Lack of skeletal muscle contraction disrupts fibrous tissue morphogenesis in the developing murine knee.

Externally applied forces, such as those generated through skeletal muscle contraction, are important to embryonic joint formation, and their loss can result in gross morphologic defects including joint fusion. While the absence of muscle contraction in the developing chick embryo leads to dissociation of dense connective tissue structures of the knee and ultimately joint fusion, the central knee joint cavitates whereas the patellofemoral joint does not in murine models lacking skeletal muscle contraction, suggesting a milder phenotype. These differential results suggest that muscle contraction may not have as prominent of a role in the growth and development of dense connective tissues of the knee. To explore this question, we investigated the formation of the menisci, tendon, and ligaments of the developing knee in two murine models that lack muscle contraction. We found that while the knee joint does cavitate, there were multiple abnormalities in the menisci, patellar tendon, and cruciate ligaments. The initial cellular condensation of the menisci was disrupted and dissociation was observed at later embryonic stages. The initial cell condensation of the tendon and ligaments were less affected than the meniscus, but these tissues contained cells with hyper-elongated nuclei and displayed diminished growth. Interestingly, lack of muscle contraction led to the formation of an ectopic ligamentous structure in the anterior region of the joint as well. These results indicate that muscle forces are essential for the continued growth and maturation of these structures during this embryonic period.

Histological and immunohistochemical guide to tendon tissue.

Tendons are unique dense connective tissues with discrete zones having specific structure and function. They are juxtaposed with other tissues (e.g., bone, muscle, and fat) with different compositional, structural, and mechanical properties. Additionally, tendon properties change drastically with growth and development, disease, aging, and injury. Consequently, there are unique challenges to performing high quality histological assessment of this tissue. To address this need, histological assessment was one of the breakout session topics at the 2022 Orthopaedic Research Society (ORS) Tendon Conference hosted at the University of Pennsylvania. The purpose of the breakout session was to discuss needs from members of the ORS Tendon Section related to histological procedures, data presentation, knowledge dissemination, and guidelines for future work. Therefore, this review provides a brief overview of the outcomes of this discussion and provides a set of guidelines, based on the perspectives from our laboratories, for histological assessment to assist researchers in their quest to utilize these techniques to enhance the outcomes and interpretations of their studies.

Learning from a failure in threat assessment: 11 questions and not enough answers.

Threat assessment theory and practice have evolved significantly since Columbine. The US Secret Service's guidelines for threat assessment include 11 questions that school officials should ask to identify, investigate, and manage students of concern. Yet, no research examines how school officials implement these questions. This qualitative case study examines the way that school officials used the 11 questions with a student of concern, who underwent a threat assessment and 3 months later shot and killed a classmate and himself on school grounds. The data include deposition testimony from 12 school and district officials and more than 8,000 pages of records in the case. For each of the 11 questions, the findings reveal what the threat assessment team knew and might have learned; the findings also demonstrate the importance of multiple sources of information, a multidisciplinary team, and an investigative mindset. The questions may prove difficult to answer in "loosely coupled" systems, like schools, where information is unintentionally lost due to the organization's structural hierarchy, specialization of tasks, and heavy workloads. The findings provide critical lessons learned for threat assessment, information gathering, and violence prevention in schools.

Sleep and delinquency: does the amount of sleep matter?

Sleep, a key indicator of health, has been linked to a variety of indicators of well-being such that people who get an adequate amount generally experience greater well-being. Further, a lack of sleep has been linked to a wide range of negative developmental outcomes, yet sleep has been largely overlooked among researchers interested in adolescent delinquency. The purpose of this study was to explore the relationship between hours of sleep and delinquent behavior among adolescents by using data from Wave 1 of the National Longitudinal Study of Adolescent Health (n = 14,382; 50.2% female, 63.5% white). A series of negative binomial regressions showed that youth who typically sleep seven or fewer hours per night reported significantly more property delinquency than youth who sleep the recommended 8-10 h. Further, youth who reported sleeping 5 or fewer hours per night reported significantly more violent delinquency than youth who reported sleeping the recommended number of hours per night. The findings suggest that sleep is an important, and overlooked, dimension of delinquent behavior and studies that focus on adolescent health should further investigate the effects of insufficient sleep. Finally, the authors recommend that sleep and other relevant health behaviors be considered in the context of more comprehensive approaches to delinquency prevention and intervention.