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.

Three-dimensional morphological analysis of the proximal femoral canal, using computer-aided design system, in Japanese patients with osteoarthrosis of the hip.

An accurate three-dimensional morphological analysis of the femur is required to produce well fitting uncemented femoral implants. A computer-aided design system made it possible to produce three-dimensional femoral models and to accurately measure certain parameters with planes standardized for all subjects. The study subjects were Japanese; there were 89 patients (113 hips) with osteoarthrosis (OA) and 18 volunteers (36 hips) free of hip joint complaints and with no abnormal radiological findings (normal; N). The femoral canal was classified into three types, A-I, A-II, and B-II, based on the shape in the frontal and sagittal planes. Either triangular (type T) or circular (type C) shapes were identified at the proximal cross section. Type A-II, which is considered the standard type, accounted for 89% of the N hips, and 42% of the OA hips. Type A-I, with a posterior canal plane strongly inclined toward the anterior, accounted for 26% of the OA hips and 6% of the N hips; 96% of type A-I hips were triangular. Type B-II, which had a steep medial canal plane, accounted for 29% of the OA hips and 6% of the N hips; 63% of type B-II hips were circular.

A new technique for morphologic measurement of the femur. Its application for Japanese patients with osteoarthrosis of the hip.

The cementless femoral prostheses developed in Western countries have commonly been used for Japanese patients, but it has been noted that it is difficult to achieve a good fit between the cementless femoral prostheses and some femora. In Japan, there are many patients with secondary osteoarthrosis (OA) of the hip, but Western designed femoral prostheses seem to be mainly for use with primary OA of the hip. To design femoral prostheses better suited to Japanese patients, a new method to study the morphometry of the femur is required--one which can determine the particular features of the femur in Japanese patients. In this study, a new morphologic measurement technique of the femur is proposed and applied to a number of Japanese OA patients in order to demonstrate its efficacy. In this technique, a three-dimensional solid model based on the outer and inner borders of the femoral cortex is constructed from 3-D CT images and computer-aided design (CAD) software. The bone axis is defined as the line of best fit to the centers of gravity of the femur cross sections in each CT plane by using the least square method. A new femur coordinate system is considered based on this bone axis. The corrected outer borders of the cortex are reconstructed in sections perpendicular to the bone axis. The angle between the principal axis of inertia of the sections and a plane defined by the femur coordinate system is selected as providing a good measurement of the torsion value to characterize the femur morphology. The angles of principal axis were measured in 110 OA and 36 normal hips, and then compared with each other. A significant difference between the OA and normal group was observed especially in the proximal region above the section 6 mm below the level of the lesser trochanter. It is suggested that the anteversion of the femoral neck influences the torsion of the parts below the lesser trochanter. From the results, it is demonstrated that the proposed measurement technique is a reliable and efficient means of determining femur morphology.