The bones in our bodies are in a constant process of being renewed via new bone replacing old bone on a daily basis. Old bone (which is broken down just by the process of active living) is removed by cells called Osteoclasts and new bone is laid down by cells called Osteoblasts. This process is normally well balanced however this balance can become upset resulting in more bone being removed than replaced. This imbalance may result in microcracks in the bone also known as “stress fractures”.
A Stress fracture is an overuse injury to the bone and can be caused by 2 states: Bone Fatigue or Bone Insufficiency.
Bone Fatigue: occurs when bone is not given enough time to repair and is repeatedly stressed. An abrupt increase in physical activity will cause bone to break down and Osteoclasts to remove these bone cells. Inadequate rest periods result in a decreased time for Osteoblasts to do their work and therefore inadequate bone repair occurs.
Bone Insufficiency: occurs in bone which is under normal strain but is structurally abnormal because of Metabolic Bone Disease or Osteoporosis.
Interestingly, the balance between Osteoblasts and Osteoclasts making and removing bone is under hormonal control. The hormone Estrogen is a good stimulator of Osteoblasts which lay down bone. Therefore women with menstrual irregularity, absent menstruation, low bone mineral density and eating disorders are at higher risk for stress fractures.
Although stress fractures can occur almost anywhere in the body the most common sites are weightbearing bones being the tibia, femoral (shaft and neck) and metatarsals.
How do I know if I have a stress fracture?
Stress fractures tend to be painful to touch at a specific localized point on the bone. Pain is generally aggravated by activity and eased by rest. As pain progresses it is felt earlier in the training session and eventually also during day to day activities. Hopping or jumping on a leg with a stress fracture will increase the pain.
It is important to note that even though you may have the above signs and symptoms, you may not necessarily have a stress fracture. The best way to confirm a stress fracture is an MRI scan. In the early stages of a stress fracture, Xray may not be helpful in diagnosis as microcracks are often not picked up . Its only a few weeks later when bone is laid down in order to repair the fracture that the results are seen on X-ray. Another advantage of MRI is the that the stage of ” bony stress reaction” (what occurs in the bone before a stress fracture takes place) can be identified on MRI and progression to a stress fracture prevented. Bone scans with injection of a tracer can also be used to diagnose stress fractures. The bone which is laid down to repair a fracture will absorb more tracer and will appear darker. However bone scans are not always specific for stress fractures and have much more radiation than MRI scans.
Management of stress fractures
Most stress fractures can be managed by a period of rest and cessation of activity. How much rest is needed depends very much on the state of the fracture and its location. In some cases the patient is advised complete rest, even from weight bearing and a cast or crutches may be given. Low impact activities (such as swimming) can often be effective in maintaining fitness while healing takes place. Once day to day activities are pain free, GRADUAL resumption of training activity can take place. Some stress fractures (again dependant on their location) are at risk of not healing and need surgical intervention.
How can stress fractures be prevented?
Like all overuse injuries, stress fractures occur from doing too much too fast too soon without adequate rest. Gradually building up of exercise performance with adequate time for recovery is the best way to prevention. Some studies show that weight training can increase muscle mass as well as bone strength and should be included in ones training programme.
Good nutrition especially in female athletes is of vital importance. Both calcium and vitamin D are very important vitamins needed in bone metabolism.
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