PEEK cages, allografts yield comparable outcomes in two-level ACDF

Polyetheretherketone (PEEK) cages show similar clinical outcomes but yield higher rates of subsidence in two-level anterior cervical discectomy and fusion (ACDF) relative to allografts, according to a new Singapore study.

“This study directly compared the clinical and radiological outcomes of allografts and PEEK cages with two similar groups who underwent two-level ACDF with anterior cervical plating,” researchers said. Aside from subsidence, “using either allografts or PEEK cages resulted in similar clinical outcomes, radiological improvements in alignment and fusion rates.”

The retrospective analysis included 88 consecutive patients undergoing two-level ACDF. Fifty-three (median age, 52.4 years; 50.9 percent male) received allografts and 35 (median age, 56.0 years; 54.3 percent male) were given PEEK cages. Both groups were demographically and clinically comparable at baseline, except for the Japanese Orthopedic Association (JOA) score, which was elevated in allograft patient (p=0.008).

Six months after the operation, participants in both groups showed significant improvements in the Neck and Pain Disability (NPD), Neck Disability Index (NDI), Visual Analogue Scale Neck Pain (VASNP), Visual Analogue Scale Limp Pain (VASLP), and JOA scales relative to baseline (p<0.001 for both groups in all outcome scales). Improvements remained significant until 2 years after surgery. [BMC Musculoskelet Disord 2020;21:331]

Comparing the interventions with each other, outcomes were generally comparable. The only exception was JOA at 2 years postsurgery, during which time scores in the allograft group were higher (p=0.03).

In contrast, cage subsidence appeared to be greater in the PEEK arm. Subsidence at the cephalad level occurred in 22.9 percent of the segments in the PEEK participants, as opposed to only 7.7 percent of segments in the allograft group. The difference was of borderline significance (p=0.057).

At the caudal level, the gap was more prominent. PEEK patients saw a subsidence rate of 37.1 percent, while those in the allograft group only saw 15.4-percent subsidence (p=0.02). This led to an overall significantly higher subsidence rate in the PEEK arm (30 percent vs 11 percent; p<0.05).

“There was a demonstrable improvement in lordosis in both the allograft and PEEK groups. However, concerning cage subsidence, it was noted that PEEK cages caused more subsidence than allograft cages,” the researchers said.

There may be several explanations for this, they continued. “First, although PEEK mimics the elastic modulus of bone, this material is nonresorbable and may result in point loading.” The formation of fibrous tissue in the interface of the bone and the implant may also slow down osteointegration and promote micromotion.

“Furthermore, our study also demonstrated that subsidence does not impact clinical outcomes, which is consistent with the literature,” the researchers added.

In the present study, the allograft used was a saline-packaged femoral or tibial cortical-cancellous allograft. It shared the same dimension to PEEK cages and was ready for intraoperative use. In terms of participants, only those who received surgical interventions for degenerative disc diseases and spondylosis, and were able to fulfil at least 2 years of follow-up, were eligible. All operations were performed at the Singapore General Hospital.