SPINE Volume 31, Number 8, pp 909 –914 ©2006, Lippincott Williams & Wilkins, Inc. Low Back Pain in Pediatric Athletes With Unilateral Tracer Uptake at the Pars Interarticularis on Single Photon Emission Computed Tomography Masakazu Takemitsu, MD,*† Georges El Rassi, MD,* Patarawan Woratanarat, MD,*‡ and Suken A. Shah, MD*§ Study Design. Retrospective clinical study with radio- graphic and medical chart review. Objective. To study the clinical characteristics and out- come of pediatric athletes with low back pain and unilat- eral tracer uptake on single photon emission computed tomography (SPECT) at the pars interarticularis but no defect on radiographs. Summary of Background Data. Some pediatric ath- letes with low back pain have no findings on plain radio- graphs but a unilateral SPECT uptake at the pars interar- ticularis. However, little is known about these patients. Methods. Twenty-two pediatric athletes who had low back pain with increased tracer uptake on SPECT unilat- erally at the pars interarticularis but no defect on plain radiograph were evaluated. The following criteria were used for evaluation: age, male-to-female ratio, duration of symptoms, vertebral level, and presence of spina bifida occulta or scoliosis. Results. The average age was 12.3  2.5 years. The male-to-female ratio was 1.2:1. The average duration of symptoms was 21  23 weeks. Nineteen (86%) had in- creased uptake at L5. Six (27%) had spina bifida occulta and 8 (36%) had scoliosis. Eighteen (82%) patients showed an excellent outcome. The patients who pre- sented with a longer history of symptoms or a concomi- tant spina bifida occulta had an increased risk of having occasional aching with vigorous activity when compared with the patients who did not (P  0.05). Conclusions. Athletes who have low back pain and increased tracer uptake unilaterally at the pars interarticu- laris on SPECT are younger than those previously re- ported patients with spondylolysis proven by a defect on radiographs. Some of these lesions do progress to “frank” spondylolysis seen on radiographs, but favorable clinical outcomes from nonoperative treatment can be expected. Patients with a longer pain history or concom- itant spina bifida occulta may need careful follow-up because they are at increased risk of having occasional low back pain. Key words: bone scintigraphy, low back pain, spina bifida occulta, spondylolysis, stress reaction. Spine 2006; 31:909 –914 Low back pain is increasingly common in pediatric athletes. The pain interferes with their performance and may prevent them from playing sports. Spondylol- ysis and spondylolisthesis are highly associated with back pain in young athletes, 1–3 although there are ath- letes who have asymptomatic spondylolysis or spon- dylolisthesis. Micheli and Wood report that 47% of adolescents with a chief complaint of low back pain had spondylolysis, 4 whereas the incidence in the gen- eral adult population was reported to be 5%. 5 A high incidence of spondylolysis in athletes has also been reported in specific sports including gymnastics, 6 weightlifting, 7 football, 8,9 swimming, 10 and diving. 7 The etiology of spondylolysis has been explained mainly as an acquired stress fracture at the pars inter- articularis resulting from repetitive flexion and exten- sion motion of the lumbar spine. 11–15 Several authors address the importance of an early, accurate diagnosis of spondylolysis with bone scintigra- phy as leading to radiographic and clinical heal- ing. 13,16,17 The sensitivity of detecting a stress reaction at the pars is increased by the addition of single photon emission computed tomography (SPECT). 18 –20 With the advent of SPECT, pediatric athletes who complain of low back pain and who have no pars defect on radio- graphs but do have a unilateral stress reaction detected by SPECT are seen frequently in the sports medicine clinic. These patients are considered to have a prespon- dylolysis; however, little has been documented about them. In this study, we focused on pediatric athletes with a chief complaint of low back pain who presented with unilateral increased uptake on SPECT but no pars defect radiographically. Their clinical characteristics, including age, male-to-female ratio, history of traumatic episode, duration of symptoms, and incidence of spina bifida oc- culta and scoliosis, were evaluated retrospectively. The severity of their low back pain at follow-up was also documented and analyzed for predictors that may affect the clinical prognosis. From the *Department of Orthopaedics, Nemours Children’s Clinic– Wilmington, Alfred I. duPont Hospital for Children, Wilmington, DE; †Department of Orthopaedic Surgery, Asahikawa Medical College, Asahikawa, Japan; ‡Department of Orthopaedics, Faculty of Medicine Ramathibodi Hospital, Bangkok, Thailand; and §Department of Orthopaedic Surgery, Jefferson Medical College, Philadelphia, PA. Acknowledgment date: January 20, 2004. First revision date: May 9, 2004. Second revision date: May 26, 2005. Acceptance date: May 26, 2005. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Address correspondence and reprint requests to Suken A. Shah, MD, Alfred I. duPont Hospital for Children, Department of Orthopaedics, 1600 Rockland Road, PO Box 269, Wilmington, DE 19899. E-mail: sshah@nemours.org 909