Korean J Pain.  2012 Apr;25(2):99-104. 10.3344/kjp.2012.25.2.99.

Ultrasonographic Measurement of the Ligamentum Flavum Depth; Is It a Reliable Method to Distinguish True and False Loss of Resistance?

• Pak MH
• Lee WH
• Ko YK
• So SY
• Kim HJ

• KMID: 1778993
• DOI: http://doi.org/10.3344/kjp.2012.25.2.99

Abstract

BACKGROUND
Previous studies have shown that if performed without radiographic guidance, the loss of resistance (LOR) technique can result in inaccurate needle placement in up to 30% of lumbar epidural blocks. To date, no study has shown the efficacy of measuring the depth of the posterior complex (ligamentum flavum, epidural space, and posterior dura) ultrasonographically to distinguish true and false LOR.
METHODS
40 cervical epidural blocks were performed using the LOR technique and confirmed by epidurograms. Transverse ultrasound images of the C6/7 area were taken before each cervical epidural block, and the distances from the skin to the posterior complex, transverse process, and supraspinous ligament were measured on each ultrasound view. The number of LOR attempts was counted, and the depth of each LOR was measured with a standard ruler. Correlation of false and true positive LOR depth with ultrasonographically measured depth was also statistically analyzed.
RESULTS
76.5% of all cases (26 out of 34) showed false positive LOR. Concordance correlation coefficients between the measured distances on ultrasound (skin to ligamentum flavum) and actual needle depth were 0.8285 on true LOR. Depth of the true positive LOR correlated with height and weight, with a mean of 5.64 +/- 1.06 cm, while the mean depth of the false positive LOR was 4.08 +/- 1.00 cm.
CONCLUSIONS
Ultrasonographic measurement of the ligamentum flavum depth (or posterior complex) preceding cervical epidural block is beneficial in excluding false LOR and increasing success rates of cervical epidural blocks.

Keyword

cervical; epidural; ultrasonography

MeSH Terms

Epidural Space
Ligaments
Ligamentum Flavum
Needles
Skin

Figure

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  Fig. 1 Transverse ultrasonographic image at the level of C6-7. Each number indicates supraspinous ligament (1), transverse process (2), ligament flavum (3), posterior dura (4), anterior complex (anterior dura, posterior longitudinal ligament, vertebral body)(5).

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  Fig. 2 Lateral fluroscopic images of cervical epidural block at the level of C6-7. Note that the contrast medium spread show non-epidural pattern (A) and epidural pattern (B) on a same patient.

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  Fig. 3 Bland-Altman precision analysis of the measured differences between ultrasound-measured depth of skin to ligamentum flavum and depth of true loss of. LOR: loss of resistance, US-lf: measured depth from skin to ligamentum flavum or posterior complex.

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  Fig. 4 Concordance correlation between ultrasound-measured depth of skin to ligament flavum and depth of compensated true loss of resistance. LOR: loss of resistance, US-lf: measured depth from skin to ligament flavum or posterior complex.

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