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Postero-lateral disc prosthesis combined with a unilateral facet replacement device maintains quantity and quality of motion at a single lumbar level.

Nayak AN, Doarn MC, Gaskins RB, James CR, Cabezas AF, Castellvi AE, Santoni BG - Int J Spine Surg (2014)

Bottom Line: ROM, ICR, and IPT measurements were compared (repeated measures ANOVA) between the three conditions.Compared to the intact spine, no significant changes in F/E, LB or AR ROM were identified as a result of unilateral FR or unilateral FR + PDR.No significant changes in adjacent L3-L4 or L5-S1 ROM were identified in any loading mode.

View Article: PubMed Central - PubMed

Affiliation: Phillip Spiegel Orthopaedic Research Laboratory, Foundation for Orthopaedic Research & Education, Tampa, FL, USA.

ABSTRACT

Background: Mechanically replacing one or more pain generating articulations in the functional spinal unit (FSU) may be a motion preservation alternative to arthrodesis at the affected level. Baseline biomechanical data elucidating the quantity and quality of motion in such arthroplasty constructs is non-existent.

Purpose: The purpose of the study was to quantify the motion-preserving effect of a posterior total disc replacement (PDR) combined with a unilateral facet replacement (FR) system at a single lumbar level (L4-L5). We hypothesized that reinforcement of the FSU with unilateral FR to replace the resected, native facet joint following PDR implantation would restore quality and quantity of motion and additionally not change biomechanics at the adjacent levels.

Study design: In-vitro study using human cadaveric lumbar spines.

Methods: Six (n = 6) cadaveric lumbar spines (L1-S1) were evaluated using a pure-moment stability testing protocol (±7.5 Nm) in flexion-extension (F/E), lateral bending (LB) and axial rotation (AR). Each specimen was tested in: (1) intact; (2) unilateral FR; and (3) unilateral FR + PDR conditions. Index and adjacent level ROM (using hybrid protocol) were determined opto-electronically. Interpedicular travel (IPT) and instantaneous center of rotation (ICR) at the index level were radiographically determined for each condition. ROM, ICR, and IPT measurements were compared (repeated measures ANOVA) between the three conditions.

Results: Compared to the intact spine, no significant changes in F/E, LB or AR ROM were identified as a result of unilateral FR or unilateral FR + PDR. No significant changes in adjacent L3-L4 or L5-S1 ROM were identified in any loading mode. No significant differences in IPT were identified between the three test conditions in F/E, LB or AR at the L4-L5 level. The ICRs qualitatively were similar for the intact and unilateral FR conditions and appeared to follow placement (along the anterior-posterior (AP) direction) of the PDR in the disc space.

Conclusion: Biomechanically, quantity and quality of motion are maintained with combined unilateral FR + PDR at a single lumbar spinal level.

No MeSH data available.


Related in: MedlinePlus

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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Figure 0002: 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).

Mentions: At the L4 and L5 levels, unilateral pedicle screws used as part of the facet replacement instrumentation (Figure 1) were implanted prior to attaching the follower load apparatus so that appropriate length screws could be used for affixing the compressive follower load system, thereby avoiding interference with pedicle screws. The follower load (FL) components and cable guides were attached mid-level to the L2, L3, L4 and L5 vertebrae using three fixation screws (two laterally and one anteriorly) and positioned approximately parallel to the endplates of the respective vertebral body and symmetrical to the mid-sagittal plane. In order to apply the FL, bilateral steel cables were passed caudally from the L1 superior vertebra potting via the cable guides attached to the FL apparatus towards the bilateral pulley guides on the S1 potting. A 400N compressive load using dead weights was attached distally to it. The cable guides were adjusted in the anterior-posterior direction such that the path of the cables passed through the approximate location of the CORs of the motion segments and followed the lordotic curvature of the lumbar spine in accordance with the approach suggested by Patwardhan et al. (Figure 2).26 All cadaveric specimens were kept hydrated throughout dissection, instrumentation and biomechanical evaluation by wrapping with saline soaked gauze and spraying regularly with 0.9% saline. Prior to biomechanical testing, all specimens were thawed overnight (8-10 hours) at and tested at room temperature.


Postero-lateral disc prosthesis combined with a unilateral facet replacement device maintains quantity and quality of motion at a single lumbar level.

Nayak AN, Doarn MC, Gaskins RB, James CR, Cabezas AF, Castellvi AE, Santoni BG - Int J Spine Surg (2014)

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).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4325497&req=5

Figure 0002: 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).
Mentions: At the L4 and L5 levels, unilateral pedicle screws used as part of the facet replacement instrumentation (Figure 1) were implanted prior to attaching the follower load apparatus so that appropriate length screws could be used for affixing the compressive follower load system, thereby avoiding interference with pedicle screws. The follower load (FL) components and cable guides were attached mid-level to the L2, L3, L4 and L5 vertebrae using three fixation screws (two laterally and one anteriorly) and positioned approximately parallel to the endplates of the respective vertebral body and symmetrical to the mid-sagittal plane. In order to apply the FL, bilateral steel cables were passed caudally from the L1 superior vertebra potting via the cable guides attached to the FL apparatus towards the bilateral pulley guides on the S1 potting. A 400N compressive load using dead weights was attached distally to it. The cable guides were adjusted in the anterior-posterior direction such that the path of the cables passed through the approximate location of the CORs of the motion segments and followed the lordotic curvature of the lumbar spine in accordance with the approach suggested by Patwardhan et al. (Figure 2).26 All cadaveric specimens were kept hydrated throughout dissection, instrumentation and biomechanical evaluation by wrapping with saline soaked gauze and spraying regularly with 0.9% saline. Prior to biomechanical testing, all specimens were thawed overnight (8-10 hours) at and tested at room temperature.

Bottom Line: ROM, ICR, and IPT measurements were compared (repeated measures ANOVA) between the three conditions.Compared to the intact spine, no significant changes in F/E, LB or AR ROM were identified as a result of unilateral FR or unilateral FR + PDR.No significant changes in adjacent L3-L4 or L5-S1 ROM were identified in any loading mode.

View Article: PubMed Central - PubMed

Affiliation: Phillip Spiegel Orthopaedic Research Laboratory, Foundation for Orthopaedic Research & Education, Tampa, FL, USA.

ABSTRACT

Background: Mechanically replacing one or more pain generating articulations in the functional spinal unit (FSU) may be a motion preservation alternative to arthrodesis at the affected level. Baseline biomechanical data elucidating the quantity and quality of motion in such arthroplasty constructs is non-existent.

Purpose: The purpose of the study was to quantify the motion-preserving effect of a posterior total disc replacement (PDR) combined with a unilateral facet replacement (FR) system at a single lumbar level (L4-L5). We hypothesized that reinforcement of the FSU with unilateral FR to replace the resected, native facet joint following PDR implantation would restore quality and quantity of motion and additionally not change biomechanics at the adjacent levels.

Study design: In-vitro study using human cadaveric lumbar spines.

Methods: Six (n = 6) cadaveric lumbar spines (L1-S1) were evaluated using a pure-moment stability testing protocol (±7.5 Nm) in flexion-extension (F/E), lateral bending (LB) and axial rotation (AR). Each specimen was tested in: (1) intact; (2) unilateral FR; and (3) unilateral FR + PDR conditions. Index and adjacent level ROM (using hybrid protocol) were determined opto-electronically. Interpedicular travel (IPT) and instantaneous center of rotation (ICR) at the index level were radiographically determined for each condition. ROM, ICR, and IPT measurements were compared (repeated measures ANOVA) between the three conditions.

Results: Compared to the intact spine, no significant changes in F/E, LB or AR ROM were identified as a result of unilateral FR or unilateral FR + PDR. No significant changes in adjacent L3-L4 or L5-S1 ROM were identified in any loading mode. No significant differences in IPT were identified between the three test conditions in F/E, LB or AR at the L4-L5 level. The ICRs qualitatively were similar for the intact and unilateral FR conditions and appeared to follow placement (along the anterior-posterior (AP) direction) of the PDR in the disc space.

Conclusion: Biomechanically, quantity and quality of motion are maintained with combined unilateral FR + PDR at a single lumbar spinal level.

No MeSH data available.


Related in: MedlinePlus