Two different posterior-stabilized mobile-bearing TKA designs: navigator evaluation of intraoperative kinematic differences.

PURPOSE: The purpose of this study was to compare two types of posterior-stabilized (PS) mobile-bearing (MB) total knee arthroplasties (TKAs). The hypothesis was that no major differences were going to be found among the two TKA designs. METHODS: Two cohorts of patients who were divided according to implant design (Cohort A, new design gradually reducing radius PS MB TKA; Cohort B, traditional dual-radius PS MB TKA) were analyzed by means of intraoperative navigation. All operations were guided by a non-image-based navigation system that recorded relative femoral and tibial positions in native and implanted knees during the following kinematic tests: passive range of motion (PROM), varus-valgus stress test at 0° and 30° (VV0, VV30) and anterior/posterior drawer test at 90° of flexion (AP90). RESULTS: There were no significative differences in kinematic tests between the two implants. Cohort A, however, showed a different post-implant trend for VV0 and VV30 that were lower than the pre-implant ones, as expected, while for Cohort B, the trend is opposite. However, the gradually reducing radius prosthesis (Cohort A) showed a trend of improving stability (29% compared to the preoperative status) in mid-flexion (VV30) which the traditional dual-radius design (Cohort B) would not. Moreover, we found no differences among postoperative results of the two TKA designs. CONCLUSION: Despite design variations, no difference has been found among the prostheses in terms of PROM, rotations and translations. Both design kinematics did not show paradoxical external rotations, but an increase in femoral translation in mid-flexion without affecting the functioning of the prosthesis. LEVEL OF EVIDENCE: II.

A new method to evaluate the influence of the glenosphere positioning on stability and range of motion of a reverse shoulder prosthesis.

PURPOSE: Shoulder instability and reduced range of motion are two common complications of a total reverse shoulder arthroplasty. In this work, a new approach is proposed to estimate how the glenoid component positioning can influence the stability and the range of motion of a reverse shoulder prosthesis. MATERIALS AND METHODS: A standard reverse shoulder prosthesis has been analysed. To perform virtual simulation of the shoulder-prosthesis assembly, all the components of the prosthesis have been acquired via a 3D laser scanner and the solid models of the shoulder bones have been reconstructed through CT images. Loads on the shoulder joint have been estimated using anatomical models database. A new virtual/numerical procedure has been implemented using a 3D parametric modelling software to find the optimal position of the glenosphere. RESULTS: Several analyses have been performed using different configurations obtained by changing the glenoid component tilt and the lateral position of the glenosphere, modified through the insertion of a cylindrical spacer. For the analysed case study, it was found that the interposition of a spacer (between the baseplate and the glenoid) and 15° inferior tilt of the glenosphere allow improving the range of motion and the stability of the shoulder. CONCLUSIONS: Some common complications of the reverse shoulder arthroplasty could be effectively reduced by a suitable positioning of the prosthesis components. In this work, using a new method based on virtual simulations, the influence of the glenosphere positioning has been investigated. An optimal configuration for the analysed case study has been found. The proposed approach could be used to find, with no in vivo experiments, the optimal position of a reverse shoulder prosthesis depending on the different dimensions and shape of the bones of each patient.

Virtual simulation of an osseointegrated trans-humeral prosthesis: A falling scenario.

INTRODUCTION: Traditional prosthetic solutions expose the amputee to numerous problems that limit his ability to safely perform the normal activities of daily life. In order to eliminate the problems related to the use of the traditional prosthesis with socket, a new technique was developed for fixing the prosthesis to the amputees based on the principle of osseointegration. The aim of this paper is to study and analyze the stress distribution on the interface between a trans-humeral osseointegrated prosthetic implant and the residual bone, identifying the most stressed areas and thus foreseeing possible failure phenomena of the entire prosthetic system and, after, to compare the stress distribution on three different prosthetic designs that differ from each other for some geometric characteristics. MATERIALS AND METHODS: A healthy individual mimics two fall scenarios of which the trans-humeral amputees can most likely be victims: Static fall and Dynamic fall. A force platform (P-6000, BTS Bioengineering) is required for load data acquisition. The CAD model of the trans-humeral osseointegrated implant was created following the guidelines of the OPRA implant. The bone model was created starting from the CAT scan of a left humerus. The FEM simulation was conducted throught a linear analysis. RESULTS: Both during static fall and dynamic fall, similar trends have been observed for the reaction force Fz, the torque moment Tz, the bending moments Mx and My. From the analysis of the von Mises stress distribution it was found that the stress distribution is more homogeneous in the case where the thread of the fixture is made by a triangular profile with height of the thread equal to 0.5 mm. However, it can be seen that, when passing from a thread with height of 0.5 mm to a 1 mm, there is a slight decrease in the stress on the whole contact zone between the fixture and the humerus. The same improvement can also be seen in the case of trapezoidal threading. CONCLUSION: By modifying the height and/or by varying the thread profile, are obtained slightly better results with respect to the case with a 0.5 mm height triangular thread.

Optimal positioning of the humeral component in the reverse shoulder prosthesis.

INTRODUCTION: Total reverse shoulder arthroplasty is becoming more and more the standard therapeutic practice for glenohumeral arthropathy with massive lesions of the rotator cuff. The biomechanical principle of this prosthesis is represented by the reversion of the normal anatomy of the shoulder joint. This non-anatomical prosthesis leads to a medialization of the rotation centre of the glenohumeral joint and also to a distalization of the humeral head. All that causes a deltoid tension increasing so allowing a larger abduction of the arm. Main complications of the reverse shoulder prosthesis are due to the joint instability, the scapular notching and the wear of the polyethylene insert. PURPOSE: The main goal of the present work is to study the effect of the positioning of the humeral component on the intrinsic stability of the reverse shoulder prosthesis. In particular, through finite element method simulations, the variation of the stability ratio of the shoulder joint has been calculated for both vertical and horizontal dislocating loads depending on the humeral stem version angle. Moreover, in order to estimate the wear of the polyethylene cup, some analyses have been developed to calculate the pressures on the polyethylene insert. RESULTS: The obtained results demonstrate the dislocation of a shoulder prosthesis and the wear of the polyethylene insert can be prevented or limited by conveniently varying the version angle of the humeral component.

Influence of sleep state on CO2 responsiveness. A study of the unloaded respiratory pump in humans.

We measured the ventilatory recruitment threshold for CO2 (RT) during wakefulness, nonrapid eye movement sleep (NREM), and rapid eye movement sleep (REM) in eight patients with respiratory failure. Because the lungs were mechanically ventilated during the RT measurements, we were able to define the effects of arousal state on the chemoresponsiveness of the unloaded respiratory system. Ventilator settings were held constant in each patient, assuring that mechanoreceptor input to the respiratory controller remained the same during all measurements. RT increased from 38 +/- 6 mm Hg during relaxed wakefulness to 42 +/- 8 mm Hg during NREM sleep (p less than or equal to 0.01), consistent with a blunting of chemoresponsiveness during sleep. In five subjects we were able to measure RT during REM sleep also. In four of them, REM RT exceeded the wakefulness measurement by at least 3 mm Hg. The remaining patient showed no demonstrable changes in RT during either sleep state. We conclude that the loss of a wakefulness stimulus contributes to sleep-induced hypercarbia in humans.

Plastic bronchitis: an old disease revisited.

Expectoration of bronchial casts (plastic bronchitis) is an uncommon but ancient problem. Herein we describe a 40-year-old man, with no prior lung disease, who had dyspnea, cough, and expectoration of long branching bronchial casts. No specific cause was delineated, although special stains for eosinophilic granule major basic protein demonstrated occasional foci of eosinophils and small amounts of extracellular major basic protein in the bronchial casts. Various diseases, such as allergic bronchopulmonary aspergillosis, bronchiectasis, and cystic fibrosis, have been associated with the formation of bronchial casts and should be considered in the differential diagnosis. Although most previously reported cases have been associated with some type of pulmonary disease, our patient had no evidence of an underlying pulmonary disorder.

Oxygen-exacerbated bleomycin pulmonary toxicity.

Bleomycin is an antineoplastic agent with potential for producing pulmonary toxicity, attributed in part to its free radical-promoting ability. Clinical and research experiences have suggested that the risk of bleomycin-induced pulmonary injury is increased with the administration of oxygen. We report a case in which the intraoperative administration of oxygen in the setting of previous bleomycin therapy contributed to postoperative ventilatory failure. Our patient recovered with corticosteroid therapy. Physician awareness of a potential interaction between oxygen and bleomycin may help reduce the morbidity and mortality related to bleomycin therapy.