Journal ofwilderness Medicine 4,407-411 (1993) ORIGINAL ARTICLE Wilderness related musculoskeletal injury: role of bone scintigraphy LISTON ORR, MD and ANDREW TAYLOR, Jr, MD* Department ofradiology, Emory University Medical Center, 1364 Clifton Road, NE, Atlanta, Georgia 30322, USA Musculoskeletal pain is a common sequela of wilderness related activities. X-ray analysis of persistent musculoskeletal pain often reveals no specific etiology. Nuclear medicine bone scintigraphy has the ability to detect several types of abnormalities which can be missed by plain film techniques. These abnormalities include: 1) stress fracture, 2) enthesopathy, 3) occult fracture. Scintigraphic diagnosis of these injuries can lead to proper and timely treatment while a negative bone scan can effectively rule out osseous injury. Key words: nuclear medicine; fracture; stress fracture; enthesopathy Introduction Wilderness related activities often test the physical limits of those who wish to experience the outdoors. Bones and joints which may not be seriously challenged in everyday life can receive various insults in a wilderness environment. A recent epidemiologic study of wilderness injuries emphasizes the predominance of musculoskeletal trauma [1]. A portion of individuals returning from these activities will seek medical aid for persistent musculoskeletal pain. Promp~ diagnosis of osseous injury can be crucial to the ultimate outcome. Evaluation of musculoskeletal pain typically includes radiographs of the affected region. A high percentage of these initial radiographs are negative and the patient is usually treated symptomatically. However, it is important to note that several types of injuries are difficult, if not impossible, to diagnose radiographically. If pain persists or seems severe in spite of a normal radiograph, bone scintigraphy can often playa valuable role by excluding more serious injury or by making a specific diagnosis (2,3). Abnormalities which are often normal on X-ray but easily detectable by bone scan include: 1) stress fracture, 2) bone injury at sites of tendon attachment (enthesopathy), and 3) occult fracture. This article will review the bone scintigraphic findings of these injuries, and discuss the advantages of nuclear medicine techniques in their diagnosis. Stress fracture Stress fractures occur in regions of bone where repetitive mechanical stress causes injury beyond the bone's ability to repair itself. In this situation, it is thought that bone 'To whom correspondence should be addressed. 0953-9859 1993 Chapman & Hall
408 Orr and Taylor resorption exceeds bone formation, leading to microfractures within the bone trabeculae [2]. If mechanical stress continues, the process can progress to a true full thickness fracture [3]. The typical bone scintigraphic appearance of a stress fracture is a focus of increased activity which is located eccentrically without extending across the total thickness of the bone. Often, two views of the area in question are necessary to confirm this finding. The severity of a stress fracture can be graded according to the percentage of bone thickness involvement [2]. Triple phase bone scintigraphy, in which blood flow and soft tissue blood pool images precede the static bone images, is useful in determining the acuity of a finding [4]. Long distance runners can develop stress fractures which are typically located in the tibia [4]. Wilderness related activities can lead to stress fractures which display their own characteristic locations. An example of metatarsal stress fractures in a long distance hiker is shown in Fig. 1 [5]. The injury occurred approximately five days prior to the scintigraphic examination. Radiographs of the foot became abnormal approximately one week after the abnormality was detected by scintigraphy. Ill-fitting boots may increase the likelihood of this injury [2]. Carrying heavy backpacks for long distances has been found to produce stress injury in the lateral aspects of the first ribs [6]. Similar injuries have been demonstrated in the region of the public symphysis in horseback riders [6]. Stress injury is typically not detected on initial radiographs [2,6]. Bone scintigraphy is Fig. 1. An outdoorsman experienced foot pain after returning from a long distance hike. Initial radiographs were normal. Scintigraphic image of the feet revealed increased activity within the fourth and fifth metatarsals, consistent with stress fracture. (Reproduced with permission, [5]).
Bone scintigraphy 409 highly sensitive for this type of trauma and can lead to proper treatment. Failure to make the diagnosis and, at least temporarily, discontinue the offending activity, may result in progression to a full thickness fracture. A less serious type of stress injury is the shin splint or tibial stress syndrome. This syndrome, characterized by pain along the medial aspect of the tibia, is typically seen in long distance runners, although prolonged hiking could produce identical findings. This type of injury is thought to result from increased stress on connective tissue fibers (Sharpey's fibers) that extend from cortical bone to adjacent soft tissue structures, such as interosseous membranes [2]. The increased stress results in a linear pattern of increased activity along the periphery of the bone cortex. The intensity of abnormal activity is usually less than that typically seen with stress fracture. Tibial stress syndrome does not require the degree of inactivity needed for treatment of stress fracture and thus should be differentiated from stress fracture. Only bone scintigraphy can make this distinction, as shin splints are rarely detected on initial radiographs [2,7]. Enthesopathy Sites of tendon and ligament attachment to bone are termed entheses. Repetitive stress to these attachment sites can lead to increased bone osteoblastic activity with corresponding increased radiotracer uptake on bone scintigraphy. Common sites of enthesopathy include the pelvis, greater trochanter, humeral tuberosity and knee [2,7]. Advanced cases can be demonstrated radiographically with findings of either bony hyperostosis or erosion [7]. Early in its course, this process cannot be detected radiographically but can be imaged by bone scintigraphy. The typical finding is a focal region of increased activity at the tendinous or ligamentous insertion site ofthe bone [2,7]. One type of enthesopathy which may be encountered in the setting of wilderness related activities is plantar fasciitis, an inflammatory condition that can be brought on by repetitive mechanical stress. The plantar fascia of the foot inserts into the medial tuberosity of the calcaneus, which can demonstrate increased bone scan activity if abnormally stressed [7,8]. Rest, anti-inflammatory medication, and othotic devices have been used to treat this condition [2,7]. Occult fracture The term occult fracture is used for fractures which are strongly suspected by physical examination but are not visualized on initial radiographic evaluation [3]. Radiographic detection of fractures relies on visualization of bone displacement at the fracture site or demonstration of a linear cortical defect in nondisplaced fractures. If a nondisplaced fracture is not positioned to produce a tangent with the X-ray beam, the fracture will not be visualized. Multiple views are helpful in this regard, but are not foolproof. Fracture locations which are especially difficult to detect radiographically include the scapula, carpal and tarsal bones, and sternum [3]. Sequelae of undiagnosed fractures range from inconsequential to disastrous. An example of the latter is the development of avascular necrosis [3]. In patients under 65 years of age with no osteoporosis, bone scintigraphy will detect 95% of fractures at 24 h post injury and virtually all fractures at 72 h. The minimum time for bone scans to return to normal following fracture ranges from 5 to 7 months, with
410 Orr and Taylor some remaining abnormal up to three years or longer [2]. An example of bone scintigraphy demonstration of occult fracture is seen in Figs 2 and 3, in which multiple rib fractures were diagnosed by bone scan. In addition to the high sensitivity for osseous trauma, a normal bone scan excludes underlying osseous pathology [8]. Summary Complaints of musculoskeletal pain following wilderness related activities may lead to radiographs which fail to reveal an abnormality. In cases of significant discordance between the clinical presentation and radiographic findings, bone scintigraphy can provide information leading to a specific diagnosis. Just as important, a negative examination effectively excludes osseous injury, and can be reassuring to both the patient and the physician. Fig. 2. A 49-year-old male collided with a tree while skiing, suffering blunt trauma to the left anterolateral aspect of his chest. Point tenderness was elicited over several rib levels anteriorly and posteriorly. Three views of the ribs (PA, LPO, RPO) show a single, minimally displaced fracture of the posterior aspect ofthe left seventh rib (arrow), noted only on the RPO view.
Bone scintigraphy 411 Fig. 3. Left lateral scintigram of the chest shows foci of increased activity involving three adjacent ribs posteriorly (arrowhead), plus additional foci involving three different ribs anteriorly (arrow). The posterior image more clearly delineates the three posterior rib fractures. References 1. Schimelpfenig, T. Epidomiology of wilderness injuries: the NOLS experience. Wild Med (Lett) 1992; 9: 6. 2. Matin, P. Basic principles of nuclear medicine techniques for detection and evaluation of trauma and sports medicine injuries. Seminars in Nucl Med 1988; 18: 90-112. 3. O'Mara, R.E. Benign bone disease. In: Gottschalk, A., Hoffer, P.B. and Patchen, E.J., eds. Diagnostic Nuclear Medicine. Baltimore: Williams and Wilkins, 1988: 1033-75. 4. Holder, L.E. Clinical radionuclide bone imaging. Radio11990; 176: 607-14. 5. Matin, P. Bone scanning of trauma and benign conditions. In: Freeman, L. and Weillman, H., eds. Nuclear Medicine Annual 1982. New York, Raven, 1982: 81-118. 6. Rogers, L.F. Traumatic lesions of bones and joints. In: Juhl, J.H., Crummy, A.B., eds. Essentials ofradiographicimaging. Philadelphia: J.B. Lippincott, 1987: 34-84. 7. Rockett, J.F., Magill, H.L., Rockett, D.C. and Moinuddin, M. Stress injuries in endurance athletes. Appl Radio11991: 44-56. 8. Rupani, RD., Holder, L.E., Espinola, D.A. and Engin, S.1. Three-phase radionuclide bone imaging in sports medicine. Radio11985; 156: 187-96.