Measurement of Bone Density Around Total Knee Arthroplasty Using Fan-Beam Dual Energy X-ray Absorptiometry

The clinical survival of joint arthroplasties is clearly associated with the quality of surrounding bone environment. Bone mineral density (BMD) is an important measure of bone strength and quality. Periprosthetic BMD can be measured by using dual-energy X-ray absorptiometry (DXA) with special software algorithms. We studied short-term reproducibility of the periprosthetic BMD measurements after total knee arthroplasty (TKA) in 30 patients with primary osteoarthrosis. The operated knees and the contralateral control knees were measured twice and the results were expressed as a coefficient of variation (CV%). The average precision error was 3.1% in femoral regions of interest (ROI) and 2.9% in tibial ROIs after TKA. In the prosthesis-free control knees, CV% were similar; 3.2% and 2.5%, respectively. The best precision was found in the femoral diaphyses above the implant (1.3%), whereas the least reproducible BMD was determined in the patellar region of the TKA knees (6.9%). Our results confirm that DXA measures precisely small bone mineral changes around TKA and makes it possible to follow bone remodeling DXA and may provide a feasible method for monitoring TKA in the future. Received: 16 September 1998 / Accepted: 29 February 2000     

Dual Energy X-Ray Absorptiometry in Small Rats with Low Bone Mineral Density

The feasibility of dual energy X-ray absorptiometry (DXA) using the Norland XR-26 Mark II bone densitometer for measurements of bone mineral content (BMC) and bone mineral density (BMD) in small rats was evaluated. Thirty-two young, isogenic, Lewis rats (weights from 119 g to 227 g) were used; normal rats (n = 7) and rats with low BMD obtained from three different vitamin D-depleted models (n = 25). DXA measurements were performed using the special software for small animals. Duplicate scans of excised femurs performed at 2 mm/second (pixel size of 0.5 mm × 0.5 mm) were very precise measurements with a coefficient of variation (CV) below 1.6% in animals with normal BMD; in rats with low BMD, the CV was significantly higher (P= 0.02–0.04), 7.8% and 4.4% for BMC and BMD, respectively. Regression analysis demonstrated that these measurements were related to the ash weight (R² > 98.6%). The CV for measurements of the lumbar spine at 10 mm/second (pixel size 0.5 mm × 0.5 mm) was 2.6% and 2.2% for BMC and BMD, respectively in rats with normal BMD, and again higher (P= 0.03–0.14) in rats with low BMD, 7.3% and 4.7%, respectively, for BMC and BMD. Even though low CVs were obtained for total body duplicate scans (scan speed of 20 mm/second and a pixel size of 1.5 mm × 1.5 mm), the measurements were problematic for accuracy because of an overestimation of both BMC and the area of bone. Using these scan parameters the measurements of total body bone mineral could not be recommended in small rats with low BMD. Received: 21 May 1999 / Accepted: 3 August 2000 / Online publication: 22 December 2000     

The Relation Between Trabecular Bone Strength and Bone Mineral Density Assessed by Dual Photon and Dual Energy X-Ray Absorptiometry in the Proximal Tibia

The feasibility of two noninvasive methods [dual photon absorptiometry (DPA) and dual energy X-ray absorptiometry (DXA)] for prediction in vivo of local variations of trabecular bone strength within the proximal tibia was evaluated in 14 cadaveric knees. Trabecular bone strength was measured using an osteopenetrometer and from destructive compression tests performed on bone cylinders, thus measuring the penetration strength and ultimate strength in the medial, lateral, and central part of the tibial bone specimens. Linear regression analysis showed significant relations between BMD measured by DPA (r²= 72%) or DXA (r²= 73%) and ultimate strength. Even closer relations between BMD (DPA: r²= 80%, DXA r²= 81%) and penetration strength of trabecular bone were found. We conclude that DPA and DXA are suitable methods for evaluation in vivo of local variations in trabecular bone strength within the proximal tibia, and could easily be performed preoperatively before insertion of total knee arthroplasty. Received: 7 September 1995 / Accepted: 16 February 1996     

Influence of Spondylopathy on Bone Densitometry Using Dual Energy X-Ray Absorptiometry

Spinal cord injury (SCI), as well as other neuromuscular disorders, not only results in osteopenia but also induces various patterns of osseous, articular, and soft tissue alterations. In the spinal column, a variety of abnormalities occur. To evaluate the magnitude of discrepancy of bone densitometry results caused by spondylopathy in SCI patients, we analyzed anteroposterior (AP) radiographs of the lumbar spine [obtained within 1 month of dual energy X-ray absorptiometry (DXA)] in 116 SCI patients for various manifestations of spondylopathy, and matched the result to each vertebral level (L1, 2, 3, 4). The dataset was stratified by individual vertebra (totally 463 vertebrae) as valid (no demonstrable other abnormal density on plain radiograph except osteopenia), abnormal without, and abnormal with hardware. The influence of spondylopathy on bone densitometry results was determined by the analysis of variance (ANOVA) and post hoc analysis. Our results showed that 227 (49%) vertebrae were abnormal. Significant elevation (15%, 15%, 18%, 20%; P < 0.001–P < 0.05) of bone mineral density (BMD; g/cm²) was observed at all levels (L1, 2, 3, 4, respectively), particularly at those abnormal vertebrae without hardware compared with valid (no other abnormal density on radiograph except osteopenia (Table 1). The L4 level was most severely affected. We concluded that in SCI patients, owing to various secondary progressive skeletal abnormalities, particularly neuropathic spondylopathy, can have strongly and significantly elevated vertebral bone densitometry results, which can obscure underlying osteoporosis, leading to misinterpretation and underestimation of fracture risk. DXA, although characterized by improving spatial resolution, cannot replace radiography in establishing the magnitude of this skeletal pathology. Therefore, determination of bone density in this region with corresponding plain radiographs is highly recommended. Received: 30 July 1996 / Accepted: 3 December 1996     

Impact of Spinal Degenerative Changes on the Evaluation of Bone Mineral Density with Dual Energy X-Ray Absorptiometry (DXA)

The purpose of this study is to evaluate degenerative factors in a postmenopausal patient group and differentiate the influence on bone mineral density (BMD) measurements by dual-energy X-ray absorptiometry (DXA). The patients and methods included an investigation of 144 postmenopausal women (mean 63.3 years) with PA-DXA of the spine. Degenerative factors (osteophytes, osteochondrosis, scoliosis, and vascular calcification) were evaluated from plain lumbar radiographs, their estimated probability was analyzed as a function of age, and their influence on BMD measured by PA-DXA was determined. The results of the study revealed osteophytes in 45.8%, vascular calcifications in 24.3%, scoliosis in 22.2%, osteochondrosis in 21.5%. The estimated probability for degenerative factors increased from 35 to 80% in the 55- to 70- year age group. Osteophytes and osteochondrosis were associated with up to a 14% increase in BMD values (P < 0.001). Vascular calcifications showed a positive trend, whereas scoliosis did not show a discernible influence. We concluded that degenerative factors, except for scoliosis, showed an influence on BMD as measured by DXA. Their prevalence increased rapidly between 55 and 70 years of age. Interpretation of PA-DXA spine data for subjects of or above this age range should be complemented by plain film radiographs. Received: 30 May 1996 / Accepted: 24 July 1996     

Calcaneus Bone Mineral Density Using Single X-ray Absorptiometry in Japanese Women

Calcaneus bone mineral density (BMD) of 738 Japanese women (605 healthy and 133 with osteoporosis) was measured using single X-ray absorptiometry (SXA). A reference range of calcaneus BMD values for healthy Japanese women was established and the usefulness of this method for screening and diagnosis of osteoporosis was evaluated. There was no significant age change of calcaneus BMD prior to menopause, though values decreased significantly thereafter. BMD loss ratio was 1.7%/year in the 10 years after menopause. The reference range of calcaneus BMD was 410 ± 43 mg/cm², calculated from the mean BMD value of subjects whose ages ranged from 25 to 50 years old. The fracture threshold for the spine was established as 294 mg/cm², which corresponded to −2.67 SD from the average BMD of the young healthy women, and the odds ratio for spine fracture in the subjects with BMD lower than this threshold was 3.52 [95% CI (confidence interval) 1.34–9.26]. The spine fracture group showed statistically lower calcaneus BMD than the nonfracture group when subjects with adjusted age and body size were analyzed. There were no significant differences in the ROC analysis for spine fracture between calcaneus BMD and spine BMD. Therefore, calcaneus BMD is not readily affected by degenerative change or soft tissue, and the annual decrement rate (1.7%/year) can be detected easily and with low precision error (0.8%). These indices may prove useful for the screening and diagnosis of osteoporosis. Received: 16 September 1998 / Accepted: 28 January 1999     

Measurement of Bone Mineral Density by Dual X-ray Absorptiometry in Paget's Disease Before and After Pamidronate Treatment

Third-generation bisphosphonates are now currently used in the treatment of Paget's disease of bone. Dual X-ray absorptiometry may make it possible to quantify the action of these bisphosphonates on bone mineral density (BMD) in pagetic and nonpagetic bone. We used Lunar DPX, a total-body software program (automatic analysis and/or manual windows according to the site and bilateral or unilateral pagetic involvement) to study BMD in 28 patients (18 men, 10 women, mean age 69.8 years) with Paget's disease before and 6 months after infusions of 60 mg (alkaline phosphatase <350 IU) or 120 mg (ALP >350 IU) of pamidronate. Before treatment, in the 28 patients, the BMD of trabecular pagetic bone was 25% higher than that of nonpagetic bone; in cortical pagetic bone the BMD was 35% higher. After treatment, the BMD of trabecular pagetic bone increased by only 1.17%. the BMD of cortical pagetic bone increased by 1.37% whereas nonpagetic cortical bone lost 0.84%, independently of the levels of parathyroid hormone or the administration of calcium and vitamin D. Received: 17 March 1998 / Accepted: 12 March 1999     

Bone Mineral Content and Density in Professional Tennis Players

Total and regional bone mineral content (BMC) as well as lean and fat mass were measured in nine male professional tennis players (TPs) and 17 nonactive subjects; dual-energy X-ray absorptiometry (DXA) was used for measuring. The mean (±SD) age, body mass, and height were 26 ± 6 and 24 ± 3 years, 77 ± 10 and 74 ± 9 kg, and 180 ± 6 and 178 ± 6 cm for the TP and the control group (CG), respectively. The whole body composition for BMC, lean mass, and fat of the TP was similar to that observed in the CG. The tissue composition of the arms and legs was determined from the regional analysis of the whole-body DXA scan. The arm region included the hand, forearm, and arm, and was separated from the trunk by an inclined line crossing the scapulo-humeral joint. In the TP, the arm tissue mass (BMC + fat + lean mass) was about 20% greater in the dominant compared with the contralateral arm because of a greater lean (3772 ± 500 versus 3148 ± 380 g, P < 0.001) and BMC (229.0 ± 43.5 versus 188.2 ± 31.9 g, P < 0.001). In contrast, no significant differences were observed either in BMC or BMD between arms in the CG. Total mass, lean mass, and BMC were greater in the dominant arm of the TP than in the CG (all P < 0.05). In the TP, BMD was similar in both legs whereas in the CG, BMD was greater in the right leg. Lumbar spine (L2–L4) BMD, adjusted for body mass and height, was 15% greater in the TP than in the CG (P < 0.05). Femoral neck BMDs (femoral neck, Ward's triangle, greater trochanter, and intertrochanteric regions) adjusted for body mass and height were 10–15% greater in the TP (all P < 0.05). Ward's triangle BMD was correlated with the maximal leg extension isometric strength (r = 0.77, P < 0.05) even when adjusted for body mass (r = 0.76, P < 0.05) and height (r = 0.77, P < 0.05). In summary, the participation in tennis is associated with increased BMD in the lumbar spine and femoral neck. These results may have implications for devising exercise strategies in young and middle-aged persons to prevent involutional osteoporosis later in life. Received: 29 April 1997 / Accepted: 14 November 1997     

Comparative Assessment of Bone Mineral Measurements Using Dual X-ray Absorptiometry and Peripheral Quantitative Computed Tomography

A measurement of bone mass is the single most important determinant of future fracture. However, controversy exists as to which technique (dual X-ray absorptiometry (DXA) or peripheral quanitative computed tomography (pQCT)), and which site of skeletal measurement (axial vs appendicular) provides the best prediction of fracture risk. The aims of this study were: (1) to determine the ability of pQCT to predict bone mass of the lumbar spine, proximal femur, and distal forearm measured using DXA, and (2) to compare the ability of DXA and pQCT to discriminate prevalent fractures in women with established osteoporosis. One hundred and sixty-five women were studied, including 47 with established osteoporosis (vertebral, hip or Colles' fractures) as well as 118 who had bone mass measurements to assess osteoporosis risk. Each subject had bone mass measured by DXA at the lumbar spine and femoral neck, and at the distal radius by both DXA and pQCT. In women with fractures, bone mass, when expressed as a standardized score, was in general lower using DXA compared with the appendicular skeleton measured using pQCT. Bone mass determinations at all sites were significantly correlated with each other. The highest correlation coefficients were observed within the axial skeleton. In women with fractures, the highest odds ratios were observed at skeletal regions measured using DXA. Likewise, the areas under the receiver-operating characteristic (ROC) curves were comparable at all skeletal regions measured using DXA; and were significantly greater than the areas under the ROC curves for pQCT measurements. In summary, the strongest discriminators of prevalent fractures were measurements using DXA. Measurements of bone mass at the appendicular skeleton, using either DXA or pQCT, were poorly associated with axial bone mass. PQCT has the poorer ability to discriminate persons with fractures, and appears to be less sensitive than measurements using DXA. Received: 15 September 1997 / Accepted: 17 February 1998     

Osteoporosis After Gastrectomy: Bone Mineral Density of Lumbar Spine Assessed by Dual-Energy X-ray Absorptiometry

Although osteoporosis is a common clinical disorder associated with gastric surgery, long-term effects of gastrectomy on bone metabolism are still unclear. The purpose of this study was to clarify the incidence and risk factors of osteoporosis after gastrectomy using univariate and multivariate analyses of quantitative measurements. The study included 59 patients who had undergone gastrectomy more than 5 years before. There were 38 men and 21 women, aged 37–81 years, mean 64 years. Bone mineral density (BMD) of L2–L4 spine was measured using dual-energy X-ray absorptiometry (DXA). Absolute value of BMD (g/cm²) and age- and sex-matched BMD (%) were given. The mean BMD was 0.766 g/cm², and the incidence of osteoporosis (BMD less than 0.70 g/cm²) was 37%: 18% in men and 71% in women. The mean age- and sex-matched BMD was 85.9%: 87.5% in men and 83.1% in women. Univariate and multivariate analyses revealed that BMD was significantly associated with the age and sex of patients, but was not influenced by the type of gastrectomy (partial versus total) and years after operation (<20 versus 20<). Our study clarified the fact that postgastrectomy osteoporosis was frequent in the aged or female patients. BMD should be evaluated after gastrectomy, especially in the aged and in women. Received: 5 January 1998 / Accepted: 13 August 1999     

Changes in Bone Mineral, Lean Body Mass and Fat Content as Measured by Dual Energy X-ray Absorptiometry: A Longitudinal Study

Bone mineral density (BMD) and soft tissue composition were measured by dual energy X-ray absorptiometry (DXA) 3–4 years apart in 273 men and women aged 23–90. We found different rates of BMD loss in different skeletal regions. There were also different rates of BMD loss in different regions within the hip. Average rates of loss for male subjects 50 years of age and above for BMD total body were 0.1%/year and for femoral neck 1.5%/year, whereas lumbar spine (L2–L4) increased by 0.4%/year. Average rates of loss for female subjects 50 years of age and above for BMD total body were 0.0%/year, femoral neck 0.9%/year, and lumbar spine (L2–L4) 0.1%/year. Received: 28 November 1997 / Accepted: 26 July 1999     

Cross-Sectional Study of Weight-Bearing Activity on Proximal Femur Bone Mineral Density

In this cross-sectional study we investigated the effect of compressive and tensile forces applied on the proximal femur during weight-bearing activities. Ninety-seven men (29.9 ± 1.7 years) were divided into two groups: 69 exercisers who had practiced regular high-impact weight-bearing activities for at least 5 years and 28 controls who had been sedentary for at least 5 years. The maximum isometric hip abduction strength was measured. The bone mineral density (BMD) of the femoral neck and the greater trochanter was assessed using dual-energy X-ray absorptiometry (DXA). Controls were considered as the reference population to calculate the Z score. Mean BMD values of the femoral neck were 0.97 g/cm² on both sides in the exercisers and 0.83 g/cm² on the right side and 0.84 g/cm² on the left side in the controls. Mean BMD values of the greater trochanter were 0.86 g/cm² on the right side and 0.87 g/cm² on the left side in the exercisers, 0.73 g/cm² on the right side and 0.72 g/cm² on the left side in the controls. The BMD was significantly higher in exercisers at both trochanteric and cervical sites (P= 0.0001). Both left and right hip abduction strength was significantly greater in the exercisers than in the controls (P < 0.05) and was positively correlated to cervical and trochanteric BMD (P < 0.01). In the exerciser group, the trochanteric Z score was higher than the cervical Z score at both right (P= 0.06) and left (P= 0.002) sides. Therefore, the proximal femoral BMD was significantly greater in exercised subjects as compared with sedentary controls. The difference was observed at the level of both the femoral neck (where it is known anatomically that only compressive gravitational forces are exerted) and the greater trochanter (where it is known that tensile forces are exerted). This result suggests the participation of both compressive and tensile forces in the mechanisms by which exercise influences bone trophicity. Received: 19 November 1997 / Accepted: 7 August 1998     

Interfemur Variation of Bone Mineral Density in Patients Receiving High-dose Thyroxin Therapy

In order to evaluate the interfemoral variability of bone mineral density (BMD) in patients receiving thyroxin (T4) replacement therapy, dual-energy X-ray absorptiometry (DXA) was performed on both hips and the lumbar spine of 114 individuals. BMD was measured in 47 patients under T4 therapy in suppressive doses because of histologically proven thyroid cancer and 67 age-matched controls free of any known local or generalized disorder that would affect the bones and joints. Variation in BMD between both hips was determined for four different regions of interest, i.e., Ward's triangle, intertrochanteric region, trochanter, and femoral neck. No significant difference in hip BMD was found between patients and controls. Even though some individuals had large interfemoral BMD variation, no significant difference in hip BMD variability between the groups was observed. In patients under suppressive T4 replacement therapy, BMD measurement in one hip is suitable to predict BMD of the other hip and therefore unilateral hip measurement may be adequate. Received: 7 June 1997 / Accepted: 27 January 1998     

Bone Density of the Spine and Femur in Adult White Females

We measured bone mineral density (BMD in g/cm²) of the spine (L2-L4) and femur (four regions) in 1472 and 1487 cases, respectively, of ambulatory white women ages 20–79 years in the USA. A DPX densitometer was used in a mobile setting. The BMD values for women up to 69 years corresponded closely with published values for the USA, the UK, and northern Europe; our values were somewhat lower than those from other studies only in women over 70 years. The USA data were combined with data from Europe to give reference curves on about 12,000 subjects. Decreases of BMD with age in women below 50 years were much smaller than in older women (0.2% versus 0.6–1.0% per year). Femoral bone decreased from the neck region, but not the trochanter with age; the decrease of total femur BMD with age was due to loss from the former region. Loss of bone mineral content (BMC in g) from the femur neck and total femur region did not accelerate until after age 50 years, much like the spine. The apparent decrease of BMD in these regions that begins about age 40 actually is due to an increase of bone area. About 20% of USA women aged 50–79 years had BMD levels for the lumbar spine, or for the femur neck, more than −2.5 SD below the average values in young adult women 20–39 years old. Body weight had several times more impact on BMD than height, and in fact, a change of 1 kg in postmenopausal women was commensurate with the effect of a 1-year change in age. Subjects in the lowest quartile of body weight had T-scores that were 1 SD below those in the highest quartile. Received: 10 September 1998 / Accepted: 15 December 1998     

Bone Mineral Density and Bone Size in Men With Primary Osteoporosis and Vertebral Fractures

The bone mineral density (BMD) at the lumbar spine, proximal femur, and total skeleton was evaluated in 38 men with primary osteoporosis and vertebral fractures. BMD of the patients was significantly reduced over all skeletal areas compared with controls. The Z-score of the lumbar spine (−2.8 ± 0.9) was less than that of the other areas (P < 0.001) except the legs (−2.5 ± 1.1) (p.n.s.) showing that bone loss had a tendency to be greater over the axial skeleton. Vertebral dimensions compared with age-matched controls were as follows: projected L2–L4 area (cm 2): 45.7 ± 5.6 versus 53.7 ± 3.6 (P < 0.001); vertebral width (cm): 4.37 ± 0.44 versus 4.90 ± 0.36 (P < 0.001). Serum biochemical parameters and testosterone levels were similar between osteoporotic and control men. We conclude that men with vertebral osteoporotic fractures have reduced vertebral BMD and vertebral dimensions compared with age-matched controls. Thus, these findings indicate that the achievement of a reduced bone size at the end of the growth period or a failure of periosteal increase during adult life is likely to contribute to the pathogenesis of the vertebral fractures observed in older men. Received: 31 January 1997 / Accepted: 2 July 1997     

Relationship Between Spine Bone Mineral Density and Vertebral Body Heights

The aim of this study was to investigate the correlation between lumbar spine bone mineral density (LS-BMD) and the vertebral body heights with advancing age and years since menopause. One hundred and sixty-three women ages 39–74 years (77 normal premenopausal, ages 39–54, and 86 normal postmenopausal, ages 46–74 years) were studied. LS-BMD was measured by dual energy X-ray absorptiometry. Vertebral heights were evaluated, using morphometry, as the sum of anterior (AHs), middle (MHs), and posterior (PHs) vertebral body heights from T₄ to L₅. The AHs/PHs ratio at the same level was also calculated. AHs, MHs, PHs, and AHs/PHs ratio directly correlated with LS-BMD; the correlations are AHs r = 0.80, P < 0.0001, MHs r = 0.75, P < 0.0001, PHs r = 0.76, P < 0.0001, and AHs/PHs r = 0.66, P < 0.001. Both LS-BMD and AHs are inversely correlated with age, and the regressions fit with both linear and cubic curves. The statistical significance of the correlations persists while maintaining age constant. The linear regression curve of AHs with age indicates that the spine height decrement rate is 2.12 mm/year, corresponding to 7.4 cm in 35 years. AHs decreases immediately after menopause fitting with a cubic curve model, with a decrement rate of about 3 cm in the first 5 years after menopause. We conclude that the measurement of the sum of vertebral body heights could usefully integrate LS-BMD evaluation in the clinical and epidemiological investigation of osteoporosis. Received: 30 May 1997 / Accepted: 14 November 1997     

Loss of Bone Mineral Density in Women Athletes During Aging

Total and regional bone mineral density (BMD) by dual-energy-X-ray absorptiometry (DXA) and bone turnover were tested in 50 highly trained women athletes and 21 sedentary control women (18–69 years; BMI < 25 kg/m²). VO_2max (ml · kg⁻¹· min⁻¹) and lean tissue mass (DXA) were significantly higher in the athletes versus controls (both P < 0.0001). Total body BMD did not decline significantly with age in the athletes whereas lumbar spine (L₂–L₄) BMD approached statistical significance (r =−0.26; P= 0.07). Significant losses of the femoral neck (r =− 0.42), Ward's triangle (r =−0.53), and greater trochanter BMD (r =−0.33; all P < 0.05) occurred with age in the athletes. In the athletes, total body BMD, L₂–L₄ BMD, and BMD of all sites of the femur were associated with lean tissue mass (r = 0.32 to r = 0.57, all P < 0.05) and VO_2max (r = 0.29 to r = 0.48, all P < 0.05). Femoral neck and greater trochanter BMD were higher in the athletes than in controls (both P < 0.05) and lumbar spine and Ward's triangle BMD approached statistical significance (both P= 0.07). Bone turnover was assessed by serum bone-specific alkaline phosphatase (B-ALP), urinary deoxypyridinoline cross-links (Dpd), and urinary aminoterminal cross-linked telopeptides (NTX). There were no relationships between B-ALP or Dpd with age whereas NTX increased with age (r = 0.46, P < 0.05) in the entire group. Levels of B-ALP and NTX were negatively associated with total body, L₂–L₄, femoral neck, Ward's triangle, and greater trochanter BMD (P < 0.05). B-ALP and Dpd were not significantly different between athletes and controls whereas NTX was lower in the athletes than in controls (P < 0.001). The high levels of physical activity observed in women athletes increase aerobic capacity and improve muscle mass but are not sufficient to prevent the loss of bone with aging. Received: 28 November 1997 / Accepted: 8 April 1998     

Bone Mineral Density in Flatwater Sprint Kayakers

To elucidate the possible skeletal benefits of the muscular contractions and the nonweight-bearing loading pattern associated with kayaking, we investigated the bone mineral density (BMD, g/cm²) of 10 elite kayakers, six males and four females, with a median age of 19 years. Each subject was compared with the mean value of two matched controls. BMD of the total body, head, ribs, humerus, legs, proximal femur (neck, wards, trochanter), spine, lumbar spine, and bone mineral content (BMC, g), of the arms was obtained using a dual energy X-ray absorptiometer (DXA). Body composition was also assessed. The kayakers had a significantly (P < 0.05–0.01) greater BMD in most upper body sites: left and right humerus (10.4% and 11.7%), respectively, ribs (6.4%), spine (10.9%), and a greater BMC of the left and right arm (15.7% and 10.6%, respectively). No significant differences in the BMD of the total body, head, or any of the lower body sites were found, except for the pelvis, which was significantly greater in kayakers (5.1%). The controls had a significantly lesser lean body mass (10.4%) and greater percentage of body fat (19.5%) than the kayakers. Bivariate correlation analysis in the controls demonstrated significant and strong relationships between BMD in upper body sites and lean body mass, weight, and fat; the effects of training seem to outweigh most such relationships in kayakers. In conclusion, it seems that the loading pattern and muscular contractions associated with kayaking may result in site-specific adaptations of the skeleton. Received: 21 April 1998 / Accepted: 1 October 1998     

Bone Mineral Density and Androgen Levels in Elderly Males

To clarify the relationship of sex male hormones and bone in men, we studied in 140 healthy elderly men (aged 55–90 years) the relation between serum levels of androgens and related sex hormones, bone mineral density (BMD) at different sites, and other parameters related to bone metabolism. Our results show a slight decrease of serum-free testosterone with age, with an increase of follicle stimulating hormone (FSH) and luteinizing hormone (LH) in a third of the elderly subjects studied. BMD decreased significantly with age in all regions studied, except in the lumbar spine. We found a positive correlation between body mass index (BMI) and BMD at the lumbar spine and femoral neck (P < 0.001). No relationship was found (uni- and multivariate regression analysis) between serum androgens or sex hormone-binding globulin (SHBG) and BMD. We found a positive correlation of vitamin D binding protein (DBP) and osteocalcin with lumbar spine BMD and with BMI, DBP, IGF-1, and PTH with femoral neck BMD. In conclusion, there is a slight decline in free testosterone and BMD in the healthy elderly males. However, sex male hormones are not correlated to the decrease in hip BMD. Other age-related factors must be associated with bone loss in elderly males. Received: 29 April 1997 / Accepted: 9 November 1997     

Evaluation of Bone Mineral Density Using Three-Dimensional Solid State Phosphorus-31 NMR Projection Imaging

A solid state magnetic resonance imaging technique is used to measure true three-dimensional mineral density of synthetic hydroxyapatite phantoms and specimens of bone ex vivo. The phosphorus-31 free induction decay at 2.0 T magnetic field strength is sampled following application of a short, hard radiofrequency excitation pulse in the presence of a fixed amplitude magnetic field gradient. Multiple gradient directions covering the unit sphere are used in an efficient spherical polar to Cartesian interpolation and Fourier transform projection reconstruction scheme to image the three-dimensional distribution of phosphorus within the specimen. Using 3–6 Gauss/cm magnetic field gradients, a spatial resolution of 0.2 cm over a field of view of 10 cm is achieved in an imaging time of 20–35 minutes. Comparison of solid state magnetic resonance imaging with dual energy X-ray absorptiometry (DXA), gravimetric analysis, and chemical analysis of calcium and phosphorus demonstrates good quantitative accuracy. Direct measurement of bone mineral by solid state magnetic resonance opens up the possibility of imaging variations in mineral composition as well as density. Advantages of the solid state magnetic resonance technique include avoidance of ionizing radiation; direct measurement of a constituent of the mineral without reliance on assumptions about, or models of, tissue composition; the absence of shielding, beam hardening, or multiple scattering artifacts; and its three-dimensional character. Disadvantages include longer measurement times and lower spatial resolution than DXA and computed tomography, and the inability to scan large areas of the body in a single measurement, although spatial resolution is sufficient to resolve cortical from trabecular bone for the purpose of measuring bone mineral density. Received: 13 March 1997 / Accepted: 4 November 1997