Biomechanical behaviour of a French femoral component with thin cement mantle: The 'French paradox' may not be a paradox after all.

OBJECTIVE: Cement thickness of at least 2 mm is generally associated with more favorable results for the femoral component in cemented hip arthroplasty. However, French-designed stems have shown favorable outcomes even with thin cement mantle. The biomechanical behaviors of a French stem, Charnley-Marcel-Kerboull (CMK) and cement were researched in this study. METHODS: Six polished CMK stems were implanted into a composite femur, and one million times dynamic loading tests were performed. Stem subsidence and the compressive force at the bone-cement interface were measured. Tantalum ball (ball) migration in the cement was analyzed by micro CT. RESULTS: The cement thickness of 95 % of the proximal and middle region was less than 2.5 mm. A small amount of stem subsidence was observed even with collar contact. The greatest compressive force was observed at the proximal medial region and significant positive correlation was observed between stem subsidence and compressive force. 9 of 11 balls in the medial region moved to the horizontal direction more than that of the perpendicular direction. The amount of ball movement distance in the perpendicular direction was 59 to 83% of the stem subsidence, which was thought to be slip in the cement of the stem. No cement defect and no cement breakage were seen. CONCLUSION: Thin cement in CMK stems produced effective hoop stress without excessive stem and cement subsidence. Polished CMK stem may work like force-closed fixation in short-term experiment.Cite this article: Y. Numata, A. Kaneuji, L. Kerboull, E. Takahashi, T. Ichiseki, K. Fukui, J. Tsujioka, N. Kawahara. Biomechanical behaviour of a French femoral component with thin cement mantle: The 'French paradox' may not be a paradox after all. Bone Joint Res 2018;7:485-493. DOI: 10.1302/2046-3758.77.BJR-2017-0288.R2.

The influence of cement thickness on stem subsidence and cement creep in a collarless polished tapered stem: When are thick cement mantles detrimental?

OBJECTIVES: Favourable results for collarless polished tapered stems have been reported, and cement creep due to taper slip may be a contributing factor. However, the ideal cement thickness around polished stems remains unknown. We investigated the influence of cement thickness on stem subsidence and cement creep. METHODS: We cemented six collarless polished tapered (CPT) stems (two stems each of small, medium and large sizes) into composite femurs that had been reamed with a large CPT rasp to achieve various thicknesses of the cement mantle. Two or three tantalum balls were implanted in the proximal cement in each femur. A cyclic loading test was then performed for each stem. The migration of the balls was measured three-dimensionally, using a micro-computed tomography (CT) scanner, before and after loading. A digital displacement gauge was positioned at the stem shoulder, and stem subsidence was measured continuously by the gauge. Final stem subsidence was measured at the balls at the end of each stem. RESULTS: A strong positive correlation was observed between mean cement thickness and stem subsidence in the CT slices on the balls. In the small stems, the balls moved downward to almost the same extent as the stem. There was a significant negative correlation between cement thickness and the horizontal:downward ratio of ball movement. CONCLUSION: Collarless polished tapered stems with thicker cement mantles resulted in greater subsidence of both stem and cement. This suggests that excessive thickness of the cement mantle may interfere with effective radial cement creep.Cite this article: E. Takahashi, A. Kaneuji, R. Tsuda, Y. Numata, T. Ichiseki, K. Fukui, N. Kawahara. The influence of cement thickness on stem subsidence and cement creep in a collarless polished tapered stem: When are thick cement mantles detrimental? Bone Joint Res 2017;6:-357. DOI: 10.1302/2046-3758.65.BJR-2017-0028.R1.

Oxidative stress by glutathione depletion induces osteonecrosis in rats.

OBJECTIVE: We recently implicated in vivo oxidative stress in the development of osteonecrosis in a steroid-induced osteonecrosis model in the domestic rabbit. In the present experiment we devised a new non-traumatic model using the rat to investigate the relationship between oxidative stress and the development of osteonecrosis. METHODS: Seven 24-week-old male Wistar rats were subcutaneously injected with the pro-oxidant buthionine sulphoximine (BSO) 500 mg/kg for 14 consecutive days (group B) and eight rats received injections of vehicle (physiological saline; group N). The rats in both groups were killed after 14 days, and their bilateral femurs were examined histopathologically. Blood levels of reduced glutathione (GSH), total cholesterol (T-cho) and triglycerides (TG) were also determined. RESULTS: GSH was significantly decreased in group B compared with group N (P < 0.01). No significant differences were found in T-cho or TG. Osteonecrosis was not detected in any animal in group N in contrast to five of seven animals in group B (P < 0.05). CONCLUSION: BSO is an inducer of oxidative stress, in particular interfering with the synthesis of GSH in vivo. In the present study, GSH levels were markedly reduced by BSO, whereas neither T-cho nor TG was significantly changed. The high rate of osteonecrosis noted in group B suggests that oxidative stress alone may be sufficient to promote the development of osteonecrosis at certain sites.

DNA oxidation injury in bone early after steroid administration is involved in the pathogenesis of steroid-induced osteonecrosis.

OBJECTIVE: Using a rabbit model, we investigated the DNA oxidation injury occurring in bone following steroid administration and focused on the relation between DNA oxidation injury and osteonecrosis. METHODS: Japanese white rabbits weighing about 3.5 kg were injected with a single intramuscular dose of methylprednisolone 4 mg/kg and divided into groups consisting of 10 rabbits each, which were killed after 3, 5 and 14 days (groups A, B and C respectively). As a control, five untreated rabbits (group N) were also studied. An immunohistochemical study of the diaphysis of the proximal femur was conducted using the monoclonal antibody N45.1, which is a highly specific antibody against 8-hydroxy-2'-deoxyguanosine, an index of DNA oxidation injury. Also, using NIH Image freeware, the positive area (8-OHdG %PA) of each group was calculated and the four groups were compared. RESULTS: Osteonecrosis was detected only in group C (70%). N45.1 positivity was noted in bone marrow haematopoietic cells and was particularly marked in groups B and C. 8-OHdG %PA was 1.6 +/- 0.2% in group N, 2.2 +/- 0.4% in group A, 4.8 +/- 0.4% in group B and 5.1 +/- 0.5% in group C, with significantly greater oxidation injury found in groups B and C (P < 0.001). CONCLUSION: Oxidative injury was demonstrated soon after the administration of methylprednisolone in a rabbit model prior to the development of osteonecrosis. This finding may suggest new strategies to prevent steroid-induced osteonecrosis, such as the optimally timed (early) administration of antioxidant agents.

[Anesthesia for tricuspid valve replacement after heart transplantation].

A 41 year old male patient had received heart transplantation in U.S. in 1993. When myocardial biopsy was performed in 1998, tendinous cords of the tricuspid valve were injured. Tricuspid regurgitation developed along with right heart insufficiency, and the patient was scheduled for tricuspid replacement. For induction of anesthesia, midazolam and fentanyl were used. After induction, both blood pressure and pulse rate were stable. During extracorporeal circulation, perfusion pressure was controlled at 70-80 mmHg, and the duration of cardio-pulmonary perfusion was about 90 minutes. For withdrawal from extracorporeal circulation, dopamine and dobutamine were used. The course was steady and normal after the withdrawal. In tricuspid valve replacement after heart transplantation, stabilized anesthetic course could be maintained using midazolam and fentanyl.