Bilateral posterior cervical cages provide biomechanical stability: assessment of stand-alone and supplemental fixation for anterior cervical discectomy and fusion

Figures & data

Figure 1 Schematic of the loading apparatus for flexibility testing in flexion–extension (left image), lateral bending (center image), and axial rotation (right image).

Figure 2 Testing protocol.

Note: (A) Intact, (B) bilateral posterior cervical cages at C5–C6, (C) plated ACDF at C6–C7, (D) addition of posterior bilateral cervical cages at C6–C7, (E) plated ACDF at C3–C5, and (F) bilateral posterior cervical cages at C3–C4 and C4–C5.
Abbreviation: ACDF, anterior cervical discectomy and fusion.

Figure 3 DTRAX Posterior Cervical Cage.

Note: The cervical cages are manufactured from implant grade titanium alloy (6AI-4V ELI Titanium) and each cage is 10 mm in length, 5.5 mm in width, and 2.5 mm in height.

Figure 4 ROM curves with 0 N preload: (A) FE, (B) LB, and (C) AR.

Abbreviations: ACDF, anterior cervical discectomy and fusion; AR, axial rotation; FE, flexion–extension; LB, lateral bending; ROM, range of motion.

Table 1 Segmental ranges of motion in degrees, (mean ± SD) for each condition under 0 N follower preload and 1.5 Nm moment for each test condition.

Testing mode	Intact	C5–C6 posterior cages	C6–C7 ACDF	C6–C7 ACDF + posterior cages	C3–C5 ACDF	C3–C5 ACDF + posterior cages
C5–C6
Flexion–extension	10.7±2.6	2.5±1.3*	2.5±1.2	2.5±1.6	2.6±1.7	2.5±1.0
Lateral bending	6.7±2.8	0.4±0.3*	0.4±0.4*	0.4±0.4	0.5±0.7	0.3±0.1
Axial rotation	7.9±2.8	1.1±1.7*	0.6±0.7*	0.5±0.3	0.8±1.3	0.6±0.2
C6–C7
Flexion–extension	11.4±2.4	12.3±2.5	2.5±0.8*	0.6±–0.3*	0.6±0.4	0.7±0.4
Lateral bending	8.2±1.7	8.9±1.5	1.6±0.7*	0.1±0.4*	0.2±0.3	0.1±0.2
Axial rotation	7.5±1.2	7.1±1.2	1.7±0.4*	0.2±0.3*	0.0±0.5	0.3±0.2
C3–C4
Flexion–extension	10.5±5.1	11.6±5.2	11.8+5.4	12.1±5.4	0.6±0.4*	0.1±0.1*
Lateral bending	13.7±2.6	13.9±2.7	15.2±2.6	15.5±2.6	0.9±0.2*	0.1±0.1*
Axial rotation	10.3±1.5	10.7±1.4	9.1±1.8	9.6±1.7	0.5±0.5*	0.1±0.2*
C4–C5
Flexion–extension	11.3±3.2	12.6±3.1	12.8±3.2	13.3±3.1	1.1±0.6*	0.2±0.2*
Lateral bending	10.7±2.4	10.8±2.3	12.3±2.4	12.0±2.7	0.8±0.5*	0.1±0.1*
Axial rotation	12.1±1.9	12.8±1.9	11.6±1.6	12.1±1.7	1.6±0.7*	0.1±0.2*
C3–C5
Flexion–extension	21.8±7.9	24.2±7.9	24.7±8.2	25.4±8.1	1.7±0.9*	0.3±0.2*
Lateral bending	24.4±4.8	24.7±4.9	27.5±4.9	27.5±5.1	1.7±0.6*	0.2±0.1*
Axial rotation	22.4±2.5	23.6±2.2	20.7±2.2	21.7±2.0	2.1±0.5*	0.3±0.2*

Note:

* Significantly different from baseline value (paired t-test, P<0.05).

Abbreviations: ACDF, anterior cervical discectomy and fusion; SD, standard deviation.

Table 2 Effectiveness of posterior cervical cages as a supplement for single-level ACDF constructs

	ROM in degrees (mean ± SD) after single level C6–C7 instrumentation
	Intact*	ACDF	Paired t-test, intact vs ACDF	ACDF + posterior cages	Paired t-test, ACDF vs ACDF + posterior cages
Flexion–extension	12.3±2.5	2.5±0.8	P=0.000	0.6±0.3	P=0.002
Lateral bending	8.9±1.5	1.6±0.7	P=0.000	0.1±0.4	P=0.005
Axial rotation	7.1±1.2	1.7±0.4	P=0.000	0.2±0.3	P=0.000

Note:

* Intact represents baseline ROM values after posterior cage placement at C5–C6.

Abbreviations: ACDF, anterior cervical discectomy and fusion; ROM, range of motion.

Table 3 Effectiveness of posterior cervical cages as a supplement for two-level ACDF constructs

	ROM in degrees (mean ± SD) after two-level C3–C5 instrumentation
	Intact	ACDF	Intact vs ACDF*	ACDF + cages	ACDF vs ACDF + cages*
Flexion–extension	25.4±8.1	1.7±0.9	P=0.000	0.3±0.2	P=0.010
Lateral bending	27.5±5.1	1.7±0.6	P=0.000	0.2±0.1	P=0.000
Axial rotation	21.7±2.0	2.1±0.5	P=0.000	0.3±0.2	P=0.000

Note:

* Paired t-test.

Abbreviations: ACDF, anterior cervical discectomy and fusion; ROM, range of motion.