Potential causes treatments for stress fractures
Thursday, September 27, 2012
Filed In: White Papers
Stress fractures are one of the five most common running-related injuries and account for 6% to 14% of all injuries sustained by runners. The most commonly injured bone is the tibia (the shin bone), with tibial stress fractures accounting for between 35% and 50% of all stress fractures. There is also a gender bias in the occurrence of stress fractures, with women being at twice the risk of sustaining stress fracture compared to male runners (Matheson, 1987; Taunton, 2002).
From a pure anatomical standpoint, all tibial stress fractures begin as “shin splints” (more correctly called medial tibial stress syndrome) and involves overloading to the tibialis posterior (a muscle on the inside of the tibia) and soleus muscles (one of the muscles which comprises the calf and Achilles tendon). These muscles control foot pronation and reduce subsequent pronatory and twisting forces experienced by the tibia and foot. Sometimes these muscles are simply weak and loading in the tibia will therefore increase. However, most times these muscles are strong but are overworked since they must compensate for other muscle imbalances. Determining exactly what muscles are weak is critical to prevent stress fractures from occurring.
Medial tibial stress syndrome can progress to micro fractures in the bone if pronatory and twisting forces continue and not enough rest is given to allow the bone to heal properly. Thus, one of most important factors in the prevention of a stress fracture is the training program you are involved in and the amount of rest you give your body as the long runs get longer. However, many biomechanical factors have also been identified in the research literature.
Potential biomechanical reasons for developing a stress fracture can be divided into three general categories: impact forces, twisting forces, and pronatory forces. Greater impact forces experienced by the foot and tibia have been measured in runners with tibial stress fractures compared to controls (Ferber, 2002; Milner, 2005). Running in the incorrect shoe (Butler, 2006; Cheung, 2007) or in shoes that are worn out (Frey, 1997) have been shown to significantly increase impact forces. It has also been shown the after rehabilitation from a stress fracture, the amount of impact experienced by runners does not change (Milner, 2004). Thus, impact forces alone do not explain why a stress fracture develops.
Twisting, or torsional forces, to the tibia can also lead to a stress fracture. If the foot excessively pronates, or collapses inwards, greater twisting forces are experienced within the tibia since foot pronation and tibial rotation and coupled biomechanical motions. However, our research, and research from other labs, has shown that hip muscle weakness is one of the most common sources for increased twisting forces (Boling, 2006; Ferber, 2007; Ireland, 2003). During the stance phase of gait, the tibia and femur internally rotate and these motions are primarily controlled by the deep external rotator muscles (the piriformis muscle to name one). In addition to the internal rotation, the knee collapses inwards and this motion is controlled by the hip abductor muscles located on the outside of the hip (the gluteus medius to name one). Weakness in either one of these muscle groups can allow the leg to collapse inwards and increase pronatory and twisting forces experienced by the tibialis posterior and soleus muscles. Despite their proven importance, hip muscle strength is often overlooked as a potential contributor in the etiology or rehabilitation of a stress fracture.
Typically, lower extremity stress fractures require 6–8 weeks of complete rest to allow the bone to heal. As discussed previously, stress fractures arise due to a number of different factors. It is critical to identify each of these factors to optimize your rehabilitation. The general approach discussed here may not apply to all runners but will focus on those factors that have been identified by researchers as most important.
For the first six weeks, the emphasis is to begin active rehabilitation and start a gradual progression back from non-weight bearing to weight bearing activities. Therefore rehabilitation should be focused on developing strength from a foot up and a hip down perspective, as well as ensuring the runner has footwear specific to their type of foot and foot mechanics.
A primary focus early in rehabilitation should be strengthening the tibialis posterior and soleus muscle groups. For the tibialis posterior muscle, sit with your knee straight and loop an elastic band around and away from your foot. Pull your forefoot inward, making sure to not allow your leg to rotate.
For the soleus muscle, calf raises are one of the best exercises. Begin by placing both feet on the ground shoulder width apart and raise up on your toes. Over the next 4–6 weeks progress to both feet on a step, then to performing raises one foot at a time. For any strengthening exercise, make sure to perform the movement in a slow and controlled manner and do these exercises on a daily basis.
The hip abductor and hip external rotator muscle groups function to stabilize the hip, knee, and ankle during walking and running. Strengthening these two muscle groups will help to eliminate the abnormal stresses that are a common cause of stress fractures of the lower limb. For a complete explanation of these exercises visit www.runninginjuryclinic.com or see a health professional.
Once the pain has been resolved, sufficient strength has been gained, and your physician or health care professional has cleared you to start weight-bearing activities, the functional phase of rehabilitation begins. The specific aim of the functional phase is to return to training gradually without re-injury. It is also important that strength is maintained which can be done simply by completing the hip and lower leg exercises 1–2 times per week. It is equally important that a gradual return to activity is implemented. The general recommendation is no more than a 10% increase in training intensity, duration, and/or distance per week, and that adequate rest is given between training sessions (at least 24-48 hours). This allows for adequate rest and recovery for the structures (muscles, joints, bones) and will help to prevent a reoccurrence of symptoms.
If an increase in symptoms arises once training has been resumed, it is essential that activity again be modified. The intensity and volume of training should be significantly reduced and the substitution of non-weight bearing activity such as deep water running or stationary biking is recommended. An increase in symptoms represents an incomplete recovery and more time must be spent in rehabilitation prior to further increases in training. If symptoms persist despite rehabilitation efforts, then a visit to a sports medicine physician or qualified health care professional is recommended for further investigation.
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