It's time to recognize the perichondrium

Subcutaneously Transplanted Fresh Cartilage in Allogeneic and Xenogeneic Immunocompetent Mouse

Cartilage is considered to be immune privileged in general. Clinically, live cells are removed from subcutaneously transplanted allogeneic cartilage mainly for preservation and for infection control. However, because maintaining cartilage feature requires live chondrocyte, it would be beneficial to subcutaneously transplant cartilage with live chondrocyte even if it was allogeneic. We harvested femoral head from 3-week-old male C57BL/6 mice, subcutaneously transplanted to 6-week-old male mice, BALB/c, BALB/c nu/nu, or C57BL/6-Tg (enhanced green fluorescent protein [EGFP] under the control of the CMV-IE enhancer, chicken beta-actin promoter, rabbit beta-globin genomic DNA [CAG promoter]), as allogeneic, allogeneic immunodeficient control, or syngeneic transplantation. We also transplanted cartilaginous particles from human induced pluripotent stem cells derived from human leukocyte antigen homozygous donor to 6-week-old male mice either BALB/c and BALB/c nu/nu as xenogeneic or xenogeneic immunodeficient control. The transplantation periods were 1, 2, 3, 4, 8, 12, and 24 weeks. As the result, we did not observe exposure of the transplant or apparent macroscopic inflammatory in all samples. Histological analysis suggested that the femoral head showed focal ossification and thinning in syngeneic transplantation. In allogeneic transplantation, slight invasion of CD3 (+) T cell and the denaturation of the cartilage were observed, suggesting immune reaction against allogeneic cartilage. In xenogeneic transplantation, slight invasion of CD3 (+) cell and CD4 (+) cell and the structure of the perichondrium-like tissue got unclear, suggesting slight immune reaction against xenogeneic cartilage. Our findings suggest that we should carefully investigate for appropriate procedure to control immune reaction against allogeneic cartilage with live chondrocyte and to maintain its cartilage feature for long time.

MRI of Pediatric Foot and Ankle Conditions

The increase in competitive sports practice among children and lack of ionizing radiation have resulted in a higher demand for MRI examinations. MRI of the children skeleton has some particularities that can lead orthopedists, pediatricians, and radiologists to diagnostic errors. The foot and ankle have several bones with abundant radiolucent and high signal intensity cartilage in several ossification centers, apophysis and physis, that can make this interpretation even harder. The present revision aims to show, how to differentiate between normal developmental findings and anatomic variants from pathologic conditions, whether mechanical, inflammatory, infectious, or neoplastic.

High-definition magnetic resonance images on medial elbow injuries in preadolescent Little Leaguers

BACKGROUND

The incidence of throwing-related elbow injuries is still rising. The study aimed to enhance the pathology of acute medial elbow injuries among young Little Leaguers by examining the medial elbows of symptomatic 9-10 years old Little Leaguers using High-Definition Magnetic Resonance Images (HDMRI), which uses a small-diameter surface coil on the target area, leading to greater image resolution.

METHOD

We identified Little Leaguers aged 9-10 years old. To minimize the detection of the chronic adaptative changes, players who experienced the medial elbow pain previously and whose HDMRI had not been taken within 4 weeks from the onset of medial elbow pain were excluded. This study considered 21 players, and the mean age was 9.4 ± 0.5 years.

RESULT

The fragmentation of the medial epicondyle apophysis via HDMRI was found in 15 elbows (71.4%), while the avulsion was seen in three cases. The signal hyperintensity at the medial epicondyle apophysis was observed in 2 cases. Our data showed abnormal changes to the medial epicondyle apophysis and surrounding structures, such as the ulnar collateral ligament (UCL), flexor-pronator tendons or the coronoid process of the ulna. We detected 11 abnormalities on X-ray imaging, while 20 subjects showed some abnormal findings via HDMRI.

DISCUSSION

The current study showed that initial medial elbow injury in Little Leaguers without a history of previous elbow injury could be attributed to multi-structure injury. Over 90% of subjects were injured in the perichondrium, while 71.4% demonstrated a fragmentation of the secondary ossification center, and 14.3% experienced an avulsion of the medial epicondyle apophysis. Because the injuries were not limited to bony structures, HDMRI may be beneficial for the appropriate evaluation of medial elbow pain. The pathology of initial medial elbow injuries in young baseball players may be due to acute trauma instead of repetitive microtrauma.

Imaging Review of Normal and Abnormal Skeletal Maturation

The growing skeleton undergoes well-described and predictable normal developmental changes, which may be misinterpreted a as pathologic condition at imaging. Primary and secondary ossification centers (SOCs), which form the diaphysis and the epiphysis of long bones, respectively, are formed by endochondral and intramembranous ossification processes. During skeletal maturation, the SOCs may appear irregular and fragmented, which should not be confused with fractures, osteochondritis dissecans, and osteochondrosis. These normal irregularities are generally symmetric with a smooth, round, and sclerotic appearance, which are aspects that help in the differentiation. The metaphysis, epiphysis, and growth plates or physes are common sites of injuries and normal variants in the pediatric skeleton. The metaphysis contains the newly formed bone from endochondral ossification and is highly vascularized. It is predisposed to easy spread of infections and bone tumors. The physis is the weakest structure of the immature skeleton. Injuries to this location may disrupt endochondral ossification and lead to growth disturbances. Pathologic conditions of the epiphyses may extend into the articular surface and lead to articular damage. At MRI, small and localized foci of bone marrow changes within the epiphysis and metaphysis are also a common finding. These can be related to residual red marrow (especially in the metaphysis of long bones and hindfoot), focal periphyseal edema (associated with the process of physeal closure), and ultimately to a normal ossification process. The authors review the imaging appearance of normal skeletal maturation and discuss common maturation disorders on the basis of developmental stage and location. ^©RSNA, 2022.

Pediatric Sports Injuries

Pediatric sports injuries are becoming more prevalent as children participate in sports. This has resulted in more imaging of pediatric injuries. The growing skeleton has features that result in unique injury patterns and radiologic findings. The article discusses the special features of bones including the growth plate, apophyses, cortex, and periosteum. Pediatric-specific sports injuries and conditions in the most common joints are then reviewed including the elbow, hip, and knee. The imaging appearances of these entities will be described with a multimodality approach including radiographs, CT, ultrasound, and MRI. The most important radiologic findings to identify will be highlighted throughout the article.

Magnetic resonance imaging of medial collateral ligament avulsion fractures of the knee in children: a potentially underestimated injury

BACKGROUND

Literature regarding medial collateral ligament (MCL) injuries is focused on adults with superficial MCL disruptions. However, children follow different injury patterns, with avulsion fractures at ligament attachment sites occurring commonly. Such avulsions have not been characterized for pediatric MCL injuries.

OBJECTIVE

To elucidate imaging findings, and review management and outcomes of pediatric MCL avulsion fractures.

MATERIALS AND METHODS

We conducted a 10-year retrospective review of knee magnetic resonance (MR) imaging reports for patients younger than 16 years old diagnosed with acute MCL avulsion fracture. MR imaging was reviewed to confirm and characterize the components of the avulsion (perichondrium without or with cartilage, and/or bone) and to identify additional knee injuries. Radiographs, if available, from the time of injury were reviewed. Clinical management and patient outcomes were recorded.

RESULTS

Eighteen patients (13 boys, 5 girls) incurred an acute MCL avulsion fracture. All avulsions involved the deep MCL attachment: 17 meniscofemoral and 1 meniscotibial component. Two avulsions also included the superficial MCL attachment. Nine boys had non-osseous avulsions, all radiographically occult. All girls had radiographically apparent avulsions. Three girls and three boys sustained associated knee derangements, most commonly anterior cruciate ligament (ACL) injury (n=4). All MCL avulsions were initially treated conservatively; one child required subsequent surgery for ongoing pain.

CONCLUSION

Pediatric MCL avulsion fractures in this study uniformly involve the attachment of the deep MCL and can be entirely non-osseous, particularly in boys who lag in skeletal maturity, making these injuries radiographically occult. MR imaging may be required to recognize these avulsions, which can impact the duration of rest and knee bracing.

Contribution of perichondrium to the mechanical properties of auricular cartilage

The poor mechanical strength of tissue-engineered auricular cartilage which is possibly due to the lack of perichondrium limits its application in auricular reconstruction surgery. However, there is insufficient research and no reliable data to support this. This study aims to investigate the contribution of perichondrium to the mechanical strength of auricular cartilage under loading. Rabbit auricular cartilage was harvested and classified into two groups. The perichondrium was removed in Group A and was left intact in Group B. Young's modulus, stress relaxation slope, and relaxation amout were analyzed through tensile and compressive tests using a material testing machine. Group B exhibited significantly higher Young's modulus in both the tensile and compressive tests (p < 0.05), lower relaxation slope (p < 0.05 in tensile test, p = 0.65 in compressive test), and lower relaxation amout (p < 0.05 in tensile test, p < 0.01 in compressive test). Our results showed that the perichondrium has a definite contribution to the mechanical properties of ear cartilage. This study may provide new insights to researchers focusing on improving the mechanical strength of tissue-engineered auricular cartilage.

Magnetic resonance imaging of the fetal musculoskeletal system

Diagnosing musculoskeletal pathology requires understanding of the normal embryological development. Intrinsic errors of skeletal development are individually rare but are of paramount clinical importance because anomalies can greatly impact patients' lives. An accurate assessment of the fetal musculoskeletal system must be performed to provide optimal genetic counseling as well as to drive therapeutic management. This manuscript reviews the embryology of skeletal development and the appearance of the maturing musculoskeletal system on fetal MRI. In addition, it presents a comprehensive review of musculoskeletal fetal pathology along with postnatal imaging.

Pitfalls in MRI of the Developing Pediatric Ankle

Normal skeletal development in the pediatric ankle is dynamic and often produces variable imaging appearances that are subject to misinterpretation. Radiologists must understand the underlying developmental phenomena, such as endochondral and membranous ossification and physeal fusion, and be familiar with their common and uncommon imaging manifestations unique to the pediatric ankle. This is especially true as the use of MRI in the evaluation of musculoskeletal trauma expands among younger populations. The authors focus on MRI evaluation of the skeletally maturing pediatric ankle and present pearls for accurately distinguishing normal findings and imaging pitfalls from true pathologic findings. The normal but often variable imaging findings of preossification, secondary ossification, and multiple ossification centers, as well as the range of bone marrow signal intensities that can be visualized within ossification centers, are described, along with tips to help differentiate these from true pathologic findings such as contusion, fracture, or tumor. The authors also review dynamic periosteal and physeal contributions to bone growth to highlight helpful distinguishing features and avoid misdiagnosis of common subperiosteal and periphyseal abnormalities. For example, the normal trilaminar appearance of the immature cortex and periosteum should not be mistaken for periosteal reaction, traumatic stripping, or subperiosteal hematoma. In addition, the physis can have several confusing but normal appearances, including normal physeal undulations (eg, Kump bump) or focal periphyseal edema, which should not be mistaken for pathologic findings such as physeal fracture, infection, or bar. ^©RSNA, 2020.