Principles

The principles of reconstructive anatomy are to start with the bones; arrange them into their normal configuration, and thereby establish their joints. Then, progressively add additional structures in some form of logical order; for example, add the ligaments (because these are next most intimately associated with the bones) followed by the muscles and fasciae (because these are next most intimately associated). Thereafter, thread the vessels and nerves around the bones and into the muscles.

For the purposes of recall, all that is required is to remember the order in which the region was reconstructed. If and once students can remember that, they will forever be equipped to reproduce the process. Then, in clinical practice, if confronted by the need to recall the entire region, they can quickly use the principles to reconstruct the region, and use the various steps to precipitate recall of necessary detail.

This will not happen automatically, or by magic. Some degree of rehearsal and practice is required. The first iteration of that practice is what follows.

The lumbar spine

The starting point is to recall that the lumbar spine consists of five vertebrae. The quintessential elements of those vertebrae are the vertebral bodies. These are stacked into a column, standing on the sacrum. The vertebral bodies are separated by the intervertebral discs.

It is the lateral view of this column that introduces the next level of detail. The vertebrae are stacked in a curved fashion, forming the lumbar lordosis (Fig. 17.1) A feature of reference in this column is that, most often, the third lumbar vertebra is the most horizontal. Higher vertebrae tilt forwards and upwards; lower vertebrae tilt forwards and downwards. Students able to invoke detail will recall that the average L1–S1 lordosis angle is about 70°, which dictates how curved the lordosis should be.

Figure 17.1 The appearance of the five lumbar vertebral bodies and their discs, as seen in a lateral view, forming a column resting on the sacrum.

In an anterior view, there is nothing remarkable about this column. The vertebral bodies appear as rectangles, separated by their discs (Fig. 17.2A). Similarly, in a posterior view the column of vertebral bodies is unremarkable. The one new feature is that the posterior surfaces of the vertebral bodies are marked by the origin of the pedicles (Fig. 17.2B).

Figure 17.2 The appearance of the five lumbar vertebral bodies and their discs, forming a column resting on the sacrum. (A) Anterior view. (B) Posterior view.

The next layer of reconstruction, in the anterior view, introduces the anterior longitudinal ligament (Fig. 17.3A). Correspondingly, in the posterior view, the posterior longitudinal ligament is introduced (Fig. 17.3B).

Figure 17.3 The lumbar vertebral bodies and their discs, onto which the longitudinal ligaments have been added (cf. Fig. 17.2). (A) Anterior longitudinal ligament. (B) Posterior longitudinal ligament.

For the time being, the reconstruction focuses on what lies behind the vertebral bodies. This introduces the dural sac, lying in the vertebral canal, and containing the caudal end of the spinal cord, which terminates opposite the L1–2 level (Fig. 17.4A). Hanging from the spinal cord are the nerve roots forming the cauda equina and the lumbar nerve roots passing around the pedicles to their intervertebral foramina (Fig. 17.4B). Eventually, these are enclosed by the posterior half of the dural sac (Fig. 17.4C).

Figure 17.4 The contents of the vertebral canal. (A) The anterior half of the dural sac, and the spinal cord terminating at L1–2. (B) The lumbar nerve roots and roots of the cauda equina. (C) The posterior half of the dural sac enclosing the cauda equina.

The vertebral canal is then covered by the posterior elements of the lumbar vertebral column (Fig. 17.5A). They consist of the laminae and zygapophysial joints, the transverse processes and the spinous processes. The laminae are joined by the ligamentum flavum, while the spinous processes are joined by the interspinous ligaments