Wolff’s law is a physiological property of bone tissue. In its most technical terms, it is the principle of bone adaptation from stress generated potentials. In more simple terms, it is the change in bone structure as a result of the stresses placed on them. So for example, it is well known that astronauts lose bone mineral density as a result of spending time in space1. This is due to the weightlessness of space, the removal of gravity as a stressor on your bones. We have spoken in a previous blog “Your Spine: The Basics” about how fundamental basic property of the spine is that it fights gravity by expending the least amount of energy possible. This is the fundamental property of all bones in your body.
What people don’t tend to realise is that the loss of bone mass/density experienced by astronauts in space, is also experienced by people who are immobilised for prolonged periods or paralysed1. Wolff’s law is bone adaptation due to stress generated potentials, therefore if there is no stress, due to lack of movement or lack of gravity, the bones lose their density, making them weak and brittle.
Your bones are maintained by a balance of the cells the build bone, called osteoblasts and the cells that resorb or break down bone, called osteoclasts. Mechanical loading, from physical activity and exercise triggers an increased in osteoblast activity2 improving bone quantity and quality3. Whereas a lack of physical activity and exercise reduces the activity of osteoblasts, and increases the activity of osteoclasts resulting in loss of bone mass and quality4,5. Eventually conditions such as osteopenia and osteoporosis occur causing the bones to be weak and brittle. These conditions of weak and brittle bones are consistent with paralysis, prolonged immobilisation and aging. Therefore, there is a physiological link between osteoporosis later in life and the amount of exercise and physical activity of elderly individuals. We have discussed the role of “Whole Body Vibration” on bone health in a previous post.
So why am I bringing up Wolff’s law specifically, rather than continuing the discussion simply on bone health? Well, this is because Wolff’s law is the physiological law that your bones follow. This is therefore relevant for everyone, regardless of age. Its is Wolff’s law that triggers the formation bone from cartilage during skeletal development of infants and children6,7. It has also been suggested that Wolff’s law is the main mechanism that triggers bone spurs (Osteophytes) during degenerative changes during aging8,9. Changes in loading of the weight bearing joints of the body; such as the spine, hips and knees as a result of degeneration (wear and tear). As a result of the abnormal loading, the bones will protect themselves by building new bone in the areas of increased pressure, such as the bone spurs (osteophytes) seen on spinal x-rays8. This process is Wolff’s law in action and its role in aging joints of the spine.
The flow chart below explains how these changes occur during spinal arthritis and disc disease (SADD) in the neck taken from Ferrara (2012)8. Notice the boxes that state that a loss in disc height results in loss of the neck curve (lordosis), which overloads the joints, resulting in osteophyte formation (bone spurs) and progressive kyphosis. As we discussed in our previous post “Spinal Biomechanics: The Basics” the normal alignment of the neck is called a lordosis. The complete reversal of this position is called a kyphosis. In their study, Harrison et al (2001) found when the cervical spine is in a kyphotic configuration, the centre of mass of the head shifts from the joints at the back of the neck (call the articular columns) to the front, over the discs where it is not meant to be. This increases the stresses and strains on the cervical spine vertebrae to 10 times normal9. As a result of this, bone spurs grow at the front of the vertebrae where the discs are to protect itself from these abnormally high stress levels.
We have discussed these processes in detail in out posts on “Obesity and Back Pain” and “Posture in Health and Disease” so have a read through these posts if you haven’t already as I won’t be recapping them here. The reason for discussing Wolff’s law is because it is a little know physical law of your bones. It is an important law to understand as it helps to explain what happens to your bones as we grow up, mature and grow old. Bone mass reduces with inactivity, therefore osteoporosis seen in the elderly may not simply be due to aging, it may be accelerated by inactivity and sedentary lifestyles in the elderly population. However, increasing physical activity and exercising more can improve bone density and bone mass. This may also be influenced by including “Whole Body Vibration” to our workouts and exercises. Not to mention changes in our diet that may also influence our bone health.
The next installment of our posts will be discussing the same property as Wolff’s law on our soft tissues; Davis’s Law, which will be followed by a detailed discussion on the neck so keep an eye out for these. Also, keep an eye on the Spriggs Chiropractic YouTube channel as we be launching a series of lectures on these blog posts to get the message out there. I know it can be difficult for people to read these posts, so putting them in a video format is a great way to get more people interacted with them.
- Sibonga J, Matsumoto T, Jones J, et al. Resistive exercise in astronauts on prolonged spaceflights provides partial protection against spaceflight-induced bone loss. Bone. 2019;128. doi:10.1016/j.bone.2019.07.013
- Chen JH, Liu C, You L, Simmons CA. Boning up on Wolff’s Law: Mechanical regulation of the cells that make and maintain bone. J Biomech. 2010;43(1):108-118. doi:10.1016/j.jbiomech.2009.09.016
- Jing D, Tong S, Zhai M, et al. Effect of low-level mechanical vibration on osteogenesis and osseointegration of porous titanium implants in the repair of long bone defects. Sci Rep. 2015;5. doi:10.1038/srep17134
- Phillips JA, Almeida EAC, Hill EL, et al. Role for beta1 integrins in cortical osteocytes during acute musculoskeletal disuse. Matrix Biol. 2008;27(7):609-618. doi:10.1016/j.matbio.2008.05.003
- Tatsumi S, Ishii K, Amizuka N, et al. Targeted Ablation of Osteocytes Induces Osteoporosis with Defective Mechanotransduction. Cell Metab. 2007;5(6):464-475. doi:10.1016/j.cmet.2007.05.001
- Bagnall KM, Harris PF, Jones PR. A radiographic study of the human fetal spine. 1. The development of the secondary cervical curvature. J Anat. 1977;123(Pt 3):777-782. http://www.ncbi.nlm.nih.gov/pubmed/885790.
- Bagnall KM, Harris PF, Jones PR. A radiographic study of the human fetal spine. 2. The sequence of development of ossification centres in the vertebral column. J Anat. 1977;124(Pt 3):791-802.
- Ferrara LA. The Biomechanics of Cervical Spondylosis. Adv Orthop. 2012;2012:1-5. doi:10.1155/2012/493605
- Harrison DE, Harrison DD, Janik TJ, William Jones E, Cailliet R, Normand M. Comparison of axial and flexural stresses in lordosis and three buckled configurations of the cervical spine. Clin Biomech. 2001;16(4):276-284. doi:10.1016/S0268-0033(01)00006-7