Volume 88, Issue 8 , Pages 1030-1035, August 2007
Osteoporosis in a Postpolio Clinic Population
Article Outline
Abstract
Haziza M, Kremer R, Benedetti A, Trojan DA. Osteoporosis in a postpolio clinic population.
Objectives
To determine (1) the frequency of osteoporosis at the hip and lumbar spine in a postpolio clinic population and (2) the association of lower-extremity muscle strength and other potential contributing factors to osteoporosis with bone density measured at the hip.
Design
Cross-sectional study involving a chart review.
Setting
A university-affiliated hospital postpolio clinic.
Participants
Patient charts (N=379) were reviewed; 164 (26%) were included, and 215 (74%) were not included primarily (74%) because of the unavailability of bone density results.
Interventions
Not applicable.
Main Outcome Measures
Bone density (in g/cm2) and T score were assessed at the femoral neck and lumbar spine. Muscle strength was evaluated by manual muscle testing in 7 bilateral lower-extremity muscles.
Results
The occurrence of osteoporosis at the hip and lumbar spine was 20 (32%) of 62 and 6 (10%) of 61 in men, 3 (9%) of 33 and 2 (6%) of 32 in premenopausal women, and 18 (27%) of 67 and 7 (11%) of 65 in postmenopausal women, respectively. In a logistic regression model, the presence of osteoporosis at the hip was significantly associated with strength sum score in the same extremity in which the bone density was performed after adjusting for other important risk factors (age, body mass index, time since polio).
Conclusions
Osteoporosis occurred commonly at the hip in a postpolio clinic population. Hip bone density was associated with muscle strength in the same lower extremity.
Key Words: Osteoporosis, Poliomyelitis, Rehabilitation, Risk factors
ACUTE PARALYTIC POLIOMYELITIS is primarily a disease of the motor unit. It occurs as a result of motor neuron invasion by the poliovirus, resulting in denervation of muscle fibers.1 This process can produce flaccid asymmetric weakness and muscle atrophy, which causes reduced mobility and increases the risk for falls. Because of the success of the poliovirus vaccine, poliomyelitis, once among the most feared human infectious diseases, is now almost entirely preventable by proper immunization. Even though acute paralytic polio is very rare in North America today, it is still a problem in less developed parts of the world and a large number of people with previous paralytic polio are alive today.1
Osteoporosis is defined as a progressive systemic skeletal disorder characterized by low bone mineral density (BMD), resulting in bone fragility and increased susceptibility to fractures.2, 3 Osteoporosis is a chronic condition of multifactorial etiology and is usually clinically silent until a fracture occurs. The prevalence of osteoporosis in a postpolio clinic population is unknown. Because of chronic weakness and reduced activity, these patients likely have a higher prevalence of osteoporosis and an increased risk for falls with resultant fractures.4 Several risk factors for osteoporosis have been identified, such as advanced age, female sex, familial predisposition, early menopause, smoking, heavy alcohol intake, reduced physical activity, and muscle weakness.2, 3, 5, 6, 7, 8 The last 2 are of particular importance for this study. Osteopenia is defined as a decrease in BMD that can be a precursor condition for osteoporosis.3 However, not every person diagnosed with osteopenia will develop osteoporosis. Because the relation between fracture rate and osteopenia is not as well established as with osteoporosis,2, 6 we have chosen to be concerned primarily with osteoporosis in this study.
The identification of patients at risk for osteoporosis could lead to a prompt diagnosis and preventative treatment instituted before a possible fall or fracture occurs. Therefore, early detection of osteoporosis would help prevent hip fractures, which cause considerable economic and social costs and increase morbidity and mortality among patients affected. In a Swedish study,8 it was found that the annual number of patient days in an acute care hospital for hip fracture was higher than for breast cancer, myocardial infarction, or diabetes.
The objectives of this study were to (1) determine the frequency of osteoporosis and osteopenia at the hip and lumbar spine in a postpolio clinic patient population; (2) to evaluate the association of lower-extremity strength with bone density at the hip; and (3) to evaluate the association of bone density and other potential contributing factors to osteoporosis such as age, weakness at acute polio, time since acute polio, body mass index (BMI), mobility status, and history of smoking and alcohol abuse.
Methods
Study Design
This was a cross-sectional study. Data were obtained from a chart review of patients who had been evaluated and followed at a university-affiliated hospital postpolio clinic. The study was approved by the institutional research ethics board.
A bone densitometry was requested depending on the doctor’s judgment after patient evaluation. A bone densitometry evaluation was considered for essentially all clinic patients. The examination was requested by the clinic physician if no such evaluation had been performed in the past few years in postmenopausal women and in premenopausal women and in men with lower-extremity weakness. All patients were evaluated by the same physician. The majority of the bone densitometry examinations were performed at the same center (50/65 [78.1%] in men, 23/32 [74.2%] in premenopausal women, 46/67 [68.7%] in postmenopausal women).
Study Population
Active patient charts (N=379) of the postpolio clinic were reviewed between October 2003 and January 2004. Inclusion criteria for the study were (1) history and physical examination consistent with previous paralytic polio and (2) bone densitometry result available. Reasons for noninclusion were (1) presence of other medical disorders that can cause osteoporosis (eg, untreated thyroid disease, Paget’s disease, primary hyperparathyroidism, Cushing’s syndrome, gastrectomy, malabsorption syndrome), (2) current or previous use of medications, which can cause osteoporosis (eg, steroids, certain anticonvulsants),2 and (3) presence of other significant neurologic difficulties (other than paralytic polio and postpolio syndrome).
Data Collection and Outcome Measures
The dependent variables were bone density at the femoral neck and lumbar spine (in g/cm2) and the presence or absence of osteoporosis and osteopenia at the femoral neck and lumbar spine. Osteoporosis and osteopenia were defined as per the World Health Organization (WHO) criteria (a T score at or below −2.5 for osteoporosis and a T score between −1 and −2.5 for osteopenia).3, 7, 9 Bone density of the hip was assessed arbitrarily on the left, if possible. Some patients had bone density assessments performed only at 1 site because of the presence of a total hip arthroplasty, spinal fusion, severe degenerative changes, and other causes.
Data on the following independent variables were obtained: age at evaluation, sex, BMI, age at polio, weakness at acute polio, age at menopause, history of fractures (yes, no), smoking history (yes, no), alcohol abuse history (yes, no), mobility, and current muscle strength. Weakness at acute polio was assessed on a 0 to 6 scale, with 6 being most severe (0, no weakness; 0.5, partial weakness; 1, complete paralysis for each of 4 limbs; respiratory involvement: 0, no involvement; 0.5, partial involvement; 1, use of iron lung or respirator; speech/swallowing dysfunction: 0, no involvement; 0.5, partial involvement; 1, significant difficulties). A similar measure has been found to be valid.10 Construct validity was evaluated by comparing weakness at acute polio in patients who were and were not hospitalized. Hospitalized patients were significantly weaker on this measure than those not hospitalized. Mobility was assessed as whether or not the patient walked daily and whether or not a wheelchair or scooter was used. If the age at menopause was unknown for a subject, it was arbitrarily set at age 50 years, as done in previous studies.2, 11, 12
Motor strength scores were calculated by using data obtained from the first postpolio clinic neurologic examination, which used a standardized form. Motor strength was evaluated by manual muscle testing by using the Medical Research Council’s (MRC) 0 to 5 scale by the same physician for all patients. Muscle strength was assessed in 7 bilateral lower-extremity muscles (hip flexors, hip extensors, hip abductors, knee extensors, knee flexors, ankle dorsiflexors, ankle plantarflexors). A sum score for each and both lower extremities was calculated for each patient by using the sum of the manual muscle testing results for hip flexors, knee extensors, and ankle dorsiflexors. A similar measure that used MRC-based physician muscle strength examination in 4 extremities has been found to have excellent interrater reliability in Guillain-Barré syndrome, a chronic neurologic disorder characterized by weakness and sensory deficits.13 Our sum score used the same 3 bilateral lower-extremity muscles.
Statistical Analysis
We calculated the occurrence of osteopenia and osteoporosis at the hip and lumbar spine (as defined by the WHO criteria) in 3 patient groups (men, premenopausal women, postmenopausal women). The association between bone density measurement at the hip and muscular strength was assessed by calculation of Pearson correlation coefficients for the same 3 groups (men, premenopausal women, postmenopausal women). Confidence intervals (CIs) for the correlation coefficients were calculated by using the Fisher r-to-z transformation. For the univariate analyses of potential predictive factors in included and not included patients and in patients with and without osteoporosis at the hip, we used t tests for continuous variables and chi-square tests for dichotomous variables. When the expected number of subjects in a cell was less than 5, we used a Fisher exact test for dichotomous variables. We present P values that were not adjusted for multiple comparisons. These tables are descriptive in nature, and the P values are used to indicate which factors might be important to include in the multivariate analyses. We compared pre- and postmenopausal women with osteoporosis and osteopenia at the hip and lumbar spine with a chi-square test or Fisher exact test. A logistic regression model was estimated in the entire population of subjects to evaluate the association of osteoporosis at the hip with lower-extremity strength after adjusting for other important predictive factors. Thus, additional variables considered for the multivariate logistic regression model were those that could be considered confounders on a substantive basis. These included the potential predictive factors previously listed. Age was dichotomized at 50 years because we assumed that women were menopausal at age 50 or more as done in previous studies.2, 11, 12 BMI was dichotomized at 25, which is commonly used as the definition of obesity. Menopausal status was not entered into the equation for women because in many cases menopausal status was unknown and women aged 50 or more were deemed to be menopausal. Sex-specific models showed a different effect of BMI in men and women, leading us to assess an interaction between sex and BMI. This interaction was also plausible from a substantive standpoint. Variables were kept in the model if they were borderline or statistically significant or if their inclusion changed other estimates materially. The statistical software used for analyzing the data was SAS.a
Results
After completion of the review, an opportunity sample of 164 patients was included in the study. A total of 215 patients were not included (159/215 [74%]) primarily because of the unavailability of bone densitometry results. Other reasons for noninclusion were the presence of other neurologic disorders (12/215 [5.6%]), other medical disorders (Cushing’s syndrome, hyperparathyroidism) (5/215 [2%]), and a diagnosis not compatible with poliomyelitis (14/215 [7%]).
To evaluate the similarity of patients included in the study to the more general postpolio clinic population, patients included were compared with those not included. Men included in the study were significantly weaker than those not included (mean strength sum score in both legs ± standard deviation [SD], 16.8±8.3 vs 23±7.8; P<.001). Premenopausal women included in the study were significantly older than those not included (44.5±4.5y vs 41.2±7.3y, P=.02). They were also significantly weaker (strength sum score in both legs, 16.1±9.7 vs 21.3±9.5; P=.02). Postmenopausal women included were also weaker at the time of the acute polio than those not included (weakness at polio score, 2.9±1.7 vs 2.2±1.5; P=.02) and were weaker at time of the evaluation (strength sum score in both legs, 17.9±8.6 vs 21.4±8.2; P=.01). The overall patient population included was weaker when comparing the strength sum score in both legs (P<.05). There were no differences between men included and not included with regard to age at evaluation, weakness at polio, time since polio, and BMI. No differences were noted between premenopausal women included and not included with regard to age at polio, weakness at polio, time since acute polio, and BMI. There were no differences between postmenopausal women included and not included with regard to age at evaluation and at polio, time since acute polio, and BMI. We also compared patients included with those not included because of the unavailability of bone density results. Similar results were noted between these 2 groups to those described earlier with the exception that men included were significantly older than those not included (58±10.8y vs 53.3±11.9y, P=.03), and premenopausal women included were not significantly weaker (strength sum score in both legs, 16.1±9.7 vs 20.2±9.8; P=.09).
The occurrence of osteoporosis and osteopenia at the hip is as follows: 20 (32%) of 62 and 26 (40%) of 62 in men, 3 (9%) of 33 and 13 (39%) of 33 in premenopausal women, and 18 (27%) of 67 and 28 (42%) of 67 in postmenopausal women, respectively. The occurrence of osteoporosis and osteopenia at the lumbar spine is as follows: 6 (10%) of 61 and 17 (28%) of 61 in men, 2 (6%) of 32 and 7 (22%) of 32 in premenopausal women, and 7 (11%) of 65 and 20 (31%) of 65 in postmenopausal women, respectively. Osteoporosis at the hip tended to occur more frequently in postmenopausal women than premenopausal women (P=.07), but there were no differences in the occurrence of osteoporosis at the lumbar spine and in the occurrence of osteopenia in premenopausal women compared with postmenopausal women.
In univariate analyses (table 1), in men, moderate correlations were found between hip bone density and hip flexor strength (Pearson correlation coefficient, r=.27; 95% CI, .02−.49) and between hip bone density and strength sum score (hip flexors, knee extensors, ankle dorsiflexors) in the same extremity in which the bone density was performed (Pearson r=.32; 95% CI, .08−.53). In premenopausal women, hip bone density and strength sum score in the same lower extremity correlated moderately (r=.35; 95% CI, .01−.62), and, in postmenopausal women, moderate correlations were found between hip bone density and same hip flexor strength (r=0.3; 95% CI, .07−.50), strength sum score in the same lower extremity (r=.25; 95% CI, .01−.46), and strength sum score in both lower extremities (r=.27; 95% CI, .03−.48).
Table 1. Association Between Hip Bone Density and Muscle Strength in a Postpolio Clinic (men, premenopausal women, postmenopausal women)
| Group | Muscle Strength Variable | n⁎ | Mean ± SD | Pearson r (95% CI)† | P |
|---|---|---|---|---|---|
| Men | Hip flexors | 62 | 3.2±1.9 | .27 (.02 to .49) | .03 |
| Hip extensors | 25 | 3.2±2.3 | .19(−.22 to .54) | .38 | |
| Hip abductors | 31 | 3.2±2.0 | .11(−.25 to .54) | .54 | |
| Strength sum score in same lower extremity | 62 | 9.3±5.1 | .32(.08 to .53) | .01 | |
| Strength sum score in both lower extremities | 62 | 16.8±8.3 | .10(−.15 to .34) | .46 | |
| Premenopausal women | Hip flexors | 33 | 3.0±2.0 | .22(−.13 to .52) | .21 |
| Hip extensors | 16 | 2.7±2.4 | .36(−.17 to .73) | .17 | |
| Hip abductors | 19 | 2.6±2.0 | .23(−.25 to .62) | .34 | |
| Strength sum score in same lower extremity | 33 | 8.7±5.8 | .35(.01 to .62) | .04 | |
| Strength sum score in both lower extremities | 33 | 16.1±9.7 | .17(−.18 to .49) | .34 | |
| Postmenopausal women | Hip flexors | 67 | 3.1±2.0 | .30(.07 to .50) | .01 |
| Hip extensors | 24 | 3.8±1.8 | .07(−.34 to .46) | .76 | |
| Hip abductors | 27 | 3.4±1.9 | .03(−.35 to .41) | .90 | |
| Strength sum score in same lower extremity | 67 | 10.0±5.2 | .25(.01 to .46) | .04 | |
| Strength sum score in both lower extremities | 67 | 17.9±8.6 | .27(.03 to .48) | .03 |
⁎The number of muscle groups or strength sum scores. |
†95% CI of the Pearson correlation coefficient. |
A comparison of potential predictive factors in patients with and without osteoporosis at the hip is presented in Table 2, Table 3. Premenopausal women with osteoporosis were younger at acute polio, and postmenopausal women with osteoporosis were weaker at acute polio, but there were no other differences between patients with and without osteoporosis with regard to age and weakness at acute polio, time since acute polio, current age, and BMI. There were also no differences between patients with and without osteoporosis in terms of mobility status and history of smoking and alcohol abuse. Because there were only 3 premenopausal women with osteoporosis, we also compared potential predictive factors for osteoporosis in premenopausal women with and without osteopenia at the hip. These results were similar to those for osteoporosis with the exception that premenopausal women with osteopenia did not differ from those without osteopenia with regard to age at acute polio.
Table 2. Comparison of Potential Predictive Factors in Patients With and Without Osteoporosis at the Hip: Categorical Variables
| Potential Predictive Factors | Osteoporosis | P | |
|---|---|---|---|
| Yes (%) | No (%) | ||
| Men | |||
| Mobility status | |||
| Walking daily | 19/20(95.0) | 35/42(83.3) | 0.26 |
| Use of wheelchair or scooter | 5/20(25.0) | 10/42(23.8) | 1.00 |
| History of smoking | 4/20(20.0) | 6/42(14.3) | 0.71 |
| History of alcohol abuse | 1/20(5.0) | 1/42(2.4) | 0.54 |
| Premenopausal women | |||
| Mobility status | |||
| Walking daily | 1/3(33.3) | 22/30(73.3) | 0.21 |
| Use of wheelchair or scooter | 2/3(66.7) | 9/30(30.0) | 0.25 |
| History of smoking | 1/3(33.3) | 8/30(26.7) | 1.00 |
| History of alcohol abuse | 0/3(0.0) | 1/30(3.3) | 1.00 |
| Postmenopausal women | |||
| Mobility status | |||
| Walking daily | 12/18(66.7) | 44/49(89.8) | 0.06 |
| Use of wheelchair or scooter | 6/18(33.3) | 13/49(26.5) | 0.76 |
| History of smoking | 4/18(22.2) | 6/49(12.2) | 0.44 |
| History of alcohol abuse | 0/18(0.0) | 1/49(2.0) | 1.00 |
Table 3. Comparison of Potential Predictive Factors in Patients With and Without Osteoporosis at the Hip: Continuous Variables
| Potential Predictive Factors | Osteoporosis | P | |
|---|---|---|---|
| Yes | No | ||
| Men | 20 | 42 | |
| Age at acute polio (y) | 5.7±5.5 | 7.5±9.8 | .34 |
| Weakness at acute polio (0−6 scale) | 1.9±1.3 | 2.5±1.5 | .15 |
| Time since acute polio (y) | 55.3±12.1 | 49.2±11.8 | .07 |
| Current age (y) | 61.0±11.3 | 56.8±10.7 | .16 |
| BMI (kg/m2) | 25.6±4.1 | 26.2±5.4 | .64 |
| Premenopausal women | 3 | 30 | |
| Age at acute polio (y) | 2.3±0.6 | 5.7±8.1 | .03 |
| Weakness at acute polio (0−6 scale) | 2.6±2.1 | 2.2±1.5 | .67 |
| Time since acute polio (y) | 41.7±2.4 | 38.9±9.6 | .62 |
| Current age (y) | 44.0±2.2 | 44.6±4.8 | .85 |
| BMI (kg/m2) | 25.6±4.6 | 25.8±3.9 | .96 |
| Postmenopausal women | 18 | 44 | |
| Age at acute polio (y) | 9.1±9.3 | 5.7±4.9 | .15 |
| Weakness at acute polio (0−6 scale) | 3.7±1.7 | 2.6±1.6 | .01 |
| Time since acute polio (y) | 56.3±13.3 | 56.2±8.9 | .97 |
| Current age (y) | 59.9±11.4 | 62.0±8.5 | .17 |
| BMI (kg/m2) | 26.3±6.2 | 26.6±5.3 | .86 |
In a multivariate model (table 4), osteoporosis at the hip was significantly associated with strength sum score in the same lower extremity (odds ratio [OR], .42 per 5-point increase in strength score; 95% CI, .28−.64; P<.001) after adjusting for time since acute polio (OR=1.04; 95% CI, 1.00−1.09; P=.03), age at evaluation less than 50 years (OR=.47; 95% CI, 0.14−1.50; P=.20), male sex (OR=.87; 95% CI, 0.28−2.62; P=.80), and interaction between weight and sex (P=.08). Being overweight appeared to be harmful for men (OR=2.4; 95% CI, 0.71−8.00) and protective for women (OR=0.57; 95% CI, 0.19−1.71).
Table 4. Adjusted (multivariate model) ORs for Osteoporosis at the Hip
| Variable | OR | 95% CI | P |
|---|---|---|---|
| Strength sum score in same lower extremity (per 5-point increase in strength score) | 0.42 | 0.28–0.64 | <.001 |
| Age at evaluation (<50y) | 0.47 | 0.14–1.5 | .20 |
| Overweight (BMI >25kg/m2) | |||
| For men | 2.37 | 0.71–8.0 | .08⁎ |
| For women | 0.57 | 0.19–1.71 | |
| Time since acute polio (y) | 1.04 | 1.003–1.089 | .03 |
| Male sex | 0.87 | 0.28–2.62 | .80 |
⁎P value for interaction. |
Discussion
In this exploratory study, we found that osteoporosis and osteopenia at the hip were common in men and in premenopausal and postmenopausal women who are referred for bone densitometry in a postpolio clinic population. However, we found a lower frequency of osteoporosis at the lumbar spine in our population. A significant correlation was found between bone mass and muscle strength (strength sum score in the same lower extremity in which bone densitometry was performed) in both our univariate and multivariate analyses. We did not find other significant associations between bone mass and other known risk factors such as smoking, alcohol consumption, age, and sex.
To our knowledge, this is the most comprehensive study of osteoporosis in postpolio patients to date. Osteoporosis is likely underdiagnosed in this population and in other neuromuscular disorders, especially in men and premenopausal women. Osteoporosis is mostly associated with older patients, primarily postmenopausal women, leaving this group of high-risk patients without appropriate treatment. Our findings of a high frequency of osteoporosis in a postpolio clinic population and a significant correlation of bone mass with lower-extremity muscular strength should alert clinicians and prompt them to systematically refer these patients for bone densitometry.
We found that osteoporosis at the hip was common in a postpolio clinic population in men (32%) and in premenopausal (12.5%) and postmenopausal women (27%). These numbers are higher than those for the general population for men at the hip in Canada (4.8%)12, 14 and for postmenopausal women at the hip in Canada (7.9%).2, 11, 12 We found that the frequency of osteopenia is very high in a postpolio clinic patient population in 3 different groups (men, 45%; premenopausal women, 37.5%; postmenopausal women, 34%). Therefore, these patients are at high risk for developing osteoporosis in the future. It has been shown that the fracture risk increases 1.5- to 3-fold for each SD decrease in BMD2 and that, at any given age, the lifetime risk of a proximal femoral fracture rises as bone density diminishes.6, 15, 16
Surprisingly, the T-score values obtained at the lumbar spine in our population did not show the same prevalence for osteoporosis as at the hip. One explanation for this finding would be that most of our patients likely have degenerative disorders of the spine, including scoliosis in some. These musculoskeletal abnormalities can likely falsely elevate the T score at the lumbar spine, as described in previous studies.17 Another explanation could be that in this patient population osteoporosis may be a regional phenomenon; the primary predictive factor for osteoporosis at the hip was weakness in the same lower extremity. Therefore, those patients with lower-extremity weakness are more susceptible to regional osteoporosis affecting mostly the hip rather than diffuse osteoporosis affecting both the lumbar spine and the hip.18 Similar findings have been reported in the spinal cord injury population.19, 20 These patients also have a higher prevalence of osteoporosis at the hip compared with the vertebral spine likely related to immobilization.19, 20 Nonetheless, osteoporosis, even if localized primarily to the hip, remains an important risk factor for hip fractures.6, 16, 21 In fact, hip fracture is most closely linked to BMD compared with other types of fractures.2, 16, 21
Moreover, in this exploratory study, in our multivariate model, we found a significant association between osteoporosis at the hip and strength sum score in same extremity with an OR of .42 for each 5-point increase in the strength sum score, after adjusting for several other risk factors (time since acute polio, age at evaluation, male sex). This indicates that with each 5-point increase in the strength sum score (ie, greater strength), postpolio clinic patients were less likely to have osteoporosis (by a factor on average of .42). In addition, we found that an increased time since acute polio (with resultant muscular weakness) was a significant predictor of osteoporosis, stressing once again the protective aspect of muscle strength. Our study reflects the important role that muscle strength plays in protecting bone from osteoporosis.4, 8, 18 In fact, it has been shown that in the general population being physically active reduces the risk of later hip fracture by up to 50%.8, 21, 22
An unexpected finding in our study was that being overweight appeared to be harmful for men tending to increase their risk to have osteoporosis, whereas for women being overweight tended to be protective. Several previous studies have shown that a low body weight is negatively correlated with peak bone mass.8 In fact, the more weight a woman gains since age 25, the lower her risk of hip fracture.5 In addition, higher adiposity is protective against the risk of both hip and vertebral fractures in women.7, 8, 22 However, we do not believe that previous studies have shown a difference in the association between osteoporosis and BMI in men and women.
Study Limitations
Our study had several potential limitations. The patients included in our study were from a university-affiliated hospital postpolio clinic and those that had undergone a bone densitometry as requested by the clinic physician. They were likely more severely affected by previous paralytic polio and more likely at greater risk for osteoporosis. Hence, our estimate on the prevalence of osteoporosis may be overestimated compared with the general postpolio population. The patients included in our study were in fact weaker than those not included. Nevertheless, the bone densitometry assessments performed were not always on the weaker side (the left side is usually done by convention). In fact, 19.3% were performed on the weaker side in men, 18% in premenopausal women, and 12% in postmenopausal women. This could have underestimated the prevalence of osteoporosis with normal bone densitometry results when not performed on the weaker side. Our study did not find a significant correlation between bone density and alcohol or tobacco use, which are 2 recognized risk factors.2, 5, 8, 21 This can be explained by an insufficient number of patients who used alcohol or tobacco and by the fact that the exact amount of cigarettes and alcohol consumption was not recorded. This study had potential bias because some potential predictive factors were ascertained by self-report and retrospectively. The strengths of our study are the relatively large study population, study comprehensiveness, and consistency in data acquisition and ascertainment of bone density (most patients evaluated at the same radiologic department and all patients evaluated by the same physician by using a standardized form).
Conclusions
In this retrospective, cross-sectional study, we found that osteoporosis and osteopenia at the hip occur commonly in postpolio clinic patients referred for bone densitometry in men, premenopausal women, and postmenopausal women compared with the general population. However, because patients included in the study were weaker than patients not included, our estimates of the occurrence of osteoporosis in a postpolio clinic population are likely elevated. Hip bone density was associated with muscle strength in the same lower extremity in which the examination was performed in men, premenopausal women, and postmenopausal women attending a postpolio clinic in both unadjusted and adjusted multivariate analyses. The diagnosis can therefore be missed if the bone densitometry is not performed on the same side as the weaker lower extremity. Based on these results, we recommend that all postpolio patients be evaluated for osteoporosis at both hips (or less preferably at the hip of the weaker lower extremity) and at the lumbar spine. It is possible that with treatment BMD will improve and fracture risk will decline. We recommend further research to confirm the results of our exploratory study and to evaluate the effects of treatment on osteoporosis and fracture rate in the postpolio and other neuromuscular disease patient populations.
Supplier
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- a Version 8.02; SAS Institute Inc, 100 SAS Campus Dr, Cary, NC 27513.
Supported by the Polio Quebec Association and the Montreal Neurological Institute (salary support).
No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.
Reprints are not available from the author.
PII: S0003-9993(07)00353-X
doi:10.1016/j.apmr.2007.05.010
© 2007 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.
Volume 88, Issue 8 , Pages 1030-1035, August 2007
