Volumetric measurement of periprosthetic bone remodeling: prospective 5 years follow-up after cemented total hip arthroplasty.

INTRODUCTION: Periprosthetic bone remodeling after total hip arthroplasty (THA) is a well recognized phenomenon. Many authors have published osteodensitometric data with DEXA analysis. This study based on computerized tomography (CT). MATERIALS AND METHODS: The objective of the current project is to collect prospective volumetric bone density data with a clinical CT study in six patients after cemented THA (titanium alloy stem). The follow-up time is 5 years. A data set of about 100,000 bone voxels for each femur was collected. Bone density was observed by dint of an osteodensitometric computer program. The median results were shown in seven regions of interest (ROI) around the prosthesis stem, according to Gruen. RESULTS: The statistical analysis of the six cases after 60 months with respect to the postoperative control demonstrated a significantly lower density in ROI 2 (-125.5HU, P = 0.014), ROI 3 (-116.7HU, P = 0.023), ROI 4 (-54.5HU, P = 0.023), ROI 5 (-90.9HU, P = 0.014) and ROI 6 (-104.9HU, P = 0.014). Maximum density decrease was observed in ROI 2 and 3. The statistical analysis of the six cases after 60 months with respect to the 24 months control demonstrated a significantly lower density in ROI 2 (-62.6HU, P = 0.014), ROI 5 (-62.9HU, P = 0.023). There was a density decrease in ROI 3, 4, 6, 7 which was not significant and a slight increase in ROI 1. CONCLUSION: To our knowledge, this is the first collection of fully prospective 5 years 3D periprosthetic density data. The CT method used in the study presented here measures three-dimensionally, while the frequently used DEXA (dual X-ray absorptiometry) method measures two-dimensionally. The data are also unique as they are suitable for direct patient-specific 3D finite element meshing and biomechanical calculation. They can be graphically post-processed in order to obtain cross-sectional or 3D displays of density patterns.

Femoral strain changes after total hip arthroplasty--patient-specific finite element analyses 12 years after operation.

Periprosthetic stress-shielding after total hip arthroplasty (THA) is a well-known phenomenon. Many authors have used the finite element (FE) method to show the effects of THA on animal or human femora. In most cases they have performed cadaver experiments. The current project is a FE analysis based on a retrospective computerized tomography (CT) in vivo data set of 11 patients 12 years after THA. In order to control the analysis, a computationally created stem was implanted at the femur model of the not operated contralateral side. In comparison to the not operated side, there was a significant reduction of the strain energy density (SED) values in all regions of interest (ROI) with the greatest effect near the distal tip of the stem. Only zone 1 showed no clear trend which may be due to load application at the greater trochanter causing local strain peaks. The median SED values changed by -31.65% (ROI 1), -25.64% (ROI 2), -30.82% (ROI 3), -12.35% (ROI 4), -40.10% (ROI 5), -30.37% (ROI 6) and -43.38% (ROI 7). As far as we are aware, the current combination of in vivo CT density data with FE strain analyses after THA is based on the largest number of patients and the longest follow-up period. This combination enables analysis and prediction of the influence of implantation upon bone and can be compared with of remodelling theories. The assessment of mechanical strain data during a follow-up trial could be a new approach for analyzing different hip stems in clinical biomechanics.

[MR-Imaging of lower leg muscle perfusion]. / Magnetresonanztomographische Diagnostik der peripheren Durchblutung.

PURPOSE: This article describes the potential of dynamic contrast- enhanced magnetic resonance tomography (DCE-MRT) for the visualization and quantification of blood flow of lower leg muscles at rest and after individually adjusted muscular exercise. PATIENTS AND METHODS: Five cases were chosen to exemplify the qualitative and semi-quantitative blood flow evaluation in the lower leg muscles. The crural muscle state was determined with an isometric maximal strength measurement from a female patient with peripheral arterial occlusive disease (pAVK), a male patient with coronary heart disease (KHK) without clinical signs of a pAVK, a volunteer with sufficient physical activity in accordance with the Freiburg Questionnaire of Physical Activity and two professional athletes. After calibration of the plantarflexion ergometer MR-PEDALO (Figures 2a and 2b) for the execution of auxotonic muscle work a 1- minute alternating foot extension and flexion exercise on MRPEDALO was performed in the MR machine. Instead of the lower leg splint shown in Figures 2a and 2b the MR coil fits exactly in MR-PEDALO used for DCE-MRT. Mechanical work performed during the 1-minute exercise ranged from 52 watt seconds (Ws) to 244 Ws (0.65 W to 4.07 W), indicating similar interindividual work loads in relation to the individual maximum isometric strength. DCE-MRT was performed at rest and immediately after auxotonic exercise test (T1w 2DFLASH- GE sequence with TR/TE/alpha: 100 ms/6 ms/70 degrees; field of view: 400; matrix: 81 x 256; slice thickness: 10 mm; acquisitions: 73 at 8.3 s each; total examination time: 9.24 min; bolus application of Magnevist, Schering, 0.02 ml/kg kg, 20 ml bolus NaCl, flow 2 ml/s, 22G cannula in a cubital vein). Signal intensity (SI) curves were analyzed with DynaVision (MeVis gGmbH, Bremen, Germany). RESULTS: Measuring peripheral blood flow needs appropriate muscular stress tests. The SI-curves of the region of interest (ROI) representing the peroneus, tibialis anterior and gastrocnemius muscle run almost parallel at rest. Workloads between 52 Ws and 244 Ws (0.65 W and 4.07 W), similar in relation to the individual maximum isometric strength, induce distinctive changes of the upslope, wash-in, peak and washout of SI-curves preferably for the peroneus muscle and less predominant also for the tibialis anterior muscle and gastrocnemius muscle respectively. The first case, a 55-year-old female patient with peripheral arterial occlusive disease (pAVK) stage Fontaine IIb before (Figure 3a) and after (Figure 3b) percutaneous transluminal angioplasty (PTA) of a right femoral artery stenosis shows after interventional treatment a rapid post-exercise SI-increase in the peroneus muscle. The steeper SI-curve indicates a better contrast medium inflow due to an improved perfusion. The second case, a 65-year-old man suffering from coronary heart disease without clinical signs of pAVK (Figure 4) exercised with a workload of 92 Ws. After stress test the ROI for the peroneus muscle shows a clear intensity increase. After exercise the SI-curve for the tibialis anterior muscle shows a similar, but less predominant change while the shape of the SI-curve of the gastrocnemius muscle remains mainly identical. A 23-year-old male person with average physical activity (Figure 5) performed DCE-MRT of the left lower leg after stress test with 172 Ws demonstrating a rapid signal increase in the peroneus muscle while the synergistic tibialis anterior muscle and antagonistic gastrocnemius muscle show a comparatively slow contrast-medium wash-in. A 26-year-old male athlete (Figure 6) exercised with 196 Ws showing a rapid contrast medium inflow in the peroneus muscle and initially also in the synergistic tibialis anterior muscle. A contrast-medium wash-out appears in both muscles, while the shape of the gastrocnemius muscle SI-curve remains substantially unchanged. A 26-year-old female athlete (Figure 7) exercised with 244 Ws. Post exercise SI-curves show a distinctive and rapid increase of contrast medium wash-in with a sharp peak particularly in the peroneus muscle and similarly in the tibialis anterior and gastrocnemius muscle. After exercise all SI-curves show a wash-out phase. CONCLUSION: SI-curves show relative increase in correlation with Time-to-Peak (TTP) decrease and Mean-Intensity to Time Ratio (MITR) increase indicating blood flow reserve mobilization after exercise. Individual muscle state seems to be linked to muscle recruitment and muscle coordination reflected by post-exercise SI-curves. The gastrocnemius muscle shows comparatively low SI-curve changes after muscular load test. Further methodological standardization and optimization of the stress test is mandatory to assure intra- and interindividual comparisons. Due to direct visualization and quantitative evaluation of the peripheral microcirculation DCE-MRT has a diagnostic potential for monitoring therapeutic response in peripheral circulation disorders and sports medicine.

Kidney transplantation into an ileocecal reservoir after total extirpation of the urinary tract for panurothelial cancer: long-term followup.

We report on the long-term followup of a young woman after total extirpation of the urinary tract for panurothelial cancer with subsequent continent urinary diversion and renal transplantation. If a patient is willing to accept the associated risks, the staged procedure can be a highly satisfactory treatment option. Life-long close surveillance is critical for the success of this concept.

Validation data for periprosthetic bone remodelling theories.

Periprosthetic adaptive bone remodelling after total hip arthroplasty (THA) has been frequently simulated in computer models, combining bone remodelling theory with finite element analysis. Unfortunately, there still subsist a lack of clinical data, which are necessary for validation of these simulation results. Therefore, the objective of the current project is to collect prospective volumetric bone density data with a clinical computerized tomography study in seven patients after THA. A retrospective study 12 years after implantation in 11 patients was added. A data set of about 100000 bone voxels for each femur was collected. In all prospective cases, the predominant change is seen during the first year. The average density reduction in the horizontal slices was between 50 and 150 Hounsfield units (HU) (approx. 10%; p<0.001) after 2 years. Loss of density is particularly strong distal of the minor trochanter and decreases from proximal to distal. For the 12 years retrospective study, the contralateral femur provided the control. Similar trends comparable to the prospective 2-year follow-up CT density values were seen in most cases with density reductions of up to 400 HU (30%). However, in one of these cases there was no difference between the operated and the control density. As far as we are aware, this is the first collection of fully prospective 3D validation data in vivo for periprosthetic adaptive bone remodelling theories. The data are also unique as they are suitable for direct patient-specific 3D finite element meshing and individual weight-related loading.