No abstract

Rotation errors of the femoral component are held responsible for occurrences such as instability in flexion and midflexion, patellar maltracking, and arthrofibrosis following total knee arthroplasty. However, in many cases, the epicondylar axis cannot be reliably identified due to bone defects or metal artifacts on computed tomography, so alternative landmarks are necessary to evaluate the femoral component rotation. The current study sought to determine the relationship of the posterior cortical bone and the anterior cortical bone in relation to the epicondylar axis. In this retrospective study, 398 consecutive patients who had undergone magnetic resonance imaging of the knee joint were included. The average angle between the posterior cortical bone and the epicondylar axis was 7.3°±3.3°. When the posterior cortical bone was used as the reference, the average absolute error was 2.6°±2.1°. In comparison, the average angle between the anterior cortical bone and epicondylar axis was 10.4°±4.5°. When this reference was used, the average absolute error was 3.6°±2.8°. The posterior cortical bone is a more consistent landmark than the anterior cortical bone is for intra- or postoperative approximation of the epicondylar axis. This appears to be due to the flat geometry of the posterior cortical bone compared with the elliptical form of the anterior cortical bone of the distal femur. In practice, an external rotation of the femoral component of 7° in relation to the posterior cortical bone is to be recommended. [Orthopedics. 2017; 40(3):188-190.].

Description of purpose: Treatment of osteoarthritis in stages of reversible disease requires high resolution visualization of early cartilage damage and of subchondral bone. Here, DEI (Diffraction Enhanced Imaging) is compared to MRI, computed X-ray tomography (CT) and ultrasound (UI) in its ability to detect early degeneration of articular cartilage. In contrast to conventional absorptive X-ray examination where cartilage is poorly visible DEI captures cartilage by detection of selected refraction. Methods: Human femoral heads were investigated by macroscopic inspection, conventional X-ray examination, DEI, MRI, CT, UI and histology. DEI is an imaging technique applying a monochromatic parallel synchrotron X-ray beam. Image features were verified by histology. Results: DEI, MRI and ultrasound lead to interpretable images of cartilage. Of all techniques, DEI provided highest image resolution revealing the structural tissue architecture. MRI needs a very long exposure time (more than 5 hours) to achieve comparable quality. Application of ultrasound is limited because of joint geometry and, at high sound frequency, the necessity of close contact between cartilage and transducer. DEI is an experimental technique which needs synchrotron radiation. Conclusion: DEI is a very promising imaging technique for visualization of cartilage and bone. It may serve as an excellent analytical tool for experimental studies. Our pictures show a part of future of optimised techniques for imaging. Synchrotron based DEI may lead the way towards optimisation of improved techniques for imaging. Upon development of adequate small scale X-ray sources, DEI will also be an important supplementation for medical imaging.

The rule of thumb for a partial overlap of the fibular head by the tibia in the case of a correct antero-posterior projection plane was also confirmed. However, a considerable interindividual variability of the position of the FH was found, which limits a conclusion regarding the quality of the radiographic projection on the basis of the position of the fibular head.