Biological apatite (BAp) crystallographic orientation and texture as a new index for assessing the microstructure and function of bone regenerated by tissue engineering

Recently, there have been remarkable advances in medical techniques for regenerating bone defects. To determine the degree of bone regeneration, it is essential to develop a new method that can analyze microstructure and related mechanical function. Here, quantitative analysis of the orientation distribution of biological apatite (BAp) crystallites by a microbeam X-ray diffractometer system is proposed as a new index of bone quality for the evaluation of regenerated bone microstructure. Preferential alignment of the BAp c-axis in the rabbit ulna and skull bone, regenerated by controlled release of basic fibroblast growth factor (bFGF) was investigated. The BAp c-axis orientation was evaluated by the relative intensity between the (002) and (310) diffraction peaks, or the three-dimensional texture for the (002) peak. It was found that new bone in the defects was initially produced without preferential alignment of the BAp c-axis, and subsequently reproduced to recover towards the original alignment. In other words, the BAp density recovered prior to the BAp orientation. Perfect recovery of BAp alignment was not achieved in the ulna and skull defects after 4weeks and 12weeks, respectively. Apparent recovery of the macroscopic shape and bio-mineralization of BAp was almost complete in the ulna defect after 4weeks. However, an additional 2weeks was required for complete repair of BAp orientation. It is finally concluded that orientation distribution of BAp crystallites offers an effective means of evaluating the degree of microstructural regeneration, and also the related mechanical function, in regenerated hard tissues.     

A Mechanical Analysis of Femoral Resurfacing Implantation for Osteonecrosis of the Femoral Head

Hip resurfacing is becoming a popular procedure for treating osteonecrosis of the femoral head. However, the biomechanical changes that occur after femoral resurfacing have not been fully investigated with respect to the individual extent of the necrosis. In this study, we evaluated biomechanical changes at various extents of necrosis and implant alignments using the finite element analysis method. We established 3 patterns of necrosis by depth from the surface of femoral head and 5 stem angles. For these models, we evaluated biomechanical changes associated with the extent of necrosis and the stem alignment. Our results indicate that stress distribution near the bone-cement interface increased with expansion of the necrosis. The maximum stress on the prosthesis was decreased with stem angles ranging from 130° to140°. The peak stress of cement increased as the stem angle became varus. This study indicates that resurfacing arthroplasty will have adverse biomechanical effects when there is a large extent of osteonecrosis and excessive varus or valgus implantation of the prosthesis.     

Alendronate treatment promotes bone formation with a less anisotropic microstructure during intramembranous ossification in rats

There are safety concerns regarding administration of bisphosphonates to children. Little is known about the effects of bisphosphonates on bone matrix organization during bone modeling. The present study examined the effects of alendronate (ALN) on bone matrices formed by intramembranous ossification in the appendicular growing skeleton. ALN was administered to 1-week-old Sprague–Dawley rats at a dose of 0, 35, or 350 μg/kg/week for 4 or 8 weeks. The position of femoral diaphysis formed exclusively by intramembranous ossification was identified, and cross sections of cortical bone at this position were analyzed. Bone mineral density (BMD) and geometric parameters were evaluated using peripheral quantitative computed tomography. The preferential orientation degree of biological apatite (BAp) crystals in the bone longitudinal direction, which shows the degree of bone matrix anisotropy, was evaluated using microbeam X-ray diffraction analysis. We analyzed bone histomorphometrical parameters and performed bone nanomechanical tests to examine the material properties of newly developing cortical bone. The preferential orientation degree of BAp crystals significantly decreased in 35 μg/kg/week ALN-treated groups compared with vehicle-treated groups, although there were no significant differences in BMD between the two groups. The periosteal mineral apposition rate significantly increased in the 35 μg/kg/week ALN-treated group. We found a high negative correlation between bone matrix anisotropy and the regional periosteal mineral apposition rate (r = −0.862, P < 0.001). Nanomechanical tests revealed that 35 μg/kg/week ALN administration caused deterioration of the material properties of the bone microstructure. These new findings suggest that alendronate affects bone matrix organization and promotes bone formation with a less anisotropic microstructure during intramembranous ossification.     

Unique alignment and texture of biological apatite crystallites in typical calcified tissues analyzed by microbeam X-ray diffractometer system

Preferential orientation of biological apatite (Ap) crystallites in typical calcified tissues of rabbit ulna, rabbit skull, and monkey dentulous mandible was investigated using a microbeam X-ray diffractometer, with a beam spot of 100 microm in diameter, to clarify relationship between the Ap orientation and mechanical function. Preferential alignment of the c-axis of the biological Ap was evaluated by the relative intensity between (002) and (310) diffraction peaks. Preferential alignment of biological Ap in each calcified tissue varied depending on the shape and stress condition in vivo; that is, the c-axes of biological Ap in the rabbit ulna and the rabbit skull bone were preferentially observed as a one-dimensional orientation along the longitudinal axis and a two-dimensional orientation along the surface, respectively. Precise analysis of the preferential alignment along the skull surface showed an elliptical distribution of the c-axis of biological Ap elongating along the suture inside the skull surface of both lamina exterior and interior. The c-axis of biological Ap in a monkey dentulous mandible basically aligned along the mesiodistal direction in the flat bone, but this alignment changed along the normal direction to the flat bone surface parallel to the biting direction near the tooth, due to the force of mastication. It was concluded that the microscale measurement of biological Ap texture is one of the useful new methods for evaluating mechanical function and stress distribution in vivo in calcified tissues.     

Role of surgical position on interface stress and initial bone remodeling stimulus around hip resurfacing arthroplasty

Valgus alignment of femoral resurfacing components has been advocated to reduce proximal femur loading and thus minimize the risk for femoral neck fractures. However, such reduction in loading may exacerbate undesirable stress shielding. This study examined the effect of extreme implant orientations (±15°) and stem canal overreaming on initial bone remodeling stimulus using finite element models. The changes in implant-cement interface stresses due to implant alignment were also evaluated. The valgus model showed increased initial bone resorption stimulus, which extended distally and peripherally around the femoral neck. The peak implant-cement interface shear stress for the varus model was 10.9 MPa, exceeding the interface shear strength. Overreaming of the stem canal eliminated distal tip loading, but proximal stress shielding was still unavoidable. These data show bone loading and interface fixation trends emanating from valgus and varus implant positions that will be of interest to practicing physicians.     

Stress analysis of an anatomically-adapted femur shaft prosthesis (Lubinus SPII)]

OBJECTIVE: Very good clinical long-term results of the Lubinus SP II hip prosthesis stem were reported in the literature. We therefore asked whether there is a relationship between these findings with biomechanical data of strain gauge measurements. METHOD: 14 strain gauges were applied at a femur being measured at 10 different load cases before and after implantation of the stem. RESULTS: After stem implantation a similar patterns of principal stress distributions was observed, however, the magnitude was markedly reduced. A striking reduction of the hoop stresses at the femoral calcar was seen in the case of a missing collar contact. Even in the case of a perfect collar contact the hoop stresses were diminished after strem implantation. The S-shaped physiological stem did not correspond with a specific stress pattern measured at the femoral surface. CONCLUSION: These results suggest that the stresses at the femoral calcar may be lower than the limits of bone growth while the other parts of the femur are more physiologically stressed. However, the prosthesis may tolerate a missing collar contact during a long follow-up period. The large experimental data file presented here could be used to validate future finite element analyses which could evaluate the stress distribution within internal parts of the bone and the cement layer.     

Evaluation of crystallographic orientation of biological apatite in vertebral cortical bone in ovariectomized cynomolgus monkeys treated with minodronic acid and alendronate

Quantitative analysis of the orientational distribution of biological apatite (BAp) crystals is proposed as a new index of bone quality. This study aimed to analyze BAp c-axis orientation in ovariectomized (OVX) monkeys treated with amino-bisphosphonates minodronic acid and alendronate as reference. Sixty female monkeys aged 9–17 years were divided into five groups: one sham group and four OVX groups. The sham group and one OVX group were treated daily with vehicle for 17 months. The other three groups were treated daily with minodronic acid at doses of 0.015 and 0.15 mg/kg, and alendronate at 0.5 mg/kg orally, respectively. The seventh lumbar vertebrae were subjected to analysis of the preferential BAp c-axis orientation in the ventral cortical bone. The BAp c-axis orientation along the craniocaudal axis was significantly increased in the OVX monkeys. The high dose of minodronic acid suppressed the OVX-induced increase in the BAp c-axis orientation, whereas alendronate showed a non-significant tendency to suppress the increase in the orientation. In analysis with other parameters, the BAp c-axis orientation was positively correlated with bone formation indices in biochemical markers and bone histomorphometry and negatively correlated with the increase in lumbar bone mineral density. On the other hand, the BAp c-axis orientation was not correlated with bone resorption indices, except for the eroded surface. These results indicate that the increase in BAp c-axis orientation was ameliorated by minodronic acid treatment in OVX monkeys, mainly by suppression of bone formation increase.     

Varus malalignment of the lower limb increases the risk of femoral neck fracture: A biomechanical study using a finite element method

IntroductionThe understanding of the stresses and strains and their dependence on loading direction caused by an axial deformity is very important for understanding the mechanism of femural neck fractures. The hypothesis of this study is that lower limb malalignment is correlated with a substantial stress variation on the upper end of the femur. The purpose of this biomechanical trial using the finite element method is to determine the effect of the loading direction on the proximal femur regarding the malalignment of the lower limb, and also enlighten the relation between the lower limb alignment and the risk of a femoral neck fracture.MethodsTen segmentations of CT scans were considered. An axial compression load was applied to the femoral head to digitally simulate the physiological configuration in neutral position as well as in different axial positions in varus/valgus alignment.ResultsThe stress at the proximal femur changes as the varus _valgus angle does. It can be observed the smaller absolute stress at angle 10° (valgus) and the higher absolute stress at angle -10° (varus). The mean maximum von Mises stress value was 14.1 (SD=±3.48) MPa for 0°, while the mean maximum von Mises stress value was 17.96 MPa (SD=4.87) for -10° in varus. The fracture risk indicator of the proximal femoral epiphyses changes inversely with angle direction. The FRI was the highest at -10° and the lowest at 10°.ConclusionBased on the biomechanical findings and the fracture risk indicator determined in this preliminary study, varus malalignment increases the risk of femoral neck fracture. Consideration of other parameters such as bone mineral density and morphological parameters should also help to plan preventive medical strategy in the elderly.     

Regional variations in mineralization and strain distributions in the cortex of the human mandibular condyle

The strain (i.e. deformation) history influences the degree of mineralization of cortical bone (DMB) as well as its osteonal microstructure. This study aimed to examine the relationships of stress and strain distributions with the variations in DMB and the osteonal orientations in the cortical bone of the human mandibular condyle. It was hypothesized that strains are inversely proportional to local DMB and that the principal strains are oriented parallel to the osteons.

To test this, ten human mandibular condyles were scanned in a microCT system. Finite element models were created in order to simulate static clenching. Within each condyle, 18 volumes of interest were selected to analyze regional differences in DMB, stress and strains.

Subchondral bone showed a lower equivalent strain (2652 ± 612 με) as compared to the anterior (p = 0.030) and posterior cortex (p = 0.007) and was less mineralized. Contrary to our hypothesis, the results show that strains correlated positively with regional variations in DMB (r = 0.750, p < 0.001). In the anterior and the posterior cortex, the first principal strain was parallel to the cortical surface and oriented supero-inferiorly with a fan-like shape. In subchondral bone, the first and the second principal strain were parallel to the surface and oriented antero-posteriorly and medio-laterally, respectively.

It was concluded that the strain distributions, by themselves, cannot explain the regional differences found in DMB. In agreement with our second hypothesis, the orientation of the osteonal network of the mandibular condyle was closely related to the strain orientations. The results of this study suggest that the subchondral and the cortical bone are structured to ensure an optimal load distribution within the mandibular condyle and have a different mechanical behaviour. Subchondral bone plays a major role in the transmission of the strains to the anterior and posterior cortex, while these ensure an optimal transmission of the strains within the condylar neck and, eventually, to the mandibular ramus.     

股骨头部分置换术精准微创治疗中老年ARCO Ⅲ期股骨头缺血坏死的有限元分析

目的通过有限元分析,初步评估股骨头部分置换术后股骨与内植物模型的应力分布和位移。 方法选择一名成年健康志愿者,获取股骨全长CT扫描数据,利用Mimics 20.0软件、Geomagic软件及UG NX 12.0软件建立股骨头缺血坏死模型,骨隧道切除股骨头坏死区域后装配设计开发的股骨头假体,模拟单腿站立环境进行有限元仿真模拟,获取股骨与内植物模型的应力分布和位移数据。 结果股骨应力分布主要集中在股骨颈下方和股骨干皮质骨两侧,最大应力为48.25 Mpa,最大位移为10.98 mm。内植物模型的应力主要分布在金属内植物主体结构下方,最大应力为147.2 Mpa,最大位移为9.58 mm。 结论股骨头部分置换后,假体头与股骨头曲率一致,应力传导模式与正常侧髋关节一致,但在假体头与茎部连接处发生应力集中,应重点考虑选择更大强度的材料。     

Modification of COL1A1 in Autologous Adipose Tissue-Derived Progenitor Cells Rescues the Bone Phenotype in a Mouse Model of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a congenital genetic disorder mainly manifested as bone fragility and recurrent fracture. Mutation of COL1A1/COL1A2 genes encoding the type I collagen are most responsible for the clinical patients. Allogenic mesenchymal stem cells (MSCs) provide the potential to treat OI through differentiation into osteoblasts. Autologous defective MSCs have not been utilized in OI treatment mainly because of their impaired osteogenesis, but the latent mechanism has not been well understood. Here, the relative signaling abnormality of adipose-derived mesenchymal stem cells (ADSCs) isolated from OI type I mice (Col1a1^+/−365 mice) was explored. Autologous ADSCs transfected by retrovirus carrying human COL1A1 gene was first utilized in OI therapy. The results showed that decreased activity of Yes-associated protein (YAP) due to hyperactive upstream Hippo kinases greatly contributed to the weakened bone-forming capacity of defective ADSCs. Recovered collagen synthesis of autologous ADSCs by COL1A1 gene modification normalized Hippo/YAP signaling and effectively rescued YAP-mediated osteogenesis. And the COL1A1 gene engineered autologous ADSCs efficaciously improved the microstructure, enhanced the mechanical properties and promoted bone formation of Col1a1^+/−365 mice after femoral bone marrow cavity delivery and might serve as an alternative source of stem cells in OI treatment. © 2021 American Society for Bone and Mineral Research (ASBMR).     

Deformation of mineral crystals in cortical bone depending on structural anisotropy

The deformation mechanism of bone at different hierarchical levels has been of wide interest. The important features of bone, its anisotropy and orientation dependent deformation are equally important, which have also gained a long run discussion. Most of the studies are concentrated on protein-rich collagen fibres and matrix, where different deformation mechanisms at the lower length scales are proposed. But in relation to this, how the mineral particles behave depending on their distribution is yet to be revealed in detail. In the present work, we demonstrate mineral crystals deformation and arrangement characteristics on the basis of experimental outcomes. Using X-ray diffraction procedures, we quantified the mineral strains, degree of orientation of the crystallites and their evolution under different applied step-loads in bovine femoral cortical specimens having different alignment with the femoral axis direction. We provide a direct quantitative comparison of these parameters in the specimens having preferential orientations roughly at 0, 30, 45, 75 and 90° with reference to the loading direction. The mineral strains in the compliant specimens, i.e. 0 and 30° oriented specimens were observed to differ with the stiffer specimens, i.e. 75 and 90° oriented specimens, whereas the 45° oriented specimen show almost equal strains at different loads. These were explained by the degree of orientation with reference to the loading direction and the preferential orientation direction of the specimens. On the basis of observed parameters, we describe deformation phenomena of mineral particles to occur in different stages, which consist of redistribution stage, elastic strain stage and inelastic strain stage. These phenomena are expected to occur at different scales and rates depending on the orientation and distribution of crystals.     

Titanium Alloy Gamma Nail versus Biodegradable Magnesium Alloy Bionic Gamma Nail for Treating Intertrochanteric Fractures: A Finite Element Analysis

ObjectiveTo using finite element analysis to investigate the effects of the traditional titanium alloy Gamma nail and a biodegradable magnesium alloy bionic Gamma nail for treating intertrochanteric fractures.MethodsComputed tomography images of an adult male volunteer of appropriate age and in good physical condition were used to establish a three‐dimensional model of the proximal femur. Then, a model of a type 31A1 intertrochanteric fracture of the proximal femur was established, and the traditional titanium alloy Gamma nails and biodegradable magnesium alloy bionic Gamma nails were used for fixation, respectively. The von Mises stress, the maximum principal stress, and the minimum principal stress were calculated to evaluate the effect of bone ingrowth on stress distribution of the proximal femur after fixation.ResultsIn the intact model, the maximum stress was 5.8 MPa, the minimum stress was −11.7 MPa, and the von Mises stress was 11.4 MPa. The maximum principal stress distribution of the cancellous bone in the intact model appears in a position consistent with the growth direction of the principal and secondary tensile zones. After traditional Gamma nail healing, the maximum stress was 32 MPa, the minimum stress was −23.5 MPa, and the von Mises stress was 31.3 MPa. The stress concentration was quite obvious compared with the intact model. It was assumed that the nail would biodegrade completely within 12 months postoperatively. The maximum stress was 18.7 MPa, the minimum stress was −12.6 MPa, and the von Mises stress was 14.0 MPa. For the minimum principal stress, the region of minimum stress value less than −10 MPa was significantly improved compared with the traditional titanium alloy Gamma nail models. Meanwhile, the stress distribution of the bionic Gamma nail model in the proximal femur was closer to that of the intact bone, which significantly reduced the stress concentration of the implant.ConclusionThe biodegradable magnesium alloy bionic Gamma nail implant can improve the stress distribution of fractured bone close to that of intact bone while reducing the risk of postoperative complications associated with traditional internal fixation techniques, and it has promising clinical value in the future.     

异体骨接骨板联合不同螺钉治疗股骨干骨折有限元分析

目的对比分析异体骨接骨板分别联合可吸收螺钉(聚-DL-乳酸)和钛合金螺钉(Ti-6Al-4V)治疗股骨干骨折的应力分布情况,验证可吸收螺钉的强度,为临床提供力学依据。方法利用螺旋CT扫描股骨,将扫描数据以DICOM格式导入mimics软件中,建立股骨三维模型。在proe5.0中建立接骨板模型和螺钉模型(简化为圆柱),装配完成后,导入ansys12.0划分网格、材料赋值,并施加700 N轴向载荷、15 N·m弯曲载荷、15 N·m扭转载荷。结果在三种载荷下6根可吸收螺钉最大主应力的最大值为5.75 Mpa、6根钛合金螺钉最大主应力的最大值为24.9 Mpa;两种不同螺钉固定下,股骨和接骨板的应力分布基本相同。结论可吸收螺钉适应于同种异体骨接骨板的固定,与钛合金螺钉相比,具有减少骨头螺钉孔处的应力遮挡的优点。     

Spatial orientation of the facies patellaris femoris

The present article reports on the geometrical conditions of the physiological movement of the patella. The geometrical shape of 18 femoral condyles and patella sliding areas was investigated in order to describe basic data for the design of endoprostheses. Surface and direction of the facies patellaris femoris were determined by means of radiographic, mechanical and optical measurements. The curvature of the deepest patella sliding groove proves a constant correlation with the dorsal condylar curvature. In the frontal plane the lowest points of the sliding area run with a dispersion of +/- 4 degrees to the vertical line related to the transverse tangent on the dorsal condylar surface. Considering deviations of leg alignment the measures come close to an angle of about 0 degrees. So the direction of the patella sliding groove differs from the normal valgus position of the distal femur. Therefore in artificial knee replacement a lateral tilt of the patella sliding groove should not be propagated as 'physiological'.     

Strain distribution in the proximal human femur. An in vitro comparison in the intact femur and after insertion of reference and experimental femoral stems

Six pairs of human cadaver femora were divided equally into two groups one of which received a non-cemented reference implant and the other a very short non-dependent experimental implant. Thirteen strain-gauge rosettes were attached to the external surface of each specimen and, during application of combined axial and torsional loads to the femoral head, the strains in both groups were measured. After the insertion of a non-cemented femoral component, the normal pattern of a progressive proximal-to-distal increase in strains was similar to that in the intact femur and the strain was maximum near the tip of the prosthesis. On the medial and lateral aspects of the proximal femur, the strains were greatly reduced after implantation of both types of implant. The pattern and magnitude of the strains, however, were closer to those in the intact femur after insertion of the experimental stem than in the reference stem. On the anterior and posterior aspects of the femur, implantation of both types of stem led to increased principal strains E1, E2 and E3. This was most pronounced for the experimental stem. Our findings suggest that the experimental stem, which has a more anatomical proximal fit without having a distal stem and cortex contact, can provide immediate postoperative stability. Pure proximal loading by the experimental stem in the metaphysis, reduction of excessive bending stiffness of the stem by tapering and the absence of contact between the stem and the distal cortex may reduce stress shielding, bone resorption and thigh pain.     

The effectiveness of the proximal femoral stem centraliser on the stem alignment in total hip replacement

We studied a new polymethylmethacrylate proximal femoral centraliser designed for use along with the distal femoral centraliser. Using cadaver femora we conducted an in vitro study to measure the influence of the proximal centraliser on the cement mantle and femoral stem alignment in a total hip replacement (THR). The cadaver femora were randomised into two groups. The Royal National Orthopaedic Hospital (RNOH) femoral stems were inserted to each femur using third-generation cementing technique .The first group was inserted using proximal and distal centralisers. The second group was inserted using distal centralisers only. All the hip specimens were X-rayed using high-tech scanner and computer software. The stem alignment and cement mantle were measured. We concluded that the proximal femoral centraliser improved the cement mantle distribution and femoral stem alignment in THR. This improvement will reflect on the long-term survival of the THR. We also showed an excellent and accurate way of measuring the femoral stem alignment in THR.     

Repair of large osteochondral defects in rabbits using porous hydroxyapatite/collagen (HAp/Col) and fibroblast growth factor‐2 (FGF‐2)

Articular cartilage has a limited capacity for self‐renewal. This article reports the development of a porous hydroxyapatite/collagen (HAp/Col) scaffold as a bone void filler and a vehicle for drug administration. The scaffold consists of HAp nanocrystals and type I atelocollagen. The purpose of this study was to investigate the efficacy of porous HAp/Col impregnated with FGF‐2 to repair large osteochondral defects in a rabbit model. Ninety‐six cylindrical osteochondral defects 5 mm in diameter and 5 mm in depth were created in the femoral trochlear groove of the right knee. Animals were assigned to one of four treatment groups: porous HAp/Col impregnated with 50 µl of FGF‐2 at a concentration of 10 or 100 µg/ml (FGF10 or FGF100 group); porous HAp/Col with 50 µl of PBS (HAp/Col group); and no implantation (defect group). The defect areas were examined grossly and histologically. Subchondral bone regeneration was quantified 3, 6, 12, and 24 weeks after surgery. Abundant bone formation was observed in the HAp/Col implanted groups as compared to the defect group. The FGF10 group displayed not only the most abundant bone regeneration but also the most satisfactory cartilage regeneration, with cartilage presenting a hyaline‐like appearance. These findings suggest that porous HAp/Col with FGF‐2 augments the cartilage repair process. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:677–686, 2010     

Radiographic Assessment of Aseptic Loosening of Tumor‐Type Knee Prosthesis in Distal Femur

ObjectiveTo measure the full‐length anteroposterior and lateral radiographs of lower limbs after the resection of a tumor in the distal femur and tumor‐type knee prosthesis replacement and to analyze the factors leading to aseptic loosening of the prosthesis.MethodsA total of 26 cases of tumor‐type knee prosthesis replacement or revision due to the distal femoral tumor at our hospital from January 2007 to December 2019 were retrospectively analyzed. The patients were divided into the loosening and unloosening groups depending on whether aseptic loosening occurred after surgery. Full‐length anteroposterior and lateral radiographs of lower limbs were used to measure bone resection length, length of prosthesis, distance of proximal apex of the medullary stem of the femoral prosthesis from the maximum arc of the anterior femoral arch, diameter of the medullary stem, etc. Data were analyzed, and the risk factors for aseptic loosening of the prosthesis were explored.ResultsThe ratio of the prosthetic length to the femoral length (63.72 ± 5.21) and the ratio of the femoral medullary stem diameter to the femoral diameter (26.03 ± 8.45) were smaller in the loosening group than in the unloosening group. The difference was statistically significant (p < 0.05). The distance between the apex of the medullary stem and the maximum arc of the anterior femoral arch was significantly shorter in the loosening group (3.47 ± 2.96) than in the unloosening group, and the difference was statistically significant (p < 0.05). The measurement of the lower limb alignment showed significant differences between the loosening and unloosening groups in terms of HKAA, mLDFA, and distance between the lower limb alignment and the center of the knee joint (p < 0.05). The logistic regression analysis showed that less than 30% ratio between the medullary stem diameter and the femoral diameter, less than 3 cm distance between the apex of the medullary stem and the maximum curvature of the anterior arch of the femur, distance between the lower limb alignment and the center of the knee joint, and presence of varus knee and valgus knee after the surgery were the risk factors for aseptic loosening of the prosthesis.ConclusionsThe diameter of the femoral medullary stem of the prosthesis, the apex position of the prosthetic stem, and the lower limb alignment are the risk factors for aseptic loosening of the prosthesis.     

Factors Influencing the Stability of Stems Fixed with Impaction Graft in Vitro

Mechanical stability of the stem is believed to be an important factor in successful impaction grafting in revision THA. We asked whether particle size, femoral bone deficiencies, stem design, graft composition, and impaction technique influenced the initial stability of the stem in vitro using model femora and human bone particles. Bone particles made with a reciprocating blade-type bone mill contained larger particles with a broader size distribution than those made by a rotating drum-type bone mill and had higher stiffness on compression testing. The stiffness on torsional testing decreased as the degree of proximal-medial segmental deficiencies increased. The stiffness and maximum torque in a stem with a rectangular cross section and wide anteroposterior surface were higher in torsional tests. Adding hydroxyapatite granules to the bone particles increased the torsional stability. To facilitate compact bone particles, we developed a spacer between the guidewire and modified femoral packers. This spacer facilitated compacting bone particles from the middle up to the proximal and the technique increased the amount of impacted bone particles at the middle of the stem and also improved the initial stability of the stem. Stem design and degree of deficiencies influenced stiffness in the torsional test and the addition of hydroxyapatite granules enhanced torsional stiffness. Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.