Hiroyoshi Iwaki

Comparative bone growth behavior in granules of bioceramic materials of various sizes

Various bioceramic materials were implanted into 6-mm-diameter holes made in the femoral condyles of mature Japanese white rabbits using different-sized granules to find an optimal material and granule diameter for use as a bone graft. Bioceramics include a bioinert ceramic (Alumina), surface-bioactive ceramics [hydroxyapatite (HAp) and Bioglass(R)], and resorbable bioactive ceramics [alphatricalcium phosphate (alpha-TCP), beta-TCP, tetracalcium phosphate (TeCP), Te. DCPD, Te. DCPA, and low-crystalline HAp]. Granule sizes were 100-300, 10, and 1-3 microm. Bone growth behavior varied with the kind of bioceramic and the size used. For surface-bioactive ceramics, 45S5 Bioglass(R) led to more rapid bone proliferation than synthetic HAp. In resorbable bioactive ceramics, the order of resorption was: low-crystalline HAp and OCP > TeCP, Te DCPD, Te DCPA > alpha-TCP, beta-TCP. In terms of biocompatibility, alpha-TCP was better than beta-TCP.

Particulate bioglass compared with hydroxyapatite as a bone graft substitute

Bioactive ceramics, notably hydroxyapatite, have been used clinically in various situations in which bone augmentation and restoration are required. Particulate material has been used either alone or in conjunction with freeze dried or autologous bone, with variable clinical success. In this study a bioactive glass, 45S5 Bioglass, has been compared with hydroxyapatite in an animal model to discover whether the 2 major disadvantages of hydroxyapatite may be overcome. These are the difficulty of placing and retaining the particulate in the defect and the length of time needed before full bony restoration is achieved. Bioglass is shown to be easy to manipulate and hemostatic and allows full restoration of bone in 2 weeks, rather than the 12 weeks needed for the particulate hydroxyapatite to produce a comparable response. The Bioglass particulate is used up in the process, and any problems that may be associated with the production of a composite of bone and biomaterial are avoided in the fully restored bone. In any procedure that requires bony augmentation, this rapid response to Bioglass is expected to provide a clinical advantage.

Anteroposterior and rotational movement of femur during knee flexion.

This study was designed to analyze anteroposterior and rotational movement of femoral condyles during knee flexion from 15 degrees to 90 degrees using magnetic resonance imaging. After a pilot study, scans were made in 10 healthy male Japanese volunteers. When centers of the circular profiles of posterior femoral condyles were used as reference points, the medial and lateral femoral condyles displaced posteriorly 1.9 +/- 0.8 mm and 2.3 +/- 0.5 mm, respectively (mean +/- standard error). Duplicate examinations on two separate occasions revealed the accuracy of this procedure was in the range of 1 to 2 mm. These results have confirmed that femoral rollback occurs in the unloaded normal knee during flexion from 15 degrees to 90 degrees, but its magnitude is small (2 mm). The results obtained in this in vivo measurement of anteroposterior movement of the femoral condyles have relevance for total knee replacement design.

The incidence of the patellar clunk syndrome in a recently designed mobile-bearing posteriorly stabilised total knee replacement

The patellar clunk syndrome describes painful catching, grinding or jumping of the patella when the knee moves from a flexed to an extended position after total knee replacement (TKR). The posterior stabilised TKR had been noted to have a higher incidence of this problem. Mobile-bearing posteriorly stabilised TKRs have been introduced to improve patellar tracking and related problems by a mechanism of self-alignment. We evaluated the patellar clunk syndrome in 113 knees in 93 patients with such a TKR at a mean follow-up of 2.3 years (2.0 to 3.2). The syndrome was identified in 15 knees (13.3%). Logistic regression analysis showed that the absolute value of the post-operative angle of patellar tilt was significantly associated with the occurrence of patellar clunk (p = 0.025). Patellar tracking should be carefully checked during surgery.

Polyethylene wear particles in synovial fluid after total knee arthroplasty.

The aims of the current study were to examine polyethylene particles in synovial fluid at an early stage, and to compare a newly introduced medial pivot total knee prosthesis with an established posterior-stabilized total knee prosthesis. Synovial fluid was obtained 1 year after knee arthroplasty from 17 patients with well-functioning prostheses (22 knees, 11 posterior-stabilized prostheses and 11 medial pivot prostheses) under complete sterile conditions. Polyethylene particles were isolated and analyzed by scanning electron microscopy. Particle size (equivalent circle diameter) was 0.78 ± 0.08 μm (mean ± standard error) in posterior-stabilized prostheses and 0.67 ± 0.06 μm in medial pivot prostheses. Particle shape (aspect ratio) was 2.30 ± 0.22 in posterior-stabilized prostheses and 1.90 ± 0.16 in medial pivot prostheses. The total numbers of particles were 1.16 ± 0.57 × 108 in posterior-stabilized prostheses and 9.01 ± 2.95 × 106 in medial pivot prostheses. Particles were smaller and rounder in medial pivot prostheses than in posterior-stabilized prostheses, but the differences were not significant. The difference in the common logarithm of particle number was significant. The medial pivot prosthesis generated less wear particles than the posteriorstabilized prosthesis, and these findings may have an impact on the incidence of osteolysis and aseptic loosening.

Hydroxyapatite granules interposed at bone-cement interface in total hip replacements: histological study of retrieved specimens.

The effect of hydroxyapatite (HA) granules interposed between bone and polymethylmethacrylate (PMMA) bone cement in total hip replacement was histologically evaluated. The technique consisted of smearing 2-5 g of HA granules (straight phi = 100-300 microm) onto the bone surface just before cementing. Four specimens containing well-fixed bone-cement interface were retrieved at 1, 2, 6, and 10 years postoperatively and examined with back-scattered electron microscopy and light microscopy. The majority of HA granules were incorporated into remodeled trabeculae, and highly convoluted bone-cement interface was maintained up to 10 years. The presence of active remodeling in the adjacent bone was observed. There were no significant inflammatory or foreign body reactions against interposed HA granules. In one specimen retrieved from a patient with rheumatoid arthritis, bone formation around HA granules was limited after 1 year. These results have provided histological evidence for the significantly reduced incidence of radiolucent lines in total hip replacement with this cementing technique, reported elsewhere.

TKA Sagittal Alignment with Navigation Systems and Conventional Techniques Vary Only a Few Degrees

Navigation systems have been developed to achieve more reliable prosthetic alignment in TKAs. However, the component alignment in the sagittal plane is reportedly less reliable than in the coronal plane even with navigation systems. We measured and compared sagittal prosthetic alignments for TKAs with the conventional technique and three navigation approaches to establish reference frames, using radiographs of the entire lower extremity while standing. The sagittal alignments simulated on the radiographs with the conventional technique and navigation systems differed by a mean of 2° to 4°. Use of navigation systems resulted in a mean of 1° to 4° hyperextension between the femoral and tibial components and use of the conventional technique resulted in a mean of 1° flexion. Use of different reference points on the distal femoral condyle for the navigation systems resulted in differences of as much as 3° alignment in the sagittal plane. Although optimal prosthetic alignment for TKA in the sagittal plane is unknown, surgeons and technicians using navigation systems should be aware of this difference in the sagittal plane and the risk of hyperextension between the femoral and tibial components, which might be associated with osteolysis and anterior post-cam impingement.

Comparison of Bone Mineral Density Between Porous Tantalum and Cemented Tibial Total Knee Arthroplasty Components

BACKGROUND Porous tantalum was recently introduced as a metallic implant material for total knee arthroplasty. Its porosity, low modulus of elasticity, and high frictional characteristics were expected to provide physiologic load transfer and relative preservation of bone stock. However, to our knowledge, the effect of a Trabecular Metal tibial component on bone mineral density has not been reported. The purpose of the present study was to compare the periprosthetic bone mineral density between patients managed with uncemented Trabecular Metal and cemented tibial components. METHODS Twenty-eight knees receiving a Trabecular Metal tibial component and twenty-eight knees receiving a cemented cobalt-chromium tibial component had dual x-ray absorptiometry scans at two weeks preoperatively and at two weeks and six, twelve, eighteen, and twenty-four months postoperatively, to assess periprosthetic bone mineral density. All of the operations were performed by one surgeon through a medial parapatellar approach. RESULTS None of the differences between the two groups in terms of preoperative bone mineral density in the femoral neck, wrist, lumbar spine, or knee were significant. In both groups, the bone mineral density in the tibia decreased postoperatively. However, the postoperative decrease in bone mineral density in the lateral aspect of the tibia was significantly less in knees with Trabecular Metal components than in knees with cemented tibial components at twenty-four months (mean and standard deviation, -6.7% +/- 22.9% compared with -36.8% +/- 24.2%; p = 0.002). At twenty-four months postoperatively, there was no significant difference between the two groups in terms of the Knee Society score, range of motion of the knee, or bone mineral density in the lumbar spine. No prosthetic migration or periprosthetic fracture was detected in either group. CONCLUSIONS The decrease in bone mineral density of the lateral tibial plateau was less in knees with a Trabecular Metal tibial component following total knee arthroplasty than in knees with a cemented tibial component. Additional research is needed to determine whether long-term clinical benefits are realized with the use of porous tantalum tibial components for total knee arthroplasty.

Effect of simvastatin on steroid-induced osteonecrosis evidenced by the serum lipid level and hepatic cytochrome P4503A in a rabbit model

ObjectiveThis study was designed to investigate the efficacy of lipid-lowering agents in preventing steroid-induced osteonecrosis and the mechanism by which they do so in a rabbit model.MethodsFemale Japanese white rabbits were randomly allocated to receive probucol (group P), pravastatin (group PS), simvastatin (group SS), or saline (group C) for 6 weeks (n = 15 in groups P, PS, and SS; n = 30 in group C). Methylprednisolone (20 mg/kg) was injected at 3 weeks after starting treatment, and the femurs were histologically examined bilaterally 3 weeks after methylprednisolone injection. Midazolam clearance was measured before treatment and before methylprednisolone injection to determine hepatic cytochrome P4503A (CYP3A) levels.ResultsThe incidence of osteonecrosis in the proximal metaphysis of the femurs in groups PS and SS was significantly lower than in group C (P < 0.05 and P < 0.0001, respectively), whereas it did not differ between groups P and C. It was significantly lower in group SS than in group PS (P < 0.05). Plasma concentrations of lipids (low-density lipoprotein, triglyceride, free fatty acid, and total cholesterol) in groups P, PS, and SS were significantly lower than in group C; and hepatic CYP3A levels were significantly higher in group SS than in groups P or PS after treatment (P < 0.005 for both).ConclusionsSimvastatin and pravastatin significantly reduced the incidence of steroid-induced osteonecrosis in rabbits. Simvastatin was more effective in reducing the incidence of the disease, and increased CYP3A activity is a possible mechanism for this effect.

In Vivo Analysis of Polyethylene Wear Particles After Total Knee Arthroplasty: The Influence of Improved Materials and Designs

Polyethylene wear particles induce macrophages to release cytokines, which can lead to osteolysis and aseptic loosening of total joint prostheses1. The generation of polyethylene wear particles is one of the most important factors that affects the midterm and long-term clinical results associated with total knee arthroplasty2,3. The generation of polyethylene wear particles is correlated with the activity level of the patient4, and greater demands are placed on a total knee prosthesis when it is implanted in a younger, more active patient5. Therefore, to achieve better long-term results for patients who have higher activity levels, modifications of materials (i.e., highly cross-linked polyethylene and alumina ceramic) and design (i.e., mobile bearing and medial pivot) have been developed to reduce polyethylene wear after total knee arthroplasty. It takes decades to evaluate the long-term results of newly introduced total knee prostheses. Thus, it is particularly important to examine in vivo polyethylene wear generation in new prostheses before they come into widespread use. It is difficult to determine the in vivo polyethylene wear of total joint prostheses (with the exception of total hips) with use of postoperative radiographs. To measure polyethylene wear in vivo, we developed and employed a method in which we isolated and analyzed polyethylene wear particles in the synovial fluid of knees that had a well-functioning total knee prosthesis6-9. The number, size, and shape of polyethylene wear particles have been reported to be critical factors in the development of osteolysis. Greater volume, submicrometer size, and an elongated shape of polyethylene wear particles all stimulate an increased macrophage response10-12. Our hypothesis was that modification of total knee arthroplasty materials and designs can influence the generation of polyethylene wear particles in vivo. In the present study, …