This work was supported by Japan Society for the Promotion of Science KAKENHI Grant Number 16K01434. The trial design was a single-arm, open-label, safety and feasibility study. All procedures used in this research were approved by Tsukuba University Clinical Research Review Board (approve number: CRB3180028) and performed in accordance with Declaration of Helsinki and Ethical Guidelines for Medical and Health Research involving Human Subjects issued by Japanese Ministry of Health, Labor and Welfare. The registration number was jRCTs031180078 (https://jrct.niph.go.jp/latest-detail/jRCTs031180078; date of registration: 11/01/2019). Written informed consents were obtained from all patients to participate in this study and for publication. The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.
Inclusion and exclusion criteria are shown in Table 2. Patients receiving long fusion of the cervical spine from C2 (or C3) to C7 (or T1) were recruited. The primary endpoint to confirm safety was any screw-related adverse events. Secondary endpoints to assess efficacy were the rate of loosening/breakage of the coated pedicle screws and duration until bony fusion. The Japanese Orthopedic Association (JOA) score and visual analogue scale (VAS) for neck/arm pain were used to assess clinical outcomes.
Preparation of screws coated with the FGF-2-calcium phosphate composite layer
An outline showing steps in formation of the FGF-2-calcium phosphate composite layer is shown in Fig. 1. The coating procedure was performed under the air cleanliness condition class 6 (ISO 14644-1) on a clean bench that is installed in a clean room (class 5) of the Cell Processing Factory at our institute. Three screws were coated with the FGF-2-calcium phosphate composite layer at one time, one for a quality check and two for surgery. The diameter and length of the pedicle screws were determined based on a preoperative CT measurement. Titanium alloy pedicle screws were used in the present study (Mounteneer®, DePuy Synthes spine, Bethesda, MA). The coating procedure is described elsewhere . Briefly, FGF-2 (Fiblast®, Kaken Pharmaceutical, Tokyo, Japan; 4µg/mL) was dissolved in a supersaturated calcium phosphate solution prepared by using clinically available infusions, and injection fluids. The screws were soaked for 48 hours at 37o C in the supersaturated calcium phosphate solution. A specific jig was made to hold the screws within the solution (Fig. 2A). After 48 hours of soaking, precipitate on the bottom of the cup and coating on the surface of the screws were confirmed (Fig. 2B, C).
One out of the three coated screws was used to check quality. The coated layer was dissolved in citrate solution and a protein assay (Bradford method), chemical analysis for the Ca/P molar ratio, and FGF-2 bioassay (NIH 3T3 cell proliferation) were performed. The supersaturated calcium phosphate solution was collected and subjected to bacteriological and endotoxin examinations.
Eight patients who underwent posterior fusion surgery of the cervical spine were enrolled in the present study (Fig. 3 and Table 3). Indications for surgery included ossification of the posterior longitudinal ligament (6 cases) and cervical spondylotic myelopathy (2 cases). The average age at surgery was 59.6 years old (48–64 yo).
The coated pedicle screws were inserted bilaterally into the lowest instrumented vertebrae (C7 or T1). All the patients were followed by assessment of clinical outcomes, X-rays, CT and laboratory investigation for one year after surgery. The definition of screw loosening was observation of a 1 mm or more lucent zone on the CT images. Bony union was evaluated by continuity between facet joints on a sagittal reconstruction CT multiplanar image.
Adverse events were defined as any symptom or disease in patients after informed consent with or without causal relationship to the coated screw. All adverse event-related terminology was coded by the investigators according to the ICH International Medical Dictionary for Regulatory Activities, Japanese version (MedDRA/J).