Woven bone

Fluorid ions stimulate bone formation by a direct mitogenic effect on osteoblasts mediated via protein kinase activation and other pathways. Further to these cellular effects, fluorides alter hydroxyapatite crystals in the bone matrix. In low doses, fluorides induce lamellar bone, while at higher doses abnormal woven bone with inferior quality is formed. The effect of fluorides on normal and abnormal (e.g. osteoporotic) bone therefore depends on the dose administered. 

The effects of raloxifene on bone histomorphometry were analyzed by Ott et al. (2002). In a group of 54 women enrolled in the MORE study, two transiliac bone biopsies were obtained at baseline and after 2 years of treatment. The results confirmed the safety of the drug on bone tissue since no woven bone, mineralization defect, cell toxicity, or medullary fibrosis was observed. Moreover, the number of empty osteocytic lacunae also suggested an antiapoptotic effect on the osteocyte. More recent experimental data further confirm this antiapoptotic effect of raloxifene on osteoblastic and osteocytic cells (Taranta et al. 2002). 

In reviewing the stained section that we are sending today to Dr. O Sullivan, Dr. Curran, Dr. Lem perl c, I agree that there is tremendous bony ingrowth throughout the implants. These sections represent some of the best ingrowth of woven bone we have seen in any implant. 

Oguma, H., Murakami, G., Takahashi-Iwanaga, H., Aoki, M., and Ishii, S. (2001). Early anchoring collagen fibres at the bone-tendon interface are conducted by woven bone formation. /. Orthopaedic Research 19, 873-880. 

At the microscopic level, bone consists of two structures woven and lamellar (Fig. la). Woven bone (with an average mineral grain size of 10 to 50 nm) is the immature, or primitive, form of bone and is normally found in the metaphyseal region of growing bone as well as in fracture callus (Kaplan et al., 1994 Park and Lakes, 1992). Woven bone is coarse-fibered and... 

The other microarchitectural form of bone, lamellar bone, actively replaces maturing woven bone and, consequently, contains up to 100 times more mineralized matrix or hydroxyapatite these hydroxyapatite crystals... 

Cortical bone, also called compact or lamellar bone, is remodelled from woven bone by means of vascular channels that invade the embryonic bone from its periosteal and endosteal surfaces. It forms the internal and external tables of flat bones and the external surfaces of long bones. The primary structural unit is an osteon, also known as a Haversian system, a cylindrical shaped lamellar bone surrounding longitudinally oriented vascular channels (the Haversian canals). Horizontally oriented canals (Volkmann canals) connect adjacent osteons. The mechanical strength of cortical bone results from the tight packing of the osteons. 

Figure 23 Mammalian bone at different levels of resolution (a) Collagen fibril with associated mineral, (b) Woven bone (random collagen distribution), (c) Lamellar bone showing separate lamellae with collagen organized in domains with preferred orientation alternating in adjacent lamellae, (d) Woven bone with blood channels shown as dark spots, woven bone stippled, (e) Primary lamellar bone orientation indicated by dashes, (f) Haversian bone, a collection of haversian systems are shown as a longitudinal structure. Each system has concentric lamellae around a central blood channel. Darkened area represents an empty (eroded) portion of the section which will be reconstituted with new bone, (g) Alternation of woven and lamellar bone, (h) Various orientations of heavily mineralized (cortical, or compact) bone, (i) Trabecular, or cancellous, bone (Wainwright et aL, 1976) (reproduced by permission of Hodder Arnold from Mechanical Design in Organisms, 1976).

Figure 7.77 (a) Histological toluidine blue-stained sections of threaded Si-HAp implants after 7 days of implantation. Woven bone growth along and in direct contact with surfaces was observed (contact osteogenesis). This woven bone is mainly recognised by the numerous large osteocyte lacunae, (b) After... 

To provide for these demands, intestinal calcium absorption is increased and medullary bone is resorbed Medullary bone is the storage system for calcium used by the bird during its reproductive phase of life It is woven bone having little structural capability and forms in response to a direct action by estradiol and testosterone on bone These two sex hormones are released as the female bird approaches maturity accounting for the initiation of medullary bone formation Egglaying birds have high levels of the renal 25-OH-D3-l-hydroxylase activity as compared to males or non-egg-laying mature females In-... 

Polyesters have also been processed into tubular form for orthopedic and cardiovascular tissue engineering applications. Meinig and co-workers evaluated bone regeneration using tubular PLLA membranes in mid-diaphyseal defects in rabbit radii. The membrane prevented soft tissue formation in the defect area, and it allowed woven bone to fill the defect. Local inflammation or systemic intolerance was not observed, and the membranes remained intact for the entire 64-week study. 

Bone resorption A type of bone loss due to the greater osteoclastic activity than the osteogenic activity. Callus Unorganized meshwork of woven bone which is formed following fracture of bone to achieve early stability of the fracture. 

Woven bone Fibrils are arranged into loosely packed and poorly oriented bundles with different diameters. It also includes a large proportion of noncollagenous material. 

The bone matrix that comprises lamellar and woven bone contains another level of porosity on the order of 5 to 10 frm that is associated with the bone cells (see Fig. 8.2a, b, c). Osteocytes, the most common type of bone cell, are surrounded by a thin layer of extracellular fluid within small ellipsoidal holes (5 /zm minor diameter, 7 to 8 /xm major diameter) called lacunae, of which there are about 25,000 per /iim in bone tissue. The lacunae are generally arranged along the interfaces between lamellae. However, the lacunae also have a lower-scale porosity associated with them. Each osteocyte has dendritic processes that extend from the cell through tiny channels ( 0.5 /on diameter, 3 to 7 /zm long) called canaliculi to meet at cellular gap junctions with the processes of surrounding cells. There are about 50 to 100 canaliculi per single lacuna and about 1 million per mm of bone. 

At the highest hierarchical level (1 to 5 mm), there are two types of bone cortical bone, which comes as tightly packed lamellar, Haversian, or woven bone and trabecular bone, which comes as a highly porous cellular solid. In the latter, the lamellae are arranged in less well-organized packets to form a network of rods and plates about 100 to 300 /xm thick interspersed with large marrow spaces. Many common biological materials, such as wood and cork, are cellular solids. ... 

The increment of bone occupied area was due to new bone formation, as evidenced in Figure 7. In actuators the area occupied by woven bone and osteoid was 64.89 19.32% of the total bone area versus. 31.72 14.54% in static devices. With the aid of the fluorochrome labeling, we measured bone mineral deposition rate in the distal third of the piezoelectric devices. Bone deposition rate was significantly higher around actuated devices (4.44 1.67 pm/day) than around static devices (2.70 0.95 pm/day). 

Nacre has been tested in human, sheep, and rabbit models (Lamghari et al., 2001). In human patients, fresh woven bone bonds itself throughout the nacre implant, augmented by the heightened activities of osteoblasts and osteoclasts (Figure 1.8). While nacre is stably tolerated in vivo, its degradation and resorption is limited and this... 

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