Andersen, K. Skou, and Otto Sneppen. “Comparative Study of Myelography Filling Defects in Root Sheaths and Operative Findings in Cases of Suspected Lumbar Intervertebral Disc Herniation”. Acta Orthopaedica, vol. 39, no. 1-3, Jan. 1968, pp. 312-20, doi:10.3109/17453676808989464.