Shigeo Niwa

Mechanical strength of calcium phosphate cement in vivo and in vitro.

Two different kinds of calcium phosphate cement were developed for implant fixation: cement A comprised of alpha-tricalcium phosphate (alpha-TCP) 95% and dicalcium phosphate dihydrate (DCPD) 5%, and cement B comprised of alpha-tricalcium phosphate 90% and dicalcium phosphate dihydrate 10%. The compression strength and pullout force of the new materials were tested both in vitro and in vivo. Microscopic observations were performed on the interface between bone and cement. Cement A showed a greater mechanical strength than cement B. The results suggest the clinical possibility of this calcium phosphate cement, which could be used as a material for enhancing implant fixation.

Prevention of postoperative venous thromboembolism in Japanese patients undergoing total hip or knee arthroplasty: two randomized, double-blind, placebo-controlled studies with three dosage regimens of enoxaparin

BackgroundEnoxaparin is a low-molecular-weight heparin indicated in Europe and North America for the prevention of venous thromboembolism (VTE) in patients undergoing major orthopedic surgery. Registration trials of enoxaparin have been conducted primarily in Caucasian populations, and the efficacy and safety of enoxaparin in Japanese patients have not been demonstrated. We evaluated three dosage regimens of postoperative enoxaparin in Japanese patients undergoing elective total hip or knee arthroplasty.MethodsTwo multicenter, randomized, double-blind studies enrolled 436 and 396 Japanese adults undergoing total hip or knee arthroplasty, respectively. The dosage regimens of enoxaparin were 20 mg once daily (qd), 40 mg qd, 20 mg twice daily (bid), or placebo for 14 consecutive days. The primary efficacy endpoint was the incidence of VTE in the modified intention-to-treat (mITT) population up to 15 days after surgery. VTE was defined as a composite of deep vein thrombosis (determined by venography) and symptomatic pulmonary embolism (confirmed by appropriate objective methods). Patients were also followed up at 90 days for VTE events. The primary safety outcome was the incidence of any bleeding during treatment and the follow-up period.ResultsIn the mITT populations, the incidence of VTE was 41.9% and 60.8% in the placebo groups after hip or knee arthroplasty, respectively, 25.9% and 44.9% in the enoxaparin 20 mg qd groups, 33.8% and 35.1% in the enoxaparin 40 mg qd groups, and 20.0% and 29.8% in the enoxaparin 20 mg bid groups. Only enoxaparin 20 mg bid significantly lowered the risk of VTE relative to placebo (by 52.2% and 51.0% after hip and knee arthroplasty, respectively). At the 90-day follow-up, no further cases of VTE were reported. In both the hip and knee studies, the four treatment groups did not differ significantly regarding the incidence of patients with any bleeding.ConclusionsOur findings support the use of enoxaparin (20 mg bid daily, commencing 24–36 h postoperatively) in Japanese patients undergoing total hip or knee arthroplasty.

Bone formation by cells from femurs cultured among three-dimensionally arranged hydroxyapatite granules

In vitro bone formation by cells derived from adult rabbit femurs was investigated on or in several substrates with small porous hydroxyapatite granules (HAGs). When the bone fragments were cultured in HAG-packed glass tubes, which were inclined (5 degrees -30 degrees ) and rotated 90 degrees per day after one week of culture, thin lamellar tissues were newly formed in narrow spaces among the HAGs. By 11 days of culture, these tissues had been mineralized except for their periphery and had well developed collagen bundles and several monolayer cells. Some cells resided in bone lacuna-like spaces. By contrast, mineralization was negligible in 6-week cultures on two-dimensional glass and polystyrene plates with or without two-dimensionally arranged HAGs on their surfaces and in three-dimensional collagen gels with or without HAGs in spite of active cell proliferation. These results suggest that osteogenesis is accelerated in a specific three-dimensional constitution of extracellular matrix and/or under the effects of mechanical forces for the new tissue and that bioactive HAGs offer favorable three-dimensional spaces for osteogenic tissue formation.

Biomechanics in orthopedics

New aspects of orthopaedic biomechanics - fracture, ligament, spine, hip joint, knee joint, gait, biomaterials modern trends of orthopaedic biomechanics in Japan - fracture, spine, hip joint, knee joint, gait analysis, miscellaneous.

Analysis of the Endosteal Geometry of the Proximal Femur in Japanese Patients with Osteoarthritic Hips: Use in Femoral Stem Design

A study was undertaken to establish a basic design for a straight femoral stem to be used in total hip arthroplasty (THA). This stem would be fitted to the endosteal geometry of femurs in Japanese patients with advanced osteoarthritis of the hip due to congenital displacement of the hip (CDH). Using our three-dimensional computer-aided design (3D-CAD) system, we investigated the geometry of the proximal femur, based on computed tomography (CT) slices obtained from 30 femurs in patients with advanced osteoarthritis and 20 femurs in healthy controls. We found that almost 90% of the femurs in the patients with advanced osteoarthritis had a straight section in the marrow cavity, between 40 and 60 mm below the tip of the lesser trochanter. An adequate basic axis, as a standard for measuring and as a guide for reaming the marrow cavity of the femur, could be obtained by extending the connecting line of the inner center of each slice in this specific straight section. Reaming along our basic axis, simulated by the 3D-CAD system, cut off less cortical bone (79 mm3) than reaming along a conventional axis determined by connecting the center of two cross sections, one at the entry point of the marrow cavity and the other at the maximum depth of reaming (203 mm3). Excessive variations were observed in the cross-sectional geometry of the upper part of the canal of the proximal femur. It was found that, in THA, to obtain a standard straight marrow cavity with no excessive variation and under-cut, the femoral neck should be cut off less than 15 mm above the tip of the lesser trochanter, with a cutting angle of less than 20°. Two radiuses of curvature (R1, 100 mm; R2, 150 mm) were proposed to simplify the curve on the medial flare of the femoral canal between the levels of 15 mm above and 40 mm below the tip of the lesser trochanter. Two taper angles (T1, 2°; T2, 1°) were proposed, to simplify the inclination of the medial femoral canal between 40 and 80 mm below the tip of the lesser trochanter. Correlations were found between patient’s canal flare indices (CFIs) and canal widths 60 mm below the tip of the lesser trochanter in both the frontal (r = −0.6697) and sagittal (r = −0.7961) dimensions. No correlation, however, was revealed between frontal and sagittal CFIs.

Clinical Features and Radiological Findings of Total Knee Arthroplasty by the International Documentation and Evaluation System

Using the evaluation form of the SICOT-IDES (Societe Internationale de Chirurgie Orthopedique et de Traumatologie-International Documentation and Evaluation System), clinical evaluation and radiological evaluation were performed on 50 joints of South East Asia Pacific (SEAP) Total Knee Arthroplasty in 31 patients. The clinical results of the SEAP total knee series could be satisfactorily described in detail, and are easily utilized for further investigation.

South East Asia Pacific (SEAP) Total Knee Arthroplasty

From a radiographic survey of Japanese knee patients, the South East Asia Pacific (SEAP) total knee prosthesis and surgical instruments were designed for the needs of somewhat smaller patients in Japan and other Oriental countries. The SEAP total knee arthroplasty has been performed in 43 cases, on 67 joints, and follow-up study was made by a clinical knee scoring system and radiological and joint biomechanical evaluation. Furthermore, the joint tension meter was developed to measure soft tissue tension for knee replacement surgery.

—Overview— Clinical Gait Analysis in Hip Patients

The relationship between ascending and descending trunk movements and the biphasic pattern of the vertical reaction force was demonstrated by practical accelerometry and reaction force measurement. The vertical reaction force directly represents the kinematic acceleration of vertical body movement. The abnormal trunk movement of hip patients was investigated with a TV motion analysis system. Patients with lateral trunk bending and shifting showed considerable lateral trunk displacement, shortening the lever arm for the dynamic weight due to body mass, gravitation, and vertical acceleration. This bending and shifting may reduce the required abductor force and the hip resultant force. In clinical gait analysis, it is important to correctly interpret gait parameters and abnormal gait patterns in terms of biomechanical considerations, and to establish criteria for gait disorders.

Simple Solid Models for Surgical Planning in Hip Arthroplasties

Our simple solid model, made of foam polystyrol, is helpful in understanding the complex shape of bony geometry (such as that found in hip joints) and is useful for carrying out surgical planning and rehearsal operations.