PEDIATRIC STRESS FRACTURES: A PICTORIAL ESSAY Nirav H. Shelat, DO, Georges Y. El-Khoury, MD

ABSTRACT More children are participating in organized and recreational athletics at a younger age. It has been well documented that increased athletic specialization and year-round activities have resulted in higher incidences of overuse injuries, including stress fractures and stress reactions. Initially, stress fractures can be radiographically occult. Continued stress on the injured bone or cartilage can lead to progressive radiographic changes. Because of the prevalence of these injuries, both orthopedic surgeons and radiologists should be aware of the radiographic and magnetic resonance imaging (MRI) features of common stress fractures in children. This article reviews frequently encountered stress fractures involving various bones in the pediatric population.

parts of the musculoskeletal system in children, are common sites for stress fractures. Abnormal stresses at these sites may result in disruption of endochondral ossification, ultimately resulting in physeal widening5. Repetitive microtrauma also leads to bony cortical defects and stress fractures, which can be in the form of fatigue fractures (excessive forces on normal bone) or insufficiency fractures (normal forces on abnormal bone)2. This article reviews the classic radiographic and MR findings of common stress fractures in children. Spine: Spondylolysis Spondylolysis is a stress fracture which occurs through the pars interarticularis, and occasionally through the pedicle. It is the result of repeated bouts of extension and rotation about the spine6. It has been observed with higher frequency not only in young athletes, but

INTRODUCTION A recent increase in the number of children participating in competitive sports has resulted in an increase in stress injuries1. These stress injuries can be difficult to diagnose. In young children, the clinical examination is often difficult given the inability of children to provide detailed histories or fully participate in the physical exam. Detection of the hallmark features of common stress injuries on both radiographs and MRI can aid in the diagnosis. Stress fractures are the result of repetitive forces on the musculoskeletal system that has not had sufficient time to recover2. In children, factors such as weaker osteochondral junctions, thinner cortices, hormonal changes, and decreased mineralization predispose to stress fractures3,4. This is further compounded by participation in sports with demanding schedules which may not allow adequate time for the child to recover. The physis and the apophysis, which are among the weaker Nirav H. Shelat, DO Georges Y. El-Khoury, MD University of Iowa Hospitals and Clinics 200 Hawkins Drive 01043 JPP Iowa City, IA 52242 319-356-3654 [email protected] [email protected] The authors have no conflicts of interest to disclose.

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Figure 1. 13-year-old basketball player complaining of low back pain. (A) Axial T1 image demonstrates transversely oriented low signal (arrow) through the L5 pedicle and pars. (B) Axial T2 image demonstrates corresponding edema (arrow), confirmed on sagittal T1 (C) and STIR (D) sequences (arrows). Findings are consistent with unilateral stress fracture through the left pars interarticularis.

Pediatric Stress Fractures: A Pictorial Essay

Figure 2. 16-year-old baseball pitcher with recent onset of low back pain. (A) Axial T1, (B) T2 and (C) sagittal STIR images demonstrates bone marrow edema (arrows) in the left L3 pedicle, consistent with non-displaced stress fracture.

in certain populations that require repetitive flexion and extension of their spine, such as the Eskimos7, 8. Lower back pain in the young patient should prompt a search for spondylolysis7. Conventional computed tomography (CT), MRI, and single photon emission computed tomography (SPECT) are all acceptable diagnostic modalities. CT is superior to MRI in the detection of spondylolysis, but involves the use of ionizing radiation. SPECT can help confirm the diagnosis in cases which are indeterminate on MRI9, 10. Typical MRI findings include low signal on T1 and increased signal on T2 or STIR sequences at the pars interarticularis and/or pedicle (Figures 1 & 2). Shoulder

Figure 3. Collegiate American football player with shoulder pain and known lesser tuberosity avulsion. (A) Axillar y shoulder radiograph performed to follow up lesser tuberosity avulsion demonstrates an unfused apophysis (arrow) at the acromion. (B) Follow up MRI demonstrates edema at the apophysis (arrow), consistent with acromial apophysiolysis.

Acromial Apophysiolysis/Os Acromiale One to four ossification centers are seen at the acromion by 15-18 years of age. From anterior to posterior, these ossification centers are the pre-acromion, the mesoacromion, the meta-acromion, and the basi-acromion. Failure of fusion of the acromion in the background of chronic repetitive traction forces from the deltoid has been termed acromial apophysiolysis11. Without healing, this may progress to an os acromiale, which can in turn lead to impingement symptoms in the shoulder. Patients typically present with chronic shoulder pain of insidious onset. In younger patients, differentiating between an os acromiale and normal apophyseal development can be challenging, as the age range of acromial fusion can vary from 18 – 2512. However, irregular cortical margins and abnormal marrow signal with adjacent bony edema favors the diagnosis of acromial apophysiolysis13 (Figure 3). Little Leaguer’s Shoulder “Little leaguer’s shoulder” is a term used to describe injury to the proximal humeral physis typically caused by repetitive overhead throwing. It is often observed in Volume 36   139

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Figure 5. 14-year-old baseball pitcher with medial elbow pain for 1 month duration. (A) AP radiograph demonstrates asymmetric widening of the right medial epicondyle physis (arrow). (B) The left elbow, submitted for comparison, is unremarkable. (C,D) MRI performed the following day demonstrates edema within the medial condyle epiphysis (arrow) and the adjacent metaphysis of the humerus. The ulnar collateral ligament (not fully shown) was intact.

A

Figure 4. 13-year-old baseball pitcher. AP radiograph of the (A) right shoulder shows diffuse widening of the right proximal humeral physis (arrow). (B) For comparison, the left shoulder demonstrates normal width of the physis.

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male baseball pitchers between the ages of 11 and 16 in whom the excessive rotational forces of overhead throwing lead to physeal injury14. Patients tend to present with focal pain over the anterolateral shoulder that is worse with overhead throwing. Radiographs demonstrate physeal widening and irregularity15 (Figure 4). MR findings include similar findings of widening of the physis, along with marrow edema on fluid sensitive sequences16. Elbow: Little Leaguer’s Elbow “Little Leaguer’s elbow” is a term used to describe injury to the medial epicondylar apophysis17. Patients are usually young adolescent pitchers or catchers presenting with medial elbow pain either with direct palpation or valgus stress to the elbow. Children can present with mild flexion contracture at the elbow secondary to pain17. While generally the physical examination is sufficient

Pediatric Stress Fractures: A Pictorial Essay

B

C

A Figure 6. 11-year-old gymnast just days away from a championship meet, with ongoing wrist pain. (A) AP radiograph of the wrist is essentially unremarkable. Specifically, there is no evidence of physeal widening, irregularity, or fraying. (B, C) T1 and T2FS coronal MRI images demonstrate marrow edema through the distal metaphyses of the radius and ulna (white arrows), and to a lesser extent, the radial and ulnar styloids (red arrows).

for making the diagnosis, radiographs demonstrate widening or fragmentation of the apophysis (Figure 5). The contralateral asymptomatic elbow can be used for reference in determining physeal widening. MRI demonstrates marrow edema and aids in determining the integrity of the common flexor tendon and ulnar collateral ligament18. Wrist: Gymnast’s Wrist Gymnasts frequently start intense training at a young age, when repetitive stress on the upper extremities can lead to physeal injury. Mechanical forces of dorsiflexion and compression triggers physeal injury at the distal radius19. Similar forces can lead to the same injury in weight lifters. Analogous to Little Leaguer’s shoulder, radiographs can demonstrate widening and fraying or irregularity of the physis, while MRI demonstrates edema through the metaphysis (Figure 6). Severe or chronic

disease can lead to premature fusion and positive ulnar variance, TFCC injury, and scapholunate or lunotriquetral ligament disruption19. Pelvis Sacral Stress Fractures Sacral stress fractures are known to have a higher incidence in female athletes, particularly in runners21. The female athlete triad describes the relationship between caloric imbalance, hormonal dysregulation, and impaired bone health22. The injury, therefore, has components of both a fatigue and insufficiency fracture. Radiographs are often normal, while MRI demonstrates linear low signal intensity on T1 images with corresponding edema (Figure 7). In endurance athletes, similar findings of a stress fracture can be seen in the inferior pubic rami23 (Figure 8).

Figure 7. 18-year-old female cross countr y runner with gradually worsening low back pain. (A) Coronal T1, (B) coronal STIR, and (C) oblique coronal T2 fat saturated images demonstrate a stress fracture of the left sacral ala extending to the sacral foramen.

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Figure 8. 15-year-old female cross countr y runner with pubic pain, referred for MRI to “rule out sports hernia.” (A) Axial T1 and (B) T2FS images demonstrate a healing fracture (arrows) through the left inferior pubic ramus. This was radiographically occult.

Pelvic Apophyseal Injury Traction apophysitis in the pelvis is a commonly recognized overuse injury in children. When chronic, children can present with dull pelvic or hip pain. This injury is more frequently found in athletes involved in twisting activity resulting in traction on the apophyses, such as dancers, runners, football and lacrosse players. The most common sites of injury include the anterior superior iliac spine (origin of the sartorius and tensor fasciae lata), the anterior inferior iliac spine (origin of the rectus femoris), and the ischial tuberosity (origin of the hamstrings)24. Radiographs can demonstrate a spectrum of findings from cortical irregularity to frank avulsion of bone. MRI most typically demonstrates marrow edema and variable signal intensity in the corresponding tendons, depending on the extent of their injury (Figure 9).

Femur: Stress Fracture Femoral stress fractures are relatively rare in comparison to stress fractures of the tibia, fibula, and foot25. Stress fractures of the femur result from repetitive loading, and are most common in endurance runners, jumpers, and dancers. Repetitive loading results in subperiosteal bone resorption and microfractures which are not given sufficient time to heal. Femoral stress fractures can present with pain at the groin, hip, or knee, and are typically aggravated by activity. While the most common site of fracture is the femoral neck, fractures can occur anywhere along the femoral diaphysis (24). While lacking in sensitivity early in the disease, radiographs will classically show linear sclerosis, periosteal elevation, and cortical thickening, consistent with a protracted healing response. MRI reveals the problem earlier, showing linear low signal intensity on T1 sequences and corre-

Figure 9. 13-year-old baseball player (shortstop) with gradually worsening groin pain. (A) Axial T1 and (B) axial T2FS images demonstrate bone marrow edema at the left ischial tuberosity (arrows). The hamstring tendons appeared normal. (C) Retrospective review of the radiograph shows subtle cortical irregularity along the lateral aspect of the left ischium (arrow).

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Pediatric Stress Fractures: A Pictorial Essay

Figure 10. 9-year-old boy with histor y of renal transplant on chronic immunosuppressive therapy presenting with thigh pain. (A, B) Frontal and lateral radiographs demonstrate a linear band of sclerosis (arrow in A) through the distal femoral metaphysis and periosteal reaction (arrow in B), consistent with healing stress fracture. Incidental note is made of fracture progression through a non-ossifying fibroma along the medial cortex.

Figure 11. 16-year-old female runner with prior histor y of pelvic stress fracture, now complaining of tibial pain. Sagittal STIR image demonstrates edema at the insertion of the patellar ligament (arrow), consistent with active Osgood Schlatter disease. There is mild pretibial edema in the soft tissues anterior to the tuberosity. There is minimally increased signal within the ligament itself.

Figure 12. 3-year-old girl with a limp. Lateral radiograph demonstrates an area of uninterrupted periosteal reaction along the posteromedial aspect of the left tibia at the middle third of the tibia, consistent with stress fracture.

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N. H. Shelat, G. Y. El-Khoury Table I. Fredericson MRI Classification System for Tibial Stress Injur y Grade

MR Findings

0

Normal

1

Periosteal edema only

2

Periosteal edema and bone marrow edema (on T2 only)

3

Periosteal edema and bone marrow edema (on T1 and T2)

4a

Multiple foci of intracortical signal abnormality and bone marrow edema on both T1 and T2

4b

Linear areas of signal abnormality on both T1 and T2

Figure 13. Two different patients. The patient in (A) is a 12-year old-girl who had been immobilized following a Lisfranc injur y. The second patient in (B) is a 12-year-old girl who had been immobilized following medial cuneiform osteotomy. (A) Lateral radiograph demonstrates a vertically oriented sclerotic line in the calcaneal tuberosity (arrow). (B) AP radiograph demonstrates periosteal reaction (arrow) surrounding the second metatarsal, consistent with stress fracture.

sponding edema on fluid sensitive images (Figure 10). Subperiosteal fluid, when present, is a useful finding to confirm the diagnosis3. Tibia/Fibula Osgood-Schlatter Disease Osgood-Schlatter is one of the most common causes of anterior knee pain in young athletes, caused by repetitive microtrauma and subsequent traction apophysitis of the tibial tuberosity. It is commonly seen in 12-15 year old boys or 8-12 year old girls who participate in jumping activities24. Patients present with anterior knee pain and swelling. Physical examination is usually diagnostic, with radiographs demonstrating soft tissue edema overlying the anterior tibial tuberosity, and some degree of fragmentation and irregularity of the tibial tubercle. MRI demonstrates edema in the tibial tuberosity and distal patellar tendon. Hoffa’s fat pad may also show increased signal on fluid sensitive sequences (Figure 11).

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Figure 14. 14-year-old boy involved in multiple sports presents with worsening ankle pain. (A) Sagittal T1 and (B) T2FS images of the ankle demonstrate linear signal abnormality in the distal tibia consistent with stress fracture (white arrow). Multiple additional areas of signal abnormality (red arrows) are also consistent with stress reaction.

Diaphyseal Stress Fracture A common site for stress fractures in adolescents is the tibia, followed by the fibula25. They are commonly found in children participating in football, soccer, tennis, and running. Radiographs demonstrate cortical irregularity and periosteal reaction, typically along the posteromedial proximal third of the tibial shaft (Figure 12). MRI can be useful in equivocal cases. The Fredericson classification system classifies MR findings for tibial stress injury, with grades 1-3 deemed as “stress response” and grade 4 as “stress fracture”26 (Table I).

Pediatric Stress Fractures: A Pictorial Essay

Figure 15. 8-year-old girl with foot pain and a limp. (A) Lateral radiograph demonstrates subtle sclerosis in the cuboid (arrow). (B) Follow up MRI demonstrates a linear low T1 signal intensity focus (arrow) through the lateral aspect of the cuboid with (C) corresponding edema on T2 (arrow), consistent with stress fracture.

Ankle and Foot In children, the most common sites of stress fractures in the foot are the metatarsals and calcaneus, followed by the cuboid, talus, and navicular27. It has been postulated that following lower extremity immobilization for conventional traumatic fractures, the child is more susceptible to subsequent stress fracture distally in the ipsilateral extremity27. At our institution, a ten year informal review of lower extremity fractures in children who were previously immobilized for other fractures yielded several cases of stress fractures (Figure 13). Radiographic findings of sclerosis and marrow edema are equivalent to stress fractures at other sites (Figure 14, 15). CONCLUSIONS With the increasing number of children participating in sports, it is important for orthopedists and radiologists to be aware of the radiographic and MRI findings associated with common overuse injuries. Familiarity with these findings leads to prompt diagnosis and helps prevent future disability. REFERENCES 1. Caine D, DiFiori J, Maffulli N. Physeal injuries in children’s and youth sports: reasons for concern? Br J Sports Med. 2006 Sep;40(9):749-60. 2. Anderson MW, Greenspan A. Stress fractures. Radiology. 1996 Apr;199(1):1-12. 3. Jaimes C, Jimenez M, Shabshin N, Laor T, Jaramillo D. Taking the stress out of evaluating stress injuries in children. Radiographics. 2012 MarApr;32(2):537-55.

4. Jones BH, Harris JM, Vinh TN, Rubin C. Exercise-induced stress fractures and stress reactions of bone: epidemiology, etiology, and classification. Exerc Sport Sci Rev. 1989;17:379-422. 5. Laor T, Wall EJ, Vu LP. Physeal widening in the knee due to stress injury in child athletes. AJR Am J Roentgenol. 2006 May;186(5):1260-4. 6. Tower SS, Pratt WB. Spondylolysis and associated spondylolisthesis in Eskimo and Athabascan populations. Clin Orthop Relat Res. 1990 Jan;(250):171-5. 7. Trainor TJ, Wiesel SW. Epidemiology of back pain in the athlete. Clin Sports Med. 2002 Jan;21(1):93-103. 8. Simper LB. Spondylolysis in Eskimo skeletons. Acta Orthop Scand. 1986 Feb;57(1):78-80. 9. Campbell RS, Grainger AJ, Hide IG, Papastefanou S, Greenough CG. Juvenile spondylolysis: a comparative analysis of CT, SPECT and MRI. Skeletal Radiol. 2005 Feb;34(2):63-73. 10. Dunn AJ, Campbell RS, Mayor PE, Rees D. Radiological findings and healing patterns of incomplete stress fractures of the pars interarticularis. Skeletal Radiol. 2008 May;37(5):443-50. 11. Roedl JB, Morrison WB, Ciccotti MG, Zoga AC. Acromial apophysiolysis: superior shoulder pain and acromial nonfusion in the young throwing athlete. Radiology. 2015 Jan;274(1):201-9.201–209. 12. K othar y P, Rosenberg ZS. Skeletal developmental patterns in the acromial process and distal clavicle as observed by MRI. Skeletal Radiol. 2015 Feb;44(2):207-15.

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N. H. Shelat, G. Y. El-Khoury 13. Winfeld M, Rosenberg ZS, Wang A, Bencardino J. Differentiating os acromiale from normally developing acromial ossification centers using magnetic resonance imaging. Skeletal Radiol. 2015 May;44(5):667-72. 14. Carson WG Jr, Gasser SI. Little Leaguer’s shoulder. A report of 23 cases. Am J Sports Med. 1998 Jul-Aug;26(4):575-80. 15. Obembe OO, Gaskin CM, Taffoni MJ, Anderson MW. Little Leaguer’s shoulder (proximal humeral epiphysiolysis): MRI findings in four boys. Pediatr Radiol. 2007 Sep;37(9):885-9. 16. Song JC, Lazarus ML, Song AP. MRI findings in Little Leaguer’s shoulder. Skeletal Radiol. 2006 Feb;35(2):107-9. 17. Bennett, D Lee; El-Khour y, Georges Y. Pearls and pitfalls in musculoskeletal imaging: variants and other difficult diagnoses. Cambridge : Cambridge University Press, 2013. Chapter 28, Little Leaguer’s Elbow: What is it? p. 58-59. 18. Wei AS, Khana S, Limpisvasti O, Crues J, Podesta L, Yocum LA. Clinical and magnetic resonance imaging findings associated with Little League elbow. J Pediatr Orthop. 2010 Oct-Nov;30(7):715-9. 19. Dwek JR, Cardoso F, Chung CB. MR imaging of overuse injuries in the skeletally immature gymnast: spectrum of soft-tissue and osseous lesions in the hand and wrist. Pediatr Radiol. 2009 Dec;39(12):1310-6.

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21. Chen YT, Tenforde AS, Fredericson M. Update on stress fractures in female athletes: epidemiology, treatment, and prevention. Curr Rev Musculoskelet Med. 2013 Jun;6(2):173-81. 22. Nattiv A, Loucks AB, Manore MM, Sanborn CF, Sundgot-Borgen J, Warren MP; American College of Sports Medicine. American College of Sports Medicine position stand. The female athlete triad. Med Sci Sports Exerc. 2007 Oct;39(10):1867-82. 23. Williams TR, Puckett ML, Denison G, Shin AY, Gorman JD. Acetabular stress fractures in military endurance athletes and recruits: incidence and MRI and scintigraphic findings. Skeletal Radiol. 2002 May;31(5):277-81. 24. Bedoya MA, Jaramillo D, Chauvin NA. Overuse injuries in children. Top Magn Reson Imaging. 2015 Apr;24(2):67-81. 25. Bennell KL, Brukner PD. Epidemiology and site specificity of stress fractures. Clin Sports Med. 1997 Apr;16(2):179-96 26. Fredericson M, Bergman AG, Hof fman KL, Dillingham MS. Tibial stress reaction in runners. Correlation of clinical symptoms and scintigraphy with a new magnetic resonance imaging grading system. Am J Sports Med. 1995 Jul-Aug;23(4):472-81. 27. Oestreich AE, Bhojwani N. Stress fractures of ankle and wrist in childhood: nature and frequency. Pediatr Radiol. 2010 Aug;40(8):1387-9.

Pediatric stress fractures: a pictorial essay.

More children are participating in organized and recreational athletics at a younger age. It has been well documented that increased athletic speciali...
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