EMS World Magazine is the most authoritative source in the world for clinical and educational material designed to improve the delivery of prehospital emergency medical care.
Issue link: https://emsworld.epubxp.com/i/53080
CE ARTICLE Figure 1: Bone structure Blood vessels Nerve Osteonic canals containing blood vessels and nerves Sharpe's fibers Periosteum Compact bone Spongy bone Endosteum Marrow There are 206 bones in the adult human body. These bones are broken down into fi ve bone types: long bones (e.g., femur), short bones (e.g., patella), fl at bones (e.g., scapula), irregular bones (e.g., vertebrae), and sesamoid bones. Sesamoid bones are bones that have a tendon embedded in them, and include the patella, the fi rst metacarpals, the fi rst metatarsals and in the great toe. All bones have the same essential structures (Figure 1). The outer lining of each bone, termed the periosteum, is a fi brous skin-like layer of connective tissue that can be torn. The periosteum is also heavily innervated with nociceptor nerve endings, making injury to the periosteum highly painful. Directly beneath this is the compact bone, which makes up the majority of the bone mass and gives it its white and smooth appearance, and also provides the bone with its strength and ability to provide support and struc- ture. The spongy bone, also called the trabecular bone, is a porous structure that allows nerves and blood vessels to pass through it. Bone marrow can also be found in the spongy bone. At the center of each bone is bone marrow, which is highly vascularized with arteries and veins. Yellow bone marrow, often found at the center of long bones, is primarily fatty cells. Red bone marrow is found in the fl at bones and is responsible for the development of red blood cells, platelets and most white blood cells. When a bone is fractured the blood vessels and nerves in all layers of the bone are interrupted. Additionally, yellow (fatty) bone marrow, if also broken loose, can enter into a bloodstream, and become an embolism. Physics of Fractures Not all bones are created alike or have identical strength. As a general rule, small bones such as the metacar- pals require a smaller amount of force to sustain injury in compared to large bones such as the femur or pelvis. An injury to the musculoskeletal system proximal to the ankle or wrist is an indication that a signifi - cant force impacted the body.1 The larger the injured bone, and the greater the force, the more suspicion EMS providers need to have for other injuries. Of particular importance, simultaneous limb injuries above and below the diaphragm signifi - cantly increase the likelihood of internal torso injury.1 Conditions such as osteoporosis, calcium defi ciencies, myeloma and malnourishment result in decreased bone strength. As a result patients with these conditions can experience bone fractures when lesser forces are involved. Fracturing a bone interrupts the integ- rity of a living organ. Patients experience pain any time an organ is injured— including the bones. Bone fractures also result in bleeding for two reasons. First, they can tear or sever vessels near the bone. Second, when the bone marrow tears during a fracture it can bleed into the body's cavities, rather than delivering red blood cells directly into the bloodstream. In particular, unstable pelvis fractures and open femur fractures have an extremely high risk of major bleeding that is signifi - cant enough to cause class III shock.1 Table I summarizes the estimated blood loss in various bone injuries while Table II highlights vital sign changes seen in the different hemorrhagic shock classes. There are a few other complications that can occur during bone fracture. When blood vessels are interrupted, pieces of bone, fat and other tissues can enter the bloodstream causing an embolism. Fat is the most common foreign debris entering the bloodstream during fracture, particu- larly when fatty marrow is broken free from the bone marrow during the injury. Injuries resulting from crushing forces can cause bone fracture and also injure large amounts of muscle mass. Injured muscles release myoglobin, which when enough muscle mass is injured can result in rhabdomyalosis. Consequences of Improper Splinting Remember it is important to limit on-scene time, particularly in major trauma. However, interventions such as splinting should still be performed while Table I: Potential Blood Loss by Injured Bone BONE Rib Radius or ulna ESTIMATED BLOOD LOSS 125mL 250-500mL Humerus 500-750mL Tibia or fi bula Femur Pelvis 500-1000mL 1-2 liters At least 1 liter, likely >2L EMSWORLD.com | FEBRUARY 2012 37 Fran Milner, www.franimation.com Photos by Dan LImmer