movement physiology: bone

yogabook / movement physiology / bone

Bones are the tensile and compression-resistant components of the vertebrate endoskeleton. Accessory bones are located outside the movement apparatus, such as the auditory ossicles. The bones of the movement apparatus belong to its passive part. Bones can have a protective function, such as the ribs (e.g. for the heart and lungs) or the skull for the brain. Erythrocytes (red blood cells), leukocytes (white blood cells) and thrombocytes (platelets) are formed in the parts of the bones with red bone marrow.
Bones can have very different lengths and shapes, see for example femur, sesamoid bones and scapula.

The bones are divided into

  • Tubular bones (Ossa longa), e.g. the long bones of the extremities such as femur, tibia, fibula, humerus, radius, ulna). These consist of a bone shaft (diaphysis) between two epiphyses (growth zones), behind which the metaphyses are located, often with condyles or tubercles.
  • plate bones (Ossa plana) such as scapula, sternum, the bones of the pelvis ( ischium, ilium, pubis), ribs, skull bones
  • short bones (Ossa brevia) without a particular shape, such as the carpal bones and tarsal bones
  • Sesamoid bones (Ossa sesamoidea), which also includes the patella
  • irregular bones such as the vertebrae and the lower jaw bone (mandible)
  • some bones (Ossa pneumatica) are not categorised as flat bones despite their shape, as they surround cavities lined with mucous membrane, such as the frontal bone

Bones are living, well-vascularised organs. They are usually surrounded by periosteum on the outside, except in the areas where they articulate with other bones, where they are covered with hyaline cartilage. Under the periosteum lies the corticalis, which is very dense and firm in the diaphysis of the long bones and is therefore referred to as compacta. More profound than the corticalis/compacta is the spongy spongiosa, a framework of fine bone beads (trabeculae), which mainly determines the stability of the bone by absorbing tensile and compressive forces according to their orientation.
Inside the cancellous bone lies the marrow cavity, a space filled with bone marrow. In many bones, the bone marrow is converted to yellow fatty marrow in the course of life; only in some bones does the blood cell-forming (haematopoiesis) red marrow remain: ribs, sternum, vertebral body, hand and foot bones, flat skull bones and the bones of the hip bone.
In addition to 25% water, bone consists of 45% inorganic material and 30% organic material, 95% of which is collagen type 1.

Bones can withstand a greater degree of tensile and compressive loading, and to a certain extent they are also flexible in bending.The bending loads are partly absorbed by tensile straps, which consist of ligaments, muscles and fasciae, the best known of which is the iliotibial tract as a tensioning belt for the femur. If the tensioning strap fails or is damaged, spontaneous fractures can occur.

Before the end of human growth, bone growth is subject to a circadian rhythm with the maximum at night. For reasons that are not yet clear, growing pains can occur. Growth takes place in the epiphyseal joints, which ossify at the end of the growth phase around the age of 18. The permanent bone remodelling (including renewal) is referred to as bone tissue remodelling.

Most bones develop from the hyaline cartilage skeleton (chondral ossification), only the skull bones from connective tissue precursors (desmal ossification).



Before the end of human growth, bone growth is subject to a circadian rhythm with the maximum at night. For reasons that are not yet clear, growing pains can occur. Growth takes place in the epiphyseal joints, which ossify at the end of the growth phase around the age of 18. The permanent bone remodelling (including renewal) is referred to as bone tissue remodelling.

Most bones develop from the hyaline cartilage skeleton (chondral ossification), only the skull bones from connective tissue precursors (desmal ossification).

Condylus

Condyles, also known as articular processes or articular cartilages, are the thickenings at the end of bones that contain the atriculation surfaces with other bones.
Sometimes epicondyles lie on the condyles, which are bony protrusions to which muscles or their tendons attach.
The best-known condyles are those of the distal humerus (in the elbow joint), the proximal tibia and the distal femur (both in the knee joint).

Epicondylus

Bony protrusions on condyles, to which muscles or their tendons are attached.

Tuberkel

Cusps on bones to which muscles or their tendons are attached, e.g. tuberculum minus and tuberculum majus of the humerus.

Apophyse

Knochenansätze von Sehnen und Bändern mit eigenem Ossifikationszentrum, das meist mit dem Hauptkern der Epiphyse verschmilzt. Gelegentlich bleibt es aber auch eigenständig. Hier ansetzende Sehnen sind über Faserknorpel mit dem Knochen verbunden, der zunehmend mineralisiert. Die Knorpel bieten dabei eine gewisse Elastizität. Die Apophysen an den Muskelinsertionen des Rectus femoris, der Adduktoren und der Ischiocruralen Gruppe sind zuweilen von Schäden betroffen. Das reicht von geringfügigen Veränderungen bis zu knöchernen Ausriss der Sehnen (Avulsion). Entsprechend der betroffenen Muskulatur liegt häufig eine Schmerzausstrahlung vor in Richtung Leiste oder des Gesäßes. Radiologisch sind diese Störungen gut zu finden, jedoch zeigt sich ihr Bild recht uneinheitlich. Differentialdiagnostisch müssen osteolytische Prozesse und Tumoren abgeklärt werden.

Diaphyse

Der Bereich eines Röhrenknochens zwischen den Wachstumsfugen. In diesem befindet sich das Knochenmark. Hier ansetzende Sehnen setzen über Sharpey-Fasern am Knochen an, die eine Dämpfung durch die Verflechtung der Kollagenfasern der Sehne mit elastischen Fasern der Knochenhaut bieten.

Epiphyse / Epiphysis ossis

das knorpelig angelegte Ende eines Röhrenknochen, in dem sich während des Wachstums Knochenkerne entwickeln, die den Knochen wachsen lassen. Die Epiphyse ist durch die Epiphysenfuge (Wachstumsfuge) von der Diaphyse getrennt, in der sich das Knochenmark befindet. In Bezug auf die Körpermitte wird von einer proximalen und einer distalen Epiphyse gesprochen. Ist die Epiphyse Teil eines Gelenks (anders als die proximale Epiphyse der distalen Phalangen von Zehen und Fingern), so ist die im Bereich der Artikulation mit hyalinem Knorpel (Gelenkknorpel) überzogen.

Epiphysenfuge / Wachstumsfuge

der knorpelige Übergangsbereich von der Epiphyse eines Röhrenknochens zur Metaphyse, in dem sich während des Wachstums Knochenkerne entwickeln, die den Knochen wachsen lassen. Mit etwa 20 Jahren ist das Längenwachstum abgeschlossen, das von den Epiphysenfugen ausgeht. Dazu verringert sich der STH-Spiegel, und die Epiphysenfugen verknöchern.

Metaphyse

Die beiden (proxmimal und distal) Bereiche des Schafts eines Röhrenknochens, in dem noch kein Knochenmark vorhanden ist.

Knochenhaut (Periost)

Bindegewebige Umhüllung der Knochen, die ihn außerhalb der mit hyalinem Knorpel überzogenen Glenkflächen vollständig umgibt. Im Bereich des Schädels wird sie auch als Pericranium bezeichnet.
Die Knochenhaut besteht aus zwei Schichten, der äußeren Kollagenschicht (Stratum fibrosum) mit elastischen Sharpey-Fasern und dem inneren Stratum osteogenicum (Kambium), in dem Knochenvorläuferzellen sich zu Osteoblasten differenzieren können, was dem Dickenwachstum des Knochens dient, aber auch wichtig ist für die Heilung des Knochens nach Brüchen.
Das Periost gehört zu den schmerzempfindlichsten Geweben des Körpers, webhalb traumatisch entstandene Ödeme unter der Knochenhaut mit deutlichem Schmerzempfinden verbunden sind.

Fracture healing

There are two mechanisms of fracture healing:

direct (secondary) fracture healing

if the periosteum remains intact or if the fracture ends are still connected, primary fracture healing takes place. If the fracture ends are less than 1 mm apart, capillary-rich connective tissue grows into the fracture gap; there is no visible formation of callus around the fracture site. Precursor cells of the osteoblasts (osteoprogenitor cells) from the periosteum and endosteum accumulate around the existing capillaries and initially form osteons arranged parallel to the fracture surface. These are later restructured in the direction parallel to the longitudinal axis of the bone by erosion tunnels. After three weeks, the bone is functional again.

indirect (secondary) fracture healing

If the above conditions were not met, for example if the gap was larger than 1 mm, the bone must be repaired in a five-stage procedure, starting with callus formation (internal and external):

  1. Injury phase with formation of a haematoma in the joint space
  2. Inflammatory phase with migration of macrophages, granulocytes and mast cells; release of histamine and heparin. Mesenchymal pluripotent stem cells differentiate into osteoblasts, fibroblasts and chondroblasts. Cytokines and growth factors control cell differentiation and angioneogenesis.
  3. Granulation phase (4th-6th week): the network in the haematoma that has now formed with fibrin and collagen is replaced by granulation tissue with fibroblasts, further collagen and capillarisation. Non-perfused bone material is broken down by osteoclasts, new bone material is built up by osteoblasts from the periosteum.
  4. Callus hardening (duration: 3-4 weeks): the resulting callus is mineralised, which leads to a still undirected interwoven bone with regard to the collagen. The capillaries and the coarse structure of the bone already correspond to the physiological direction of flow and the main direction of loading
  5. Remodelling phase: modelling and remodelling: the interwoven bone is remodelled into physiological lamellar bone with Haversian and Volkmann canals and the medullary canal is restored. Complete healing should be completed after 6 – 24 months.

If fracture healing is disturbed, pseudoarthrosis may occur, i.e. an insufficiently hardened and remodelled fracture site with inferior stability (non-union). If fracture healing lags behind the time frame (delayed fracture healing), it must be checked whether the immobilisation was sufficient or needs to be improved. If the fracture pieces were not correctly reduced, this results in fracture healing in a malposition (malunion), whereby the longitudinal axes of the two (main) bone pieces may be unequal or one bone piece may be twisted around the longitudinal axis in relation to the other. If a malunion occurs at one end of the bone through the articulating surface, this can result in an incongruence. In addition, a fracture healing can remain fibrous for a long time. The fibrous tissue is usually replaced by bone tissue after a period of time.