Screw oversizing for anterior cruciate ligament graft fixation in primary and enlarged tibial tunnels: A biomechanical study in a porcine model

Background

Ideal diameter for tibial interference screw fixation of the anterior cruciate ligament (ACL) graft remains controversial. Tibial graft fixation with screws matching the tunnel diameter vs. one-millimetre oversized screws were compared.

No difference in clinical results between femoral transfixation and bio-interference screw fixation in hamstring tendon ACL reconstruction. A preliminary study

Hamstring tendon autograft has become a popular graft choice for anterior cruciate ligament (ACL) reconstruction, but there is no consensus on the ideal technique of fixation. We performed a pilot randomized controlled study to compare the clinical and mechanical outcome of two femoral fixation techniques for anterior cruciate ligament (ACL) reconstruction using hamstrings graft. We recruited 30 patients with a chronic unilateral tear of the anterior cruciate ligament. In all patients, quadrupled hamstring graft was used for ACL reconstruction. In 15 patients, femoral graft fixation was performed using Bio-interference Screws fixation (Arthrex, Inc. Naples USA) (Group 1). In the other 15 patients, femoral graft fixation was performed using BioTransFix femur extra cortical transverse fixation (Arthrex, Inc. Naples USA) (Group 2). In both groups, tibial fixation was achieved with a Delta bio-absorbable interference screw (Arthrex). Both groups were comparable with regard to demographic data, pre-operative activity level, mechanism of injury, interval between the injury and the operation, and pre-operative knee laxity measurements. An independent observer, who was blinded with regard to the involved leg and the type of graft, performed the outcome assessment with the use of a Rolimeter® arthrometer (Aircast), and the International Knee Documentation Committee. At 13 months follow up, all patients except one had functionally normal or nearly normal IKDC objective scores. The mean IKDC subjective score was 83.38 ± 9.4 in Group 1 and 79.92 ± 11.01 in Group 2 (P > .05). The side to side laxity as measured with the Rolimeter® arthrometer was 1.5 mm ± 1 (range 0–3) for Group 1, and 2 mm ± 1 (range 0–3) for Group 2 (P > .05). Femoral Biotransfix fixation and Bio-interference Screws fixation provide comparable mechanical stability and clinical outcome at 13 months follow up. BiotransFix fixation is an effective alternative to other devices. Our preliminary study shows that there is no evidence to prefer femoral transfixation to the more traditional, technically less demanding, and more economical interference screw fixation. A full study requires 368 participants.     

Effect of cyclic tension on the biomechanical properties of flexor tendon grafts. Results of an ex-vivo porcine study

BackgroundAutologous flexor tendons are widely used for anterior cruciate ligament (ACL) reconstruction. Pretension of the graft before fixation has been described as part of the surgical technique, nevertheless there is no consensus on the type and amount to tension needed to increase the stiffness without affecting its biomechanical properties.Our hypothesis is cyclic tension increases flexor tendon stiffness without affecting its ultimate failure at maximum loads (UFML).MethodsForty-five flexor digitorum profundus tendons harvested from domestic pigs (Sus scrofa domestica) were randomly divided into three groups: E1 (n = 15), E2 (n = 15) and C (n = 15). Groups E1 and E2 were subjected to 50 cyclic loads at a 1 Hz frequency, at 70 N and 100 N respectively, group C was not intervened. The three groups were then tested for UFML. Cyclic loads and measurements were performed using a Stress-Strain machine (SST 1.0 Kinetecnic ^®). Results were analyzed using GrapgPad statistical software. Groups were compared using Mann-Whitney test with a 95% confidence interval.ResultsSignificant increased stiffness for group E1 (p = 0.02) and group E2 ( p < 0.01) when compared to group C. The stiffness of group E2 was also significantly higher than E1 (p = 0.03). There was a significant reduction on the UFML between group E2 and C (p < 0.01), which was not observed when comparing groups E1 and C.ConclusionCyclic loads at 70 N result in an increased stiffness of flexor tendons without affecting its ultimate failure at maximum loads. Cyclic loads at higher tensions might cause a deleterious effect on the biomechanical properties of flexor tendon grafts.     

Mechanical analysis of fixation methods for anterior cruciate ligament reconstruction with hamstring tendon graft. An experimental study in sheep knees

This study evaluates the structural properties of the femur-anterior cruciate ligament (ACL) graft-tibia complex, comparing different graft fixation techniques in sheep knees. Four fixation devices were tested both for femoral fixation (Transfix, absorbable screw, RCI screw and Linx-HT) and tibial fixation (bone plug with metal screw, absorbable screw with staple, RCI screw and cancellous screw with spiked washer). The graft used for ACL reconstruction was fresh ovine doubled Achilles tendon (DAT). Femurs and tibias were tested separately. Two mechanical test series were performed on the specimens: a load-to-failure test and a cyclic loading test. On the femoral side, transcondylar screw showed the greatest fixation strength and stiffness and the lowest elongation at cyclic loading. Tibial fixation complexes seemed to have poorer structural properties in comparison to femoral fixation. Among the tibial fixation devices, absorbable screw with staple fixation showed the greatest strength and stiffness. Spiked washer fixation showed the greatest elongation under cyclic loading.     

MPFL reconstruction using a quadriceps tendon graft: Part 1: Biomechanical properties of quadriceps tendon MPFL reconstruction in comparison to the Intact MPFL. A human cadaveric study

BackgroundThe aim of this study was to analyze the structural properties of the original MPFL and to compare it to a MPFL-reconstruction-technique using a strip of quadriceps tendon.MethodsIn 13 human cadaver knees the MPFLs were dissected protecting their insertion at the patellar border. The MPFL was loaded to failure after preconditioning with 10 cycles in a uniaxial testing machine evaluating stiffness, yield load and maximum load to failure. In the second part Quadriceps-MPFL-reconstruction was performed and tested in a uniaxial testing machine. Following preconditioning, the constructs were cyclically loaded 1000 times between 5 and 50 N measuring the maximum elongation. After cyclic testing, the constructs have been loaded to failure measuring stiffness, yield load and maximum load. For statistical analysis a repeated measures (RM) one-way ANOVA for multiple comparisons was used. The significance was set at P < 0.05.ResultsDuring the load to failure tests of the original MPFL the following results were measured: stiffness 29.4 N/mm (+ 9.8), yield load 167.8 N (+ 80) and maximum load to failure 190.7 N (+ 82.8). The results in the QT-technique group were as follows: maximum elongation after 1000 cycles 2.1 mm (+ 0.8), stiffness 33.6 N/mm (+ 6.8), yield load 147.1 N (+ 65.1) and maximum load to failure 205 N (+ 77.8). There were no significant differences in all tested parameters.ConclusionsIn a human cadaveric model using a strip of quadriceps-tendon 10 mm wide and 3 mm deep, the biomechanical properties match those of the original MPFL when tested as a reconstruction.Clinical relevanceThe tested QT-technique shows sufficient primary stability with comparable biomechanical parameters to the intact MPFL.     

Cage椎弓根内固定联合自体颗粒骨打压植骨的即时生物力学稳定性

背景：自体骨移植结合椎间融合器联合椎弓根螺钉常运用于椎体融合,但单纯颗粒骨打压联合椎弓根钉的临床生物力学研究报道不多。 目的：比较后路自体颗粒骨打压植骨内固定及Cage内固定的即时生物力学稳定性。 方法：利用腰椎后路附件逐级破坏和椎间盘切除制作腰椎不稳模型。12具猪腰椎标本随机分为两组：打压植骨结合椎弓根螺钉内固定组(实验组),Cage结合椎弓根螺钉内固定组(对照组)。使用脊柱三维运动测试机模拟人体对两组标本在正常、不稳、融合3个状态下进行前屈、后伸、左右侧屈、左右旋转等各个活动的生物力学测试,三维激光扫描仪测定不同载荷下不稳节段的运动范围。 结果与结论：正常状态下,两组间L2~3节段各方向运动范围差异无显著性意义(P > 0.05),说明两组标本均衡性好,具有可比性;与正常状态相比,两组不稳状态各方向运动范围亦明显增加(P < 0.05);融合后对照组L2~3节段椎间各方向运动范围均较实验组小,但差异无显著性意义(P > 0.05)。说明自体颗粒骨打压植骨内固定与Cage内固定均能明显提高脊柱的即时生物力学稳定性,而且两组对于改善脊柱稳定性无显著性差异。     

硫酸钙促进ACL重建后腱-骨愈合的实验研究*

目的研究外科级硫酸钙促进腱-骨愈合的效应。方法实验采用比格犬33只建立动物模型,分别在实验侧采用注射型硫酸钙。在双侧后肢切取趾长屈肌腱进行前交叉韧带（ACL）重建。重建模拟临床方式：肌腱两端采用悬吊式固定,肌腱只充填骨隧道靠近关节腔的一部分。在实验侧,重建术后隧道内间隙充填硫酸钙;对侧不作类似处理,作为对照。术后2、4、6、8、10、12周,各取3只犬行组织学检查,了解腱-骨界面的组织学变化;术后2、4、6周各取5只作生物力学检查,测试腱-骨愈合强度;通过对比了解实验侧硫酸钙对腱-骨愈合的效应。结果实验侧组织学观察术后4周在腱-骨界面形成许多骨岛,出现不规排列的sharpey’s纤维;8周时腱-骨间sharpey’s纤维集结成束;12周时腱-骨间肌腱与骨出现密集的纤维连接。对照组4周腱骨间隙存在间隙;8周时腱-骨间隙才出现稀疏的sharpey’s纤维;12周时腱-骨界面出现的密集分布sharpey’s纤维。生物力学测试对比,实验侧和对照侧在术后6周内,有明显差异（0.05）。结论硫酸钙可以早期促进腱-骨界面的愈合。     

The primary stability of pelvic reconstruction after partial supraacetabular pelvic resection due to malignant tumours of the human pelvis: A biomechanical in vitro study

BackgroundUp until now, reconstructions after partial supraacetabular pelvic resection have been done with the use of megaprostheses or allo-/autografs, including screws. The literature states complications in up to 100%. Therefore, the university hospital of Muenster has successfully established a reconstruction using poly-axial screws and titanium rods in combination with a Palacos^® shroud. The aim of this study was to gather data on primary stability of five different types of reconstruction.MethodsUsing a biomechanical model Load (N), displacement (mm) and stiffness (N/mm) were recorded in load cycles from 100 N up to 1050 N.FindingsThe data shows that reconstructions with poly-axial screws, titanium rods and Palacos^® can bear a load of up to 1050 N without structural damages. The same is valid with an additional bone graft and for a full metal prosthesis. Referring to reconstructions with just bone graft or without graft and Palacos^® the load-bearing capacity is significantly worse. Additionally, structural damages were recorded in those reconstructions from 700 N onwards.InterpretationDue to the biomechanical results and the save and easy handling, reconstructions with poly-axial screws, titanium rods and Palacos^® (and, if necessary, bone graft) can be recommended achieving high primary stability for pelvic ring reconstruction after partial supraacetabular pelvic resection.     

喙肩弓对肩关节前上方稳定性作用的生物力学研究

目的探讨对喙肩弓进行不同程度破坏时肩关节前上方稳定性所受到的影响。方法选取新鲜成人冷冻肩关节尸体标本36个,随机平均分为3组后进行不同的处理。组1,保留完整的喙肩韧带;组2,破坏一半喙肩韧带;组3,将喙肩韧带全部破坏。然后分别将肩关节标本固定生物力学试验机上进行力学实验;对肱骨干施加轴向压力时,肱骨头向前上方移动,记录肱骨头在50 N压力时的位移距离。结果在50 N压力作用下,组1、2、3肱骨头位移距离分别为(2.50±0.59)、(5.38±0.71)、(6.49±0.81)mm。3组数据组间比较均存在明显统计学差异(P0.05)。结论喙肩弓的破坏会影响肩关节前上方的稳定性。喙肩弓的破坏程度越大,肩关节前上方的稳定性就越差。     

三维有限元模型分析3种内固定方式治疗严重腰椎不稳定型骨折的生物力学特点

背景：严重腰椎不稳定型骨折的内固定修复方法未形成统一的观点。 目的：应用三维有限元模型对比分析不同内固定方式治疗严重腰椎不稳定型骨折的生物力学性能。 方法：选取1个健康成年志愿者,用CT图像和Mimics软件建立T12~L2椎体三维模型,模拟L1椎体爆裂性骨折,并分别模拟后路减压短节段椎弓根钉固定、前路减压钛网置入内固定和后路减压内固定+前路椎体次全切除钛网置入内固定3种治疗方法。将模型导入到有限元分析软件Abaqus,施加约束和载荷分别加载260 N压力和10 N•m转矩,模拟3种模型在不同工况下的椎体位移、应力传导情况,以及前后路固定器械的受力情况。 结果与结论：从椎体位移分布情况来看,前后联合内固定方式下的位移要较其他两种内固定方式小。从应力分布情况来看,前后联合内固定方式更加符合载荷分布原则。从生物力学角度来看,前后联合内固定方式优于其他两种内固定方式。     

Effects of periosteum wrapped around tendon in a bone tunnel: A biomechanical and histological study in rabbits

The present study demonstrated the effects of periosteal autograft on tendon-to-bone healing in the rabbits. In 20 Japanese white rabbits, proximal end of the long digital extensor tendon that was wrapped around by a periosteum was transplanted into a drill hole in the proximal tibial metaphysis. A fresh periosteum was used in the left tibia and a frozen periosteum was used in the right tibia. Six specimens were harvested at each 2, 4, and 6 weeks postoperatively. Radiological features showed progressive remodeling of trabecular bone surrounding the implanted tendon. This remodeling in fresh periosteal graft was earlier than that in frozen graft. Generally, the pull-out strength of the transplanted tendons with a fresh or frozen periosteum increased progressively according to the length of the healing periods. The strength was significantly greater in a fresh periosteal graft than that in a frozen graft at 4 weeks postoperatively. In histological analysis, a 4-week specimen with the fresh periosteal graft showed fibrocartilage formation in the bone tendon interface, whereas the specimens with the frozen graft demonstrated simple approximation of oriented fibrous tissue. In conclusion, the fresh periosteal autograft produced the premature form of fibrocartilagenous attachment in a bone tunnel and provided good mechanical strength.     

Acetabular defect reconstruction with impacted morsellized bone grafts or TCP/HA particles. A study on the mechanical stability of cemented cups in an artificial acetabulum model.

In revision surgery of the acetabulum bone defects can be filled with impacted human morsellized bone grafts. Because of a worldwide limited availability of human bone, alternatives are being considered. In this study we compared the initial stability of acetabular cups after reconstructing a cavitary defect with various compositions of impacted tricalciumphosphate-hydroxyapatite (TCP/HA) particles and mixes of TCP/HA particles and human grafts in a realistic acetabulum model. Primary cemented cups and reconstructions with impacted human cancellous grafts were used as reference. A dynamic load displaced the acetabular cups superomedially. The primary cemented cups showed the highest stability. The cups with impacted human grafts produced the most displacement. All reconstructions with the TCP/HA particles showed a high stability of the cups. However, especially when using large TCP/HA particles this was probably due to a large amount of cement penetration. Mixing TCP/HA particles with human grafts seemed to decrease cement penetration. although still a high stability was obtained. In this perspective, we concluded that TCP/HA particles might be useful as a bone graft extender in the reconstruction of acetabular bone defects.     

An experimental study on biomechanical properties of hepatic tissue using a new measuring method.

Hepatic tissue is an important internal organ for life. In this paper, we combined the moire method (an optical method) and indentation technique to investigate biomechanical response of hepatic tissue. To examine this measuring technique, we first measured the biomechanical properties of the block of pig's hepatic tissue using this method. The experimental result indicated that the pig's hepatic tissue was obviously a viscoelastic material. We closely analyzed the change of curves for force relaxation, creep, and nonlinear deformation of the block of pig's liver. Meanwhile, we also compared the changes in the biomechanical parameters of normal and cirrhosis hepatic tissue of humans.     

Early healing processes of free tendon grafts within bone tunnels is bone-specific: a morphological study in a rabbit model

In order to function as effective ligament replacements, free tendon grafts must become firmly healed into bone tunnels as soon as possible. We hypothesized that graft incorporation would be bone-specific. Free semitendinosus tendon grafts were inserted into drill holes in a lapine medial collateral ligament reconstruction model; thus, creating tibial and femoral bone-specific incorporation sites. Femur-semitendinosus tendon-tibia complexes were harvested from 26 rabbits for histological analysis at various healing times: 0, 6, 12, or 24 weeks post-surgery. Incorporation and remodeling of the graft in the chondral callus was much more extensive at the cancellous-filled femoral insertion than within the marrow-dominated tibial insertion, suggesting that tendon graft healing may depend on the cancellous bone architecture at the graft site.     

Improvement of monocyte secretion function in a porcine pancreatitis model by continuous dose dependent veno-venous hemofiltration

OBJECTIVE: Monocyte and its secreted cytokines play a crucial role in the process of severe acute pancreatitis (SAP). It has been known that continuous veno-venous hemofiltration (CVVH) can partially attenuate the inflammatory process by removal of cytokines, but the effect of CVVH on monocyte secretion function remains unknown. This study investigated the effect of different doses of CVVH on monocyte secretion function as well as the plasma cytokine profile in a SAP porcine model. METHODS: After successful induction of SAP by pressure-controlled (100 mmHg), intraductal injection of sodium taurocholate (4%, 1 ml/kg) and trypsin (2 U/kg), 24 swine were randomly assigned to 3 groups. Swine in group I (n=8) serving as SAP controls received only standard medical therapy (SMT). Besides SMT, swine in two other groups received zero-balanced CVVH, one hour after the induction of SAP, with low volume fluid exchange (group II, n=8, ultrafiltration rate (UFR) 20 ml/kg/h, LV-CVVH) or high volume (group III, n=8, UFR 100 ml/kg/h, HV-CVVH). Using heparin as anticoagulant, the filter (AN69, Hospal, Lyon, France) was changed every 24 hours. Monocytes were isolated from porcine blood at various timepoints for detection of cytokine secretion (interleukin-6, IL-6; interleukin-10, IL-10; tumor necrosis-a, TNF-a) after LPS stimulus; plasma cytokines were measured simultaneously. RESULTS: CVVH showed a dose-dependent beneficial effect on the animals' survival time. In control animals, plasma pro-inflammatory cytokine levels exhibited a double-phase fluctuation after SAP induction: IL-6 and TNF-alfa rapidly increased to a peak level within 6-12 hours, then dropped to very low level in the late stage. Unlike pro-inflammatory cytokines, the plasma level of anti-inflammatory cytokine IL-10 reached a plateau within 6-12 hours but dropped little. In CVVH-treated animals, the peak-nadir patterns of 3 cytokines were all flattened, most prominently in the HV-CVVH group. Similarly to plasma cytokine patterns, the monocyte ex vivo response to LPS stimulus showed an over-production of cytokines within 6-12 hours, but low production in the late stage. Although unable to totally prevent the abnormality of the monocyte secretion function, CVVH showed a dose-dependent ameliorative effect on it. CONCLUSIONS: Monocytes are over-reactive to stimulus in the early stage of SAP, accompanied by a high level of plasma cytokines, and hypo-reactive to stimulus in the late stage of SAP, accompanied with a low level of plasma cytokines. CVVH treatment has a dose-dependent improvement effect on monocyte responsiveness.     

A murine model for bone marrow metastasis established by an i.v. injection of C-1300 neuroblastoma in A/J mice

A reproducible tumor model for bone marrow metastasis has been developed by an injection of murine C-1300 neuroblastoma (C-1300 NB) cells into the tail vein of syngeneic A/J mice. The animals died with liver metastases at 18–21 days after an injection of 10⁵ tumor cells and often had bone marrow metastasis in the femur. N-methylformamide (NMF), a maturational agent, was administered to inhibit liver metastases and to extend survival in mice with advancing bone metastasis. Histological examination of bone marrow metastasis, demonstrated lesions varying from a few small colonies of C-1300 NB cells either in metaphysis or diaphysis to large foci replacing normal hematopoietic bone marrow, simultaneously invading epiphysis or cortex of bone as bone metastasis. This assay demonstrated the ability to detect neuroblastoma cells in the bone marrow histologically and could determine bone marrow TD₅₀ by extraction of bone marrow cells after treatment with various doses of drug. Fifty per cent of mice injected with cyclophosphamide (CY) developed bone marrow metastasis without liver metastasis. Treatment with tamoxifen, an anti-calmodulin drug, suppressed tumor takes in the recipient mice with tamoxifen-dose-dependent fashion. This experimental system allows for investigations into the therapeutic response and biology of neuroblastoma metastases in the bone marrow.     

A study of complement fixation by rheumatoid factor using a haemolytic assay system.

Complement fixation by rheumatoid factor (RF) in sera from rheumatoid arthritis patients has been investigated by means of a haemolytic assay system employing sheep erythrocytes (SRBC) coated with reduced and alkylated rabbit IgG anti-SRBC antibody. Haemolysis was almost invariably detected with RF-positive sera whereas haemolysis was not observed with RF-negative sera; It was evident from a marked increase in haemolysis, obtained following isolation of IgM-RF of high purity from several RF-positive sera, that the full in vitro complement-fixing ability and hence lytic potential of RF in serum is masked. Parallel observations were also made with synovial fluids. The inhibition of haemolysis by RF in sera and synovial fluids commonly involved a reduction in degree of lysis at high concentration of test material as well as a more generalized inhibition in overall percentage lysis. Complete replication of typical RF-positive serum and synovial fluid patterns of lysis on dilution was achieved by addition of heat-aggregated human IgG to isolated IgM-RF preparations and demonstrated that the two inhibitory effects are separable in terms of complement depletion and reduction of free rheumatoid factor antibody activity, respectively.     

Importance of a distal centralizer in experimental malpositioning of cemented stems. A biomechanical study on human femora

Introduction

Femoral centralizers in total hip arthroplasty (THA) are designed to improve the neutral implant position and ensure a homogeneous cement mantle without implant-bone impingement. To date there are no data about the cement mantle configuration and implant position after malinsertion, as seen in mini-open approaches or adipose patients with a limited view. The present biomechanical study was performed to investigate whether a distal centralizer may correct and optimize the position of a malinserted femoral stem.

Material and methods

Thirteen MS 30 stems with and without a distal centralizer each were implanted in paired fresh human femora. Malinsertion was performed using a 3D guiding device with 10° deviation to the femoral axis in the sagittal plane. The thickness of the cement mantle was measured on the anterior, posterior, medial and lateral side of the implanted stem at a distance of 1 cm each. For each side data were taken at 13 points.

Results

Digital evaluation of the cement mantle thickness revealed compareable values in frontal plane when a centralizer was used (p > 0.4). In contrast the cement mantle thicknesses without a centralizing device varied in the distal region between 3.38 mm and 5.09 mm (p ≤ 0.001) and in the central region between 3.52 mm and 4.19 mm (p ≤ 0.009).

Conclusions

A distal centralizer allows a more uniform cement mantle and neutral alignment even with a malinsertion of the femoral stem. This could reduce the failure rate and early loosening in complex THA.     

Acellular dermal tissue study: an ultrastructural evaluation of human and porcine derived tissues in a rat model

The purpose of this study was to evaluate the host response of a human and a porcine derived acellular dermal tissue (ADT) implanted in the subcutaneous tissue of a rat model. Two subcutaneous pockets were surgically created along the dorsal midline of 25 rats (5 rats/group). The human ADT was placed superiorly and the porcine ADT, inferiorly. The animals were sacrificed at 07, 15, 30, 60 and 180 postoperative days (PO) and the ADTs and surrounding soft tissues were assessed for ultrastructural evaluation by transmission electron microscopy. The ultrastructural findings were similar in both materials. Normal collagen and elastic fibers bundles were observed during all experimental moments, as well as macrophages presenting cytoplasmic enlargements digesting cellular portions after 15 PO. From 30 until 180 PO, vacuolar structures filled with an amorphous, electron-transparent substance, were present inside and outside the fibroblasts. Both human and porcine ADT showed similar pattern of ultrastructural response when implanted in the subcutaneous tissue of rats. The porcine ADT appears as a good alternative to be used as a biomaterial.