Introduction:

Spondylolysis, a stress fracture of the pars interarticularis, is a common occurrence in adolescent athletes with low back pain. It has been reported that T2-weighed fat-saturated magnetic resonance imaging (MRI) is useful for the detection of bone marrow edema (BME) in the pedicle in the early stage of spondylolysis, however quantitative assessment of BME in spondylolysis has not been reported. The purpose of this study was to quantitatively evaluate BME in the pedicle on MRI for adolescent athlete patients with spondylolysis.

Methods:

Adolescent athletes with spondylolysis, including the symptom of low back pain, were enrolled in this study. The sporting activity of patients was restricted, and a hard brace was attached to the spine. BME were defined as the area of increased signal intensity (SI) around the pars interarticularis on T2-weighed fat-saturated MRI. The BME range of interest was taken on T2-weighed fat-saturated MRI, and the SI of the BME (SI_edema) was measured. The contrast ratio (CR) between the SI of the BME and SI of the spinal cord (SI_cord) was calculated (CR_edema=(SI_edema-SI_cord)/(SI_edema+SI_cord)). The CR of the normal pedicle was measured as a control (CR_control=(SI_control-SI_cord)/(SI_control+SI_cord)).

Results:

There were 32 men and 1 woman, and the mean age was 15.2 years (range: 12 to 18 years). The athletic events comprised 18 football, 10 baseball, 2 basketball and tennis, and 1 volleyball. The level of sporting activity was school or club team. The spinal level of spondylolysis was L2 in 2 patients, L3 in 3 patients, L4 in 7 patients, and L5 in 21 patients. The laterality of spondylolysis was right in 10 patients, left in 7 patients and both in 16 patients. Staging based on computed tomography (CT) showed early stage in 21 patients, progressive stage in 12 patients, and no terminal stage. The mean duration from onset of low back pain to the first MRI was 2.2 weeks (range: 1 to 8 weeks). After the treatment with spinal hard brace and restriction of sporting activity, 25 patients (75.8%) showed bone union on CT at 3 months. The mean CR of the edema and normal pedicle at the first visit was 0.506 (range: 0.097 to 0.804) and 0.137 (range: -0.741 to 0.572), respectively. The CR of the edema was significantly higher than that of the normal pedicle (P<0.01). On MRI one month after the first visit, the CR of the edema decreased to 0.204 (range: -0.152 to 0.517). The CR of the edema one month later was significantly lower than that at the first visit (P<0.01).

Discussion:

Quantitative assessment of BME using CR on MRI is useful for evaluating the healing process of spondylolysis.