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A Paramedian Approach for Epidural Block: An Anatomic and Radiologic Description
  1. Johannes M. Boon, M.Med.,
  2. E. Prinsloo, B.Sc. and
  3. Russell P. Raath, M.Med.
  1. From the Department of Anatomy, Section of Clinical Anatomy, School of Medicine, Faculty of Health Sciences (J.M.B., E.P.), University of Pretoria, Pretoria, South Africa; and Little Company of Mary Hospital, Eugene Marais Hospital (R.P.R.), Pretoria, South Africa.
  1. Reprint requests: Professor Johannes M. Boon, Head, Section of Clinical Anatomy, Department of Anatomy, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa. E-mail: jmboon{at}


Background and Objectives Certain factors, such as intervertebral disc herniation, previous spinal surgery, and osteoarthritis may cause problems during the midline epidural procedure. The purpose of this study was to investigate the placement of the needle tip in an alternative paramedian approach in a cadaver, and radiographically measure the target interlaminar area at different levels (L3/L4; L4/L5; L5/S1) in different age groups.

Methods The placement of epidural needles by an anesthetist using an alternative paramedian approach on 36 cadavers was evaluated by subsequent dissection along the needle to determine the location of the needle’s terminal end. Radiographic measurements performed on anteroposterior lumbar spine x-rays in different age groups were used to determine the dimensions of the interlaminar area (horizontal, left vertical paramedian, and right vertical paramedian).

Results Measurements of the interlaminar area significantly diminished with increasing age at L3/L4 (except for the horizontal measurement), L4/L5 (except for the vertical left paramedian measurement), as well as at L5/S1 in all measurements.

Conclusion This anatomically-based study confirms needle placement through the interlaminar space using an alternative paramedian approach and may explain the difficulties encountered during placement of an epidural needle with increasing age.

  • Epidural anesthesia
  • Paramedian approach
  • Interlaminar area

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