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Purpose Our aim was to assess the outcome with respect to cumulative revision rates of unicompartmental knee arthroplasty (UKA) by comparing published literature and arthroplasty registry data. Our hypothesis was that there is a superior outcome of UKA described in dependent clinical studies compared to independent studies or arthroplasty registers. Methods A systematic review of all clinical studies on UKA in the past decade was conducted with the main endpoint revision rate. Revision rate was calculated as “revision per 100 component years (CY)”. The respective data were analysed with regard to a potential difference of the percentage of performed revision surgeries as described in dependent and independent clinical studies. Clinical data were further compared to arthroplasty registers in a systematic search algorithm. Results In total, 48 study cohorts fulfilled our inclusion criteria and revealed 1.11 revisions per 100 CY. This corresponds to a revision rate of 11.1% after 10 years. No deviations with regard to revision rates for UKA among dependent and independent clinical literature were detected. Data from four arthroplasty registers showed lower survival rates after 10 years compared to published literature without being significant. Conclusions The outcomes of UKA in dependent and independent clinical studies do not differ significantly and are in line with arthroplasty register datasets. We cannot confirm biased results and the authors recommend the use of UKAs in properly selected patients by experts in their field.

Introduction Motion preserving techniques in C1 ring fractures are increasingly used especially in young patients. Therefore, lateral mass screws are inserted in the first vertebra and connected by a rod. The purpose of this study was to determine safe zones regarding the vertebral arteries and the medulla oblongata for optimal lateral mass screw positioning when fusing the C1-ring. Materials and methods Images of the cervical spine of 50 patients (64-line CT scanner) were evaluated and virtual screws were positioned in both lateral masses of the first vertebra using 3D-reconstructions of CT scans. The length of the screws, the insertion angles in two planes, the distance to the vertebral artery, and the spinal canal was investigated. Descriptive statistics was used and gender-dependent differences were calculated using student t-test. A diameter of 4 mm was chosen for the screws. Results The mean screw length was 30.0 ± 2.3 mm on the right and 30.1 ± 2.1 mm on the left side. The arithmetic mean for the transverse angle was 16.4 ± 5.6° on the right and 15.6 ± 6.3° on the left, the sagittal angle averaged 8.3 ± 3.8° on the right, and 11.0 ± 4.9° on the left side. The mean distance between screw and spinal canal has been determined on the right with 2.4 ± 0.7 mm and 2.2 ± 0.6 mm on the left side. The distance from the C1 lateral mass screw to the vertebral artery was on average 7.1 ± 1.5 mm on the right side (significant correlation with gender, p value: 0.03) and 7.4 ± 1.4 mm on the left side. Conclusions Screws should be positioned with a slightly converging angle of 16° and a slightly ascending angle of 10°. Due to the required high precision technique intraoperatively multiplanar 2 D or 3 D imaging is recommended to avoid harm to the vertebral artery or the spinal canal.