Beirut

Beirut Spine Conference May 14th 2005 Minimally-invasive Spine Surgery

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Update on Artificial Disc Replacement B. Poffyn G. Sys K. Van der Donckt P. Verstraete D. Uyttendaele  2

Target of therapy in Degenerative Disc Disease (DDD)

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Pain Relief  Preservation of Range of Motion  Segmental Stabilisation and Replication of the Natural Function of the Disc 

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Indications 1. Symptomatic DDD in young patients (<50 years) * Neg or Pos Modic signs on MRI * > 6 months unsuccessful conservative treatment * Backpain of discogenic origin confirmed by history and radiografic studies 3rd Dubai Spine Conference March 10th 2005

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MRI

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Discography

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• Foraminal Stenosis ? • Ideal Indication Monosegmental lumbar symptomatic DDD without herniation with an average disc height > 5 mm

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• Good Indication * Bisegmental lumbar DDD without herniation with an average disc height > 5 mm

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* Failed disc surgery syndrome without laminectomy or severe facetalterations

* Spondylolysis after lytic repair 3rd Dubai Spine Conference March 10th 2005

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• Borderline Indication * Post fusion adjacent level instabilities * 3 - level instabilities

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CASE 1 - VB, woman 29 y - L4-L5 herniation - discectomy dec. 99 - chronic low back pain with antalgic posture - interference ADL

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CASE 1 - VB, woman 29 y - operation date 31/10/00 - disc prosthesis L4-L5 - no complications - good subjective status at 6 months follow-up

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CASE 2 - AR, man 40 y - discectomy L5-S1 1990 - chronic low back pain - NMR black disc at L4-L5 - positive discography L4-L5

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CASE 2 - AR , man 40 y - operation date 08/05/01 - disc prothesis L4-L5 - no post-op complications

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CASE 3 - Female - Low Back pain with several periods of lumbago •

Postoperative X-Rays

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CASE 4

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CASE 4

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Contraindications 

Absolute contraindications Translational Significant

instability

facetarthrosis

Hypertrophic facet Recessus

stenosis (option for fusion)

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Contraindications –Spondylolisthesis •Degenerative •Isthmic

–Metabolic

Bone diseases Osteoporosis –Neurological and Neuromuscular diseases

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Contraindications –Infection

–Tumor

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Contraindications –Spinal

canal stenosis

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Contraindications –Spinal

deformity –Radiculopathy

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Contraindications –>

50 years

•Quality

of subchondral bone decreases

with age •Facet joint degeneration increases •Large blood vessels must be mobilised –Risk

thrombosis or stenosis increases –(smokers)

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Contraindications 

Relative Contraindications Post

op segment ?

Psychological Socio

factors

– economic factors

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Biomechanics

With a SB Charité Artificial Disc the load is transmitted from one vertebra to the next via the cobalt-chrome Endplates encasing an UHMW Polyethylene Core between their highly polished interfaces. 3rd Dubai Spine Conference March 10th 2005

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Biomechanics The Endplates and the Sliding Cores Size 5 4 3 2 1 7.5

9.5 11.5 Height / mm

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Biomechanics - Core provides cushioning and spacing required during flexion , extension and torsion - Anchoring teeth on the endplates grip the bone of the endplates

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Biomechanics After 20 million cycles = 20 years of life , the SB prosthesis was still efficient with 10 % less height of the polyethylene core and increase of its width

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Biomechanics

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Biomechanics Axial rotation Y-axis

1 2 The opposite Zygapophysial joint is gapped.

As the posterior elements swing around, the right inferior articular process of the upper vertebra impacts the superior articular process of the lower vertebra.

 1 Bogduk, Nikolai: „Functional Anatomy of the Disc and Lumbar Spine“, The Artificial Disc, 2001

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Biomechanics Relation of Facets to Disc - from various studies “Facet loads were more sensitive to the anteposterior location of the artifiacial disc than to the amount of anulus removed.“ 1 “Biomechanical and histologic studies have highlighted the close functional relationship between lumbar discs and their associated facet joints, and it is conceivable that their degenerative changes are interdependent.“ 2 1 Dooris AP et al: Load-sharing between anterior and posterior elements in a lumbar motion segment implanted with an artificial disc. Spine 2001 Mar 15; 26(6):E122-129 2 Gries NC et al: Early histologic changes in lower lumbar discs and facet joints and their correlation. Eur Spine J 2000 Feb; 9(1):23-29

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Biomechanics Relation of Facets to Disc - from various studies “It has been reported that facet arthrosis and degeneration never occur without the presence of adjacent disc degeneration. This suggests that intact discs protect the facets from severe loading and degeneration.“ 1 

1 Haher TR et al: The role of the lumbar facet joints in spinal stability. Identification of alternative paths of loading. Spine 1994 Dec 1; 19(23):2667-2670

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Biomechanics The “Mobile Sliding Core“ Artificial Disc ... in it‘s degree of mobility

a)

b)

defines the required interaction between soft tissues (a), facet joints (b) and implant geometry to maintain a stable articulation ... 3rd Dubai Spine Conference March 10th 2005

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Biomechanics Axes of Rotation

X-axis X-axis: sagittal rotation (flexion and extension) Y-axis: axial rotation Z-axis: lateral bending Z-axis  1 Bogduk, Nikolai: „Functional Anatomy of the Disc   and Lumbar Spine“, The Artificial Disc, 2001

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Biomechanics Translation Force

Motion + + + -

Z Z Y Y X X

translation - Forward slide or glide translation - Backward slide translation - Longitudinal or axial distraction translation - Longitudinal or axial compression translation - Left axial rotation translation - right axial rotation

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Biomechanics

Vertebrae loaded in Flexion Fixed inferior component

Sliding intermediate component

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Biomechanics

Vertebrae loaded in Extension Fixed inferior component

Sliding intermediate component

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Biomechanics Correct Placement

Sagittal Plane

Frontal Plane

Disc is major compression carrying component 1 Nucleus in lumbar spine is nearer to the disc’s posterior surface 2

Center of Prosthesis = Center of Intervertebral Space Center A/P

Center M/L MRI Image Intensifier / Sizing Gauge Center of Nucleus

Image Intensifier / Sizing Gauge

Center of Prosthesis

Center of Prosthesis ≈ Center of Nucleus ≈ 2 mm dorsal of saggital vertebral midline

1 White, Panjabi: „Clinical Biomechanics of the Spine“ pg. 4 2 Gray‘s Anatomy 1995, pg. 513

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Biomechanics

Important: Use oblique endplates to maintain or restore lumbar lordosis Although literature reflects no association of lumbar lordosis with back pain, it is preferable to maintain respectively restore lumbar lordosis when implanting the Intervertebral Disc Endoprosthesis: 1) Load on Sliding Core should be distributed equally

Endplate to Sliding Core = parallel 2)

As 80% of lumbar lordosis occurs through wedging of Intervertebral Disc (and only 20% because of lordotic configuration of vertebral bodies) normal lordosis should be restored when implanting the Disc Endoprosthesis.

To maintain or restore normal lumbar biomechanics.

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