Georg von Salis-Soglio

Finite element analysis of shear stresses at the implant-bone interface of an acetabular press-fit cup during impingement / Finite-Elemente-Berechnung der Schubspannungen im Implantat-Knochen-Interface einer acetabulären Press-Fit-Pfanne bei Impingement

Abstract After total hip replacement (THR) impingement of the implant components causes shear stresses at the acetabular implant-bone interface. In the current study the finite element method (FEM) was applied to analyse the shear stresses at a fully bonded implant-bone interface assuming total ingrowth of the cup. The FE model of a press-fit acetabular component and the proximal part of the femoral component incorporates non-linear material and large sliding contact. The model was loaded with a superior-medial joint load of 435 N simulating a two-legged stance. Starting at initial impingement, the femoral component was medially rotated by 20°. The peak tilting shear stress of -2.6 MPa at the impingement site takes effect towards the pole of the cup. The torsional shear stress at the impingement site is zero. On each side of the impingement site, there are extrema of torsional shear stress reaching -1.8 and 1.8 MPa, respectively. The global peak shear stress during impingement may indicate a possible starting point for cup loosening. The pattern of the torsional shear stresses suggests that besides the symmetric lever-out, an additional asymmetrical tilting of the cup occurs that can be explained by the orientation of the applied joint load. Zusammenfassung Nach Hüftgelenkersatz kann Impingement (Anschlagen) der Implantatkomponenten Schubspannungen im acetabulären Implantat-Knochen-Interface verursachen. In der vorliegenden Studie wurde die Finite-Elemente-Methode (FEM) angewendet, um die Schubspannungen in einem durchgängig verbundenen Implantat-Knochen-Interface nach dem vollständigen knöchernen Einwachsen der Pfanne zu berechnen. Es wurde ein Finite-Elemente-Modell von einer acetabulären Press-Fit-Komponente und von dem proximalen Abschnitt einer femoralen Komponente erstellt. Das Modell berücksichtigt nichtlineares Materialverhalten und große Verschiebungen im Kontaktbereich. Während der Simulation des Zwei-Bein-Standes wurde das Modell mit einer superior-medial ausgerichteten Gelenkkraft von 435 N belastet. Die femorale Komponente wurde ausgehend von initialem Impingement um 20° nach medial rotiert. Der höchste Betrag der Kipp-Schubspannungen befindet sich mit -2,6 MPa an der Impingement-Stelle und ist in Richtung Pfannenpol orientiert. Die Torsions-Schubspannung ist an der Impingement-Stelle null. Auf beiden Seiten von der Impingement-Stelle liegt je ein Extremwert der Torsions-Schubspannung mit -1,8 und 1,8 MPa. Das globale Maximum der Schubspannung weist prinzipiell darauf hin, dass eine Impingement-Stelle ein möglicher Ausgangspunkt für die Pfannenlockerung sein könnte. Die Verteilung der Torsions-Schubspannungen deutet darauf hin, dass neben dem symmetrischen Hebelmechanismus eine zusätzliche asymmetrische Kippbewegung der Pfanne auftritt, die durch die Ausrichtung der aufgebrachten Gelenkkraft erklärt werden kann.

Diagnostic work-up strategy for periprosthetic joint infections after total hip and knee arthroplasty: a 12-year experience on 320 consecutive cases

BackgroundElective knee and hip arthroplasty is followed by infections in currently about 0.5–2.0 % of cases – a figure which is on the increase due to the rise in primary implants. Correct diagnosis early on is essential so that appropriate therapy can be administered. This work presents a retrospective analysis of the diagnoses of patients suffering infections after total hip or knee arthroplasty.Methods320 patients with prosthetic joint infection (PJI) following knee or hip arthroplasty were identified. They comprised a) 172 patients with an infection after total hip arthroplasty (THA): 56 % females (n = 96) and 44 % males (n = 76) with a mean age of 70.9 (39–92) years; and 148 patients with an infection after total knee arthroplasty (TKA): 55 % females (n = 82) and 45 % males (n = 66) with a mean age of 70.7 (15–87) years.ResultsAlthough significantly more TKA than THA patients reported pain, erythema, a burning sensation and swelling, no differences between the two groups were observed with respect to dysfunction, fever or fatigue. However, significant differences were noted in the diagnosis of loosening (THA 55 %, TKA 31 %, p < 0.001) and suspected infection using conventional X-rays (THA 61 %, TKA 29 %, p < 0.001). FDG-PET-CT produced very good results in nearly 95 % of cases. There were no differences between THA and TKA patients regarding levels of inflammation markers. Histological evaluation proved to be significantly better than microbiological analysis.SummaryThe clinical picture may be non-specific and not show typical inflammatory symptoms for a long time, particularly in PJI of the hip. As imaging only provides reliable conclusions after the symptoms have persisted for a long time, morphological imaging is not suitable for the detection of early infections. FDG-PT-CT proved to be the most successful technique and is likely to be used more frequently in future. Nevertheless, there are currently no laboratory parameters which are suitable for the reliable primary diagnosis of PJI. Diagnosis requires arthrocentesis, and the fluid obtained should always be examined both microbiologically and histologically.

On the permanent hip-stabilizing effect of atmospheric pressure

Hip joint dislocations related to total hip arthroplasty (THA) are a common complication especially in the early postoperative course. The surgical approach, the alignment of the prosthetic components, the range of motion and the muscle tone are known factors influencing the risk of dislocation. A further factor that is discussed until today is atmospheric pressure which is not taken into account in the present THA concepts. The aim of this study was to investigate the impact of atmospheric pressure on hip joint stability. Five joint models (Ø 28-44 mm), consisting of THA components were hermetically sealed with a rubber capsule, filled with a defined amount of fluid and exposed to varying ambient pressure. Displacement and pressure sensors were used to record the extent of dislocation related to intraarticular and ambient pressure. In 200 experiments spontaneous dislocations of the different sized joint models were reliably observed once the ambient pressure was lower than 6.0 kPa. Increasing the ambient pressure above 6.0 kPa immediately and persistently reduced the joint models until the ambient pressure was lowered again. Displacement always exceeded half the diameter of the joint model and was independent of gravity effects. This experimental study gives strong evidence that the hip joint is permanently stabilized by atmospheric pressure, confirming the theories of Weber and Weber (1836). On basis of these findings the use of larger prosthetic heads, capsular repair and the deployment of an intracapsular Redon drain are proposed to substantially decrease the risk of dislocation after THA.

Experimental evidence of impingement induced strains at the interface and the periphery of an embedded acetabular cup implant.

After total hip arthroplasty, impingement of implant components may occur during every-day patient activities causing increased shear stresses at the acetabular implant-bone interface. In the literature, impingement related lever-out moments were noted for a number of acetabular components. But there is little information about pelvic load transfer. The aim of the current study was to measure the three-dimensional strain distribution at the macrostructured hemispherical interface and in the periphery of a standard acetabular press-fit cup in an experimental implant-bone substitute model. An experimental setup was developed to simulate impingement loading via a lever arm representing the femoral component and the lower limb. In one experimental setup 12 strain gauges were embedded at predefined positions in the periphery of the acetabular cup implant inside a tray, using polyurethane composite resin as a bone substitute material. By incremental rotation of the implant tray in steps of 10 and 30 deg, respectively, the strains were measured at evenly distributed positions. With the described method 288 genuine strain values were measured in the periphery of an embedded acetabular cup implant in one experimental setup. In two additional setups the strains were evaluated at different distances from the implant interface. Both in radial and meridional interface directions strain magnitudes reach their peak near the rim of the cup below the impingement site. Values of equatorial strains vary near zero and reach their peaks near the rim of the cup on either side and in some distance from the impingement site. Interestingly, the maximum of averaged radial strains does not occur, as expected, close to the interface but at an interface offset of 5.6 mm. With the described experimental setup it is now possible to measure and display the three-dimensional strain distribution in the interface and the periphery of an embedded acetabular cup implant. The current study provides the first experimental proof of the high local stresses gradients in the direct vicinity of the impingement site. The results of the current study help for a better understanding of the impingement mechanism and its impact on acetabular cup stability.

Single-Stage Epidural Catheter Lavage with Posterior Spondylodesis in Lumbar Pyogenic Spondylodiscitis with Multilevel Epidural Abscess Formation

BACKGROUND Despite significant advances in the conservative management of pyogenic spondylodiscitis, consecutive instability, deformity, and/or neurologic compromise demands a prompt surgical intervention. However, in rare cases involving additional multilevel epidural abscess formation, the appropriate surgical strategy remains controversial. In this retrospective cohort analyses, we evaluated the efficacy of a single-stage posterior approach with the addition of a one-time multilevel epidural lavage via the surgically exposed interlaminar fenestration of the infected segment. METHODS From January 2009 through December 2010, 73 patients presenting pyogenic spondylodiscitis with instability of the lumbar spine were admitted. In all cases, the surgical strategy included a radical resection of the affected intervertebral disc and stabilization by intervertebral fusion using a titanium cage with autologous bone grafting in a level-dependent posterior approach with additional pedicle screw-and-rod instrumentation. In cases where multilevel abscess formation was evident, the standard surgical procedure was complemented by drainage and irrigation of the abscess from posterior by carefully advancing a soft infant feeding tube via the surgically exposed epidural space under fluoroscopic guidance. All patients received complementary oral antibiotic therapy for 12 weeks and were followed-up for a minimum of 12 months postoperatively. RESULTS Ten patients (three male and seven female patients; mean age: 64.9 ± 10.9 years) presented with an additional lumbar epidural abscess extending beyond three levels proximal or distal to the infected disc. In all 10 patients the laboratory-chemical inflammatory parameters (leukocyte count, C-reactive protein) remained within the physiologic range after completing antibiotic therapy throughout the 1-year follow-up period. The plain radiographs and magnetic resonance imaging demonstrated solid fusion and the complete remission of the initial abscess formation after 3 to 6 months with no recurrence of infection, respectively. CONCLUSION The onetime epidural lavage presented in this small patient cohort proved to be an effective surgical adjunct with minimal exposure-related morbidity. We believe that the possibility of early mobilization and the patients increased rehabilitation potential reduce the risk of nosocomial complications that often coincide with this multimorbid high-risk group of patients.

In vivo glenohumeral analysis using 3D MRI models and a flexible software tool: Feasibility and precision†

To implement a PC‐based morphometric analysis platform and to evaluate the feasibility and precision of MRI measurements of glenohumeral translation.

Primäre septische Gonarthritis durch Salmonella enteritidis bei systemischem Lupus erythematodes

M. Borte Universitätsklinik und Poliklinik für Kinder und Jugendliche Universität Leipzig AöR Der nachfolgende Beitrag gehört zu unserer Rubrik „Prima Vista“. Diese Rubrik lehnt sich an die „Images in Clinical Medicine“ des New England Journal of Medicine an und soll aus einem oder zwei instruktiven und originellen Bildern mit einer kurzen Erläuterung bestehen. Es kann sich dabei sowohl um ein interessantes klinisches Foto als auch ein Röntgen-, Ultraschalloder histologisches Bild handeln. Auch andere, patientenbezogene Abbildungen (z.B. ein EMG), sind denkbar, wenn sie interessant und gut verständlich sind. Hiermit laden wir alle rheumatologisch interessierten Leser ein, ihre Beiträge einzusenden an:

Bipolar hip arthroplasty as salvage treatment for loosening of the acetabular cup with significant bone defects

Introduction: Revision arthroplasty of the hip is becoming increasingly important in recent years. Early primary arthroplasty and longer life expectancy of the patients increases the number of revision surgery. Revision surgery of hip arthroplasty is major surgery for the patients, especially the elderly, with significant risks concerning the general condition of the patient. The aim of this work is to evaluate the outcome of bipolar hip arthroplasty as a salvage procedure for treatment of loosening of the acetabular cup with significant acetabular bone defects after total hip replacement (THR) in multi-morbid patients. Patients and methods: During the period from January 1st 2007 to December 31st 2011 19 revision hip surgeries were performed in 19 patients, in which the loosened acetabular cup was replaced by a bipolar head. The examined patient group consisted exclusively of female patients with an average of 75 years. The predominant diagnosis was “aseptic loosening” (84.2%). All patients in our study were multi-morbid. We decided to resort to bipolar hip arthroplasty due to the compromised general condition of patients and the major acetabular bone defects, which were confirmed intraoperatively. The postoperative follow-up ranged from 0.5 to 67 months (average 19.1 months). Results: Evaluation of the modified Harris Hip Score showed an overall improvement of the function of the hip joint after surgery of approximately 45%. Surgery was less time consuming and thus adequate for patients with significantly poor general health condition. We noticed different complications in a significant amount of patients (68.4%). The most common complication encountered was the proximal migration of the bipolar head. The rate of revision following the use of bipolar hip arthroplasty in revision surgery of the hip in our patients was high (21%). Despite the high number of complications reported in our study, we have noticed significant improvement of hip joint function as well as subjective pain relief in the majority of patients. We clearly achieved clinically satisfactory results in 14 patients. Conclusion: Bipolar hip arthroplasty is by no means to be regarded as standard procedure in revision surgery of THR. It provides an option or salvage procedure for patients with poor general condition in whom the quickest possible surgical intervention preserving mobility is required. This is particularly true for multi-morbid patients in whom sufficient acetabular fixation is not possible.

Therapeutic options to prevent recurrence of an aggressive aneurysmatic bone cyst of the cervical spine of a 16 year old boy - a case report

The aneurysmatic bone cyst (ABC) is a benign primary bone tumour. If located in the cervical spine, its expansive growth and destructive behaviour may lead to instability and serious neurological impairment. We report a case of a 16-year-old boy with an aggressive ABC in the 7th cervical vertebra. Computertomographic and magnetic resonance imaging revealed the envelopment of the left 7th and 8th spinal nerve along with the anterior displacement of the left vertebral artery. The interdisciplinary surgical strategy consisted of a partially incomplete cyst resection, subtotal spondylectomy with posterior screw-and-rod fixation from C6-Th1, iliac crest bone grafting and anterior plating from C6-Th1. With regard to the high rate of recurrence after incomplete resection published in the recent literature, the patient was postoperatively treated by megavoltage radiotherapy with a total dose of 30Gy (daily dose of 1.8 Gy for 3 weeks). The clinical and radiographic follow-up showed complete recovery of all neurologic impairments and no signs of tumour recurrence at 3, 6 and 12 months after surgery. This case highlights diverse treatment regimens and shall outline the challenge and the problems of the interdisciplinary decision-making in adolescents presenting with ABC in high-demanding anatomical regions.

WISSENSCHAFTLICHER BEITRAG: Verletzungen und Fehlbelastungsfolgen im Jazz Dance

Zusammenfassung Die Auswirkungen von Jazz Dance auf den Stutz- und Bewegungsapparat werden an 50 Berufs- und Amateurtanzern untersucht. Die wichtigsten Ergebnisse: wochentliche Trainingszeit der Berufstanzer im Durchschnitt 26,8 Stunden, der Amateure 5,7 Stunden; geringes Verletzungsrisiko, Berufstanzer haufiger als Amateure, es dominierten Supinationstraumen bzw. Frakturen im Bereich der Sprunggelenke und Fuse, gefolgt von Verletzungen der WS und paravertebralen Muskulatur sowie Zerrungen und Muskelfaserrissen im Oberschenkelbereich. Innerhalb der spezifischen Tanztechnik sind besonders Lay-out-Kombinationen (Hyperflexion und Hyperextension der WS), Falls (Bewegungen zum Boden) und kniende Bewegungsablaufe stark belastungsintensive Bewegungsmuster.