Choosing an Interbody Cage Steven R. Garfin, MD Distinguished - PowerPoint PPT Presentation

Choosing an Interbody Cage Steven R. Garfin, MD Distinguished Professor and Chair Department of Orthopaedic Surgery UC San Diego

Disclosures • Magnifi Group • AO Spine • Medtronic • Benvenue Medical • NuVasive, Inc. • EBI • SI Bone, Inc. • Globus Medical • Spinal Kinetics • Intrinsic Therapeutics • Vertiflex • Johnson & Johnson, DePuy Spine

How to choose an interbody graft? • ALIF • TLIF • PLIF What are the goals of surgery?? • LLIF • Expandable

Interbody Fusion • Helps stabilize anterior column / motion segment • Enhances fusion rate • Improvement in sagittal and coronal alignment • Restoration/improvement in disc height • Allows for indirect decompression of foraminal stenosis by increasing disc/foraminal site

Interbody Indications • Risk factors for non-union – Smoking, obesity, diabetes, etc. • Dynamic, (symptomatic), instability • Failed posterior fusion • Deformity Correction

Anterior Lumbar Interbody Fusion • Fusion for discogenic back pain • Particularly L5-S1 DDD, maybe L4-5 • Allows direct midline view for endplate prep disc space Allows large implant size and surface area  • anatomical correction and fusion success • Failed interbody fusion (LLIF, TLIF, TLIF) • Complications include: – Vascular and visceral injury – Retrograde ejaculation – Difficulty accessing disc space / mobilizing vessels (and have to abandon)

ALIF Cages • Tricortical iliac crest graft • Ring allografts • PEEK • PEEK + Vertebral body screws/”wings” • Titanium – Polished – Plasma spray – 3D modeling with large/small pores

Transforaminal Lumbar Interbody Fusion TLIF is pedicle based approach  requires facetectomy, partial lami, and • some dural retraction PLIF requires + neural retraction (not needed with TLIF)  nerve root • injury, dural tears and some epidural fibrosis • TLIF can preserve midline structures (intra/supraspinous ligaments) • Direct decompression • Smaller footprint than with other cages • May achieve less lordosis than LLIF/ALIF • ? Safety at higher lumbar levels ?

Lateral Lumbar Interbody Fusion (To me - the Work Horse) • Indirect decompression • Large footprint • Endplate to endplate support (more than others) • Common complications – Anterior thigh dysesthesias/weakness in 20- 30% – Inability to access disc space (nerve root)

LLIF Limitations • Anatomy – psoas, iliac crest, lumbar plexus • Large, central HNP can be difficult to address • Learning curve • L5-S1 • Sometimes L4-5 spondy Incidence of thigh pain by year

LLIF Advantages & Results: Indirect Decompression • Reduction of Vertebral bodies utilizing ligamentotaxis of ALL and PLL • Central and Foraminal Decompression

• Radiographic assessment of LLIF ability to indirectly decompress neural elements • 42% average disc height increase • 13.5% foraminal height increase • 25% foraminal area increase • 33% central canal area increase • Indirect decompression limited if there is congenital stenosis or cage subsidence

Graft Subsidence is a Concern Euro Spine 2015 • 24 disc spaces (48 endplates) • 6 disc spaces for each procedure – ALIF, PLIF, TLIF and XLIF • ALIF -- least amount of relative endplate prep (35% of disc space) • TLIF -- endplate damage highest (48% of specimens) • XLIF -- greatest endplate preparation (60%of disc space) with least damage

• Placement of large cage across apophyseal rings (cortical bone) ALI F Dimensions 21-24mm AP 32-36mm wide Lateral Access Cages Dimensions 18-22mm AP 45-60mm wide PLI F/ TLI F Dimensions 25-35mm AP 10-12mm wide

Lower Subsidence Rates with LLIF vs PLIF/TLIF ≥30% endplate cage coverage = decreased subsidence TLIF / PLIF LLIF (22mm) 22% Subsidence 7 2% Subsidence 8 Vaidya R, Sethi A, Bartol S, Jacobson M, Coe C, Le TV, Baaj AA, Dakwar E, Burkett CJ, Murray G, Craig JG. Complications in the use of rhBMP-2 in Smith DA et al. Subsidence of PEEK cages for interbody spinal fusions. J Spinal polyetheretherketone intervertebral cages in Disord Tech 2008;21:557-62. minimally invasive lateral retroperitoneal transpsoas lumbar interbody fusion. Spine 2012;37:1268-73. Uribe et. al., 2012

Spine 2017

• Randomized cadaveric study of 40 lumbar vertebras • 4 groups • (A) Endplate decortication with short cage Short cage does not extend across apophyseal ring • (B) Endplate decortication with long cage Long cage spanning apophyseal ring

• Long cages spanning endplates provides more strength in compression with less subsidence • Spanning ring apophysis increases load to failure by 40% with intact endplates and 30% with decorticated endplates • Good endplate prep and longer cages paramount in osteoporotic patients to decrease subsidence

How do the different grafts affect lordosis? International Journal of Spine Surgery, 2016

• Retrospective, comparative radiographic analysis of LLIF, ALIF and TLIF • Compared standing pre- and 6wks post op x-rays • Looked at segmental lordosis at operative level and regional lordosis (L1-S1) and anterior and posterior disc heights • 121 pts  176 levels – LLIF – 35pts, 54 levels – ALIF – 36 pts, 57 levels – TLIF – 50 pts, 65 levels

ALIF results in the greatest single level lordosis change – but not statistically significant compared to LLIF/TLIF

Coronal and Sagittal Plane alignment after LLIF Acosta et al Lee, Kim, et al Significantly ↑↑ coronal alignment: segmental, regional, and globally ↑↑ regional lordosis/global sagittal alignment with OPEN techniques (not necessarily with Percutaneous or MIS techniques Significantly more segmental and regional lordosis of L- spine when osteotomies are performed

Deformity Correction using LLIF International Spine Study Group JNSurg 2016 • Best Group: -significantly less post-op SVA ( 3.4 vs 6.9 cm, p = 0.043) -significantly less post-op PI-LL mismatch than the worst group. ( 10.4° vs 19.4°, p = 0.027)

LLIF in Adult Degenerative Scoliosis Phillips, Isaacs, et al. Spine 2010 • 24 month f/u prospective study • In hypolordosis pts: LL 28°  34° at 24 months (P < 0.001). • Overall Cobb angle corrected 21°  15°,

Akbarnia et al (IMAST, 2010) • 2 yr f/u, • Ave cobb: 47°  17° • ↑↑ in SRS-22, VAS & ODI • Coronal L4 tilt: 23 °  10 ° • 45% coronal correction w lateral IB alone 70% w posterior instrumentation

Implant Materials • PEEK – Modulus close to bone – Radiolucent – Hydrophobic polymer – Does not allow for cell adhesion – Good x-rays/MRI • Titanium – Modulus higher than bone • Stress shielding, altered load – Surface allows for bone on- growth (particularly porous coated) • Enhanced cell adhesion – Some artifact on MRI

Pelletier, Punjabi, et al. JSD 2013 Comparison of in vitro and in vivo biomechanics, fusion and bone apposition of PEEK and Ti at 26 weeks • 2 level ALIF performed in 9 sheep  performed initial biomechanical studies to establish initial stability of graft • At 26wks – no difference in the amount of fusion mass (sheep sacrificed)

Peek Ti • Ti/plasma coated = 42% of implant surface had bone contact • PEEK = 12% of implant surface had bone contact

J. Clin Neuro No statistical difference in fusion rates btw PEEK vs titanium Titanium has higher incidence of graft subsidence

Expandable Cages • Original designs – Fill cage with graft material – After expansion what happens to graft • Spreads up with expansion (leaving gap in middle) • Stays put (leaving gap at ends) – New designs • Fill cage after expansion • Fill around cage

My Preference for Technique • ALIF – L5-S1 – L4-5 only when also doing L5-S1 – Revision • XLIF – Thoracic to L4-5, if anatomy permits • TLIF – Lower lumbar (L3-4, L4-5 or L5-S1), if not able to get there via XLIF or ALIF • Expandable Cages – For MIS post-lat/lateral corpectomies

Conclusions • End plate preparation is key!! – Technology doesn’t make up for good surgical technique • Which interbody technique best? – Each has its own unique complications/advantages – Get some correction of sagittal alignment with each method • What do you need to achieve? – Alignment – Fusion – Both • What device/approach? Opportunity for studies

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