**1. Introduction**

Blood vessel branching of the proximal femur by its scheme differs from all other major joints. This scheme changes during the individual's development, dynamically depending on age. Namely, the caliber, blood flow rate, and dominance of certain arteries from the entire network of blood vessels that participate in hip vascular supply are not equally expressed in all stages of development. In each successive stage, blood supply is dominated by a different artery that, after a certain period of time, shifts its major role to another artery. Anastomoses between individual arteries are not constant in all stages of development, and they represent

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a great importance for compensatory mechanisms. The disturbance of local arterial blood vessels, at a time when they dominate the blood supply and affect the quality of hip development and maturation, leads to reduced perfusion, and consequently, to the lack of development, ossification, and possible osteonecrosis.

The problem of the circulation and vascular network supplying bones is exposed as a main problem in the etiology and pathogenesis of hip disorders in children which can affect later stages of life. The authentication of the problem is quite hard since bone biology is inappropriate for the assessment of vascular status. Results and first signs of diseases are visible after a couple of months or even longer.

Acute or chronic ischemia in other tissues has a specific clinical presentation and symptomatology, which is not the case with the hip joint. Also, techniques that are applicable for vascular status assessment in other tissues are almost useless for the estimation of the vascular status on bone tissue.

## **2. Bone vascular system**

As in other tissues, vascular system of the bones can be divided into three levels: afferent and efferent blood vessel and a microvascular network that fills in the space between them (**Figure 1**). Afferent blood vessel is composed of epiphyseal, metaphyseal, nutrient, and periosteal arteries. Microvascular network consists of medullar sinusoid, cortical, and periosteal capillaries, while the efferent blood vessel is formed of epiphyseal, metaphyseal, nutrient and periosteal veins, and collective sinusoids. None of the mentioned vascular elements can be considered independent. There are numerous anastomoses between them and opinions about one's participation in bone nutrition are still divided.

**Figure 1.** Bone vascularization.

The nutrient artery is the main artery supplying the cortex of the bone. Its branches separate under a sharp angle and do not divide further. In medullar cavity, the nutrient artery is divided into ascendant and descendant medullar arteries. Branches separate radially out of these supply cortices. In normal bone structure, there is a centrifugal flow meaning that blood vessel interchange is parallel to Haver's channels and bone axis. These blood vessels drain into venules on the periosteal bone surface. This type of vascular organization has functional meaning allowing relatively high intramedullary pressure that can affect movements of the interstitial fluid in bones [1].
