Development of spondylolytic olisthesis in adolescents

Abstract

Background context: Although it has been well documented that slippage in patients with spondylolysis is most prevalent during the growth period, the exact time when slippage initiates and halts during the growth period is still unknown. Moreover, the contribution of spinal deformities, such as wedging of the vertebral body to the slippage, remains controversial.

Purpose: To clarify when slippage in pediatric spondylolysis initiates and halts. Study design: Retrospective study. Patient sample: We radiographically examined 46 athletes under 18 years of age with spondylolysis at the fifth lumbar vertebra (L5). The mean age at the first consultation was 13.3 years. The average follow-up period was 6.0 years. Outcome measures: Longitudinal observation of slippage at L5 on radiogram in correlation with the maturity of the lumbar spine. Methods: From a lateral radiogram of each patient, percent slippage, lumbar index (LI), and skeletal age of the affected vertebra were measured. Changes in the percent slippage over time were investigated, and the correlation between the percent slippage and LI was analyzed. Results: From the cartilaginous stage to the apophyseal stage, the slippage increased in 80.0% of the patients (16 of 20). From the cartilaginous stage to the epiphyseal stage, slippage increased in 11.1% of the patients (3 of 27). None of the patients (0 of 22) showed an increase after the epiphyseal stage. In 20 patients in whom slippage increased during the follow-up period, the percent slippage at the final consultation and the LI at the first consultation showed no significant correlation; however, the percent slippage and the LI at the final consultation were significantly (p<.01) correlated. Conclusion: In conclusion, slippage was more prevalent in individuals of a younger skeletal age whose lumbar spine was immature, and it halted during the epiphyseal stage when the growth period was over and the vertebra matured. Furthermore, the results suggest that wedge deformity of an affected vertebra might be the result rather than the cause of slippage.

Introduction

Spondylolysis is not a rare condition in children and adolescents. Wiltse et al. indicated that the basic lesion of spondylolysis was a fatigue fracture 1, 2, and many clinical studies have supported this assumption 3, 4, 5, 6. In clinical practice, symptoms of patients with spondylolysis are usually mild 1, 7, and many physicians seem to think that defects of the pars interarticularis are not lesions that should be repaired. However, some pediatric patients with spondylolysis certainly show deformities of the lumbosacral spine, including wedging of the vertebral body and/or slippage 1, 8, 9, 10, 11. Saraste [12] reported that approximately 80% of patients with spondylolysis showed a slippage, and in one fifth of them exceeded 25% in the percent slip. We have demonstrated that wedging of the fifth lumbar vertebra and rounding of the upper end plate of the sacrum are not evident if the pars defect is in the early stage [9]. The degree of deformity increases as the stage of the pars defect advances and as slippage develops. These results suggest that the deformities are not the causes of spondylolysis or slippage and that they occur secondary to spondylolysis at the end plate. Thus, spondylolysis in pediatric patients may be the cause of subsequent spinal deformities and slippage.

The mechanism of slippage in children and adolescents has not been well demonstrated. Anatomically, in an immature spine, there is a growth plate between the vertebral body and the apophyseal ring. Farfan et al. [3] hypothesized that spondylolisthesis in children with spondylolysis was a slippage at the growth plate. Our previous clinical study using magnetic resonance imaging suggested that slippage of the lumbar spine secondary to pars defects occurred between the osseous and cartilaginous end plates, not through the disk [9]. Biomechanical studies have also shown that the site including the growth plate is the weakest link to anterior shearing forces 13, 14, 15. These results support Farfan's hypothesis, and it is not difficult to assume that the maturity of the spine is an important factor regarding the development of slippage in children and adolescents. Although it has been well documented that slippage in patients with spondylolysis is most prevalent during the growth period and is very rare thereafter 7, 16, 17, 18, the exact time when the slippage initiates and halts during the growth period is still unknown.

Thus, we retrospectively reviewed patients under the age of 18 who presented spondylolysis to study the relationship between the maturity of the lumbosacral spine and the development of slippage.