Intertransversarii, Interspinales, Levatores Costarum What are the (deep layer) intrinsic back muscles? Transversospinalis (Semispinalis, Multifidus, Rotatores brevis/longus).

• The intertransversarii musculi are small muscles that pass between transverse processes, between articular and transverse processes or between mamillary and transverse processes. They are separable into different groups: Intertransversarii lumborum: medial bundles run ventrocranially from mamillary processes to transverse (or accessory) processes.
• Lateral flexors of the vertebral column (10) back 29. Intertransversarii and levatores costarum. Intertransversarii: posterior and anterior.

Interspinales Muscle

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  Superficial landmarks enable gross determination of the anatomic level. Proximally, C7 and T1 are the largest spinous processes and may serve as palpable anatomic landmarks. Distally, the intercrestal line approximates the L4-L5 interspace.
  
  
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  There are three layers to the posterior musculature of the spine (FIG 1; Table 1):
  
  
  
  
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    Superficial layer: trapezius, latissimus dorsi, rhomboid major and minor, and the levator scapulae
    
    
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    Intermediate layer: superior and inferior serratus posterior and the levatores costarum
    
    
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    Deep layer: erector spinae, transversospinalis, interspinalis, and the intertransversarii
  
  
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  The superficial and intermediate layers receive their nervous supply from peripheral nerves, which are not encountered through the posterior approach (FIG 2). The deep layer receives its nervous supply segmentally from the posterior dorsal rami. There is a large amount of redundancy in the innervation of the deep layer.
  
  
  
  
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    The midline approach is a true internervous plane. Nerve injury occurs only with excessive lateral dissection.
  
  
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  The vascular supply to the deep layer is from segmental branches of the aorta. These vessels enter the operative field at the level of the intertransverse ligament and can be a source of significant bleeding.
  
  
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  The facet joint capsules have a shiny white appearance and the individual fibers can be seen inserting onto the lateral edge of the laminar trough. Care should be taken to avoid violating the capsular fibers, unless that segment is being fused.
  
  
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  The ligamentum flavum has a yellow appearance with the fibers running in a cephalocaudal direction. The cephalad end of the ligament has a broad insertion from the base of the spinous process to between 50% and 70% of the anterior surface of the lamina. The caudal end of the ligament inserts from the superior edge of the lamina to between 2 and 6 mm of the anterior surface of the lamina.⁴
  
  
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  Particularly at the L5-S1 level, the interspace may be widened or the posterior bony anatomy only partly formed. Care should be exercised when exposing this level as inadvertent plunging into the canal may occur.
  
  
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  Laterally, the intertransverse membrane overlies the iliopsoas and protects the neural structures that lie beneath.
  
  
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  In children, the spinous process apophysis has not fused. During dissection, the apophysis is split down to the bone and then elevated with the paraspinal musculature.

Levatores Costarum Innervation