Part 1

Stress structure can take place almost everywhere the bones are overused but they are quite common on the lower part of the body where the stress is very high because of the impact and other activities that require the lower parts of the body to bear a lot of weight. Most of the stress fracture takes place on the tibia or shin bone.  This occurrence is 75% of all overuse stress and fractures. They are common especially when the athletes have to run a lot or jump more often.  This is why most of those injured are triple jump or long jump female athletes. Other than the tibia, a stress fracture is common in the feet. A foot has several small bones that run to the toes and are called metatarsals, each foot has five metatarsals (Brukner, Bennell,  & Matheson, 2019).

There are two categories of risk factors. The two categories are intrinsic and extrinsic. The later factors take place outside one’s body. These factors are also called environmental factors. The extrinsic factors may include the following;

Poor diet intake which does not have enough caloric intake while practicing for a sporting event.Low vitamin D level in the bodyEarly stages of sport specialization among young female athletes. For instance, women who spend a whole year playing a single sport without a break.Practicing on a track or roads that are not well balanced.Using very poor sports equipment or gears that are improper such as worn-out shoes among others.Abrupt change of the track where the female athletes are exercising. For instance, changing from a soft surface to a hard surface such as concrete or even gravel.Repetitively engaging in the sports activity that is high-impact. Some of the sports activities include basketball, long-distance running, gymnastics, tennis, dancing among others.Engaging in training programs that are too rapid or have a very high volume of activities. If such activities are engaged with breaks.Lastly, practicing a given type of sport in the wrong technique or method ( Kahn, & Xu, 2017).

The risk factors classified as intrinsic are related to the patient or athlete themselves.  Thresher factors include;

Medical conditions: there are diseases that weaken the bone.  Diseases such as osteoporosis affect the strength of the bone as well as its density.  If a female athlete has weak bones, handling a change in activity may be very hard.Sex: well, though we are constrained to females, this stress fracture problem is common among female athletes more than it is with the male counterpart. This is common especially when they have irregular periods or when there have not periods.Anatomy: the body has different shapes and sizes. It is very difficult for people who have legs that are not equal in length. This is affecting how the foot strikes the floor when running or exercise. Some of the problems include tendonitis, bunions, and blisters. An Inflexible female has a high chance of having a stress fracture.Weight: it goes without saying the more a female athlete weighs, the more stress is exerted on the tibia. However, those with low BMI or are underweight and those with higher BMI are at risk of experiencing tibia fracture. Female athletes that are underweight are known to have weak bones.  Those that have high BMI overuse their lower anatomies by repetitively loading weight.Age:  older athletes already have issues with their bones such especially when it comes to bone density.  When a bone is weak, it develops stress reaction faster than those that are healthy.

Specific biomechanical movements that put the athlete at risk of the stress fracture

Tibia fracture among female athletes is usually incomplete or partial when the stress accumulates on a given area of the tibia. The stress fracture is not due to a single-time stress application but because of repetitive subjecting the tibia to stresses (Nicholas, & Hershman, 2015).

Forces are applied on the tibia through shear, tension, torsion, compression, or bending. Cancellous bones experience compressional forces more often than the rest of the bones in the body. Also, the femoral neck experiences compressional forces among the female athletes. However, the tensional forces are the force common in the tibia and femur. This is due to bones pulling against each other.  Below is an image of the typical tibia bone.

Figure 1: Types of forces applied on the tibia

When a bone is subjected to forces as shown in the figure 1 above, the is the tensional strain that is experienced on the outer surface of the shaft (the convex surface). The concave side of the bone experiences compressive forces.  

What about the muscles on the bone?  The muscles surrounding the bones absorb some of the load intensity and sometimes they may increase intensity. The muscles attached to the bone surface that experiences compressive force can give tensional forces that act around the bone. In other words, they act as shock absorbers whereby they assist in controlling the strain experienced on the bones (Springer, Ross Borden, & Dougherty, 2012).

When the muscle is pulled excessively, it is possible to develop a stress fracture near the junction between the bone and the tendon.  However, this is only common among other bones that do not bear weight. If the muscles get tired or are weakened, most of the stress is transmitted to the bones. When this happens, the risk of developing a stress fracture.

part 2 

The lower area of the shin usually has fractures that are referred to as the overuse injury.  Some of the reasons why the overuse injury might occur include the cumulative trauma that may have occurred to the bones.  When this takes place, the bone may develop a crack or a fracture that is not visible when the leg is radiographed. More often than not, such kinds of stress are not easy to diagnose. It is quite common to have doctors misdiagnose this as a shin splint. The overuse injuries do not take place all at once. However, they develop over time when the trauma accumulates on bones and muscles. This occurs when the bones and the muscles are overused. The muscles become overloaded and fatigued hence they are unable to absorb either the shock of the stress from repetitive impacts. So, this lower leg muscle tends to transfer the stress from the repeated use to the bone that is nearby. This is why the crack develops on the bone of the lower leg (Tejwani, 2016).

This type of fracture occurs when a sportsman overtrain.  The major cause of stress is a few things which include the time of time training or use.  The other factor that may cause an overuse is the intensifying the exercise very fast.  Additionally, if an athlete repeatedly pounds his or her legs on a hard surface such as a concrete surface, the stress is bound to increase. Some of the sports activity such as the volleyball, running, or gymnastics increases the chances of stress on the lower leg.  All the above-mentioned sports activity has a tendency to require the sportsman to strike feet of very hard surface repetitively which causes trauma.  Well-cited research has shown that women are more susceptible to this type of tibia fracture than men (Nicholas, & Hershman, 2015).

There is a reason why women tend to have this problem more often than men. It could be related to the condition known as the female athlete triad.  This triad is made up of three things, amenorrhea, poor nutrition, and an eating disorder. The three items mentioned causing them to experience a bone-related problem called osteoporosis. When this bone-related problem occurs, the bone density decreases and thereby multiplying the chances of bone fracture due to stress.  An athlete needs to have adequate rest between workouts to reduce the chances of stress fracture.

1.      Anatomy of the region that gets injured

Figure 2: The bones of feet where tibia fracture takes place

Before tibia fracture takes place, there is the stress reaction which grows to stress fracture.  This constitutes about 50% of all sports injuries.

The body of athletes is changing constantly to respond to the load that is being placed on them.  The cells are constantly turned over when the bone is trying to repair itself. In connection to that, the more load a section of the bone receives, the higher the chances of more calcium placement on that area. So, the less the load a given area receives, the less the amount of calcium it will receive.  Research shows that repetitive loading over tasks the bone’s ability to repair themselves and this causes very small cracks to develop (Tejwani, 2016). The bones on the foot have to absorb shocks and forces created when a female athlete is jumping, walking, or running. According to the studies done on the bone structures, it is estimated that about 12 times the of an athlete is generate with each move she makes.  It is the function of the muscles and ligaments to cushion the body against such forces. When the ligaments and muscles become exhausted, the stress is then transferred to the bones and hence the stress fracture.

Bones on the lower part of the foot are always in homeostasis (or in a standing still position). So, naturally, the bone cells are in balance between osteoblast activity and osteoclast activity. When a load is transferred to the bone, there is microscopic damage to the bone cells. the injured site is made weak. If the bone is given enough time to rest, there are more bone cells created to heal the damaged area. There is no enough time afforded the areas with microscopic damage, the small fractures can join to create an even larger crack called the stress fracture (Tejwani, 2016).

This type of stress fracture is characterized by swelling and a lot of pain in the area of the fracture. It is possible to miss this type of fracture if the x-ray is used during the diagnosis. If the fracture continues, it might be large enough for the x-ray.

2.      Stress estimation 

Some assumptions have to be made before estimating the stress that causes the tibia fracture in female athletes.

The mass of the female athlete is 65 kg (or 143 lbs.) The area of the tibia is  10 cm^2All the weight of the athlete is exerted on a single leg at the time of fracture.

Stress =   . . . . . . . . . . . . . . . ..  . . . . . . . . . . ..  . . . .. .  . . . . . . . . . . . . . . . . . . . . . . .  . . . .Equation 1

    = 63765 N/m^2

  = 63.7 kPa

So, from the above calculation, the direct stress needed to cause the tibia fracture is around 63.7 kPa.

Movement patterns

From a biomechanical perspective, the tibia fractures caused by stress are results of tired muscles which have the excess stress transferred to the bones (Springer, Ross Borden, & Dougherty, 2012). It is also known that the lower part of the leg plays a very important role in stress fractures. Factors that cause an increased risk of a stress fracture are as follows;

Leg-length discrepancyNarrow tibiaPes cavusThe high degree of hip rotationAnkle hyper pronationA varus forefoot and ankle.

Bones are made up of cancellous and cortical cells.  the cortical part of the bone is well organized to withstand more pressure from compression than tension. They are very dense.  The cancellous only withstand stress depending on how well the fiber matrix is organized. Tibia and other long bones are mainly made up of cortical while the ends of such bones are made up of cancellous materials. The central part of the tibia is also made up of cancellous materials.

The basic unit that makes the cortical part of the bone is the osteon. There are small channels called Haversian canals that are surrounded by layers of lamellar bone. These channels are home to blood vessels and nerves. The outer surface on long bones is surrounded by an outer coating that has a very high concentration of vessels. This coating is known as the periosteum. This where the nutrients that the outer part of the bone come from.  This coating is also responsible for cortex enlargement when the remodeling is taking place (Brukner, Bennell, & Matheson, 2019).

Figure 3: Anatomy of a long bone such as the tibia. The basic unit that makes the cortical part of the bone is the osteon. There are small channels called Haversian canals that are surrounded by layers of lamellar bone

A deeper review of different works of literature review shows an existing confusion when it comes to name and other classification schemes. Tibial stress fractures and bone remodeling has been described by names such as medial tibial syndrome, shin split, and medial tibial stress syndrome.

The responses that bones have to stress are currently under evaluation between remodeling and cortical stress on a dynamic continuum. It is very important for researchers to understand the stress reaction changes that bones have in response to stress are only a few of the physical findings.

A real stress fracture is visible on the cortical part of the tibia. There are two classes of stress fractures; a) insufficiency and b) fatigue stress fracture.  So, when abnormally excessive stress is exerted on the normally elastic bone, fatigue stress fracture takes place. Factors affecting stress include sex, age, BMI, the activity of the female athlete among others (Nicholas, & Hershman, 2015).

Out of all bone-related fractures among female athletes, up to 75% of them are related to the tibia stress fracture. Proper training gear, methods, and tracks are necessary to reduce the prevalence of stress fracture among female athletes. Breaks are necessary during training to give the cells time to heal the bones to avoid accumulated cracking that leads to a more advanced stress fracture.

References

In Kahn, S., & In Xu, R. Y. (2017). Musculoskeletal sports and spine disorders: A comprehensive guide.

Brukner, P., Bennell, K., & Matheson, G. (2019). Stress fractures. Victoria: Blackwell Science.

In Tejwani, N. C. (2016). Fractures of the Tibia: A Clinical Casebook. Cham: Springer International Publishing.

Springer, B. A., Ross, A. E., Borden, I. W. R. A. M. C., & Dougherty, P. J. (2012). Musculoskeletal Injuries In Military Women. Pittsburgh: United States Dept. of Defense.

Nicholas, J. A., & Hershman, E. B. (2015). The lower extremity and spine sports medicine: Vol.1. St.Louis: Mosby.