Orthopedics Hyperguide Review | Dr Hutaif General Ortho -...

Vitamin D3 is converted into its active form in the proximal tubules of the kidney. The active form is 1,25 dihydroxyvitamin D3. Remember that the liver performs the conversion to 25 hydroxyvitamin D3 and the kidney further hydroxylates to 1,25
dihydroxyvitamin D3. Correct Answer: Kidney

Increased serum calcium, increased serum phosphate level, and decreased parathyroid hormone all convert vitamin D to its inactive from â 24,25 dihydroxyvitamin D3.
Elevated serum parathyroid hormone and decreased calcium and phosphorus levels will increase conversion to the active form â
1,25 dihydroxyvitamin D3.

The guidelines for the daily elemental calcium requirement are as follows:
Children 500 mg to 700 mg
Growth spurt to young adult
(10 to 25 years of age)
1,300 mg
Adult male 750 mg
Adult female
Postmenopausal Elderly Pregnancy Lactation
  Â
1,500 mg
1,200 mg
1,500 mg
2,000 mg
Note: 1 daily equivalent = 250 mg elemental calcium (one glass of milk) Correct Answer: 1,500 mg

The guidelines for the daily elemental calcium requirement are as follows:
Children 500 mg to 700 mg
Growth spurt to young adult
(10 to 25 years of age)
1,300 mg
Adult male 750 mg
Adult female
Postmenopausal Elderly Pregnancy Lactation
  Â
1,500 mg
1,200 mg
1,500 mg
2,000 mg
Note: 1 daily equivalent = 250 mg elemental calcium (one glass of milk) Correct Answer: 1,200 mg

The guidelines for the daily elemental calcium requirement are as follows:
Children 500 mg to 700 mg
Growth spurt to young adult
(10 to 25 years of age)
1,300 mg
Adult male 750 mg
Adult female
Postmenopausal Elderly Pregnancy Lactation
  Â
1,500 mg
1,200 mg
1,500 mg
2,000 mg
Note: 1 daily equivalent = 250 mg elemental calcium (one glass of milk) Correct Answer: 1,500 mg

The guidelines for the daily elemental calcium requirement are as follows:
Children 500 mg to 700 mg
Growth spurt to young adult
(10 to 25 years of age)
1,300 mg
Adult male 750 mg
Adult female
Postmenopausal Elderly Pregnancy Lactation
  Â
1,500 mg
1,200 mg
1,500 mg
2,000 mg
Note: 1 daily equivalent = 250 mg elemental calcium (one glass of milk) Correct Answer: 2,000 mg

Parathyroid hormone, 1,25 dihydroxyvitamin D, and calcitonin have the following effects on end organs:
Parathyroid hormone
Kidney
1/. Stimulates 1,25 dihydroxyvitamin D formation
2/. Increases fractional resorption of filtered calcium
3/. Promotes urinary excretion of phosphorus
Bone
1/. Stimulates osteoclast resorption of bone
1,25 dihydroxyvitamin D
Intestine
1/. Stimulates small intestine absorption of calcium and phosphorus
Calcitonin
Bone
1/. Inhibits osteoclastiCresorption of bone

Parathyroid hormone, the active form of vitamin D (1,25 dihydroxyvitamin D), and calcitonin each have a net effect on calcium and phosphorus concentrations in extracellular fluid and serum:
Net Effect
Parathyroid hormone Increased serum calcium
Decreased serum phosphate
Vitamin D3 (1,25 dihydroxyvitamin D) Increased serum calcium
Increased serum phosphate
Calcitonin Decreased serum calcium
(transient) Correct Answer: Increased calcium, decreased phosphate

Parathyroid hormone, the active form of vitamin D (1,25 dihydroxyvitamin D), and calcitonin each have a net effect on calcium and phosphorus concentrations in extracellular fluid and serum:
Net Effect
Parathyroid hormone Increased serum calcium
Decreased serum phosphate
Vitamin D3 (1,25 dihydroxyvitamin D) Increased serum calcium
Increased serum phosphate
Calcitonin Decreased serum calcium
(transient) Correct Answer: Increased calcium, increased phosphate

Parathyroid hormone, the active form of vitamin D (1,25 dihydroxyvitamin D), and calcitonin each have a net effect on calcium and phosphorus concentrations in extracellular fluid and serum:
Net Effect
Parathyroid hormone Increased serum calcium
Decreased serum phosphate
Vitamin D3 (1,25 dihydroxyvitamin D) Increased serum calcium
Increased serum phosphate
Calcitonin Decreased serum calcium
(transient)

There are two conditions that cause osteonecrosis secondary to the marrow cavity becoming packed with abnormal cells â
Gaucher disease and sickle cell disease. There is probable occlusion of the intraosseous arteries with both of these conditions.
With Gaucher disease, the marrow cavity is filled with Gaucher cells (macrophages filled with cerebroside). In sickle cell disease, the marrow cavity is filled with sickled red blood cells.

There is complete death of all the elements inside the bone in osteonecrosis: osteoblasts, osteocytes, hematopoietiCcells, capillary endothelial cells, and lipocytes.
In animal models, there are no histologiCchanges after the first week, but during the second week, there is evidence of death of all marrow cells. The osteocytes shrink and the lacunae are empty. The fat in the marrow dies and there is release of lysosomes. The pH is lower and the released calcium forms an insoluble soap with the saponified free fatty acids.

The majority of the increased radiographiCbone density in osteonecrosis is caused by new bone formation laid down on the necrotiCbone trabeculae. This occurs through the process of creeping substitution.
There is calcification of the necrotiCmarrow and insoluble soap formation from the combination of the free fatty acids and released calcium. However, this does not cause the majority of the increased radiodensity.
There is resorption of the Haversian canal bone, but this results in decreased radiodensity on the radiograph rather than increased radiodensity.
NecrotiCbone that has not gone through the repair process appears normal on the plain radiograph (neither bone resorption or creeping substitution has occurred).

This college student has sustained a low-energy twisting injury, also known as a boot-top injury. The fracture pattern is a short spiral fracture and the mechanism of injury is torsion loading of the tibia.
The other patterns included:
Oblique fracture â uneven bending: This type of injury typically occurs following motorcycle accidents when the tibia is subjected to uneven bending forces.
Transverse fracture â pure bending: This fracture is typical of a soccer injury because the tibia is subjected to pure bending forces.
Oblique fracture with a butterfly fragment â bending and compression: This is a common fracture that occurs with low- and high-speed injuries. These fractures may occur from car bumpers and motorcycles.
Segmental fracture â four-point bending: This pattern is typical of high-energy injury, such as a pedestrian being struck by a car bumper.

The mechanism in this patient is four-point bending. A segmental fracture is common. The other patterns included:
Oblique fracture â uneven bending: This type of injury typically occurs following motorcycle accidents when the tibia is subjected to uneven bending forces.
Transverse fracture â pure bending: This fracture is typical of a soccer injury because the tibia is subjected to pure bending forces.
Oblique fracture with a butterfly fragment â bending and compression: This is a common fracture that occurs with low- and high-speed injuries. These fractures may occur from car bumpers and motorcycles.
Short spiral fracture â torsion: This mechanism is usually from a low velocity skiing injury. Correct Answer: Segmental fracture â four-point bending

A transverse fracture is secondary to a pure bending force. The other patterns included:
Oblique fracture â uneven bending: This type of injury typically occurs following motorcycle accidents when the tibia is subjected to uneven bending forces.
Segmental fracture â four-point bending: This injury most commonly follows a high-energy injury, such as a pedestrian being struck by a car bumper.
Oblique fracture with a butterfly fragment â bending and compression: This is a common fracture that occurs with low- and high-speed injuries. These fractures may occur from car bumpers and motorcycles.
Short spiral fracture â torsion: This mechanism is usually from a low velocity skiing injury. Correct Answer: Transverse fracture â pure bending

An injury caused by a car bumper is a high-energy injury.
All of the other distracters are low-energy injuries. Note that the cutoff for muzzle velocity between low- and high-energy injuries is 2,000 to 2,500 ft/sec.

Gun shot injuries with a muzzle velocity greater than 2,500 ft/seCare high-energy injuries. These injuries cause cavitation in the soft tissues. Often the projectiles yaw, increasing the amount of soft tissue damage. High-velocity injuries require aggressive debridement. Low-velocity projectiles have a muzzle velocity that is less than 1,500 ft/sec. There is minimal soft tissue damage such that debridement of the wound edge is all that is required.

The lowest load to failure in long bones occurs with pure torsional forces. A long bone is weakest when loaded in pure torsion. Throwing may cause a humerus fracture through pure torsional loading. The skiing injury is also a torsional injury, however, the comminution indicates a greater amount of energy storage by the bone prior to failure.

The hematoma at a bone fracture site is believed to serve as a source of signaling molecules to control cellular events. Inflammatory cells produce cytokines, such as interleukin 1 and 6, and platelets in the clot release transforming growth factor- beta (TGF-B) and platelet derived growth factor (PDGF).
An old theory was that the hematoma served as a fibrin scaffold and added mechanical stability.
The hypertrophied chondrocytes produce matrix vesicles that control mineralization. The hypertrophiCcartilage cells are invaded by blood vessels that bring in the perivascular cells, which are the progenitors of the osteoblasts.

The femoral neck fracture, metatarsal fracture, rib fracture, and the tibial fracture are stress fractures that result from repetitive loading.
In contrast, the humeral fracture in the baseball catcher is secondary to failure of the humerus secondary to a pure torsional force. Long bones are at their weakest when loaded in pure torsion.

In the normal long bone, the periosteal vessels supply the outer one-third of the cortex. The nutrient artery enters at the diaphysis of a long bone and has ascending and descending vessels that supply the inner two-thirds of the cortex.
Important points to remember:
The periosteal blood supply cannot supply the inner two-thirds of the cortex even if the endosteal blood supply has been interrupted, as in intramedullary reaming.
Blood flow markedly drops at the fracture site at the time of the fracture and peaks at 2 weeks.
Intramedullary reamed rods destroy the endosteal blood supply. In dog experiments, the blood supply is reconstituted to normal in 120 days.
In dog experiments, the blood supply is decreased in both plated and rodded tibias at 42 and 90 days. The decrease is greater in the rodded tibias.
The oxygen tension is low in the fracture hematoma and in the newly formed cartilage and bone. The oxygen tension is highest in the fibrous tissue. The hypoxiCstate favors cartilage formation.

Important points to remember concerning molecular events at the fracture site:
Type II collagen production is highest during the first 2 weeks. Cartilage is the first tissue produced at the fracture site. The chondrocytes hypertrophy and release matrix vesicles that prepare the extracellular matrix for mineralization of the cartilage. Blood vessels grow into the hypertrophied cartilage cells and perivascular cells become osteoblasts and begin mineralization. This is the exact same process that occurs at the growth plate with formation of the primary and secondary spongiosa.
Type I collagen production is low during the first 2 weeks as cartilage is initially formed. Type I collagen production is highest as the cartilage is mineralized later.
Periosteal type III collagen serves as a substrate for the migration of osteoprogenitor cells and capillary ingrowth. Type IX collagen contributes to the mechanical stability of type II collagen.
Types V and XI collagen regulate the growth and orientation of types I and II collagen fibrils.

There are several noncollagenous proteins that are important in bone repair and regeneration:
Osteonectin â The gene for osteonectin is expressed at the onset of both intramembranous and enchondral ossification. It may play a role in the regulation of cell function in the early stages of ossification.
Osteocalcin â Osteocalcin is expressed in the fracture callus only by osteoblastiCcells. This protein may have a role in intramembranous subperiosteal bone formation.
Osteopontin â This protein is found in the extracellular matrix and is important in cellular attachment. It is found in osteocytes and osteoprogenitor cells. Osteopontin may play a role in bone remodeling.
Fibronectin â This protein plays a role in early fracture healing and is found in the fracture hematoma within 3 days. Fibronectin mediates adhesion and migration. It is found in the fibrous portions of provisional matrices and in cartilage matrix. The potential role for this protein is the establishment of provisional fibers in cartilaginous matrices.

Localized bone pain is not a common finding in rickets. In contrast, in osteomalacia, bone pain is very common. The features of rickets that one should remember include:
* Apathy
* Irritability
* Short stature
* Positive Gowers sign
* Laxity
* Frontal bossing
* RachitiCrosary, Harrisonâs groove enlarged physes

Features of primary hyperparathyroidism include bone pain, brown tumors, pathologiCfractures, and kidney stones. Tetany is not a finding.
Here are some common features to remember: Common, incidence 1 in 500-1,000
Females (usually postmenopausal) greater than men, 3:1
Etiology
Benign, solitary adenoma (80%) Four gland parathyroid hyperplasia Parathyroid carcinoma (

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