SPINE Volume 34, Number 13, pp 1399 –1401 ©2009, Lippincott Williams & Wilkins Prevalence of Vertebral Pars Defects (Spondylolysis) in a Population With Osteogenesis Imperfecta Wiebe C. Verra, Bsc,* Hans J. Pruijs, MD, PhD,* Erik J. Beek, MD, PhD,† and Rene´ M. Castelein, MD, PhD* Study Design. We performed a retrospective study of spinal roentgenograms of a large cohort of patients suf- fering from osteogenesis imperfecta. Objective. To determine the prevalence of vertebral pars defects (spondylolysis) in patients with osteogenesis imperfecta. Summary of Background Data. Patients suffering from osteogenesis imperfecta are known to be prone to patho- logic fractures. Pathologic fractures due to microtraumas, repetitive activities, and posture acting together on a con- genitally weakened pars interarticularis may lead to ver- tebral pars defects. The prevalence of vertebral pars de- fects in patients with osteogenesis imperfecta has never been studied before to our knowledge. Methods. We performed a retrospective study of pos- terior-anterior and lateral, standing, roentgenograms of the spine of patients with osteogenesis imperfecta for the occurrence of vertebral pars interarticularis defects. Results. The patients (5.3%) in our series showed ver- tebral pars defects, this is not significantly different from the prevalence of vertebral pars defects in the general population. Conclusion. 5.3% of the patients with osteogenesis imperfecta showed vertebral pars defects, this does not differ significantly from the occurrence in the general pop- ulation. Key words: vertebral pars defects, osteogenesis im- perfecta, spondylolysis, spondylolisthesis, prevalence. Spine 2009;34:1399 –1401 Osteogenesis imperfecta (OI) is a genetic collagen dis- order characterized by different degrees of bone fragil- ity and low bone mass due to a mutation in 1 of the 2 genes that encode the -chains of collagen type 1; COL1A1 and COL1A2. 1 The disorder affects approx- imately 1 in 20.000 births. 2 Because of the features of OI, patients are known to be prone to pathologic frac- tures. Defects of the vertebral pars interarticularis, known as spondylolysis, are generally supposed to be stress fractures. 3 Although vertebral body deformities, sco- liosis, kyphosis, and basilar impression are character- istic spinal manifestations of OI, 4 so far only few cases of spondylolysis have been described in patients suf- fering from OI. Besides a few case reports and an in- cidental description in the literature of patients suffer- ing from OI with pars defects, to our knowledge a systematic study concerning the prevalence of verte- bral pars defects in patients with OI has never been performed. We performed a retrospective radio- graphic study in a relatively large group of young pa- tients with different types of OI to determine the prev- alence of defects in the pars interarticularis. Materials and Methods The Wilhelmina Children’s Hospital of the University Medical Centre Utrecht, the Netherlands, is a tertiary referral center for all patients in the Netherlands with osteogenesis imperfecta. As part of the general work-up of these patients, a standing pos- terior-anterior and lateral roentgenogram of the spine is taken to search for vertebral impressions, scoliosis, basilar impres- sions, and other spinal deformities. All spinal roentgenograms were examined by an experienced pediatric radiologist (EB) and judged for the presence of vertebral pars defects, pars elon- gations, and slipped vertebrae (spondylolisthesis). The severity of a spondylolisthesis was graded according to Meyerding. 5 Patient’s age at time of the last roentgenogram, type of OI according to Sillence, 6 and gender were recorded. Since spon- dylolysis is considered a developmental disorder that does not occur at a very young age, patients under the age of 6 were excluded. Statistics were performed with the Statistical Package of Social Sciences version 12. Results Radiograms of 143 patients with OI were available for analysis. Thirty patients were excluded from the study because of an age below 6, none of them showed a spon- dylolysis. The 113 remaining patients consisted of 61 girls and 52 boys. The average age at the time the evaluated roent- genograms were made was 12.5 years old (6 –24 years old). The occurrence of the different types of OI is summa- rized in Table 1. Patients with pars defects are summa- rized in Table 2. A total of 6 patients with vertebral pars defects and different types of OI were found in the studied group, this is 5.3%. In the general population, 4.4% is reported as prevalence for spondylolysis at the age of 6, with a re- ported increase to 6.0% at the age of 18. 2 The difference From the *Department of Orthopedics, Wilhelmina Children’s Hospi- tal, University Medical Center Utrecht, Utrecht, The Netherlands; and †Department of Pediatric Radiology, Wilhelmina Children’s Hospital Utrecht, Utrecht, The Netherlands. Acknowledgment date: October 21, 2008. Revision date: December 9, 2008. Acceptance date: December 29, 2008. 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 R. M. Castelein, MD, PhD, Department of Orthopedics, Wilhelmina Children’s Hospital / University Medical Center Utrecht, Utrecht, PO Box 85500, 3508 GA Utrecht, The Netherlands; E-mail: r.m.castelein@umcutrecht.nl 1399