Similar patient positioning: A key factor in follow-up studies when using model-based radiostereometric analysis of the hip.

INTRODUCTION: Despite protocols, patients are not positioned exactly alike at radiostereometric (RSA) follow-up examinations, and it is unknown how much variation is tolerable. We report precision for optimal and extreme position differences from a phantom hip-study, and clinical precision of hip-RSA. METHODS: A femoral stem with 3 bead-towers was fixed in a saw bone with bone-markers (phantom), and series of RSA examinations within optimal (5 × 5 cm and 5°) and extreme (20 × 30 cm and 30°) phantom positions were obtained. Double-examination RSA of 12 patients with the same femoral stem type were analyzed. Both model-based (CAD) and marker-based (MM) analysis was used. Precision was reported as standard deviation of differences. RESULTS: Precision for translations in the optimal and extreme phantom position were below 0.06 mm and 0.02 mm for MM analysis, and below 0.05 mm and 0.18 mm for CAD analysis, respectively. Precision for rotations in the optimal and extreme phantom rotation were below 0.18° and 0.26° for MM analysis, and below 0.34° and 0.52° for CAD analysis, respectively. Clinical precision was 0.29 mm and 0.44° for MM analysis, and 0.40 mm and 1.59° for CAD analysis. CONCLUSION: Extreme differences in patient position during RSA examination negatively affects precision, and CAD model-analysis was more sensitive than MM analysis. Longitudinal translation and rotation about the long stem-axis are the effect parameters which are most affected by position and rotation changes, and also the best indicators of implant loosening. IMPLICATIONS FOR PRACTICE: Based on our research, we recommend that similar patient positioning between follow-up RSA examinations is debated and prioritized.

Marker free model-based radiostereometric analysis for evaluation of hip joint kinematics: A validation study.

OBJECTIVES: To validate the precision of digitally reconstructed radiograph (DRR) radiostereometric analysis (RSA) and the model-based method (MBM) RSA with respect to benchmark marker-based (MM) RSA for evaluation of kinematics in the native hip joint. METHODS: Seven human cadaveric hemipelves were CT scanned and bone models were segmented. Tantalum beads were placed in the pelvis and proximal femoral bone. RSA recordings of the hips were performed during flexion, adduction and internal rotation. Stereoradiographic recordings were all analyzed with DRR, MBM and MM. Migration results for the MBM and DRR with respect to MM were compared. Precision was assessed as systematic bias (mean difference) and random variation (Pitman's test for equal variance). RESULTS: A total of 288 dynamic RSA images were analyzed. Systematic bias for DRR and MBM with respect to MM in translations (p < 0.018 mm) and rotations (p < 0.009°) were approximately 0. Pitman's test showed lower random variation in all degrees of freedom for DRR compared with MBM (p < 0.001). CONCLUSION: Systematic error was approximately 0 for both DRR or MBM. However, precision of DRR was statistically significantly better than MBM. Since DRR does not require marker insertion it can be used for investigation of preoperative hip kinematics in comparison with the postoperative results after joint preserving hip surgery. Cite this article: L. Hansen, S. De Raedt, P. B. Jørgensen, B. Mygind-Klavsen, B. Kaptein, M. Stilling. Marker free model-based radiostereometric analysis for evaluation of hip joint kinematics: A validation study. Bone Joint Res 2018;7:379-387. DOI: 10.1302/2046-3758.76.BJR-2017-0268.R1.

Validation of static and dynamic radiostereometric analysis of the knee joint using bone models from CT data.

OBJECTIVES: Static radiostereometric analysis (RSA) using implanted markers is considered the most accurate system for the evaluation of prosthesis migration. By using CT bone models instead of markers, combined with a dynamic RSA system, a non-invasive measurement of joint movement is enabled. This method is more accurate than current 3D skin marker-based tracking systems. The purpose of this study was to evaluate the accuracy of the CT model method for measuring knee joint kinematics in static and dynamic RSA using the marker method as the benchmark. METHODS: Bone models were created from CT scans, and tantalum beads were implanted into the tibia and femur of eight human cadaver knees. Each specimen was secured in a fixture, static and dynamic stereoradiographs were recorded, and the bone models and marker models were fitted to the stereoradiographs. RESULTS: Results showed a mean difference between the two methods in all six degrees of freedom for static RSA to be within -0.10 mm/° and 0.08 mm/° with a 95% limit of agreement (LoA) ranging from ± 0.49 to 1.26. Dynamic RSA had a slightly larger range in mean difference of -0.23 mm/° to 0.16 mm/° with LoA ranging from ± 0.75 to 1.50. CONCLUSIONS: In a laboratory-controlled setting, the CT model method combined with dynamic RSA may be an alternative to previous marker-based methods for kinematic analyses.Cite this article: K. Stentz-Olesen, E. T. Nielsen, S. De Raedt, P. B. Jørgensen, O. G. Sørensen, B. L. Kaptein, M. S. Andersen, M. Stilling. Validation of static and dynamic radiostereometric analysis of the knee joint using bone models from CT data. Bone Joint Res 2017;6:376-384. DOI: 10.1302/2046-3758.66.BJR-2016-0113.R3.

Protein modification by fermentation: effect of fermentation on the potential allergenicity of pea.

The effect of fermentation on components of potential significance for the allergenicity of pea was analyzed. Pea flour was fermented with three lactic acid bacteria, Pediococcus pentosaceus, Lactococcus raffinolactis, and Lactobacillus plantarum, and two fungi, Rhizopus microsporus, var. oligosporus and Geotrichum candidum. Residual antigenicity against antipea antibodies was reduced to 10% by the three lactic acid bacteria and R. microsporus. Reactions to anti-pea profilin and anti-Bet v 1 were still detectable after fermentation. The contents of lectin and pea protease inhibitor were not reduced by the microorganisms.

[Patient assessment in ambulatory surgery. A questionnaire study]. / Patientevaluering af sammedagskirurgi. En enqueteundersøgelse.

In our department, from the beginning of December 1994 to the end of February 1995, we operated upon a selected group of 199 patients, hospitalized as day surgery patients. Each patient was given a questionnaire to fill in after discharge. We asked them to evaluate day surgery from the consumer's point of view. We did not record any data which could identify the single patient. We received 158 questionnaires (79%) of which 151 were accepted. One hundred and seven patients (71%) found day surgery acceptable and a good alternative to conventional hospitalization, 82% preferred having the same doctor and primary nursing during the treatment. One hundred and sixteen patients were discharged as planned (77%). There were no serious complications. Provided that patients are carefully selected, we find day surgery a highly satisfactory method of management which is safe and efficient.

Anger camera imaging of perfused and nonperfused brain tissue with intra-arterial 133Xenon technique.

The regional cerebral blood flow, the regional blood flow distribution, and the regional distribution of perfused (= vital) brain tissue been imaged with a digitalized conventional Anger camer. An analog scaler was placed behind the PM-tubes to reduce dead-time loss. The input pulse rate was doubled to counteract the effect of scaling on counting statistics, and the gamma emission was filtered through 1 mm of brass to increase the fraction of the integral count rate within the 40% window. In this way the 31 keV peak disappears, and Compton scatter and disturbing coincidences are markedly reduced. This improves spatial resolution. The flow parameters are imaged regionally in 3 X 3 mm2 matrix elements after flat field correction and smoothing. The matrix is 64 X 64 interpolated to 128 X 128. Patient studies emphasized the importance of imaging the distribution of perfused and nonperfused tissue in cases of infarctions, dilacerations, etc., where angiography and conventional brain scanning may often be negative.

The effects of droperidol and fentanyl on intracranial pressure and cerebral perfusion pressure in neurosurgical patients.

The effects of droperidol and fentanyl on the intracranial pressure (i.c.p.) and cerebral perfusion pressure (c.p.p.) were studied in eight anaesthetized normocapnic patients with intracranial space-occupying lesions. The infection of droperidol resulted in a small and not significant increase in i.c.p. from 24.0 to 27.2 mm Hg, while c.p.p. decreased from 75.9 mm Hg to 57.8 mm Hg, as a result of a decrease in systemic arterial pressure. The addition of fentanyl produced no change in i.c.p., but a further decrease in arterial pressure decreased c.p.p. from 60.4 mm Hg to 47.8 mm Hg. In four patients values of c.p.p. less than 40 mm Hg were obtained. C.p.p. was was increased by hyperventilation in all but one of these patients. It is concluded that droperidol and fentanyl should be used in patients with intracranial hypertension only if hypocapnia has been established and when the arterial pressure is normal or increased.

Intracranial pressure during recovery from nitrous oxide and halothane anaesthesia in neurosurgical patients.

Seven patients with intracranial disorders were studied during recovery from anaesthesia with nitrous oxide and halothane. Arterial, intracranial, and central venous pressure, and arterial carbon dioxide tension were measured and compared with the patient's clinical state. No patient had evidence of increased brain volume when the dura was closed. All had been hyperventilated during the surgical procedure. Cessation of hyperventilation and the continued administration of anaesthetics was followed by a moderate increase in intracranial pressure and a reduction in cerebral perfusion pressure, but critically low values were not seen. Spontaneous respiration returned when the PaCO2 was in the range of 33-51 mm Hg. When spontaneous respiration was judged to be normal, anaesthesia was interrupted and the endotracheal tube was removed. In the following minutes, until the patients were awake, the intracranial pressure decreased to normal or near normal values, with minimal change in PaCO2. In these seven patients in whom there were no signs of brain swelling, the skull was closed, the patients were allowed to resume spontaneous respiration, and anaesthesia was terminated without major changes in intracranial pressure or cerebral perfusion pressure. However, hyperventilation is advocated after operation in patients with marked brain swelling.