Demographic variables: |
   • Women versus men |
   • Age < 40 years versus > 40 years |
   • Smoking versus non-smoking |
Anamnestic and neurological variables: |
   • Influence of back extension versus no influence |
   • Predominant low back pain versus leg pain |
   • Quetelet index < 25 versus > 25 |
Radiological variables: |
   • Low disc height versus high disc height |
   • Nerve root compression underneath pseudojoint versus nerve root compression between pedicle and slipped disc |
   • Grade I versus grade II spondylolytic spondylolisthesis |
   • Small cross section versus large cross section of neuroforamen |
   • Low grade versus high grade epidural fat |