Sonoanatomy relevant for lumbar plexus block in volunteers correlated with cross-sectional anatomic and magnetic resonance images.

BACKGROUND: Ultrasound imaging of the anatomy relevant for lumbar plexus block (LPB) is challenging because of its deep anatomic location and the "acoustic shadow" of the overlying transverse processes. A paramedian transverse scan (PMTS) of the lumbar paravertebral region with the ultrasound beam being insonated through the intertransverse space (ITS) and directed medially toward the intervertebral foramen (PMTS-ITS) may overcome the problem of the "acoustic shadow" and allow clear visualization of the anatomy relevant for LPB. This study assessed the feasibility of using PMTS-ITS for imaging the anatomy relevant for LPB in healthy volunteers.

METHODS: Thirty young volunteers underwent a PMTS-ITS of the right lumbar paravertebral region. The sonoanatomy was defined in corresponding cadaver anatomic sections and magnetic resonance images. Visibility of the paravertebral structures in the sonograms was assessed by 4 independent observers using a 4-point Likert scale (0, not visible; 1, hardly visible; 2, well visible; 3, very well visible), and the mean total ultrasound visibility score (UVS; maximum score possible, 30) was determined. Overall ultrasound visibility was judged as good if the total UVS was greater than 20, average if it was 10 to 20, and poor if it was less than 10.

RESULTS: Ultrasound imaging of the right lumbar paravertebral region at the L3-L4-L5 vertebral level was successfully performed through the PMTS-ITS scan window in all volunteers studied. The lumbar nerve root, lumbar paravertebral space, lumbar plexus, and the psoas compartment were delineated in 57%, 27%, 57%, and 87% of volunteers, respectively. Overall ultrasound visibility of the lumbar paravertebral structures was judged as "good" (mean [SD] total UVS, 20.4 [3]).

CONCLUSIONS: A PMTS-ITS can be used to image the sonoanatomy relevant for LPB including the lumbar nerve root, lumbar paravertebral space, lumbar plexus, and the psoas compartment.