Magnetic resonance imaging evaluation of intervertebral test spacers: an experimental comparison 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 resonance 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 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.

The interobserver-validated relevance of intervertebral spacer materials in MRI artifacting.

Intervertebral spacers for anterior spine fusion are made of different materials, such as titanium, carbon or cobalt-chrome, which can affect the post-fusion MRI scans. Implant-related susceptibility artifacts can decrease the quality of MRI scans, thwarting proper evaluation. This cadaver study aimed to demonstrate the extent that implant-related MRI artifacting affects the post-fusion evaluation of intervertebral spacers. In a cadaveric porcine spine, we evaluated the post-implantation MRI scans of three intervertebral spacers that differed in shape, material, surface qualities and implantation technique. A spacer made of human cortical bone was used as a control. The median sagittal MRI slice was divided into 12 regions of interest (ROI). No significant differences were found on 15 different MRI sequences read independently by an interobserver-validated team of specialists (P>0.05). Artifact-affected image quality was rated on a score of 0-1-2. A maximum score of 24 points (100%) was possible. Turbo spin echo sequences produced the best scores for all spacers and the control. Only the control achieved a score of 100%. The carbon, titanium and cobalt-chrome spacers scored 83.3, 62.5 and 50%, respectively. Our scoring system allowed us to create an implant-related ranking of MRI scan quality in reference to the control that was independent of artifact dimensions. The carbon spacer had the lowest percentage of susceptibility artifacts. Even with turbo spin echo sequences, the susceptibility artifacts produced by the metallic spacers showed a high degree of variability. Despite optimum sequencing, implant design and material are relevant factors in MRI artifacting.

Intraarticular migration of a broken biodegradable interference screw after anterior cruciate ligament reconstruction.

Poly-L: -lactic acid biodegradable screws have been used effectively for graft fixation in anterior cruciate ligament (ACL) reconstruction. The overall complication rate associated with the use of this implant is low, although some authors reported complications, such as osteolysis and aseptic effusion of the knee joint. We report a case of a 29-year-old female patient with a failure of a biodegradable interference screw at 22 months after ACL reconstruction using bone-patellar tendon-bone graft. In this illustrated case, the screw broke and migrated into the knee joint. In addition, we performed a detailed review of the medical literature from 1990-2005 to identify possible causes of biodegradable screw failures. We identified six published cases of bioabsorbable interference screw failure with migration into the knee joint. Several authors have reported small diameter of the screw, poor bone quality, bone resorption, and screw divergence as potential causes for intraarticular migration of metallic interference screws. With regard to bioscrews, no specific risk factors for screw breakage and intraarticular migration have been reported. ACL reconstruction with the use of bioabsorbable interference screws for fixation is considered to be reliable. However, we need to be aware of potential problems associated with the use of this implant. Early recognition of bioscrew failure may prevent associated morbidities, such as subsequent cartilage damage.

The Nottingham health profile-experiences after hip revision arthroplasty.

INTRODUCTION: Considering patients after hip revision arthroplasty postoperative quality controls allows an evaluation of the individual implant situation as well as the achieved postoperative quality of life. With regard to a possible loss of data reliable statements about the used implant system with special consideration to the implant survival rate could not be received. In this connection standardized self-assessment questionnaires like the Nottingham Health Profile (NHP) are in the centre of interest. The main focus of this study was to demonstrate a correlation between the Nottingham Health Profile and the Merle d'Aubigne (MDA) Score. PATIENTS AND METHODS: Fifty-one patients after femoral stem revision were re-examined. All patients received a written appointment for an ambulatory re-examination together with the NHP 4 weeks before. The clinical evaluation was carried out by using the MDA Score. Correlations between the NHP and the MDA were calculated. RESULTS: Overall the data of 39 patients could be evaluated completely. Three patients (5.9%) did not appear to the ambulatory re-examination, four patients (7.8%) deceased in the meantime. With further five patients (9.8%) the NHP questionnaire could not be rated due to an incorrect treatment. The mean follow-up after revision was 5.8 years. Correlations between the category 'Pain' NHP/MDA as well as to the combination of the NHP-categories 'Pain' + 'Physical Mobility' and the total MDA-Score could be demonstrated. CONCLUSION: Out of our personal experiences the use of the NHP makes an individual follow-up evaluation after revision hip arthroplasty possible. Patient-referred changes can lead to direct re-examinations. Correlation coherences between the NHP and the MDA could be demonstrated equivalent to already published results. In what way a survival rate analysis of an implant by using the NHP is possible could not be answered clearly. It has to be included that wrong answered questionnaires lead to an additional drop-out rate beneath the lost to follow-up rate.

Expandable vertebral body replacement in patients with thoracolumbar spine tumors.

INTRODUCTION: The objectives of surgical interventions for tumoral lesions of the spine include the establishment and improvement of tumor-related symptoms. Anterior tumor resection followed by reconstruction indicated if surgical treatment allowed a marginal removal of the tumor or could extend the individual survival rate in combination with adjuvant therapy options. Sufficient re-stabilization depends on adequate anterior column reconstruction. The purpose of this retrospective study was to present our experiences and results after anterior tumor resection followed by reconstruction with the expandable vertebral body replacement device (VBR, Ulrich, Germany) based on clinical application over 4 degrees years. PATIENTS AND METHODS: We carried out an anterior tumor resection followed by reconstruction using an anterior extendable device in 32 patients with different spine tumors between 1996 and 2000. A retrospective evaluation was executed considering the patients medical records and radiological findings. Additionally, a clinical and radiological investigation of still living postoperative patients was carried out. RESULTS: The mean surgical time of all evaluated patients was 317.2 min. The average blood loss was 1,272.5 ml. According to the Tokuhashi score, patients with a postoperative survival time of at least 12 months demonstrated a score value > or = 9 points. According to our evaluated patients group metastatic lesions of the spine represented the largest group (78.1%). The average survival rate of this group amounted to 18.4 months postoperatively. Considering primary tumors the average survival rate at the time of last re-examination amounted to 34.8 months postoperatively. Preoperative neurological pathologies were present in 12 patients (Frankel stage C-D). During the postoperative monitoring period 58.3% of the patients demonstrated an improvement in initial neurological findings. There were no intraoperative complications or perioperative deaths. Implant dislocations were not observed. CONCLUSION: On account of the underlying, the anterior tumor resection with supplementary instrumentation represented a sufficient procedure in spinal tumor surgery. Adjuvant therapy can influence the postoperative survival period positively in addition to the surgical procedure. Following anterior tumor resection, extendable vertebral body replacements like the VBR device provide immediate spine stability by excellent defect adaptation. With regard to their intraoperative flexibility, expandable cages are more advantageous in contrast to non-expandable implants or bone grafts.

Centralization of the femoral component in cemented hip arthroplasty using guided stem insertion.

In order to improve the positioning of the stem within the femur, to centralize it within the cement and to achieve a complete and homogeneous cement mantle, a new hip endoprosthesis with guided stem insertion was developed. The femoral component has a longitudinal channel that takes up a guidewire which directs it during insertion into the centre. The guidewire is attached to the cement stopper which is positioned in the marrow cavity before applying the bone cement. The first 100 endoprostheses of this type with an observation period of at least 6 years were assessed radiologically and clinically. The clinical evaluation according to the hip scores of Merle d'Aubigne and Harris revealed a marked improvement between preoperative and postoperative values for all criteria. On radiological assessment 94% of the stems had a neutral position within the femur; 98% of the stems were found to be ideally centred within the cement distally, 80% distally and proximally; 74% of the cement cuffs had a complete and homogeneous cement layer between 2 and 5 mm medially and laterally, while 25% had partially a dimension of more than 5 mm, predominantly proximally. In only 3 cases was one part of the cement mantle found to be less than 2 mm. The radiological follow-up was also documented according to the delineated zones of Gruen. It revealed zonal radiolucent lines in 15 cases, combined in 11 cases with reactive lines, never extending up to 4 zones out of 14. Five prostheses had subsided moderately between 2 and 3 mm, and only one 8 mm. None of these radiological signs was associated with clinical symptoms. There were five cement fractures. Two stems were symptomatic, radiologically loose and revised. Beside these two cases of aseptic loosening there was one septic case, so that in total 97% of the implants are still functioning well.