in the rate of outlier skeletal age estimates, defined as an estimate >1 year off from the true skeletal age, between the demographics+ratios model and the demographics+GP model (5.9% vs. 8.4%, P =0.12).

CONCLUSIONS

When combined with CA and sex data, measurement of the epiphyseal:metaphyseal ratios of the left first and third metacarpals allows for improved skeletal maturity estimation compared with the GP technique.

CLINICAL RELEVANCE

Our modified wrist skeletal maturity system offers a relatively quick and reproducible method for estimating skeletal maturity extending into the juvenile age range. This study is a level III retrospective study of longitudinal human growth data obtained from the Bolton Brush Collection in Cleveland, Ohio.

Using Skeletal Maturity in Pediatric Orthopaedics: A Primer

This article provides researchers with the background and guidance necessary to practically incorporate skeletal maturity estimation into any study of adolescents with imaging of the shoulder, elbow, hand, hip, knee, or foot. It also provides clinicians with a comprehensive, concise synopsis of systems that can be used to estimate skeletal maturity in clinical practice. In the article, we provide a relatively brief overview of each currently available skeletal maturity system that has been validated on a longitudinal dataset. The supplementary files include 2 PowerPoint files for each skeletal maturity system. The first PowerPoint file offers examples and instructions for using each radiographic system. The second PowerPoint file includes 20 graded radiographs that can be used for reliability analyses in the research setting. We have also developed a free mobile application available on the iOS and Android platforms named "What's the Skeletal Maturity?" that allows clinicians to rapidly estimate skeletal maturity on any patient using any commonly obtained orthopaedic radiograph.

The Utility of the Modified Fels Knee Skeletal Maturity System in Limb Length Prediction

BACKGROUND

Predicting ultimate lower extremity length is important in the treatment of lower limb length discrepancy (LLD), congenital limb deficiency, and other etiologies. Utilizing skeletal age over chronological age improves the prediction of ultimate lower extremity length. The recently described modified Fels knee skeletal maturity system allows for skeletal age estimation via imaging always available in LLD patients. We sought to compare the accuracy of the modified Fels knee skeletal maturity system versus chronological age in ultimate limb length prediction of a modern adolescent clinical population.

METHODS

The medical records of all patients treated at our institution over a 20-year period with unilateral lower extremity pathology and available lower extremity imaging before and after reaching skeletal maturity were reviewed. Skeletal maturity was defined radiographically by closed distal femoral, proximal tibial, and proximal fibular physes. The femoral, tibial, and lower extremity length was measured in all radiographs. The modified Fels knee skeletal maturity system was applied to all radiographs obtained before maturity to estimate skeletal age. The accuracy of 3 widely utilized lower extremity length prediction systems was compared when utilizing estimated Fels skeletal age versus chronological age inputs.

RESULTS

A total of 245 radiographs (109 before maturity) from 43 patients were eligible for inclusion. On cross-sectional analysis, linear modeling using Fels skeletal ages was uniformly associated with higher (improved) R2 values than chronological age-based models. On longitudinal analysis, skeletal age mixed-effects models had significantly lower (improved) Akaike information criterion and Bayesian information criterion values than chronological age models in all cases. Cohen d values were also significantly different (P<0.05) for the skeletal age models compared with chronological age models in all cases.

CONCLUSIONS

In the treatment of LLD, the modified Fels knee skeletal maturity system can be readily applied to available imaging to improve the prediction of ultimate femoral, tibial, and lower extremity length. This skeletal maturity system may have significant utility in the estimation of ultimate LLD and determination of appropriate timing of epiphysiodesis.

LEVEL OF EVIDENCE

Level III.

The Optimized Oxford Hip Skeletal Maturity System Proves Resilient to Rotational Variation

BACKGROUND

The recently described optimized Oxford skeletal maturity system utilizes anteroposterior (AP) hip radiographs to accurately, rapidly, and reliably estimate skeletal maturity. However, in the real-world setting, significant positional variation in AP hip radiographs may influence the accuracy of optimized Oxford skeletal age estimates. We sought to evaluate the consistency of skeletal age estimations using the optimized Oxford system between differently rotated radiographs.

METHODS

Thirty normal computerized tomography scans of males (15 children, 9 to 15 y) and females (15 children, 8 to 14 y) were obtained retrospectively, converted into 3D reconstructions, and then used to produce simulated hip radiographs in five different rotational positions. The optimized Oxford system was applied to the 150 simulated AP hip radiographs (5 differently rotated views of 30 hips) to produce a skeletal age estimate for each.

RESULTS

Rotational position did not have a statistically significant effect on the skeletal age (P=0.84) using 1-way repeated measures analysis of variance. Of the 5 radiographic parameters in the optimized Oxford system, only greater trochanter height showed significant rotational variation after Greenhouse-Geisser correction (F2.58, 74.68=5.98, P<0.001). However, post hoc analyses showed that the greater trochanter height obtained at the most centered position was not different from the other 4 rotational positions (P>0.05 for all).

CONCLUSION

The optimized Oxford skeletal maturity system is resilient to rotational variation. Mildly to moderately rotated radiographs obtained in the modern clinical setting can be used for skeletal age estimation by this method, broadening the clinical usage of this system.

LEVEL OF EVIDENCE

Level III-diagnostic study.

Systematic Isolation of Key Parameters for Estimating Skeletal Maturity on Anteroposterior Wrist Radiographs

BACKGROUND

The ability to make a continuous skeletal maturity estimate from a wrist radiograph would be useful in the treatment of adolescent forearm fractures, scoliosis, and other conditions. We attempted to create a reliable, rapid, and accurate method to do this.

METHODS

Many anteroposterior wrist radiographic parameters from 3 skeletal maturity systems were simplified to 23 based on relevance to the peripubertal age range, univariate correlation with skeletal maturity, and reliability. These 23 parameters were evaluated on serial peripubertal anteroposterior hand-wrist radiographs. We determined the Greulich and Pyle (GP) skeletal age and Sanders hand system (SHS) stage. We used stepwise linear regression and generalized estimating equation (GEE) procedures to identify important radiographic and demographic parameters for estimating skeletal maturity, creating the "Modified Fels wrist skeletal maturity system." Its accuracy predicting skeletal maturity was evaluated and compared with that of 4 other systems: (1) GP system, (2) SHS, (3) GP parameters along with age and sex, and (4) SHS parameters along with age and sex.

RESULTS

Three hundred and seventy-two radiographs of 42 girls (age range, 7 to 15 years) and 38 boys (age range, 9 to 16 years) were included. Fifteen radiographic parameters were excluded from the Modified Fels wrist system by stepwise regression and GEE analyses, leaving age, sex, and 8 radiographic parameters in the final model. Use of the Modified Fels wrist system resulted in more accurate skeletal maturity estimations (0.34-year mean discrepancy with actual skeletal maturity) than all other systems (p < 0.001 for all). The Modified Fels wrist system had a similar rate of outlier skeletal maturity estimations as the age, sex, and SHS model (1.9% versus 3.5%, p = 0.11) and fewer outliers than all other systems (p < 0.05 for all).

CONCLUSIONS

A system that included demographic factors and 8 anteroposterior wrist radiographic parameters estimates skeletal maturity more accurately than the 2 most-used skeletal maturity systems in the United States.

CLINICAL RELEVANCE

The Modified Fels wrist skeletal maturity system may allow for more accurate, reliable, and rapid skeletal maturity estimation than current systems, and also may be used when treating adolescent forearm fractures as it does not require imaging past the metacarpals.

LEVEL OF EVIDENCE

Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

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

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.

Skeletal Maturity Using Knee X-rays: Understanding the Resilience of 7 Radiographic Parameters to Rotational Position

BACKGROUND

Recently, a skeletal maturity system using knee radiographs, named the modified Roche-Wainer-Thissen (RWT) system, has been developed using 7 discrete radiographic parameters. While the system has been shown to significantly outperform the Greulich and Pyle atlas, the effect of rotational variation of the knee radiograph on skeletal maturity determinations has not been studied.

METHODS

Normal knee computed tomography scans of 12 male children ages 10 to 16 years and 8 female children ages 8 to 14 years were obtained retrospectively, converted into 3-dimensional reconstructions, and then used to simulate knee radiographs in 5 different rotational positions. Images were graded using the modified RWT system, and 1-way repeated measures analysis of variance was used to compare skeletal age in the patella centered view versus the other positions. We next retrospectively found 85 pediatric patients with both bilateral standing anteroposterior hip to ankles and separate knee radiograph within 6 months of each other. The skeletal maturity values from the 2 different radiographs were compared in 39 males between the ages of 10 and 16 years and 46 females between 8 and 14 years of age using paired t test and Wilcoxon-signed rank test.

RESULTS

On the computed tomography scan-based images, there was no statistically significant effect of rotational position on the modified RWT score using repeat measures analysis of variance (P=0.210). Only the width ratio of the tibial epiphysis and metaphysis and the width ratio of the fibular epiphysis and metaphysis were statistically different between rotational positions (P<0.05). Comparing clinical full length versus knee radiographs, we found a small difference of 0.069 years which trended towards a statistically significant difference (P=0.009).

CONCLUSIONS

This retrospective study supports the resilience of the RWT model to rotational variation, reassuring clinicians that bone age estimation can be performed in a slightly rotated knee x-ray within a reasonable margin of error. These results can minimize the number of radiographs needed to assess skeletal maturity limiting radiation exposure and expedite clinical flow.

LEVEL OF EVIDENCE

Level-III-diagnostic study.

Estimating Skeletal Maturity Using Knee Radiographs During Preadolescence: The Epiphyseal:Metaphyseal Ratio

BACKGROUND

Though skeletal maturity is most relevant during adolescence, it has utility in treatment of younger patients in some circumstances. Accurate estimation of skeletal maturity using knee radiographs would be useful when treating limb length discrepancy and other general medical conditions in preadolescent patients. Currently, a quick, accurate, and reproducible method of estimating skeletal maturity in preadolescents is lacking.

METHODS

Serial anteroposterior knee radiographs taken at historical growth study visits leading up to the chronological age associated with 90% of final height (an enhanced skeletal maturity standard as compared with peak height velocity) were analyzed in 75 children. Epiphyseal and metaphyseal widths of the distal femur, proximal tibia, and proximal fibula were measured and the epiphyseal:metaphyseal ratio was calculated. Greulich and Pyle (GP) bone ages were also assigned by an experienced pediatric endocrinologist using left hand radiographs. Stepwise linear regression and generalized estimating equation analyses were used to make a skeletal maturity model incorporating demographics (age+sex) and knee epiphyseal:metaphyseal ratios.

RESULTS

A total of 258 left knee radiographs from 39 girls (mean age 8.6 y, range: 2.9 to 13 y) and 36 boys (mean age 10.6 y, range: 3.8 to 15 y) were included. The demographics+ratios model had similar prediction accuracy (0.49 vs. 0.48 y, P=0.84) and rate of outliers (11% vs. 9%, P=0.11) as the demographics+GP model. The demographics+ratios model outperformed all other models evaluated, including a demographics-only model (P<0.001 for all).

CONCLUSIONS

When combined with chronological age and sex, epiphyseal:metaphyseal ratio measurement in the knee allows for skeletal maturity estimation comparable to using the GP technique.

CLINICAL RELEVANCE

We have defined a knee skeletal maturity system that could be applied in treatment of orthopaedic conditions in preadolescents where a knee radiograph is already obtained, avoiding the need for an additional hand radiograph.

Systematic Isolation of Key Parameters for Estimating Skeletal Maturity on AP Hip Radiographs

BACKGROUND

The ability to estimate skeletal maturity using a hip radiograph does not yet exist, but may have utility in the treatment of scoliosis, slipped capital femoral epiphysis, and lower limb deformity. We sought to develop a fast, accurate, and reproducible method.

METHODS

Fourteen hip radiologic parameters were evaluated on serial anteroposterior hip radiographs from 3 years before to 2 years after the skeletal age associated with 90% of final height, a validated skeletal maturity definition which correlates with the timing of peak height velocity. The Greulich and Pyle (GP) left hand bone age was obtained for comparison. Stepwise linear regression and generalized estimating equation analyses were used to isolate key hip and demographic parameters, creating the "optimized Oxford" skeletal maturity system. The accuracy of the optimized Oxford system in predicting years from 90% of final height was evaluated and compared with systems of demographics only, the modified Oxford, demographics+modified Oxford, and demographics+GP.

RESULTS

A total of 284 hip radiographs from 41 girls (range: 7 to 15 y) and 38 boys (range: 9 to 17 y) were included. Following multivariate analyses, 5 of the original 14 hip radiographic parameters remained significant. The predictions made by the optimized Oxford model had greater accuracy and fewer outlier predictions (predictions >1 y off from actual years from 90% of final height) than the demographics only and modified Oxford only models (P<0.05 for all). The optimized Oxford model had greater prediction accuracy than the demographics+modified Oxford model, but similar rates of outlier predictions (P=0.903). No differences in mean prediction accuracy or rate of outlier predictions were observed between the optimized Oxford and the demographics+GP model (P>0.05).

CONCLUSION

High precision in skeletal maturity estimation can be achieved by using chronological age, sex, and 5 hip radiographic parameters.

CLINICAL RELEVANCE

We have developed a skeletal maturity system that utilizes anteroposterior hip radiographs and performs as accurately as GP.