Bone growth increases the knee flexion contracture angle: A study using rats

Homo sapiens May Incorporate Daily Acute Cycles of “Conditioning–Deconditioning” to Maintain Musculoskeletal Integrity: Need to Integrate with Biological Clocks and Circadian Rhythm Mediators

Human evolution required adaptation to the boundary conditions of Earth, including 1 g gravity. The bipedal mobility of Homo sapiens in that gravitational field causes ground reaction force (GRF) loading of their lower extremities, influencing the integrity of the tissues of those extremities. However, humans usually experience such loading during the day and then a period of relative unloading at night. Many studies have indicated that loading of tissues and cells of the musculoskeletal (MSK) system can inhibit their responses to biological mediators such as cytokines and growth factors. Such findings raise the possibility that humans use such cycles of acute conditioning and deconditioning of the cells and tissues of the MSK system to elaborate critical mediators and responsiveness in parallel with these cycles, particularly involving GRF loading. However, humans also experience circadian rhythms with the levels of a number of mediators influenced by day/night cycles, as well as various levels of biological clocks. Thus, if responsiveness to MSK-generated mediators also occurs during the unloaded part of the daily cycle, that response must be integrated with circadian variations as well. Furthermore, it is also possible that responsiveness to circadian rhythm mediators may be regulated by MSK tissue loading. This review will examine evidence for the above scenario and postulate how interactions could be both regulated and studied, and how extension of the acute cycles biased towards deconditioning could lead to loss of tissue integrity.

Developmental programming of bone deficits in growth-restricted offspring

Recent evidence links low birthweight and poor adult bone health. We characterised bone size, mineral content, density and strength (stress strain index of bone bending strength (SSI)) in rats from weaning to 12 months. Bilateral uterine vessel ligation (Restricted) or sham surgery (Control) was performed on gestational Day 18 in rats inducing uteroplacental insufficiency. Postmortem of male and female offspring was performed at postnatal Day 35 and at 2, 4, 6 and 12 months. Femur mineral content, density and strength were measured using quantitative computed tomography (pQCT). Restricted pups were born 10%-15% lighter and remained smaller with shorter femurs than Controls (P<0.05). Male and female Restricted rats had lower trabecular bone content compared with Controls (P<0.05), without trabecular density changes. Cortical content was reduced in Restricted males (Day 35 and 6 and 12 months) and at all ages in Restricted females (P<0.05). Cortical density was lower at Day 35 in Restricted males (P<0.05). SSI was lower at Day 35 and at 6 and 12 months in Restricted males, and at all ages in Restricted females (P<0.05). Skeletal deficits were detected in Restricted offspring with gender-specific differences during juvenile and adolescent periods. Bone deficits observed at 6 months in males were greater than at 12 months, indicating that aging can exacerbate programmed bone phenotypes.

Physiological skeletal gains and losses in rat mothers during pregnancy and lactation are not observed following uteroplacental insufficiency

Fluctuations in maternal bone mass during pregnancy and lactation facilitate calcium transfer to offspring. Uteroplacental insufficiency causes fetal growth restriction and programs poor adult bone health. We aimed to characterise maternal skeletal phenotype during normal pregnancy and pregnancy complicated by uteroplacental insufficiency. Uteroplacental restriction (Restricted) or sham surgery (Control) was performed on gestational Day 18 (term=22 days) in pregnant Wistar-Kyoto rats. Maternal right femurs were collected on embryonic Day 20, postnatal Day 1 and Weeks 5, 7 and 9 postnatal. Dual-energy X-ray absorptiometry was used to quantify global bone mineral content, density and body composition. Peripheral quantitative computed tomography was utilised to determine trabecular and cortical content, density, circumferences and strength. Control rats exhibited expected reductions in trabecular and cortical content, density and bone strength from embryonic Day 20 to postnatal Day 1 (P<0.05). These skeletal alterations were absent in Restricted rats. By postnatal Day 7, bone parameters in Control and Restricted rats were not different from non-pregnant rats, indicating restoration of maternal bone. The lack of bone loss in mothers suffering uteroplacental insufficiency suggests that calcium transfer to pups would be impaired. This reduction in calcium availability is a likely contributor to the programming of poor adult bone health in growth-restricted offspring.

Ontogeny of skeletal maturation in the juvenile rat

Systemic regulation of the cellular processes that produce endochondral elongation and endochondral mineralization during postnatal skeletal maturation are not completely understood. In particular, a mechanism coupling the decline of cellular activity in the bone microenvironment to the onset of sexual maturity remains elusive. The purpose of this study was to empirically integrate the dynamic progression of bone mineral accrual and endochondral elongation as a function of animal age in growing male and female Sprague-Dawley rats. We used serial dual-energy X-ray absorptiometry (DXA) and radiography to study the temporal progression of bone growth and mineral accrual from weaning to adulthood. We observed that skeletal maturation proceeds in a pattern adequately described by the Gompertz function. During this period of growth, we found that serum markers of osteoblastic bone formation declined with age, while osteoclastic bone resorption activity remained unchanged. We also report a slight lag in the age at inflection in the rate of bone mineral accrual relative to the rate of tibial elongation and that both endochondral processes eventually come to asymptotic equilibrium by approximately 20 weeks of age. In addition, we studied tibial growth plate histomorphometry at select time points through 1 year of age. We report that, despite the histologic persistence of physeal cartilage, very little proliferative or elongative activity was measured in this tissue beyond 20 weeks of age. Taken together, these data provide insight to the temporal coordination of postnatal endochondral growth processes.

Progression of an arthrogenic motion restriction after immobilization in a rat experimental knee model

BACKGROUND

Contracture is defined as a decrease in both active and passive ranges of motion after immobilization. A fibrotic change of a capsule is suggested to be one of the main causes of the joint contracture. The goal of this study is to determine the effect of capsule on limiting the range of motion after immobilization.

MATERIALS AND METHODS

We immobilized the knee joint of 35 rats with an internal fixator with the knee joint flexed at 150 degrees. The rats were sacrificed at 1, 2, 4, 6, 8, 12, and 16 weeks after surgery and the lower extremities were disarticulated at the hip joint. After extra-articular myotomies around the tibia and femur, x-rays were taken to measure the angles of extension of the knee joint under 3 different torques. The measurements were repeated after releasing the posterior capsule in order to observe their effects on knee motion.

RESULTS

Joint contracture was rapidly progressed until 8 weeks and advanced slowly after 8 weeks. After releasing the posterior capsule, both the immobilized and the control groups gained the angle of knee extension. The acquired angle in the immobilized group was significantly greater than in the control group after 4 weeks and became plateau after 8 weeks.

CONCLUSION

Joint contracture develops at the early stage of immobilization and progresses over time. The posterior capsule significantly contributes to the limitation in extension.