abduction: Movement away from the midline. Lifting one’s arms out to the side abducts them.
acromegaly: Swelling of hands, feet, facial features, and internal organs caused by increased secretion of growth hormone by the pituitary gland, often due to pituitary tumor.
acromioclavicular joint: The joint connecting the clavicle with the acromion, a superolateral boney projection of the scapula.
adduction: Movement toward the midline, even crossing it. To touch the left shoulder with the right hand one must adduct the right arm.
ankylosing spondylitis: Progressive inflammation and eventual fusion of vertebral bodies, largely in males; hereditary. Fusion and virtual rigidity of the spine is frequently complete by the early 20s, yielding a stooped or hunched thorax.
architectonic: The arrangement of supporting forces within a structure.
arthritis: Destructive inflammation of a joint or joints. When referring to types of arthritis, the plural is arthritides, in the manner of ancient Greek.
atomic force microscopy: Very high resolution probe that measures a local property such as height or magnetic force by placing a micromachined tip close to the sample.
autosomal: Trait or condition that is determined by genes carried and inherited in the nongender portion of the chromosomes. The traits may be dominant (requiring only one gene from one parent) or recessive (requiring the gene from both parents), or may have a more complex relationship to the individual’s genetic makeup.
axon: The thin extended outgrowth from a neuron cell body that normally propagates impulses away from that cell body toward another neuron, a muscle, or a gland. It derives from the Greek word for axis.
bisphosphonates: Any synthetic analog of pyrophosphate that is used in treating osteoporosis to inhibit the action of osteoclasts, which resorb and thereby weaken bone. Examples include Fosamax, Actonel.
bone quality: Bone’s material and structural nature, which determines its strength and resistance to fracture. Its internal and external form as well as its structure. It is often determined in part by atomic force microscopy.
brachial plexus: Region at each side of the neck where nerve roots from the lower cervical spine combine and split again to form the major nerves of the upper extremities such as the median, ulnar, and radial nerves.
bursa: A closed sac with a synovial lining and joint fluid within, generally separating a bone from a tendon. They are thought to evolve from joints, since they have the same basic structure, retained because they usefully prevent the tendon from bruising the bone, and the bone from fraying the tendon. The Latin word bursa means “purse.”
calcitonin: A hormone secreted by the parafollicular cells of the thyroid that lowers blood calcium. It balances the effects of parathyroid hormone, which raises blood calcium. This relationship regulates calcium metabolism. Synthesized and available under the brand name Miacalcin (salmon calcitonin). An oral preparation is being readied for the U.S. market.
cartilage: The semi-stiff substance that lines joints and forms movable tubes in the body such as the trachea, the nasal cavity, and the Adam’s apple. There are three forms: hyaline cartilage, elastic cartilage, and fibrocartilage.
cartilaginous: Made of cartilage.
cauda equina: In adults, the spinal cord proper ends at the lower thoracic or upper lumbar levels above where lumbar nerve roots exit the spinal canal. Collections of nerve fibers descend through the lumbar portion of the canal, giving the appearance of a horse’s tail.
Chiari malformations: A range of congenital defects at the base of the skull that may be mild, with dizziness, neuromuscular symptoms, and impaired coordination (Type I); involve defects of the cervical vertebrae and spinal canal that may lead to paralysis (Type II, Arnold-Chiari); or be even more serious, causing hydrocephalus and similar difficulties (Type III).
chondrocytes: Cells that secrete the fibers that constitute cartilage.
collagen: A triple helix of three long protein chains that wrap around one another. Cross-linked molecules of collagen become undistensible (they cannot be stretched) and are stronger than many metals.
collagenase: An enzyme that breaks down collagen into its constituent amino acids.
contralateral: The opposite side. The right is contralateral to the left.
conus medullaris: The enlargement of the spinal cord in the lower thoracic spine where it gives off the fibers for all 5 levels of the lumbar spine below the level at which the cord proper terminates.
cytokine: A protein or glycoprotein between 8 and 30 daltons in size that, like hormones, signals cells and calls forth a number of specific activities at the cellular level.
dendrite: The branching outgrowth from a neuron that acquires impulses that are then transmitted through the cell body to the axon, and hence to another cell. The Greek word for dendrites means “pertaining to a tree.”
DEXA-scan: Dual energy X-ray absorptiometry, the very low-dose standard examination to determine bone density.
distal: Farther from the point of reference or axis.
eccentric contraction: Muscular effort that resists and controls its relaxation against resistance—for example, how the quadriceps lengthen when you gradually bend your knees.
elastin: Polypeptide (protein) chains that cross-link like collagen, but with the opposite effect: They coil into a form that may uncoil when the fiber is stretched and retract when the stretch is terminated.
estrogen: A female hormone synthesized in the ovaries.
extension: Motion of bones at a joint away from each other, or away from the torso. Exception: Ankle and toe extension brings the foot and toes upward.
external rotation: Clockwise revolving motion of the right arm and leg; counterclockwise revolving motion of the left limbs. At the ankle and wrist, these movements are termed supination.
extrude: To send forth, in this context, out of a cell through its membrane.
firm: Used as a verb; to contract a muscle without moving the bones to which it is attached.
flexion: Motion of bones at a joint toward each other, or in closer to the torso. Exception: Ankle and toe flexion points the toes away from the torso.
gait cycle: The repetitive series of movements that each foot, ankle, knee, and hip and the trunk and arms go through with each pair of steps.
glycoprotein: A molecule made up of a carbohydrate and a protein. They are prominent in joint fluid and vital for many immune system functions.
gout: Generally intermittent, extremely painful condition deriving from the body’s overproduction of uric acid, a derivative of the nucleic acid purine. It is associated with a protein-rich diet and is related to obesity.
greater trochanter: An outward projection of bone on the proximal femur to which abductors and external rotators of the hip are attached.
growth hormone: A protein substance secreted by the pituitary gland that acts on the liver and other tissues to regulate growth and metabolism. Also known as somatotropin.
hydroxyapatite: The mineral and protein amalgam salt that is the major component of bone.
internal rotation: Counterclockwise revolving motion of the right arm and leg; clockwise revolving of the left limbs. At the ankle and wrist, these movements are termed pronation.
isometric: Action of contracting a muscle or muscle group without it moving, generally against resistance either from antagonistic muscle or muscle group, or outside force equal to it. In pressing the palms together, one isometrically contracts the pectoralis muscles.
mechanoreception: The capacity of cells to respond to mechanical stimulation, be it in the form of pressure or movement of the cell’s membrane, or collision of molecules (for example, hearing, feeling, smell, and taste), or other physical modalities (sight).
metamorphoses: The changing of living organisms from one form to another, as a caterpillar becoming a butterfly.
micro-MRI: A magnetic imaging device that can focus on very small regions and is valuable for determining the structure of bone interior and thus a determinant of bone quality.
multiple myeloma: A malignancy of plasma cells, which produce antibodies. Multiple myeloma has no cure, but is treated with chemotherapy, steroids, and thalidomide. Stem cell transplantation appears to be an effective fourth treatment modality.
myotatic reflex: Contraction of a muscle in response to a sudden stretching force, due to stretch of the intrafusal fibers. Examples include the patellar reflex, the Achilles tendon reflex.
neuroforamen: Anatomical openings between each two vertebrae through which nerve roots pass.
neutral: The position of limbs or torso that is without flexion, extension, abduction, adduction, or external or internal rotation. The entire body in neutral is also known as the anatomical position. This is different from the yogi’s Savasana, in which arms and legs are somewhat externally rotated.
nonsteroidal anti-inflammatory: Medications related to aspirin that interfere with prostaglandin-mediated pathways that generate pain and enhance inflammation. These medicines reduce both pain and inflammatory responses such as swelling and redness. However, they have varying degrees of side effects associated with their use, such as gastric irritation, ulcer, and prolonged bleeding time. Examples are Motrin, Relafen, Voltaren, Celebrex, and Mobic.
normal distribution: A totally random array of values; standard deviations indicate the probability of a given value, for example, 1 in 10 or 1 in 250.
osteitis fibrosis cystica: Fibrous replacement of healthy bone as osteoclasts absorb it. Also known as Recklinghausen’s disease of bone, it is caused by an excess of parathyroid hormone, among other conditions that increase the reabsorption of calcium and phosphorus.
osteoarthritis: Erosion of the cartilage at joints, either without single cause or due to trauma. It is characterized by irregular boney outgrowths at the joint and painful restrictions of movement and swelling, mainly of weight-bearing and very active joints. Since chronic conditions are cumulative, it is more common in older persons.
osteoarthropathy: Any disorder that affects bones and joints. Its origins are Greek: osteo, bone; arthron, joint; pathos, suffering.
osteoblast: Cells that lie just outside of bones and are destined to make the protein matrix of the bones.
osteoclast: Large cells containing up to 50 nuclei. They attach to bones and secrete cytokines, which dissolve bones’ substance, returning the minerals and proteins to the bloodstream.
osteocyte: Cells descended from osteoblasts, located within the bones, actively secreting the protein matrix that comes to surround them.
osteoid: Protein matrix secreted by osteocytes that attracts calcium, phosphate, and other minerals. Together, these minerals fuse into hydroxyapatite, the basic constituent of bone.
osteomalacia: Insufficient calcification of bones, often due to low vitamin D or kidney dysfunction, in which the bones’ osteoid component bends painfully under stresses. It may begin during pregnancy.
osteonecrosis: Death and degeneration of bone tissue within a living individual. A relatively rare occurrence associated with long-term bisphosphonate use and dental procedures.
osteopenia: Low bone mineral density in which the T-score is between –1.0 and –2.5.
osteopetrosis: Excessive trabecular growth and calcification, particularly of long bones, that obliterates the marrow cavities, leading to anemia of varying severity, possibly leading to deafness, blindness, and death. More severe forms are autosomal dominant.
osteophyte: A nonanatomical outgrowth of bone, generally occurring at the joints, where it may limit range of motion and narrow neuroforamina.
parathyroid hormone (PTH): A hormone produced by the parathyroid glands that raises blood calcium levels by simultaneously stimulating bone resorption, reducing calcium excretion by the kidneys, and increasing intestinal absorption. Its effects are modified by calcitonin and other hormones. Synthesized and available under the brand name Forteo.
paraesthesias : Strange sensations such as tingling, pins and needles, insects crawling on the skin. Numbness is when you do not feel what is there; paraesthesias are when you feel what is not there.
perichondrium: Cells lining cartilage, except at joint interfaces; supplies oxygen and nourishes the chondrocytes, the cells that make cartilage.
plantar fasciitis: Painful inflammation of the insertion of the plantar fascia into the calcaneus, also known as heel spur.
progesterone: A gender-active steroid hormone that opposes estrogen’s effects on the uterus and also helps create and maintain bone. Influencing osteoblasts to become osteocytes, it has been found to increase bone mineral density as much as 10 percent in one year.
proteoglycan: A large molecule found in most vertebrates’ bone and cartilage, composed of proteins and glycosaminoglycans (i.e., polysaccharides) such as derivatives of glucosamine and galactosamine.
protraction: Movement of the scapulae or shoulder blades forward, toward the ventral or navel-bearing side of the body. In human anatomy, it is nearly equivalent to abducting them (bringing them away from the spine).
proximal: Closer to the point of reference or axis.
pseudogout: Gout-like episodes caused by calcium pyrophosphate crystals, rather than the urate crystals that irritate the synovial membrane in true gout. It is also associated with calcification of the articular cartilage.
radiculopathy: Compression of or injury to the nerve roots that exit the spine.
resorption: Reabsorption of a substance into the circulatory system.
retraction: Movement of the scapulae or shoulder blades backward, toward the dorsal aspect of the thorax. In human anatomy, it is nearly equivalent to adducting them (bringing them toward the spine).
rheumatoid arthritis: Arthritic damage to the joints resulting from the immune system’s actions, generally on the joint capsules’ lining or synovium, also eroding the cartilage and the bone itself.
rickets: A condition caused by vitamin D deficiency producing undercalcified bones and subsequent skeletal and growth disturbances, fractures, spasm, weakness, and irritability.
sacroiliac joint: A bilateral synovial joint between the outer edges of the sacrum and the inner edges of the iliac bones.
scapulothoracic: The relationship between the shoulder blade or scapula and the backs of ribs 2–6, a large area over which the shoulder blade normally moves. It is often referred to as a joint, although its size and structure are quite different from any other joint.
sentinel event: An occurrence of greater significance than its immediate medical consequences. A harbinger of change.
sesamoid bone: A bone encapsulated within a tendon. There is one in the flexor tendon of the big toe as it rounds the joint that connects the toe to the foot. The patella is the largest sesamoid bone in the human body.
sigma: See standard deviation.
spicules: The small pieces of protein extruded by osteocytes that make up osteoid, the initial ground substance of bone that attracts calcium and phosphorus to become true bone.
spondyloarthropathy: See ankylosing spondylitis.
spondylolisthesis: The sliding of one vertebra (generally forward) on the one below it, resulting in narrowing of the central canal, stenosis, or narrowing the neuroforamina. In either case it may cause radiculopathy.
standard deviation: The interval one must consider to include 34.1 percent of the values above or below the mean in a normal distribution. Denoted by the Greek letter sigma σ.
steroid: Biological molecules, including gender hormones and cortisone, containing a five-carbon ring and three rings each of six carbon atoms.
surgical neck: The part of the proximal femur that connects the ball of the hip joint to the shaft.
synapse: The point at which impulses are passed from one neuron to another, generally by neurotransmitter molecules, but sometimes by direct (electrotonic) propagation of the signal. (For more on this, see B. Gutkin and G. B. Ermentrout, “Spikes too kinky in the cortex?” Nature 20 [April 2006]: 999–1000.)
synovial fluid: The yellowish-white fluid that bathes each joint. It serves three essential purposes: It is a first-class lubricant; it brings oxygen, food, and protein building blocks to the cartilage of the joint; and it protects the joint from mechanical and biological causes of disruption
synovial membrane: Similar to a gasket; seals the synovial fluid in the joint. It is quite vascular and richly invested with nerves. It secretes and resorbs the synovial fluid and is exquisitely sensitive, causing pain with distension, inflammation, or disruption.
testosterone: A male steroid hormone produced in the testes, but also by ovaries and adrenal cortices. A potent stimulator of bone formation.
Wollf’s law: The architectonic of bone follows the lines of force to which that bone is subjected. First formulated by the German surgeon and anatomist Julius Wollf in 1861.