老年女性髋部骨折与DXA骨强度参数的相关性研究

目的探讨髋部骨强度参数对老年女性髋部骨折的影响。方法对2014年10月-2017年2月至南京市中医院骨伤科就诊体检、年龄大于60岁的受试者进行双能X线测定,并收集受试者髋部骨折病史等临床资料进行回顾性分析。共纳入93名受试者,按骨折史分为髋部骨折组33人,胸腰椎骨折组32人,正常组28人,对骨密度、髋部几何参数及髋部力学参数进行统计学分析。结果股骨颈BMD(g/cm~2)、全髋BMD(g/cm2)、股骨颈皮质比率(%)、股骨颈最小宽度(mm)、d3(mm)、y(mm)等参数与老年女性髋部骨折具有显著相关性。结论本项研究基于双能X线测定法,发现部分髋部几何力学参数与老年女性髋部骨折相关,具有重要的临床指导意义,同时改变了单一的"低骨量—高骨折风险"预测模式,形成"骨密度+髋部几何力学分析"多元化模式,可有效提高老年女性髋部骨折风险的预测能力。     

A longitudinal study of supine lateral DXA of the lumbar spine: A comparison with posteroanterior spine,hip and total-body DXA

We report a study to assess whether supine lateral dual-energy X-ray absorptiometry (DXA) scans of the lumbar spine provide better data for monitoring response to treatment than alternative measurement sites such as the posteroanterior (PA) spine, hip and total body. The study population was 152 women enrolled in a placebo-controlled clinical trial of cyclical etidronate therapy. All subjects were 1–10 years after the menopause with bone mineral density (BMD) between 0 and –2 SD of age-matched normal women. Paired PA and lateral spine, left hip and total-body DXA scans were performed at baseline, 1 year and 2 years on a Hologic QDR-2000. One hundred and thirty-one subjects completed the study. Mean percentage change from baseline at 2 years in the treated (n=61) and control (n=70) groups was calculated for vertebral body, width-adjusted (WA) vertebral body, mid-vertebral body and WA mid-vertebral body BMD measurements on the lateral scans and compared with the percentage changes in PA spine, femoral neck, trochanter, Ward's triangle and total-body BMD. The long-term precision for each BMD measurement site was obtained by linear regression analysis in subjects taking placebo. Overall treatment effect, defined as the difference in the percentage change in BMD in the two treatment groups at 2 years, was divided by long-term precision to give an index of the ability of each site to monitor response to treatment. Results (and standard errors) normalized to the ratio of treatment effect/precision for PA spine BMD were as follows: PA spine, 1.00; vertebral body, 0.89 (0.14); WA vertebral body, 0.78 (0.14); mid-vertebral body, 0.65 (0.14); WA mid-vertebral body, 0.60 (0.13); femoral neck, 0.35 (0.15); trochanter, 0.45 (0.15); Ward's triangle, 0.59 (0.22); total body, 0.52 (0.19). Although treatment effect was larger for lateral than for PA spine BMD, this advantage was offset by the greater precision errors. PA spine BMD remains the optimum measurement for longitudinal studies in recently postmenopausal women.     

定量与半定量方法评估DXA影像发现椎体骨折的比较

目的比较形态学定量评估方法和Genant半定量方法对DXA影像进行椎体骨折评估的一致性。方法对217例≥50岁绝经后女性作骨密度检测的同时进行胸腰椎T4~L5正侧位扫描,采用形态学定量评估方法和Genant半定量方法进行椎体骨折评估,比较二种方法确定椎体骨折的一致性和二种方法确定椎体骨折组与无椎体骨折组的临床特征。结果形态学定量评估方法确定59例椎体骨折,椎体骨折率为27.19%;Genant半定量方法确定60例椎体骨折,椎体骨折率为27.65%。kappa一致性分析,κ=0.80。二种方法确定椎体骨折组与无椎体骨折组的临床特征无统计学差异。结论 Genant半定量方法和形态学定量评估方法均是评估椎体骨折的有效方法。     

Lumbar vertebral body compressive strength evaluated by dual-energy X-ray absorptiometry, quantitative computed tomography, and ashing

Bone densitometry with DXA (dual energy X-ray absorptiometry) and QCT (quantitative computed tomography) techniques are used for in vivo assessment of bone strength and thereby prediction of fracture risk. However, only few in vitro studies have investigated and compared these techniques’ ability to determine vertebral compressive strength. The aim of the present study was to (1) assess the predictive value of DXA, QCT, and pQCT (peripheral QCT) for vertebral bone compressive strength assessed by mechanical testing; (2) describe both linear and power relationship between density and strength; and (3) evaluate whether gender-related differences in the above relations were present. The material comprised human lumbar vertebrae L3 from 51 women and 50 men (age range: 18 to 96 years). The study showed that both DXA and CT techniques (QCT and pQCT) have a high predictive value for vertebral strength. The DXA BMD had a high correlation with maximum compressive load (r² = 0.86). The QCT and pQCT had high correlations with maximum compressive stress (r² = 0.75 and r² = 0.86, respectively). The correlation between ash density of the biomechanically tested specimen and maximum compressive stress was r² = 0.88. There were no differences between linear and power fit in the degree of determination between density and strength. There was no gender-related difference in the relationship between volumetric density and maximum compressive stress. In conclusion, it was demonstrated that DXA, QCT, and pQCT are ex situ equally capable of predicting vertebral compressive strength with a degree of determination (r²) between 75% and 86%. No differences were found between linear and power analysis of the relationship between density and strength, and no difference was found in the density strength relationship between women and men.     

Evaluation of hip flexion strength following lateral lumbar interbody fusion

Background context

Lateral interbody fusion (LIF) is a minimally invasive procedure that is designed to achieve a solid interbody fusion while minimizing the damage to the surrounding soft tissue. Although short-term results have been promising, few data have been published to date regarding its risks and complication rate.

Purpose

The aim was to evaluate the extent of injury to the psoas muscle after the LIF procedure by measuring hip flexion strength.

Study design

A prospective case series was used in the study.

Method

Hip flexion strength was measured using a handheld digital dynamometer while the patient was seated on a chair; the examiner held the device against the patient’s attempt to flex the hip. Both sides were measured to compare the operated and nonoperated psoas muscles. Each side was measured three times and the average amount (in pounds) was recorded. Measurements were done before and after surgery on Day 2-3, at 2 weeks, 6 weeks, and at 3 and 6 months.

Results

Thirty-three patients were recruited for this study. Mean preoperative hip flexion strength values were 20.7±3.47 lb and 21.3±4.31 lb for operated and nonoperated legs, respectively, with no significant difference (p=.85). With a mean of 11.2±2.24 lb postoperative measurements on Day 2, the operated side showed statistically significant reduction of strength (p=.0001). The nonoperated side was also weaker postoperatively, but not significantly (mean=19.12±1.74 lb; p=.097). From the first follow-up visit at 2 weeks, the values on the operated leg had returned to baseline values (20.6, p=.97) and were not significantly different from preoperative values on either side.

Discussion

Hip flexion was weakened immediately after the LIF procedure, which may be attributed to psoas muscle injury during the procedure. However, this damage was temporary, with almost complete return to baseline values by 2 weeks.     

Reliability of the assessment of disc degeneration on the lateral DXA scans

IntroductionGiven the prevalence and costs induced by osteoarthritis (OA), it is necessary to find a cheap and safe technique to evaluate it reliably.ObjectiveTo assess the value of the lateral dual energy X-ray absorptiometry (DXA) spine scans for the diagnosis of disc degeneration.MethodSeventy-seven individuals aged 18 and over, with or without disc degeneration, had both lateral thoracolumbar spine radiographs and DXA spine scans (≤ 6 months between both exams). Disc degeneration was assessed using the Lane score. The images of 20 randomly selected individuals were assessed by two readers.ResultsAlmost 13% of the thoracic levels were not assessable on the DXA scans. For the identification of the intervertebral levels on the DXA scans as interpretable or not, the intra-reader agreement was good (κ = 0.81) and the inter-reader agreement was fair (κ = 0.27–0.36). For the diagnostic criteria (osteophytes, disc space narrowing, osteosclerosis, overall grade), the intra-reader agreement was excellent for the radiographs (κ = 0.89–0.92), good for the DXA scans (κ = 0.64–0.83) and fair to moderate for the between-method comparison (κ = 0.25–0.44). The inter-reader agreement was moderate to good for the radiographs (κ = 0.49–0.66) and fair to good for the DXA scans (κ = 0.32–0.74). In the per patient analysis (the most severe grade), the intra-reader agreement was excellent for the radiographs (κ = 0.85–0.94), moderate to excellent for the DXA scans (κ = 0.53–0.85) and poor to good for the between-methods comparison (κ = 0.17–0.63).ConclusionOur results do not support the use of DXA scans for the assessment of thoracolumbar disc degeneration.     

Monitoring Bone Growth Using Quantitative Ultrasound in Comparison with DXA and pQCT

Quantitative ultrasound (QUS) is a safe, inexpensive, and nonradiation method for bone density assessment. QUS correlates with, and predicts fragility fractures comparable to, dual-energy X-ray absorptiometry (DXA)-derived bone mineral density (BMD) in postmenopausal women. However, its validity in monitoring bone growth in children is not well understood. Two hundred and fifty-eight 10–13 yr pubertal girls and 9 37–43 yr adults without diseases or history of medications known to affect bone metabolism were included in the 2-yr prospective study. Calcaneal broadband ultrasound attenuation (cBUA) was assessed using QUS-2 (Quidel, Santa Clara, CA), speed of sound of tibial shaft (tSOS) using Omnisense (Sunlight Technologies, Israel), apparent volumetric BMD (vBMD) of tibial shaft using peripheral quantitative computed tomography (pQCT; XCT2000, Stratec), and femoral neck (FN) and lumbar spine 2–4 (LS) areal BMD (aBMD) using DXA (Prodigy, GE). Over the 2 yr in girls, FN and LS aBMD showed the largest increases (17 ± 8% and 20 ± 8%, respectively), followed by tibial vBMD and cBUA (10 ± 5% and 9 ± 9%, respectively). There was no apparent change in tSOS (2 ± 3%). The increase in FN and LS aBMD attenuated 48% and 40%, respectively, after adjustment of the change in body size. The change of cBUA correlated significantly with change in tibial vBMD and FN and LS aBMD (r = 0.24–0.40). At the matched location, tSOS correlated only with cortical vBMD, not with cortical thickness, apparent vBMD, or bone size. The long-term reproducibility, assessed using the concordance correlation coefficient of young adults' pre-post measurements, was substantially lower in tSOS than cBUA, tibial vBMD, FN, and LS aBMD (0.65 vs 0.97, 0.95, 0.98, and 0.96; p < 0.05). The transverse transmission method-derived calcaneal BUA, but not the axial transmission method-derived SOS, is comparable to DXA and pQCT for monitoring bone densitometric change in pubertal girls. The role of QUS in fracture-risk prediction in children and adolescents needs further investigation.     

Accuracy of DXA scanning of the thoracic spine: cadaveric studies comparing BMC, areal BMD and geometric estimates of volumetric BMD against ash weight and CT measures of bone volume

Biomechanical studies of the thoracic spine often scan cadaveric segments by dual energy X-ray absorptiometry (DXA) to obtain measures of bone mass. Only one study has reported the accuracy of lateral scans of thoracic vertebral bodies. The accuracy of DXA scans of thoracic spine segments and of anterior-posterior (AP) thoracic scans has not been investigated. We have examined the accuracy of AP and lateral thoracic DXA scans by comparison with ash weight, the gold-standard for measuring bone mineral content (BMC). We have also compared three methods of estimating volumetric bone mineral density (vBMD) with a novel standard–ash weight (g)/bone volume (cm³) as measured by computed tomography (CT). Twelve T5–T8 spine segments were scanned with DXA (AP and lateral) and CT. The T6 vertebrae were excised, the posterior elements removed and then the vertebral bodies were ashed in a muffle furnace. We proposed a new method of estimating vBMD and compared it with two previously published methods. BMC values from lateral DXA scans displayed the strongest correlation with ash weight (r=0.99) and were on average 12.8% higher (p<0.001). As expected, BMC (AP or lateral) was more strongly correlated with ash weight than areal bone mineral density (aBMD; AP: r=0.54, or lateral: r=0.71) or estimated vBMD. Estimates of vBMD with either of the three methods were strongly and similarly correlated with volumetric BMD calculated by dividing ash weight by CT-derived volume. These data suggest that readily available DXA scanning is an appropriate surrogate measure for thoracic spine bone mineral and that the lateral scan might be the scan method of choice.     

Comparison of antero-posterior and lateral measurements of the vertebral mineral contents by dual-energy x-ray absorptiometry

Bone mineral measurements of the 2nd and 3rd vertebrae were made using dual energy x-ray absorptiometry (DEXA) in both antero-posterior (AP) and lateral (Lat) projections in 49 women (Group I; 24 young controls, II; 11 elderly controls, III; 14 osteoporotics). The coefficients of variation of the AP and Lat measurements of BMC in 3 young women were 2.2% and 8.4% of the respective mean values. In Group I, BMCs obtained by the Lat measurement were 11.6±15.7% below BMC_AP (p<0.05). In Group II and III, on the other hands, BMC_Lat was as low as below 34.2±11.9% (Group II) and 40.1±21.5% (Group III) of respective AP contents (p<0.01). This discrepancy between BM C_Lat and BMC_AP in Group II and III could not be acounted by the measurement error of Lat determination alone. Furthermore, the difference of bone mineral density (BMD) between Group I and II (or III) appeared to be much more pronounced when compared by the data obtained from the Lat measurements than the comparison using BMD_AP. Extra-skeltal calcification projected on the AP plane, including calcified aorta and ligaments, may attribute such a difference between AP and Lat measurements. Our observation indicated the possibility of an overestimation of BMC and BMD by the AP determination of the spine. Therfore, an improvement of the reproducibility to measure the spine by the Lat determination with DEXA is mandatory for the detection of subclinical osteoporosis.     

Dual-energy X-ray absorptiometry of the calcaneus: Comparison with vertebral dual-energy X-ray absorptiometry and quantitative computed tomography

The purpose of this study was to determine the efficacy of using bone mineral measurements of the calcaneus to evaluate osteoporosis. Dual energy X-ray absorptiometry (DXA) of the calcaneus was compared with posteroanterior lumbar absorptiometry (DXA) and vertebral quantitative computed tomography (QCT) measurements in 171 white women (78 normal and 93 osteoporotic). DXA measurement of os calcis mineralization decreased significantly in osteoporosis, but to a lesser extent than in vertebral sites. In normal subjects, good correlations were observed between calcaneal and lumbar DXA (0.69) and QCT (0.56). In subjects with vertebral fractures, there was also good correlation between calcaneal DXA and QCT (0.59–0.69). This suggests that trabecular bone in calcaneus and vertebrae have related involution in cases of vertebral osteoporosis. However, the extent of bone loss is less marked in the calcaneus than in the vertebrae and is not sufficient to be accurately measured over time. We conclude, therefore, that although the global densitometric measurement at this site is not sufficiently sensitive for general use, it can be useful as a epidemiological research tool.     

Ex vivo estimation of thoracolumbar vertebral body compressive strength: The relative contributions of bone densitometry and vertebral morphometry

The estimation of vertebral fracture risk in individuals with suspected osteopenia is commonly based on measurements of lumbar spine bone density. The efficacy of vertebral size and deformity, as assessed by vertebral morphometry, in the prediction of fractures has been less studied. In an ex vivo investigation the regional relationships between vertebral size, vertebral deformity, bone density and compressive strength throughout the thoracolumbar spine were examined. In 16 vertebral columns (T1–L5) the bone mineral content (BMC) and bone mineral density (BMD) of each segment were measured using lateral projection dual-energy X-ray absorptiometry, and the vertebral cancellous density (VCD) and mid-vertebral cross-sectional area (CSA) measured using quantitative computed tomography. Vertebral body heights were determined from mid-sagittal CT scans, and vertical height ratios calculated for each segment. The failure load and failure stress of the isolated vertebral bodies were determined using a material testing device. Separate analyses were performed for the upper (T1–4), middle (T5–8) and lower (T9–12) thoracic, and lumbar (L1–5) segments. In all regions, failure load was strongly correlated with BMD (r=0.82–0.86), moderately correlated with VCD (r=0.60–0.71) and vertebral height (r=0.22–0.49), and poorly correlated with the height ratios (r=0.04–0.33). Failure stress was best predicted by BMD (r=0.73–0.78) and VCD (r=0.70–0.78) but was poorly correlated with all morphometric variables (r=0.01–0.33). The segmental correlations between BMD and VCD ranged fromr=0.49 tor=0.79. For all regions, BMD and VCD were included in the stepwise regression models for predicting failure load and failure stress. Either the mid-vertebral height or CSA were included in all the failure load models, while mid-vertebral height was included in only one of the failure stress models. The results suggest that vertebral deformity and size (as assessed by vertebral morphometry) make only a minor contribution to the prediction of vertebral strength additional to that provided by bone densitometry alone. The consistent regional relationships between variables appear to support the practice of global fracture risk assessment based on lumbar spine densitometry.     

Early postmenopausal diminution of forearm and spinal bone mineral density: A cross-sectional study

Diminution of bone mineral density (BMD) in the spine and forearm was studied cross-sectionally in 363 women who were 6 months to 10 years postmenopausal. BMD was determined by dual-energy X-ray absorptiometry (DXA) (Hologic QDR-2000) in the lumbar spine, in both the supine lateral (LAT) and anteroposterior (AP) projections, and in the distal third of the forearm. The postmenopausal diminution of BMD was best described by an exponential fit. The initial rate of postmenopausal diminution of BMD was highest in the most trabecular sites (LAT>AP> forearm), but 10-year diminution was similar at all sites (12%–13%, corresponding to about 1.0–1.5 SD), and extrapolation suggested reverse order of the rates of diminution thereafter (forearm>AP>LAT). When bone mineral content of the entire L3 vertebra (tBMC) was measured in vivo, AP tBMC could account for only 67% of the variation in LAT tBMC, compared withr ²=0.997 in vitro. This observation suggests an accuracy problem in vivo in one of the spine measurement methods. We conclude that the initial rate of BMD diminution after the menopause seems to be highest in the spine, especially when measured laterally, but that this rate levels off within the first decade. The lower precision error of a forearm measurement (0.8% v 1.6 for AP and 3.1 for LAT) therefore implies that this method may require a shorter observation period than spine measurements for the detection of bone loss 5–10 years after menopause. Long-term longitudinal spine and forearm measurements are, however, needed to confirm these conclusions.     

The predictive value of quantitative computed tomography for vertebral body compressive strength and ash density

Whole lumbar vertebral sections (L₂ and L₃) were obtained from 30 elderly individuals aged 43–95 years, mean 81 years (13 females, 17 males). None of the subjects had had malignant diseases. Quantitative computed tomography (QCT) was performed on an EMI 7070 scanner. One 8 mm slice parallel to the end-plates was obtained from the center of each vertebral body. The trabecular bone mass in each slice was outlined interactively by means of a tracer-ball. A CT-histogram was recorded inside this area, and average CT-values were expressed in Hounsfield Units (HU).

The whole vertebral body (L₂) was compressed in a materials testing machine. From the central part of L₃, vertical cylindrical pure trabecular bone specimens were obtained. The biomechanical competence of these specimens was also assessed by means of a materials testing machine. Finally, all bone specimens were incinerated for determination of apparent ash-density.

Highly significant positive correlations were found between average CT-values and (a) stress values of the trabecular bone (r = 0.81, p < 0.001) and (b) ash-density of the pure trabecular bone (r = 0.81, p < 0.001). Furthermore, a significant positive correlation was found between CT-values and (a) total vertebral body load (r = 0.72, p < 0.001), (b) total vertebral body stress (load/cross-sectional area) (r = 0.55, p < 0.001) and (c) ash-density of the whole vertebral body (r = 0.76, p < 0.001).

It is concluded that quantitative computed tomography gives valid predictions of both vertebral trabecular bone mass and mechanical competence. The predictive value for whole vertebral body load, stress and ash-density, although less marked, is still highly significant.     

Differentiation between post-menopausal women with and without hip fractures: enhanced evaluation of clinical DXA by topological analysis of the mineral distribution in the scan images

Summary  We introduce an algorithm to evaluate hip DXA scans using quantitative image analysis procedures based on the Minkowski functionals (MF) for differentiation between post-menopausal women with and without hip fracture. In a population of 30 post-menopausal women, the new parameter has a highly discriminative potential with a performance superior to standard densitometry providing complementary information compared to BMD. Introduction  We introduce a novel algorithm to evaluate DXA scans of the hip using quantitative image analysis based on the Minkowski functionals (MF) to identify post-menopausal women with hip-fracture and to compare the results with densitometry. Methods  BMD of 30 women (73.9 ± 10.3 years), 15 of whom had a recent hip fracture, is obtained by DXA using the “total hip” ROI. The topology of mineral distribution in the scan images is evaluated using the MF-based parameter MF2D. ROC analysis is employed to assess the discriminative potential (fracture/non-fracture). Results  The area-under-the-curve (AUC) for identification of patients with/without fractures by BMD is .72(p = 0.04), AUC for MF2D is .85(p = 0.001). No statistically significant correlation exists between MF2D and BMD. By discriminant analysis we can show that by combination of MF2D and BMD the outcome increases significantly: using BMD or MF2D alone, 63% and 70% of cases are classified correctly versus 77% of cases in the multivariate model. Conclusion  The topology-based parameter has a high predictive potential with respect to identification of patients with high risk of hip fracture, performance is superior to densitometry. The new method provides information complementary to BMD. Best classification results are obtained when BMD and MF2D are combined in a multivariate model.     

Comparison of the radiographic vertebral trabecular pattern with the vertebral fracture prevalence and spinal bone density

Spinal bone densitometry allows accurate and precise measurement of the severity of bone loss. Where densitometry is not yet available medical practitioners have to continue to rely on clinical radiography. Since the grey levels of the radiographic image are highly inaccurate we studied the radiographic vertebral trabecular pattern for its suitability as a semiquantitative assessment of vertebral bone loss. We defined four vertebral trabecular pattern indices (VTPI 4=normal, VTPI 1=severe bone loss) and tested these for correlations with the prevalence of vertebral fractures, and with spinal and hip bone mineral density measured by dual-energy X-ray absorptiometry (DXA). We found negative correlations between VTPI and the percentage of patients with vertebral fractures (p=0.0001), between VTPI and the number of vertebral fractures per patient (r=0.606,p=0.001) and between VTPI and the severity of vertebral fractures, and a positive correlation between VTPI and spinal (r ²=0.556,p=0.0001) and hip DXA values (r ²=0.315,p=0.0001). We conclude that the vertebral trabecular pattern index can be used to assess the severity of spinal bone loss when a bone densitometer is not available.     

Prediction of bone strength at the distal tibia by HR-pQCT and DXA

Background

Areal bone mineral density (aBMD) at the distal tibia, measured at the epiphysis (T-EPI) and diaphysis (T-DIA), is predictive for fracture risk. Structural bone parameters evaluated at the distal tibia by high resolution peripheral quantitative computed tomography (HR-pQCT) displayed differences between healthy and fracture patients. With its simple geometry, T-DIA may allow investigating the correlation between bone structural parameter and bone strength.

Methods

Anatomical tibiae were examined ex vivo by DXA (aBMD) and HR-pQCT (volumetric BMD (vBMD) and bone microstructural parameters). Cortical thickness (CTh) and polar moment of inertia (pMOI) were derived from DXA measurements. Finally, an index combining material (BMD) and mechanical property (polar moment of inertia, pMOI) was defined and analyzed for correlation with torque at failure and stiffness values obtained by biomechanical testing.

Results

Areal BMD predicted the vBMD at T-EPI and T-DIA. A high correlation was found between aBMD and microstructural parameters at T-EPIas well as between aBMD and CTh at T-DIA. Finally, at T-DIA both indexes combining BMD and pMOI were strongly and comparably correlated with torque at failure and bone stiffness.

Conclusion

Ex vivo, at the distal tibial diaphysis, a novel index combining BMD and pMOI, which can be calculated directly from a single DXA measurement, predicted bone strength and stiffness better than either parameter alone and with an order of magnitude comparable to that of HR-pQCT. Whether this index is suitable for better prediction of fracture risk in vivo deserves further investigation.     

Pullout strength of anterior spinal instrumentation: a product comparison of seven screws in calf vertebral bodies

A lot of new implant devices for spine surgery are coming onto the market, in which vertebral screws play a fundamental role. The new screws developed for surgery of spine deformities have to be compared to established systems. A biomechanical in vitro study was designed to assess the bone–screw interface fixation strength of seven different screws used for correction of scoliosis in spine surgery. The objectives of the current study were twofold: (1) to evaluate the initial strength at the bone–screw interface of newly developed vertebral screws (Universal Spine System II) compared to established systems (product comparison) and (2) to evaluate the influence of screw design, screw diameter, screw length and bone mineral density on pullout strength. Fifty-six calf vertebral bodies were instrumented with seven different screws (USS II anterior 8.0 mm, USS II posterior 6.2 mm, KASS 6.25 mm, USS II anterior 6.2 mm, USS II posterior 5.2 mm, USS 6.0 mm, USS 5.0 mm). Bone mineral density (BMD) was determined by quantitative computed tomography (QCT). Failure in axial pullout was tested using a displacement-controlled universal test machine. USS II anterior 8.0 mm showed higher pullout strength than all other screws. The difference constituted a tendency (P = 0.108) when compared to USS II posterior 6.2 mm (+19%) and was significant in comparison to the other screws (+30 to +55%, P < 0.002). USS II posterior 6.2 mm showed significantly higher pullout strength than USS 5.0 mm (+30%, P = 0.014). The other screws did not differ significantly in pullout strength. Pullout strength correlated significantly with BMD (P = 0.0015) and vertebral body width/screw length (P < 0.001). The newly developed screws for spine surgery (USS II) show higher pullout strength when compared to established systems. Screw design had no significant influence on pullout force in vertebral body screws, but outer diameter of the screw, screw length and BMD are good predictors of pullout resistance.     

Parathyroid hormone monotherapy and cotherapy with antiresorptive agents restore vertebral bone mass and strength in aged ovariectomized rats

Previous studies have shown that parathyroid hormone (PTH) monotherapy and cotherapy with estrogen or risedronate augment vertebral bone mass and bone strength in young, ovariectomized (OVX) rats. The current study was designed to determine whether PTH has similar bone anabolic effects in aged OVX rats at a much later stage of estrogen depletion. Female Sprague Dawley rats were subjected to sham surgery or bilateral ovariectomy at three months of age and maintained untreated for one year after surgery to allow for the development of vertebral osteopenia in OVX rats. Groups of baseline control and OVX rats were sacrificed at the end of this pretreatment period. The remaining OVX rats were then treated for ten weeks with vehicle, antiresorptive agents alone (estrogen, risedronate, or calcitonin), or PTH alone. Other groups of OVX rats were treated concurrently with PTH and each of the antiresorptive agents. The first and fourth lumbar vertebral bodies were processed undecalcified for quantitative bone histomorphometry and biomechanical testing, respectively. As expected, bone mass and compressive strength were decreased in the lumbar vertebral body of baseline OVX rats compared to baseline control rats. This bone loss was associated with decreases in trabecular number and width and an increase in trabecular separation. Treatment with estrogen, risedronate, or calcitonin alone failed to reverse the changes in bone mass, structure, and strength induced by ovariectomy. In contrast, treatment of OVX rats with PTH alone restored vertebral cancellous bone volume and ash density to the level of vehicle-treated control rats and increased vertebral maximum load, stress, and normalized load to well above this level. The hormone significantly increased trabecular width, but not number, in the lumbar vertebral body of OVX rats. Concurrent treatments with PTH and the antiresorptive agents did not augment cancellous bone and biomechanical competence to a greater, or lesser, extent than treatment with PTH alone. Compressive strength correlated significantly with bone mass and trabecular width in the lumbar vertebral body. These results indicate that PTH completely restores lost bone mass and improves bone strength in the vertebral body of aged OVX rats with established osteopenia. With our previous study in younger OVX rats, the current study demonstrates that the anabolic effect of PTH is independent of age and the stage of estrogen depletion in the rat skeleton.     

Quantification of bone strength by intraoperative torque measurement: a technical note

Introduction

Bone strength describes the resistance of bone against mechanical failure. Bone strength depends on both the amount of bone and the bone’s quality, and the bone strength may be looked upon as a relevant parameter to judge an osteosynthesis’ stability. Information about bone strength was barely available intraoperatively in the past. The previous work of our group reported on development and laboratory evaluation of mechanical torque measurement as a method for the intraoperative quantification of bone strength. With the clinical series presented here we intend to verify that the im gesamten Text DensiProbe? instrumentation for intraoperative torque measurement and the related measurement method are eligible for intraoperative use based on the following criteria: application of the method may not create complications, the measurement can be performed by the surgeon himself and may only cause a limited increase in the procedure time.

Patients and methods

From December 2006 until May 2007 ten patients with a pertrochanteric femoral fracture or a lateral femoral neck fracture eligible for stabilization with DHS^® were included in the study after having received informed consent. Any medication and comorbidity that might have influenced bone quality or bone mineral density (BMD) in these patients was documented. Bone strength was intraoperatively measured with DensiProbe^®. Complications that were obviously related with torque measurement were documented as well as any deviation from the suggested procedure; 6 and 12 weeks postoperative follow-up included clinical and radiological examination. The time required for torque measurement, the overall operating time and the number of persons present in the operating room were protocolled. BMD values of the contralateral femoral neck were postoperatively assessed by dual energy X-ray absorptiometry (DEXA) and compared to intraoperative peak torque values measured by DensiProbe^®.

Results

No major complication was observed during intraoperative application of DensiProbe^®by trained surgeons. The unintended extraction of the guide wire together with the torque measurement probe was reported only once and is looked upon as a minor complication. Fracture healing was uneventful in all patients. The mean time for torque measurement was 2.35 ± 0.9 min accounting for 2.2 ± 1.1% of total surgery time. The presence of an additional person was not required to perform torque measurement but to protocol the data. There was a tendency towards correlation between BMD values of the femoral neck and intraoperative peak torque values.

Discussion

The data presented clearly indicate that the DensiProbe^® instrumentation and measurement principle are eligible for routine intraoperative use by trained surgeons. Interpretation of possible correlations between BMD values measured by means of DEXA and the Peak Torque values assessed by DensiProbe^® has to be considered very carefully, because BMD and Peak Torque analyse bone at a different scale. Only within the framework of a multicenter study it will be possible to include a sufficient number of patients for calculation of the methods’ predictive value towards implant failure and to verify acceptance of the method by the surgeons.

     

Heel ultrasound in women after long-term ERT compared with bone densities in the forearm,spine and hip

To compare heel ultrasound values with bone densitites at different measurement sites as determined by single photon absorptiometry (SPA) and dual-energy X-ray absorptiometry (DXA) in long-term users of estrogen replacement therapy (ERT), we analyzed data from 30 users of estradiol implants (mean duration of treatment 16 years) and 32 non-users, comprising 28 complete age-matched pairs. The precision errors in vivo of ultrasound measurements were 0.18%, 1.3% and 1.5% for speed of sound (SOS), broadband ultrasound attenuation (BUA) and stiffness index, respectively. In the controls, ultrasound parameters correlated well with values from SPA and DXA measurements (r=0.51–0.63,p<0.004). In long-term users of ERT, however, measurements with ultrasound did not correlate with DXA in the spine and hip (r=0.01–0.31, NS) but correlated well with SPA in the forearm (r=0.47–0.66,p<0.009). Implant users, compared with non-users, had small and just significantly different values when measured by ultrasound (at most 12%,p=0.03–0.04) but significantly higher bone mineral densities (18%–25%,p=0.0001–0.01) in the forearm, spine and hip when measured by SPA or DXA. Data indicated that a substantial proportion of long-term users of estrogen may be non-responders concerning the effect of estrogen on bone qualities expressed in heel ultrasound values. In a multivariate regression analysis the effect of increasing age and increasing treatment duration were both negative for the ultrasound parameters. This is in contrast to our previous finding for bone density parameters in which the negative effect of increasing age was more than compensated by the positive effect of increasing treatment duration. Heel ultrasound correlated poorly with DXA measurement of axial bone density in long-term estrogen users. It has been stated that ultrasound measurements of bone status represent architecture and structure independently of bone mass. If so, then longterm ERT seems, in a substantial proportion of women, to preserve the bone mass and density better than the structure of the bone. Thus, the present study demonstrates a situation where ultrasound determinations can not simply be extrapolated to reflect the mineral density of the central skeleton.