Jiro Tamura

In vivo three-dimensional knee kinematics using a biplanar image-matching technique.

A biplanar image-matching technique was developed and applied to a study of normal knee kinematics in vivo under weightbearing conditions. Three-dimensional knee models of six volunteers were constructed using computed tomography. Projection images of the models were fitted onto anteroposterior and lateral radiographs of the knees at hyperextension and every 15° from 0° to 120° flexion. Knee motion was reconstructed on the computer. The femur showed a medial pivoting motion relative to the tibia during knee flexion, and the average range of external rotation associated with flexion was 29.1°. The center of the medial femoral condyle translated 3.8 mm anteriorly, whereas the center of the lateral femoral condyle translated 17.8 mm posteriorly. This rotational motion, with a medially offset center, could be interpreted as a screw home motion of the knee around the tibial knee axis and a posterior femoral rollback in the sagittal plane. However, the motion of the contact point differed from that of the center of the femoral condyle when the knee flexion angle was less than 30°. Within this range, medial and lateral contact points translated posteriorly, and a posterior femoral rollback occurred. This biplanar image-matching technique is useful for investigating knee kinematics in vivo.

Bioactive titanium: effect of sodium removal on the bone-bonding ability of bioactive titanium prepared by alkali and heat treatment.

As reported previously, bioactive titanium is prepared by simple alkali and heat treatment, and can bond to living bone directly. The purpose of this study was to accelerate the bioactivity of bioactive titanium in vivo. In in vitro study, sodium removal by hot water immersion enhanced the apatite-forming ability of bioactive titanium in simulated body fluid dramatically. The specific anatase structure of titania gel was effective for apatite formation in vitro. In the current study, we investigated the in vivo effect of sodium removal on the bone-bonding strength of bioactive titanium. Sodium-free bioactive titanium plates were prepared by immersion in an aqueous solution of 5 M NaOH at 60 degrees C for 24 h, followed by immersion in distilled water at 40 degrees C for 48 h before heating them at 600 degrees C for 1 h. Three kinds of titanium plates were inserted into rabbit tibiae, including untreated cp-Ti, conventional alkali- and heat-treated Ti, and sodium-free alkali- and heat-treated Ti. In vivo bioactive performance was examined mechanically and histologically after 4, 8, 16, and 24 weeks. Sodium removal enhanced the bone-bonding strength of bioactive titanium at 4 and 8 weeks postoperatively; however, its bone-bonding strength was inferior to that of conventional alkali- and heat-treated titanium at 16 and 24 weeks. Histological examinations after the detaching test revealed breakage of the treated layer in the sodium-free alkali- and heat-treated titanium group. In conclusion, sodium removal accelerated the in vivo bioactivity of bioactive titanium and achieved faster bone-bonding because of its anatase surface structure, but the loss of the surfaces graded structure due to the complete removal of sodium decreased the adhesive strength of the treated layer to the titanium substrate. Further investigations are required to determine the optimum conditions for preparation of bioactive titanium.

Mechanical and biological properties of two types of bioactive bone cements containing MgO-CaO-SiO2-P2O5-CaF2 glass and glass-ceramic powder.

In this study two types of bioactive bone cement containing either MgO-CaO-SiO2-P2O5-CaF2 glass (type A) or glass-ceramic powder (type B) were made to evaluate the effect of the crystalline phases on their mechanical and biological properties. Type A bone cement was produced from glass powder and bisphenol-a-glycidyl methacrylate (BIS-GMA) resin, and type B from glass-ceramic powder containing apatite and wollastonite crystals and BIS-GMA resin. Glass or glass-ceramic powder (30, 50, 70, and 80 by wt %) was added to the cement. The compressive strength of type A (153-180 MPa) and B (167-194 MPa) cement were more than twice that of conventional polymethylmethacrylate (PMMA) cement (68 MPa). Histological examination of rat tibiae showed that all the bioactive cements formed direct contact with the bone. A reactive layer was seen at the bone-cement interface. In specimens with type A cement the reactive layer consisted of two layers, a radiopaque outer layer (Ca-P-rich layer) and a relatively radiolucent inner layer (low-calcium-level layer). With type B cement, although the Ca-P-rich layer was seen, the radiolucent inner layer was absent. Up to 26 weeks there was progressive bone formation around each cement (70 wt %) and no evidence of biodegradation. The mechanical and biological properties of the cements were compared with those of a previously reported bone cement containing MgO-free CaO-SiO2-P2O5-CaF2 glass powder (designated type C).

Histological and mechanical investigation of the bone-bonding ability of anodically oxidized titanium in rabbits.

The purpose of this study was to histologically and mechanically investigate the in vivo bone-bonding ability of anodically oxidized titanium (AO Ti) with an anatase crystal layer on its surface. AO Ti plates, anodically oxidized at 155 V in 1 M H2SO4, were implanted into the proximal metaphyses of mature rabbit tibiae for 4, 8, 16, and 24 weeks and investigated by light microscopy, scanning electron microscopy and detaching test. High bone-bonding ability, comparable to our previous study data of the bioactive titanium produced by sodium-free alkali and heat treatment, was observed at the early stages of implantation. However, no substantial increase was demonstrated. AO Ti plates bonded to bone directly, with no intervening soft tissue layer, and no breakage of the AO Ti layer was observed. The AO Ti layer was porous through to the titanium substrate, while the porosity was low. Apatite-like deposition into the pores of the AO layer was observed only in the superficial zone. The lack of improvement of bone-bonding ability in the later stages of implantation may be attributed to the low porosity and to the superficial ingrowths of apatite-like deposits into the pores of the AO Ti layer.

Development of bioactive bone cement and its clinical applications

This paper is a summary of already published papers on the bioactive bone cement (BA cement) which consists of CaO-SiO2-P2O5-MgO-CaF2 (AW glass-ceramic) powder and bisphenol-a-glycidyl methacrylate (Bis-GMA) resin. Two types of BA cement, dough and injection type, were prepared by changing their chemical compositions slightly. They harden in a few minutes exhibiting much lower curing temperature than PMMA cement. They have significantly higher compressive, bending, and tensile strengths than PMMA cement and have a character of bonding directly with bone in 4-8 weeks in vivo. Intercalary prosthetic replacement of the femur and total prosthetic replacement of the hip were performed in dogs using either PMMA cement or BA cement. Mechanical tests demonstrated that fixation strengths of these prostheses with BA cement increased with time and were significantly greater than those with PMMA cement tested at any time. Results of histological examinations showed direct bonding between BA cement and bone, and that the bone trabeculae around BA cement mantle grew with time, while with PMMA cement an intervening soft tissue layer was always observed at the cement-bone interface. BA cement was used in a few aged patients to install a hip prosthesis either in cases of revision or femoral neck fracture. The longest follow-up period of the patient is 4 yrs. The patients have been doing well with no adverse effect of the cement to date.

Mechanical and biological properties of bioactive bone cement containing silica glass powder

Silica glass powder (SG-P) made by a fusing-quenching method was added as a second filler to a bioactive bone cement consisting of MgO-CaO-SiO2-P2O5-CaF2 apatite and wollastonite containing glass-ceramic powder (AW-P) and bisphenol-a-glycidyl methacrylate (Bis-GMA)-based resin, to achieve a higher mechanical strength and better handling properties in use. Five types of cement were used, containing different weight ratios of AW-P/SG-P (Group 1 = 100/0; Group 2 = 75/25; Group 3 = 50/50; Group 4 = 25/75; and Group 5 = 0/100) as filler, to evaluate the effect of SG-P content on the biological, mechanical, and handling properties. The total proportion of filler added to the cements was 85% w/w. The compressive, bending, and tensile strengths and fracture toughness of the cements increased with SG-P content. The viscosity of cements also increased with SG-P content, and every cement could be handled manually. The cements were evaluated in vivo by packing the intramedullary canals of rat tibiae. An affinity index was calculated for each cement; this was the length of bone directly apposed to cement expressed as a percentage of the total length of the cement surface. Histological examination of implanted tibiae for up to 26 weeks showed that the affinity indices decreased with SG-P content and that those of all the cement groups increased with time. At 26 weeks, Groups 1 and 2 had almost identical affnity indices (79% and 75%; no significant difference) but those of the other groups remained at <50%. Group 2 had better mechanical and handling properties than Group 1, and an SG-P content in the filler of no more than 25% w/w did not interfere strongly with the bioactivity of the cement.

Effect of alumina femoral heads on polyethylene wear in cemented total hip arthroplasty

We examined the behaviour of alumina ceramic heads in 156 cemented total hip arthroplasties, at a minimum follow-up of eight years. They were divided into three groups according to the size of the femoral head; 22, 26, and 28 mm. We measured polyethylene wear radiologically using a computer-aided technique. The linear wear rate of polyethylene sockets for the 28 mm heads was high (0.156 mm/year), whereas those for the 22 and 26 mm heads were relatively low (0.090 and 0.098 mm/year, respectively). Moreover, the surface roughness data of retrieved femoral heads clearly showed maintenance of an excellent surface finish of the current alumina. We conclude that the alumina ceramic femoral heads currently used are associated with a reduced rate of polyethylene wear.

The modified Spitzy shelf operation for patients with dysplasia of the hip: A 24-YEAR FOLLOW-UP STUDY

We evaluated the long-term results of a modified Spitzy shelf operation for secondary osteoarthritis in 119 hips with a mean follow-up of 23.8 years. The mean age of the patients at the time of surgery was 25 years. Preoperative osteoarthritic change, the age at operation and shelf height were important factors in determining the outcome. Of the 61 hips in the pre-stage (three) and the initial stage (58) of osteoarthritis, 53 (87%) had good results, compared with only 30 (51%) of 58 hips with advanced osteoarthritis. Of the latter, 72% of those aged less than 25 years had good results compared with only 40% of patients aged over 25 years. The shelf height in the group with good results was significantly lower than in those with poor results. This operation is a safe procedure and indicated for acetabular dysplasia or subluxation of the hip with early osteoarthritic change in patients aged less than 25 years.

Bone bonding ability of bioactive bone cements.

The bone bonding ability of three types of bioactive bone cement A, B, and C consisting of glass or glass ceramic powder and bisphenol-alpha-glycidyl methacrylate resin was evaluated. Type A contained MgO-CaO-SiO2-P2O5-CaF2 glass powder; Type B, MgO-CaO-SiO2-P2O5-CaF2 glass ceramic powder; and Type C, MgO free CaO-SiO2-P2O5-CaF2 glass powder. Rectangular plates (2 x 10 x 15 mm) of Types A, B, C, and polymethylmethacrylate cements were implanted into the tibial metaphyses of male rabbits and the failure load measured by mechanical failure testing (detaching test) 10 and 25 weeks after implantation. The failure loads of Types A, B, C, and polymethylmethacrylate cements were respectively, 29.52, 41.48, 28.22, and 0.29 N at 10 weeks and 33.42, 41.27, 33.64, and 0.20 N at 25 weeks. Examination of the bone cement interface revealed that all the bioactive bone cements achieved direct bone contact with the bone. These results showed that all three types of bioactive bone cement have the ability to bond to bone, and the cement containing glass ceramic powder revealed higher bonding strength than did those containing glass powder.

Bioactive bone cement: Effects of phosporic ester monomer on mechanical properties and osteoconductivity

A new bioactive bone cement, designated GBC, has been developed. It consists of polymethyl methacrylate (PMMA) as an organic matrix and bioactive glass beads as an inorganic filler. The bioactive beads, consisting of MgO--CaO--SiO(2)--P(2)O(5)--CaF(2) glass, have been newly designed, and a novel PMMA powder was selected. The purpose of the present study was to evaluate the effects on mechanical properties and osteoconductivity of adding a phosphoric ester (PE) monomer to the cement as an adhesion-promoting agent. Four kinds of cements were prepared: GBC, GBC with PE (designated GBC/PE), a cement consisting of the same PMMA used in GBC with apatite- and wollastonite-containing glass-ceramic (AW-GC) powder (designated AWC), and AWC with PE (designated AWC/PE). Each filler was added to the cement at 70 wt %. Adding PE to either GBC or AWC resulted in increases in the bending strength and decreases in the Youngs modulus compared with the unmodified cements. Cements were packed into the intramedullar canals of rat tibiae to evaluate osteoconductivity as determined by an affinity index. Rats were sacrificed at 4 and 8 weeks after operation. The affinity index (length of bone in direct contact with the cement expressed as a percentage of the total length of the cement surface) was calculated for each cement. Adding PE to either GBC or AWC resulted in significant increases in the affinity index compared with the unmodified cements. The affinity index for GBC was significantly higher than that of AWC, and that for GBC/PE was also significantly higher than that of AWC/PE. The affinity indices for each cement increased significantly with time up to 8 weeks. Our study revealed that the higher osteoconductivity of GBC/PE was due to the large alkyl group in the PE monomer, to the hydrophilicity of the phosphoric acid in the PE monomer, and to the higher bioactivity of the bioactive glass beads at the cement surface. GBC/PE shows promise as an alternative bone cement with improved properties compared with conventional PMMA bone cement.