Chronic Pain, Osteoporosis, and Bone Density Testing
Written by E. Michael Lewiecki, MD, FACP | Article Featured on PPP
Osteoporosis is a disease manifested by low bone density and poor quality of bone, resulting in skeletal fragility and increased risk of fracture.1 While osteoporosis is generally a silent and asymptomatic disease until a fracture occurs, pain and osteoporosis are often associated. Fractures usually cause sudden and severe pain, with non-union fractures and some vertebral fractures resulting in chronic pain. Recent evidence suggests that pressure-induced tibial pain may be an indicator of low bone density in patients without fracture.2 Some metabolic disorders that cause low bone density, such as vitamin D deficiency and osteomalacia, can cause bone and muscle pain,3 proximal muscle weakness, and postural instability4 in the absence of fracture. Chronic pain is associated with many risk factors for osteoporosis and fragility fractures. These risk factors may be categorized according to whether they are due to the underlying disease, the pain itself, or the treatment for pain (see Table 1).
Risk Factors
Diseases associated with chronic pain and osteoporosis include prevalent vertebral fracture, rheumatoid arthritis, inflammatory bowel disease, multiple myeloma, and insulin-dependent diabetes5 with diabetic neuropathy. Regional bone loss may occur with painful disorders such as reflex sympathetic dystrophy6 (Sudeck’s atrophy, algodystrophy) or immobilization of a limb due to trauma — with or without fracture.7
Chronic pain and its associated diseases may result in poor nutrition, impaired cognition, elevated serum cortisol8 or high levels of inflammatory cytokines,9 with potential adverse effects on bone density.
Some treatments for chronic pain disorders, such as glucocorticoids10 and anticonvulsants,11 may be harmful to bone. Other medical treatments, such as narcotics and antidepressants, may impair balance and mobility, resulting in increased risk of falls and fractures.12 Hypogonadism, another risk factor for osteoporosis, has been reported in men13 and women14 treated with opioids.
The consequences of a fracture may include additional acute and chronic pain, limited ambulation, disability, loss of independence, increased risk of future fractures and death.15 Chronic pain patients at risk for osteoporosis should be considered for bone density testing so that appropriate therapeutic intervention may be started to prevent fractures and their clinical consequences.
“…dual-energy X-ray absorptiometry (DXA) of the spine and hip is the recommended method for diagnosing osteoporosis and monitoring the effects of therapy.”
Bone Density Testing
Bone density testing is a non-invasive technique used to diagnose osteoporosis or low bone density, predict the risk of fracture, and monitor the effectiveness of therapy for osteoporosis. While measurement of bone density at peripheral skeletal sites with a variety of technologies is useful to increase osteoporosis awareness and predict fracture risk, dual-energy X-ray absorptiometry (DXA) of the spine and hip is the recommended method for diagnosing osteoporosis and monitoring the effects of therapy. The key to effective clinical management is the identification of high risk patients before the first fracture occurs, so that therapy can be initiated to reduce the risk of fracture.
Dual-energy X-ray Absorptiometry
DXA is used to measure bone mineral density (BMD) at the spine and proximal femur. With appropriate software, many DXA instruments can also measure BMD at the forearm and total body. DXA measures areal BMD (aBMD in g/cm2) by using ionizing radiation with photon beams of two different energy levels. DXA is the “gold-standard” method for the diagnosis of osteoporosis and monitoring the effects of therapy for the following reasons:
- biomechanical studies have shown a correlation between mechanical strength and BMD measured by DXA,16
- epidemiological studies have established a strong relationship between fracture risk and BMD measured by DXA,17
- the World Health Organization (WHO) classification of BMD for the diagnosis of osteoporosis and osteopenia is based on reference data obtained by DXA,18
- randomized clinical trials showing a benefit with pharmacologic intervention have selected subjects based on low BMD measured by DXA,19
- there is a relationship between reduction in fracture risk with pharmacologic therapy and BMD increase as measured by DXA,20
- the accuracy and precision of DXA is excellent.21
DXA is widely available in the United States, with an estimated 10,000 instruments in operation. Radiation exposure from DXA is extremely small,22 typically about the same as the normal daily level of background radiation. Conventional radiography, on the other hand, is an insensitive and subjective technique for evaluating bone density at any skeletal site, requiring 30-40% bone loss before a problem is detected. The best use of standard X-ray in the management of osteoporosis is to diagnose fractures, to monitor the healing of fractures, and to evaluate for some secondary causes of osteoporosis. If an X-ray is suggestive of low bone density, a quantitative measurement of BMD by DXA should be done.
When to Order a Bone Density Test
As with any clinical test, bone density measurement should only be done when the potential benefits outweigh the risks, and when the results are likely to play a role in making patient management decisions. The risks of bone density testing are extremely low. Pregnancy should be considered an absolute contraindication to doing any X-ray-based bone density test. Many organizations have developed guidelines to aid in the selection of those at risk for low BMD who most likely to benefit from knowledge of the results. The most comprehensive guidelines are those of the International Society for Clinical Densitometry23 upon the recommendation of an international panel of experts (see Table 2).
| Due to Underlying Disease Rheumatoid Arthritis Insulin Dependent Diabetes Mellitus Inflammatory Bowel Disease Fragility Fracture Reflex Sympathetic Dystrophy Multiple Myeloma |
| Due to Effects of Pain Elevated Cortisol Poor Nutrition Weight Loss Poor Balance Cognitive Impairment |
| Due to Pain Treatments Narcotics Antidepressants Anticonvulsants Immobilization |
Diagnosis of Osteoporosis
A clinical diagnosis of osteoporosis may be made in a patient with a fragility fracture, provided other causes of fracture have been excluded. A fragility fracture is usually defined as a fracture resulting from a fall from the standing position. It is preferable, however, to identify patients at high risk for fracture before the first fracture occurs, just as risk factors for stroke and myocardial infarction should be identified and managed before a critical event occurs. The World Health Organization (WHO) classification of BMD uses the standard deviation (SD) difference between the patient’s BMD and the mean BMD of a young healthy population (Table 3). This is usually expressed as a T-score, which is calculated by subtracting the mean BMD of the reference population from the patient’s BMD and dividing by the SD of the reference population. A T-score of -2.5 or less is used for a densitometric diagnosis of osteoporosis in a postmenopausal woman.
“If a fracture has occurred, the goal of therapy is to stabilize the fracture, relieve pain, return the patient to pre-fracture levels of activity as soon as possible, and prevent future fractures.”
BMD and Fracture Risk
There is an exponential relationship between BMD and fracture risk, with fracture risk approximately doubling for every 1 SD decrease in BMD.24 Low bone density at any skeletal site is predictive of fractures at any skeletal site although, in general, site-specific fracture risk is best predicted by BMD measurement at that skeletal site. This principle does not hold true with spine BMD and spine fracture risk in the elderly, who often have degenerative arthritis in the spine that may result in an artifactual increase in spine BMD. There is no “fracture threshold.” Instead, there is a continuous relationship between BMD and fracture risk, so that fracture risk is never zero, regardless of how high the BMD, and it is never certain that a fracture will occur, regardless of how low the BMD. In clinical practice, patient management decisions must consider factors in addition to BMD that may affect fracture risk. The most important of these non-BMD risk factors are age25 and previous fracture.26 Fracture risk increases with age, even when BMD remains the same. Other clinical risk factors, such as family history of hip fracture, poor health, low body weight, and frailty, play a role as well. Since most hip fractures occur as a result of a fall, frailty and falling are potent predictors of hip fracture, independent of bone density. The risk of falling is affected by factors that include balance, mobility, strength, reaction time, visual impairment, medications, and cognitive impairment.
When to Repeat a Bone Density Test
A bone density test should be repeated when the expected amount of change in bone density equals or exceeds the Least Significant Change (LSC) — if knowledge of this change is likely to influence clinical management. The LSC is established for each technologist for each instrument used according to well-established guidelines,27 and is best expressed as an absolute value (g/cm2) with a 95% level of confidence. Values for precision error supplied by the manufacturer of the DXA instrument, which are automatically included on some computer printouts, are generally more optimistic than what is achievable in bone densitometry centers and should not be used. It is reasonable to repeat a DXA study 1-2 years after starting pharmacologic therapy to be sure that BMD is stable or increasing, and then repeat the study at intervals of 2 or more years to assure continuing response to therapy. In patients at risk for rapid bone loss, such as those being started on high dose glucocorticoid therapy, it is appropriate to repeat the DXA study every 6 months until stable. For elderly patients in whom a typical age-related bone loss of 0.5-1.0% per year is expected, it may take 3-6 years before a statistically significant change in BMD can be detected.
Women discontinuing estrogen should be considered for bone density testing according to the indications listed above |
Implications for Therapy
Non-pharmacologic therapy for patients at risk for osteoporosis and fragility fracture includes regular weight-bearing exercise as tolerated; good nutrition with adequate daily intake of protein, calcium, and vitamin D; balance training, fall prevention, and hip protectors for those with high risk of falling; and avoidance of bone toxic agents, such as cigarette smoking and excess alcohol. Pharmacologic therapy with FDA-approved agents can be expected to stabilize or increase BMD, and reduce the risk of fragility fractures by approximately 50%.28 If a fracture has occurred, the goal of therapy is to stabilize the fracture, relieve pain, return the patient to pre-fracture levels of activity as soon as possible, and prevent future fractures. Vertebroplasty and Kyphoplasty may offer pain relief for selected patients with vertebral fractures, although the indications for these procedures and the long-term benefits and risks are not well defined.29
| Classification | T-score |
| Normal | -1.0 or greater |
| Osteopenia | Between -1.0 and -2.5 |
| Osteoporosis | -2.5 or less |
| Severe Osteoporosis | -2.5 or less with a fragility fracture |
Conclusions
Patients with chronic pain may be at increased risk for osteoporosis and fragility fractures due to the underlying disease or disorder causing the pain, as well as factors associated with the pain itself and treatments given for the pain. BMD testing is an essential tool for the early diagnosis of osteoporosis or low bone density, allowing for identification of high risk patients and selection of appropriate therapy. Currently available therapy can reduce the risk of future fracture and its clinical consequences.
New Mexico Orthopaedics is a multi-disciplinary orthopaedic clinic located in Albuquerque New Mexico. We have multiple physical therapy clinics located throughout the Albuquerque metro area.
New Mexico Orthopaedics offers a full spectrum of services related to orthopaedic care and our expertise ranges from acute conditions such as sports injuries and fractures to prolonged, chronic care diagnoses, including total joint replacement and spinal disorders.
Because our team of highly-trained physicians specialize in various aspects of the musculoskeletal system, our practice has the capacity to treat any orthopaedic condition, and offer related support services, such as physical therapy, WorkLink and much more.
If you need orthopedic care in Albuquerque New Mexico contact New Mexico Orthopaedics at 505-724-4300.
