Wolffs law

The remodeling of bone structure results from the activities of osteoblasts and osteoclasts, which provide constant deposition and re-adsorption of bone matrix, respectively. This occurs through a phenomenon known as Wolffs Law in response to the application of weight bearing loads, often through daily routines such as walking or exercising, osteoblasts and osteoclasts will remodel bone structure [18,19],... 

Stress Shielding. Beyond the traditional biocompatibility issues, hard tissue biomaterials must also be designed to minimize a phenomenon known as stress shielding. Due to the response of bone remodeling to the loading environment, as described by Wolffs law, it is important to maintain the stress levels in bone as close to the preimplant state as possible. When an implant is in parallel with bone, such as in a bone plate or a hip stem, the engineered material takes a portion of the load— which then reduces the load, and as a result, the stress, in the remaining bone. When the implant and bone are sufficiently well bonded, it can be assumed that the materials deform to the same extent and therefore experience the same strain. In this isostrain condition, the stress in one of the components of a two-phase composite can be calculated from the equation ... 

According to Wolffs law, alteration of function results in a change in the structure of bone. The mastoid processes are barely existent in a newborn infant but become larger, knob-like projections from the temporal bone by adnlt-hood. Hypertrophy of the inion most likely indicates chronic tension introdnced by the trapezius and splenii muscles. Asyimnetric or even symmetric stressors on bone or other bodily components bring abont long-term changes in structure. 

Research based on Wolff s law of bone transformation has resulted in some other important observations. Fluctuating loads, such as those that occur in walking, are better for bone than consistentiy appUed loads, such as weight gain. However, if the effective appUed load becomes extreme, pressure necrosis, ie, bone death, occurs. Pressure necrosis is a significant concern in hip arthroplasty. Necrosis means the localized death of living tissue. Undue pressure on living cells causes death. Some total hip replacement failures are the direct result of pressure necrosis. 

HC1 is efficiently absorbed into H2S04-H20 and into HN03-H2S04-H20 solutions, which as discussed earlier, are found in the stratosphere in the form of aerosol particles and Type I PSCs under some conditions (Wolff and Mulvaney, 1991). The solubility of HC1 in these liquid solutions can be expressed in terms of the usual Henry s law constant (Elrod et al., 1995 Abbatt, 1995 Luo et al., 1995 Hanson, 1998). Table 12.4 shows some typical measurements of the Henry s law constants for HC1 in several typical binary and ternary solutions, respectively. Hanson (1998) has shown that the solubility data for HC1 in binary mixtures of H2S04 and water in these and other studies can be fit by the form... 

Brunner, S., Hornung, E., Santl, H., Wolff, E., Piringer, O.G., Altschuh, J., and Bruggemann, R. 1990. Henry s law constants for polychlorinated biphenyls Experimental determination and structure-property relationships. Environ. Sci. Technol. 24, 1751-1754. 

Wolff s Law Bone develops or adapts its structure to that most suited to resist the forces acting upon it. 

Kaplan, D. G., "Bone Response to Mechanical Forces, (A Proposed Explanation for Wolff s Law)", presented at the 198th American Chemical Society Meeting, Miami Beach, Florida, Sept. 1989. 

Thus the amount of the stress reduction in bone when an implant is included depends on the modulus and cross-sectional area of the implant. Implants with a higher modulus and a larger cross-sectional area will shield the bone from a greater proportion of its normal physiological stress, resulting in bone loss according to Wolff s law. 

As the growth plate is subjected to forces, the sacrum will deform. It will round off and dome and L5 will become trapezoidal because of Heuter Volkman and Wolff s laws. The pars interarticularis will become elongated through repeated stress fractures [7]. If the posterior tether is weak L5 slips off. We can understand the entire event of spondylolisthesis from birth to spondyloptosis with this thinking. We can also understand the various spinal pathoanatomies that are seen at various times with x-rays. 

It is clear that severe spondylolisthesis is seen in growing children. The developmental type of spondylolisthesis with high dysplasia is the problem (a poor bony hook). For whatever reason the pelvis rotates and lordosis increases. This now causes stress on the growth of the plates of L5 and SI. These deform because of Heuter Volkman Rule and Wolff s law. The dys-plastic bony hook may stretch or separate or both. The sacrum may bend. The disc may fail. Eventually in the worst case scenario the spondylolisth-... 

Christian Wolff, gentium methodo scientifico pertractum (1764) Engl, trans. The Law of Nations Treated According to Scientific Method (Oxford, 1934). - Eds. 

---