Impact of Epidural Anesthesia on Low Back Function

The lumbar (or lower back) region is made up of five vertebrae (L1-L5), sometimes including the sacrum. Stability of the spine is provided by the ligaments and muscles of the back and abdomen (Floyd and Thompson, 2008).

The primary biomechanical function of the spine is to provide structural support, to allow the body to move freely, and to protect the spinal cord and nerves. Muscles balance external loads to the spine, which supports the load and allows for the motion through its multilevel joint arrangement (Dreischarf et al., 2016).

Low back pain (LBP) is a common minor yet unpleasant complication after epidural anesthesia. Different mechanisms are suggested such as needle trauma and myotoxicity of local anesthetic (Louizos et al., 2005) and incidence of backache after epidural anaesthesia might be expected to be higher than that after spinal anaesthesia (Brown and Elman, 1961).

In most episodes of low back pain, a specific underlying cause is not identified or even looked for, with the pain believed to be due to mechanical problems such as muscle or joint strain (Casazza, 2012). Most cases are idiopathic but usually attributable to muscle strain or ligament injury; found in 65% to 70% of patients with mechanical chronic back pain (Cohen et al., 2008) while totally mechanical low back pain is reported as the cause in about 80% to 95% of patients with low back pain (Cohen et al., 2008) \& (Dixit, 2017).

Caesarean section is when a baby is born through an incision in the mother's abdomen and uterine wall. This requires effective anaesthesia which can be regional (epidural or spinal) or a general anaesthetic. With regional epidural anaesthesia, the anaesthetic is infused into the space around the mother's spinal column, whilst with regional spinal anaesthesia, the drug is injected as a single dose into the mother's spinal column. With the two types of regional anaesthesia, the mother is awake for the birth but numbed from the waist down while with general anaesthesia, the mother is unconscious for the birth with the anaesthetic affecting her whole body (Afolabi and Lesi, 2012).

The epidural needle can be placed using the midline or paramedian approach. In both cases, lidocaine 1% is infiltrated in the epidural needle insertion area.

In the midline approach technique, the needle is placed in the midline between 2 spine processes. In the paramedian approach technique, the needle is inserted 1 cm lateral and 1 cm caudal to the lower border of the upper spinous process.

The epidural needle in the medline approach is advanced through ligaments: supraspinous ligament, interspinous ligament, ligamentum flavum and into the target epidural space. Each ligament has different density and texture, which affects the feel of the needle and the resistance to insertion (Vaughan et al., 2013).

Some explanations for Low Back Dysfunction after Epidural Anaesthesia:

The incidence of back pain after epidural anesthesia is over 20% (Rose, 2012) \& (Saghafinia et al., 2009) \& (Muslu et al., 2009). It occurs rarely after spinal anesthesia (Schwabe and Hopf, 2001). This indicates that back pain may be associated with local trauma and nerve injury caused by the epidural needle, leading to aseptic periosteitis, tendonitis, ligamentous inflammation and/or osteochondritis, which result in lumbar pain (Kalso, 2013).

• Excessive elongation of spinal ligaments can cause micro-trauma of the ligament fibers and tears or ruptures occur. Also, the interspinous ligaments are the first structures damaged (excessive stretching) when the spine is hyperflexed (Adams et al., 1998).
• Degeneration and excessive stress on the thoracolumbar fascia may also cause micro-trauma, and resulting in tears. Thoracolumbar fascia may become damaged by over-stretching or excessive stress, potentially eliciting pain (Bogduk, 1983).
• Other contributing factors include needle trauma, surgical positioning, injection of saline or local anesthetic into the interspinous ligaments and development of a supraspinous hematoma (Covet et al., 1967), (Crawford, 1972).
• Excessive stretching of ligaments after relaxation of paraspinal muscles and localized trauma to the intervertebral disc has also been implicated in causing back pain (Agarwal and Kishore, 2009).

Visual analogue scale (VAS):

The visual analogue scale is a validated, subjective measure for acute and chronic pain. Scores are recorded by making a handwritten mark on a 10-cm line that represents a continuum between "no pain" and "worst pain." (Delgado et al., 2018).

Pressure algometry:

Pressure algometry has been described as a semi-objective method, or subjective measure and Pain Pressure Threshold (PPT) is a quantitative sensory test of tissue sensitivity, and it is defined as the minimal amount of pressure that produces pain, measured via a pressure algometer (Ylinen, 2007).

Inclinometers:

An inclinometer or tilt meter is an instrument for measuring angles of slope (or tilt), elevation or depression of an object or body segment with respect to gravity (Nielsen et al., 2011).

Oswestry Disability Index:

The Oswestry Disability Index (ODI) is a valid, reliable, and responsive condition-specific assessment tool that is suited for use in clinical practice. It is easy to administer and score, objectifies clients' complaints, and monitors effects of therapy (Vianin, 2008).

Isokinetic dynamometry:

The isokinetic dynamometer is a gold standard instrument for measuring muscle strength and is safe, valid, and reliable, based on the use of kinetic parameters that also include the angular measurement of a corporeal segment throughout the range of motion (Gonosova et al., 2018) \& (Habets et al., 2018) \& (Roth et al., 2017) \& (Guilhem et al., 2014).

Ultrasound Elastography:

Ultrasound elastography (EUS) is a recently developed ultrasound-based method, which allows the qualitative visual or quantitative measurements of the mechanical properties of tissue (Hall, 2003), (Garra, 2007) \& (Garra, 2011).

Myoton Pro Device:

A MyotonPRO (Myoton AS, Estonia) is a portable hand-held myotonometer that can assess muscle tone and soft tissue stiffness. According to prior research, the MyotonPRO is a reliable quantitative measurement for assessing the mechanical properties of muscles (Pruyn et al., 2016).

The MyotonPRO can differentiate the viscoelastic properties of a trigger point from a non-trigger point. Our findings support the reliability of this myotonometer. This affordable and portable tool can be used to objectively measure viscoelastic properties of trigger points (Roch et al., 2020).