A tissue engineering strategy for the treatment of avascular necrosis of the femoral head

Background & purposeSkeletal stem cells (SSCs) and impaction bone grafting (IBG) can be combined to produce a mechanically stable living bone composite. This novel strategy has been translated to the treatment of avascular necrosis of the femoral head. Surgical technique, clinical follow-up and retrieval analysis data of this translational case series is presented.MethodsSSCs and milled allograft were impacted into necrotic bone in five femoral heads of four patients. Cell viability was confirmed by parallel in vitro culture of the cell-graft constructs. Patient follow-up was by serial clinical and radiological examination. Tissue engineered bone was retrieved from two retrieved femoral heads and was analysed by histology, microcomputed tomography (μCT) and mechanical testing.ResultsThree patients remain asymptomatic at 22- to 44-month follow-up. One patient (both hips) required total hip replacement due to widespread residual necrosis. Retrieved tissue engineered bone demonstrated a mature trabecular micro-architecture histologically and on μCT. Bone density and axial compression strength were comparable to trabecular bone.ConclusionsClinical follow-up shows this to be an effective new treatment for focal early stage avascular necrosis of the femoral head. Unique retrieval analysis of clinically translated tissue engineered bone has demonstrated regeneration of tissue that is both structurally and functionally analogous to normal trabecular bone.     

Enhanced trabecular micro-architecture of the femoral neck in hip osteoarthritis vs. healthy controls: a micro-computer tomography study in postmenopausal women

Purpose

A controversial relationship between osteoarthritis (OA) and bone fragility has been attracting considerable attention. However, despite interest in the effects of OA on femoral neck fracture risk and numerous studies analysing the changes in the arthritic femoral head, there is insufficient data about femoral neck 3D bone micro-architecture in individuals with hip osteoarthritis. We compared trabecular micro-architecture of the femoral neck between postmenopausal women with coxarthrosis and controls to explore whether coxarthrosis may indicate reduced bone fragility from the trabecular micro-architectural perspective.

Methods

The study sample included nine women with hip osteoarthritis and 13 age-matched controls. The femoral neck sections were scanned using micro-computed tomography, evaluating the cancellous bone from the superolateral and inferomedial neck subregions.

Results

Osteoarthritic subjects demonstrated a general trend of improved trabecular micro-architecture in both analysed subregions when compared with age-matched controls. In particular, several architectural properties that are important predictors of cancellous bone strength showed significantly better values in the OA group, even after adjusting for bone volume fraction. Namely, the OA group expressed higher trabecular connectivity (p = 0.008), lower SMI indicating more plate-like structure (p = 0.005), and reduced anisotropy (p = 0.006) particularly in the inferomedial neck. Osteoarthritic cases also trended towards higher BV/TV, particularly in the superolateral neck. All micro-architectural parameters displayed significant regional heterogeneity (p ≤ 0.01), with the inferomedial neck region showing more favourable values than the superolateral region.

Conclusions

Enhanced trabecular micro-architecture of the femoral neck in postmenopausal osteoarthritic subjects suggests reduced cancellous bone fragility in comparison with their age-matched healthy controls.     

Osteochondritis Dissecans Capituli Humeri) (Untersuchungen an 168 Fällen)

We examined the subchondral bone architecture of the femoral head in relation to trabecular microfracture. Three groups of femoral head specimens were studied. Twenty-eight specimens taken during hip replacement had grade III or IV arthrosis (70 × 8 years). From autopsy, 40 femoral heads were obtained, 18 in a group greater than 50 years of age (72 × 10 years) and 22 in a group less than 50 years of age (25 × 11 years). None of these 40 heads had worse than grade II arthrosis. Coronal slices of the femoral heads were macerated and examined under a dissecting microscope to count trabecular microfractures. For bone histomorphometry, blocks were taken from the subchondral principal compressive and tensile trabeculae. The bone volume, trabecular thickness, and marrow space were quantified. In the subchondral principal compressive region, the arthrotic group had more bone volume, thicker trabeculae, similar trabecular space, and trabecular microfractures when compared with the group greater than 50 years old. In the tensile region, there were no differences except for decreased trabecular microfracture number in the arthrotic group. With the thinnest trabeculae in the compressive region occurring in the greater than 50 years old group, the trabeculae of the younger age group have thinned with age, but with the onset of arthrosis, the thinning is overtaken by pathologic thickening of trabeculae.     

Microfractures in coxarthrosis

We examined the subchondral bone architecture of the femoral head in relation to trabecular microfracture. Three groups of femoral head specimens were studied. Twenty-eight specimens taken during hip replacement had grade III or IV arthrosis (70 × 8 years). From autopsy, 40 femoral heads were obtained, 18 in a group greater than 50 years of age (72 × 10 years) and 22 in a group less than 50 years of age (25 × 11 years). None of these 40 heads had worse than grade II arthrosis. Coronal slices of the femoral heads were macerated and examined under a dissecting microscope to count trabecular microfractures. For bone histomorphometry, blocks were taken from the subchondral principal compressive and tensile trabeculae. The bone volume, trabecular thickness, and marrow space were quantified. In the subchondral principal compressive region, the arthrotic group had more bone volume, thicker trabeculae, similar trabecular space, and trabecular microfractures when compared with the group greater than 50 years old. In the tensile region, there were no differences except for decreased trabecular microfracture number in the arthrotic group. With the thinnest trabeculae in the compressive region occurring in the greater than 50 years old group, the trabeculae of the younger age group have thinned with age, but with the onset of arthrosis, the thinning is overtaken by pathologic thickening of trabeculae.     

Microfractures in coxarthrosis

We examined the subchondral bone architecture of the femoral head in relation to trabecular microfracture. Three groups of femoral head specimens were studied. Twenty-eight specimens taken during hip replacement had grade III or IV arthrosis (70 +/- 8 years). From autopsy, 40 femoral heads were obtained, 18 in a group greater than 50 years of age (72 +/- 10 years) and 22 in a group less than 50 years of age (25 +/- 11 years). None of these 40 heads had worse than grade II arthrosis. Coronal slices of the femoral heads were macerated and examined under a dissecting microscope to count trabecular microfractures. For bone histomorphometry, blocks were taken from the subchondral principal compressive and tensile trabeculae. The bone volume, trabecular thickness, and marrow space were quantified. In the subchondral principal compressive region, the arthrotic group had more bone volume, thicker trabeculae, similar trabecular space, and trabecular microfractures when compared with the group greater than 50 years old. In the tensile region, there were no differences except for decreased trabecular microfracture number in the arthrotic group. With the thinnest trabeculae in the compressive region occurring in the greater than 50 years old group, the trabeculae of the younger age group have thinned with age, but with the onset of arthrosis, the thinning is overtaken by pathologic thickening of trabeculae.     

老年与青年股骨头内松质骨组织形态计量学比较研究

目的 研究老年部骨折患股骨头松质骨结构。方法 取股骨示本４９只,分成老年组２６例及青年组２３例。在股骨头致密区（负重区）和疏松区（非负重区）各截取软骨下３ｍｍ处７ｍｍ×５ｍｍ×５ｍｍ松质骨各一块作骨组织形态计量测定。结果 老年组致密区和稀疏区骨组织形态参数松质骨体积（ＴＢＶ）、平均骨小梁密度（ＭＴＰＤ）、平均骨小梁厚度（ＭＴＰＴ）、骨小梁间连接点数（Ｔｂ、ｎ）均明显低于青年组（Ｐ〈０．０５～０．     

Micro-architecture study of the normal odontoid with micro-computed tomography

Introduction: Odontoid fractures easily lead to instability, causing spinal cord injury. The aim of this study was to measure and analyze the micro-architecture and morphometric parameters of the normal odontoid with high-resolution three-dimensional (3D) micro-computed tomography (micro-CT).

Methods: Micro-CT scans were obtained from five normal odontoid processes. The scanned data were reconstructed with micro-CT software, and the nutrient foramina and the ossification center of the base of the odontoid were revealed. The trabeculae of the odontoid were measured and divided into four parts to obtain the volume fraction of regions of interest.

Results: High-resolution 3D images of the micro-structures’ parameters were obtained from the odontoid using micro-CT software. The images demonstrated sponge-like trabecular bone, with the trabeculae showing a complex, net-like micro-construction. The subchondral bone plate was of lamella-like, compact construction and extended and transformed into a net-like structure with rod-shaped trabeculae arranged radially in all directions. There was a statistically significant difference in the volume fraction compared with the region of interest in the fourth part of the trabeculae and the first part of the odontoid (P?<?0.05). The nutrient foramina and the ossification center of the odontoid were also observed.

Conclusions: It is feasible to use high-resolution 3D micro-CT to evaluate the micro-architecture of the normal odontoid. Other studies can benefit from use of the micro-CT images, such as finite element evaluations.     

Ischemic necrosis of the femoral head: An experimental rabbit model

To describe the morphology of the proximal femoral epiphysis in a rabbit model from the ischemic insult to the end of the revascularization process. Ischemia of the femoral head was induced in 32 rabbits at the 8th day of life, by sectioning the joint capsule and the ligamentum teres and dislocating the femoral head. Rabbits were sacrificed at 4, 8, 12, 18, 21, 26, 34, and 48 days after surgery and femoral heads were observed histologically. During the first days following the ischemic injury, large areas underwent necrotic changes. Both epiphyseal and physeal cartilage were thicker than normal and less trabecular bone formation was evident. Bone marrow was also diffusely necrotic within the secondary center of ossification. After day 12th, reparative process started with formation of extensive areas of fibrocartilage and several secondary centers of ossifications. At that stage femoral head deformity was already evident. In the following days the secondary centers of ossification cohalesced and epiphyseal and physeal cartilage resumed a normal appearance, but the femur showed a permanent deformity. In newborn rabbits, the ischemic injury to the femoral head blocked the ossification of the epiphyseal and physeal cartilage associated to necrotic bone marrow within the secondary center of ossification of the femoral head as well as to extensive areas of necrosis of epiphyseal and physeal cartilage. Extensive areas of fibrocartilage and small newly formed ossification centers within the femoral epiphysis were the results of the revascularization process, and femoral head deformity became stable afterward. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:535–541, 2015.     

Subchondral fracture after ischemic osteonecrosis of the immature femoral head in piglet model

This experimental investigation was performed to study the development of a subchondral fracture after ischemic osteonecrosis of the immature femoral head using a piglet model. Forty-eight male piglets were studied after placing a ligature tightly around the femoral neck to disrupt the blood supply to the femoral head. Animals were euthanized 2-8 weeks after the induction of ischemia. Radiographic, histologic, and histomorphometric assessments were made. A subchondral fracture was seen in 12 out of 32 infarcted femoral heads (38%) that were in the initial radiographic stage of ischemic osteonecrosis. The fracture was seen mainly in those femoral heads that had a prolonged period of the initial stage where the initiation of revascularization and repair was delayed. Histomorphometric assessment showed decreased trabecular thickness and volume in the subchondral region of the infarcted femoral heads compared with the contralateral normal heads. After ischemic osteonecrosis, the trabecular bone in the subchondral region is thinner and less bone volume is present because of a lack of new bone formation. The results of this study support the hypothesis that a subchondral fracture in the immature femoral head develops as a result of mechanic failure of the trabecular bone in the subchondral region.     

Morphological analysis of collapsed regions in osteonecrosis of the femoral head

In order to investigate the mechanisms of collapse in osteonecrosis of the femoral head, we examined which part of the femoral head was the key point of a collapse and whether a collapsed region was associated with the size of the necrotic lesion. Using 30 consecutive surgically removed femoral heads we retrospectively analysed whole serial cut sections, specimen photographs, specimen radiographs and histological sections. In all of the femoral heads, collapse consistently involved a fracture at the lateral boundary of the necrotic lesion. Histologically, the fractures occurred at the junction between the thickened trabeculae of the reparative zone and the necrotic bone trabeculae. When the medial boundary of the necrotic lesion was located lateral to the fovea of the femoral head, 18 of 19 femoral heads collapsed in the subchondral region. By contrast, when the medial boundary was located medial to the fovea, collapse in the subchondral region was observed in four of 11 femoral heads (p = 0.0011). We found that collapse began at the lateral boundary of the necrotic lesion and that the size of the necrotic lesion seemed to contribute to its distribution.     

The thermal effects of lavage on 57 ox femoral heads prepared for hip resurfacing arthroplasty

Background and purpose Previously, we have documented surface temperatures recorded by thermography great enough to cause osteonecrosis of the femoral head during hip resurfacing. We now performed an in vitro investigation with 3 questions: (1) whether water irrigation reduced bone surface temperature, (2) whether external bone temperatures were similar to core temperatures, and (3) whether blunting of the reamer affected temperature generation.

Methods Using an ox-bone model, 57 femoral heads were peripherally reamed. The surface temperatures of bone were measured using a thermal camera and internal bone temperatures were measured using 2 theromocouples. We measured the effects of cooling with water at room temperature and with ice-cooled water. Progressive blunting of reamers was assessed over the 57 experiments.

Results Mean and maximum temperatures generated during peripheral reaming were greater when no irrigation was used. Ice-cold saline protected femoral heads from thermal damage. External bone temperatures were much greater than internal temperatures, which were not sufficiently elevated to cause osteonecrosis regardless of lavage. Blunting of the reamer was not found to have a statistically significant effect in this study.

Interpretation Cooling with ice-cooled water is recommended. Internal bone temperatures are not elevated despite the high surface temperatures reached during femoral head resurfacing.     

Transphyseal osseous bridges in experimental osteonecrosis of the femoral head of the rat. Histologic study of the bony bridges connecting the epiphyseal with the metaphyseal bony trabeculae through gaps in the physeal cartilage

In view of the lifelong persistence of the physis, the femoral head of rats may serve to model Perthes disease and slipped capital femoral epiphysis. To produce osteonecrosis, the blood supply of one femoral head of 133, 6-month-old animals was severed by circumferentially incising the periosteum of the neck and cutting the ligamentum teres. The rats were killed 7 days to 90 days postoperatively. Associated with resorption of the necrotic bone and marrow, remodeling of the epiphysis was characterized by an ingrowth of vascularized fibrous tissue, formation of new bone and some cartilage, architectural deformation and flattening of the head. In 22 of 83 rats killed 30 days or more postoperatively, gaps in the continuity of the physeal cartilage were occupied by osseous bridges, connecting newly formed epiphyseal bony trabeculae with either the preexisting or newly formed metaphyseal osseous trabeculae. This healing mode may follow ischemic death of physeal chondrocytes or be owing to another mechanism, e.g., release of mediatory substances of inflammation. These findings raise the possibility that fixation of the healing epiphysis of a child's previously necrotic femoral head to the metaphysis occurs by transphyseal osseous growth in cases in which the physis is involved in the necrotic process.     

A new bone adhesive candidate- does it work in human bone? An ex-vivo preclinical evaluation in fresh human osteoporotic femoral head bone

IntroductionThe fixation of small intraarticular bone fragments is clinically challenging and an obvious first orthopaedic indication for an effective bone adhesive. In the present study the feasibility of bonding freshly harvested human trabecular bone with OsStic^R, a novel phosphoserine modified cement, was evaluated using a bone cylinder model pull-out test and compared with a commercial fibrin tissue adhesive.MethodsFemoral heads (n=13) were collected from hip fracture patients undergoing arthroplasty and stored refrigerated overnight in saline medium prior to testing. Cylindrical bone cores with a pre-inserted bone screw, were prepared using a coring tool. Each core was removed and glued back in place with either the bone adhesive (α-tricalcium phosphate, phosphoserine and 20% trisodium citrate solution) or the fibrin glue. All glued bones were stored in bone medium at 37°C. Tensile loading, using a universal testing machine (5 kN load cell), was applied to each core/head. For the bone adhesive, bone cores were tested at 2 (n=13) and 24 (n=11) hours. For the fibrin tissue adhesive control group (n=9), bone cores were tested exclusively at 2 hours. The femoral bone quality was evaluated with micro-CT.ResultsThe ultimate pull-out load for the bone adhesive at 2 hours ranged from 36 to 171 N (mean 94 N, SD 42 N). At 24 hours the pull-out strength was similar, 47 to 198 N (mean 123 N, SD 43 N). The adhesive failure usually occurred through the adhesive layer, however in two samples, at 167 N and 198 N the screw pulled out of the bone core. The fibrin tissue adhesive group reached a peak force of 8 N maximally at 2 hours (range 2.8-8 N, mean 5.4 N, SD 1.6 N). The mean BV/TV for femoral heads was 0.15 and indicates poor bone quality.ConclusionThe bone adhesive successfully glued wet and fatty tissue of osteoporotic human bone cores. The mean ultimate pull-out force of 123 N at 24 hours corresponds to ～ 300 kPa shear stress acting on the bone core. These first ex-vivo results in human bone are a promising step toward potential clinical application in osteochondral fragment fixation.     

淫羊藿苷干预兔早期激素性股骨头坏死的实验研究

目的探讨淫羊藿苷对激素诱导的兔早期激素性股骨头坏死干预效果。方法50只成年新西兰兔(体质量2.5~3.0 kg)随机分为对照组(n=10)、模型组(n=20)及实验组(n=20)。模型组和实验组采用脂多糖联合甲泼尼龙注射制备早期激素性股骨头坏死模型;实验组首次注射甲泼尼龙开始每日灌服淫羊藿苷药液1次,对照组及模型组灌服等量生理盐水,连续6周。于6周后取左侧股骨头行大体观察;Micro-CT扫描观察骨小梁微结构,测量骨小梁相对体积(bone volume to total volume,BV/TV)、骨小梁数量(trabecular number,Tb.N)、骨小梁厚度(trabecular thickness,Tb.Tn)及骨小梁分离度(trabecular separation,Tb.Sp),并构建三维图像观察;HE染色观察骨小梁结构、骨细胞及骨髓脂肪细胞形态变化,按照病理学诊断标准检测股骨头坏死模型造模是否成功,计算空骨陷窝率。结果实验期间共7只动物死亡,最终对照组9只、模型组16只、实验组18只纳入研究。大体及Micro-CT扫描、三维重建显示,与对照组相比,模型组股骨头塌陷明显,骨小梁断裂、排列紊乱稀疏;实验组股骨头表面皱褶,塌陷不明显,骨小梁结构轻度退变。与对照组相比,模型组和实验组Tb.N、Tb.Tn、BV/TV下降、Tb.Sp升高;与模型组相比,实验组Tb.N、Tb.Tn、BV/TV升高、Tb.Sp降低;组间比较差异均有统计学意义(P<0.05)。HE染色示模型组骨小梁中骨细胞减少,空骨陷窝较多,骨小梁间脂肪细胞堆积,部分呈囊状融合;实验组骨小梁形态较模型组完整,骨细胞坏死及脂肪细胞肥大不明显。按照股骨头坏死病理学诊断标准,对照组无骨坏死发生,模型组骨坏死发生率为81.3%(13/16),实验组为66.7%(12/18),差异无统计学意义(P=0.448)。模型组和实验组发生坏死的股骨头标本其空骨陷窝率分别为33.1%±1.4%及18.9%±0.8%,均高于对照组12.7%±1.5%,且模型组明显高于实验组,差异均有统计学意义(P<0.05)。结论淫羊藿苷对激素诱导的兔早期激素性股骨头坏死具有保护作用,可以降低骨细胞凋亡,改善骨微结构,延缓骨坏死发生。     

Mechanical torque measurement for in vivo quantification of bone strength in the proximal femur

IntroductionBone strength determines fracture risk and fixation strength of osteosynthesis implants. In vivo, bone strength is currently measured indirectly by quantifying bone mineral density (BMD) which is however only one determinant of the bone's biomechanical competence besides the bone's macro- and micro-architecture and tissue related parameters. We have developed a measurement principle (DensiProbe? Hip) for direct, mechanical quantification of bone strength within the proximal femur upon hip fracture fixation. Previous cadaver tests indicated a close correlation between DensiProbe? Hip measurements, 3D micro-CT analysis and biomechanical indicators of bone strength. The goal of this study was to correlate DensiProbe? Hip measurements with areal bone mineral density (BMD).MethodsForty-three hip fracture patients were included in this study. Intraoperatively, DensiProbe? Hip was inserted to the subsequent hip screw tip position within the femoral head. Peak torque to breakaway of local cancellous bone was registered. Thirty-seven patients underwent areal BMD measurements of the contralateral proximal femur. Failure of fixation was assessed radio graphically 6 and 12 weeks postoperatively.ResultsPeak torque and femoral neck BMD showed significant correlations (R = 0.60, P = 0.0001). In regression analysis, areal BMD explained 46% of femoral neck BMD variance in a quadratic relationship. Throughout the 12-week follow-up period, no failure of fixation was observed.ConclusionsDensiProbe? Hip may capture variations of bone strength beyond areal BMD which are currently difficult to measure in vivo. A multicenter study will clarify if peak torque predicts fixation failure.     

Ibandronate for prevention of femoral head deformity after ischemic necrosis of the capital femoral epiphysis in immature pigs

BACKGROUND: Femoral head deformity is the most serious sequela of ischemic necrosis of the immature femoral head. The purpose of this study was to determine if a highly potent antiresorptive agent, ibandronate, can inhibit bone resorption during the repair of the infarcted femoral head and thus alter the repair process. We hypothesized that preservation of the trabecular framework by inhibiting osteoclastic bone resorption would minimize the development of deformity in a piglet model of ischemic necrosis. The effect of ibandronate on long-bone growth was also assessed. METHODS: Ischemic necrosis of the right femoral head was produced in twenty-four piglets by placing a ligature tightly around the femoral neck. The animals were divided into three groups according to whether they received saline solution, prophylactic treatment, or post-ischemia treatment. The contralateral, untreated femoral heads from the animals that had received saline solution served as the normal control group. At eight weeks, the femoral heads were assessed for deformity with radiography and for trabecular bone indices with histomorphometry. Also, the length of femur from the untreated side was measured on the radiographs and compared among the groups. RESULTS: Radiographic assessment showed that the epiphyseal quotient, determined by dividing the maximum height of the osseous epiphysis by the maximum diameter, was better preserved in the prophylactic (p < 0.001) and post-ischemia (p = 0.02) treatment groups than in the group treated with saline solution. Histomorphometric assessment also showed that the trabecular bone indices were better preserved in the prophylactic and the post-ischemia treatment groups than in the group treated with saline solution (p < 0.01). The mean femoral length on the untreated side of the animals treated with ibandronate was reduced compared with the length on the untreated side of the animals that had received saline solution (p 相似文献   

血管束植入联合细胞移植治疗兔股骨头坏死模型的实验研究

目的:探讨血管束植入联合同种异体骨髓基质干细胞移植治疗兔股骨头坏死骨缺损模型的可行性,探索治疗股骨头坏死的一种新方法.方法:36只新西兰大耳白兔随机分成A、B、C3组,每组12只,所有动物的双侧股骨头均参加实验.用液氮冷冻法造模,股骨头钻孔造成骨缺损.A组为空白对照组,B组为同种异体骨髓基质干细胞移植组,C组为同种异体骨髓基质干细胞移植联合血管束植入组.分别于术后2、4、8、12用处死3只实验动物.所获的股骨头标本分别做组织切片HE染色,进一步测算股骨头冠状截面的血管密度及新生骨小梁在骨缺损区所占的面积百分比,做统计分析.结果:C组股骨头缺损区2周时可见新生骨小梁和原始毛细血管形成,8周时新生骨小梁板层状或编织状,毛细血管丰富,12周时骨小梁变宽变粗,排列规则,可见成熟的骨小梁及新生骨髓.B、C两组股骨头冠状截面的血管密度及新生骨小梁在骨缺损区所占的面积比,2周时差异无统计学意义,4、8、12周时C组股骨头冠状截面的血管密度及新生骨小梁在骨缺损区所占的面积比均比同时期B组大.结论:体外培养的同种异体骨髓基质干细胞能在股骨头坏死骨缺损区形成新生骨小梁,可以用作异体移植.植入股骨头坏死骨缺损区的血管束可以有效改善股骨头的血运,促进新生骨小梁的形成.     

The role of sclerotic changes in the starting mechanisms of collapse: A histomorphometric and FEM study on the femoral head of osteonecrosis

PurposeTo assess the distributions of stress, strain, and fractured areas using a finite element model (FEM), and examine the osteoclastic activity histopathologically in osteonecrosis of the femoral head.MethodsThree femoral heads were obtained during hip arthroplasty for femoral head osteonecrosis. One sample with a normal area, two samples with a non-sclerotic boundary without collapse (Type 1), two samples with a non-collapsed sclerotic boundary (Type 2), and two samples with a collapsed sclerotic boundary (Type 3) were collected from each femoral head for the FEM and histopathological analyses. FEM was performed using CT data, and the distributions of von Mises equivalent stress, octahedral shear stress, octahedral shear strain, and simulated fractured area were evaluated. Furthermore, the osteoclast count at the boundary was compared for each type.ResultsIn normal and Type 1 samples, the distributions of von Mises equivalent stress, octahedral shear stress, octahedral shear strain, and the fractured area were equally concentrated along the whole analytical range; however, in the Type 2 and 3 samples, they were concentrated along the thickened bone trabeculae at the boundary, which corresponded to the fractured area. Histopathologically, a significantly increased osteoclast number was observed only at the collapsed sclerotic boundary.ConclusionThese results demonstrated that both shear stress and shear strain tend to be concentrated on thickened bone trabeculae at the boundary. Fracture analyses revealed that the boundary of sclerotic changes, which results from the repair process, may be the starting point of the fracture. Additionally, the osteoclastic activity increases after collapse.     

Trabecular microfractures in the femoral head with osteoporosis: Analysis of microcallus formations by synchrotron radiation micro CT

Trabecular bone microfracture pathogenesis and associated healing processes are not well understood. We analyzed the microcalluses that form subsequent to microfractures in patients with osteoporosis (OP) using synchrotron radiation micro CT (SRCT).Subchondral bone columns were extracted from the femoral heads of 11 female patients with a femoral neck fracture. SRCT scanning was performed with 5.9 × 5.9 × 5.9 μm³ voxel size and the microcallus number was measured in a 5-mm cubic subchondral bone region. The trabecular bone microstructure was measured and its relationship to the microcallus number was analyzed. In addition, the degree of mineralization of the microcallus region and that of the rest of the trabecular bone were measured and compared.Microcallus formations were detected in all cases, with a mean microcallus number of 4.9 (range, 2–11). The microcallus number had a significantly negative correlation with bone volume fraction (BV/TV), trabecular thickness (Tb.Th), and degree of mineralization, and had a positive correlation with specific bone surface (BS/BV). The degree of mineralization of the microcallus region was lower than that of the rest of the trabecular bone and had a wider range of values.Microcallus formations were frequently detected in patients with OP, and more prevalent in the bone with thinner trabeculae, suggesting microfractures might occur due to activities of daily living as the OP progresses. The degree of mineralization of microcallus might represent the process of bone healing from immature woven bone to mature trabecular bone.     

Pathology of femoral head collapse following transtrochanteric rotational osteotomy for osteonecrosis

We investigated the pathology of femoral head collapse following transtrochanteric anterior rotational osteotomy. Six femoral heads were obtained during total hip arthroplasty some 2–12 years after osteotomy. In all cases, the preoperatively necrotic lesions exhibited mostly osteonecrosis with accumulation of bone marrow cell debris and trabecular bone with empty lacunae, although repair tissue such as granulation tissue and appositional bone formation were observed in limited areas in some cases. In the transposed intact articular surface of the femoral head, osteoarthritic changes such as fissure penetration to the subchondral bone and osteophyte formation were commonly observed. In newly created subchondral areas at weight-bearing sites, trabecular thickness and the number of trabecular bones had decreased, with few osteoblasts, osteoclasts, and osteocytes being present, resulting in a coarse lamellar structure of the trabecular bone. These findings suggest that transposed areas in cases of failure consist mostly of low-turnover osteoporotic lesions which could cause collapse of the femoral head. Received: 5 October 1999