Musculoskeletal ImagingStress fracture
an injury to normal or abnormal bone that results from repeated cyclic loading. Two types of stress
fracture are recognized: fatigue
fracture, which occurs after application of abnormal stress to a bone with normal elastic resistance; and
insufficiency fracture, which results when normal stress is placed on a bone with deficient elastic resistance. Typical examples of fatigue fractures are those occurring in the metatarsal bones of military recruits (march fractures), and in the lower
extremities in athletes, joggers and dancers. Causes of insufficiency fractures are diverse and include rheumatoid arthritis,
osteoporosis, Paget's disease, osteomalacia or rickets,
renal osteodystrophy and irradiation.
Routine radiography plays an essential role in the diagnosis of stress fractures; however, scintigraphy possesses greater diagnostic sensitivity. Stress fractures are associated with focal fusiform, sharply marginated areas of increased radionuclide activity. In addition, MR imaging has comparable sensitivity and superior specificity to bone scintigraphy in the assessment of stress fractures. Stress fractures appear most typically as a linear zone of low signal intensity surrounded by a broader, poorly defined area of slightly higher (although still low) signal intensity on T1-weighted spin-echo MR images and as a linear area of low signal intensity surrounded by a broader region of high signal intensity on T2-weighted spin-echo images. Stress fractures can occur at almost any skeletal site (Table 1).
Stress fracture, Table 1. Sites of stress fractures by activity.
| Location | Activity or event |
|---|
| Sesamoids or metatarsal bones: | Prolonged standing |
| Metatarsal shaft: | Marching, stamping on ground, prolonged standing, ballet, postoperative bunionectomy |
| Tarsal navicular bone: | Stamping on ground, marching, long distance running |
| Calcaneus: | Jumping, parachuting, prolonged standing, recent immobilization |
| Tibia: | |
| Midshaft and distal shaft | Long distance running |
| Proximal shaft (children) | Running |
| Fibula: | |
| Distal shaft | Long distance running |
| Proximal shaft | Jumping, parachuting |
| Patella: | Hurdling |
| Femur: | |
| Shaft | Ballet, long distance running |
| Neck | Ballet, marching, long distance running, gymnastics |
| Pelvis: | |
| Obturator ring | Stooping, bowling, gymnastics |
| Lumbar vertebra (pars interarticularis): | Ballet, lifting heavy objects, scrubbing floors |
| Lower cervical, upper thoracic spinous process: | Clay shovelling |
| Ribs: | Carrying heavy pack, golf, coughing |
| Clavicle: | Postoperative radial neck |
| Coracoid of scapula: | Trapshooting |
| Humerus, distal shaft: | Throwing a ball |
| Ulna, coracoid process: | Pitching a ball |
| Ulna, shaft: | Pitchfork work, propelling a wheelchair |
| Hook of hamate: | Holding golf club, tennis raquet, baseball bat |
Modified from Daffner RH: Skel Radiol 2:221, 1978.
In the spine almost all cases of spondylolysis represent a stress fracture. Rarely, a single traumatic episode can result in spondylolysis.
The trabecular alterations that characterize bone bruises appear to be very similar if not identical to those associated with stress fractures; however, bone bruises result from an acute episode of trauma rather than chronic repetitive stress.
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