Why do long-distance runners not have more bone? A vital biomechanical explanation and an estrogen effect

Inanimate structures cannot detect and repair their fatigue damage or microdamage, so to minimize it they need more structural material and strength. Living bone handles this matter differently. Bone modeling drifts adapt bone architecture and strength to the loads on bones in ways that tend to keep strains from exceeding a “modeling threshold” range. Strains (or equivalent features) above that threshold switch mechanically controlled modeling ON. Where strains stay below that threshold, this modeling goes OFF. Repeatedly loading-deloading a bone causes microdamage in it, and basic multicellular unit (BMU)-based bone remodeling normally repairs it. Where strains stay below an operational “microdamage threshold,” remodeling can repair whatever microdamage happens for as long as it happens. Strains above that threshold can cause too much microdamage to repair completely and lead to fatigue fractures of trabeculae or whole bones. The modeling threshold normally lies comforably below the microdamage threshold. Since modeling normally adjusts bone architecture to keep strains from exceeding the modeling threshold, this keeps strains below the microdamage threshold, too, and voluntary activities do not cause more microdamage than remodeling can repair. Therefore, long-distance runners do not need more bone mass and strength than nonrunners of comparable age, sex, and body size.     

Improving Femoral Bone Density Measurements

Femoral bone density measurements are clinically important because of their strong relationship with hip fracture. However, current densitometers have not improved upon femoral densitometry since the introduction of dual-energy X-ray absorptiometry (DXA) systems. Recently, several advances in DXA measurement of the proximal femur have been proposed by various published studies. These advances can be added to existing DXA systems, while maintaining the conventional femoral regions of interest. Both upper neck bone mineral density (BMD) and hip axis length have been reported to be associated with hip fractures. With newer technology that enables a rapid assessment of both hips, bilateral femur measurements are now clinically practical and are of importance in those with T-scores approaching, yet not reaching, diagnostic or therapeutic thresholds. Bilateral femur measurements also reduce precision error compared to a single femur measurement, yielding precision errors less than observed at the spine. With this decrease in precision error, monitoring of bone changes is now possible at the femur with the utility comparable to the spine.     

Human imaging of phosphorus in cortical and trabecular bone in vivo.

Phosphorus was imaged in vivo in human cortical and trabecular bone and the T(1) and T(2) (*) were measured. An ultrashort TE (UTE) pulse sequence (TE = 70 microm) was used with half pulse excitation and radial mapping of k-space from the center out. T(2) (*) was measured using multiple echo times and T(1) was measured both by saturation recovery and by a method using different RF pulse amplitudes. Seven normal subjects (32-85 years) were examined. Phosphorus was imaged, with a true in-plane resolution of 2.9 x 2.9 mm and a signal-to-noise ratio (SNR) of 19:1, in both cortical and trabecular bone. The mean T(2) (*) value was 207 +/- 12 micros, and the mean T(1) value was 8.6 +/- 3.0 sec. Images and measurements were obtained in realistic times on a clinical MR system. This may provide a new approach to characterizing disease of bone.     

Guided bone regeneration for immediate non‐submerged implant placement using bioabsorbable materials in Beagle dogs

The aim of the present study was to evaluate the combined application of different bioabsorbable materials for healing of residual peri‐implant defects after placement of non‐submerged implants into fresh extraction sockets. Second and third mandibular premolars were extracted from 10 Beagle dogs, the coronal part of the distal sockets were surgically enlarged and this was followed by immediate placement of specially designed hollow‐screw non‐submerged dental implants. For each animal, the coronal peri‐implant defects were further treated with one of the 4 following procedures: 1) no treatment, control site: 2) grafting with porous hydroxyapatite (HA); 3) collagen membrane tightly secured around the implant and over the defect and 4) grafting with HA covered with a collagen membrane. After 16 weeks of healing, specimens were removed from the mandibule and prepared for a histomorphometric evaluation. The bone-to-implant contact length (BIC) was measured and compared amongst the different treatment modalities. In the defect area, the irregular bone regeneration was similar between all the treatment procedures ( P >0.10). In the sites covered with a collagen membrane alone, the total BIC (47%) was greater than in control sites (28.7%. P <0.05) or sites grafted with HA (22.2%, P <0.02). Total BIC in sites treated with the HA‐membrane combination (43%) was only significantly different from sites treated with HA ( P <0.10). It is concluded that the use of bioabsorbable materials results in a limited increase of osseointegration when used in conjunction with immediate placement of non-submerged implants, although the principle of the one stage surgical approach can be maintained.     

低剂量激素替代治疗对绝经后妇女骨代谢的影响

目的 探讨低剂量结合型雌激素（ＣＥ）和安宫黄体酮（ＭＰＡ）联合应用对骨代谢的影响，方法３４例绝经后妇女随机分为两组，试验组１７例，ＣＥ０．６２５ｍｇ与ＭＰＡ２ｍｇ隔日口服交替应用，对照组１７例，口服ＣＤ０．６２５ｍｇ／ｄ，每月连续服用２５ｄ，后１０ｄ加用ＭＰＡ４ｍｇ。两组均连续服用４周期，于用药前后分别测定血碱性磷酸酶（ＡＬＰ）及尿Ｃａ／Ｃｒ比值。结果 实验组完成治疗者１６例，对照组完成治疗者１５     

糖尿病患者第3腰椎骨密度测量的意义

糖尿病（ＤＭ）患者继发骨质疏松较多见，为探讨早期诊断，对３０例非胰岛素依赖型糖尿病（ＮＩＤＤＭ）患者和４０例正常对照者，进行血清钙（Ｃａ）、磷（Ｐ）、碱性磷酸酶（ＡＫＰ）的测定，拍照胸部、腰椎和骨盆Ｘ线片，并分别经ＣＴ进行第３腰椎骨密度（ＢＭＤ）测量。结果，ＤＭ组ＢＭＤ均值为１２７．１±２５．７７ｍｇ／ｃｍ３，对照组ＢＭＤ均值为１８９．１１±７１．６８ｍｇ／ｃｍ３，两组比较有非常显著差异（Ｐ＜０．０１），提示第３腰椎骨密度测量对ＤＭ患者骨质疏松的早期诊断有一定价值。     

Bone morphogenetic proteins: background and implications for oral reconstruction

Abstract For over 30 years now, research has been carried out to isolate and purify bone morphogenettc protein (BMP), a substance which has been shown to induce heterotopic bone formation in various animal species. Recent advances in the fields of developmental biology, molecular biology, genetics and wound healing, have shown that the BMPs are not only responsible for postfetal bone induction (including normal bone remodeling, healing and repair), but are also critical during embryogenesis, not only in regards to the skeletal system, but quite possibly in the morphogenesis and pattern formation of other tissues and organs as well, Therefore. BMPs have the potential as a therapeutic utility in orthopedic and dento-alveolar reconstruction.     

Rapid decrease of urinary pyridinoline excretion in growth hormone deficient children following discontinuation of growth hormone therapy

In order to examine the effect of growth hormone on urinary pyridinoline excretion, 32 patients with complete or partial growth hormone deficiency had their urinary pyridinoline excretion measured while receiving growth hormone and for 14 days after it was discontinued. There was a significant positive correlation between increases in growth velocities during the first year of growth hormone administration compared to before it, and the ratio of the urinary pyridinoline excretion levels while receiving growth hormone to those after discontinuation. Therefore, urinary pyridinoline excretion rapidly decreased in patients with growth hormone deficiency when the administration of growth hormone was stopped. Exogenous growth hormone appears to stimulate bone resorption in these patients.     

异体胸腺的解剖、组织学及吻合血管移植治疗晚期恶性骨肿瘤的研究

本文对20例20～36周引产死胎胸腺进行了解剖学,组织学观察,并应用吻合血管胎儿胸腺移植治疗晚期恶性原发及继发骨肿瘤12例。结果表明,胎儿胸腺的血供主要来自胸廓内动脉,其次为甲状腺下动脉和心包膈动脉胸腺支,7～8个月胎儿胸腺静脉血管壁较厚,适合作血管吻合,胸腺细胞发育成熟,组织结构正常,已有分泌胸腺素及转化免疫细胞的功能,在解剖学,组织学,免疫学方面均具备了良好的移植条件。12例接受吻合血管胎儿胸腺移植的晚期恶性骨肿瘤患者,其临床症状、体征、X线、免疫指数均有明显改善,患者生存6个月至37个月以上。     

Laser Doppler flowmetry of blood perfusion in mucoperiosteal flaps covering membranes in bone augmentation and implant procedures. A pilot study in dogs.

In guided tissue regeneration (GTR) procedures, flap recession or sloughing may occur as an unwanted sequel to the placement of a membrane. This study was designed to assess the applicability of laser Doppler flowmetry (LDF) in the evaluation of blood perfusion in the mucoperiosteal flap covering the membrane. Five Labrador dogs were initially used inthe study, but one animal was later excluded due to post‐operative problems. Maxillary premolar teeth were extracted and full thickness mucoperiosteal flaps were raised. Following removal of the buccal bone plate, 4 titanium implants were placed on each side. An experimental biodegradable polylactic‐acid membrane was placed over the fixtures on one side to allow for GTR. The mucoperiosteal flap was repositioned and secured with sutures. The contralateral side served as control with no membrane. Blood perfusion was measured in the flaps before surgery, immediately after suturing and at 24, 48 and 72 h postoperatively. A laser Doppler flowmeter was used to assess the blood perfusion. In 3 animals the membrane was exposed within 2 weeks post‐operatively, and in these 3 animals the LDF values were lower on the membrane side than on the control side. The mean LDF value was lower on the membrane side for each of the 4 periods studied. The tindings suggest that LDF can be a valuable method to study blood perfusion of oral mucosal flaps and that there may be a relationship between a reduced relative LDF value and subsequent exposure of the membrane to the oral environment.