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CURRENT CONCEPTS
ISAKOS Clinical Update
on Stress Fractures: Classification and Management
Timothy L. Miller, MD
Granville, OH, USA
Christopher C. Kaeding, MD
Director of Sports Medicine The Ohio State University Columbus, OH, USA
Stress fractures are not a single consistent injury. They occur along a spectrum of severity that impacts treatment and prognosis. Not only does the extent of the fracture vary, but the clinical behavior varies by location and causative activity. An understanding of common sport-specific stress injuries can help the clinician in the diagnosis, prevention, and treatment of these sports-related stress injuries. The most frequently reported anatomic sites of stress fractures in the literature involve the tibia, metatarsals, and fibula.
When treating these injuries, it should be borne in mind that no two stress fractures behave exactly alike. Treatment protocols should be individualized to the patient, the causative activity, the anatomical site, and the extent of the fracture. As athletes become more competitive and focus solely on one sport, the incidence of stress fractures continues to increase. A wholistic approach to the treatment of these injuries should be taken.
Pathophysiology
Stress fractures are a fatigue failure of bone. These stress injuries result from an overuse mechanism. Repeated episodes of bone strain can result in the accumulation of enough microdamage to become a clinically symptomatic stress fracture. Any stress or load causes some strain of or deformation to bone, and any strain of bone results in some microdamage. Healthy bone is in homeostasis between microcrack creation and repair.
Fatigue failure of bone has three stages: crack initiation, crack propagation and complete fracture.
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Crack initiation typically occurs at sites of stress concentration during bone loading. Crack propagation occurs if loading continues at a frequency or intensity above the level at which new bone can be laid down and microcracks repaired. Continued loading and crack propagation allows for the coalescence of multiple cracks to the point of becoming a clinically symptomatic stress fracture. If the loading episodes are not modified or the reparative response is not increased, crack propagation can continue until structural failure or complete fracture occurs.
Through the adaptive process of remodeling, bone is able to respond to crack initiation and propagation such that the loaded bone is strengthened in preparation for future loading. This positive adaptive response is known as Wolff’s law and is an essential part of bone health.
Risk Factors for Stress Fractures
A variety of biological and mechanical factors are thought to influence the body’s ability to remodel bone and therefore impact an individual’s risk for developing a stress fracture. These include, but are not limited to sex, age, race, hormonal status, nutrition, neuromuscular function, and genetic factors. Other predisposing factors to consider include abnormal bony alignment, improper technique / biomechanics, poor running form, poor blood supply to specific bones, improper or worn-out footwear, and hard training surfaces. It is important to remember that the cause of stress fractures is multi-factorial, and individual athletes will vary in their susceptibility to stress injuries.
The key modifiable risk factors in the development of overuse injuries of bone relate to the pre-participation condition of the bone and the frequency, duration and intensity of the causative activity. Without pre-conditioning and acclimation to a particular activity, athletes are at significantly increased risk for the development of overuse and fatigue-related injuries of bone. Multiple intrinsic and extrinsic factors can influence the balance between the creation/propagation of microcracks and the body’s ability to repair them.
Classification / Grading
Stress fractures are classified in multiple ways but most commonly by the size of the fracture line seen on imaging, the severity of pain or disability, the biologic healing potential of the particular injury or location, the natural history of the particular fracture, or some combination of these parameters. The classification of stress fractures as either “high- risk” or “low-risk,” has been suggested by multiple authors. High risk stress fractures have at least one of the following characteristics: risk of delayed or non-union, risk of refracture, and significant long term consequences if they progress to complete fracture.