Epiphyseal ossification centers in the assessment of fetal maturity: sonographic correlation with the amniocentesis lung profile

The epiphyseal secondary ossification center: Evolution, development and function

Bone age is used widely by pediatricians to assess the skeletal maturity of a child and predict growth potential. This entails measuring the size of secondary ossification centers (SOCs), which develop with age in the ends of long bones, which are initially cartilaginous. However, little is presently known about the developmental biology, evolution and functional role of these skeletal elements. Here, we summarize the knowledge currently available in this area and discuss potential primary functions of the SOC.

Sonographic Assessment of Fetal Growth Abnormalities

Fetal growth abnormalities have significant consequences for pregnancy management and maternal and fetal well-being. The accurate diagnosis of fetal growth abnormalities contributes to optimal antenatal management, which may minimize the sequelae of inadequate or excessive fetal growth. An accurate diagnosis of abnormal fetal growth depends on accurate pregnancy dating and serial growth measurements. The fetal size at any given stage of pregnancy is either appropriate or inappropriate for the given gestational age (GA). Pregnancy dating is most accurate in the first trimester, as biologic variability does not come into play until the second and third trimesters. The authors describe the determination of GA with use of standard US measurements and how additional parameters can be used to confirm dating. Once dates are established, serial measurements are used to identity abnormal growth patterns. The sometimes confusing definitions of abnormal growth are clarified, the differentiation of a constitutionally small but healthy fetus from a growth-restricted at-risk fetus is described, and the roles of Doppler US and other adjunctive examinations in the management of growth restriction are discussed. In addition, the definition of selective growth restriction in twin pregnancy is briefly discussed, as is the role of Doppler US in the classification of subtypes of selective growth restriction in monochorionic twinning. The criteria for diagnosing macrosomia and the management of affected pregnancies also are reviewed. The importance of correct pregnancy dating in the detection and surveillance of abnormal fetal growth and for prevention of perinatal maternal and fetal morbidity and mortality cannot be overstated. The online slide presentation from the RSNA Annual Meeting is available for this article. ^©RSNA, 2020.

Conditional disruption of the osterix gene in chondrocytes during early postnatal growth impairs secondary ossification in the mouse tibial epiphysis

In our previous studies, we have found that the prepubertal increase in thyroid hormone levels induces osterix (Osx) signaling in hypertrophic chondrocytes to transdifferentiate them into osteoblasts. To test if Osx expressed in chondrocytes directly contributes to transdifferentiation and secondary ossification, we generated Osx flox/flox ; Col2-Cre-ERT2 mice and knocked out Osx with a single injection of tamoxifen at postnatal day (P) 3 prior to evaluation of the epiphyseal bone phenotype by µCT, histology, and immunohistochemistry (IHC) at P21. Vehicle (oil)-treated Osx flox/flox ; Col2-Cre-ERT2 and tamoxifen-treated, Cre-negative Osx flox/flox mice were used as controls. µCT analysis of tibial epiphyses revealed that trabecular bone mass was reduced by 23% in the Osx conditional knockout (cKO) compared with control mice. Trabecular number and thickness were reduced by 28% and 8%, respectively, while trabecular separation was increased by 24% in the cKO mice. Trichrome staining of longitudinal sections of tibial epiphyses showed that bone area and bone area adjusted for total area were decreased by 22% and 18%, respectively. IHC studies revealed the presence of abundant Osx-expressing prehypertrophic chondrocytes in the epiphyses of control mice at P10, but not in the cKO mice. Furthermore, expression levels of MMP13, COL10, ALP, and BSP were considerably reduced in the epiphyses of cKO mice. We also found that Osx overexpression in ATDC5 chondrocytes increased expression of Col10, Mmp13, Alp, and Bsp. Our data indicate that Osx expressed in chondrocytes plays a significant role in secondary ossification by regulating expression of genes involved in chondrocyte hypertrophy and osteoblast transdifferentiation.

New diagnostic modalities and emerging treatments for neonatal bone disease

Bone disease in the neonatal period has often been regarded as an issue affecting premature infants, or a collection of rare and ultra-rare disorders that most neonatologists will see only once or twice each year, or possibly each decade. The emergence of targeted therapies for some of these rare disorders means that neonatologists may be faced with diagnostic dilemmas that need a rapid solution in order to access management options that did not previously exist. The diagnostic modalities available to the neonatologist have not changed a great deal in recent years; blood tests and radiographs still form the mainstays with other techniques usually reserved for research studies, but rapid access to genomic testing is emergent. This paper provides an update around diagnosis and management of bone problems likely to present to the neonatologist.

Ossification center of the humeral shaft in the human fetus: a CT, digital, and statistical study

Purpose

The knowledge of the development of the humeral shaft ossification center may be useful both in determining the fetal stage and maturity and for detecting congenital disorders, as well. This study was performed to quantitatively examine the humeral shaft ossification center with respect to its linear, planar, and volumetric parameters.

Materials and method

Using methods of CT, digital image analysis, and statistics, the size of the humeral shaft ossification center in 48 spontaneously aborted human fetuses aged 17–30 weeks was studied.

Results

With no sex differences, the best-fit growth dynamics for the humeral shaft ossification center was modeled by the following functions: y = −78.568 + 34.114 × ln (age) ± 2.160 for its length, y = −12.733 + 5.654 × ln(age) ± 0.515 for its proximal transverse diameter, y = −4.750 + 2.609 × ln (age) ± 0.294 for its middle transverse diameter, y = −10.037 + 4.648 × ln (age) ± 0.560 for its distal transverse diameter, y = −146.601 + 11.237 × age ± 19.907 for its projection surface area, and y = 121.159 + 0.001 × (age)⁴ ± 102.944 for its volume.

Conclusions

With no sex differences, the ossification center of the humeral shaft grows logarithmically with respect to its length and transverse diameters, linearly with respect to its projection surface area, and fourth-degree polynomially with respect to its volume. The obtained morphometric data of the humeral shaft ossification center are considered normative for respective prenatal weeks and may be of relevance in both the estimation of fetal ages and the ultrasonic diagnostics of congenital defects.

Thyroid hormone receptor-β1 signaling is critically involved in regulating secondary ossification via promoting transcription of the Ihh gene in the epiphysis

Thyroid hormone (TH) action is mediated through two nuclear TH receptors, THRα and THRβ. Although the role of THRα is well established in bone, less is known about the relevance of THRβ-mediated signaling in bone development. On ther basis of our recent finding that TH signaling is essential for initiation and formation of secondary ossification center, we evaluated the role of THRs in mediating TH effects on epiphysial bone formation. Two-day treatment of TH-deficient Tshr(-/-) mice with TH increased THRβ1 mRNA level 3.4-fold at day 7 but had no effect on THRα1 mRNA level at the proximal tibia epiphysis. Treatment of serum-free cultures of tibias from 3-day-old mice with T3 increased THRβ1 expression 2.1- and 13-fold, respectively, at 24 and 72 h. Ten-day treatment of Tshr(-/-) newborns (days 5-14) with THRβ1 agonist GC1 at 0.2 or 2.0 μg/day increased BV/TV at day 21 by 225 and 263%, respectively, compared with vehicle treatment. Two-day treatment with GC1 (0.2 μg/day) increased expression levels of Indian hedgehog (Ihh) 100-fold, osterix 15-fold, and osteocalcin 59-fold compared with vehicle at day 7 in the proximal tibia epiphysis. Gel mobility shift assay demonstrated that a putative TH response element in the distal promoter of mouse Ihh gene interacted with THRβ1. GC1 treatment (1 nM) increased Ihh distal promoter activity 20-fold after 48 h in chondroctyes. Our data suggest a novel role for THRβ1 in secondary ossification at the epiphysis that involves transcriptional upregulation of Ihh gene.

Ultrasound Assessment of the Skeletal Development of the Proximal Tibial, Proximal Femoral, and Distal Femoral Epiphyses in Premature and Mature Newborns

We evaluated postnatal skeletal development of the proximal femoral epiphysis, distal femoral epiphysis (DFE) and proximal tibial epiphysis (PTE) in 178 premature and mature newborns, between 25 and 47 wk of biological age, using high-resolution B-mode musculoskeletal ultrasound. Approximate age-related values were determined based on the ossification center size and epiphyseal cartilage thickness. The earliest onsets of visible mineralization were at 30 wk of maturity in the DFE, 31 wk in the PTE and 43 wk in the proximal femoral epiphysis. In preterm and term neonates, significant correlations were observed for transverse and longitudinal length of the DFE and PTE with biological age (R² = 0.35-0.50, p < 0.01). No significant age-dependent increases or decreases in cartilage thickness were seen between the ossification centers and cartilage surface in the DFE and PTE. High-resolution B-mode musculoskeletal ultrasound is an excellent tool for assessing skeletal development in premature and mature newborns.

Epiphyseal chondrocyte secondary ossification centers require thyroid hormone activation of Indian hedgehog and osterix signaling

Thyroid hormones (THs) are known to regulate endochondral ossification during skeletal development via acting directly in chondrocytes and osteoblasts. In this study, we focused on TH effects on the secondary ossification center (SOC) because the time of appearance of SOCs in several species coincides with the time when peak levels of TH are attained. Accordingly, micro-computed tomography (µCT) evaluation of femurs and tibias at day 21 in TH-deficient and control mice revealed that endochondral ossification of SOCs is severely compromised owing to TH deficiency and that TH treatment for 10 days completely rescued this phenotype. Staining of cartilage and bone in the epiphysis revealed that whereas all of the cartilage is converted into bone in the prepubertal control mice, this conversion failed to occur in the TH-deficient mice. Immunohistochemistry studies revealed that TH treatment of thyroid stimulating hormone receptor mutant (Tshr(-/-) ) mice induced expression of Indian hedgehog (Ihh) and Osx in type 2 collagen (Col2)-expressing chondrocytes in the SOC at day 7, which subsequently differentiate into type 10 collagen (Col10)/osteocalcin-expressing chondro/osteoblasts at day 10. Consistent with these data, treatment of tibia cultures from 3-day-old mice with 10 ng/mL TH increased expression of Osx, Col10, alkaline phosphatase (ALP), and osteocalcin in the epiphysis by sixfold to 60-fold. Furthermore, knockdown of the TH-induced increase in Osx expression using lentiviral small hairpin RNA (shRNA) significantly blocked TH-induced ALP and osteocalcin expression in chondrocytes. Treatment of chondrogenic cells with an Ihh inhibitor abolished chondro/osteoblast differentiation and SOC formation. Our findings indicate that TH regulates the SOC initiation and progression via differentiating chondrocytes into bone matrix-producing osteoblasts by stimulating Ihh and Osx expression in chondrocytes.

Sonographic identification and measurement of the epiphyseal ossification centers as markers of fetal gestational age

PURPOSE

This study was conducted to verify the predictive value of epiphyseal ossification center measurements in estimating gestational age.

METHODS

Women with singleton pregnancies of 30-40 weeks gestation (n = 377) were enrolled in this prospective study. The distal femoral, proximal tibial, and proximal humeral ossification centers were identified and measured. A nomogram of fetal bone development was created using the sum of the three diameters.

RESULTS

Gestational age correlated well with the diameters of the distal femoral and the proximal tibial epiphyseal ossification centers but even better with the sum of the three ossification centers. Positive predictive values of the fetus having gestational age of at least 37 weeks when the sum of the three centers was 7, 11, and 13 mm were 82%, 94%, and 100%, respectively. A nomogram was created using the sum of the ossification centers for 30-40 weeks' gestational age.

CONCLUSIONS

Ultrasonographic visualization of the epiphyses ossification centers may be a useful marker of fetal gestational age.

Determination of gestational age after the 24th week of gestation from fetal kidney length measurements

OBJECTIVE

To evaluate the application of kidney length measurement to the determination of gestational age between the 24th and 38th weeks and to compare its accuracy with that of other fetal biometric indices.

STUDY DESIGN

Seventy-three women with singleton uncomplicated pregnancies underwent standard ultrasound fetal biometry and kidney length measurement every 2 weeks between 24 and 38 weeks' gestation. These measurements were used to date the pregnancies relative to crown-rump length dating between 8 and 10 weeks' gestation. Linear regression models for estimation of gestational age were derived from the biometric indices and kidney length. In addition, stepwise regression models were constructed to determine the best model for determining gestational age between 24 and 38 weeks. Comparisons were then made between the accuracy of these models in the determination of gestational age.

RESULTS

The best model for estimating gestational age in late pregnancy included the variables kidney length, biparietal diameter, head circumference, femur length and abdominal circumference. This model accurately predicted gestational age with a standard error of +/- 8.48 days. A model including kidney length, biparietal diameter, head circumference and femur length accurately predicted gestational age with a standard error of +/- 8.57 days. These models were slightly more accurate than models derived from the biometric indices of biparietal diameter, head circumference and femur length (+/- 9.87 days), biparietal diameter, head circumference, femur length and abdominal circumference (+/- 9.45 days) and biparietal diameter and femur length (+/- 9.9 days). Kidney length and femur length were the most accurate single parameters for predicting gestational age using simple linear regression models (+/- 10.29 and 10.96 days, respectively); the abdominal circumference was the least accurate (+/- 14.54 days).

CONCLUSION

Kidney length is a more accurate method of determining gestational age than the fetal biometric indices of biparietal diameter, head circumference, femur length and abdominal circumference between 24 and 38 weeks' gestation. When combined with biparietal diameter, head circumference and femur length, the precision of dating is improved by 2 days. This measurement is easy to make and could therefore be easily incorporated into the model for dating pregnancies after 24 weeks of gestation, in particular when measurements of the biparietal diameter and head circumference are difficult.

Estimating gestational age in the term pregnancy with a model based on multiple indices of fetal maturity

A prospective ultrasonographic study was conducted in 100 normal pregnant women with gestational ages that ranged from 36 to 42 weeks in which multiple biometric measurements were obtained. Dimensions of the distal femoral, proximal tibial, and proximal humeral epiphyseal ossification centers, as well as the placental and colonic grades, were also evaluated. A high statistical correlation was found between gestational age and each of the five variables (p less than 0.001). With a stepwise linear logistic regression analysis, we determined that gestational ages (36 to 39 weeks and 40 to 42 weeks) could be ascertained with a high probability with the use of a combination of the proximal humeral epiphysis and colonic grades. Probability estimates were not significantly affected by the addition of the distal femoral, proximal tibial epiphyses, placental grade, or amniotic fluid volume. From these data, probability prediction tables were generated. The results of this study provide an alternate method by which gestational age may be estimated in late pregnancy.

Sonographic assessment of the distal femoral and proximal tibial ossification centers in the prediction of pulmonic maturity in normal women and women with diabetes

A noninvasive method for the assessment of fetal pulmonic maturity via the sonographic characterization of fetal distal femoral and proximal tibial epiphyseal ossification centers was evaluated. The study population included 82 patients in the third trimester of pregnancy, 47 of whom had uncomplicated gestations, while 35 had insulin-dependent diabetes. In uncomplicated pregnancies a distal femoral epiphysis measuring greater than or equal to 3 mm in the axial plane or the sonographic identification of a proximal tibial epiphysis of any dimension correlated with pulmonic maturity. The combination of a distal femoral epiphysis greater than or equal to 3 mm and the presence of a proximal tibial epiphysis was highly correlated with a lecithin/sphingomyelin ratio greater than or equal to 2:1 (sensitivity 100%, specificity 63%, negative predictive value 100%, and false-negative rate 0%). The Kappa value (K) for testing the agreement between ultrasound results and amniocentesis results was 0.39 (p less than 0.002). In diabetic pregnancies neither a distal femoral epiphysis greater than or equal to 3 mm nor a proximal tibial epiphysis of any dimension correlated precisely with the presence of phosphatidyl glycerol in the amniotic fluid. However, the combination of a distal femoral epiphysis greater than or equal to 3 mm and a proximal tibial epiphysis greater than or equal to 2 mm improved the prediction of phosphatidyl glycerol (sensitivity 83%, specificity 79%, negative predictive value 96%, false-negative rate 17%). The K value in this instance was 0.36 (p greater than or equal to 0.19). It is concluded that the sonographic assessment of the distal femoral and proximal tibial epiphyses and their dimensions in the axial plane may be useful as markers for pulmonic maturity in uncomplicated pregnancies.

Ultrasonographic assessment of gestational age with the distal femoral and proximal tibial ossification centers in the third trimester

A prospective sonographic evaluation of the distal femoral and proximal tibial epiphyseal ossification centers in 228 normal pregnant women was carried out from 28 to 40 weeks' gestation. The mean gestational age at which the distal femoral epiphysis and proximal tibial epiphysis were imaged was 34 and 38 weeks, respectively. The distal femoral epiphysis was not identifiable before 28 weeks but was observed in 72% of fetuses at 33 weeks and in 94% of fetuses at 34 weeks' gestation. The presence of a distal femoral epiphysis measuring 1 or 2 mm was associated with a gestational age of greater than 33 weeks in 87.0% of fetuses, whereas a distal femoral epiphysis measuring greater than or equal to 3 mm was associated with a gestational age greater than 37 weeks in 85% of fetuses. The proximal tibial epiphysis, which was absent before 34 weeks' gestation, was observed in 56% of fetuses at 36 weeks, in 80% of fetuses at 37 weeks, and in 100% of fetuses at 39 weeks of gestation. The presence of a proximal tibial epiphysis of 1 or 2 mm was associated with a gestational age of greater than 36 weeks in 88% of fetuses, whereas a proximal tibial epiphysis greater than or equal to 3 mm was associated with a gestational age of greater than 38 weeks in 94% of fetuses. The sonographic evaluation of distal femoral epiphysis/proximal tibial epiphysis can be used as independent markers for estimation of gestational age during the third trimester, a period in which standard fetal biometric estimates of gestational age are least accurate.