Current strategies for the restoration of adequate lordosis during lumbar fusion

Table 1 Consequences of hypolordotic construct

Inadequate restoration of lordosis (hypolordosis) during lumbar fusion exposes to
Short term	Mechanical low back pain
	Anterior unbalance requiring compensatory mechanisms[15]
Long term	Adjacent segment degeneration

Table 2 Significance of spino-pelvic parameters

Anatomical	Pelvis	PI	Shape of the pelvis
Positional	Pelvis	SS	Inclination of the pelvis base
		PT	Position of the pelvis related to the femoral heads
	Spine	LL	Curve in extension above the pelvis to maintain the sagittal balance
		TK	Provide resistance and rigidity to the spine

PI: Pelvis incidence; SS: Sacral slope; PT: Pelvis tilt; LL: Lumbar lordosis; TK: Thoracic kyphosis.

Table 3 Theoretical values for positional pelvis and spinal parameters related to pelvis incidence

PI class	PI (°)	PTth (°)	LLth (°)
I	< 38	4	PI + 18
II	38-47	8	PI + 13
III	48-57	12	PI + 9
IV	58-67	16	PI + 6
V	68-77	20	PI + 2
VI	> 78	24	PI - 5

PT: Pelvis tilt; LL: Lumbar lordosis; PT_th: Theoretical PT; LL_th: Theoretical LL. As examples, for PI measured to 40°, expected PT should be 8° and LL should be 53°; for PI measured to 52°, expected PT should be 12° and LL should be 61°; and for PI measured to 64°, expected PT should be 16° and LL should be 70°.

Table 4 Amount of lordosis to restore related to the pelvis incidence and the length of spinal construct

PI	LLth	Length of fusion
		L5-S1	L4-S1	L3-S1	L2-S1	L1-S1
		40% of LLth	67% of LLth	85% of LLth	97% of LLth	100% of LLth
40°	55°	22°	37°	47°	53°	55°
50°	60°	24°	40°	51°	58°	60°
60°	65°	26°	44°	55°	63°	65°
70°	70°	28°	47°	59°	68°	70°

PT: Pelvis tilt; LL_th: Theoretical Lumbat lordosis.

Table 5 Technical key points permitting to restore lordosis

Operative positioning	Avoid knee-chest position
Release	Allow for mobilization of the spinal segments
Instrumentation	Contouring of the rod
	Screw-rod connection
	Interbody implants
Spinal osteotomies	Indicated only when the spine is fixed in kyphotic position
Surgical sequence	AP sequence should be promoted