Experimental and probabilistic analysis of distal femoral periprosthetic fracture: a comparison of locking plate and intramedullary nail fixation. Part B: probabilistic investigation

The following is Part B of a two-part study. Part A evaluated, biomechanically, intramedullary (IM) nails versus locking plates for fixation of an extra-articular, metaphyseal wedge fracture in synthetic osteoporotic bone. Part B of this study introduces deterministic finite element (FE) models of each construct type in synthetic osteoporotic bone and investigates the probability of periprosthetic fracture of the locking plate compared with the retrograde IM nail using Monte Carlo simulation. Deterministic FE models of the fractured femur implanted with IM nail and locking plate, respectively, were developed and validated using experimental data presented in Part A of this study. The models were validated by comparing the load-displacement curve of the experimental data with the load-displacement curve of the FE simulation with a root-mean square error of less than 3?mm. The validated FE models were then modified by defining the cortical and cancellous bone modulus of elasticity as uncertain variables that could be assumed to vary randomly. Monte Carlo simulation was used to evaluate the probability of fracture (POF) of each fixation. The POF represents the cumulative probability that the predicted shear stresses in the cortical bone will exceed the expected shear strength of the cortical bone. This investigation provides information regarding the significance of post-operative damage accumulation on the POF of the implanted bones when the two fixations are used. The probabilistic analysis found the locking plate fixation to have a higher POF than the IM nail fixation under the applied loading conditions (locking plate 21.8% versus IM nail 0.019%).     

锁定钢板与解剖钢板内固定在pilon骨折治疗中的应用比较

目的探讨锁定钢板与解剖钢板内固定在pilon骨折治疗中的应用效果。方法选取我院收治的pilon骨折患者91例为研究对象,根据治疗方式不同分为对照组45例和观察组46例。对照组予以解剖钢板内固定治疗,观察组患者采用锁定钢板内固定治疗,并对两组患者的治疗效果进行比较分析。结果观察组患者的手术时间、骨折愈合时间、住院时间、下地负重时间均明显短于对照组,差异具有显著统计学意义(P0.05)。观察组的优良率为91.1%,对照组的优良率为64.4%,两组比较差异有统计学意义(P0.05)。两组患者治疗前各项生活质量评分无明显差异(P0.05);治疗后,观察组的生理功能、身体疼痛、总体健康、活力、情感职能、心理健康评分均明显优于对照组(P0.05)。结论锁定钢板内固定在pilon骨折治疗中的应用效果优于解剖钢板内固定,值得临床推广应用。     

Numerical investigation of mechanical effects caused by various fixation positions on a new radius intramedullary nail

Fracture of the radius diaphysis is an unusual injury in adults. Open reduction and plate osteosynthesis has been recommended by most of the authors. However, this trend has started to change with the recent introduction of newly designed interlocking intramedullary (IM) nails. New generation of IM nails are developed in order to utilise the advantages of IM nails against plates. Because of its anatomical structure, the radius bone has a complex geometry. Therefore, the callus structure, which forms during the healing period, should not be affected from external effects, such as excessive loads or motion. In this study, effects of radial styloid process (RSP), dorsal side and ulnar notch edge fixations of a new design radius IM nail on the healing period were numerically investigated. A three-dimensional solid model of radius was obtained from computed tomography images of a volunteer and callus structure model, was placed accordingly and different fixations of implants were performed. The models were analysed under axial loads transferring from the wrist to the radius bone using finite element method. As a result of the analysis, fixation of IM nail from RSP was found to be beneficial on healing period in terms of both callus motion and emerging stresses.     

Biomechanical factors affecting fracture stability and femoral bursting in closed intramedullary rod fixation of femur fractures

Intramedullary rodding of femur fractures, although a safe and rapidly performed procedure, can result in several complications. If the rod fit is too loose, fracture instability, rod migration, and delayed union may result. If the rod fit is too tight, cracking of the femur may occur during rod insertion. These complications were investigated in terms of geometric and mechanical parameters of the bone-implant system. Results showed that rods of the same nominal size from different manufacturers showed more than twofold difference in flexural rigidity and a threefold difference in torsional modulus. These differences appear to be due to differences in cross sectional shape and wall thickness of the rods. Measurements of pushout force and hoop stress in cadaver femora showed a large difference in pushout force with different rods, and significantly lower forces in distal than in proximal femoral fracture components. Pushout force decreased with fracture component length proximally and dropped to zero in distal components less than 170 mm long. An increase in ream diameter in the distal components of just 1 mm was found to decrease the mean pushout force from 740N to 90N. The most significant variable was found to be anterior offset of the starting hole more than 6 mm from the centerline of the medullary canal which resulted in consistent lifting of the anterior cortex during insertion of the rod.     

Revision of a nonunited subtrochanteric femoral fracture around a failed intramedullary nail with the use of RIA products, BMP-7 and hydroxyapatite: a case report

Introduction

Küttner's tumor is characterized through histology by peri-ductal fibrosis, dense lymphocytic infiltration with lymphoid follicles, loss of acini, and occasional marked sclerosis of the salivary gland. On occasion, Küttner's tumor can be difficult to distinguish from malignant neoplasm.

Case presentation

A 58-year-old Japanese man was referred to our hospital with a three-month history of a painless swollen mass in the right sub-mandibular region. Histological findings revealed both lymphoid follicles with reactive germinal centers and variously sized lymphoid follicle-like nodules without definitive germinal centers or mantle zones. B-cells of similar size and shape occupied the lymphoid follicle-like nodules and stained positive for B-cell lymphoma. These cells were detected in the polyclonal B-cells by flow cytometric analysis and tested negative for CD10. Unusual B-cell proliferation was observed, but as there was no definitive evidence of B-cell lymphoma, the lesion was diagnosed as Küttner's tumor.

Conclusion

We report on a rare case of Küttner's tumor associated with fibrosclerosis and atypical lymphoid hyperplasia in both the sub-mandibular gland and regional lymph nodes. Although more cases need to be investigated, our findings might be helpful to further studies seeking to clarify the etiology of idiopathic sclerosing lesions arising in the organs and regional lymph nodes.     

Prospects of implant with locking plate in fixation of subtrochanteric fracture: experimental demonstration of its potential benefits on synthetic femur model with supportive hierarchical nonlinear hyperelastic finite element analysis

Background

Effective fixation of fracture requires careful selection of a suitable implant to provide stability and durability. Implant with a feature of locking plate (LP) has been used widely for treating distal fractures in femur because of its favourable clinical outcome, but its potential in fixing proximal fractures in the subtrochancteric region has yet to be explored. Therefore, this comparative study was undertaken to demonstrate the merits of the LP implant in treating the subtrochancteric fracture by comparing its performance limits against those obtained with the more traditional implants; angle blade plate (ABP) and dynamic condylar screw plate (DCSP).

Materials and Methods

Nine standard composite femurs were acquired, divided into three groups and fixed with LP (n?=?3), ABP (n?=?3) and DCSP (n?=?3). The fracture was modeled by a 20?mm gap created at the subtrochanteric region to experimentally study the biomechanical response of each implant under both static and dynamic axial loading paradigms. To confirm the experimental findings and to understand the critical interactions at the boundaries, the synthetic femur/implant systems were numerically analyzed by constructing hierarchical finite element models with nonlinear hyperelastic properties. The predictions from the analyses were then compared against the experimental measurements to demonstrate the validity of each numeric model, and to characterize the internal load distribution in the femur and load bearing properties of each implant.

Results

The average measurements indicated that the constructs with ABP, DCPS and LP respectively had overall stiffness values of 70.9, 110.2 and 131.4?N/mm, and exhibited reversible deformations of 12.4, 4.9 and 4.1?mm when the applied dynamic load was 400?N and plastic deformations of 11.3, 2.4 and 1.4?mm when the load was 1000?N. The corresponding peak cyclic loads to failure were 1100, 1167 and 1600?N. The errors between the displacements measured experimentally or predicted by the nonlinear hierarchical hyperelastic model were less than 18?%. In the implanted femur heads, the principal stresses were spatially heterogeneous for ABP and DCSP but more homogenous for LP, meaning LP had lower stress concentrations.

Conclusion

When fixed with the LP implant, the synthetic femur model of the subtrochancteric fracture consistently exceeds in the key biomechanical measures of stability and durability. These capabilities suggest increased resistance to fatigue and failure, which are highly desirable features expected of functional implants and hence make the LP implant potentially a viable alternative to the conventional ABP or DCSP in the treatment of subtrochancteric femur fractures for the betterment of clinical outcome.     

Correction: Prospects of implant with locking plate in fixation of subtrochanteric fracture: experimental demonstration of its potential benefits on synthetic femur model with supportive hierarchical nonlinear hyperelastic finite element analysis

The first publication of the work [1] did not present one of the authors' names. Kunalan Ganthel has now been added to the author list. In addition, Habib Sherkat has been added to the Acknowledgements, with thanks for providing help with the use of hyperelastic module of Abaqus Software.     

Biomechanical comparison of conventional and optimised locking plates for the fixation of intraarticular calcaneal fractures: a finite element analysis

Intraarticular calcaneal fractures can result in poor prognosis. Although operative fixation can improve the functional outcomes in most cases, surgical complications such as loss of reduction and wound healing problems may increase the risk of reoperation. Hence, this study aimed to design calcaneal locking plate with a lower profile and better biomechanical performance and to compare the redesigned plate with the traditional calcaneal plate via the finite element method. A Sanders’ type II-C intraarticular calcaneal fracture was simulated. Two fixation models utilising the branch-like calcaneal locking plate and the full plate were constructed. Topology optimisation was conducted to generate a new calcaneal plate design. A biomechanical comparison among the three groups of plates was performed using the finite element method. For the fracture simulated in this study, the optimised plate was superior to the traditional plate in terms of fixation stability and safety but was reduced in volume by approximately 12.34%. In addition, more rational stress distributions were observed in the redesigned plate, underscoring the superiority of this new design in terms of fatigue strength. These results demonstrate that the topology optimisation can be used to design a new implant with a minimised profile and no loss of fixation stability.     

A new technique for internal fixation of femoral fractures in mice: impact of stability on fracture healing

Mouse models are of increasing interest to study the molecular aspects of fracture healing. Because biomechanical factors greatly influence the healing process, stable fixation of the fracture is of interest also in mouse models. Unlike in large animals, however, there is a lack of mouse models which provide stable osteosynthesis. The purpose of this study was therefore to develop a technique for a more stable fixation of femoral fractures in mice and to analyze the impact of stability on the process of fracture healing. The new technique introduced herein includes an intramedullary pin and an extramedullary metallic clip. Ex vivo biomechanical analysis revealed a significantly higher implant stiffness of our pin-clip technique when compared with previously described intramedullary fixation techniques. In vivo, we studied the course of healing after the more stable fixation with our pin-clip technique and compared the results with that observed after unstable fixation with the pin-clip technique after cutting the clip. After 2 and 5 weeks of fracture healing radiological analysis demonstrated that the more stable fixation with the pin-clip technique results in a significantly higher union rate compared to the unstable fixation. Torsional stiffness at 5 weeks was almost 3-fold of that measured after unstable fixation. Histomorphological analysis further showed that fractures stabilized with the pin-clip technique healed with a smaller periosteal callus area, an increased fraction of bone and a reduced amount of fibrous tissue. Of interest, the pin-clip fixation showed reliable union after 5 weeks, whereas the unstable pin fixation did not regularly achieve adequate fracture healing. In conclusion, we introduce a novel, easily applicable internal osteosynthesis technique in mice, which provides rotational stability after femoral fracture fixation. We further show that a more stable osteosynthesis significantly improves the process of fracture healing also in mice.     

Patient specific quantitative analysis of fracture fixation in the proximal femur implementing principal strain ratios. Method and experimental validation

Computational patient-specific modeling has the potential to yield powerful information for selection and planning of fracture treatments if it can be developed to yield results that are rapid, focused and coherent from a clinical perspective. In this study we introduce the utilization of a principal strain fixation ratio measure (SR) defined as the ratio of principal strains that develop in a fixated bone relative to the principal strains that develop in the same bone in an intact state. The SR field output variable is theoretically independent of load amplitude and also has a direct clinical interpretation with SR<1?a representing stress shielding and SR>1+b representing overstressed bone. A combined experimental and numerical study was performed with cadaveric proximal femora (n=6) intact and following fracture fixation to quantify the performance of the SR variable in terms of accuracy and sensitivity to uncertainties in density–elasticity relationships and load amplitude as model input variables. For a given axial compressive force the SR field output variable was found to be less sensitive to changes in density–elasticity relationships and the response function to be more accurate than strain values themselves; errors were reduced by 44% on comparing SR with strain in the fixated model. In addition, the experimental data confirmed the assumption that the SR values behave independent of load amplitude. The load independent behavior of SR and its direct clinical interpretation may ultimately provide an appropriate and easily understood comparative computational measure to choose between patient specific fracture fixation alternatives.     

Particle disease. A comprehensive theory of periprosthetic osteolysis: a review

Aseptic loosening and osteolysis are considered the main long-term problems of hip arthroplasty. Pathogenesis of periprosthetic osteolysis is multifactorial, and both the biological and mechanical factors seem to play an important role. Bearing surfaces continuously generate excessive amounts of micron and submicron particles provoking an adverse inflammatory response of periprosthetic connective tissues. In general, a key role has been attributed to macrophages. Cytokines, growth factors, PGE2, and enzymes are secreted with activated periprosthetic cells resulting in formation of osteolytic granulomas. The final osteolytic step is taken predominantly by osteoclasts which are getting ready for action mainly by an osteoprotegerin ligand (RANKL) and TNFalpha. Rankl is expressed by activated macrophages, osteoblasts, and lymphocytes. In parallel, a repetitive hydraulic effect of the joint fluid is manifested on the susceptible bone.     

Rheological analysis of soft collagenous tissue. Part II: experimental evaluations and verifications

As a direct continuation of Part I, where the theoretical background for the rheological model was discussed, possible operations on the model are discussed and performed on anterior cruciate ligament preparations from rabbits. Different methods of evaluating model constants are compared and other mathematical expressions than those of the model proposed are tried and discussed. Model parts are verified and numerical values are given for certain constants.     

Potency assays for Anistreplase: comparison of the fibrin plate assay and a 96-well plate assay.

Several production lots of Anistreplase (Eminase) were assayed for potency by either two fibrin plate assays or a clot lysis assay performed in 96-well microtiter plates. The 96-well plate assay yielded comparable data to the fibrin plate assays and had the advantage of greater efficiency with respect to both time and reagents. As a result the newer method appears to be a suitable alternative to the fibrin plate assays for lot release of Anistreplase.     

Cryomacroscopy of vitrification, Part II: Experimental observations and analysis of fracture formation in vitrified VS55 and DP6

A new imaging device, termed a "cryomacroscope", was used to observe macrofractures in the cryoprotectant cocktails DP6 and VS55. Details of the design and construction of the cryomacroscope were presented in Part I of this report, which focused on describing the apparatus and observations of crystallization. Part I and the current paper (Part II) describe events that occur as 1 m? of cryoprotectant contained in a glass vial is cooled from room temperature down to cryogenic temperatures (～ -135°C). The presence of cracking, as well as patterns in their position and orientation, are found to be dependent on the cooling rate and on the specific cryoprotectant cocktail. Cracks, if present, disappear upon rewarming, although they appear to be sites for later preferential crystallization. Computations which predict temperatures and mechanical stresses are used to explain observations of cracking. In conjunction with these reports, additional photos of cryomacroscopy of vitrification, crystallization, and fracture formation are available at http://www.me.cmu.edu/faculty1/rabin/CryomacroscopyImages01.htm.     

Loosening of cementless femoral stems: a biomechanical analysis of immediate fixation with loading vertical, femur horizontal

Large joint implants must have immediate fixation to be successful. Unfortunately, the magnitude and consistency of achieving this remains largely unknown. For cementless femoral components it is being increasingly appreciated that torsional loading as occurs during stair climbing or rising from a chair leads to loosening and thigh pain in some cases. A biomechanical test was developed to evaluate fixation in this position. Twelve pairs of human cadaveric femora were press-fit with an AML stem. Each femur was secured in a horizontal position, and the prosthetic head cyclically loaded in a vertically downward direction. The offset of the prosthetic head resulted in a combined torsional and compressive load being applied to the stem within the proximal femur. Loosening was found to consistently occur and rapidly accelerate when the head subsided more than 0.2 mm during 100 cycles. For the AML stem, loosening developed at loads from 62 to 171% of body weight and after as few as 800 cycles. This is within the physiologic range of normal daily activities as measured by others with instrumented prostheses. This poses a challenge to the ability of press-fit stems to tolerate torsional loads in vivo. Patients with a cementless prosthesis should be protected from torsional loading until porous ingrowth and/or bone remodelling have had time to occur. Testing the same stem in paired femora demonstrated no right vs left difference (p greater than 0.6).     

A serological comparison of the three morphological phases of coccidioides immitis: Complement fixation tests with a Pooled antiserum obtained from rabbits with experimental Coccidioidomycosis

Summary A sonicated spherule preparation was more reactive than a sonicated arthrospore antigen in complement fixation tests with a pooled serum from rabbits with experimental coccidioidomycosis. The reactivity of the sonicated spherule approximated the reactivity of coccidioidin. When the sonicated spherule was separated into its supernatant and sediment fractions, both preparations exhibited serological activity.

---

Zusammenfassung Ein mit Schallwellen hergestelltes Kügelchen-Präparat war activer in dem Komplement-Tests mit Blutserum von Kaninchen mit einer Coccidioidomycosisinfektion als ein mit Schallwellen hergestelltes Arthrosporantigen. Die Reaktivität der mit Schallwellen hergestellten Kügelchen war der des Coccidioidin ähnlich. Wurden diese Kügelchen in Niederschlag und Lösung getrennt, so hatten beide Präparate serologische Aktivität.

---

---

Part of a dissertation submitted to the Graduate School of Duke University in partial fulfillment of requirements for the Ph.D. degree.This work was supported by contract with the Department of the Army, Fort Detrick, Frederick, Maryland.In conducting the research reported herein, the investigators adhered to Guide for Laboratory Animal Facilities and Care established by the Committee on the Guide for Laboratory Animal Facilities and Care of the Institute of Laboratory Animal Resources, NAS—NRC.