Investigators have found that nanocoated polyetheretherketone (PEEK) cages for posterior lumbar interbody fusion (PLIF) achieve a better fusion rate than uncoated PEEK cages at one year follow-up—while also having similar safety and efficacy outcomes. These are the conclusions of a randomised controlled trial, conducted by Karel Willems (Department of Orthopedic Surgery, AZ Delta, Roselare, Belgium) and colleagues, published in the International Journal of Spine Surgery.
According to the study team, PEEK is among the most popular materials for fusion cages alongside Titatnium (Ti and its alloys). The material is an inert biocompatible polymer, with a relatively low elastic modulus, similar to that of bone, and has been found to have reduced subsidence and implant failure. However, they note that due to the inert and hydrophobic nature of the material, osseintegration is limited, meaning that fibrous layers often appear at the PEEK-bone surface. “Given its interesting material properties,” Willems and colleagues wrote, “PEEK may be an attractive platform upon which to tailor new biomaterials”. They add that various types of bioactive coatings have been developed to improve the limited osseointegration of PEEK, including calcium phosphate (CaP), hydroxyapatite (HA), carbon coatings and Ti.
The study aimed to investigate the clinical outcome improvements of nanocoated PEEK cages compared with those of uncoated PEEK cages, to ascertain the safety of the nanocoated devices, as well as study the radiological outcomes to assess the osseointegration or fusion rate of the nanocoated vs. uncoated cages. Comparisons were made until one-year after the surgical procedures.
Three clinical centres participated in the study: Regionaal Ziekenhuis Sint-Trudo (Sint Truiden, Belgium), AZ Maria Middelares (Gent, Belgium), and AZ Delta (Roeselare, Belgium), and patients were recruited between August 2013 and October 2014. Inclusion criteria stipulated that patients needed to be aged between 18 and 75 years with chronic mechanical low back pain with or without pain radiation to the knee (>6 months). Patients requiring surgical treatment at more than one level or with previous fusion surgery at the affected levels were excluded from the study.
Three different types of cages were used in the trial: a PEEK cage with Ti nanocoating (TSC), an uncoated PEEK cage (reCreo), and a PEEK cage with CaP nanocoating (osteoCon) (Orthobion, Konstanz, Germany). The PLIF procedures were performed by three orthopaedic surgeons using a standardised surgical technique, which was identical for all three types of cages in the study.
Primary clinical outcome parameters were the scores from the visual analogue scale (VAS) for back and leg pain, the Oswestry Disability Index (ODI) and the 36-Item Short Form Survey (SF-36). Patients were asked to report VAS back and leg pain score and ODI score pre-operatively and at three, six and 12 months after the surgery. The SF-36 was completed pre-operatively and 12 months after the surgery.
The primary radiological outcome was the implant stability and fusion status, assessed by X-ray and computed tomography (CT) scans. To assess possible cage migration, standing anteroposterior and lateral radiographs were performed pre-operatively, and at three, six and 12 months after surgery.
In total, 127 patients from the three centres met the inclusion criteria and were enrolled into the trial. Forty-four were randomised into Group A (using PEEK cages with Ti nanocoating), 37 patients into group B (using uncoated PEEK cages, and 46 into group C (PEEK cages with CaP nanocoating). Gender and age were comparable among the three treatment groups. The most common operated levels were L4-L5 (50 out of 127 patients) and L5-S1 (64 out of 127 patients). Sixty one of the patients were male, and 66 female, with an average overall age of 50.51.
Outlining the results, the study team note there was a significant improvement in back pain intensity, measured through the VAS score, between the pre-operative and the last follow-up measurements for each group. However, there was no significant difference between each of the three groups. This proved also to be the case for the ODI scores, with no significant overall difference between each of the groups. Physical functioning and bodily pain, as included in the SF-36 survey were also found to improve significantly over time in each group, with no significant difference between each. In terms of the radiological outcomes—which were determined by an independent spine radiologist—the study team found that 77.1% of patients in the group with Ti nanocoated cages had fusion grade 1, while in the group with CaP nanocoated cages, 79.3% of patients achieved definite fusion. Comparatively, 29.4% of patients in the control group, using uncoated PEEK cages, had fusion grade 1.
Discussing the findings, the study team wrote: “When investigating the radiological outcome of the study, it is immediately clear that the nanocoated PEEK cages achieved significantly more definite fusion compared with the uncoated PEEK cages. Only 65.5% of the patients who received uncoated PEEK cages were identified with definite fusion 12 months after the surgery. Definite fusion already appeared after six months in 77% to 79% of patients with nanocoated PEEK cages. After one year, over 90% of the patients with nanocoated PEEK cages had definite fusion, indicating that better and faster osseointegration arises when using a nanocoating.”
Willems and colleagues concluded that the similarity in clinical outcomes across all three of the cage types, demonstrate the safety and efficacy of nanocoated PEEK cages compared to the uncoated cages. Additionally, they note that the results of the study are clinically relevant as the enhanced osseointegration is a significant predictor of positive long term clinical outcomes. They end: “Furthermore, patients at risk for incomplete fusion might benefit from enhanced osseointegration of nanocoated PEEK cages. The findings of this study will be revisited in a five-year follow-up study of the randomised controlled trial.”