Chang Ho Shin

Background: Knee bone age can differ from hand bone age and is more relevant to lower-extremity pediatric conditions. This study developed and validated a quantitative method for estimating skeletal maturity using knee MRI images. Methods: We identified 695 participants aged 18 years or younger without conditions affecting knee anatomy or maturation who underwent knee MRI. Participants were randomly allocated to the modeling (n=417) and validation (n=278) groups. Twenty-six maturation-related parameters were measured on coronal MRI, including the articular and peripheral cartilaginous thicknesses, physeal thicknesses, ossified epiphyseal width, and capping interval. The capping interval was defined as the distance from the medial or lateral metaphyseal end to the nearest ossified epiphysis. Each parameter was normalized to metaphyseal width and assessed by univariable linear regression against log-transformed chronological age. Top-ranked variables were entered into sex-specific multivariable models. Results: The sums of the medial and lateral capping intervals from the femur and tibia were the only parameters with R ² >0.9 in both sexes and were defined as the femoral and tibial capping interval indices (CIIs), respectively. Final models were age=exp(−1.918[femoral CII]−1.797[tibial CII]+2.813) for males and age=exp(−2.056[femoral CII]−2.487[tibial CII]+2.738) for females. In the validation group, estimated knee bone age showed minimal difference from chronological age (0.1±1.1 y, P =0.534) and very strong correlation ( r _s =0.960). Conclusions: Knee bone age estimated from the femoral and tibial CII showed close agreement with chronological age in the independent validation cohort. This study introduces a novel, simple quantitative method that enables estimation of bone age on knee MRI using a minimal number of parameters. Level of Evidence: Level III—diagnostic.

Background: Children with neurological complex chronic conditions (NCCCs) frequently undergo hip reconstruction for hip displacement. Impaired airway clearance and respiratory muscle weakness may increase the risk of postoperative respiratory events. This study evaluated the incidence and predictors of postoperative respiratory events in this population. Methods: We retrospectively reviewed children with NCCCs who underwent hip reconstruction between 2015 and 2024. Baseline characteristics included age, sex, diagnosis, comorbidities, feeding method, ambulatory status, and respiratory support. Operative and anesthesia‐related variables included the number of osteotomies, operative duration and scheduling, estimated blood loss, airway device, and arterial blood gas measurements. The primary outcome was postoperative desaturation (SpO ₂ < 95%) requiring supplemental oxygen. Secondary outcomes included pulmonary complications and intensive care unit (ICU) utilization. Predictors were initially evaluated using an expanded multivariable logistic regression model, followed by a reduced model using Firth's penalized logistic regression. Results: Among 126 children (mean age, 7.7 ± 4.1 years), postoperative desaturation occurred in 30 (23.8%). Pulmonary complications included respiratory failure ( n = 6), atelectasis ( n = 5), pulmonary edema ( n = 3), and pneumonia ( n = 1). ICU care was required for 22 children (17.5%). Predictors of postoperative desaturation included congenital brain malformation (adjusted odds ratio [aOR], 21.76; 95% confidence interval [CI], 3.33–249.48), surgery performed on Friday (aOR, 3.35; 95% CI, 1.11–10.24), ≥ 3 osteotomies (aOR, 7.82; 95% CI, 1.83–36.36), and elevated intraoperative bicarbonate (HCO ₃ ⁻ > 26 mEq/L; aOR, 6.49; 95% CI, 2.36–19.14). Conclusion: Postoperative desaturation was common after hip reconstruction in children with NCCCs, with a subset developing pulmonary complications or requiring ICU care. Identification of perioperative risk factors may improve risk stratification and support targeted respiratory monitoring and preventive strategies in this high‐risk population. Level of Evidence: Level III, retrospective cohort study.

Purpose: Side-to-side differences in bone age may exist due to somatic mosaicism in congenital hemihyperplasia or hemihypoplasia. We aimed to assess bone age differences between limbs in these conditions. Methods: We retrospectively identified 118 children who underwent molecular testing for congenital hemihyperplasia or hemihypoplasia. Diagnoses included Beckwith-Wiedemann syndrome (BWS) ( n = 34), Silver-Russell syndrome ( n = 14), PIK3CA-related overgrowth spectrum (n = 14), and idiopathic isolated hemihyperplasia or hemihypoplasia ( n = 56). Hand and knee bone ages were compared between the right and left limbs and between the longer and shorter limbs. Results: In the overall cohort or each disease group, there was no difference in hand or knee bone age between the right and left limbs. However, the hand bone age of the longer limb was 1.2 ± 2.6 months older than that of the shorter limb ( p = 0.005). In subgroup analysis, patients with BWS showed older knee (7.1 ± 9.9 months, p = 0.031) and hand (3.2 ± 2.5 months, p = 0.026) bone ages in the longer limb compared to the shorter limb. No significant differences were observed in the other disease groups. Conclusions: Pediatric patients with congenital hemihyperplasia or hemihypoplasia generally show minimal bone age differences between limbs. However, in BWS, the longer limb may have a bone age several months older than the shorter limb. Significance of study: Surgeons need to consider potential side-to-side differences in bone age when estimating remaining growth and determining the timing for epiphysiodesis in these patients. Level of Evidence: III—Study of nonconsecutive patients

Heterotopic ossification (HO), a pathological process in which bone forms in soft tissues is rare and debilitating without effective treatment. Gain-of-function mutations in ACVR1 cause fibrodysplasia ossificans progressiva (FOP). Here we report a novel, ultrarare gain of function mutation in BMPR2 (c.1126G > A, p.E376K) that causes a systemic HO simulating FOP. The pathological features associated with BMPR2 ^E376K appear reminiscent of classic FOP, yet manifest a number of distinct hallmarks, including lack of stereotypic malformation of the big toes. BMPR2 ^E376K appears to function as a neomorph, displaying an exaggerated response to Activin A stimulation by selectively interacting with ACVR1. These findings are consistent with the central role of Activin A mediated ACVR1 signaling in FOP. Taken together, our data illustrates the complex molecular features underlying the pathophysiology of HO and highlight the importance of BMPR2 as a nexus for ACVR1 and Activin A interaction. Moreover, our findings provide a theoretical framework for developing novel therapeutic options for HO.

Osteogenesis imperfecta (OI) is a heterogeneous group of genetic skeletal disorders characterized by bone fragility and low bone mass, manifesting as multiple fractures and deformities of the spine and extremities. Although genotype‐phenotype correlations have been studied in various populations, large‐scale data in Koreans have been lacking. This study is aimed at characterizing the clinical and genetic spectrum of nonlethal OI in the Korean population and explore genotype–phenotype associations. This retrospective cohort study analyzed 198 genetically confirmed Korean OI probands evaluated at a single center between 2004 and 2024, with clinical features reviewed and genetic testing performed using Sanger sequencing and targeted next‐generation sequencing. A total of 160 distinct pathogenic variants were identified, including 44 novel variants. Variant pathogenicity was assessed according to the ACMG/AMP variant classification guidelines. Pathogenic variants of COL1A1 and COL1A2 accounted for 87.4% of cases, with COL1A1 variants being the most prevalent (66.7%). Only 4.0% of cases had autosomal recessive OI. Glycine substitution (GS) variants were associated with significantly more severe phenotypes than other variants, including shorter height (median z‐score−3.67 [IQR −8.37 to −1.78] vs. −1.17 [−1.96 to −0.16], p < 0.001) and earlier fracture onset (1.00 [0.00–8.25] vs. 15.00 [7.00–24.75] months, p < 0.001). In COL1A1 , GS variants closer to the C‐terminus correlated with significantly more severe height reduction (Spearman ρ = −0.478, p = 0.005). The genotype–phenotype analysis confirmed the phenotypic severity of GS, particularly for variants closer to the C‐terminus of COL1A1 , consistent with previous studies. Additionally, the identification of 44 novel variants expands the variant spectrum of OI. These findings provide valuable insights into genetic diagnosis, prognostic assessment, and clinical management of OI.

Purpose: X-linked hypophosphatemia is characterized by skeletal abnormalities, particularly lower limb angular deformities. Although burosumab has demonstrated short-term clinical improvements, its mid- to long-term effects on skeletal alignment remain underexplored. This study evaluated skeletal outcomes of burosumab therapy over 2 years, focusing on lower limb deformities. Methods: We retrospectively analyzed 20 pediatric X-linked hypophosphatemia patients (10 boys and 10 girls) who initiated burosumab at a mean age of 7.5 ± 2.4 years. Rickets severity score, mechanical axis deviation, mechanical lateral distal femoral angle, medial proximal tibial angle, lateral distal tibial angle, and standing height were assessed at baseline, 12 months, and 24 months. Outcomes were analyzed using age-standardized z -scores. Results: Rickets severity improved from the first year, with Rickets Severity Score decreasing from 3.5 ± 1.2 to 0.6 ± 0.5 at 24 months (mean change 2.9; 95% confidence interval 2.4–3.4). Lower limb alignment also improved: | z |-mechanical axis deviation decreased from 2.3 ± 1.6 to 1.0 ± 1.0 (change 1.3; 95% confidence interval 0.9–1.7), showing progressive correction from the first year. | z |-mechanical lateral distal femoral angle improved mainly at 24 months, decreasing from 2.7 ± 2.1 to 1.3 ± 1.2 (change 1.4; 95% confidence interval 0.8–2.0). | z |-medial proximal tibial angle and | z |-lateral distal tibial angle showed smaller overall changes (0.8 and 0.9, respectively), indicating modest tibial correction. Standing-height z -scores remained stable (−1.5 ± 0.8 to −1.3 ± 0.7), with no measurable change in growth over 2 years. Conclusions: Burosumab therapy may improve skeletal deformities in pediatric X-linked hypophosphatemia. Early improvements in rickets severity were followed by gains in alignment, particularly mechanical axis deviation and mechanical lateral distal femoral angle, though standing height remained unaffected. Longer-term follow-up is required to confirm sustained skeletal benefits. Level of Evidence: Level IV

Background: Spinal muscular atrophy (SMA) destroys spinal cord anterior horn cells, causing progressive muscle weakness and atrophy. Despite the introduction of disease-modifying therapies (DMTs), their effects on hip displacement remain unclear. This study investigated the development and progression of hip displacement in SMA, with emphasis on the impact of DMTs. Methods: Patients diagnosed with SMA between 2000 and 2022 who underwent hip surveillance ≥3 times at different ages were included. SMA classification, bilaterality, radiographic parameters, age at DMT initiation, and hip pain were analyzed. Hip displacement was classified by migration percentage. Study-defined early (SDE) DMT use was defined as treatment before 6 months in type 1 SMA or before 2 years in type 2 SMA. Results: Twenty-one patients (10 with type 1 and 11 with type 2 SMA) were included, with a mean follow-up of 31±6 months. In type 1 SMA, 90% of patients developed hip displacement (2 with subluxation and 7 with dislocation), occurring at mean ages of 22.0±7.0 months and 33.0±7.8 months, respectively. In type 2 SMA, 72% of patients developed hip displacement (7 with subluxation and 1 with dislocation), occurring at mean ages of 37.8±16.2 months and 32 months, respectively. SMA classification ( P =0.016), bilaterality ( P P =0.006), and final acetabular index ( P =0.002) were associated with final hip displacement. SDE DMT use was not statistically significant ( P =0.163); however, one type 1 SMA patient who initiated DMT at 1 month maintained a contained hip throughout follow-up. Hip pain was absent in contained or subluxated hips but occurred in 75% of dislocated hips. Conclusions: Hip displacement in SMA begins early, with progression patterns differing by disease severity. Hip displacement is also associated with pain, which was observed primarily in dislocated hips. These findings highlight the need for routine hip surveillance from early infancy and pain assessment. DMT initiation may confer only minimal benefit when instituted at a later age, but may yield more substantial benefit when administered presymptomatically soon after birth. Level of Evidence: Level III.

Background: Both tibial spine fractures (TSFs) and anterior cruciate ligament (ACL) tears result in functional loss of knee stability. Nonetheless, it remains unclear why some patients sustain ACL tears, whereas others have TSFs. Purpose: To identify the common morphological risk factors for pediatric ACL tears and TSFs and to determine the morphological differences between them using multiplanar reconstruction of magnetic resonance imaging (MRI). Study Design: Cohort study; Level of evidence, 3. Methods: Age- and sex-matched participants (159 total [53 ACL tears, 53 TSFs, and 53 controls]) aged P = .001) and TSFs (RRR, 1.33 [95% CI, 1.10-1.62]; P = .004). A high notch width index was a protective factor against ACL tears (RRR, 0.86 [95% CI, 0.77-0.96]; P = .006) but not against TSFs (RRR, 1.01 [95% CI, 0.91-1.12]; P = .848). Conclusion: A high articular lateral tibial slope was a common risk factor for ACL tears and TSFs. Patients with ACL tears had a narrower intercondylar notch than those with TSFs and controls.

Background: Physeal-sparing procedures are preferred for treating early-onset slipped capital femoral epiphysis (SCFE), reducing limb-length discrepancy (LLD), and femoroacetabular impingement (FAI). This study aimed to investigate the treatment outcomes after physeal-sparing procedures for early-onset SCFE. Methods: We reviewed medical and radiographic records of SCFE patients from 1992 to 2022. Patients under 11 years old and followed up to skeletal maturity were included. Physeal-sparing procedures using a long screw with a short-threaded tip were performed in patients with mild to moderate slips since 2008. Patients were dichotomized into physeal-sparing and traditional in situ fixation (ISF) groups. Radiographic and clinical outcomes were comparatively analyzed between the groups. Results: Fifteen patients underwent physeal-sparing procedures, whereas 12 patients underwent traditional ISF. There was no further slippage in either group. During follow-up, slip angle was significantly decreased in the physeal-sparing group compared with the traditional ISF group (22.0 vs. 8.8 deg, respectively, P20 mm did not occur in the physeal-sparing group, but was observed in the traditional ISF group (PP=0.08, P=0.25, P=0.14, P=0.13), but differences were seen in healthy versus traditional ISF sides (PPPP<0.01, respectively). In addition, consistent growth was observed in the physeal-sparing side, but premature physeal arrest developed in the traditional ISF side. Six physeal-sparing patients required screw change procedures as the proximal femur outgrew the screw. The physeal-sparing group scored higher modified Harris Hip Score points than the traditional ISF group (89.5 vs. 85.3, respectively). Conclusions: Using a long screw with a short-threaded tip can stabilize the proximal femoral physis. It may also allow the continual growth and remodeling of the proximal femur in the treatment of early-onset SCFE. Level of Evidence: Level III.

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.