of the Posterior Lumbar Muscles: Study of Lumbosacral Malformations and the Extraforaminal Approach (ELIF)

Fig. 1

CT-scan lateral and axial views L4–L5. Measurement of the surfaces of Multifidus and the three posterior muscles (M + L + IC) with horizontal cross-section

Table 1

True levels

		Normal lumbar spine	Lumbar spine with sacralization
False or non-functional disc		S1S2	L5S1
Free disc	First disc	L5–S1	L4–L5
	Second disc	L4–L5	L3–L4
	Third disc	L3–L4	L2–L3
	Fourth disc	L2–L3

Instead, a disc, under a vertebra completely or partially attached to the pelvis is a false or non-functional disc. Usually, this disc is S1S2.

The surface of the posterior muscles has been measured at the level of the four last “free discs” and, if necessary, the “non-functional disc ”, with horizontal cross-sections, that go through the posterior part of the inferior endplate.

These horizontal cross-sections are studied from native slides acquired during CT scan and not with cross-sections made in the axis of the disc.

The axis of the disc varies with lumbar lordosis. The cross-sections overlap and represent a shifting surface of the muscles. Instead, horizontal cross-sections, by definition, are parallel and represent a specific surface of the muscle.

Two muscular surfaces have been measured: the surface of the Multifidus (MS) alone and the global surface (GS) of the three muscles (M + L + IC). The ratio of the two surfaces (MS/GS) has been calculated.

The vertebrae have been named in accordance with classic data:

Five free lumbar vertebrae
The L3 transverse process is longer, larger and more horizontal than any other
Instead the L4 transverse process is short, slender with an oblique ascending slope
The innominate line crosses the disc L5S1 in its posterior part, on the lateral X-ray
The sacral slope (S1 endplate) is 38° (± 8°)
The superior attachment of the psoas muscle is at T12L1 level

Results

The results are reported in Table 2.

Those of a lumbar spine that has been seen as normal
Those of lumbar spine with lumbosacral malformation

Table 2

Surfaces ratio of the lumbar posterior muscles at every disc level

$\mathrm{Surfaces}\ \mathrm{ratio}=\frac{\mathrm{Multifidus}}{\mathrm{Multifidus}+\mathrm{Longissimus}+\mathrm{Iliocostalis}}$
		Normal lumbar spine	Sacralization
Number of spines		59	31
False or non-functional disc		–	–
Free disc	First disc	95% (80–100%)	64% (43–81%)
	Second disc	51% (43–66%)	37% (33–42%)
	Third disc	34% (27–39%)	20% (15–27%)
	Fourth disc	18% (15–21%)	15% (12–18%)