Case Study Osteoporosis

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Case Study

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. 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.

Mid-way through the bone, these "compressive" and "tearing" forces cancel each other out, and thus tough, compact bone is not needed in the middle. Instead, this middle area (or "medullary cavity") is filled with yellow and red bone marrow.

The outer rim (or "bony collar") is what experiences the greatest stress on lateral impact. It withstands this stress in the following ways: (A) On the side of impact, the bony collar withstands compressive crushing by virtue of the tough hydroxyapatite crystals in its extracellular matrix. Arranged in concentric layers within the osteons (Haversian systems) of compact bone, these hydroxyapatite crystals serve as weight-bearing pillars for the bone.

(B) On the side opposite of the impact, the bony collar withstands tearing apart by virtue of the vertically arranged bundles of tough collagen in the extracellular matrix of bone. This collagen is oriented in a spiraling vertical pattern in which the fibers in each concentric lamella are roughly perpendicular to those in adjacent lamellae (i.e. a "plywood-like" design).

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. Steps in repair:

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