Bone Structure
May 21, 2016 11:57:41 GMT 10
Post by Tom Meulman on May 21, 2016 11:57:41 GMT 10
Bone Structure
Skeletal System
The skeleton gives the Greyhound its shape and protects the vital organs; such as the skull protects the brain, and the ribs protect the internal organs.
A Greyhounds bone is living tissue supplied with nerves and blood cells, and there are 321 individual bones in a Greyhounds skeleton.
Where two bones meet they form a joint, the end of each bone is covered in cartilage, in between the two layers of cartilage there is a lubricating fluid (Synovial fluid) that facilitates movement.
Muscles are attached to the bones by tendons, when they contract, it causes the tendons to pull on the bones and flex or extend the joints.
The Structure of Bone
Bone formation is a complex process that involves proteins combining and changing into a collagen structure, which then becomes impregnated with mineral salts such as calcium, phosphorus, carbonate and citrate.
Bone is a living tissue made up of three kinds of cells, these are osteoblast, osteocytes and osteoclast.
Bone Cells
OSTEOBLAST, OSTEOCYTES AND OSTEOCLASTS
Osteoblast cells develop in the bone growth plate tissue and secrete protein and collagen; this collagen forms a structure around each individual cell completely enclosing the cell.
These structures then combine with the structures of other osteoblast cells and form the bone matrix.
The bone matrix is then hardened into bone by the addition of a mineral complex of calcium, phosphorus, carbonate and citrate.
While the surrounding area is being mineralised, the osteoblasts create minute channels in the bone matrix and once the mineralization is complete, the osteoblasts now embedded in bone, become Osteocytes.
These are still living cells that can add or remove calcium and other minerals from or to the bone as various stresses are placed on them.
The third type of bone cell is the Osteoclast, its function is to erode and reabsorb old bone structures to their components so that new bone can be made.
Bone Remodeling
Bone is continually being remodeled in the Greyhound due to the stressed placed on the bones by racing or trailing, but the greatest activation of bone cells occurs when there is a fracture of a bone.
With a break or a fracture the bones have to heal back together, and it is the inflammation caused by the fracture that triggers the activation of all the Osteoblast cells in the immediate area.
This massive activity by the osteoblast cells creates a callus formation over the fracture site, and osteoclasts are activated to remove the damaged bone.
This activation by inflammation in the bone surface of the osteoblast cells is the reason for using substances such as “Bone Radiol” or a blistering agent such as “Blestre” or 10% Iodine when strengthening of the bone is required.
It is also the same reaction to inflammation that causes the formation of a callus when a Greyhound strikes the inside of its hind leg with the elbow causing “track leg”.
During the healing of bone damage it is extremely important to not allow any movement between the fractured ends of the bone as this will cause the osteoblasts to compensate for the instability by making more bone than is desirable.
This process is called EXOSTOSIS and the excessively large callus produced by this process may occasionally cause problems with tendons or ligaments that overlie or move against this area.
Growth Plates
To understand the development of bone growth it is important to understand the nature of growth plates and the consequences of damage to them.
Each long bone in the Greyhounds body has a growth plate at each end of the bone, these growth plates contain cartilage cells that are multiplying and producing the protein matrix that becomes bone.
Therefore bones grow in length as the animal ages, due to the growth plates at each end of the bone.
Other bone growth plates lie under areas of major tendon attachments; one example of such a growth plate is where the ligament from the kneecap attaches to the shinbone at an area called the tibial crest.
Growth plates in immature Greyhounds lack the strength of bone and are common fracture sites.
The growth plates continue to produce new bone until the animal is mature, at which time the cartilage cells stop multiplying and all of the growth plate becomes mineralised into bone.
The time of maturation or “closure” varies between different bones, however the maturation time of all of the growth plates is generally completed by 14 to 15 months of age.
Excessive inflammation in the growth plates will lead to a premature closure of some or all of the growth plates and therefore a reduction in the size that the animal will grow to.
While a partial closure or damage of the growth plates of one of the long bones (generally the RADIUS) in the front leg may cause outwards angulation of the wrist, increasing the strain on the wrist joint.
Bone Health
Bone being a living tissue, requires a constant flow of nutrients and minerals from the arteries and veins of the circulatory system.
All bones (Except tiny Sesamoids) have an artery and vein supplying the medullar canal, which is the hollow of the bone that contains the bone marrow.
The outer shell of the bone receives its nutrition from the PERIOSTEUM.
This is the thin fibrous outer covering of the bone, which is richly endowed with a network of blood vessels and nerves.
Under certain conditions of increased workload on a bone, the periosteum becomes inflamed, thickened and painful. A problem referred to as periostitis.
(Periost as from periosteum—itis meaning inflammation)
Bone Joints
Bones are attached to each other by means of a fibrous tissue called a ligament, and the area where two or more bones are attached together is called a joint.
The most relevant of these are the synovial joints where the outer ligament capsule extends from one bone to the next, completely surrounding the ends of the bones.
The inner layer of the joint capsule contains a tissue (Synovial Membrane) that secretes a lubricating joint fluid, this fluid fills the cavity formed by the joint capsule allowing the cartilage-capped ends of the bones to move smoothly against each other.
In addition the joint fluid carries nutrients to the cartilage and removes waste products.
Joint disease occurs when the cartilage at the ends of the bones is damaged, or when the synovial membrane is inflamed or when there is an infection within the joint.
The greater the range of movement required of the joint, the more critical the health of the joint becomes to the performance of the Greyhound.
X-rays and or the analysis of a sample of the joint fluid are the two most useful diagnostic tools used by veterinarians to evaluate the presence of a disease of the joint.
Bone Function
Bones have a number of functions in the body; the most obvious is that they act as a framework for the rest of the body organs and structures, and act as levers with areas of attachment for muscles, and with muscles on either side of the bone flex or rotate body parts.
Bones also contain the factories for some of the components of blood including the red and white blood cells and the platelets, which are part of the blood clotting mechanism.
The shafts of the long bones are hollow and contain the bone marrow that produces these essential blood components.
Finally, bones act as the storehouse for the minerals calcium and phosphorus, which are needed not only by the bone for strength and hardness, but also by the various systems of the body such as muscle contraction and nerve function.
The Skull
The skull consist of two distinctly separate areas; they are the upper part, which houses the brain, eyes and ears as well as the upper jaw, the lower section being the lower jaw (the mandible) which is attached to the upper section by a hinge type joint. (The TEMPOROMANDIBULAR joint)
The upper jaw has 20 teeth while the lower jaw has 22.
Also in the upper part of the skull are the sinuses, these are air filled cavities within the skull bones, lined with a membrane that secretes a clear mucus, the sinuses are connected to the nasal openings.
An infection in the sinus may be caused by an upper respiratory infection such as kennel cough or by a severely infected tooth as the roots of some of the teeth in the upper jaw lie very close to the sinus cavities.
The Spine
The spine of the Greyhound is made up of approximately 50 small bones called vertebrae, keep in mind that there are approximately 50 bones because all the tailbones are included.
These bones are all connected in a line and can be divided into five distinct groups due to a variation in the shape of the bones of each group.
These are; Cervical or neck, Thoracic the upper spine or chest, Lumbar the lower back or loin, Sacral the pelvic and Caudal the tail vertebrae.
The spine acts as a rod through which all of the force generated by the back legs is transmitted to the rest of the body; in other words the spine is a group of bones to which everything else is connected.
In between the vertebrae are the discs, these are doughnut shaped fibrous pads that act as shock absorbers and at the top of the vertebrae are paired joints that allow for flexion, extension and rotation.
The spinal cord runs through the centre of the vertebrae with branches that exit from in between each pair of vertebrae, and in this way provides a connection between every part of the body to the brain, including all of the internal organs.
In the neck, starting at the back of the skull are the 7 CERVICAL vertebrae, the top one of these is called the atlas, and it is in this area that Greyhounds often sustain some damage due to catching the lure awkwardly during an arm trial.
The cervical vertebrae are commonly referred to as C1 to C7, C as for cervical.
Just for interest sake, the reason that this particular spinal segment is called the atlas is this:
As you probably know, it was the ancient Greeks that first named the bones of the human body and the names for the bones of the dog where simply copied from that.
The Greeks believed and rightly so that you, your ego and your whole world as you perceived it to be, existed in your skull.
In other words your head was your world and in ancient Greek Mythology, it was the god named Atlas that held the world up and stopped it from falling into the void.
And that is the reason the first neck vertebrae is called the ATLAS.
The upper part of the spine in the saddle area has 13 THORACIC vertebrae that are the support for the 13 pairs of ribs that form the chest cavity, and the chest cavity contains the heart and the lungs.
At the bottom of the chest the ribs are connected to the STERNUM that consists of 8 interconnecting bones that form the floor of the chest.
The thoracic vertebrae are commonly referred to as T1 to T13, T as for thoracic.
Next in the spine are the 7 LUMBAR or lower back vertebrae, to which are attached the strong lumbar muscles that provide much of the galloping power of the Greyhound.
Due to the fact that this area of the spine does much of the work during the running action of the Greyhound that many of the spinal injuries suffered by the Greyhound are found in this area.
In particular the area where the pelvic or SACRUM vertebrae join the LUMBAR vertebrae.
The lumbar vertebrae are commonly referred to as L1 to L7, L as for lumbar.
The three sacral vertebrae are fused together and form the SACRUM and this is connected to the PELVIS at the ILIO-SACRAL joint and supported by the SACRO-ILIAC ligament.
At the rear of the PELVIC bone is the SACROTUBERAL ligament that also provides support and stability to the rear of the SACRUM.
This is an area that takes considerable strain when the Greyhounds spin or run in tight turns and often sustains some damage.
Because one section of the SACROTUBERAL ligament also connects to the first tail or CAUDAL vertebrae, damage in this area often shows as a severe pain response if the tail is pulled sideways.
Each side of the PELVIC bone is in fact made up by a fusion of four separate bones.
These are the ILEUM or hip, the PUBIS which is the lower front section, the ACETABULUM where the FEMUR bones of the back legs join the pelvis, and the ISCHIUM, the rear section of the pelvis at the end of which the SACROTUBERAL ligament is connected.
The last group of vertebrae is the CAUDAL vertebrae that are the bones of the tail, approximately all 20 or 22 of them.
The SCAPULA bone (shoulder blade) is connected to the chest wall by a series of muscles that form an effective sling, in addition to supplying the forward and backward movement to the legs.
The SCAPULA is a flat, triangular shaped bone with bony ridge called the SPINE on the outer surface of the bone; the Spine of the Scapula is an very thin bone and a common fracture site in young dogs.
At its lower end the scapula it forms the shoulder joint with the single bone, the HUMERUS that forms the top half of the front leg, and it is this shoulder joint that is the most common site of the joint disease OCD. (Osteochondritis dessicans) (Damaged cartilage)
However it should be noted that the initial damage to this joint that results in OCD is often aggravated by damage to the supporting muscles and ligaments of the joint. This allows excessive flexion of the joint, resulting in uneven pressure on the cartilage surfaces and possible cartilage damage.
At the lower end of the Humerus, it forms the elbow joint with the two bones of the forearm the RADIUS and the ULNA.
The Radius is the larger of the two and the main weight bearing bone, and lies at the front and inside part of the forearm, while the Ulna bone lies at the back and outside part of the forearm.
The rotational stress placed on the forearm, in particularly when the Greyhound turns towards the lure during an arm trial, may result in minute stress fractures to the central area of the Radius as well as to the top of the Radius in an area called the Tuberosity of the Radius.
Stress fractures are also common in the lower part of the Ulna in an area called the Styloid Process.
Front Feet and Wrists
At the lower end the Radius and Ulna form the wrist joint with the two rows of CARPAL bones.
The top row of Carpal bones, and there are three of them, are named after their location, namely the RADIAL Carpal bone below the Radius, the ULNAR Carpal bone below the Ulna, and the ACCESSORY Carpal bone or STOPPER bone at the back of the wrist.
The four lower Carpal bones roughly correspond to the four main METACARPAL bones of the wrist.
There are three joints in the wrist; they are the joint between the Radius and Ulna and the top row of Carpal bones, the joint between the two rows of Carpal bones and the joint between the lower row of Carpal bones and the Metacarpal bones below them.
There are five Metacarpal bones in the foot of the Greyhound and they are counted from the inside of the wrist on out, the first being the dewclaw.
At the rear of the lower end of the Metacarpal bones is a pair of small bones called SESAMOID bones; these bones are part of the toe joint.
At the lower end of the Metacarpals are the toes or digits, each toe consisting of three toe bones or PHALANGES commonly referred to as P1, P2 and the lower one P3.
There are also smaller Sesamiod bones in the foot of the Greyhound and they are located on the front surface of the first toe joint.
The wrist is one of the two most complicated joints in the body and there are a large number of injuries that may be sustained by the racing Greyhound in the wrist and foot, however these will be covered in greater detail in the “foot &limb injuries” session.
The upper bone of the hind limb the FEMUR is attached to the pelvis via a cup and socket type joint.
The Femur is the long bone of the thigh and is the heaviest bone in the body; at its lower end it forms the knee joint with the tibia.
At the front of the Femur is a Sesamiod type bone called the PATELLA or KNEECAP, also part of the knee joint are two C shaped pieces of cartilage that lie between the Femur and Tibia, their function is to insure smooth movement between the bone surfaces.
At the rear and to the outside of the Tibia is a thin long bone called the FIBULA, being long and thin and easily fractured, the Fibula is a source of much frustration to many Greyhound trainers.
At their lower end the Tibia and Fibula form the HOCK joint with the seven TARSAL bones, besides the wrist joint, this is the other most complex series of joints in the Greyhounds body.
At the rear of the hock joint is the FIBULAR TARSAL bone, this is the largest of the Tarsal bones it protrudes out from the hock and has the tendon group known as the ACHILLES tendon either running over it or connected to it.
The other Tarsal bone in the top section of the hock is the TIBIAL TARSAL bone, and it is this bone that actually provides the joint surface by which the Tibia and Fibula are connected to the hock.
Just below the Tibial Tarsal bone lays the CENTRAL TARSAL bone and it is this bone that is the most common to fracture when hock damage occurs.
And that is not difficult to understand if one looks at how the pressure of the driving force of the leg is transferred to the foot.
It is the Tibial tarsal bone that is the only Tarsal bone in the hock that takes the direct pressure from the Tibia and Fibula and the Central Tarsal bone is located directly below the Tibial Tarsal bone.
The FOURTH TARSAL bone is a largest Tarsal bone of the bottom row of Tarsal bones, it lays on the outside of the hock and extends all the way up from the Fourth and Fifth METATARSAL bones to the underside of the Fibular Tarsal bone.
The other three lower Tarsal bones more or less lay in a row besides it and connect the Central Tarsal bone to the rest of the METATARSALS.
While there are only four Metatarsals in the Greyhounds hind foot, the dewclaw being missing from the hind foot, the Metatarsals are still counted as if the dewclaw is there.
The rest of the Greyhounds hind foot is structured the same as the front foot.