Use of polyetheretherketone spacer and recombinant human bone morphogenetic protein-2 in the cervical spine: a radiographic analysis

Abstract

Background context: Results recently reported in the literature have raised some concerns regarding the use of recombinant human bone morphogenetic protein (rhBMP-2) in the cervical spine.

Purpose: We undertook a radiological and clinical review of cervical fusions performed at our institution with polyetheretherketone (PEEK) interbody cage and rhBMP-2.

Study design: Observational study.

Patient sample: Perioperative clinical and radiologic data of all patients who underwent an anterior cervical discectomy and fusion using PEEK and rhBMP-2 for cervical spondylotic radiculopathy or myelopathy were collected.

Outcome measures: Images were examined for fusion, heterotopic ossification, end-plate resorption, subsidence, and segmental sagittal alignment.

Methods: All patients underwent detailed postoperative radiologic analysis using a computed tomography (CT) scan obtained at least 6 months postoperatively and plain X-rays obtained at regular intervals.

Results: Twenty-two patients had 38 levels fused using PEEK and varying doses of rhBMP-2. No anterior cervical swelling requiring additional procedures or longer than anticipated hospital stays occurred. Pseudoarthrosis, shown as a horizontal radiolucent fissure through the midportion of the PEEK cage on CT, occurred in four patients. Excessive bone growth into the spinal canal or foramina occurred in 26 (68%) patients but did not result in neurologic sequelae. Cystic regions in the core of the PEEK spacer were seen in most patients, with 15 levels (39%) having cysts measuring 3mm or greater. Moderate or severe osteolysis of the end plates occurred in 57% of levels, and this led to subsidence of the construct and loss of some of the segmental sagittal alignment (ie, lordosis) that had been achieved with surgery.

Conclusions: The unlimited supply of PEEK spacers and rhBMP-2 and their ease of use make them attractive platforms to achieve fusion. This study has demonstrated that the fusion process using rhBMP-2 is a dynamic one, with osteolysis dominating the initial phase, leading to end-plate resorption and consequently loss of some of the disc space height and sagittal alignment that was achieved with surgery. There is a high incidence of bone growth beyond the core of the PEEK spacer and cystic regions within the cage. Given our experience, we currently reserve the use of PEEK and rhBMP-2 for use in those patients who are at greatest risk of pseudoarthrosis.