Bones can fracture in response to many different types of forces:
● Squeezing forces (compression)
● Stretching forces (tensile)
● Twisting forces (torsion)*
● Any combination thereof.
* The long bones of the body have the weakest response to twisting forces.
Football Creates Strong Bones
Bone studies have shown that football players have a significantly higher bone mineral density* than sedentary people throughout the whole body in general and specifically in the spine, hip, leg, and heel bones.
In fact, football players also generally have a higher bone mineral density in the hip and spine than people who are runners.
* Bone mineral density tests measure how many grams of calcium and other bone minerals are packed into (or how densely they are present in) a section of bone and are good predictors of osteoporosis or the likelihood of suffering a bone fracture.
Football Fractures: How Do They Happen
Some common football events that can cause a tibial or leg fracture include:
► contact during a slide or leg tackle
► a collision with the goalkeeper
► two opposing players colliding while swinging for a loose ball
► a player on the ground being kicked by a standing opponent.
Of course, in football other bones in the body may also fracture, like bones in the forearm or shoulder when landing awkwardly after being undercut by another player (while going for a head ball) or bones in the foot when players step hard onto the boot of another player.
In the case of fractures where there is no contact, already weakened bones are often to blame, usually weakened by some other physiological response like:
○ a disease such as osteoporosis
○ metabolic/chemical deficiencies
○ cancerous tumors
○ a previous injury.
Why Do Broken Bones Hurt?
Some of the nerve endings that surround bones (or are on the outer surface of bones) include pain receptors, so when you suffer a fracture these fibers become damaged or irritated, causing you to feel pain. Another reason why broken bones hurt is because the muscles that surround them (at the injured area) often go into spasm, as a protective or reactive response by the body to injury. Muscle spasms may cause pain by themselves.
The Healing Process
The repair of a bone fracture is a complicated process and is made more complex by the fact that different types of fractures and different types of bones may heal in different ways.
Here is a typical example of how a bone fracture might heal (one that could take place at the middle of the long bones, such as the bones of the leg):
1. As a result of broken blood vessels in the bone and surrounding soft tissues like the periosteum (the soft tissue covering of the bone) and endosteum (the lining of the central medullary canal), the initial response is one of immediate bleeding into the area, inflammation, and eventually a blood clot forms at the fracture site (fracture hematoma)*.
* Interestingly, the fractured ends of the bones usually necrose, or die, as the damaged blood vessels go into spasm and the oxygen supply is lost.
2. Other blood vessels infiltrate the area and cells called fibroblasts (which produce fibrous tissue in the body) start to replicate and accumulate in and around the fracture site. They release the base components of an extracellular matrix (which provides structural support, introduces a framework for growth, and helps to regulate cell functions) and create a loose framework called granulation tissue. Undifferentiated stem cells infiltrate the area and convert into chondroblasts* (which produce cartilage in the body) and later osteoblasts (which produce bone in the body). The chondroblasts lay down cartilage intermixed with existing fibrous connective tissue, forming a soft callusª. The soft callus cannot be seen on an x-ray.
* Fibroblasts may also convert into chondroblasts.
ª This callus is very weak in the first 4 to 6 weeks of the healing process, which is why broken bones require adequate protection in the form of equipment like casts or boots/braces. It's also why taking weight off of the affected limb may be required (a stabile area is very important for early fracture repair, especially for things like blood vessel growth and callus formation). Pins, plates, rods, and screws also help in this regard and, in some cases, allow players to put weight on fractures much earlier. In the geriatric population, an inability to put weight on a limb may cause much more harm to a person's overall health than the bone fracture alone (a sedentary person, for instance, may be at greater risk for health complications).
3. With the presence of the soft callus, the body starts to undergo two processes: intramembranous ossification* and endochondral ossificationⁿ. In intramembranous ossification, primary or "woven" boneʶ forms on the outside edges of the fracture gap and in the bone's central medullary canal (the places where the soft tissue, stem cell containing linings of the periosteum and endosteum are located). In endochondral ossification, osteoblasts gradually replace the "cartilage cells" toward the interior of the fracture site. The osteoblasts release osteoid, their extracellular matrix. Osteoid eventually surrounds the osteoblasts and the remaining cartilaginous "model" that was left behind, before the osteoid is mineralized and hardened into primary or woven bone. The final result is the formation of a hard callusª.
* Intramembranous ossification occurs within a template of flat, membrane-like layers of connective tissue. It does not involve the replacement of hyaline cartilage, as occurs in endochondral ossification. It is primarily responsible for the formation of the flat bones of the body during gestation and human development, like the jaw, the collar bones, and most of the bones of the skull. It also helps to increase the thickness of the long bones of the body.
ⁿ Endochondral ossification occurs after the chondroblasts have multiplied, grown, and produced/released substances that form a structural scaffold, one that eventually calcifies. This hinders the access of cartilage cells, now called chondrocytes, to nourishment and the waste removal process necessary for cell survival; eventually this leads to chondrocyte death and degeneration. The cavities that remain behind allow blood vessels, precursor bone marrow cells, and osteoblasts (or their precursors) to enter the area, using the remaining structures as a template for bone growth.
ʶ Woven bone is less organized and weaker than normal bone.
ª The hard callus is formed as the woven bone tissue fills the fracture gap, eventually joining the ends of the fracture site. It is usually formed within 6 to 12 weeks after the fracture. The callus' larger mass and diameter (compared to the original bone) give the bone greater stability despite its lower levels of stiffness and strength (compared to the final bone product).
4. Finally, the bone begins to remodel. The woven bone is gradually replaced by stronger secondary or lamellar bone* (developing into either cancellous bone or cortical boneª). This bone continues to remodel itselfʶ over months or even years until it more closely resembles the original bone segment.
* Lamellar bone is made up of collagen fibers parallel to each other (in columns) in the same layer of bone, but the fibers run in opposite direction in alternating layers, similar to plywood, providing bone with its significant strength.
Bone Illustrations (for more information):
ª Some lamellar bone becomes "cancellous bone" (a spongy-looking honeycomb of porous bone that forms 20% of the body's normal bone mass) and some turns into hard "compact bone" (dense and solid, forming 80% of the body's bone mass, but with 1/10th the surface area of cancellous bone) [Figure 1].
ʶ In the remodeling process, osteoclasts (cells that break down or dissolve bone cells and matrix) assist osteoblasts in reshaping the bone in late-stage fracture repair.
But All Fractures Don't Heal In The Same Manner?
Indeed, different types of fracture heal differently (not all fracture repair is the same).
Here are some examples of other ways that bone fractures can heal*: ► Contact Healing - It occurs in fractures with a small space (less than a 0.1 mm gap) and where there is little or no movement between the fractured ends. Lamellar bone is formed as the first stage of this healing process (crossing the gap to join the bone ends) and grows in alignment with the existing bone (no callus or woven bone forms). ► Gap Healing - It occurs when there is a slightly larger gap (less than 800 µm or 1 mm) between the bone ends, again with little or no movement. In smaller gaps, lamellar bone is laid down at right angles to the normal bone and later becomes remodeled to its proper orientation in line with the existing bone. In larger gaps, woven bone may be laid down first as a scaffold (to subdivide the area into smaller compartments) before the initial lamellar bone is laid down (no callus forms). * In some cases, a fracture will not heal on its own and will require surgical intervention.
Here are some examples of other ways that bone fractures can heal*:
► Contact Healing - It occurs in fractures with a small space (less than a 0.1 mm gap) and where there is little or no movement between the fractured ends. Lamellar bone is formed as the first stage of this healing process (crossing the gap to join the bone ends) and grows in alignment with the existing bone (no callus or woven bone forms).
► Gap Healing - It occurs when there is a slightly larger gap (less than 800 µm or 1 mm) between the bone ends, again with little or no movement. In smaller gaps, lamellar bone is laid down at right angles to the normal bone and later becomes remodeled to its proper orientation in line with the existing bone. In larger gaps, woven bone may be laid down first as a scaffold (to subdivide the area into smaller compartments) before the initial lamellar bone is laid down (no callus forms).
* In some cases, a fracture will not heal on its own and will require surgical intervention.
When Bones Don't Heal
Some risk factors that may prevent proper bone healing include:
■ Steroid and NSAID (non-steroidal anti-inflammatory drug) use
■ Alcohol use
■ Vitamin A, C, and D deficiency
■ An infection in the area
■ Pre-existing medical diagnoses, like diabetes
■ Altered hormone levels . . . potentially, hormones like parathyroid hormone, thyroid hormone [Figure 2], estrogen, androgens (i.e. testosterone), insulin, growth hormone, calcitonin, and corticosteroids.
Figure 2: Normal thyroid and parathyroid gland responses to calcium in the blood
The type of fracture may be another factor that determines if a bone can heal itself. Some types that are less likely to heal by themselves include:
■ those with a wide gap or with multiple distracted fragments
■ those that are pathologic (i.e. ones weakened by a tumor)
■ those that have a poor blood supply.
Can I Help The Fracture To Heal?
One of the most important elements for fracture healing is proper nutrition. Typically, this means making sure that you get enough calcium and vitamin D in your diet.
◊ Calcium & Vitamin D: As most of us know, calcium is an essential building block for the bones and teeth. It is also important for many of the body's key functions, like the transmission of nerve signals and the contraction of muscles.
One of the main roles of Vitamin D is to help the body absorb calcium into the body. Without enough vitamin D, the body can't form enough of the hormone calcitriol (known as "active Vitamin D"). Calcitriol helps the body absorb calcium from your diet (from your digestive system), but it also prevents the kidneys from releasing it from the body.*
If this hormone is not created, however, and calcium levels in the blood are too low, the body must take calcium from somewhere else, usually from the skeleton, which weakens existing bone and prevents the formation of strong, new bone.
* Among its normal functions, calcitriol has the ability to release calcium from your bones, but its capacity to make calcium readily available for bone growth is thought to far outweigh this effect.
◊ Phosphorous: Phosphorous too is important as it works together with calcium to build strong bones and teeth. In most cultures though, a regular diet incorporates phosphorous in sufficient amounts for the body's needs. Generally, foods high in protein like meat, fish, beans, and cheese are high in phosphorous. Whole grain foods like breads and cereals are also high in phosphorous. Basically, if you eat a balanced diet, you more than likely get enough phosphorous (which is why it's not often included as a dietary recommendation).
Speak with Your Doctor!
Follow your doctor's recommendations during the fracture healing process in order to return to the pitch safely. That does not mean that a patient should not ask his or her doctor about fracture healing alternatives (for example, surgery is not necessary for every type of fracture). In addition, the patient should ask the doctor about any possible changes to their bodies after the fracture heals; for example,
■ any slight differences in joint alignment (i.e. bones may shorten, lengthen, or become angled after healing)
■ changes to the body's posture, like leg length changes that affect how the two sides of the body interact
■ the potential effects on future bone growth (in children and adolescents)
■ changes in the surrounding soft tissues (i.e. muscle weakness, scar tissue, circulation issues, etc.)
■ the risk that hardware used for fracture repair (like screws in the foot or knee) will move in the body, causing new pain*
* This effect is more likely to occur during the healing process rather than after it.
This knowledge can help give players a better awareness of the need to participate in specific injury prevention strategies and a better understanding of the factors that may contribute to future injury.
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