Osteoporosis is a metabolic disease that reduces the amount of bony tissue in the body. This condition leads to an actual thinning of the bones throughout the body. While the bones thin, the body’s interior framework in the form of the skeletal system becomes compromised.
In many ways, this compromised thinning leads to a weaker, more unstable structure that becomes increasingly susceptible to injury.
How do the bones become thin with osteoporosis? The answer is not quite as simple as termites nibbling away at the wooden structure of your house. The thinning process actually occurs both outside and inside the bone.
Typically, the outer perimeter of the bone, called cortical bone, loses its thickness. The inner portion, called trabecular bone, loses its density. This makes the bone more fragile because the wall of the bone is thinner, and the core of the bone is more porous. The result is an inherently less stable structure.
The loss of bone actually begins at the cellular level, where cells that help make bone (osteoblasts) are simply outperformed by cells that break down bone (osteoclasts). The result is that more bone is broken down than replaced.
Types of Osteoporosis
The most prevalent type of osteoporosis (Type 1) is found in postmenopausal women, who produce drastically less estrogen. Without estrogen, much more bone is broken down in the body.
The second type is primarily age-related (Type 2), and is usually due to low levels of calcium. As the body ages, it becomes much less efficient at absorbing calcium from the intestines.
Both vitamin D and parathyroid hormone help the intestines absorb calcium from the intestines into the bloodstream. Low levels of vitamin D (obtained from exposure to the sun or through diet) and lower hormone levels such as parathyroid hormone can contribute to lower levels of calcium in the body. If there is less calcium in the bloodstream, calcium is then taken from the bone to return the calcium to the bloodstream. This blood-calcium level is crucial for many body systems to function normally.
Reduced physical activity, which is typical of the aging process, also can reduce bone strength. If you compound all these processes together, the skeletal framework of the body is presented with a daunting physiological hurdle to clear.
And the safety blanket of “youth” won’t protect you for long from osteoporosis. The thinning process of the bone can start as early as one’s mid-30s. One’s bone density or bone mass generally peaks at about 35 years of age, and from then on begins a steady decline.
For some, the process presents without symptoms, but for others, symptoms may appear as low back pain, hip pain, and neck pain. Other signs, such as loss of height and stooped posture or dowagers hump (thoracic kyphosis), may slowly appear. Because the bones have thinned, there is an increased propensity for fractures of the hip, femur, vertebrae, and wrist (Colles fracture).
Postural changes that correlate with the condition tend to make the trunk bend more to the front, which changes the body’s center of gravity. Because the body is not stacked evenly above its center of gravity, longer response times may be needed to correct challenges to balance. This forward change of posture makes people more prone to falls, as weight is now unevenly distributed over the center of the body. The increased fall risk, combined with weaker bones, further increases the threat for bone fractures.
Due to the natural aging process and the inevitable certainty of menopause in females, prevention of osteoporosis is not an easy endeavor. Proper nutrition including a calcium-rich diet is typically recommended. Vitamin D (D3) and calcium co-supplements are often effective and may help reduce the incidence of fractures associated with osteoporosis.
These dietary supplementations, in combination with hormone replacement therapy — such as estrogen, parathyroid hormone, and short term androgens — may offer some additional protection.1,2
Role of Exercise and Gait Training
Besides diet and hormone factors, physical therapy can help address the effects of lack of physical activity. Postural exercises, walking (gait training), weight bearing exercises, and balance/proprioceptive exercise are often implemented to address physical limitations. These exercises have been shown to have a positive effect on functional limitations in older populations.3,4
What can exercise do to combat the effects of a pathology that seems to be so inherently inevitable in its progression? Postural exercises can help address fractures of the spine that are often associated with osteoporosis. These fractures often fall into two patterns — compression and wedging.
Compression fractures result in reduced height of the spinal vertebrae, which results in overall reduced height of the person. A wedging fracture can result in the collapse of the front of the vertebrae (anterior), which can in turn lead to a stooped spine and back (dowagers hump or Sheuermanns disease).5
To address this type of fracture, extension-based exercises often help by redistributing the force to the back (posterior) aspect of the vertebrae, where there is less wedging. These exercises are often conducted in the supine position, which uses gravity to promote a less forward, kyphotic posture.
Forward posture can also cause tight trunk flexors and weak/long trunk extensors. This can contribute to reduced lung volume and reduced range of motion at the hips and knees.6 If this forward kyphotic posture has slowly accumulated over time, stretching of the anterior muscles on the front of the upper and lower extremities may also be necessary.
Gait exercises are important to address the instability that accompanies osteoporosis. Remember that the forward posture typical of osteoporosis changes the center of gravity to the front, which sets up a postural bias. Walking in a more upright, tall, extended posture will allow this forward posture to be placed into a more neutral center of gravity.
Another gait trend in older populations is that stride length decreases, and the number of steps to go the same speed (cadence) increases to make up for this.6 The resulting instability that may come from these changes can be addressed with training to make the gait a more stable pattern.
The simple act of walking is a weight bearing activity that can also promote bone remodeling. Walking introduces a weightbearing mechanical force onto the body that stimulates some bone regeneration. This phenomenon takes advantage of Wolfe’s Law, whereby remodeling of bone is influenced by a mechanical load placed on a bony structure in the form of gravity and/or muscle activity.5
Resistance Exercise and Balance Training
Resistance training offers the potential to minimize osteoporotic bone loss. Resistance training takes advantage of Wolfe’s Law, as noted above. Muscle activity in the form of resistance bands, free weights and/or one’s own body weight provide a mechanical load on bone that contributes to bone remodeling.
Progressive resistance training has been shown to provide a host of other benefits to reduce disability. Studies have shown that a program of regular progressive resistance exercise can provide the obvious strength gains that one would expect of such programs. Other studies have shown that gait speed and balance can improve even though treatment on gait/balance is not specifically provided.3,4
Because the skeletal framework of the body is more fragile and one’s center of gravity is altered with osteoporosis, balance/proprioceptive exercises are a keystone intervention. With a forward displacement over the center of gravity due to the collapse of the vertebrae in the spine, the sway to correct posture (postural sway) can increase. In essence, this compromises the body’s ability to maintain and correct posture. If postural sway increases, there is a likelihood that fall risk will increase.6
Shorter muscles of the hips, knees and ankles that are typical of such postures reduce the mechanical advantage of the muscles to correct loss of balance and compound the problem further. Stretching these muscle groups can help reverse this mechanical disadvantage. If the strengthening is done in conjunction with a prescribed balance retraining program, studies show benefits for reducing the risk of falls.7
When it comes to treatment for fall prevention, a key component appears to be individuality. Interventions that appear to be more successful at reducing the likelihood of falls in the elderly are those that are designed specifically for the patient. These “custom-prescribed” interventions are more likely to meet the individual needs of the patient, and as such may be more effective.7
The one exception to this rule is Tai Chi. Group Tai Chi programs have been shown to reduce falls. Home hazard assessment that is professionally prescribed also appears to reduce the rate of falls.7 Physical therapy is crucial to individually prescribe these home balance, strengthening, and safety programs.
While the onslaught of osteoporosis is an inevitable thing for some people, many things can be done to slow its progression and prevent further damage to the thinning skeletal system. Being part of a proactive intervention for individuals who have osteoporosis has the potential to greatly improve the safety, function and general mobility for these people.
1. Gillespie, WJ, Avenall, A. et. al., Vitamin D (2003). Vitamin D and vitamin D analogues for preventing fractures associated with involitional and post-menopausal osteoporosis. Cochrane Database of Systematic Reviews, Vol 3.
2. Avenell A, Gillespie WJ, Gillespie LD, O’Connell D (2009). Vitamin D and related vitamin D compounds for preventing fractures resulting from osteoporosis in older people. Cochrane Database of Systematic Reviews.
3. Latham N, Anderson C, Bennett D, Stretton C. Progressive resistance strength training for physical disability in older people. Cochrane Database for Systematic Reviews, Vol 3.
4. Liu CJ, Latham N. 2011. Can progressive resistance strength training reduce physical disability in older adults? A meta-analysis study. Disabil Rehabil. 33(2):87-97.
5. Neumann, D. 2009. Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation, 2nd Ed., 36-37, 288-291.
6. Laura Smith, E. (Beth Weiss, Don Lehmkuhl.) 1995. Brunnstrom’s Clinical Kinesiology, 5th Ed., 405-406, 431-432.
7. Gillespie LD, Gillespie WJ, Robertson MC, Lamb SE, Cumming RG, Rowe BH. 2003. Interventions for preventing falls in elderly people. Cochrane Database for Systematic Reviews. Vol 3.
Ben Wiggin is practice manager of Huggins Hospital Back Bay Rehabilitation in Tamworth, NH. He has clinical interest in manual interventions and sports medicine. He can be reached at firstname.lastname@example.org