Hannes A. Rüdiger

Biomechanical concept and clinical outcome of dual mobility cups

Dual mobility cup systems in total hip arthroplasty consist of a metal back with a non-constrained liner, in which a constrained standard head articulates. While superior stability of such implants in comparison with standard total hip replacements is assumed, it is the purpose of this study to outline the biomechanical concept of dual mobility cups and to describe implant survival and dislocation rate based on the series published in the English-speaking and Francophone literature. A growing body of evidence indicates reduced dislocation rates in primary and revision total hip arthroplasty and in selected tumour cases. The limited availability of studies evaluating long-term implant survival and existing concerns with regard to increased wear rates and aseptic loosening, leads to the conclusion that such implants have to be used with prudence, particularly in standard primary hip arthroplasty and in young patients.

Comparisons of Preoperative Three-Dimensional Planning and Surgical Reconstruction in Primary Cementless Total Hip Arthroplasty

Reconstruction of important parameters such as femoral offset and torsion is inaccurate, when templating is based on plain x-rays. We evaluate intraoperative reproducibility of pre-operative CT-based 3D-templating in a consecutive series of 50 patients undergoing primary cementless THA through an anterior approach. Pre-operative planning was compared to a postoperative CT scan by image fusion. The implant size was correctly predicted in 100% of the stems, 94% of the cups and 88% of the heads (length). The difference between the planned and the postoperative leg length was 0.3 + 2.3 mm. Values for overall offset, femoral anteversion, cup inclination and anteversion were 1.4 mm ± 3.1, 0.6° ± 3.3°, -0.4° ± 5° and 6.9° ± 11.4°, respectively. This planning allows accurate implant size prediction. Stem position and cup inclination are accurately reproducible.

Reconstruction after external hemipelvectomy using tibia-hindfoot rotationplasty with calcaneo-sacral fixation

BackgroundExternal hemipelvectomy is associated with high post operative morbidity and a poor functional outcome. We aim to explore a reconstruction technique to improve function and post operative appearance for patients who undergo external hemipelvectomy.Case presentationWe present a Case where extensive cancer involvement of pelvis and femur was managed with a novel surgical technique, which involved a calf sparing modified anterior flap hemipelvectomy combined with rotationplasty of the spared calf and fixation of calcaneus to the sacrum, thereby recreating a new thigh stump.ConclusionTibia-hindfoot rotationplasty result in good functional outcome and appearance for selected patients undergoing external hemipelvectomy with unaffected external iliac and femoral vessels.

Multiple non-ossifying fibromas as a cause of pathological femoral fracture in Jaffe-Campanacci syndrome

BackgroundJaffe-Campanacci is a rare syndrome characterised by the association of café-au-lait spots, axillary freckles, multiple non-ossifying fibromas of the long bones and jaw, as well as some features of type 1 neurofibromatosis. There are less than 30 reported cases, and a genetic profile has not yet been determined. Furthermore, it has not been clarified whether it is a subtype of type 1 neurofibromatosis or a separate syndrome. The risk of pathological fracture is over 50%, due to substantial cortical thinning of the weight-bearing bones.Case presentationA 17-year-old female patient, known for type 1 neurofibromatosis, presented with a low-energy distal femoral fracture due to disseminated large non-ossifying fibromas. Investigations revealed all of the distinctive signs of Jaffe-Campanacci syndrome. Both her distal femurs and proximal tibias exhibited multiple non-ossifying fibromas. The fracture was treated by open reduction and internal plate fixation. Some of the bony lesions were biopsied to confirm the diagnosis. The fracture healed eventless, as did the lesions biopsied or involved in the fracture. The other ones healed after curettage and bone grafting performed at the time of plate removal.ConclusionJaffe-Campanacci is a rare syndrome having unclear interactions with type 1 neurofibromatosis, which still needs to be characterised genetically. It is associated with a high risk of pathological fracture, due to the presence of multiple large non-ossifying fibromas of the long bones, with an expected normal healing time. Curettage and bone grafting promote healing of the lesions and should be considered to prevent pathological fracture. We agree with other authors that all patients with newly-diagnosed type 1 neurofibromatosis should undergo an osseous screening to detect disseminated non-ossifying fibromas, and evaluate the inherent risk of pathological fracture.

Impact of individual anatomy on the benefit of cup medialisation in total hip arthroplasty

Introduction In total hip arthroplasty, cup medialisation with compensatory increase of femoral offset has been proposed to increase the moment arms of abductor muscles. However, this technique is associated with a loss of acetabular bone stock. Previous data indicates that the potential benefit is not constant among patients and is likely related to patient anatomy. Method Therefore, to be able to select patients who would benefit most from this technique, we measured several anatomical parameters of the pelvis and femur in 15 patients; and evaluated correlations between them and the changes of moment arms associated with cup medialisation. The anatomical measurements were performed on 3-D reconstructions of preoperative CT scans. The moment arms of the gluteus medius and gluteus minimus were calculated for an abduction and flexion movement using patient-specific finite element models. Results 6 anatomical parameters were correlated with muscle moment arm variations after cup medialisation. This effect was not systematic for either muscles or movements. Among all parameters, femoral anteversion was the most important parameter in explaining the effect of cup medialisation. Discussion Patients with small femoral anteversion or low-riding greater trochanter benefit more from cup medialisation in terms of moment arm increase in abduction motion.

Full-field measurement of micromotion around a cementless femoral stem using micro-CT imaging and radiopaque markers

A good primary stability of cementless femoral stems is essential for the long-term success of total hip arthroplasty. Experimental measurement of implant micromotion with linear variable differential transformers is commonly used to assess implant primary stability in pre-clinical testing. But these measurements are often limited to a few distinct points at the interface. New techniques based on micro-computed tomography (micro-CT) have recently been introduced, such as Digital Volume Correlation (DVC) or markers-based approaches. DVC is however limited to measurement around non-metallic implants due to metal-induced imaging artifacts, and markers-based techniques are confined to a small portion of the implant. In this paper, we present a technique based on micro-CT imaging and radiopaque markers to provide the first full-field micromotion measurement at the entire bone-implant interface of a cementless femoral stem implanted in a cadaveric femur. Micromotion was measured during compression and torsion. Over 300 simultaneous measurement points were obtained. Micromotion amplitude ranged from 0 to 24µm in compression and from 0 to 49µm in torsion. Peak micromotion was distal in compression and proximal in torsion. The technique bias was 5.1µm and its repeatability standard deviation was 4µm. The method was thus highly reliable and compared well with results obtained with linear variable differential transformers (LVDTs) reported in the literature. These results indicate that this micro-CT based technique is perfectly relevant to observe local variations in primary stability around metallic implants. Possible applications include pre-clinical testing of implants and validation of patient-specific models for pre-operative planning.

Impact of the Femoral Head Position on Moment Arms in Total Hip Arthroplasty: A Parametric Finite Element Study

BACKGROUND Although the importance of accurate femoral reconstruction to achieve a good functional outcome is well documented, quantitative data on the effects of a displacement of the femoral center of rotation on moment arms are scarce. The purpose of this study was to calculate moment arms after nonanatomical femoral reconstruction. METHODS Finite element models of 15 patients including the pelvis, the femur, and the gluteal muscles were developed. Moment arms were calculated within the native anatomy and compared to distinct displacement of the femoral center of rotation (leg lengthening of 10 mm, loss of femoral offset of 20%, anteversion ±10°, and fixed anteversion at 15°). Calculations were performed within the range of motion observed during a normal gait cycle. RESULTS Although with all evaluated displacements of the femoral center of rotation, the abductor moment arm remained positive, some fibers initially contributing to extension became antagonists (flexors) and vice versa. A loss of 20% of femoral offset led to an average decrease of 15% of abductor moment. Femoral lengthening and changes in femoral anteversion (±10°, fixed at 15°) led to minimal changes in abductor moment arms (maximum change of 5%). Native femoral anteversion correlated with the changes in moment arms induced by the 5 variations of reconstruction. CONCLUSION Accurate reconstruction of offset is important to maintaining abductor moment arms, while changes of femoral rotation had minimal effects. Patients with larger native femoral anteversion appear to be more susceptible to femoral head displacements.

Percutaneous cryoablation for a symptomatic non-ossifying fibroma. A case report

Non-ossifying fibromas (NOFs) are common benign metaphyseal bone lesions of unknown etiology that occur in children and young adults [1]. They commonly arise in the distal femur, proximal tibia and fibula. The peak incidence is between 4—8 years [2] and they are often discovered incidentally on plain radiographs [3]. Physical examination is usually unremarkable. While the vast majority of NOFs are asymptomatic, lesions causing chronic pain and pathologic fractures have been described [4].

MDCT Arthrography of the Hip: Value of the Adaptive Statistical Iterative Reconstruction Technique and Potential for Radiation Dose Reduction

OBJECTIVE The purpose of this article is to assess the effect of the adaptive statistical iterative reconstruction (ASIR) technique on image quality in hip MDCT arthrography and to evaluate its potential for reducing radiation dose. SUBJECTS AND METHODS Thirty-seven patients examined with hip MDCT arthrography were prospectively randomized into three different protocols: one with a regular dose (volume CT dose index [CTDIvol], 38.4 mGy) and two with a reduced dose (CTDIvol, 24.6 or 15.4 mGy). Images were reconstructed using filtered back projection (FBP) and four increasing percentages of ASIR (30%, 50%, 70%, and 90%). Image noise and contrast-to-noise ratio (CNR) were measured. Two musculoskeletal radiologists independently evaluated several anatomic structures and image quality parameters using a 4-point scale. They also jointly assessed acetabular labrum tears and articular cartilage lesions. RESULTS With decreasing radiation dose level, image noise statistically significantly increased (p=0.0009) and CNR statistically significantly decreased (p=0.001). We also found a statistically significant reduction in noise (p=0.0001) and increase in CNR (p≤0.003) with increasing percentage of ASIR; in addition, we noted statistically significant increases in image quality scores for the labrum and cartilage, subchondral bone, overall diagnostic quality (up to 50% ASIR), and subjective noise (p≤0.04), and statistically significant reductions for the trabecular bone and muscles (p≤0.03). Regardless of the radiation dose level, there were no statistically significant differences in the detection and characterization of labral tears (n=24; p=1) and cartilage lesions (n=40; p≥0.89) depending on the ASIR percentage. CONCLUSION The use of up to 50% ASIR in hip MDCT arthrography helps to reduce radiation dose by approximately 35-60%, while maintaining diagnostic image quality comparable to that of a regular-dose protocol using FBP.

Dual-energy computed tomography molecular imaging of pigmented villonodular synovitis

Kallenberg CG. Measurement of increases in anti-doublestranded DNA antibody levels as a predictor of disease exacerbation in systemic lupus erythematosus. A longterm, prospective study. Arthritis Rheum 1990;33:634 43. 24 Biesen R, Dahnrich C, Rosemann A et al. Anti-dsDNANcX ELISA:dsDNA-loaded nucleosomes improve diagnosis and monitoring of disease activity in systemic lupus erythematosus. Arthritis Res Ther 2011;13: R26.