Orthopedics

Orthopedic Surgery in Korea 

ASSESSMENT OF BONE MINERAL DENSITY IN POSTMENOPAUSAL AND SENILE OSTEOPOROSIS USING QUANTITATIVE CT

Jun Seop Jahng, MD; Koon Soon Kang, MD; Hui Wan Park, MD; Myoung Hoon Han, MD

Abstract

ABSTRACT

The authors analyzed bone mineral density in 213 patients from January 1988 to September 1989. Bone mineral density of the vertebral body in the osteoporosis group of patients was compared with that in the normal group to investigate the correlation between bone mineral density and age distribution, and to estimate fracture threshold in the osteoporosis group. It was fonnd that men, by linear regression, lose an average of 0.91 % of bone per year, and women, by cubic regression, lose an average of 1.14% per year, accelerating at menopause. In the osteoporotic group, bone mineral density of men decreased an average of 29.7% compared with the nonosteoporotic gronp; that of women decreased an average of 29.9%. There was no difference between sexes. The fracture threshold of the osteoporotic patient was estimated to be about 90 mg/cmp 3.

Abstract

ABSTRACT

The authors analyzed bone mineral density in 213 patients from January 1988 to September 1989. Bone mineral density of the vertebral body in the osteoporosis group of patients was compared with that in the normal group to investigate the correlation between bone mineral density and age distribution, and to estimate fracture threshold in the osteoporosis group. It was fonnd that men, by linear regression, lose an average of 0.91 % of bone per year, and women, by cubic regression, lose an average of 1.14% per year, accelerating at menopause. In the osteoporotic group, bone mineral density of men decreased an average of 29.7% compared with the nonosteoporotic gronp; that of women decreased an average of 29.9%. There was no difference between sexes. The fracture threshold of the osteoporotic patient was estimated to be about 90 mg/cmp 3.

Osteoporosis is a skeletal condition characterized by reduction in bone mass and an increased vulnerability to fracture, particularly of the proximal femur and the vertebrae. Unfortunately, osteoporosis does not usually manifest itself until a patient presents with a fracture. For this reason, it has been referred to as the silent epidemic. While radiologic examination remains the mainstay in the diagnosis of osteoporosis, there are certain disadvantages associated with this technique. Almost one third of the skeletal mass must be lost before osteoporosis becomes apparent on a plain radiograph, and radiologic artifacts are not uncommon.

Many methods have been developed for quantitative assessment of the skeleton. Consequently, osteoporosis can be detected early, and its progression and response to therapy can be monitored carefully. Recently, quantitative computed tomography has been investigated as a means for noninvasive quantitative determination of bone mineral density of the spine. A highly significant correlation has been found between vertebral trabecular mineral amount and the quantity determined by quantitative CT. Furthermore, vertebral strength and failure load have been found to correlate well with trabecular density determined by quantitative CT.

MATERIALS AND METHODS

The authors analyzed 213 patients from January 1988 to September 1989 with complaints of back pain and other symptoms. The ages ranged from 21 to 87. There were 101 men and 112 women. Age and sex distribution are shown in Table 1.

A lumbosacral film was taken of all patients, who were then divided into two groups: patients with no back pain were graded as 0, 1 by Seville's index (normal group); and those who had frequent and longstanding back pain were graded as 2,3,4 by Seville's index (osteoporosis group).

The normal group consisted of 136 patients (67 men and 69 women). The osteoporosis group consisted of 77 patients (34 men and 43 women). Their ages ranged from 42 to 87 years. Thirty-seven patients showed spontaneous compression fracture with osteoporosis by lumbosacral plain film (Table 2).

Table

Table 1AGE AND SEX DISTRIBUTION

Table 1

AGE AND SEX DISTRIBUTION

Table

Table 2AGE AND SEX DISTRIBUTION IN THE OSTEOPOROSIS GROUP WITH COMPRESSION FRACTURE

Table 2

AGE AND SEX DISTRIBUTION IN THE OSTEOPOROSIS GROUP WITH COMPRESSION FRACTURE

Table

Table 3AGE AND SEX DISTRIBUTION AND BONE MINERAL DENSITY (mg/cmp 3) IN THE NORMAL GROUP

Table 3

AGE AND SEX DISTRIBUTION AND BONE MINERAL DENSITY (mg/cmp 3) IN THE NORMAL GROUP

Table

Table 4AGE AND SEX DISTRIBUTION AND BONE MINERAL DENSITY (mg/cmp 3) IN THE OSTEOPOROSIS GROUP

Table 4

AGE AND SEX DISTRIBUTION AND BONE MINERAL DENSITY (mg/cmp 3) IN THE OSTEOPOROSIS GROUP

Patients with metabolic or endocrinologie disease, or other chronic illness or compression fracture by trauma were excluded from this study.

All patients were examined by quantitative CT (model 8800, GE). A custom-made, crescentshaped calibration phantom consisting of separate chambers filled with 0, 50, 100, 150, and 200 mg/cmp 3 Kp 2HPO4 solution was placed under the patient during scanning. An average CT value was determined at the central trabecular portion of the first, second, and third lumbar vertebral bodies. Because of the many compression fractures in the first and second lumbar vertebral body, we chose the third lumbar vertebral body as the measuring site of bone mineral density. In cases of compression fracture of the third lumbar vertebral body, we obtained the bone mineral density at the first and second lumbar.

RESULTS

Age and sex distribution and their bone mineral densities in the normal group are shown in Table 3 and Figure 1 . After 20 years of age, men lose an average of 0.83% of bone per year and women lose an average of 0.96% of bone per year. The women's loss seems to accelerate during and after menopause.

To be exact, premenopausal women lose an average of 0.80% per year, and postmenopausal women lose 1.2% per year. When the bone mineral densities of the same age group were compared, there was no statistically significant difference between first, second, and third lumbar vertebral bodies or between sexes.

Age-related changes of bone mineral density in the osteoporosis group are shown in Table 4. There was a similar pattern in the normal control group. The bone mineral densities of the osteoporosis group are lower than those of the normal group, averaging 29.4% for men and 29.9% for women. There was little difference between sexes (Table 4, Fig 2).

In the osteoporosis group, compression fractures occurred in 37 cases (25 cases in the first lumbar vertebra, 10 cases in the second vertebra, and 2 cases in the third vertebra). We chose the bone mineral density of the third lumbar vertebral body for the base of data. The distribution of bone mineral density by age change in the osteoporosis group is shown in Table 5 and Figure 3. Although the number of cases was not enough to suggest the fracture threshold, we noted that compression fractures were liable to occur from below 100 mg/cmp 3 of bone mineral density. Also, the incidence of fracture increased up to 90% below 90 mg/cmp 3 of bone mineral density.

Consequently, we suggested that 90 mg/cm3 of bone mineral density be the fracture threshold for the normal Korean. We investigated fracture threshold by calculating the fracture rate in the same bone mineral density group when it is above 90%.

Among 46 men over 50 years old, 26 (56.5%) had osteoporosis and 9 (19.6%) had a spontaneous compression fracture. Among 63 women over 50 years, 36 (57.1%) had osteoporosis and 25 (39.7%) had a spontaneous compression fracture. Among 67 postmenopausal women, 43 (64.2%) showed osteoporosis on the plain film, and 26 (38.8%) had compression fractures on the vertebral body. The age-related compression fracture rate is shown in Table 6.

DISCUSSION

Osteoporosis is a metabolic bone disease that results in decreased density of bone; it is second only to arthritis as the leading cause of musculoskeletal morbidity in elderly people.1'3 It is closely related to the cause of fractures, because decreased bone mineral content leads to the loss of absorptional capacity for external forces.4,5 Thus, fractures of the vertebrae, the proximal end of the femur, and the distal part of the forearm occur frequently in elderly people. Because these fractures in elderly patients often lead to many complications, it is important to prevent osteoporosis.5-8

Many methods have been developed for quantitative assessment of the skeleton that enable osteoporosis to be detected early and assist the careful monitoring of its progression and response to therapy. Numerous methods such as the Singh index of the femoral neck,9 radiogrammetry of metacarpal bone, photon absorptiometry,10 compton scattering, and quantitative CT have been studied. In recent years, both dual energy absorptiometry and quantitative CT have been investigated as a means for noninvasive quantitative determination of bone. However, measurement by dual energy absorptiometry, although decreasing the radiation exposure from quantitative CT, requires contributions from both cortical and trabecular bone of the vertebral body and from the posterior element. Elderly patients with osteoporosis, who are the main subjects for study, often exhibit endplate sclerosis, osteophyte formation, articular facet hypertrophy, and aortic calcification; these changes can be expected to make uncertain contributions to vertebral strength.11-13

The measurement by quantitative CT excluded these causes of low sensitivity or error and included purely trabecular bone. The radiation exposure is 10 to 15 minutes of approximately 200 mrem (one tenth the dose of a routine CT study) and recent improvements in CT scanner technique have further increased precision and reduced radiation exposure.14-16

Fig 1: Age-related change of bone mineral density in the normal group.

Fig 1: Age-related change of bone mineral density in the normal group.

Fig 2: Age-related change of bone mineral density in the osteoporosis group.

Fig 2: Age-related change of bone mineral density in the osteoporosis group.

The source of any error on quantitative CT is mechanical. Reproducibility for selective scanning localization from the amount of marrow fat and beam hardening effect reduce the measured spinal mineral density.17

Table

Table 5FRACTURE THRESHOLD IN POSTMENOPAUSAL AND SENILE OSTEOPOROSIS

Table 5

FRACTURE THRESHOLD IN POSTMENOPAUSAL AND SENILE OSTEOPOROSIS

Fig 3: The distribution of bone mineral density according to age change in the osteoporotic group.

Fig 3: The distribution of bone mineral density according to age change in the osteoporotic group.

Quantitative CT numbers exhibited a significant positive correlation with direct measurements of the apparent density of the vertebral trabecular bone. The strong correlation between quantitative CT and vertebral compression strength suggests that quantitative CT should be investigated clinically as a predictor of the risk of vertebral fracture.18

All patients were examined by lumbosacral plane film and divided into two groups according to Seville's index.19

Osteoporosis is a metabolic bone disease whose incidence is closely related to the aging process. There have been many studies of change in age-related bone mineral density. Morgan20 and Johnston et al21 reported that the loss of bone mineral density starts from the fifth decade in the female and from the sixth decade in the male.7

Richardson et al16 and Cann et al22 reported that men lose an average of 0.94% of bone per year and that women lose an average of 1 .2% of bone per year, accelerating at menopause. Fujii et al23 reported that men lose an average of 0.9% per year and women lose an average of 1 .2% per year in healthy Japanese. Our findings show similar age-related bone loss. However, studying the bone mineral density of a normal Korean by utilizing dual photon absorptiometry, Lim et al24 reported that men (the age-related change of bone mineral density) show linear regression of 0.3% per year, while women show a cubic pattern, increasing so significantly in me third and fourth decades that they reach a peak bone mass at about 35 years of age. Then women show a slow decrease of 0.7% per year until 50 years of age, and a rapid decrease of 1 .2% per year after 50 years of age. This slows to 0.55% per year after 65 years of age.

Bone mineral density by age using quantitative CT25 and dual photon absorptiometry2,24,26 is lower than thai of American whites, revealing the racial difference. Recently, Fujii et al23 reported that in a comparison with American whites of comparable age and sex, the Japanese appeared to have about 20 mg/cm3 lower vertebral trabecular bone mineral density at all ages. Our results show no significant difference from American whites.8,11,16,17,23 We suggest further studies on the measurement of the bone mineral density in healthy Koreans.

Contributing factors to osteoporosis in females are decreased activity, menopause, birth control, nutrient imbalance, and intake of hyperphosphate diet.26

Johnston et al21 and Wallach8 reported that the frequency of osteoporosis is well recognized. Fifty percent of women who are 45 years old or older exhibit radiographic evidence of osteoporosis in the lumbar spine. McBroom et al18 found that in 44% of the subjects spontaneous fracture occurred during or after menopause.

In the present study, 38.8% of postmenopausal women showed a compression fracture of the vertebral body not caused by external forces.

Riggs et al7 defined the fracture threshold of the vertebral body as 0.965 g/cmp 2 by calculating bone mineral density on the 90th percentile from low level using dual photon absorptiometry. Buchanan et al27 proposed the following guideline for use of quantitative CT in assessing prophylaxis and treatment of osteoporosis in postmenopausal women: in patients with an initial measurement of bone density of more than 125 mg/cmp 3, the bone density should be remeasured at intervals of 2 years. If the initial value is between 100 and 125 mg/cmp 3, the measurement should be repeated annually. They consider a value between 70 and 1 00 mg/cmp 3 to be a relative indicator for prophylaxis and a value of less than 70 mg/cmp 3 to be an absolute indicator for vigorous prophylaxis and treatment of fracture.

In this study, we suggest that the fracture threshold is about 90 mg/cmp 3, calculating fracture rate in the same bone mineral density interval whenever it is above 90%. Genant et al14 suggested that the fracture threshold of the vertebral body is about 110 mg/cmp 3.

There is a need for further studies of the age-related changes of bone mineral density, especially after menopause, the effectiveness of treatment, and a possible relationship between the incidence of second fracture and bone mineral density.

Table

Table 6OSTEOPOROSIS AND FRACTURE RATE

Table 6

OSTEOPOROSIS AND FRACTURE RATE

REFERENCES

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5. Lane JM, Vigorita VJ. Osteoporosis (current concepts review). J Bone Joint Surg. 1 983; 65A:274-278.

6. Cann CE, Genant HK, KoIb FO, Ettinger BE. Quantitative computed tomography for prediction of vertebral fracture risk. Metab Bone Dis. 1984; 5:1-7.

7. Riggs BL, Wanner HW, Differential changes in bone mineral density of the appendicular axial skeleton with aging. J Clin Invest. 1981; 67:328-335.

8. Wallach SH. Management of osteoporosis. Hosp Pract. 1978; 13(12):91-98.

9. Pogrund H, Rigai WM, Makin MR. Determination of osteoporosis in patient with fractured femoral neck using the Singh index. A Jerusalem Study. Clin Orthop. 1981; 156: 189195.

10. Posner I. Griffiths HJ. Comparison of CT scanning with photon absorptiometric measurement of bone mineral content in the appendicular skeleton. Invest Radiol. 1977; 12:542-544.

11. Genant HK, Ettinger B, Cann CE. Osteoporosis: assessment by quantitative tomography. Orthop Clin North Am. 1985; 16:557-568.

12. Powell MR, KoIb FO. Genant HK, Cann CE, Stabler BG. Comparison of dual photon absortiometry and quantitative computed tomography of the lumbar spine in the same subject. In: Frame B, Potts JT (eds). Clinical Disorders of Bone Mineral Metabolism. Amsterdam: Excerpta Medica; 1985:58-61.

13. Sambrook PN, Bartlett C, Evans R, Hesp R, Kartz D, Reeve J. Measurement Of lumbar spine bone mineral: a comparison of dual photon absorptiometry computed tomography. Br J Radiol. 1985; 58:621-624.

14. Genant HK, Wilson JS. Bovili EG. Computed tomography of musculoskeletal system. J Bone Joint Surg. 1980; 62A: 1088-1101.

15. Grethe FJ, Claus C. Epidemiology of postmenopausal spine and long bone fracture. Clin Orthop. 1982; 166:75.

16. Richardson ML, Genant HK, Cann CE, et al. Assessment of metabolic bone diseases by computative computed tomography. Clin Orthop. 1985; 195:224-238.

1 7. Block. JE. Smith R, Glueer CC, Steiger P, Ettinger B, Genant HK. Models of spinal trabecular bone loss as determined by quantitative computed tomography. J Bone Min Res. 1989;4:249-257.

18. McBroom RJ, Hayes WC. Edward WT, Godenberg RP, White AA III. Prediction of vertebral body compressive fracture using quantitative tomography. J Bone Joint Surg. 1985;67A:1206-1214.

19. Savi lie PD, Kharmosh 0. A quantitative approach to simple radiographic diagnosis of osteoporosis: its application to the osteoporosis of rheumatoid arthritis. Arthritis Rheum. 1967; 10:5.

20. Morgan DB. Aging and osteoporosis in particular spinal osteoporosis. Clin Endocrinol. 1973; 2:187-201.

21. Johnston DD Hr. Norton JA, Kairi RA. Age related bone loss. In Barzel A (ed). Osteoporosis II. 1977:91-100.

22. Cann CE, Martin MC, Genant HK. Jaffe RB. Decreased spinal mineral content in premenopausal amenorrheic women. JAMA. 1984;251:626-629.

23. Fujii Y, TsuLsumi M, Tsuenenari T, et al. Quantitative computed tomography of lumbar vertebrae in Japanese patients with osteoporosis. Bone and Mineral. 1989; 6:8794.

24. Lim SK, Huh KB, Park BM, Kim NH. Bone mineral density of normal Korean adults. Journal of the Korean Medical Association. 1988; 31: 1350-1358.

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Table 1

AGE AND SEX DISTRIBUTION

Table 2

AGE AND SEX DISTRIBUTION IN THE OSTEOPOROSIS GROUP WITH COMPRESSION FRACTURE

Table 3

AGE AND SEX DISTRIBUTION AND BONE MINERAL DENSITY (mg/cmp 3) IN THE NORMAL GROUP

Table 4

AGE AND SEX DISTRIBUTION AND BONE MINERAL DENSITY (mg/cmp 3) IN THE OSTEOPOROSIS GROUP

Table 5

FRACTURE THRESHOLD IN POSTMENOPAUSAL AND SENILE OSTEOPOROSIS

Table 6

OSTEOPOROSIS AND FRACTURE RATE

10.3928/0147-7447-19911001-08

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