The tips of the vertebral spinous processes do not always lie in the same horizontal plane as their corresponding vertebral bodies. In thoracic regions, the spinous processes are long and sharply sloped downward so that their tips lie at the level of the vertebral body below. In other words, the tip of the TIII vertebral spinous process lies at vertebral level TIV.
In lumbar and sacral regions, the spinous processes are generally shorter and less sloped than in thoracic regions, and their palpable tips more closely reflect the position of their corresponding vertebral bodies. As a consequence, the palpable end of the spinous process of vertebra LIV lies at approximately the LIV vertebral level.
Visualizing the inferior ends of the spinal cord and subarachnoid space
The spinal cord does not occupy the entire length of the vertebral canal. Normally in adults, it terminates at the level of the disc between vertebrae LI and LII; however, it may end as high as TXII or as low as the disc between vertebrae LII and LIII. The subarachnoid space ends at approximately the level of vertebra SII (Fig. 2.68A).
Because the subarachnoid space can be accessed in the lower lumbar region without endangering the spinal cord, it is important to be able to identify the position of the lumbar vertebral spinous processes. The LIV vertebral spinous process is level with a horizontal line between the highest points on the iliac crests. In the lumbar region, the palpable ends of the vertebral spinous processes lie opposite their corresponding vertebral bodies. The subarachnoid space can be accessed between vertebral levels LIII and LIV and between LIV and LV without endangering the spinal cord (Fig. 2.68B). The subarachnoid space ends at vertebral level SII, which is level with the sacral dimples marking the posterior superior iliac spines.
A number of intrinsic and extrinsic muscles of the back can readily be observed and palpated. The largest of these are the trapezius and latissimus dorsi muscles (Fig. 2.69A and 2.69B). Retracting the scapulae toward the midline can accentuate the rhomboid muscles (Fig. 2.69C), which lie deep to the trapezius muscle. The erector spinae muscles are visible as two longitudinal columns separated by a furrow in the midline (Fig. 2.69A).
Fig. 2.1 Skeletal framework of the back.
Fig. 2.2 Curvatures of the vertebral column.
Cervical curvature(secondary curvature)Thoracic curvature(primary curvature)Lumbar curvature(secondary curvature)Sacral/coccygeal curvature(primary curvature)Gravity lineConcave primarycurvature of backEarly embryoAdultSomites
Fig. 2.3 Back movements.
Fig. 2.4 Nervous system.
Fig. 2.5 Vertebrae.
Fig. 2.6 A typical vertebra. A. Superior view. B. Lateral view.
Fig. 2.7 Back muscles. A. Extrinsic muscles. B. Intrinsic muscles.
Deep groupSerratus posteriorinferiorSerratus posteriorsuperiorSuboccipitalLevator scapulaeSpleniusRhomboid minorSuperficial groupABIntermediate groupIntrinsic musclesTrue back muscles innervated by posterior rami of spinal nervesRhomboid majorSpinalisIliocostalisErector spinaeLongissimusLatissimusdorsiTrapeziusExtrinsic musclesInnervated by anterior rami of spinal nerves or cranial nerve XI (trapezius)
Fig. 2.8 Vertebral canal.
Spinal cordPia materSubarachnoid spaceDura materArachnoid materAnterior ramusPosterior ramusPosition of spinal ganglionTransverseprocessSpinousprocessPosterior longitudinalligamentAnterior internal vertebralvenous plexusIntervertebral discExtradural spaceExtradural fatVertebral body