Chief Complaint: 72-year-old woman who fell on her right hip.
History: Margaret Donovan, a 72-year-old white female, was brought to the emergency room by her son-in-law after falling in her bathtub. She was previously in good health, despite leading a relatively sedentary lifestyle and having a 30-pack-year history of cigarette smoking. The only medication she currently takes is Inderal (propranolol) for mild hypertension. She fell upon entering the bathtub when her right leg slipped out from under her; she landed on her right hip. There was no trauma to her head, nor does she complain of right or left wrist pain. However, she reports severe pain in the right hip and upper thigh, and was unable to get up after her fall. An injection of oxymorphone hydrochloride
(Numorphan) helped relieve her pain and she was taken to the radiology department for an X-ray of her right leg and hip .
Physical Examination: The patient was alert, oriented to time, place, and date, and was responding appropriately to questions despite being in considerable pain. There were no signs of trauma to the head, neck, torso, arms, or left leg. The right thigh and hip were extremely tender and were immobilized by a leg splint. Heart and lung sounds were normal, and abdominal sounds were reduced.
Radiology Report: The X-ray of the right hip revealed a complete, comminuted, intertrochanteric fracture of the right hip. No other fractures were noted in the right leg. There were also long-term osteoporotic changes in the femur, tibia, and fibula.
Questions:
1. What is meant by a "complete, comminuted, intertrochanteric fracture of the right hip"?
A.
Complete - refers to a fracture completely through the bone:
B.
Comminuted - refers to a fracture in which the broken bone has shattered into several smaller pieces:
C.
Intertrochanteric - refers to a fracture located between the greater trochanter and lesser trochanter of the femur
2. Draw a picture of what you think Margaret's fracture looks like.
3. The radiologist reported signs of osteoporosis. Describe the characteristics of an osteoporotic femur as seen on an X-ray. (How does it differ in appearance from a normal femur?)
osteoporosis is marked by a decreased bone volume. Loss of spongy ("cancellous") bone is greater than loss of compact bone. In the femur, osteoporotic changes would include a thinning of the outer layer of compact bone around the epiphyses and thinning of the bony collar around the diaphysis. There would also be loss of cancellous bone in the proximal and distal epiphyses. These changes weaken Margaret's femurs and make them more vulnerable to fracture. In osteoporosis, the normal balance between the activity of bone-building osteoblasts and bone-resorbing osteoclasts is upset in favor of the osteoclasts.
Thus, over time, there is loss of total bone volume. While everyone experiences slow, gradual loss in bone volume after age 30, those with osteoporosis have accelerated loss.
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4. Describe the microscopic features of osseous tissue that normally help long bones
withstand lateral stress without breaking.
A lateral stress placed on a bone (e.g. on Margaret's right femur) actually causes (A) compression of the bone on the side of impact and (B) stretching (tearing) on the side opposite of the impact.
5. Describe the microscopic features of osseous tissue that normally help long bones withstand compressive stress without breaking. Surgeons performed an open reduction of
Margaret's fracture, immobilizing the bones with internal pins.
The bony collar of long bones helps them withstand compressive stress by the mechanism described in
#4A above (i.e. hydroxyapatite, weight-bearing pillars).
In addition, long bones also withstand compressive forces by virtue of the spongy ("cancellous") bone in the epiphyses. The interlocking network of bony plates (called "trabeculae") found in spongy bone help to distribute the weight of the body out to the tough bony collar of the diaphysis. In this way, bony plates act much like the trusses or struts in old-time railroad bridges which distribute the weight of the train evenly over the entire bridge. Given the above considerations, Margaret's osteoporotic femurs are vulnerable to fracture because of (A) the loss of spongy bone in the epiphyses and (B) the thinning of the bony collar in the diaphysis.
6. Describe the changes that a broken bone undergoes as it is healing.
The bony collar of long bones helps them withstand compressive stress by the mechanism described in
#4A above (i.e. hydroxyapatite, weight-bearing pillars). In addition, long bones also withstand compressive forces by virtue of the spongy ("cancellous") bone in the epiphyses. The interlocking network of bony plates (called "trabeculae") found in spongy bone help to distribute the weight of the body out to the tough bony collar of the diaphysis. In this way, bony plates act much like the trusses or struts in old-time railroad bridges which distribute the weight of the train evenly over the entire bridge.
7. During her long recovery, Margaret is advised by her physician to begin weight-bearing as soon as she can. How does weight-bearing influence the process you described in question #6?
(Be specific in your answer and describe what weight-bearing does to bone at the microscopic level.) The most popular hypothesis regarding the effect of weight-bearing on bone remodeling is called
Wolff's law . Wolff's law states that bone grows and remodels in response to the mechanical stresses placed upon it (e.g. from muscle pull or gravitational pull). Thus, bone is laid down along lines of maximal stress. This is presumably why:
A.
long bones are the thickest midway down the diaphysis, where the stresses are the greatest.
B.
curved bones are the thickest where they are most likely to buckle (e.g. note the thick greater trochanter of the proximal femur).
C.
the bony plates in spongy bone are oriented like weight-bearing trusses.
D.
large bony processes are located where muscles attach to (and pull on) bone.
When Margaret begins to bear weight on her right femur, she is introducing a lateral stress in the direction shown below: Physiological measurements reveal that placing stress on a bone generates a negative electrical charge on the compressed surfaces of the bone and a positive electrical charge on the stretched surfaces of the bone (see above drawing). Furthermore, studies have shown that negatively charged bony surfaces prevent parathyroid hormone (PTH) from stimulating bone resorption by osteoclasts. Thus, bone builds up in these areas. Conversely, bone resorption occurs on positively charged bony surfaces.
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8. Aside from any effect on the healing process, why else might Margaret's physician want her to avoid a prolonged period of bed-ridden inactivity?
Extended bedrest can have detrimental effects on an individual, especially if that individual is elderly.
Prolonged bedrest increases one's risk of developing bedsores, respiratory infections, thrombophlebitis with possible pulmonary embolism as a complication, and further loss of bone volume (i.e. exacerbating
Margaret's already present osteoporosis). This last point, in fact, is an excellent illustration of the other side of Wolff's law -- i.e. bone is reabsorbed where it is no longer needed. Prolonged bedrest and immobility means less daily stress placed upon the skeleton. Over time, bone mass will be lost. This is seen in astronauts who spend several weeks in space -- the loss of gravity means that less stress is placed on the weight-bearing bones. Upon their return to earth, these astronauts are found to have notable loss
in bone volume.
9. What risk factors does Margaret have for osteoporosis?
Margaret has several risk factors for osteoporosis:
A.
She is elderly. (Osteoporosis is more common in the elderly, particularly postmenopausal women.)
B.
She is a cigarette smoker.
C.
She is Caucasian. (Osteoporosis is more common in Caucasians than in individuals of other races.)
D.
She is sedentary. (This lack of exercise means that she is placing less stress on her skeleton -- see discussion of Wolff's law in question #7.)
Other potential risk factors for osteoporosis include:
A.
estrogen depletion (the primary reason why postmenopausal women are commonly affected)
B.
decreased bone mass at the end of development
C.
testosterone depletion
D.
alcohol abuse
E.
calcium deficiency (especially a problem in the elderly because of decreased intestinal absorption of calcium)
10. What parts of the skeleton (i.e. what bones) are most vulnerable to the ravages of osteoporosis?
The loss in bone volume due to osteoporosis is seen throughout the skeleton, affecting spongy bone slightly more than it affects compact bone. This loss in bone volume places bones at risk for fracture. The most common site of fracture is in the lower thoracic and upper lumbar vertebrae. Fractures here are typically compression fractures which may occur slowly and gradually over time, or occur suddenly. The gradual compression of the anterior portion of the vertebral bodies in the cervical and thoracic vertebrae give rise to the kyphosis deformity ("humpback") of osteoporosis.
Another common place for a fracture is in the distal radius, as the victim of osteoporosis attempts to break his/her fall by reaching out with the hands.
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The proximal femur is another common site of fracture (as occurred in Margaret). These hip fractures occur primarily in individuals over 75 and are associated with substantial morbidity and mortality (for reasons discussed in #8 above). Hip fractures are almost always associated with a fall, but it is not always clear whether the fracture precedes or follows the fall.
Osteoporosis affects over 20 million Americans. In addition, over 1.5 million people over age 45 suffer from osteoporosis-related fractures annually, most common of which are fractures of the hip, vertebrae, and limb bones The medical cost of treating patients with osteoporosis and osteoporotic fractures was
estimated in 1990 to exceed $10 billion annually. This number will rise as the baby boomers age.
11. Following her recovery, Margaret was placed on three medications: (A) oral calcium supplementation,(B) oral estrogen, and (C) oral alendronate sodium (Fosamax). Specifically
describe how each of these medications works to treat Margaret's condition.
A) oral calcium supplementation - Calcium provides an important raw material for bone formation.
(B) oral estrogen - Studies clearly show that estrogen deficiency can accelerate osteoporosis, but the mechanism for the protective effect of estrogen is not clear. Estrogen may stimulate osteoblasts to lay down new bone (estrogen receptors have recently been found on osteoblasts).
(C) oral alendronate sodium (Fosamax) - This drug inhibits the bone resorbing capabilities of osteoclasts.
12. Other treatments for osteoporosis include calcitonin. Describe how this medication works to treat osteoporosis. calcitonin - Calcitonin is a natural peptide hormone secreted by C-cells in the thyroid gland. Calcitonin is an inhibitor of osteoclasts, and thus slows down bone resorption. It also increases vitamin D production and absorption of calcium in the small intestine.
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