Period 3
Coroners report Human physiology
BONE REMODELING:
Bone remodeling is the constant reshaping and replacement of bone. It occurs when you grow, get injured, and live. In the first year of life almost 100 percent of your skeleton is replaced. In adult bodies, 10 percent is remodeled every year. Our bodies are constantly changing in order to create the best formation of bone for the optimum functionality. When muscles pull on bone stronger, bone must become stronger as well. When it is used less often your bone will be less thick. By looking at peoples bones you can tell many things about there lifestyle and injuries. In the following scenarios we will see different examples of how bones can change through the process of bone remodeling.
The Carpals
Scenario 1:
Skate boarding accident causes scaphiod bone to break
When people fall forward it is a common reaction to put your hands down first, often causing weight and force to sprain or completely break the bone of the wrist, the scaphiod bone, also called the navicular bone. In this instance a young boy fell off a skateboard and broke his fall with his hands. In the process he got a hairline fracture. The scaphiod is a carpal located at the base of the thumb. It is the most commonly fractured carpal bone. This is probably because it actually crosses two rows of carpal bones, forming a hinge.
Necrosis will occur along the break line, phagocytes will migrate to the area, a callus of cartilage and collagen fibers will form and granulation tissue forms to bring blood and new tissue to the bone. Osteoblasts secrete an ECM on Ca/P fibers and a bony callus of spongy bone forms. The area of fracture is not stronger and there will most likely be a bump on the Scaphiod bone.
Below is a picture of the typical scaphoid fracture.
Scenario 2:
Carpal tunnel due to excessive manual labor
Carpal tunnel is caused by the inflammation or thickening of bone and tendons in the wrist and hand. Eight carpal bones surround your median nerve. Through trauma they can thicken and squeeze the median nerve that gives sensation to the fingers. This particular person was a construction worker, who often used drills. The muscles in his hands pulled on the carpals. Bone chipped off and after a while this bone reformed. The trabeculae however, reconstructed differently than before. This time, osteoblasts deposited extra calcium salts that made the carpals stronger and thicker in these areas to ensure no problems in the future. This however put pressure on the median nerve and eventually caused him to develop severe carpal tunnel.
Below is a visual of the carpal tunnel and the carpals, muscles, and ligaments that surround it. As you can see the Median nerve is encased by the carpal bones so when they thicken through remodeling CT syndrome can occur.
Scenario 3:
Dislocation of Distal carpal row
While rollerblading, this person outstretched their hands in order stop themselves from falling. Instead of a strong impact that would break their scaphiod, they hit the ground and twisted in an unusual way. This caused the dislocation of carpals.
This kind of injury is very delicate because the carpal bones have such intricate articulations with one another. In order to heal the person must rest, usually attend physical therapy, and wait while the wrist heals itself. Although this form of injury is uncommon, it is very tricky. If any bone remodeling occurs so that carpals have bumps or thicken in areas, there is a chance of a smaller range of motion (due to poor articulations) or Carpal tunnel as seen above.
Shown below is an x-ray of a wrist in which the dorsal row is shifted out of place.
Femur
Scenario 1:
Car accident causes the fracture of the femur which leads to the thickening of bone.
The Femur, being the largest strongest bone in the body is difficult the break but it can happen. In this situation, the person was in a high speed car accident in which they suffered a complete fracture. It was not comminuted because it was a young bone and not very brittle.
When the break first occurred blood vessels inside the bone broke creating an area filled with blood which made a hematoma. Some parts of the bone die due to loss of blood flow and macrophages come in to breakdown these dead pieces of bone. The bone begins to bridge the two pieces together, forming new blood vessels and a fibro cartilaginous callus. Osteoblasts migrate to the area, making an ECM of calcium and phosphorus salts and making it a bony callus. The bone heals and bone remodeling occurs. The area that is broken now becomes harder so that it will not break again. It is thicker and has a stronger ECM.
^ Above are the steps to healing the femur and a representation of how the broken area becomes thicker
Scenario 2:
Bone atrophy due to paralyzation
When this person became paralyzed from the waist down they no longer were able to contract muscles in their legs, leaving the femur immobile. After several months with little use the bone no longer needed to be as strong and stable as before. It was not holding the body’s weight, and muscles no longer pulled on the femur. It wasn’t at risk of fracture of sprain so its ECM didn’t need to be as strong. Osteoclasts began to encourage the release of calcium from the ECM into the blood. This is called skeletal atrophy or the thinning of bone. There is a loss of mass and strength and is seen in any situation in which a bone has little to no pressure put on it. This is shown in the picture below.
Scenario 3:
Gymnastics causes dislocation of patella:
When a gymnast hurdles, they put a lot of weight and pressure on their knee joint and also can also cause the femur to twist in odd manors in order to plant before pushing off the ground. When this occurs the femur can awkwardly twist on the tibia, pushing the patella to the side, dislocating it. The patella is a sesimoid bone that is encased in tendons and ligaments and is held in place by the quadriceps tendon from above. These quadriceps are what cause the shift because the move along with the femur. The tendons holding the patella are torn. Ligaments and tendons are stretched and will never be as strong again. Re-dislocation can easily reoccur.
When the femur twists in such a way and the patella dislocates. It is possible that cartilage may chip off, causing injury to the joint in the long term.
^ Picture of knee joint
^ dislocated patellar
Ribs
Scenario 1:
Strength training creates thicker, dense ribs
A professional fighter wanted stronger ribs that could take more blows without breaking or damaging his rib cage. Everyday he was hit with a plank 150 times. With each small hit his trabeculae in the spongy bone sandwich were damaged. This spongy bone healed itself creating stronger more densely packed columns. This made the ribs stronger to allow more trauma and therefore a better ribcage for protection.
This is an example of Wolfe law described by Julian Wolfe in 1868. The law says that every change in form or function is changed by adaptive changes in its internal architecture (trabeculae in this case) and its external shape (thicker). Below is a picture example of how ribs get thicker (external shape) through constant pounding and restructure
Scenario 2:
Fall from ladder causes broken rib/ articulation with thoracic vertebrae
When a painter was painting a house he fell backwards off a ladder, doing damage to his spinal cord and rib. The spinal cord is connected to a rib by the costal facets found on the thoracic vertebrae. This articulation is vital for the protection of our lungs, heart and other organs.
The thoracic vertebrae and the rib will bind together again but this time they will have a stronger bond. During the healing process the person must be very careful as to not do any further damage and may have to wear something so they have restricted movement to allow healing. Bone remodeling will occur the same as it did in the scaphoid bone fracture and the femur fracture.
Below is a picture of a thoracic vertebrae and where the ribs articulate with it.
Scenario 3:
Weightless/ zero gravity causes atrophy of ribs
An astronaut is in space for a year and his body is under less pressure. His rib cage doesn’t need to be as strong. There is nothing pulling on the rib cage. Atrophy will occur as shown in the scenario in which paralyzation causes the femur to get thinner.
The ribs, over a one year period will become slightly thinner, making up for the no gravity environment.
Below is a visual depiction of a thinning rib