The Growing Skeleton: MR Imaging Appearances of Developing Cartilage

Femoral epiphyseal cartilage matrix changes at predilection sites of equine osteochondrosis: Quantitative MRI, second-harmonic microscopy, and histological findings

Osteochondrosis is an ischemic chondronecrosis of epiphyseal growth cartilage that results in focal failure of endochondral ossification and osteochondritis dissecans at specific sites in the epiphyses of humans and animals, including horses. The upstream events leading to the focal ischemia remain unknown. The epiphyseal growth cartilage matrix is composed of proteoglycan and collagen macromolecules and encases its vascular tree in canals. The matrix undergoes major dynamic changes in early life that could weaken it biomechanically and predispose it to focal trauma and vascular failure. Subregions in neonatal foal femoral epiphyses (n = 10 osteochondrosis predisposed; n = 6 control) were assessed for proteoglycan and collagen structure/content employing 3T quantitative MRI (3T qMRI: T1ρ and T2 maps). Site-matched validations were made with histology, immunohistochemistry, and second-harmonic microscopy. Growth cartilage T1ρ and T2 relaxation times were significantly increased (p < 0.002) within the proximal third of the trochlea, a site predisposed to osteochondrosis, when compared with other regions. However, this was observed in both control and osteochondrosis predisposed specimens. Microscopic evaluation of this region revealed an expansive area with low proteoglycan content and a hypertrophic-like appearance on second-harmonic microscopy. We speculate that this matrix structure and composition, though physiological, may weaken the epiphyseal growth cartilage biomechanically in focal regions and could enhance the risk of vascular failure with trauma leading to osteochondrosis. However, additional investigations are now required to confirm this. 3T qMRI will be useful for future non-invasive longitudinal studies to track the osteochondrosis disease trajectory in animals and humans. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1743-1752, 2016.

Forensic age estimation from the clavicle using 1.0T MRI--preliminary results

OBJECTIVES

As forensic age estimations in the living are performed without medical indication, there is a need for the development of non-ionizing methods. This study investigates the use of 1.0T MRI to visualize the ossification status of the medial end of the clavicle.

MATERIAL AND METHODS

T2 weighted 3D images were collected from a 1.0T MR system. We prospectively scanned 102 subjects, 47 autopsy cases and 55 living volunteers (12-33 years). Images were scored in blind trials by three observers using a 4-stage system. Observers differed by level of training and radiological expertise.

RESULTS

Motion artefacts reduced image resolution in living subjects. However, mean age at stage 4 was significantly different from mean age at stage 2 and 3. The minimum age at stage 4 was 19.8 years. Inter-observer agreement was moderate for autopsy cases and slight for living subjects. By contrasting subjects of "incomplete fusion" (≤ stage 3 on both sides) against "fused" (at least one stage 4), agreement rate rose to moderate (K=0.414) for living subjects. Despite the low agreement rate, no subject younger than 18 years was assessed as having "fused" clavicles.

CONCLUSION

At lower image resolution, a 2-stage system increases agreements rates among observers. To further increase accuracy, clavicle staging needs to be performed by trained observers. If available, a 1.0T MR system may be used for age estimation in the living. However, further studies are needed to ensure that the ability to discriminate adults from minors, i.e. 18 years, is maintained.

Susceptibility weighted imaging of cartilage canals in porcine epiphyseal growth cartilage ex vivo and in vivo

PURPOSE

High-resolution visualization of cartilage canals has been restricted to histological methods and contrast-enhanced imaging. In this study, the feasibility of non-contrast-enhanced susceptibility weighted imaging (SWI) for visualization of the cartilage canals was investigated ex vivo at 9.4 T, further explored at 7 and 3 T and demonstrated in vivo at 7 T, using a porcine animal model.

METHODS

SWI scans of specimens of distal femur and humerus from 1 to 8 week-old piglets were conducted at 9.4 T using 3D-GRE sequence and SWI post-processing. The stifle joints of a 2-week old piglet were scanned ex vivo at 7 and 3 T. Finally, the same sites of a 3-week-old piglet were scanned, in vivo, at 7 T under general anesthesia using the vendor-provided sequences.

RESULTS

High-contrast visualization of the cartilage canals was obtained ex vivo, especially at higher field strengths; the results were confirmed histologically. In vivo feasibility was demonstrated at 7 T and comparison of ex vivo scans at 3 and 7 T indicated feasibility of using SWI at 3 T.

CONCLUSIONS

High-resolution 3D visualization of cartilage canals was demonstrated using SWI. This demonstration of fully noninvasive visualization opens new avenues to explore skeletal maturation and the role of vascular supply for diseases such as osteochondrosis.

The trochlear pre-ossification center: a normal developmental stage and potential pitfall on MR images

BACKGROUND

The hypertrophic changes that occur in the cartilage of an epiphysis prior to the onset of ossification are known as the pre-ossification center. Awareness of the appearance of the pre-ossification center on MR images is important to avoid confusing normal developmental changes with pathology.

OBJECTIVE

The purpose of this study was to determine the characteristics of the trochlear pre-ossification center on MR imaging and examine age and gender differences.

MATERIALS AND METHODS

We retrospectively analyzed MR images from 61 children. The trochleas were categorized into three types on the basis of signal intensity (SI). Trochlear types were compared to age and gender.

RESULTS

There was no significant difference between the ages of boys and girls. Type 1 trochleas showed homogeneous SI on all pulse sequences. Type 2 trochleas demonstrated a focus of high SI in the epiphyseal cartilage on fat-suppressed water-sensitive sequences, with high or intermediate SI on gradient-echo images (pre-ossification center). Type 3 trochleas showed low SI on fat-suppressed water-sensitive sequences and gradient-echo images. Thirty-seven trochleas were described as type 1, sixteen as type 2 and eight as type 3. ANOVAs confirmed a statistically significant difference in the age of children with type 3 trochleas and those with types 1 and 2 (P < 0.001). Spearman rank correlations determined a positive relationship between trochlear type and age of the children (r = 0.53).

CONCLUSION

Development-related changes in the trochlea follow a predictable pattern. The signal characteristics of the pre-ossification center likely reflect normal chondrocyte hypertrophy and an increase in free water in the matrix.

The paediatric wrist revisited--findings of bony depressions in healthy children on radiographs compared to MRI

BACKGROUND

The presence of erosions is used for diagnosis and monitoring of disease activity in juvenile idiopathic arthritis (JIA). Assessment of carpal bone erosions in children is challenging due to lack of normal references.

OBJECTIVE

To define normal appearances of bony depressions in the wrist on radiographs and MRI.

MATERIALS AND METHODS

MRI and radiography of the wrist were performed in 88 healthy children, 5-15 years of age. We assessed the number of bony depressions within the carpals/proximal metacarpals on both modalities, separately and combined.

RESULTS

A total of 75 carpal depressions were identified on radiography compared to 715 on MRI. The number of bony depressions identified radiographically showed no statistically significant difference across age-groups. Within the metacarpals, there was no significant difference between bony depressions identified by MRI or radiography, except at the bases of the second metacarpal.

CONCLUSION

Bony depressions that resemble erosions are normal findings in the wrist in children. MRI identifies more depressions than radiographs in the carpus. Some bony depressions occur at typical locations and should be accounted for when assessing the wrist in JIA to avoid overstaging.

MR imaging of the neonatal musculoskeletal system

Experience in magnetic resonance (MR) imaging of the neonatal musculoskeletal system is rapidly increasing. The exquisite ability of MR to image the soft tissues, especially cartilage, without radiation is its key strength. Although it is not practical or sensible to undertake MR imaging in conditions in which radiography and ultrasound provide adequate information, MR is proving to be a useful adjunct and problem-solving tool in many neonatal musculoskeletal conditions.