Jorg Roosen

Routine thymectomy in congenital cardiac surgery changes adaptive immunity without clinical relevance

The actual importance of the thymus in both children and adults is largely unclear. In congenital cardiac surgery, a partial or total thymectomy is frequently performed to improve access to the heart and great vessels. We performed a literature search to evaluate the effect on the adaptive immune system of the removal of thymus tissue in patients with congenital heart disease. A PubMed search according to Dunnings standard provided 149 articles, of which 13 addressed our search question. Each study has been tabulated with author, cases, controls, follow-up, methods, results and limitations. A first group of articles repeatedly showed the effect on the T-cell compartment, including the impact on subgroups of this compartment. More recent studies, usually with a longer follow-up, confirm that the earlier changes in T-cell population appear to be permanent. Only one author found a normalization of T-cell population five years after thymectomy. In contrast to these clear changes in T-cell population, there is currently no clear clinical relevance. A literature search on thymectomy in congenital cardiac surgery revealed clear changes in T-cell-related immunity; however, there is a lack of clinical relevance. Further investigation of the adaptive immune system is required to explain this discrepancy.

Development of an acoustic measurement protocol to monitor acetabular implant fixation in cementless total hip Arthroplasty: A preliminary study

In cementless total hip arthroplasty (THA), the initial stability is obtained by press-fitting the implant in the bone to allow osseointegration for a long term secondary stability. However, finding the insertion endpoint that corresponds to a proper initial stability is currently based on the tactile and auditory experiences of the orthopedic surgeon, which can be challenging. This study presents a novel real-time method based on acoustic signals to monitor the acetabular implant fixation in cementless total hip arthroplasty. Twelve acoustic in vitro experiments were performed on three types of bone models; a simple bone block model, an artificial pelvic model and a cadaveric model. A custom made beam was screwed onto the implant which functioned as a sound enhancer and insertor. At each insertion step an acoustic measurement was performed. A significant acoustic resonance frequency shift was observed during the insertion process for the different bone models; 250 Hz (35%, second bending mode) to 180 Hz (13%, fourth bending mode) for the artificial bone block models and 120 Hz (11%, eighth bending mode) for the artificial pelvis model. No significant frequency shift was observed during the cadaveric experiment due to a lack of implant fixation in this model. This novel diagnostic method shows the potential of using acoustic signals to monitor the implant seating during insertion.

Determination of replicate composite bone material properties using modal analysis

Replicate composite bones are used extensively for in vitro testing of new orthopedic devices. Contrary to tests with cadaveric bone material, which inherently exhibits large variability, they offer a standardized alternative with limited variability. Accurate knowledge of the composites material properties is important when interpreting in vitro test results and when using them in FE models of biomechanical constructs. The cortical bone analogue material properties of three different fourth-generation composite bone models were determined by updating FE bone models using experimental and numerical modal analyses results. The influence of the cortical bone analogue material model (isotropic or transversely isotropic) and the inter- and intra-specimen variability were assessed. Isotropic cortical bone analogue material models failed to represent the experimental behavior in a satisfactory way even after updating the elastic material constants. When transversely isotropic material models were used, the updating procedure resulted in a reduction of the longitudinal Youngs modulus from 16.00GPa before updating to an average of 13.96 GPa after updating. The shear modulus was increased from 3.30GPa to an average value of 3.92GPa. The transverse Youngs modulus was lowered from an initial value of 10.00GPa to 9.89GPa. Low inter- and intra-specimen variability was found.

A biomechanical testing system to determine micromotion between hip implant and femur accounting for deformation of the hip implant: Assessment of the influence of rigid body assumptions on micromotions measurements

Background: Accurate pre‐clinical evaluation of the initial stability of new cementless hip stems using in vitro micromotion measurements is an important step in the design process to assess the new stems potential. Several measuring systems, linear variable displacement transducer‐based and other, require assuming bone or implant to be rigid to obtain micromotion values or to calculate derived quantities such as relative implant tilting. Methods: An alternative linear variable displacement transducer‐based measuring system not requiring a rigid body assumption was developed in this study. The system combined advantages of local unidirectional and frame–and–bracket micromotion measuring concepts. The influence and possible errors that would be made by adopting a rigid body assumption were quantified. Furthermore, as the system allowed emulating local unidirectional and frame–and–bracket systems, the influence of adopting rigid body assumptions were also analyzed for both concepts. Synthetic and embalmed bone models were tested in combination with primary and revision implants. Single‐legged stance phase loading was applied to the implant – bone constructs. Findings: Adopting a rigid body assumption resulted in an overestimation of mediolateral micromotion of up to 49.7 &mgr;m at more distal measuring locations. Maximal average relative rotational motion was overestimated by 0.12° around the anteroposterior axis. Frontal and sagittal tilting calculations based on a unidirectional measuring concept underestimated the true tilting by an order of magnitude. Interpretation: Non‐rigid behavior is a factor that should not be dismissed in micromotion stability evaluations of primary and revision femoral implants. Highlights:Implant and bone motion can be measured simultaneously at several locations.Non‐rigid behavior has a major influence on implant stability measurement results.Under a rigid body assumption, distal micromotion was overestimated by up to 49.7 &mgr;m.Under a rigid body assumption, relative rotational motion was overestimated by up to 0.12°.