Position and anatomical landmarks
The procedure can be performed with the patient in a prone position, lying on his side, or a sitting position. In the latter two positions, the patient should assume a forward flexed or 'foetal' position. The sitting position is considered to be the most comfortable for the patient as well as for the pain specialist. It allows correct assessment of the midline and avoids the rotation of a lateral flexion position.
Determination of the right level can be made with reference to the iliac crest or by means of fluoroscopy. The skin is disinfected.
With the medial approach, local anaesthetic will first be infiltrated into the middle of the spinal processes. Thereafter, the subcutaneous tissue and supraspinal ligament are approached with an epidural needle. The latter offers enough resistance for the epidural needle to remain in position when it is released. Then the needle enters the interspinal ligament and the ligamentum flavum, both of which provide additional resistance. A false sensation of loss of resistance may occur upon entering the space between the interspinal ligament and the ligamentum flavum. The ligamentum flavum provides the greatest resistance to the epidural needle since it is almost entirely composed of collagen fibres. Breaking through this ligament to the epidural space is accompanied by a significant loss of resistance. When injecting medication into the epidural space, normally no resistance is felt since it is filled with fat, blood vessels, lymph tissue and connective tissue. The epidural space is 5-6 mm wide at the L2/L3 level when the patient is in a flexion position. In addition, injection of contrast agent can verify the correct positioning in the epidural space. When blood is aspirated, the needle must be reoriented. When cerebrospinal fluid is aspirated, the procedure must be repeated at another level. In the latter case, an overflow of cerebrospinal fluid is possible. Therefore, this procedure must be carried out with caution. Classically, infiltration consists of an injection of a local anesthetic with a corticosteroid.
- Dural puncture with or without transient headache.
- Aseptic meningitis, arachnoiditis, epidural abscess.