Postero-Lateral Disc Prosthesis Combined With a Unilateral Facet Replacement Device Maintains Quantity and Quality of Motion at a Single Lumbar Level

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Fig. 1
Images of the facet (A) and posterior total disc (B) replacement devices.
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Fig. 2
Biomechanical testing set up showing moment application rod (A) attached at cranial potting and 400N follower load (A, B) using cable guides, steel cables and dead weights (not shown in figure).
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Fig. 3
Diagram showing interpedicular travel (IPT) measurement technique. Position coordinates of radiopaque beads on the superior aspect of the L4 and L5 vertebrae were tracked at extremes of planar motion to determine IPT.
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Fig. 4
Lateral radiographs indicating sequential index level (L4-L5) instrumentation with the facet and disc replacement devices. As shown [L-R]: Unilateral FR and Unilateral FR + PDR.
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Fig. 5
Range of motion (ROM) histogram showing index level ROM (y-axis) as a function of instrumentation for various loading modes (x-axis).
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Fig. 6
Representative lateral radiographs with plot of the center of rotation for all six specimens at the L4-L5 level as a function of instrumentation.

Table 1

Interpedicular Travel (IPT,mm) at index L4-5 level. Reported as Mean ± Standard deviation.

Loading Mode	Intact	Uni-FR	Uni-FR + PDR
Flexion-Extension (No FL)	130 ± 3.9	14.6 ± 4.1¹	14.3 ± 3.8²
Flexion-Extension (FL)^**	10.2 ± 3.5	10.5 ± 3.7	11.5 ± 3.0
Lateral Bending^**	9.6 ± 3.3	10.7 ± 3.8	12.2 ± 4.4
Axial Rotation^**	3.5 ± 1.8	3.9 ± 3.3	4.8 ± 5.3

↵1 Indicates Uni-FR IPT > Intact IPT (p = 0.008)
↵2 Indicates Uni-FR + PDR IPT > Intact IPT (p = 0.043)
↵** Indicates no significant difference (p > 0.05) between instrumentation conditions

Table 2

Adjacent level ROM derived from Hybrid Loading Protocol [mean ± stdev].

	Instrumentation Condition at Index L4-L5 Level
Loading Mode	Intact			Uni-FR			Uni-FR + PDR
Superior L3-L4 Level^**
Flexion-Extension ROM [w/o FL]	8.8	±	3.7	8.5	±	3.7	8.9	±	4.2
Flexion-Extension ROM [w/400 N FL]	8.8	±	4.1	8.6	±	4.2	9.3	±	5.2
Lateral Bending ROM	11.4	±	5.9	12.1	±	4.7	11.7	±	6.7
Axial Rotation ROM	5.5	±	2.6	5.4	±	2.1	5.6	±	2.3
Inferior L5-S1 Level^**
Flexion ROM	6.5	±	3.1	6.4	±	3.1	6.9	±	3.0
Flexion-Extension ROM	8.1	±	3.0	8.5	±	3.9	8.9	±	4.3
Lateral Bending ROM	8.0	±	2.9	8.1	±	2.9	8.8	±	3.3
Axial Rotation ROM	4.1	±	1.2	4.1	±	1.2	4.6	±	1.5