|M.Sc Student||Golan Saar|
|Subject||The Relationship between the Anatomy of the Canaliculi, the|
Pressure at it's Ends and the Blood Flow through
|Department||Department of Biomedical Engineering||Supervisors||Professor Emeritus Uri Dinnar (Deceased)|
|Professor David Elata|
The incidence of pathological bone disorders is growing rapidly in recent years. This study attempted to shed light on possible micro-level mechanical processes leading to Osteoporosis and Osteonecrosis.
Recently, serum (blood) flow within bone tissue has been extensively studied and a mechanism explaining the small-scale flow has been proposed. This flow is A-Vascular in nature - not driven by the heart. According to the proposed mechanism, loads applied to the bone result in pressure gradients at the Lacunar Canalicular porosity. These gradients drive the serum flow. Experimentally observed data and former research suggest that the anatomical site of strain generated potentials within the bone is the Lacunar Canalicular porosity. Serum flow at this porosity induces shear stresses that are applied to Osteocyte cells processes. These cells are the mechanical sensory input of the bone for the functional adaptation processes. A model of the bone structure has been proposed (Weinbaum et al., 1994) in which the tissue is constructed as a multi-hierarchical porous media. Each hierarchy is idealized as a geometrically isotropic porous material.
The suggested mechanism for explaining the small-scale blood serum flow has not been studied for pathological cases. Moreover, no clinical or theoretical work has connected this mechanism with bone pathologies. In fact no micro-scale mechanism has been suggested as the base for bone tissue related pathologies such as Osteoporosis and Osteonecrosis.
This study constitutes primary understanding relating to the effects of deposition at the Lacunar-Canalicular level of bone. Such a deposition is shown to have great effects on the cells in terms of shear stresses and serum mass flow required to supply the cells nutrients.
Until today no relation has been proposed between Osteoporosis and Osteonecrosis. These were always treated as two distinct unrelated bone pathologies. This study establishes the basis for connecting the two by their possible micro-structural origins under certain conditions. The conditions refer to the nature of the deposition taking place at the Lacunar-Canalicular porosity.
Analysis of the results suggests three pathologies or pathogenic symptoms that may develop in bone tissue. Each pathology is related to a certain aspect of the evident deposition within the system:
1. Birth Stage Stresses (BSS): highly increased shear stresses (more than 30 times the normal) applied to the Osteocyte process at the beginning of the deposition formation may result in membrane rupture (i.e. Osteonecrosis or Osteonecrotic symptoms).
2. Birth Stage Erosion (BSE): highly increased shear stresses (more than 30 times the normal) applied to the Canaliculus bone matrix at the beginning of the deposition formation may result in matrix erosion (i.e. Osteoporosis or Osteoporotic symptoms).
3. Mature Stage ‘Suffocation’ (MSS): a high reduction in the serum flow to the cells (up to 98% reduction) occurring at the Canaliculi in the advanced stages of the deposition formation may result in insufficient nutrients supply to the cells and their ultimate death (i.e. Osteonecrosis or Osteonecrotic symptoms).
The treatment measures currently used by the medical community have been investigated in connection with the micro-structural mechanisms of bone disorder. Physiotherapy is mostly effective for mobile patients and improper for treating BSS or BSE. However, it is cheap and can be performed by the patient at his premises. External pressure is expensive and bone disorder patients are not first priority for chamber time. However, this technique is suitable for all patients and all pathologies. BSS or BSE treatment should be combined with rest. MSS treatment should not be used too often to avoid the death of bone cells when the patient is absent from the chamber for a long period of time. For this reason external pressure achieves slower results than physiotherapy.
Future work is suggested for improving the theoretical model and performing clinical study to confirm the proposed mechanisms.