Abstract

Background: Multiple anterior cervical diskectomy/fusion (ACDF) techniques now use a variety of Polyehteretherketone (PEEK) cages; stand-alone (SA) and zero-profile (ZP) with/without screws, cages filled with demineralized bone matrix/autograft, and cages coated with hydroxyapatite or titanium. We compared the safety/ efficacy between different PEEK ACDF cage constructs in 17 studies, and in some cases, additionally contrasted results with “routine” ACDF (i.e. series/historical data performed with combinations of iliac autograft/allograft and plates).

Methods: We focused on the clinical outcomes, fusion rates, postoperative radiographic changes/lordosis/ subsidence, and/or reoperation rates for various PEEK ACDF constructs vs. “routine” ACDF.

Results: One to 3 and 4-level PEEK ACDF cages demonstrated high fusion rates, few cage failures, and low reoperation rates. Subsidence for PEEK ACDF cages did not reduce fusion rates or diminish the quality of postoperative outcomes. Further, titanium-coated (T-C) PEEK cages lowered fusion rates in one study (i.e. 44.1% fusions vs. 88.2% for routine PEEK ACDF) while ACDF PEEK cages coated with hydroxyapatite (HA) showed only a “trend” toward enhanced arthrodesis.

Conclusion: One to 3-4 multilevel ACDF PEEK cage constructs demonstrated comparable safety/efficacy when compared with each other, or in select cases, with “routine” ACDF (i.e. using autograft/allograft and plates).

Keywords: Anterior cervical diskectomy fusion (ACDF), Cages, Complications, Fusion rates, Hydroxyapatite Coated (HA), Outcomes, Polyetheretherketone (PEEK), Screws, Stand-Alone (SA), Subsidence, Titanium-Coated (T-C), Zero Profile (ZP)

INTRODUCTION

Multiple anterior cervical diskectomy/fusion (ACDF) Polyetheretherketone (PEEK) cage constructs/techniques are now available. Their various designs include; Stand Alone (SA) or Zero Profile (ZP) cages with/without screws, cages filled with demineralized bone matrix (DBM) and/or autograft, and PEEK cages coated with hydroxyapatite or titanium [ Table 1 ].[ 1 - 17 ] Here, we reviewed 17 papers comparing the relative safety/efficacy of different single to 3 and 4-level PEEK cage ACDF constructs, with select comparisons to “routine” ACDF controls (i.e. typically using iliac autograft or allograft, and plates). Analyses focused on the clinical outcomes, fusion rates, postoperative radiographic findings (i.e. lordosis, subsidence, disc space height), and/or reoperation rates in these studies.

Table 1:

Summary of findings of papers using PEEK cages for ACDF.

Methods

Seventeen studies focused on the safety/efficacy between different ACDF PEEK cage constructs with occasional comparisons to “routine” ACDF controls [ Table 1 ].[ 1 - 17 ]

Cho et al. Study from 2002 Fusion Rates and Complications for PEEK ACDF vs. Iliac Autograft ACDF

Cho et al. (2002) compared the complications, fusion rates, and outcomes for 40 patients undergoing ACDF with PEEK cages vs. 40 having ACDF utilizing iliac crest autograft (IA) [ Table 1 ].[ 4 ] PEEK ACDF cages resulted in comparable fusion rates, the same increases in foraminal area, and similar outcomes vs. ACDF/IA. However, PEEK ACDF cages had the added benefits of; increasing the cervical lordosis (i.e. an average of + 2.33 mm), decreasing the complication rate (2.5% vs. 17.5% for ACDF/IA), reducing artifact, and providing better visualization on postoperative MR studies.

Results of 1-Level PEEK ACDF

Several 1-level PEEK ACDF studies showed good/excellent postoperative results with high fusion rates [ Table 1 ].[ 3 , 5 ] Faldini et al. (2011) looked at 25 patients undergoing 1-level PEEK ACDF with a 2-year follow-up; there was nearly a 100% fusion rate at 5 postoperative months leading the authors to conclude that single-level PEEK ACDF constructs were safe and effective.[ 5 ] Comparing 41 single-level PEEK ACDF with hydroxyapatite (HA) coated cages vs. 47 PEEK ACDF cages without HA, Chin et al. (2021) found significant differences in VAS (Visual Analog Scale) and NDI (Neck Disability Index) scores (i.e. improvement) with the addition of HA at 2 postoperative years.[ 3 ] There was also a “trend” toward faster fusion with HA PEEK ACDF cages (i.e. as early as 3-5 postoperative months) vs. slower fusion rates (i.e. of 7-8 months) for those performed without HA impregnated into cages.

Results of 1 to 2-Level PEEK ACDF

Multiple 1 to 2-level PEEK ACDF studies also demonstrated high fusion rates and improved outcomes [ Table 1 ].[ 13 - 15 , 17 ] Of the 1-level (127 patients) and 2-level (125 patients) SA PEEK ACDF performed by Shiban et al. (2016), high fusion rates (85% and 95%), comparable frequencies of adjacent segment disease (20% and 29%) and subsidence (25% and 27%), and low reoperations rates were respectively encountered.[ 13 ] Outcomes for Shiban et al. (2018) 194 patients undergoing single (98 patients) and 2-level (96 patients) SA PEEK ACDF supplemented with demineralized bone matrix (DBM) revealed improvement in postoperative VAS scores, high fusion rates (79% 1-level and 82% 2-level), low reoperation rates for ASD (7% and 8%), and low implant failure rates (7% and 8%).[ 14 ] Further, there was no correlation between X-ray findings and clinical status at one postoperative year. When Spanos et al. (2018) evaluated clinical and X-ray outcomes for 74 patients undergoing 1-2 level PEEK ACDF, they found significantly reduced postoperative cervical lordosis and sagittal range of motion (ROM) that did not significantly impact disability as determined utilizing the NDI-PS (Neck Disability Index-Polish Rating Scale)and NRS (Numerical Rating Scale). After Zapolsky et al. (2019) performed 30 single to 2-level SA PEEK ACDF, they found that patients demonstrated 100% fusion rates with significant reductions in pain (97%), and significant improvement in the NDI - PL at one postoperative year.[ 17 ]

Results of 2-Level PEEK ACDF

Several 2-level PEEK ACDF studies verified high fusion rates and better outcomes with these constructs [ Table 1 ].[ 10 , 16 ] In 2009, Topuz et al. supplemented 79 two-level adjacent PEEK ACDF with demineralized bone matrix (DBM) and autograft; outcomes were excellent/good (Odom’s Criteria) in 69 patients.[ 16 ] Further, 91.7% fused (based on X-rays alone obtained 3-24 mos. postoperatively); there were no cage failures/dislocations, and no reoperations [ Table 1 ]. Additionally, as Ng et al. (2019) used SA Peek ACDF Cages for 2-level procedures in 31 patients, they demonstrated a 100% fusion rate, no significant cage migration, and very satisfactory outcomes (i.e. improvement from 10.2 to 13.89 in the mean JOA Score (Japanese Orthopedic Association Score) over an average 24 month follow-up period).[ 10 ] Notably, 2 patients who developed ASD required secondary laminoplasties performed 3 years following their index surgery.[ 10 ]

Results of 3-4 Level PEEK ACDF

Several other series additionally documented the safety/ efficacy of 3 and 4-level PEEK ACDF [ Table 1 ].[ 1 , 12 , 13 ] Pereira et al. (2013) looked at outcomes over 2 postoperative years for 3 (23 patients) and 4-level (7 patients) ACDF PEEK cage fusions performed without anterior plating [ Table 1 ].[ 12 ] They observed significant postoperative improvement in VAS and JOA scores for these patients. Notably, 10% of patients exhibited recurrent disease at the index level warranting secondary posterior decompressions. When Shiban et al. (2016) evaluated 3-level stand-alone (SA) PEEK ACDF, the fusion rate was 94%, the incidence of adjacent segment disease (ASD) was 15%, and the rate of subsidence was 15%. Of interest, in their latter series that included 1 to 3-level procedures, overall reoperation rates were low (i.e. 16 (6%) for ASD and 4 (1.5%) for implant failures).[ 13 ] Analysis by Ashour et al. (2020) regarding the safety/efficacy of 66 4-level SA PEEK ACDF performed without plates revealed significant improvement in the mean postoperative JOA scores while adequately preserving the cervical lordosis (i.e. no significant changes in the curvature index).[ 1 ]

Results of Zero Profile PEEK Cages vs. Stand Alone PEEK Cages for 3-4 Level ACDF

Zero Profile (ZP) PEEK ACDF, comprised of a radiolucent polyetheretherketone (PEEK) cage with an anterior titanium 4 hole plate for screw placement, were developed to avoid complications of anterior cervical plates, while maintaining stability (i.e. of interbody cages with plates). Two studies confirmed excellent results with ZP PEEK ACDF devices [ Table 1 ].[ 2 , 6 ] In 2016, Gerszten et al. (2016) placed 3 to 4-level (i.e. total 110 levels) ZP PEEK ACDF with screws in 33 patients vs. SA PEEK ACDF cages in 35 patients without screws or plates; they found comparable VAS outcomes for both groups, but showed that ZP PEEK cages reduced dysphagia rates.[ 6 ] When Balakumar et al. (2021) compared the results for 83 SA PEEK ACDF cages (i.e. at 111 levels) vs. 79 ZP PEEK ACDF cage-Screw constructs (i.e. at 111 levels) performed over a 2-24 month follow-up period, they found no significant differences between the two regarding; adverse events/complications, sagittal balance, fusion rates, or incidence of subsidence [ Table 1 ].[ 2 ]

Lower Fusion Rates for Titanium-Coated (T-C) PEEK ACDF vs. PEEK ACDF Alone

In 2022, Godlewski et al. compared fusion rates for 85 PEEK ACDF cages vs. 59 T-C PEEK ACDF cages.[ 7 ] At 12 months postoperatively, CT scans had been performed in 86 patients, and X-rays in 102 patients. These studies demonstrated total fusion in 101 patients and partial fusion in 43 patients; none showed complete fusion failure. Of interest, however, the PEEK ACDF without T-C showed significantly higher 88.2% fusion rates vs. a much lower 44.1% rate for T-C PEEK ACDF.

Subsidence Rates Following Single or Multilevel PEEK ACDF Cage Constructs Varying from Stand-Alone Devices to Titanium-Coated (T-C) PEEK Cages

Several studies documented various postoperative subsidence rates (i.e. defined as a decrease in interbody height of >3 mm on X-rays at 1-year postoperatively) following single to multilevel PEEK ACDF cage procedures [ Table 1 ].[ 2 , 9 - 11 , 13 , 14 ] Park et al, (2016) studied subsidence rates following 77 1-level stand-alone PEEK ACDF cage procedures (2005–2012); subsidence occurred in 26 of 77 (33.8%) patients, 25 of whom solidly fused, while another 47 of 51 patients without subsidence fused.[ 11 ] They concluded subsidence did not negatively impact fusion rates or outcomes. Subsidence rates in Shiban et al. (2016) varied from 25% for 1-level, to 27% for 2-level, and 15% for 3-level SA PEEK ACDF cage procedures (265 cases); reoperations were warranted for ASD (16 patients) or implant failures (4 patients), but none required repeat surgery for subsidence.[ 13 ] Later in 2018, Shiban et al. found in their 1-2 level SA PEEK ACDF cage series (184 patients) that subsidence did not negatively impact patients’ clinical outcomes.[ 14 ] Ng et al. (2019) noted that for 31 patients undergoing 2-level SA PEEK ACDF, the subsidence rate was 22.5%, but it also did not negatively impact JOA scores or fusion rates.[ 10 ] When Nakanishi et al. (2020) looked at the safety of performing 62 single to 2-level T-C SA PEEK cage procedures (i.e. followed for at least 6 months), subsidence occurred in 11 (17.7%) of 62 cases, and was moderate in 14.5%, but severe in 3.2% of cases.[ 9 ] Interestingly, the frequency of subsidence was similar for those <65 and >65 years of age (i.e. concluded safe/effective in elderly), and did not negatively impact outcomes. When Balakumar et al. (2021) compared SA PEEK ACDF (83 patients) vs. ZP PEEK ACDF cage procedures (79 patients), there were just 2 instances of subsidence in the SA PEEK ACDF group, but none in those receiving ZP devices.[ 2 ]

Double Lucency X-ray Sign of Titanium-Coated PEEK ACDF (Plus Autograft) Fusion

Hellbusch et al.(2012) described the double lucency sign for confirming fusion based on X-rays performed in 148 patients undergoing 1-level Titanium-Coated (T-C) PEEK ACDF cage fusions filled with autograft [ Table 1 ].[ 8 ] This sign, defined as consisting of a “complete radiolucent ring around Titanium markers” was seen in 91% of patients, and added confirmation of fusion.

CONCLUSION

Comparison between multiple types of ACDF PEEK cage constructs and select instances of “routine” ACDF largely demonstrated comparable safety/efficacy for these procedures.

Declaration of patient consent

Patients’ consent not required as patients’ identities were not disclosed or compromised.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

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