Biomedical subjects

Yasuo Shikinami

Publications and source records attributed to Yasuo Shikinami.

6 recordsLinked to original sources

PubMed2003

Long-term study of high-strength hydroxyapatite/poly(L-lactide) composite rods for the internal fixation of bone fractures: a 2-4-year follow-up study in rabbits.

Biodegradation of hydroxyapatite (HA)/poly(L-lactide)(PLLA) composite bone implant rods was studied with the use of two types of HA particles as reinforcing fillers: uncalcined HA (u-HA) or calcined HA (c-HA). Composite rods of u-HA/PLLA and c-HA/PLLA containing 30 or 40% (w/w) HA were implanted in the distal femur of 21 rabbits, and specimens were examined by light microscopy, scanning-electron microscopy (SEM), and transmission-electron microscopy (TEM) 2-4 years later. For u-HA/PLLA, trabecular bone bonding directly onto the rod was maintained for up to 2 years. By 3 years, surface collapse had begun, and the implants were shrinking. By 4 years, they had shrunk further, with complete bone encapsulation. The u-HA particles were small and needle shaped in the peripheries, and TEM confirmed their resorption. The cross-sectional area after 4 years decreased by 23.3+/-8.4%. The mean ratio of bony ingrowth to the initial cross-sectional area around the shrunken rods was 6.7+/-1.3 %. The viscosity molecular weight of PLLA reduced from 2 x 10(5) to less than 1 x 10(3). Thus, most of the PLLA had released from the rods. The c-HA/PLLA implants also showed good osteoconductivity, but shrinkage and infiltration of histiocytes were less. No osteolytic or osteoarthritic changes were found.

Absorbable Implants↗

PubMed2003

Comparative biomechanical analysis of a cervical cage made of an unsintered hydroxyapatite particle and poly-L-lactide composite in a cadaver model.

STUDY DESIGN: A new cage made from a forged composite of unsintered hydroxyapatite particles and poly-L-lactide (F-u-HA/PLLA) is compared biomechanically with the Ray threaded fusion cage. OBJECTIVES: To compare the stability imparted to the human cadaveric spine by two different threaded cervical cages and the effect of cyclic loading on construct stability. SUMMARY OF BACKGROUND DATA: Threaded cages have been developed for use in anterior cervical interbody fusions to provide initial stability during the fusion process. However, metallic instrumentation has several limitations. Recently, totally bioresorbable bone fixation devices made of F-u-HA/PLLA have been developed, including a cage for spinal interbody fusion. However, no biomechanical study has compared the F-u-HA/poly-L-lactide (PLLA) cage with metallic cages. METHODS: For this study, 12 fresh ligamentous human cervical spines (C4-C7) were used. After anterior discectomy across C5-C6, stabilization was achieved with the F-u-HA/PLLA cage in six spines and with the Ray threaded fusion cage in the remaining six spines. Biomechanical testing of the spines was performed with six degrees of freedom before and after stabilization, and after cyclic loading of the stabilized spines (5000 cycles of flexion-extension at 0.5 Nm). RESULTS: The specimens stabilized with either the F-u-HA/PLLA cage or the Ray cage were significantly more stable than the discectomy case in all directions except in extension. In extension, both groups were stiffer, although not at a significant level (P > 0.05). After fatigue, the stiffness, as compared with that in the prefatigue case, decreased in both groups, although not at a significant level. The Ray cage group exhibited better stability than the F-u-HA/PLLA cage group in all directions, although a significant difference was found only in right axial rotation. CONCLUSIONS: The F-u-HA/PLLA cage has the possibility to supplant the use of metallic devices in interbody fusions of the cervical spine.

Biomechanical Phenomena↗

PubMed2003

Bone ingrowth fixation of artificial intervertebral disc consisting of bioceramic-coated three-dimensional fabric.

STUDY DESIGN: The bone-bonding characteristic of the new artificial intervertebral disc consisting of bioceramic-coated three-dimensional fabric was evaluated mechanically and histologically in an in vivo sheep model. OBJECTIVES: To investigate the mechanical properties and the histologic appearance of the interface between the three-dimensional fabric disc and the vertebral body, and to evaluate these alterations in vivo under a spinal segmentally mobile condition. SUMMARY OF BACKGROUND DATA: Bone ingrowth to the bioceramic-coated three-dimensional fabric surface had been demonstrated already under a stable environment in preliminary animal studies. METHODS: For this study, 20 sheep underwent two-level lumbar intervertebral disc replacement with three-dimensional fabric discs (Group I) or bioceramic spacers as a comparative material (Group II). All operative segments were stabilized temporarily with spinal instrumentation for the initial ingrown phase. Four animals each were killed at 4, 6, 15, and 24 months in Group I and at 6 months in Group II, and the operative segments were subjected to either a detachment test or histologic evaluation. RESULTS: The interfacial tensile strength at 6 months was significantly higher in Group I than in Group II. No significant decrease in tensile strength was detected until 24 months after surgery in Group I. Histologically, bone ingrowth to the three-dimensional fabric surface was observed 4 months after surgery, and no aseptic loosening occurred until 24 months after surgery. CONCLUSIONS: The findings show that the three-dimensional fabric disc was firmly fixed to the vertebral body by bone ingrowth, and that this biologic fixation was preserved even under the spinal segmentally mobile condition.

Animals↗

PubMed2003

Mechanical evaluation of novel spinal interbody fusion cages made of bioactive, resorbable composites.

Osteoconductive and totally bioresorbable spinal/cervical interbody fusion cages were fabricated from a forged composite of raw particulate hydroxyapatite/poly L-lactide (u-HA/PLLA) with an u-HA 40wt% fraction (F-u-HA 40). The mechanical strengths of three types of cages, designed for open-box, screw and cylinder constructs, were compared with those of existing metal and carbon-fiber/polymer cages. Compressive strengths of these composite cages surpassed those of existing metal and carbon-fiber cages. Fatigue resistance to alternate and static compressive loading persisted for longer than the minimum period (6 months) necessary for spinal devices in simulated body fluid (SBF) at 37 degrees C. These novel interbody fusion cages await clinical application in humans.

Absorbable Implants↗

PubMed2002

Artificial intervertebral disc replacement using bioactive three-dimensional fabric: design, development, and preliminary animal study.

STUDY DESIGN: A new artificial intervertebral disc was developed, and its intrinsic biomechanical properties, bioactivity, and the effectiveness as a total disc replacement were evaluated in vitro and in vivo. OBJECTIVES: To introduce a new artificial intervertebral disc and to evaluate the in vitro mechanical properties, fusion capacity to bone, and segmental biomechanics in the total intervertebral disc replacement using a sheep lumbar spine. SUMMARY OF BACKGROUND DATA: The loss of biologic fusion at the bone-implant interface and prosthetic failures have been reported in previous artificial discs. There have been no clinically applicable discs with detailed experimental testing of in vivo mechanics and interface fusion capacity. METHODS: The artificial intervertebral disc consists of a triaxial three-dimensional fabric (3-DF) woven with an ultra-high molecular weight polyethylene fiber, and spray-coated bioactive ceramics on the disc surface. The arrangement of weave properties was designed to produce mechanical behavior nearly equivalent to the natural intervertebral disc. Total intervertebral disc replacement at L2-L3 and L4-L5 was performed using 3-DF disc with or without internal fixation in a sheep lumbar spine model. The segmental biomechanics and interface histology were evaluated after surgery at 4 and 6 months. RESULTS: The tensile-compressive and torsional properties of prototype 3-DF were nearly equivalent to those of human lumbar disc. The lumbar segments replaced with 3-DF disc alone showed a significant decrease of flexion-extension range of motion to 28% of control values as well as partial bony fusion at 6 months. However, the use of temporary fixation provided a nearly physiologic mobility of the spinal segment after implant removal as well as excellent bone-disc fusion at 6 months. CONCLUSION: An artificial intervertebral disc using a three-dimensional fabric demonstrated excellent in vitro and in vivo performance in both biomechanics and interface histology. There is a potential for future clinical application.

Animals↗

PubMed2002

Influence of bioresorbable, unsintered hydroxyapatite/poly-L-lactide composite films on spinal cord, nerve roots, and epidural space.

The effect of forged unsintered hydroxyapatite/poly-L-lactide (u-HA/PLLA) composite films on spinal cord and nerve roots and its degradation behavior and osteoconductivity in epidural space were compared with those of calcined HA (c-HA)/PLLA and unfilled PLLA films. Partial laminectomy was performed on 20 rabbits, and u-HA/PLLA and PLLA films were implanted in the intervertebral space. Total laminectomy was performed on 30 rabbits to implant u-HA/PLLA, c-HA/PLLA, and PLLA films in both epidural and subcutaneous spaces. For up to 50 weeks, there were no histological changes in the spinal cord or nerve root, and no inflammatory cell infiltration into the epidural space around the films. The rate of decrease in viscosity average molecular weight of both composite films was initially higher than that of PLLA but eventually became lower, although there was no difference in the degradation behavior of the three films in either the epidural or subcutaneous spaces after 50 weeks. Scanning electron microscopic and energy-dispersive X-ray analysis indicated calcium phosphate deposits on the surface of composite films with new bone formation from 4 weeks. The u-HA/PLLA composite film therefore has good biocompatibility, osteoconductivity, and fast primary degradation rate, which may prove compatible with application to spinal surgery.

Animals↗