Evaluation of fixation of various screws in the lumbar vertebrae of dogs

Various screws for posterior fixation of the lumbar spine were evaluated for their firmness of fixation in mongrel dogs. Four types of screws: stainless steel, titanium base alloy, porous-coated, and hydroxyapatite-coated were inserted into vertebrae in dogs and examined for firmness of fixation in bone. Dogs were killed immediately and 2, 4, 6, and 8 weeks after insertion, and firmness of fixation was assessed by measuring the twisting force (i.e., the torque) required to loosen the screws. Also, the interface between screws and bone was histologically investigated. The hydroxyapatite-coated screws required the highest torque, compared with other screws, 2 weeks after insertion. At 8 weeks, the torque was 235% of that of the titanium alloy screws, indicating that the fixation of the hydroxyapatite-coated screws was highly stable. With the hydroxyapatite-coated screw, bone formed a direct bond with the hydroxyapatite, the connection to bone apparently being augmented with time. The results of these experiments suggest that the hydroxyapatite-coated screw has the advantage of firmer fixation in vertebrae over other conventional screws. A summary of this work was presented at the tenth annual Orthopaedic Research Meeting of the Japanese Orthopaedic Association at Karuizawa, Japan, in 1995     

A novel in silico method to quantify primary stability of screws in trabecular bone

Insufficient primary stability of screws in bone leads to screw loosening and failure. Unlike conventional continuum finite‐element models, micro‐CT based finite‐element analysis (micro‐FE) is capable of capturing the patient‐specific bone micro‐architecture, providing accurate estimates of bone stiffness. However, such in silico models for screws in bone highly overestimate the apparent stiffness. We hypothesized that a more accurate prediction of primary implant stability of screws in bone is possible by considering insertion‐related bone damage. We assessed two different screw types and loading scenarios in 20 trabecular bone specimens extracted from 12 cadaveric human femoral heads (N = 5 for each case). In the micro‐FE model, we predicted specimen‐specific Young's moduli of the peri‐implant bone damage region based on morphometric parameters such that the apparent stiffness of each in silico model matched the experimentally measured stiffness of the corresponding in vitro specimen as closely as possible. The standard micro‐FE models assuming perfectly intact peri‐implant bone overestimated the stiffness by over 330%. The consideration of insertion related damaged peri‐implant bone corrected the mean absolute percentage error down to 11.4% for both loading scenarios and screw types. Cross‐validation revealed a mean absolute percentage error of 14.2%. We present the validation of a novel micro‐FE modeling technique to quantify the apparent stiffness of screws in trabecular bone. While the standard micro‐FE model overestimated the bone‐implant stiffness, the consideration of insertion‐related bone damage was crucial for an accurate stiffness prediction. This approach provides an important step toward more accurate specimen‐specific micro‐FE models. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2415–2424, 2017.

     

Effect of surgical fit on integration of cancellous bone and implant cortical bone shear strength for a porous titanium

Porous scaffold dowels of Ti₆Al₄V were prepared and implanted into cancellous and cortical bone sites in adult sheep. Cancellous implants were examined under gap, line-to-line, and press-fit conditions, whereas line-to-line implantation was used in cortical sites. Cortical shear strength increased significantly with time and reached 26.1 ± 8.6 MPa at 12 weeks, accompanied by a concomitant increase in bone integration and remodeling. In cancellous sites, bone integration was well established at 4 and 12 weeks under conditions of press-fit and line-to-line match between implant and surgical defect. New bone growth was also found in the gap conditions, although to a lesser extent. These findings suggest that the porous Ti₆Al₄V could prove an effective scaffold material for uncemented fixation in cortical and cancellous sites.     

微不锈钢种植体支抗的稳定性研究

目的：分析不同施力时间对微不锈钢种植支抗稳定性的影响。方法：选择20例错牙合畸形患者（男10例,女10例）,年龄16～18岁,分别将种植钉被植入每位患者上颌两侧第一前磨牙和第一磨牙区作为种植钉支抗内收前牙,共植入40颗不锈钢种植钉。男女患者按加载时间不同被随机平分为两组,实验组1：种植钉植入后便采用镍钛拉簧即刻加力,实验组2：4周后在进行加力,分别通过头颅侧位片测量种植钉加载前后半年的位移变化。然后对两个实验组进行统计学分析。结果：实验组1：种植钉在矢状向上平均移动了1.31mm,垂直向上平均移动了1.53mm。实验组2：种植钉在矢状向和垂直向的平均位移是0.83mm和1.03mm。结论：不锈钢种植钉能够为内收前牙提供稳定和可靠的支抗,植入4周后再施力更有助于种植钉的稳定。     

Effects of indomethacin on bone ingrowth

The effects of indomethacin, a nonsteroidal antiinflammatory agent, on bone ingrowth were studied using a rabbit animal model and a porous cylindrical implant system. Bone ingrowth was found to be independent of pore size in the range tested (0.6-1.0 mm). In the control (placebo-treated) group, there was a significant increase in bone ingrowth between the 2- and 8-week groups of animals. However, in the indomethacin-treated group, there was no increase in bone ingrowth with time.     

Effect of load on the bone around bone‐anchored amputation prostheses

Osseointegrated transfemoral amputation prostheses have proven successful as an alternative method to the conventional socket‐type prostheses. The method improves prosthetic use and thus increases the demands imposed on the bone‐implant system. The hypothesis of the present study was that the loads applied to the bone‐anchored implant system of amputees would result in locations of high stress and strain transfer to the bone tissue and thus contribute to complications such as unfavourable bone remodeling and/or elevated inflammatory response and/or compromised sealing function at the tissue‐abutment interface. In the study, site‐specific loading measurements were made on amputees and used as input data in finite element analyses to predict the stress and strain distribution in the bone tissue. Furthermore, a tissue sample retrieved from a patient undergoing implant revision was characterized in order to evaluate the long‐term tissue response around the abutment. Within the limit of the evaluated bone properties in the present experiments, it is concluded that the loads applied to the implant system may compromise the sealing function between the bone and the abutment, contributing to resorption of the bone in direct contact with the abutment at the most distal end. This was supported by observations in the retrieved clinical sample of bone resorption and the formation of a soft tissue lining along the abutment interface. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1113–1122, 2017.

     

Effect of cortical thickness and cancellous bone density on the holding strength of internal fixator screws

Internal fixators are a new class of implants designed to preserve the periosteal blood supply of the bone. In contrast to conventional plate fixation in which the screws have spherical heads and are loaded mainly by axial pullout forces, screws in internal fixators are “locked” within the plate and therefore subjected to axial as well as bending loads. In this study the ultimate loads of screws of a commercially available internal fixator system were tested in a pullout (n = 72) and cantilever bending mode (n = 72) in metaphyseal and diaphyseal regions of four pairs of human tibiae with different bone qualities. Cortical thickness and cancellous bone density were determined at the screw insertion sites. Stepwise multiple linear regression revealed that cortical thickness and cancellous density can explain 93% and 98% of the variance of the ultimate load of the screws in an axial pullout and cantilever bending mode. Screws in internal fixators are better suited to transmit shear forces and thereby make better use of the strength potential of bone than screws used in conventional plate fixation: this is especially advantageous when bone strength is reduced, e.g. due to osteoporosis. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.     

皮质骨轨迹螺钉在腰椎融合术中的初步应用

正腰椎椎弓根螺钉置入是目前腰椎融合手术中常用的固定方法。从后方结构经椎弓根直至椎体内贯穿"三柱"的螺钉可以为固定提供充足的把持力。然而,对于骨质疏松患者,由于骨密度降低,骨松质薄弱、稀疏,使得椎弓根螺钉固定的强度减弱,以致出现松动、切割、拔出等并发症,影响腰椎融合术的手术效果。为此,有学者通过改进螺纹设计、改良置钉方法以及应用骨水泥强化等方法提高骨质     

Supraphysiological loading induces osteocyte‐mediated osteoclastogenesis in a novel in vitro model for bone implant loosening

We aimed to develop an in vitro model for bone implant loosening, allowing analysis of biophysical and biological parameters contributing to mechanical instability‐induced osteoclast differentiation and peri‐implant bone loss. MLO‐Y4‐osteocytes were mechanically stimulated for 1 h by fluid shear stress using regimes simulating: (i) supraphysiological loading in the peri‐prosthetic interface (2.9 ± 2.9 Pa, 1 Hz, square wave); (ii) physiologic loading in the cortical bone (0.7 ± 0.7 Pa, 5 Hz, sinusoidal wave); and (iii) stress shielding. Cellular morphological parameters, membrane‐bound RANKL expression, gene expression influencing osteoclast differentiation, nitric oxide release and caspase 3/7‐activity were determined. Either Mouse bone marrow cells were cultured on top of loaded osteocytes or osteocyte‐conditioned medium was added to bone marrow cells. Osteoclast differentiation was assessed after 6 days. We found that osteocytes subjected to supraphysiological loading showed similar morphology and caspase 3/7‐activity compared to simulated physiological loading or stress shielding. Supraphysiological stimulation of osteocytes enhanced osteoclast differentiation by 1.9‐fold compared to physiological loading when cell‐to‐cell contact was permitted. In addition, it enhanced the number of osteoclasts using conditioned medium by 1.7‐fold, membrane‐bound RANKL by 3.3‐fold, and nitric oxide production by 3.2‐fold. The stimulatory effect of supraphysiological loading on membrane‐bound RANKL and nitric oxide production was higher than that achieved by stress shielding. In conclusion, the in vitro model developed recapitulated the catabolic biological situation in the peri‐prosthetic interface during instability that is associated with osteoclast differentiation and enhanced RANKL expression. The model thus provides a platform for pre‐clinical testing of pharmacological interventions with potential to stop instability‐induced bone implant loosening. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1425–1434, 2018.

     

Effect of periosteal stripping on cortical bone perfusion: A laser doppler study in sheep

The goals of internal fixation are an accurate reduction and stable fixation in the presence of adequate bony vascularity. This can be achieved by a variety of means including plate fixation. A certain amount of periosteal stripping is necessary for proper open reduction of a fracture and for proper plate application. With displaced diaphyseal fractures, cortical bone perfusion (CBP) is already compromised. Further damage, in terms of periosteal stripping for plate fixation, may not be acceptable. Little information is available as to what extent the periosteum contributes to cortical bone perfusion. The purpose of this study was to determine the acute effects of periosteal stripping on cortical bone perfusion in a sheep tibia model. Twenty-three sheep were operated on and had the medial aspect of their right tibia exposed. Cortical bone perfusion measurements were obtained using laser Doppler flowmetry prior to periosteal stripping and after periosteal stripping. The results of this study show that the cortical bone perfusion significantly decreased by 20% after periosteal stripping over the entire length of the tibia. We therefore conclude that the periosteum contributes to diaphyseal bone perfusion and that it is important to preserve this source with fractures where blood supply is already significantly compromised.     

椎弓根皮质骨螺钉固定与传统椎弓根螺钉固定钉道周围骨质CT值比较

目的 :比较椎弓根皮质骨螺钉固定与传统椎弓根螺钉固定钉道周围骨质的平均CT值,为椎弓根皮质骨螺钉的应用提供理论依据。方法:调取我院2014年1月~2016年10月21~70岁男女性腰椎高分辨率CT扫描影像资料,每10岁一个年龄组,单组随机抽取30例共300例数据。将各组数据导入Mimics 18.0中进行骨组织三维重建,在L4和L5椎体上模拟椎弓根皮质骨螺钉与传统椎弓根螺钉的置入,分割出各模拟螺钉与骨质相交的感兴趣区域并测量其平均CT值。结果:同年龄段同性别同种置钉方式L4、L5椎体感兴趣区域平均CT值均无统计学差异,皮质骨螺钉置钉与传统椎弓根螺钉置钉钉道周围感兴趣区域的平均CT值21~30岁组男性分别为547.4±48.2Hu和311.1±20.3Hu,女性为517.3±56.0Hu和279.1±41.7Hu;31~40岁组男性分别为519.6±48.9Hu和258.7±26.5Hu,女性为521.5±58.8Hu和287.8±33.2Hu;41~50岁组男性分别为490.9±69.8Hu和249.7±37.5Hu,女性为500.7±81.0和262.0Hu±72.1Hu;51~60岁组男性分别为436.5±65.7Hu和217.4±20.8Hu,女性为438.8±45.8Hu和222.1±22.6Hu;61~70岁组男性分别为396.1±40.0Hu和204.0±36.4Hu,女性为364.5±73.6Hu和153.5±27.1Hu;两种置钉方式各年龄组同性别间比较均有统计学差异(P0.05),皮质骨螺钉为传统螺钉的1.7~2.3倍。同种置钉方式不同性别间平均CT值比较,传统螺钉置钉在21~30岁、31~40岁和61~70岁组有统计学差异(P0.05);皮质骨螺钉置钉在21~30岁和61~70岁组有统计学差异(P0.05)。结论 :椎弓根皮质骨螺钉固定钉道周围骨质CT值明显高于传统椎弓根螺钉固定,椎弓根皮质骨螺钉固定具有更高骨-螺钉界面强度。     

Factors affecting the stability of screws in human cortical osteoporotic bone: a cadaver study

We investigated several factors which affect the stability of cortical screws in osteoporotic bone using 18 femora from cadavers of women aged between 45 and 96 years (mean 76). We performed bone densitometry to measure the bone mineral density of the cortical and cancellous bone of the shaft and head of the femur, respectively. The thickness and overall bone mass of the cortical layer of the shaft of the femur were measured using a microCT scanner. The force required to pull-out a 3.5 mm titanium cortical bone screw was determined after standardised insertion into specimens of the cortex of the femoral shaft. A significant correlation was found between the pull-out strength and the overall bone mass of the cortical layer (r(2) = 0.867, p < 0.01) and also between its thickness (r(2) = 0.826, p < 0.01) and bone mineral density (r(2) = 0.861, p < 0.01). There was no statistically significant correlation between the age of the donor and the pull-out force (p = 0.246), the cortical thickness (p = 0.199), the bone mineral density (p = 0.697) or the level of osteoporosis (p = 0.378). We conclude that the overall bone mass, the thickness and the bone mineral density of the cortical layer, are the main factors which affect the stability of a screw in human female osteoporotic cortical bone.     

A novel suture anchor constructed of cortical bone for rotator cuff repair: a biomechanical study on sheep humerus specimens

Purpose

The aim of this study was to evaluate biomechanical properties of a new type of suture anchors constructed of human cortical allograft bone and compare it with the similar standard titanium screw anchor for rotator cuff tears in sheep humerus model.

Methods

Twenty-four paired sheep humeri were harvested from 12 male sheep aged 18 months. Specimens were divided into cortical bone anchor group and titanium screw anchor group. The anchors loaded with two sutures were placed at the footprint of infraspinatus tendon. Cyclic loading test was performed from 10 to 60 N at 1 Hz for 500 cycles and followed by a load-to-failure test at 33 mm/sec. A paired t-test was used to compare the biomechanical properties of the anchors of each type.

Results

No anchors failed during the cyclic phase, and the cortical bone anchors were all pulled out intact. The cyclic displacement of the cortical bone anchor was not significantly greater than that of the titanium screw anchor (P?>?0.05). Student’s t test showed no statistically significant difference between anchors in terms of failure load (cortical bone anchor: 304.74?±?64.46 N versus titanium screw anchor: 328.45?±?89.58 N; P?=?0.213), ultimate load (cortical bone anchor: 325.82?±?76.45 N versus titanium screw anchor: 345.61?±?83.56 N; P?=?0.183), yield load (cortical bone anchor: 273.78?±?44.75 N versus titanium screw anchor: 284.72?±?56.37 N; P?=?0.326) or stiffness (cortical bone anchor: 52.97?±?14.28 N/mm versus titanium screw anchor: 62.38?±?18.35 N/mm; P?=?0.112).

Conclusions

In vitro, this experimental study suggested no statistically significant difference in initial fixation stability between the new type anchor and titanium screw anchor at a chosen level of significance (P?<?0.05). The new type of suture anchor constructed of cortical bone provides comparable initial fixation strength to a similar metallic anchor for rotator cuff repair.

     

天鹅型形状记忆合金接骨器对实验性骨折愈合中皮质骨胶原构筑与力学性能的影响

目的探讨天鹅型形状记忆合金接骨器(SMC)对实验性骨折愈合中皮质骨胶原构筑和力学性能的影响。方法45只新西兰大白兔双侧肱骨干截骨后,随机选取一侧用SMC固定,另一侧用4孔动力加压接骨板(DCP)固定;分别于术后2、4、8、16、32周各处死9只动物取材,4只用于扫描电镜观察固定段皮质骨胶原构筑的变化,5只用于骨干扭转生物力学性能的测定。结果SMC组在整个固定过程中,皮质骨结构与正常对照组相比无明显变化。而DCP组术后4周,胶原排列出现稀疏,局部有小吸收陷窝形成;术后8周时,胶原排列紊乱,且有多个吸收腔形成;术后16周时,胶原纤维出现中断;术后32周,骨质疏松化更加明显。术后2周时,两组肱骨骨断端尚未形成骨性连接,不能测得力学数据。术后4～32周,SMC组骨折愈合部位的扭转刚度明显优于DCP组,差异有统计学意义(F= 5．468,P＜0．05)。术后16周,SMC组骨折愈合部位的力学性能即接近正常,而DCP组术后16周扭转刚度即不再增加。结论SMC具有材料特性和几何构型上的优势,对骨干不产生应力遮挡效应,而且能有效防止骨质疏松的发生,使骨的力学性能尽早恢复。     

Development and initial validation of a novel smoothed‐particle hydrodynamics‐based simulation model of trabecular bone penetration by metallic implants

A novel computational model of implant migration in trabecular bone was developed using smoothed‐particle hydrodynamics (SPH), and an initial validation was performed via correlation with experimental data. Six fresh‐frozen human cadaveric specimens measuring 10 × 10 × 20 mm were extracted from the proximal femurs of female donors (mean age of 82 years, range 75–90, BV/TV ratios between 17.88% and 30.49%). These specimens were then penetrated under axial loading to a depth of 10 mm with 5 mm diameter cylindrical indenters bearing either flat or sharp/conical tip designs similar to blunt and self‐tapping cancellous screws, assigned in a random manner. SPH models were constructed based on microCT scans (17.33 µm) of the cadaveric specimens. Two initial specimens were used for calibration of material model parameters. The remaining four specimens were then simulated in silico using identical material model parameters. Peak forces varied between 92.0 and 365.0 N in the experiments, and 115.5–352.2 N in the SPH simulations. The concordance correlation coefficient between experimental and simulated pairs was 0.888, with a 95%CI of 0.8832–0.8926, a Pearson ρ (precision) value of 0.9396, and a bias correction factor Cb (accuracy) value of 0.945. Patterns of bone compaction were qualitatively similar; both experimental and simulated flat‐tipped indenters produced dense regions of compacted material adjacent to the advancing face of the indenter, while sharp‐tipped indenters deposited compacted material along their peripheries. Simulations based on SPH can produce accurate predictions of trabecular bone penetration that are useful for characterizing implant performance under high‐strain loading conditions. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1114–1123, 2018.

     

Effect of a hypergravity environment on cortical bone elasticity in rats

There is considerable interest in determining whether hypergravity can be used as a countermeasure for microgravity-induced bone loss. This study was conducted on 20 immature male rats in order to investigate possible elastic adaptations of cortical bone in rapidly growing rats exposed to chronic hypergravity. Ten rats were continuously centrifuged for 14 days at twice gravitational acceleration (2G) on a 12.75 foot radius centrifuge and 10 rats concurrently acted as stationary controls. The effect of hypergravity on the elastic characteristics of cortical bone was quantified via ultrasonic wave propagation. Propagation velocities of longitudinal and shear waves were measured through cubic cortical specimens from the posterior femoral diaphyses. Density was measured with an Archimedes' technique. The orthotropic elastic properties were calculated and used to compare the difference between groups. Results showed an average increase in both the Young's moduli (E_ii, + 2.2%) and shear moduli (G_ij, + 4.3%) with a statistically significant increase only in G₁₂ (+15.7%, P= 0.046). The ratio of transverse to axial strain (Poisson's ratio, ν_ij) demonstrated statistically significant changes in ν₁₂, ν₂₁, ν₁₃, and ν₃₁ (P < 0.05). These findings suggest that although slight elastic changes were incurred via a hypergravity environment, the treatment level or duration in this study do not dramatically perturb the normal elastic behavior of cortical bone and that dramatic biomechanical differences noted in previous studies were due more to structural changes than material elasticity changes. Hypergravity applied post facto to a microgravity environment would offer further illucidation of this method as treatment for a degenerative spaceflight experience. Received: 12 August 1995 / Accepted: 23 February 1996     

Osteointegration of titanium and hydroxyapatite rough surfaces in healthy and compromised cortical and trabecular bone: in vivo comparative study on young, aged, and estrogen-deficient sheep.

The osteointegration rate of titanium (Ti; TI01) and duplex Ti plus HA (HT01) coating systems with high surface roughness was investigated in healthy, aged, and oestrogen-deficient sheep. After having evaluated the bone quality, TI01 and HT01 rods were implanted in the tibial diaphyses (two implants for each tibia) and epiphyses (1 implant for each tibia) of five young (YOUNG), five aged (AGED), and five aged and ovariectomized (OVX) sheep. The iliac crest trabecular bone volume (BV/TV) and number (Tb.N) in OVX sheep were respectively 33.5% and 28.5% lower than in YOUNG sheep (p < 0.005) and lower than in the AGED group (BV/TV, -17%; Tb.N, -13.5%; not significant); in the OVX group the trabecular separation was 77.9% higher than in YOUNG (p < 0.05) and 30.9% higher than in AGED animals. Lumbar vertebrae L5 bone mineral density was significantly lower in AGED (8.9%, p < 0.05) and OVX sheep (19.3%, p < 0.0005) when compared with YOUNG animals. Five samples of five sheep from each group were analyzed for each observation. At 3 months, in cortical bone both affinity index and pushout test results showed no significant differences between the two materials in each group of animals. In trabecular bone, the affinity index of HT01 was significantly higher than that of TI01 in each group of animals (YOUNG, 90.7%; AGED, 76.9%; OVX, 49.9%) with no significant differences between groups. In conclusion, the performance of TI01 and HT01 surfaces was high not only in YOUNG, but also in OVX animals and, therefore, they might be useful for aged and osteoporotic patients.     

Wear analysis of a retrieved hip implant with titanium nitride coating

There is increasing interest in using surface modification technology to improve the wear properties of titanium alloy and limit articular surface wear of metal and polyethylene components. This report details the in vivo wear performance of titanium nitride coating on a retrieved hip implant obtained postmortem from a low demand patient 1 year after total hip arthroplasty. Analysis of the well-functioning implant revealed that wear debris can originate from a titanium nitride coated femoral head, as delaminated surface asperities, and manifest as adhesive wear on the articular surface. The wear observed on this implant indicates that rigorous testing and evaluation of titanium nitride coating technology should be conducted prior to widespread use on total joint implants.     

Evaluation of hydroxyapatite-coated screws for lumbar spine fixation in dogs

To evaluate the firmness of fixation of hydroxyapatite(HA)-coated screws used for spinal fixation, research has been done to measure the force required to pull out such screws. However, despite its importance, no research has been done to evaluate the twisting force necessary to loosen the screw. With regard to the twisting force, we evaluated the effects of HA coating on securing titanium alloy screws to canine lumbar vertebrae. Bonding of HA-coated (HA) screws and titanium alloy (Diapason; D) screws to the bone was examined serially over a period of 24 weeks by measuring the torque required to loosen the screws after a period of fixation and by histological examination of the screw-bone interface. Twelve screws (six screws of each type) were used in each of seven mongrel dogs, on each side of the lumbar vertebrae (L1–L6). The torque required to loosen D screws 6 weeks after insertion was three times higher than that used at time 0. With the HA scew, the torque at 2 and 6 weeks was four and six times higher, respectively, than that at time 0. Eight weeks after insertion, the torque for the HA screw was 2.3 times greater than that for the D screw (P<0.01). Histological examination showed direct binding of HA to the bone early after insertion. Our results indicate that HA screws are firmly fixed in bone within a short period after insertion into the vertebra. In the clinical setting, the use of HA screws for spinal fixation may produce stable spine fixation within a short period after operation. A summary of this paper was presented at the 11th Annual Orthopaedic Research Meeting of the Japanese Orthopaedic Association (Kagoshima, October, 1996)