4 Posterior Interbody Cages

Adam B. Wiggins, Benjamin Khechen, Brittany E. Haws, Ankur S. Narain, Fady Hijji, Kamran Movassaghi, Kaitlyn L. Cardinal, Jordan A. Guntin, and Kern Singh

4 Posterior Interbody Cages

4.1 Introduction

4.1.1 Interbody Cage Overview

Interbody cage technology has continued to evolve since its first use in spinal fusion. Initially, autologous bone graft was utilized to induce fusion; however, this was often associated with substantial postoperative complications. ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ Interbody cages were eventually developed as a standalone construct to improve stability and distraction within the intervertebral space while also promoting bone ingrowth. ⁶ ^, ⁷ As such, interbody cages have allowed for improved fusion rates while decreasing postoperative pain, hospital length of stay, and complication rates. ⁸ Indications for posterior lumbar interbody cages are provided in Table 4.1.

A variety of lumbar interbody cages have been developed to maximize the implant’s ability to correct deformity, provide mechanical stability, and provide the optimal environment for vertebral arthrodesis. In order to perform this, a cage must exhibit a small material volume in order to maximize the volume for bone graft. ⁹ Additionally, the interbody cage must exhibit a large footprint to optimize the interface between the prepared vertebral end plates and interbody cage. ¹⁰ Finally, the interbody cage should provide restoration of disk height and lordosis along with the restoration of load bearing to the anterior column. ¹¹

4.1.2 Interbody Cage Classification

Interbody Cage Geometry—Standard Cages

Interbody cages are classified by one of three different structures: horizontal cylinders (HCs), vertical rings (VRs), and open boxes (OBs). HCs were one of the first structures to be developed and have been considered successful in correcting deformity and providing stability. ¹² However, these interbody cages are not frequently utilized in today’s surgical setting.

A VR is another type of interbody cage. These interbody cages are utilized with anterior and lateral approaches to the lumbar spine. The design of VR cages was initially adapted from the design of femoral cortical rings. ¹³ This structure of cage has exhibited moderate ability to correct mechanical deformation. Disk height has previously been demonstrated to be maintained well with this implant, typically exhibiting an average loss of 1 mm at 1 year postoperatively. ⁹ Additionally, the increase in neuroforaminal area is similar to that provided by HCs. ⁹

**Table 4.1** Overview of surgical indications for posterior lumbar interbody cages
Indications
Degenerative disk disease (one or two level) Spondylolisthesis (Grade 1 only) Spinal stenosis Spinal deformity

Fig. 4.1 Open box interbody cage.

OB cages are the third type of geometry for interbody cages ( Fig. 4.1). They are one of the most frequently utilized interbody cage structures, and are often used for minimally invasive transforaminal lumbar interbody fusions (MIS TLIFs). ¹⁴ OB cages have exhibited satisfactory outcomes in correcting mechanical deformity, achieving stability, and promoting arthrodesis. ⁹ With appropriate surgical technique, OB cages can restore disk height and potentially increase neuroforaminal area. ⁹ Restoration of lumbar lordosis with OB cages has also been demonstrated to be similar to that achieved with HC cages. ¹⁴ These cages have recently been developed to exhibit a wedge shape in order to improve lordosis. OB cages have also demonstrated successful fusion rates, likely due to the sufficient volume available for bone graft and wide surface area for contact with the vertebral end plates. ⁹

Interbody Cage Geometry—Expandable Cages

Expandable interbody cages have recently been developed in attempts to overcome some of the challenges associated with minimally invasive techniques. ¹⁵ Due to the narrow surgical access corridor and anatomic positioning of minimally invasive posterior approaches, the interbody cages utilized in these techniques are often limited in size. ¹⁵ ^, ¹⁶ These smaller implants reduce the contact surface area between the vertebral end plates and the interbody cage, increasing the risk for subsidence and pseudarthrosis. ¹⁶ ^, ¹⁷ ^, ¹⁸

Some expandable interbody cages are capable of expansion in both the medial-lateral and cranial-caudal planes. These attributes may facilitate fusion and reduce the rate of subsidence by increasing the surface area of the vertebral end plate that is in contact with the implant. However, despite these theorized benefits, there remains limited data regarding the clinical efficacy of expandable cages. ¹⁵ ^, ¹⁹

Interbody Cage Materials

Two predominant materials are typically utilized for interbody cages: metal and carbon fiber. Titanium is the predominant material utilized for metal cages, and polyetheretherketone (PEEK) is typically utilized in carbon fiber cages. To determine the success of a particular material for use as an interbody cage, the biologic response, biomechanical strength, and radiographic characteristics are typically assessed.

Both titanium and PEEK cages have exhibited favorable outcomes for arthrodesis and biomechanical strength. Due to the material’s strength, titanium cages are thought to have increased stability and reduced micromotion when compared to PEEK cages. ⁹ However, PEEK cages may exhibit several advantages over titanium cages, including the avoidance of metal allergies, radiolucency, and reduced artifact on MRI. ²⁰ ^, ²¹ ^, ²² ^, ²³ ^, ²⁴ These radiographic advantages allow for better analysis of arthrodesis postoperatively. PEEK cages also exhibit moderate stiffness with some elasticity, potentially increasing fusion rates. ²¹ However, despite these proposed benefits, superiority of PEEK cages over titanium cages remains controversial. ²⁵ Previous studies have demonstrated varying results, with similar fusion rates between titanium and PEEK cages. ²⁵

4.1.3 Minimally Invasive Transforaminal Lumbar Interbody Fusion

Since its introduction by Holly et al, ²⁶ MIS TLIF has been demonstrated to reduce blood loss, postoperative pain, and length of hospital stay when compared to traditional open posterior techniques. ²⁷ ^, ²⁸ ^, ²⁹ ^, ³⁰ ^, ³¹ ^, ³² As such, MIS TLIF has been increasingly utilized for the treatment of degenerative lumbar disease, trauma, and deformity. However, this technique requires surgeon experience with a variety of MIS instrumentation as well as comfortability with the approach.

4.2 Static Carbon Fiber Interbody Cages

**Table 4.2** Alphatec Spine Novel^® SD
Design
Cage type Static	Composition PEEK	Design feature Multiple insertion points allow for added flexibility

Modular aspects and variations
Width 9 mm	Length 22, 25, 28 mm	Height 8–15 mm (1-mm increments)	Lordotic angle 0°

Procedures
MIS TLIF

Supplemental fixation systems
Alphatec Spine Zodiac^® Polyaxial Spinal Fixation System

**Table 4.3** Alphatec Spine Novel^® Tapered TL
Design
Cage type Static	Composition PEEK	Design feature Biconvex shape allows for increased endplate contact

Modular aspects and variations
Width 10 mm	Length 24, 28, 30 mm	Height 6–15 mm (1-mm increments)	Lordotic angle 0°

Procedures
MIS TLIF

Supplemental fixation systems
Alphatec Zodiac^® Polyaxial Spinal Fixation System

**Table 4.4** DePuy Synthes OPAL™ Spacer System
Design
Cage type Static	Composition PEEK	Design feature Design variations allow for two insertion options

Modular aspects and variations
Width 9 and 10 mm	Length 28 and 32 mm	Height 7–17 mm (1-mm increments)	Lordotic angle 0°

Procedures
MIS PLIF
Radiographs unavailable
Supplemental fixation systems
DePuy Synthes posterior stabilization system for MIS

**Table 4.5** DePuy Synthes T-PAL™ Interbody Spacer System
Design
Cage type Static	Composition PEEK	Design feature Incorporated TRACK technology improves implant stability

Modular aspects and variations
Width 10 and 12 mm	Length 28 and 32 mm	Height 7–17 mm (1-mm increments)	Lordotic angle 5°
Procedures
MIS TLIF

Supplemental fixation systems
DePuy Synthes posterior stabilization system for MIS

**Table 4.6** Globus Medical SUSTAIN®-R Arch
Design
Cage type Static	Composition PEEK	Design feature Unique shape designed to follow contour of vertebral body

Modular aspects and variations
Width 10 mm	Length 27 and 30 mm	Height 7–17 mm (2-mm increments)	Lordotic angle 0°

Procedures
MIS TLIF
Radiographs unavailable
Supplemental fixation systems
Globus Medical REVOLVE® posterior stabilization system

**Table 4.7** Globus Medical SUSTAIN^®-O
Cage design
Cage type Static	Composition PEEK	Design feature Superior and inferior surfaces feature directional teeth to resist expulsion

Modular aspects and variations
Width 8, 10, 12 mm	Length 22, 26, 30 mm	Height 8–13, 15, 17 mm	Lordotic angle 7°

Procedure
MIS TLIF
Radiographs unavailable
Supplemental fixation systems
Globus Medical REVOLVE^® posterior stabilization system for MIS

**Table 4.8** Globus Medical SUSTAIN^®-R Small and Small Narrow
Design
Cage type Static	Composition PEEK	Design feature Large axial window for graft material

Modular aspects and variations
Width 8 and 10 mm	Length 22 mm	Height 7–17 mm (2-mm increments)	Lordotic angle 7°

Procedures
MIS TLIF
Radiographs unavailable
Supplemental fixation systems
Globus Medical REVOLVE^® posterior stabilization system for MIS

**Table 4.9** K2 M ALEUTIAN® AN and AN Oblique Interbody Systems
Design
Cage type Static	Composition PEEK	Design feature Bulleted nose with convex design to minimize endplate preparation

Modular aspects and variations
Width 8.5 mm Oblique: 8.5, 10, 12 mm	Length 22 and 28 mm Oblique: 28 and 32 mm	Height 6–13 mm, 15, 17 mm Oblique: 7–15 mm	Lordotic angle 0°

Procedures
MIS TLIF

Supplemental fixation systems
K2 M Terra Nova® Minimally Invasive Access System

**Table 4.10** K2 M ALEUTIAN® TLIF 2
Design
Cage type Static	Composition PEEK	Design feature Articulating inserter allows for variable angulation from 0 to 60° in situ

Modular aspects and variations
Width 10 and 12 mm	Length 28, 32, 36 mm	Height 7–15 mm (1-mm increments)	Lordotic angle 0 and 7°
Procedures
MIS TLIF
Radiographs unavailable
Supplemental fixation systems
K2 M Terra Nova® Minimally Invasive Access System

**Table 4.11** NuVasive CoRoent® Large Contoured
Design
Cage type Static	Composition PEEK	Design feature Cage curvature matches contour of vertebral body

Modular aspects and variations
Width 9 and 11 mm	Length 25 mm	Height 8–14 mm (2-mm increments)	Lordotic angle 8°

Procedures
MIS TLIF, MIS LLIF
Radiographs unavailable
Supplemental fixation systems
NuVasive Precept® posterior stabilization system

**Table 4.12** NuVasive CoRoent^® Large Narrow and Wide
Design
Cage type Static	Composition PEEK	Design feature Designed for utilization in transforaminal, posterior, or lateral approach

Modular aspects and variations
Width 9 and 11 mm	Length 25 and 30 mm	Height 8–14 mm (2-mm increments)	Lordotic angle 0°

Procedures
MIS PLIF, MIS TLIF
Radiographs unavailable
Supplemental fixation systems
NuVasive Precept® posterior stabilization system

**Table 4.13** NuVasive CoRoent® Large Oblique (LO) Interbody Cage Device
Design
Cage type Static	Composition PEEK	Design feature Designed specifically for oblique placement

Modular aspects and variations
Width 10 mm	Length 25, 30, 35, 40 mm	Height 8, 10, 12, 14 mm	Lordotic angle 5°

Procedures
MIS TLIF, MIS LLIF

Supplemental fixation systems
NuVasive Precept® posterior stabilization system

**Table 4.14** NuVasive CoRoent® Large Tapered Interbody Cage Device
Design
Cage type Static	Composition PEEK	Design feature Anatomical lordotic design induces proper sagittal balance

Modular aspects and variations
Width 9 mm	Length 20 mm	Height 8–14 mm (2-mm increments)	Lordotic angle 8 and 15°

Procedures
MIS PLIF, MIS LLIF
Radiographs unavailable
Supplemental fixation systems
NuVasive Precept® posterior stabilization system

**Table 4.15** NuVasive CoRoent® MAS® PLIF
Design
Cage type Static	Composition PEEK	Design feature Contoured lateral edge designed to avoid the exiting nerve root

Modular aspects and variations
Width 9 mm	Length 23 and 28 mm	Height 8–14 mm (1 mm increments)	Lordotic angle 4, 8, 12°

Procedures
MIS PLIF

Supplemental fixation systems
NuVasive Precept® posterior stabilization system

**Table 4.16** RTI surgical bullet-tip
Design
Cage type Static	Composition PEEK	Design feature Bullet-shaped tip provides self-distraction

Modular aspects and variations
Width 8–17 mm (1-mm increments)	Length 22, 26, 32 mm	Height 8–17 mm (1-mm increments)

Procedures
MIS TLIF
Radiographs unavailable
Supplemental fixation systems
RTI Surgical Streamline® MIS spinal fixation system

**Table 4.17** RTI surgical T-Plus™
Design
Cage type Static	Composition PEEK	Design feature Cage curvature matches contour of vertebral body

Modular aspects and variations
Width 10 mm	Length 27 and 36 mm	Height 7–15 mm (1-mm increments)	Lordotic angle 0 and 6°
Procedures
MIS TLIF

Supplemental fixation systems
RTI Surgical Streamline® MIS spinal fixation system

**Table 4.18** SeaSpine Hollywood™
Design
Cage type Static	Composition PEEK	Design feature Cage curvature matches that of vertebral end plate

Modular aspects and variations
Width 11 mm	Length 27 mm	Height 7–18 mm (1-mm increments)	Lordotic angle 8°
Procedures
MIS TLIF

Supplemental fixation systems
SeaSpine posterior stabilization systems for MIS

**Table 4.19** SeaSpine Ventura™
Design
Cage type Static	Composition PEEK	Design feature Convex surfaces for a more secure interbody fit

Modular aspects and variations
Width 9 and 11 mm	Length 28 and 32 mm	Height 7–13 mm (1-mm increments), 15, 17 mm	Lordotic angle 0°
Procedures
MIS TLIF

Supplemental fixation systems
SeaSpine posterior stabilization systems for MIS

**Table 4.20** Zimmer Biomet Zyston® Curve Interbody Spacer System
Design
Cage type Static	Composition PEEK	Design feature Articulating mechanism allows for multiple insertion angles

Modular aspects and variations
Width 10 mm	Length 27 and 32 mm	Height 7–18 mm (1-mm increments)	Lordotic angle 0 and 6°

Procedures
MIS TLIF
Radiographs unavailable
Supplemental fixation systems
Zimmer Biomet posterior stabilization systems for MIS