Experiences with Al2O3 implantations in humans to bridge resection defects

The SNAP trial: a double blind multi-center randomized controlled trial of a silicon nitride versus a PEEK cage in transforaminal lumbar interbody fusion in patients with symptomatic degenerative lumbar disc disorders: study protocol

Background

Polyetheretherketone (PEEK) cages have been widely used in the treatment of lumbar degenerative disc disorders, and show good clinical results. Still, complications such as subsidence and migration of the cage are frequently seen. A lack of osteointegration and fibrous tissues surrounding PEEK cages are held responsible. Ceramic implants made of silicon nitride show better biocompatible and osteoconductive qualities, and therefore are expected to lower complication rates and allow for better fusion.

Purpose of this study is to show that fusion with the silicon nitride cage produces non-inferior results in outcome of the Roland Morris Disability Questionnaire at all follow-up time points as compared to the same procedure with PEEK cages.

Methods/Design

This study is designed as a double blind multi-center randomized controlled trial with repeated measures analysis. 100 patients (18–75 years) presenting with symptomatic lumbar degenerative disorders unresponsive to at least 6 months of conservative treatment are included. Patients will be randomly assigned to a PEEK cage or a silicon nitride cage, and will undergo a transforaminal lumbar interbody fusion with pedicle screw fixation. Primary outcome measure is the functional improvement measured by the Roland Morris Disability Questionnaire. Secondary outcome parameters are the VAS leg, VAS back, SF-36, Likert scale, neurological outcome and radiographic assessment of fusion. After 1 year the fusion rate will be measured by radiograms and CT. Follow-up will be continued for 2 years. Patients and clinical observers who will perform the follow-up visits will be blinded for type of cage used during follow-up. Analyses of radiograms and CT will be performed independently by two experienced radiologists.

Discussion

In this study a PEEK cage will be compared with a silicon nitride cage in the treatment of symptomatic degenerative lumbar disc disorders. To our knowledge, this is the first randomized controlled trial in which the silicon nitride cage is compared with the PEEK cage in patients with symptomatic degenerative lumbar disc disorders.

Trial registration

NCT01557829

Biocompatibility of atomic layer-deposited alumina thin films

Presented in this paper is a study of the biocompatibility of an atomic layer-deposited (ALD) alumina (Al2O3) thin film and an ALD hydrophobic coating on standard glass cover slips. The pure ALD alumina coating exhibited a water contact angle of 55 degrees +/- 5 degrees attributed, in part, to a high concentration of -OH groups on the surface. In contrast, the hydrophobic coating (tridecafluoro-1,1,2,2-tetrahydro-octyl-methyl-bis(dimethylamino)silane) had a water contact angle of 108 degrees +/- 2 degrees. Observations using differential interference contrast microscopy on human coronary artery smooth muscle cells showed normal cell proliferation on both the ALD alumina and hydrophobic coatings when compared to cells grown on control substrates. These observations suggested good biocompatibility over a period of 7 days in vitro. Using a colorimetric assay technique to assess cell viability, the cellular response between the three substrates can be differentiated to show that the ALD alumina coating is more biocompatible and that the hydrophobic coating is less biocompatible when compared to the control. These results suggest that patterning a substrate with hydrophilic and hydrophobic groups can control cell growth. This patterning can further enhance the known advantages of ALD alumina, such as conformality and excellent dielectric properties for bio-micro electro mechanical systems (Bio-MEMS) in sensors, actuators, and microfluidics devices.

Uncemented short-length diaphyseal segmental replacement prosthesis fixation--finite element analysis and long-term results

INTRODUCTION

Extensively porous coated segmental replacement prostheses with intramedullary cementless fixation to bone over the whole length of stem often exhibit resorption of the surrounding bone due to stress-shielding. This makes them particularly susceptible to aseptic loosening.

STUDY

A finite element analysis of the state of loading of a short-length fixation in a new prosthetic stem design has shown a definite advantage over long-length fixation. The stress pattern within the bone surrounding the prosthesis confirmed that shortening of the ongrowth area in length increases the stress values at the resection level significantly. This stem (Endlock) has been used for diaphyseal anchorage in the treatment of tumors in combination with an artificial joint of proven design in order to reduce stress shielding.

RESULTS

No Endlock stem fractures or aseptic loosenings were observed at recent follow-up. The early clinical results comply with the theoretical assumptions.

CONCLUSIONS

A short-length fixation system based on intramedullary anchorage of segmental replacement endoprostheses would possibly support physiologic adaptive processes more than fixation over the full length of the stem.

Contamination of titanium castings by aluminium oxide blasting

OBJECTIVES

It is desirable that the surfaces of surgical implants be uncontaminated by foreign materials to avoid untoward tissue reactions, and grit blasting is widely assumed to leave clean metal surfaces. SEM examination and X-ray microanalysis of a recovered 'pure' titanium implant casting that was associated with tissue breakdown revealed embedded particles of alumina. The casting had been cleaned of investment by blasting with alumina grit.

METHODS

A variety of treatments of cast titanium plates was used: (a) to establish that the observed aluminium was due to the blasting grit, and (b) to determine whether removal of investment could be achieved effectively by other means. SEM examination and X-ray microanalysis were used.

RESULTS

The detected aluminium was associated with embedded fragments identified as coming from the blasting grit. Acid-pickling and mechanical (rotary instrument) trimming produced minimally contaminated surfaces.

CONCLUSIONS

Whilst unproven, the presence of the alumina is viewed with great concern as a possible causative agent in the observed tissue breakdown and procedures avoiding alumina blasting are recommended as a precautionary measure.

Elongation of brachymetatarsy with ceramic implant: a roentgenographic evaluation of its utility

The metatarsal bone was elongated by intercalary implantation of a single-crystal alumina ceramic in 7 patients with brachymetatarsy. The implants were encased with new bone 24 months after surgery and resulted in 5.2 to 9.2 mm elongation of the metatarsal bone. The response of the bone to the ceramic implant was observed roentgenographically. No resorption or pseudoarthrosis of the bones, nor loosening or breakage of the implants, were observed. The alumina ceramic implant proved to be a useful substitute for a bone graft, because of its biocompatibility and strength.

Porous ceramic implants in the alveolar ridge of humans. A 3 1/2-year follow-up study

Porous ceramic (Al2O3) material with pore size of 100--750 micrometer was used for alveolar ridge augmentation in five patients. Clinical and radiographic examination at observation times varying from 11 months to 3 1/2 years revealed that seven out of a total number of nine implants were in function, covered by normal soft tissue. All patients were wearing complete dentures over the implant sites. In one of the patients treated with three ceramic pieces placed subperiosteally to restore alveolar height, one of the implants was lost after 3 1/2 years. In another individual, a minor dehiscence was found on examination after 2 1/2 years' implantation time. Interviews revealed that one of the patients had hypoesthesia and paresthesia in the mental nerve area on one side after ridge augmentation, while the remaining four patients had no complaints. All five individuals told of considerable improvement of denture stability after the implantation procedures.

Rebuilding of deficient edentulous alveolar ridge with porous ceramic implants

Porous ceramic (Al2O3) implants with a pore size of 100--750 mum were used in the surgical treatment of four patients at the Department of Oral Surgery and Oral Medicine, Dental Faculty, University of Oslo. In two of the cases, ceramic implants were placed in small surgical defects in the edentulous maxillary alveolar ridge, while two patients were treated with mandibular ridge augmentation. All four individuals healed uneventfully, and the implants were firm and immovable 3 weeks postoperatively. No adverse tissue reactions were observed. Dentures were inserted over the implants 8 days to 6 weeks after implantation. In one of the cases, reoperation was performed because of 2 X 2 mm zone of exposure of the ceramic 4 weeks after denture insertion. Examination after observation times up to 15 months revealed clinically normal soft tissue over the implants. There were no complaints about wearing of the dentures. Radiographs at varying intervals after implantation did not disclose any pathologic changes or signs of resorption of bone adjacent to the ceramic implants.