Artifacts in spine magnetic resonance imaging due to different intervertebral test spacers: an in vitro evaluation of magnesium versus titanium and carbon-fiber-reinforced polymers as biomaterials.

INTRODUCTION: Intervertebral spacers are made of different materials, which can affect the postfusion magnetic imaging (MRI) scans. Susceptibility artifacts especially for metallic implants can decrease the image quality. This study aimed to determine whether magnesium as a lightweight and biocompatible metal is suitable as a biomaterial for spinal implants based on its MRI artifacting behavior. MATERIALS AND METHODS: To compare artifacting behaviors, we implanted into one porcine cadaveric spine different test spacers made of magnesium, titanium, and carbon-fiber-reinforced polymers (CFRP). All test spacers were scanned using two T1-TSE MRI sequences. The artifact dimensions were traced on all scans and statistically analyzed. RESULTS: The total artifact volume and median artifact area of the titanium spacers were statistically significantly larger than magnesium spacers (p < 0.001), while magnesium and CFRP spacers produced almost identical artifacting behaviors (p > 0.05). CONCLUSION: Our results suggest that spinal implants made with magnesium alloys will behave more like CFRP devices in MRI scans. Given its osseoconductive potential as a metal, implant alloys made with magnesium would combine the advantages to the two principal spacer materials currently used but without their limitations, at least in terms of MRI artifacting.

In-vitro MRI detectability of interbody test spacers made of carbon fibre-reinforced polymers, titanium and titanium-coated carbon fibre-reinforced polymers.

The purpose of this study was to investigate how different materials affect the magnetic resonance imaging (MRI) detectability of interbody test spacers (ITS). We evaluated the post-implantation MRI scans with T1 TSE sequences for three different ITS made of titanium, carbon fibre-reinforced polymers (CFRP) and titanium-coated CFRP, respectively. The main target variables were total artefact volume (TAV) and median artefact area (MAA). Additionally, implant volume (IV)/TAV and cross section (CS)/MAA ratio were determined. The t test and Newman-Keuls test for multiple comparisons were used for statistical analysis. TAV and MAA did not differ significantly between CFRP and titanium-coated CFRP, but were approximately twice as high for the titanium ITS (p < 0.001). MRI detectability was optimum for CFRP and titanium-coated CFRP, but was limited at the implant-bone interface of the titanium ITS. The material's susceptibility and the implant's dimensions affected MRI artefacting. Based on TAV, the volume of titanium surface coating in the ITS studied has no influence on susceptibility in MRI scans with T1 TSE sequences.

Preclinical evaluation by flat-panel detector-based volumetric CT versus MRI of intervertebral spacers implanted in a porcine model.

BACKGROUND CONTEXT: Image quality and implant detectability by conventional imaging methods are suboptimal for perioperative spinal diagnostics, primarily limited by implant-related artifacts. PURPOSE: To evaluate the imaging quality of various intervertebral spacers examined by flat-panel detector-based volumetric computed tomography (FD-VCT) versus magnetic resonance imaging (MRI). STUDY DESIGN/SETTING: A preclinical comparative study on an experimental porcine model. The study was performed at a university research facility. METHODS: Three different intervertebral spacer types (titanium, carbon fiber-reinforced polymer, cobalt-chrome-molybdenum) were implanted in a cadaveric porcine spine and then examined by MRI using T1-weighted spin echo (T1w-SE) and turbo spin echo (T1w-TSE) sequences. Comparative imaging was performed with an experimentally approved FD-VCT prototype featuring two-dimensional and three-dimensional imaging and high isotropic spatial resolution. Data analysis focused on spacer shape, implant positioning, and implant-bone interface. RESULTS: Compared with MRI, and despite the use of T1w-SE and T1w-TSE sequences, the image quality and detectability of all target characteristics were better with FD-VCT absent the usual artifacts. Using its option for implant-specific imaging, the experimental FD-VCT imager allowed reliable determination of additional variables such as dimension and volume. CONCLUSIONS: This experimental study provides initial evidence that FD-VCT produces excellently sharp, high-accuracy, artifact-free imaging quality that is superior to MRI in distinguishing key characteristics of intervertebral implants in a preclinical setting.

Postimplantation MRI with cylindric and cubic intervertebral test implants: evaluation of implant shape, material, and volume in MRI artifacting--an in vitro study.

BACKGROUND CONTEXT: Interbody spacers for anterior spine fusion are made of different materials, which can affect the postfusion magnetic resonance imaging (MRI) scans. Susceptibility artifacts specially for metallic implants can decrease the image quality. PURPOSE: This study focused on the influence of determined implant parameters like shape, implant volume, and implant material in MRI artifacting with regard to solid geometrical titanium and carbon test spacers. STUDY DESIGN/SETTING: A comparative study on an in vitro spine model. The study was performed at a university research facility. METHODS: In this study we evaluated the postimplantation MRI scans of three determined cuboids and six cylinders, which were made of titanium alloy and carbon fiber reinforced polymer. MRI scans were carried out by using T1 turbo spin echo (TSE) sequences. The total artifact volume (TAV) as well as median artifact area (MAA) were calculated. Additionally the implant volume (IV)/TAV and cross-sectional area (CSA)/MAA relation were determined. Statistical analyses were calculated with the t test and Newman-Keuls test for multiple comparisons. RESULTS: Considering all test implants with an increasing implant size, the TAV and the MAA became significantly larger (p<.001) with simultaneous reduction of the IV/TAV and CSA/MAA relation. In contrast to the carbon implant group, for titanium cylinders with an implant volume equivalent to the cuboids significant differences in MRI artifacting (p<.05) could be demonstrated. CONCLUSIONS: Susceptibility artifacts were clearly affected by the implant material, shape, and implant volume. Independent of the implant material, with regard to a more advantageous IV/TAV and CSA/MAA relation, for larger implants the artifact rate was more limited to the implant's direct surroundings. On the basis of a high magnetizability for titanium implants with an equal IV, the range of implant-related susceptibility artifacts was influenced by the material as well as implant shape in favor of cylindric implants. According to the very low MRI artifact rate of carbon implants, the implant shape did not have any significant effect on the artifact behavior.

Postfusion magnetic resonance imaging artifacts caused by a titanium, cobalt-chromium-molybdenum, and carbon intervertebral disc spacer.

Intervertebral spacers for anterior spine fusion are made of different materials, such as titanium and CoCrMo-alloys or carbon fiber reinforced polymers (CFRP). Implant-related susceptibility artifacts can decrease the quality of magnetic resonance imaging (MRI) scans. This cadaveric study aimed to demonstrate the extent that implant-related MRI artifacting affects the postfusion differentiation of the spinal canal (SC) and intervertebral disc space (IDS). In 6 cadaveric porcine spines, we evaluated the postimplantation MRI scans of a titanium, CoCrMo-spacer and CFRP-spacer that differed in shape and surface qualities. A spacer made of human cortical bone was used as a control. A defined evaluation unit was divided into regions of interest (ROI) to characterize the SC and IDS. Considering 15 different MRI sequences read independently by an interobserver-validated team of specialists artifact-affected image quality of the median MRI slice was rated on a score of 0-1-2-3. A maximum score of 15 points for the SC and 9 points for the IDS (100%) was possible. Turbo spin echo sequences produced the best scores for both spacers and the control. Only the control achieved a score of 100%. For the IDS the CoCrMo-spacer, titanium and CFRP-spacer maximally scored 0%, 0% and 74%, for the SC 60%, 80% and 99%, respectively. By using favored T1 TSE sequences the CFRP-spacer represented clear advantages in postfusion spinal imaging. Independent of artifact dimensions the used scoring system allowed us to create an implant-related ranking of MRI scan quality in reference to the bone control.

Implant detectibility of intervertebral disc spacers in post fusion MRI: evaluation of the MRI scan quality by using a scoring system--an in vitro study.

INTRODUCTION: Intervertebral spacers for anterior spine fusion are made of different materials, such as titanium and cobalt chromium alloys and carbon fiber-reinforced polymers. Implant-related susceptibility artifacts can decrease the quality of MRI scans. The aim of this cadaveric study was to demonstrate the extent that implant-related MRI artifacting affects the postfusion differentiation of determined regions of interest (ROIs). METHODS: In six cadaveric porcine spines, we evaluated the postimplantation MRI scans of a titanium, cobalt-chromium and carbon spacer that differed in shape and surface qualities. A spacer made of human cortical bone was used as a control. A defined evaluation unit was divided into ROIs to characterize the spinal canal as well as the intervertebral disc space. Considering 15 different MRI sequences read independently by an interobserver-validated team of specialists the artifact-affected image quality of the median MRI slice was rated on a score of 0-3. A maximum score of 18 points (100%) for the determined ROIs was possible. RESULTS: Turbo spin echo sequences produced the best scores for all spacers and the control. Only the control achieved a score of 100%. For the determined ROI maximum scores for the cobalt-chromium, titanium and carbon spacers were 24%, 32% and 84%, respectively. CONCLUSION: By using favored T1 TSE sequences the carbon spacer showed a clear advantage in postfusion spinal imaging. Independent of artifact dimensions, the scoring system used allowed us to create an implant-related ranking of MRI scan quality in reference to the bone control.

Vertebrectomy and anterior reconstruction for the treatment of spinal metastases.

The purpose of this study was to retrospectively analyse the outcome of modular vertebral body replacement in conjunction with vertebrectomy in cancer patients with skeletal metastases. Between 1996 and 2000, we performed vertebrectomy with subsequent implantation of a modular vertebral body replacement in 24 patients with skeletal metastases of the spine. The findings were analysed retrospectively. The mean postoperative survival period for all patients was 15.6 months. Improvement of preoperative back pain was achieved in 85%. Remission of initial neurological symptoms based on the Frankel classification was achieved in 57.1% of the patients. Implant dislocations were not observed during follow-up. Vertebrectomy for vertebral metastasis is indicated in selected patients. Type of underlying malignancy, metastatic spread and adjuvant treatment options are an important basis for the indication. In anterior defect reconstructions, modular implants can directly restore stability while reducing tumour-related symptoms.

A study of effectiveness of knee arthroscopy after knee arthroplasty.

PURPOSE: The purpose of this study was to investigate the outcome of arthroscopy in painful knee arthroplasty without evidence of infection, fracture, wear, and component loosening or malposition that had been refractory to conservative treatment. In addition, a literature review of 498 cases (MEDLINE 1966 to 2002) was performed. TYPE OF STUDY: Case series. METHODS: From 1997 to 2000, 27 patients (20 women, 7 men) had undergone arthroscopies because of poor results following total knee arthroplasty. Before the operation, the patients had suffered symptoms for an average of 11 months (range, 3 to 41 months). The average onset of symptoms after knee arthroplasty was 26 months (range, 3 to 59 months). The average patient age was 70 years (range, 42 to 81 years) and the average follow-up was 34 months (range, 24 to 52 months). At the initial operation, 19 patients had received total condylar surface replacement and 8 had received hemireplacement. Patients were evaluated using the Knee Society rating system. A review of the literature was performed by initial identification of the articles from a MEDLINE database followed by the use of cross references. RESULTS: All of the patients were available for follow-up. Eighteen of the 27 procedures resulted in an improvement in the patient's knee score. The average Knee Society ratings increased from 71 points before arthroscopy to 85 at follow-up for the knee score. The average functional scores were 69 and 83 points, respectively. The Knee Society pain score improved from 32 to 41 points. Nine patients underwent a subsequent open revision after arthroscopic diagnosis or treatment. Operative diagnoses included arthrofibrosis, impinging hypertrophic synovitis, impinging posterior cruciate ligament stump, prosthesis loosening or wear, symptomatic pseudomeniscus, an infrapatellar spur, and meniscal rupture. There was 1 infection as a complication associated with the arthroscopic procedure. CONCLUSIONS: Arthroscopic treatment of painful knee arthroplasty provides reliable expectations for improvement in function, decrease in pain, and improvement in knee scores for most patients. LEVEL OF EVIDENCE: Level IV, Case Series.

Arthroscopic debridement of massive rotator cuff tears: negative prognostic factors.

INTRODUCTION: The purpose of this study was to identify the factors that may lead to poor outcomes after arthroscopic debridement in massive rotator cuff tears. MATERIALS AND METHODS: Thirty-three patients (10 women and 23 men) with massive, irreparable rotator cuff tears underwent arthroscopy by a single surgeon. The preoperative diagnosis was based on the clinical examination and MRI. Their mean age was 69 years (range 62-79 years), and the average follow-up was 31 months (range 24-46 months). If indicated, the performed arthroscopic debridement included acromioplasty, debridement of the cuff, resection of the distal part of the clavicle or tenotomy of the long head of the biceps. In 28 cases (85%) acromioplasties and in 6 cases (18%) biceps tenotomies were performed, 2 of which were a single tenotomy without any associated acromioplasty. One patient had been managed with concomitant resection of the distal part of the clavicle. RESULTS: The Constant and Murley Score improved by a mean of 30 points, from a mean of 37 points (range 21-52) preoperatively to a mean of 67 points (range 31-82) at the time of follow-up. Some 82% of the patients were satisfied with the procedure. The result was considered unsatisfactory because of inadequate pain relief in 4 shoulders, because of limited active abduction in 1 and because of limited external rotation in 1. A poor outcome was associated with a complete tear of the subscapularis tendon in 6 patients. The radiological study showed no significant narrowing of the subacromial space. CONCLUSION: Our early results suggest that arthroscopic debridement is an excellent treatment for elderly patients with modest functional demands. However, its long-term consequences remain to be evaluated by studies with lengthy follow-up. Prognostic factors that may lead to a negative outcome are preoperative superior migration of the humeral head, presence of subscapularis tear, presence of glenohumeral arthritis and decreased range of motion.