Introduction
A cortical disruption (arrow), along with a fine line of increased density, is noted. This is consistent with the appearance of sclerotic bone following a stress fracture.
T1-weighted sagittal magnetic resonance image from the ankle. A stress fracture is noted as a linear area of low signal intensity in the calcaneus. Courtesy of Drs. Mike Handlon, Jennifer Keilp, and Molly Hester.
Background
The term "stress fracture" refers to the failure of the skeleton to withstand submaximal forces over time.
The following 2 forms of stress fracture have been defined:
- Fatigue fracture is classically described in military recruits and runners in whom normal bone is exposed to repeated abnormal stresses.1
- Insufficiency fracture results when normal stress is applied to abnormal bone (such as bone with osteoporosis or Paget disease).
Related eMedicine topics:
Stress Fractures (Orthopedic Surgery)
Stress Fracture (Physical Medicine and Rehabilitation)
Femoral Neck Stress Fracture
Metatarsal Stress Fracture
Pelvis, Insufficiency Fractures
Presentation
Natural history and presentation
While stress fractures can occur in any bone, stress fractures of the tibia are the most common. The proximal one third of the tibia is usually involved in children and the elderly, while the tibia's distal one third is typically involved in long-distance runners. Stress fractures of the pubis also are common in long-distance runners, as is distal fibula involvement. Other common fracture sites are the navicular, calcaneus, and metatarsals, particularly the second, third, and fourth.
Stress fractures are less common in the upper extremity and the axial skeleton. They have been described in the ribs of golfers, the sternum of wrestlers, the acromioclavicular joints of weight lifters, and the humerus of tennis players. Insufficiency fractures are relatively common in patients with osteoporosis, with femoral neck fractures and compression fractures of the vertebrae occurring the most often. Insufficiency fractures of the sacrum can occur in individuals with osteoporosis or who have had radiation therapy.
Normal bone is a dynamic organ with constant and simultaneous bone deposition by osteoblasts and bone resorption by osteoclasts. Bone reacts to stress by increasing bone density at the site of stress through increasing osteoblastic activity. However, there is a limit to the adaptability of bone to stress. On continuous or repeated trauma to the same site, osteoclastic activity can exceed osteoblastic activity, and trabecular microfractures can result. With the persistence of the traumatic forces, the trabecular microfractures progress to small cortical fractures, termed stress fractures. If the trauma persists, a complete fracture can result.A commonly associated condition is shin splints. These are believed to result from periosteal reaction caused by microperiosteal tears from abnormal stress mediated by Sharpey fibers, which connect the tendons to the bones. Shin splints usually do not progress to further trauma to the bone. Repeated microperiosteal tears with the associated periosteal reaction and healing response can cause increased tracer uptake in a technetium-99m (99m Tc) methylene diphosphonate (MDP) bone scan.
On T2-weighted magnetic resonance images, any form of microtrauma would result in a signal increase. Fat suppression is helpful in distinguishing the signal abnormalities from the surrounding fat marrow. In a T1-weighted series, a low signal area is demonstrated corresponding to the finding in the T2-weighted images.
The patient typically complains of pain at the fracture site, which is precipitated in a reproducible way by exercise. This can happen in a beginner who has just started a rigorous program or in an athlete who has suddenly stepped up his or her training program.2,3,4 In the patient with osteoporosis, a clear history of trauma may not always be available. Bone mineral density may be so reduced that only a minimal trauma can cause a fracture.As many as 10% of the patients who are seen in sports medicine clinics have stress fractures.5
Preferred Examination
The first examination in evaluating a possible stress fracture is the plain film (see Image below and Image 1 in Multimedia).
A cortical disruption (arrow), along with a fine line of increased density, is noted. This is consistent with the appearance of sclerotic bone following a stress fracture.
If the plain film turns out to be negative, which is quite frequently the case, than magnetic resonance imaging (MRI) or bone scintigraphy should be considered to further evaluate the clinical finding.
The advantage of MRI is better spatial resolution and specificity. MRI can easily detect minor stress reactions, such as bone contusions on a short T1 inversion recovery (STIR) sequence or a fat-suppressed T2-weighted fast spin echo (FSE) sequence. If in addition the typical linear low signal component is identified, then the classic criteria for a stress fracture are present (see Image below and Image 2 in Multimedia).
T1-weighted sagittal magnetic resonance image from the ankle. A stress fracture is noted as a linear area of low signal intensity in the calcaneus. Courtesy of Drs. Mike Handlon, Jennifer Keilp, and Molly Hester.
In the example of a sacral fracture (see Images below and Images 3-4 in Multimedia), MRI can obtain a screening of the pelvis with different sequences (coronal and axial STIR and T1 SE).
An area of hyposignal is noted in the T1 sequence at the left sacrum, at the site of an acute stress fracture.
Same patient as in Image above. The acute stress fracture in the left sacrum appears as a linear area of hypersignal with adjacent edema.
In addition, MRI is sensitive enough to detect further malignant entities causing a marrow replacement, which would make the bone prone to insufficiency fracture.
Another approach can be 3-phase skeletal scintigraphy with99m Tc MDP. In an adult, typically about 25 mCi of99m Tc MDP is injected intravenously, with the patient positioned under the gamma camera. The dose for pediatric patients is adjusted accordingly. It is important to image the contralateral normal side as well. The first phase of the study is the dynamic phase, and rapid-sequence dynamic images are obtained for approximately 1 minute. The second phase is the blood pool phase. Static planar images are obtained immediately after the dynamic images. The third-phase images consist of static planar images obtained 2-3 hours later.
Compared with MRI, the advantage of scintigraphy is that the entire skeleton can be screened.
Limitations of Techniques
Plain radiographs often are negative in the early stages of the evolution of stress fractures.
As described above, MRI is very sensitive in the immediate documentation of the bony structures' stress reactions. It is well documented that MRI is able to show even minor stress changes (for example, after a marathon) at a much earlier stage than that of the actual stress fracture. Indeed, it seems sometimes to be an arbitrary cutoff between a severe bone contusion, which will contain multiple microfractures, and the actual stress fracture, which requires a linear component.
Scintigraphic changes can precede plain film changes by up to a few weeks because the increased osteoblastic activity associated with a stress fracture is more easily detected by scintigraphy.
Differential Diagnoses
Bone Metastases
Osteoid Osteoma
Osteomyelitis, Acute Pyogenic
Osteomyelitis, Chronic
Other Problems to Be Considered
A severe, underlying stress-reaction bone contusion without a linear component can be challenging to distinguish from an actual stress fracture on a magnetic resonance image.
A bone contusion associated with a stress fracture can be difficult to distinguish with MRI from red marrow. However, the linear low signal line helps demonstrate the actual fracture.
Considering scintigraphy, the differential diagnosis may be more complicated because of the lack of specificity and spatial resolution that MRI provides.
A physiologic periosteal reaction, a bone tumor, avascular osteonecrosis (AVN), plantar fasciitis, or a bone spur can cause problems.
More on Stress Fracture |
 Overview: Stress Fracture |
| Imaging: Stress Fracture |
| Follow-up: Stress Fracture |
| Multimedia: Stress Fracture |
| References |
| Further Reading |
| Next Page » |
References
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Kelsey JL, Bachrach LK, Procter-Gray E, et al. Risk Factors for Stress Fracture among Young Female Cross-Country Runners. Med Sci Sports Exerc. Sep 2007;39(9):1457-1463. [Medline].
Loud KJ, Micheli LJ, Bristol S, et al. Family history predicts stress fracture in active female adolescents. Pediatrics. Aug 2007;120(2):e364-72. [Medline].
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Savoca CJ. Stress fractures. A classification of the earliest radiographic signs. Radiology. Sep 1971;100(3):519-24. [Medline].
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Moed BR, Ajibade DA, Israel H. Computed tomography as a predictor of hip stability status in posterior wall fractures of the acetabulum. J Orthop Trauma. Jan 2009;23(1):7-15. [Medline].
Cheung Y, Perrich KD, Gui J, Koval KJ, Goodwin DW. MRI of isolated distal fibular fractures with widened medial clear space on stressed radiographs: which ligaments are interrupted?. AJR Am J Roentgenol. Jan 2009;192(1):W7-W12. [Medline].
Gregg JM, Schneider T, Marks P. MR Imaging and Ultrasound of Metatarsalgia-The Lesser Metatarsals. Radiol Clin North Am. Nov 2008;46(6):1061-78. [Medline].
Lancianese SL, Kwok E, Beck CA, Lerner AL. Predicting regional variations in trabecular bone mechanical properties within the human proximal tibia using MR imaging. Bone. Dec 2008;43(6):1039-46. [Medline].
Lee JK, Yao L. Stress fractures: MR imaging. Radiology. Oct 1988;169(1):217-20. [Medline]. [Full Text].
Rosen PR, Micheli LJ, Treves S. Early scintographic diagnosis of bone stress and fractures in athletic adolescents. Pediatrics. Jul 1982;70(1):11-5. [Medline].
Zwas ST, Elkanovitch R, Frank G. Interpretation and classification of bone scintigraphic findings in stress fractures. J Nucl Med. Apr 1987;28(4):452-7. [Medline]. [Full Text].
Further Reading
Related eMedicine topics:
Stress Fractures (Orthopedic Surgery)
Stress Fracture (Physical Medicine and Rehabilitation)
Femoral Neck Stress Fracture
Metatarsal Stress Fracture
Pelvis, Insufficiency Fractures
Guidelines:
Stress/Insufficiency Fracture, Including Sacrum, Excluding Other Vertebrae
Keywords
stress fracture, fatigue fracture, march fracture, insufficiency fracture, shin splint, shinsplint
