REVIEW ­­Imagingf ­o ­running-induced­­ osseous­injuries Osseous overuse and stress-related injuries commonly occur in individuals who participate in the sport of running. While the clinical history and physical examination are important first steps in establishing the correct diagnosis, imaging often plays a vital role in confirming the diagnosis and in determining the extent of injury and prognosis for the injured athlete. This article will provide a thorough review of the numerous osseous stress injuries that occur in runners, including a summary of the high-risk stress fractures. Imaging strategies are discussed and the typical radiographic, CT, MRI and nuclear scintigraphic findings are described for each of the various stress-related injuries associated with running. † keywords: bone scan n CT n MrI n running injury n sports medicine n stress fracture Timothy G Sanders n stress injury & Terry A Sanders1 1Columbia Podiatry Foot & Ankle Running continues to grow in popularity as a more likely to occur in the elderly population, Center, Columbia, MO, USA †Author for correspondence: sport and is also an important component of in women or in individuals with predispos- NationalRad Weston, FL, USA the training and conditioning of athletes who ing illnesses, such as rheumatoid arthritis or Tel.: +1 954 698 9390 Fax: +1 434 295 5265 participate in numerous other sports includ- renal disease, or exogenous steroid use [3,5,6]. [email protected] ing American football, basketball and soccer to Hormonal factors, including the menopause and Department of Radiology, University of name a few. Therefore, it is not surprising that or amenorrhea, especially when associated with Kentucky, Lexington, KY, USA the number of running-associated injuries is on minimal body fat or anorexia can play a role in the rise [1]. Many factors can put a runner at risk stress fractures in females [7,8]. As a result, stress of injury but the majority of injuries result from fractures in female athletes are considered by overuse, often following a sudden increase in many to be a combination of both fatigue and activity level or an abrupt change in the training insufficiency. Insufficiency fractures should be regimen. While obtaining an accurate clinical differentiated from pathologic fractures, which history and performing an appropriate physical occur secondary to an underlying bone lesion examination are the most important factors in such as a tumor, cyst or infection. establishing the correct diagnosis, imaging often plays a vital role in establishing or confirming n Biomechanics of osseous stress injury a suspected diagnosis. Imaging can often dif- There is a broad continuum of stress-related ferentiate soft tissue from osseous injury, can bone injuries that occur as a result of exces- help guide therapy and aid in determining the sive repetitive force placed on a given bone, prognosis for a specific injury. Here we review and these injuries are common in the lower the clinical and imaging findings associated extremities of runners. This repetitive force with common osseous stress-related injuries that is a combination of many factors including occur in runners. weight-bearing, muscular contraction as well as bending and torsional forces that are applied o sseous injuries to the affected bone. Bone is a dynamic tissue Stress fractures can be categorized as fatigue that responds to various stresses placed upon stress fractures or insufficiency stress fractures it. When these stresses exceed the bone’s abil- [2–4]. Fatigue fractures occur in bones that have ity to remodel and repair itself, then we see a normal mineralization and normal elasticity spectrum of osseous injury that begins with properties and most often occur in the young microtrabecular injury and culminates with a athletic population or in military recruits, result- complete fracture. ing from rigorous physical activity or training. Insufficiency fractures occur in bones that have radiographs decreased mineralization and or abnormal elas- Radiographs are typically normal during the ticity properties and result from the normal first 2–3 weeks following the onset of pain in activities of daily living. These fractures are a runner who develops an osseous stress injury. 10.2217/IIM.10.37 © 2010 Future Medicine Ltd Imaging Med. (2010) 2(4), 417–432 ISSN 1755-5191 417 REVIEW Sanders­&­Sanders Radiographs can remain normal for consider- imaging will demonstrate a detectable abnor- ably longer periods of time. When abnormal, mality (Figure 2). Repetitive stresses placed on the radiographic appearance depends upon a bone resulting from increased activity level the timing and the location of injury. Injuries or a change in training regimen will result in that involve cortical bone (i.e., the shaft of a increased turnover of bone, and the focal area of long bone) will usually present with a cortical increased uptake on the bone scan corresponds lucency oriented perpendicular to the long axis to the area of increased osteo blastic activity. A of the bone (Supplementary Figure 1a, see online normal bone scan has a high negative predictive www.futuremedicine.com/doi/suppl/10.2217/ value and in the past was thought to exclude the iim.10.37). Periosteal new bone formation and possibility of a stress fracture even in clinically cortical thickening are late radiographic find- suspected cases [15]. However, more recently, ings. When stress changes occur in cancellous several reports of abnormal MRI examinations bone (i.e., metaphyseal regions of a long bone, in the setting of a normal nuclear-medicine femoral neck, and small bones of the foot and bone scan have demonstrated that MRI pro- ankle), radiographs most often show an ill- vides a higher level of sensitivity in the detec- defined linear area of sclerotic density located tion of early osseous stress changes [7,16–20]. within the medullary space of the bone. The In addition, Bryant et al. demonstrated that area of sclerosis is typically oriented perpendicu- SPECT imaging can detect early stress-related lar to the primary trabeculae of the involved changes of the femoral neck in the setting of a bone (Supplementary Figure 1B) [2,3]. normal planar bone scan [18] . Zwas et al. devel- oped and later refined a classification of bone CT scan scintigraphic findings, grading the extent of CT imaging only plays a limited role with stress lesions from mild to severe. The grade of regard to the evaluation of suspected osseous lesion as determined by bone scan is useful in stress injuries of the lower extremities. However, directing therapy (taBle 1) and in establishing an there are a few specific instances when CT appropriate prognosis [15]. imaging can be of particular help. These include When performing a bone scan on a runner evaluation of a potential longitudinal stress frac- with a suspected osseous stress injury, it is rec- ture of the tibial shaft, evaluation of the tarso- ommended that the area of imaging include navicular bone (Figure 1) or of the sesamoids of the entire pelvis and bilateral lower extremities the great toe, and in detecting the presence of a regardless of the symptomatic site, as patients nidus when attempting to differentiate an oste- may demonstrate additional asymptomatic oid osteoma from a stress injury of the bone lesions in contralateral bones or in additional (Supplementary Figure 2) [9,10]. areas within the ipsilateral lower extremity. The rate of resolution of bone scan abnormality is Nuclear-medicine bone scan generally related to the severity of lesion, with Nuclear-medicine bone scan demonstrates most low-grade lesions resolving within the first excellent sensitivity for the detection of osseous 4–6 months. Persistent unresolved lesions in stress-related injuries of the lower extremity and most cases are believed to be related to a lack of has long been considered the gold standard with rest and are generally associated with persistent regard to detecting early stress-related changes symptoms. Occasionally patients with persist- of bone. More recently, MRI has supplanted ent activity will show new lesions on subsequent bone scintigraphy as the imaging modal- follow-up examinations [15,21]. ity of choice in most instances of suspected stress-related osseous injuries of the lower MrI extremity [11–13]. MRI demonstrates sensitiv- With regard to the detection of osseous stress- ity equivalent to bone scan for the detection of related injuries and stress fractures, MRI has stress-related injuries and has improved specifi- been shown to demonstrate both improved sen- city with regard to differentiating stress changes sitivity and specificity relative to bone scinti- from tumor, infection or other bone lesions and graphy [11]. MRI findings typically parallel also nicely depicts soft tissue injuries that often bone scintigraphic changes. Early findings may accompany or mimic an osseous stress-related include subperiosteal edema with or without abnormality [14]. adjacent soft tissue edema. Medullary edema, Nuclear-medicine bone scan will detect an manifested as low T1 and increased T2 signal area of increased uptake within areas of osseous on short TI inversion recovery or T2- weighted stress response much earlier than radiographic imaging with fat saturation, can also be an early 418 Imaging Med. (2010) 2(4) future science group ­­Imaging­of­running-induced­osseous­injuries REVIEW Figure 1. stress fracture: CT imaging appearance. (A) Coronal CT reconstruction through the proximal tibia reveals a transverse linear area of sclerosis (arrow) involving the proximal medial tibial metaphysis representing a stress fracture. (B) Axial CT image through the midfoot shows a linear lucency (arrow) extending across the short axis of the tarsal navicular, indicating a stress fracture. finding. As the extent of osseous stress-related involving the lateral aspect of the superior pubic changes progress, marrow edema may become ramus or the medial aspect of the inferior pubic more intense and more extensive with eventual ramus. Stress fractures can also occur in the intra cortical signal abnormality developing.