A clinical trial will be conducted comparing healing of a posterior lumbar vertebra stress reaction in children treated either with cessation of sports activities for a period of six weeks and wearing a soft spinal brace 16 hours per day or cessation of sports activities only. Primary outcome is the change in stress reaction on MRI at 6 weeks compared to pre-treatment MRI.

A clinical trial will be conducted comparing healing of an acute posterior lumbar vertebra stress reaction in children treated either with cessation of sports activities for a period of six weeks and wearing a soft spinal brace 16 hours per day or cessation of sports activities only. Inclusion criteria will be a child or an adolescent aged between 8 and 18 years with a posterior lumbar vertebra stress reaction uni- or bilaterally in one or more lumbar vertebra. Bone marrow edema in the dorsal parts of the lumbar spine must be confirmed in a recent (under 3 weeks) MRI examination. Exclusion criteria will be a fracture line (spondylolysis), spondylolisthesis or other abnormalities on lumbar CT examination. Other exclusion criteria are skeletal disorder or not consenting to be a patient in this study.

110 Patients/ participants are randomized into two groups. The first group of 55 patients is treated with cessation of all sports activities and a soft spinal brace. The other group is treated only with cessation of sports activities. Treatment in both groups is 6 weeks, starting at doctor's appointment after all necessary examinations are complete. Minimum follow-up will be 6 months.

In the beginning of this study a blood plasma vitamin D values will be measured from all our patients. Patients with D-vitamin values below 50 nmol/l will receive vitamin D prescription.

Lateral x-ray picture of the lumbar spine is taken with axial loading (standing) from all study patients at the beginning and at the end (6 months) of the study. This enables to see the possible change in sacral slope during the 6-month follow-up. The possible change will then indicate a change in lumbar posture during this time. This is important to clarify whether lumbar posture has a role in the etiology - and treatment - of lumbar vertebra stress injury.

According to statistical power analysis a total of 110 patients - 55 in each group- will be needed to provide evidence for the effectiveness or no effectiveness of a soft spinal brace on the natural history of pars interarticularis stress reaction.

Primary outcome is the change in stress reaction on MRI at 6 weeks compared to pre-treatment MRI.

Secondary outcomes are:

1. SRS-24 - (Scoliosis Research Society) score at the beginning of the treatment and during the six-month follow-up ( at 0, 6 weeks, 6 months appointments)
2. Back and lower extremity pain at the beginning of the treatment and during the six months follow-up (pain drawing including VAS-score (Visual Analogue Pain Score) in children under 16 years old, Oswestry disability index including VAS-score in patients over 16 years old)
3. Relapse of symptoms during the six months follow-up
4. Vitamin D values at the beginning of the study
5. "Pain time table" during the 6-week period of treatment - to clarify the moment of ending of pain during treatment.
6. Change in sacral slope on lateral lumbar x-ray with axial loading during the 6 months of follow-up.
7. Pain in one-legged back extension test at 0, 6 weeks and 6 months follow-up appointments

Inclusion Criteria:

• Uni- or bilateral acute stress reaction of pars interarticularis or other part of posterior lumbar vertebra on MRI
• No signs of fracture line on MRI or CT
• Age between 8 and 18 years
• Written informed consent
• Low back pain

Exclusion Criteria:

• Spondylolysis
• Spondylolisthesis
• Systemic skeletal disorder (Osteogenesis imperfecta, skeletal dysplasia), osteoporosis
• Systemic diseases (e.g. Diabetes mellitus type 1, rheumatic diseases, inflammatory bowel diseases, Marfan syndrome)
• Other bony abnormalities seen on lumbar MRI examination (e.g. Scheuermann disease, L5 sacralisation, spina bifida)

Not necessary