Normal bone homestasis involves a constant delicate balance of remodeling and repair.
Every week, we recycle as much as 5-7% of our bone mass
As much as half a gram of calcium may enter or leave the adult skeleton every day
Osteoclasts and osteoblasts make up remodeling units
Control of remodeling is regulated by hormones and by forces acting on the skeleton
Parathyroid hormone (PTH) and calcitonin are the two interacting pieces of hormonal control of bone remodeling/repair
PTH is released when calcium levels in the blood decline, stimulating osteoclast action
Calcitonin is secreted when calcium levels in the blood rise; it activate osteoblast action
Hypercalcemia can lead to extra deposition of calcium salts into soft organs such as the blood vessels and kidneys
Wolff’s Law
holds that a bone grows or remodels in response to the forces or stresses placed on it. The stresses tend to cancel each other out in the middle of a long, weight-bearing bone, hence the fact that these bones can be "hollow" in the middle
Heavy usage of a bone results in a thicker bone
Non-usage of a bone results in a thin, brittle bone that is easily broken
Osteoporosis
is a disease where osteoclast action overtakes the osteoblast action; bone remodeling is abnormal.
Bones become porous, lighter
Compression fractures of the vertebrae and femur are common
Occurs mostly in menopausal women, due to the lack of estrogen (estrogen helps to regulate PTH)
Lack of exercise (see Wolff’s law) may also contribute, as might a diet poor in vitamin D and/or calcium, smoking (which reduces estrogen levels), or other hormone-related conditions
Osteoporosis may also occur due to immobility
It is usually treated with supplemental calcium, vitamin D, increased weight-bearing exercise and use of low-heeled shoes (to decrease spine stress); estrogen replacement therapy is also used as a protection measure
Etidronate
, used in Paget’s disease, shows promise in treating osteoporosis as well
Prevention includes a good calcium intake in bone forming years (bones reach peak density at ages 35-40), also drinking fluoridated water not only prevents cavities, but also hardens bones, and increasing weight-bearing activity.
Osteomalacia
and rickets are related diseases that result in "soft bones."
Osteomalacia
is usually seen in adults, where calcium salts are not deposited properly so the extracellular matrix does not harden. Weight bearing bones may fracture, bend or deform. The main symptom is pain when weight is put on the affected bone(s)
Rickets
is mainly a childhood disease and is characterized by bowed legs, deformed pelvis and possibly thorax and skull deformities as well. The epiphyseal plates do not calcify due to the lack of vitamin D and so continue to widen, resulting in visibly enlarged ends of long bones.
Both osteomalacia and rickets can be treated through supplements of vitamin D, plus increasing UV exposure (sunlight) to hasten vitamin metabolism in the skin.
Paget’s Disease
is characterized by rapid bone remodeling
Newly formed bone (Pagetic bone) has an abnormally high ratio of woven bone to compact bone and along with reduced calcium deposition, results in soft, weak bones
Osteoclast activity wanes late in the disease, and with the osteoblasts still working overtime, abnormal bone thickening occurs, sometimes filling the medullary cavity with Pagetic bone
It is usually a localized condition, but can affect any part of the skeleton
Rarely seen before age 40, cause is unknown (viral?)
Etidronate is one drug therapy
Herniated disks
or slipped disks can result from severe or sudden physical trauma to the spine
It involves the protrusion of the spongy nucleus pulposus of the disk, after the rupture of the annulus fibrosus
If the disk presses on the spinal cord and/or spinal nerves, numbness, pain, paralysis or nerve damage may occur
Treatment involves bed rest, traction and/or painkillers; surgery is also an option, but usually a last resort
Abnormal spine curvatures
can be congenital or may result from disease, poor posture or unequal muscle pull on the spine.
Scoliosis
is the most familiar – it is lateral curvature of the spine, most often in the thoracic region. It results from abnormal vertebrae structure, unequal lengths of lower limbs or muscle paralysis of lower limbs. It is treated with body braces or surgery; without treatment, permanent deformity and breathing difficults may occur
Kyphosis
is hunchback, a dorsal exaggeration of the thoracic curvature. Osteoporosis in older people may cause this, but it could also be due to tuberculosis of the spine, rickets or osteomalacia
Lordosis
, swayback, is an accentuated lumbar curvature and can also result from spinal tuberculosis or rickets. It can also be temporarily caused by pot belly or pregnancy
Carpal tunnel syndrome is caused with the concavity called the "carpal tunnel" is filled with inflammed and overused tendons crowding the median nerve. The nerve is pushed against the carpals, numbing it.
Fallen arches may occur due to overused and stretched out tendons and ligaments in the feet
Standing immobile for extended periods or running on hard surfaces without proper arch support can contribute to it
Sometimes it is genetic
Being overweight increases the likelihood of having flat feet due to the extra strain on those ligaments and tendons
Common Joint Injuries
: sprains and dislocations
Sprains
are stretched or torn ligaments (also called strains)
Ankles, lumbar spine and the knee are common sprain areas
Sprains heal slowly due to poor vascularization of ligaments
Partially torn ligaments can heal by themselves; completely ruptured ones must be surgically repaired or else wither away
Cartilage injuries
are characterized by the snapping and popping the overworked cartilage
Most cartilage injuries involve the knee menisci or, in younger atheletes, the epiphyseal plates
Because cartilage is avascular, once it is damaged, it stays damaged
"loose bodies" (cartilage fragments) are typically removed through arthroscopic surgery to avoid binding a joint
Dislocations
(luxations) occurs when the joint is out of alignment; it is accompanied by sprains, inflammation and joint immobilization; subluxation is partial dislocation
Occurs usually during fall
shoulders, fingers and thumbs are most common
the dislocation is "reduced" through manipulation by a physician
Inflammatory and degenerative conditions
: bursitis, tendonitis, arthritis
Bursitis
is inflammation of a bursa, usually caused by excessive friction or stress
Falling on the knees may result in "housemaid’s knee" or "water on the knee" – a bursitis of the prepatellar bursa
Prolonged leaning on the elbows may damage the olecranon bursa, resulting in "student’s elbow" or olecranon bursitis.
Bursitis may also be caused by bacterial infection
Symptoms are pain made worse by joint movement, redness, and swelling
Tendonitis
is inflammation of tendon sheaths and the causes and symptoms are almost identical to bursitis
Arthritis
is inflammation and/or degeneration of a joint – there are over 100 different types of it; it is the most widespread debilitating disease in the US. One in seven Americans will suffer from some type of arthritis.
All types of arthritis have, to some degree, the same symptoms: pain, stiffness and swelling of a joint
Depending on the type of arthritis, the synovial membrane, the articular cartilages, the articulating bones, or all of these may suffer damage
Some forms of acute arthritis are the result of bacterial infection and can be treated with antibiotics; chronic forms include osteoarthritis, rheumatoid arthritis and gouty arthritis (gout).
Osteoarthritis
(OA) is the most common chronic arthritis, accounting for half of all cases. It is a degenerative joint disease, and is due to wear and tear of a joint. It is usually seen in older people, though early damage to a joint may result in its appearance in the young
The abnormal breakdown of articular cartilage results in bone-to-bone friction in a joint, wearing down the bones, destroying the remaining cartilage and resulting in severe pain
Bony spurs develop in response to the grinding, restricting joint movements
Symptoms can be controlled with aspirin, but the course of the disease can not be stopped
Experimental treatments involve magnetic therapy and injection of hyaluronic acid
Rheumatoid arthritis
usually appears between 30-40 years of age and is more common in women.
In early stages, fatigue and joint tenderness/stiffness are common; joints are affected in a symmetrical fashion
The course of the disease is marked by flare-ups and remissions (rheumatoid)
It is an autoimmune disease – the body is attacking its own tissues
It starts in the synovial membranes but eventually all of the joint tissues will be affected. Without treatment, synovial fluid accumulates, causing swelling of the joint.
The cartilage is eaten away by enzyme activity, then the synovial membrane thickens into a pannus. Scar tissue forms and connects the bone ends, eventually fusing them.
Ankylosis
is the condition of fused bones due to rheumatoid arthritis
There is no "wonder drug" for this disease; right now, anti-inflammatory drugs (like aspirin) or physical therapy are prescribed
Gouty arthritis
, or gout, is caused by abnormal levels or uric acid in the bloodstream
High levels of uric acid may cause urate crystal deposition in joints particularly the joint of the big toe
More common in males than females, seems to have a genetic component
Untreated, the bones can fuse
Drugs are available (colchicine, allopurinol, et al) that terminate or prevent gout attacks – therapy is usually withheld until two or more gout attacks have occurred, since many people may only experience one attack in their lifetimes.
Lyme Disease
: caused by a spirochete transmitted by the deer tick