Bidirectional Expandable Technology for Transforaminal or Posterior Lumbar Interbody Fusion: A Retrospective Analysis of Safety and Performance

Expandable cage technology in minimally invasive transforaminal interbody fusion: where are we and what does the future hold?

INTRODUCTION

Expandable cages are designed to address the limitations of static cages in minimally invasive transforaminal lumbar interbody fusion (MI-TLIF). These devices enable collapsed insertion with in-situ expansion, aiming to restore disc height and lordosis, indirect foraminal decompression, and sagittal alignment with reduced neural and tissue trauma. Advancements in bi-dimensional cage expansion, endplate interaction, and innovative materials have been designed in attempt to improve fusion rates and clinicoradiographic outcomes.

AREAS COVERED

This review examines the structural design and mechanisms of expandable interbody cages, their clinical outcomes compared to static cages, and their limitations, including subsidence and cost. PubMed, Scopus, and Google Scholar were reviewed for relevant literature published up until November, 2024. We also discuss emerging technologies, such as bi-planar expansion cage technology and patient-specific implants, and their potential to optimize fusion procedures.

EXPERT OPINION

Expandable cages offer clear benefits for MI-TLIF, mainly restoring disc height and minimizing insertion-related risks. Innovations like bi-planar and patient-specific designs help address limitations, but cost and long-term outcomes remain concerns. These devices can improve fusion outcomes, especially in degenerative or deformity cases.

Minimally Invasive Posterior Cervical Fusion Strategies

Thoracolumbar minimally invasive spine surgery (MIS) has become widely adopted over the past two decades. MIS cervical fixation has lagged behind, largely because of complex and variable cervical spinal anatomy. Traditional open spine fixation techniques are associated with high fusion rates but are plagued by significant approach-related morbidity. This morbidity is due to paraspinal muscle denervation and atrophy secondary to disruption of the posterior musculoligamentous complex leading to wound healing difficulties, including relatively high rates of wound infection and dehiscence as well as aesthetic issues. Therefore, novel MIS fixation techniques have focused on percutaneous tissue-sparing approaches in an effort to decrease wound morbidity and hospital readmission. In addition, more biomechanically robust minimally invasive constructs may provide smaller alternative surgical solutions. Previously described fluoroscopic MIS cervical pedicle screw placement has been revitalized with the recent description of a navigated percutaneous minimally invasive technique. With the incorporation of new enabling navigation technologies, this technique is feasible, reproducible, and safe. In addition, these procedures have provided unique solutions for approaching cervical pathology in line with currently accepted MIS principles of the thoracolumbar spine. This review article discusses current minimally invasive posterior fusion strategies with a description of the technique and case demonstrations.

Expandable interbody cages for lumbar spinal fusion: a systematic review

BACKGROUND CONTEXT

Since the early 2000s, various expandable spinal fusion cages have been developed to facilitate less invasive procedures, however, expandable cages have often been evaluated as a homogeneous group, neglecting differences in shape, size, material, expandability and lordotic adjustability. This systematic review aimed to comprehensively survey the literature on expandable spinal fusion cages, discuss their differentiating factors, and identify gaps in the literature regarding these devices.

PURPOSE

To demonstrate the range of design features included in expandable interbody devices and identify which of these features are associated with improved surgical outcomes.

STUDY DESIGN

Systematic review.

METHODS

The study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. An electronic search of MEDLINE and Embase using the search terms "lumbar" AND "fusion" AND ("expandable cage" OR "expandable interbody") including only English language articles that contained sufficient detail to correlate a specific expandable cage design to patient outcomes. Relevant elements, including device design parameters, patient population information, details of the intervention, comparison data, outcome variables, and the timeframe were extracted. Statistical analysis was conducted to correlate patient outcomes with different device features.

RESULTS

While 387 different articles were initially identified, 49 met all the criteria for inclusion. Design differences contributed to disparate outcomes, with rectangular titanium cages featuring medial-lateral and vertical expansion and continuous lordotic adjustability being correlated with significantly improved patient-reported outcomes. The surgical approach and location were also found to be correlated with patient outcomes, indicating that confounding factors are present.

CONCLUSIONS

We recommend that expandable cage technologies not be considered a homogenous group, as long-term outcomes likely are dependent upon specific design characteristics. Categorizing devices based on design features such as material composition, shape, vertical expandability, horizontal expandability, and restoration of segmental lordosis may allow for more rapid identification of device characteristics associated with better outcomes.

Exploring the differences in radiologic and clinical outcomes of transforaminal lumbar interbody fusion with single- and bi-planar expandable cages: a systematic review and meta-analysis

Transforaminal lumbar interbody fusion (TLIF) is a universal surgical technique used to achieve lumbar fusion. Traditionally static cages have been used to restore the disc space after discectomy. However, newer technological advancements have brought up uniplanar expandable cages (UECs) and more recently bi-planar expandable cages (BECs), the latter with the hope of reducing the events of intra- or postoperative subsidence compared to UECs. However, since BECs are relatively new, there has been no comparison to UECs. In this PRISMA-compliant systematic review, we sought to identify all Medline and Embase reports that used UECs and/or BECs for TLIF or posterior lumbar interbody fusion. Primary outcomes included subsidence and fusion rates. Secondary outcomes included VAS back pain score, VAS leg pain score, ODI, and other complications. A meta-analysis of proportions was the main method used to evaluate the extracted data. Bias was assessed using the ROBINS-I tool. A total of 15 studies were pooled in the analysis, 3 of which described BECs. There were no studies directly comparing the UECs to BECs. A statistically significant difference in fusion rates was found between UECs and BECs (p = 0.04). Due to lack of direct comparative literature, definitive conclusions cannot be made about differences between UECs and BECs. The analysis showed a statistically higher fusion rate for BECs versus UECs, but this should be interpreted cautiously. No other statistically significant differences were found. As more direct comparative studies emerge, future meta-analyses may clarify potential differences between these cage types.

Transforaminal lumbar interbody fusion with an expandable interbody device: Two-year clinical and radiographic outcomes

Background

The use of interbody cages as an adjunct to lumbar spinal fusion remains an important technique to enhance segmental stability, promote solid arthrodesis, maintain neuroforaminal decompression, and preserve/improve segmental lordosis. Appropriate segmental lumbar lordosis and sagittal balance is well-known to be critical for long-term patient outcomes. This study sought to evaluate the radiographic and clinical results of TLIF in patients using an articulating, expandable cage. Primary endpoint was clinical and radiographic outcomes, including complications, at 12 and 24 months.

Methods

A total of 37 patients underwent open single-level or 2-level TLIF by a single surgeon using an expandable cage with concomitant bilateral pedicle screws and posterolateral arthrodesis. Clinical outcomes included ODI and VAS for back and legs. Radiographic outcomes included pelvic incidence and tilt, lumbar and segmental lordoses, and disc height at the operative level(s). All outcomes were collected at baseline, 2-weeks, 6-weeks, 3-months, 6-months, 12-months, and 24-months postop.

Results

A total of 28 patients were available for analysis. Nine patients failed to follow-up at 24 months. Mean ODI scores showed significant improvement, from pre-to-postoperative at 24 months (55%; p<.0001). VAS for back and legs was significantly lower at 24 months on average by 72 and 79%, respectively (p<.0001 for both). Both segmental and lumbar lordoses significantly improved by 5.3° and 4.2° (p<.0001 and p=.049), respectively. Average disc height improved by 49% or 6.1 mm (p<.001). No device-related complications nor instances of measured subsidence. One patient had a superficial infection, and another had an intraoperatively repaired incidental durotomy.

Conclusions

The use of an expandable cage contributed to improvement in both segmental and lumbar lordosis with no reported complications at 24-month follow-up. All clinical measures significantly improved as well. The expandable cage design represents an effective and safe option to increase cage size and allow significant segmental lordosis correction.

Biplanar Expandable Cages for Transforaminal Lumbar Interbody Fusion Are Safe and Achieve Good 1-Year Clinical and Radiological Outcomes in an Asian Population

BACKGROUND

This study investigated 1-year clinical and radiological outcomes of biplanar expandable (BE) cages following transforaminal lumbar interbody fusion (TLIF) in an Asian population.

METHODS

A retrospective review was conducted of all consecutive patients who underwent TLIF with BE cages performed by 2 fellowship-trained spine surgeons from 2020 to 2021. Inclusion criteria included open or minimally invasive (MIS) TLIF, of up to 3 spinal segments, performed for treatment of degenerative disc disease, spondylolisthesis, or spinal stenosis. Patient-reported outcomes, including visual analog score (VAS) for back and lower limb pain, Oswestry Disability Index (ODI) and North American Spine Society neurogenic symptom score (NSS), and various radiographic parameters, were evaluated.

RESULTS

A total of 23 patients underwent TLIF with BE cages with a follow-up duration of 1.25 years. Of those patients, 7 (30%) underwent 1-level TLIF, 12 (52%) underwent 2-level TLIF, and 4 (18%) underwent 3-level TLIF, with a total of 43 spinal segments fused. Four patients (17%) underwent MIS TLIF while 19 patients (83%) underwent open TLIF. VAS for back pain scores improved by 4.8 ± 3.4 (P < 0.001) from 6.5 ± 2.6 to 1.7 ± 2.2; VAS for lower limb pain scores improved by 5.2 ± 3.8 (P < 0.001) from 5.7 ± 3.4 to 0.5 ± 1.6; ODI scores improved by 29.0 ± 18.1 (P < 0.001) from 49.4 ± 15.1 to 20.4 ± 14.2; and NSS scores improved by 36.8 ± 22.1 (P < 0.001) from 53.3 ± 21.1 to 16.5 ± 19.8. Significant improvements in radiological parameters included increase in anterior disc height, posterior disc height, foraminal height, segmental lordosis, and lumbar lordosis. There were no implant-related complications, cage subsidence, cage migration, or revision surgery at 1 year.

CONCLUSIONS

TLIF performed with BE cages led to significantly improved patient-reported outcomes and radiographic parameters at 1 year and is safe for use in Asians.

CLINICAL RELEVANCE

The results of this study support the effectiveness and safety of TLIF with biplanar expandable cages.

LEVEL OF EVIDENCE: 4

Device profile of the FlareHawk interbody fusion system, an endplate-conforming multi-planar expandable lumbar interbody fusion cage

INTRODUCTION

The FlareHawk Interbody Fusion System is a family of lumbar interbody fusion devices (IBFDs) that include FlareHawk7, FlareHawk9, FlareHawk11, TiHawk7, TiHawk9, and TiHawk11. These IBFDs offer a new line of multi-planar expandable interbody devices designed to provide mechanical stability, promote arthrodesis, and allow for restoration of disc height and lordosis through a minimal insertion profile during standard open and minimally invasive posterior lumbar fusion procedures. The two-piece interbody cage design consists of a PEEK outer shell that expands in width, height, and lordosis with the insertion of a titanium shim. Once expanded, the open architecture design allows for ample graft delivery into the disc space.

AREAS COVERED

The design and unique features of the FlareHawk family of expandable fusion cages are described. The indications for their use are discussed. Early clinical and radiographic outcome studies using the FlareHawk Interbody Fusion System are reviewed, and properties of competitor products are outlined.

EXPERT OPINION

The FlareHawk multi-planar expandable interbody fusion cage is unique amongst the many lumbar fusion cages currently on the market. The multi-planar expansion, open architecture, and adaptive geometry set it apart from its competitors.