Katsutoshi Hara

Manipulation of the anabolic and catabolic responses with BMP-2 and zoledronic acid in a rat femoral fracture model

Bone repair involves a complex set of regulated signaling pathways that control the formation of new bone matrix and the resorption of damaged bone matrix at the fracture site. It has been reported that the optimal time point for single-dose zoledronic acid (ZA) administration systemically increased the strength of bone morphogenetic protein (BMP)-7-mediated callus. However, its repair mechanism during bone fracture healing remains unknown. We aimed to investigate the synergic effect of recombinant human (rh) BMP-2 and ZA in a rat femoral fracture model. Fifty-eight rats were divided into 4 groups. Group I (n=14) animals were implanted with a carrier alone. Group II (n=15) animals were implanted with a carrier containing 1-μg rhBMP-2. Group III (n=14) animals were implanted with a carrier and a subcutaneous systemic ZA injection 2 weeks after surgery. Group IV (n=15) animals were implanted with a carrier containing 1-μg rhBMP-2 and ZA subcutaneous injection 2 weeks after surgery. The rats were euthanized after 6 weeks and their fractured femurs were explanted and assessed by manual palpation, radiographs, and high-resolution micro-computerized tomography (micro-CT) and were subjected to biomechanical and histological analysis. The fusion rates in Group IV (93.3%) were considerably higher than those in Groups I (28.6%), II (53.3%), and III (57.1%). Additionally, the radiographic scores of Group IV were higher than those in Groups I, II, and III. In micro-CT analysis, the tissue volume (TV) of the callus was higher in Group IV than in Groups I and II (p<0.05). New bone volume (BV) and trabecular spacing (Tb.Sp) also showed essentially the same trend as that of TV. The ratio of BV to TV (BV/TV), the trabecular number (Tb.N), and the trabecular thickness (Tb.Th) was higher in Groups III and IV than in Groups I and II (p<0.05). In biomechanical analysis, the ultimate loads at failure and stiffness in Groups III and IV were on average higher than those in Groups I and II (p<0.05), while the energy absorption of Group IV was higher than those of Groups I and II (p<0.05). The synergic effect of rhBMP-2 and ZA given systemically as a single dose at the optimal time was efficacious for fracture repair and significantly enhanced bone fusion. Our results suggest that this combination facilitates bone healing and has potential clinical application.

Analysis of wear and oxidation on retrieved bipolar polyethylene liner

BackgroundFor bipolar prostheses, most of the previous studies attributed the occurrence of osteolysis to wear debris generated from the bearing surface. We looked closely into the wear debris and reported on our findings with respect to the oxidation index and the rate of wear in ultra-high molecular weight polyethylene (UHMWPE) inserts retrieved from bipolar prostheses after various spans of time in vivo.MethodThe inserts were retrieved from the heads of three types of bipolar prosthesis (UH1, UPF1, UPF2). We retrieved 24 bipolar prostheses from 23 patients whose mean implantation period was 10.0 years (2.7–15.4 years).ResultsAll the retrieved polyethylene had a burnished bearing surface. In all, 92% (22/24) of these inserts had indentation and roughness at the rim and flange, suggesting neck-cup impingement; periprosthetic fracture occurred in the other two inserts. The mean linear wear rate was 0.035 mm per year. The average maximum oxidation index for the inserts with osteolysis was 3.34, and it was was 3.49 for the inserts without osteolysis. We, therefore, could not detect any significant difference between the aforesaid groups of inserts.ConclusionsThe results strongly suggest that most of the polyethylene wear debris was not generated from the bearing surface. Moreover, the wear debris generated from neck-cup impingement may well be the cause of an inflammatory reaction, which in turn has a strong potential to become the primary cause of osteolysis.

Influence of the volume of bone defect, bone grafting methods, and hook fixation on stress on the Kerboull-type plate and screw in total hip arthroplasty: three-dimensional finite element analysis.

For total hip arthroplasty or revision surgery using acetabular reinforcement cross-plates, choosing between bulk and morselized bone grafts for filling acetabular defects is challenging. We used finite element model (FEM) analysis to clarify various stresses on the cross-plate based on bone defect size, bone graft type, and presence or absence of hook fixation to the bone. We constructed 12-pattern FEMs and calculated the maximum stress generated on the Kerboull-type (KT) plate and screw. Bone defects were classified into four patterns according to the volume. Regarding the bone graft type, bulk bone grafts were considered as cortical bone, and morselized bone grafts were considered to consist of cancellous bone. Models were compared based on whether hook fixation was used and whether a gap was present behind the plate. The upper surface of the host bone was fixed, and a 1,000-N load was imposed on the horizontal axis at 71°. Larger bone defects increased the stress on the KT plate and screws. This stress increased when no bone was grafted; it was lower when bulk cortical bone grafts were used for filling than when morselized cancellous bone grafts were used. For cortical bone grafts, the increased stress on the KT plate and screws was lowered with hook removal. Attaching the hook to the bone and filling the gap behind the KT plate with an adequate bone graft reduced the stress on the KT plate and screws, particularly for large bone defects filled by bulk bone grafting.

Contact between the acetabulum and dome of a Kerboull-type plate influences the stress on the plate and screw

Abstract We used a three-dimensional finite element method to investigate the conditions behind the Kerboull-type (KT) dome. The KT plate dome was divided into five areas, and 14 models were created to examine different conditions of dome contact with the acetabulum. The maximum stress on the KT plate and screws was estimated for each model. Furthermore, to investigate the impact of the contact area with the acetabulum on the KT plate, a multiple regression analysis was conducted using the analysis results. The dome–acetabulum contact area affected the maximum equivalent stress on the KT plate; good contact with two specific areas of the vertical and horizontal beams (Areas 3 and 5) reduced the maximum equivalent stress. The maximum equivalent stress on the hook increased when the hardness of the bone representing the acetabulum varied. Thus, we confirmed the technical importance of providing a plate with a broad area of appropriate support from the bone and cement in the posterior portion of the dome and also proved the importance of supporting the area of the plate in the direction of the load at the center of the cross-plate and near the hook.

Fixation strength at the interface between Kerboull-type plate and bone cement

Purpose. To evaluate the fixation strength at the interface between the Kerboull-type plate and bone cement in 6 experimental conditions. Methods. Experimental materials comprised a simulated acetabular block, a simulated Kerboull-type plate, a pressuriser cover, a pressuriser arm, and bone cement. The simulated Kerboull-type plate was placed on the simulated acetabular block, with the pressuriser cover. Bone cement was added and the pressuriser arm was inserted. After 6 days of curing, pulling tests were performed to measure the fixation strength at the interface between the plate and the bone cement. Six experimental conditions were evaluated. In condition 1, a 1-mm plate was used with no gap between the plate and the acetabular block. In condition 2, a 2.5-mm plate was used with no gap. In condition 3, a 2.5-mm plate was used with a 2-mm gap. In condition 4, the plate was not used. In condition 5, condition 2 was tested with the model rotated 45°. In condition 6, condition 3 was tested with the model rotated 45°. Results. The maximum fixation strengths in conditions 1, 2, 3, 5, and 6 were 44.4 N, 59.1 N, 122.5 N, 86.9 N, and 185.2 N, respectively. The most important factor affecting the maximum fixation strength was bone cement at the interface between the plate and the acetabular block, followed by 45° rotation during testing, and then thickness of the plate. Conclusion. To enhance fixation of the Kerboull-type plate with cemented acetabular cup, penetration of cement into the outer side of the Kerboull-type plate should be minimised.