脊柱后路减压治疗胸腰段骨折脱位合并脊髓损伤术式选择

目的研究两种不同脊柱后路减压方法治疗胸腰段骨折脱位合并脊髓损伤的手术治疗效果。方法回顾分析本院1996年3月～2002年6月收治的胸腰段骨折脱位并脊髓损伤患者76例，按不同减压方法将其分为两组：切除一侧或两侧椎板、椎弓根或部分关节突行侧前方环状减压AF内固定者40例，为直接减压组；体位复位结合AF器械矫正复位36例，为间接减压组。统计学分析，两组资料具有可比性。对术后神经功能恢复情况，按ASIA神经功能评定标准进行评定。中晚期并发症，根据是否有腰背痛，下肢根性痛、麻木无力，两便功能障碍进行评定。生活能力按FIM评定。结果两组病例获6个月～5年随访，结果表明，术前脊髓完全性损伤，术后均无恢复；术前脊髓不完全性损伤，术后两组间比较差异无显著性。中晚期并发症发生，直接减压组高于间接减压组；术后生活自理能力，间接减压组好于直接减压组。结论间接减压手术方法治疗胸腰段骨折脱位合并脊髓损伤不失为一种早期治疗的首选方法。     

Acute Median Neuropathy and Carpal Tunnel Release in Perilunate Injuries Can We Predict Who Gets a Median Neuropathy?

This study addressed the following null hypotheses: 1) There are no demographic differences between patients with perilunate dislocation (PLD) or fracture-dislocation (PLFD); 2) There are no factors associated with the development of median nerve symptoms in the setting of a PLD or PLFD; and 3) There are no factors associated with carpal tunnel release. Using a retrospective search of a prospective trauma database, we identified all patients who had sustained a radiologically confirmed PLD or PLFD over a 10-year period at two trauma centers. From the medical records we identified median nerve symptoms and carpal tunnel release in addition to demographic and injury characteristics. Among the 71 patients treated for PLD or PLFD, acute median neuropathy was diagnosed in 33 patients (47 %). The only significant difference between PLD and PLFD was a younger age with PLFD. No demographic or injury factors were associated with symptoms of median neuropathy. Carpal tunnel release surgery during the initial operative management was related to the presence of median nerve symptoms and the trauma center. We report a high incidence of acute median neuropathy accompanying perilunate injuries. As there are no demographic or injury factors associated with symptoms of median neuropathy; all patients with PLD/PLFD merit equally high vigilance for acute median neuropathy.Level of Evidence: Level III, prognostic study     

带袢钢板治疗陈旧性肩锁关节脱位

2009年12月～2012年5月,我们对陈旧性肩锁关节脱位患者应用带袢钢板人工韧带重建治疗,疗效满意,报道如下。1材料与方法1.1病例资料本组13例,男9例,女4例,年龄21～65岁。左侧6例,右侧7例,均为闭合损伤。陈旧性损伤原因:漏诊2例,保守治疗无效3例,内固定失败3例,延误治疗5例。患者受伤至本次手术时间1～13个月。     

尺骨冠状突骨折合并肘关节后脱位有限元模型的建立与分析

目的：建立尺骨冠状突骨折合并肘关节后脱位的有限元模型,并对肘关节后脱位在关节稳定性方面的影响进行数字化研究。方法：建立正常肘关节-前臂（IEJF）有限元模型与尺骨冠状突骨折肘关节-前臂（FUCF）有限元模型。采用压缩、屈曲两组生理荷载（每组3种幅值）,进行计算、验证和应力分析。结果：建立了结构完整的IEJF与FUCF有限元模型,并对模型进行验证,情况与临床实际符合。计算得出FUCF有限元模型较IEJF有限元模型桡骨头出现了严重的应力集中现象,不同压缩荷载作用下的肘关节纵向压缩位移与不同屈曲力矩导致的屈曲角都有所增加。结论：尺骨冠状突骨折及肘关节后脱位对肘关节-前臂纵向不稳有一定程度的影响。本研究所构建的肘关节-前臂有限元模型对尺骨冠状突骨折合并肘关节后脱位的临床稳定性评估研究及手术治疗方案的制定具有一定的参考价值。     

Scaling confirmation of the thermodynamic dislocation theory

The thermodynamic dislocation theory (TDT) is based on two highly unconventional assumptions: first, that driven systems containing large numbers of dislocations are subject to the second law of thermodynamics and second, that the controlling inverse timescale for these systems is the thermally activated rate at which entangled pairs of dislocations become unpinned from each other. Here, we show that these two assumptions predict a scaling relation for steady-state stress as a function of strain rate and that this relation is accurately obeyed over a wide range of experimental data for aluminum and copper. This scaling relation poses a stringent test for the validity of the TDT. The fact that the TDT passes this test means that a wide range of problems in solid mechanics, previously thought to be fundamentally intractable, can now be addressed with confidence.

For almost a century, the dislocation theory of crystalline deformation has played a central role in materials science. Unfortunately, this theory has made only modest progress for about seven decades. Although crystalline solids are essential in engineering applications and although modern experimental techniques have provided a wealth of information about dislocations in these solids, the theories developed to explain dislocation-driven phenomena have been primarily phenomenological. They describe phenomena mathematically but do not explain them; they are not predictive.The cause of this theoretical failure is clear. Dislocation-driven deformations of solids are complex nonequilibrium processes involving macroscopic numbers of dynamical degrees of freedom. Theoretical physicists know that they must use statistical methods to deal with such situations. Especially important is the second law of thermodynamics, which states that driven complex systems must move toward their most probable configurations (i.e., that their entropies must be nondecreasing functions of time). However, leading materials scientists since the 1950s have asserted that dislocation energies are too large, and that dislocation entropies are too small, for the second law to be applicable (1, 2).We have argued for a decade that those assertions are wrong. The thermodynamic dislocation theory (TDT) is based directly on the second law. It was introduced in 2010 (3) and has been shown in a series of publications since then (4–13) to be capable of solving a wide range of the most important problems in solid mechanics including strain hardening, elastic–plastic yielding, shear banding, grain-size effects, and the like. Those problems were out of reach of the conventional approaches. However, questions remain. How sure are we that the TDT is more reliable than the observation-based phenomenologies? Can we use it confidently to solve important materials problems that have been left untouched by the conventional methods?To test the reliability of the TDT, we have used it to derive a scaling law for steady-state deformations. Such scaling laws have been proposed in the past. For example, Kocks and Mecking (14) devoted much of their review article to the search for scaling relations based on experimental data and phenomenological strain-hardening formulas. The TDT-based scaling relation, however, is derived directly from first principles. As we shall show, it is accurately obeyed over a wide-enough range of experimental data to make it seem highly unlikely that there is anything fundamentally incorrect about its underlying assumptions. Our increased confidence in the TDT now leads us to raise some issues that urgently need to be addressed for both basic and applied reasons.The thermodynamic basis of the TDT has been presented in earlier publications (especially refs. 3, 7, and 9). Its main premise is that the dislocations in a deforming crystalline solid can be described—indeed, must be described—by an effective temperature Te f f that differs greatly from the ordinary, ambient temperature T. Te f f is truly a “temperature” in the conventional sense of that word; it is derived by invoking the second law of thermodynamics. It is also a true temperature in the sense that, as energy flows through an externally driven system containing dislocations, effective heat is converted to ordinary heat and dissipated. Thus, this driven, nonequilibrium system should be visualized as consisting of two weakly coupled subsystems: the dislocations at temperature Te f f and the rest of the system playing the role of a thermal reservoir at temperature T.For present purposes, we need to know only that, in steady-state shear flow, the areal density of dislocations is given by the usual Boltzmann formula:ρss=1a2 exp −eDkB Te f fss,[1]where a is a minimum spacing between dislocations, eD is a characteristic dislocation energy, and Te f fss is the steady-state effective temperature. The quantity kB Te f fss/eD, usually denoted by the symbol χ~ss, is a measure of the degree of disorder of the subsystem of dislocations. It is determined by the rate at which this subsystem is being driven at the strain rate ϵ˙. If that driving rate is slow enough that irreversible atomic rearrangements have time to relax before the strain has changed appreciably, then χ~ss must be independent of the strain rate. Typical timescales for atomic motions are of the order of 10−10s. Thus, χ~ss must be a constant for strain rates up to 106/s or even higher. It then follows from Eq. 1 that steady-state dislocation densities must also be constant across this range of driving rates, which includes most ordinary applications. In ref. 3, we used a Lindemann-like argument to estimate that χ~ss∼0.25, which turns out to be roughly correct.The second core ingredient of the TDT is the depinning (“double-exponential”) formula, which also is based on a comparison of timescales. We know that the dislocations in a deforming solid, under a wide range of circumstances, are locked together in an entangled mesh that can deform only via thermally activated depinning of pairwise junctions. The pinning times are very much longer than the times taken by dislocation segments to jump from one pinning site to another. Thus, the depinning rate controls the deformation rate, and no other rates are relevant in this approximation.To be more specific, define the depinning rate to be τP−1=τ0−1 exp[−UP(σ)/kB T], where τ0 is a microscopic timescale and UP is a pinning energy that depends on the applied stress σ. Write this energy in the form UP(σ)=kBTP exp[−σ/σT(ρ,T)], where σT(ρ,T) is a characteristic stress that determines the magnitude of σ necessary to reduce the pinning barrier by a factor of 1/e. If a′ is the separation between dislocations needed to produce this reduction and 1/ρ is the average distance between dislocations, then a′ ρ is a strain, and σT(ρ,T)=μ(T) a′ ρ is a stress, where μ(T) is the (temperature-dependent) shear modulus. In fact, σT(ρ,T) is the Taylor stress. To compute the plastic strain rate, use the Orowan formula ϵ˙pl=ρ b v, where b is the magnitude of the Burgers vector and v is the average dislocation speed 1/(τP ρ). The result isϵ˙pl=bτ0ρ exp−TPTe−σ/σT(ρ,T)[2]or equivalently,σσT(ρ,T)=−ln TTPlnϵ˙0(ρ)ϵ˙pl,[3]where ϵ˙0(ρ)≡b ρ/τ0. This is the scaling relation.For steady-state situations in which ρ=ρss remains constant, Eq. 3 contains three system-dependent but theoretically strain rate-independent parameters: σTss≡σT(ρss,T), ϵ˙0ss≡ϵ˙0(ρss), and TP. Thus, plots of measured values of σ/σTss as functions of (T/TP) ln(ϵ˙0ss/ϵ˙pl) should collapse onto a single curve after we have identified the values of those three parameters, which we can do by using known values of the modulus μ(T) and using a least-squares method to find the best fit between the parameters and the scaling curve.To check this scaling prediction, we have used a set of compression measurements by Samanta (15). These are old results, but they have the special advantage for us of using two different materials and testing them at different temperatures and strain rates under otherwise identical conditions. Our scaling graph shown in Fig. 1 contains 32 points: 12 for pure copper at three temperatures in the range (600○C to 900○C) and four strain rates (960 /s to 2,300/ s) and 20 for pure aluminum at four temperatures in the range (250○C to 550○C) and five strain rates (520 /s to 2,200 /s). Clearly, these points fall very accurately on the smooth curve predicted by the TDT analysis, which adds greatly to our confidence in this theory. The most physically interesting fitting parameters are TP=45,000 K for copper and TP=27,800 K for aluminum, which differ somewhat from previous estimates, possibly because of differing sample preparations or measurement techniques.Open in a separate windowFig. 1.Scaling relation given by Eq. 3. The solid curve is the function f(x)=ln(1/x), with x=(T/TP) ln(ϵ˙0ss/ϵ˙pl). The data points are from ref. 15 as interpreted in ref. 16.The time-dependent TDT consists of three physics-based equations of motion. The first is Hooke’s law with the (“hypo-elasto-plastic”) assumption that elastic and plastic shear rates are additive:σ˙=2 μ(1+ν) (ϵ˙tot−ϵ˙pl),[4]where ν is Poisson’s ratio and ϵ˙tot is the total elastic plus plastic strain rate. ϵ˙pl is given by Eq. 2, making this a highly nonlinear equation.Second is an equation of motion for ρ, which is a statement of energy conservation:ρ˙=κρ σ ϵ˙plγD 1−ρρss(χ~).[5]Here, γD is the dislocation energy per unit length, and κρ is the fraction of the input power σ ϵ˙pl that is converted into dislocations. The second term inside the square brackets determines the rate at which dislocations are annihilated. It does this by invoking a detailed balance approximation using the effective temperature χ~; that is, it says that the density ρ must approach the value given by Eq. 1 but with the steady-state χ~ss replaced by a time-dependent χ~ during the approach to steady-state deformation.Finally, the equation of motion for χ~ is a statement of the first law of thermodynamics:ce f f eD χ~˙=σ ϵ˙pl 1−χ~χ~ss−γD ρ˙,[6]where ce f f is the effective specific heat. The second term in the parentheses is proportional to the rate at which effective heat is converted to ordinary heat, which reminds us that χ~ is a thermodynamically well-defined temperature. Like the comparable term in Eq. 5, this is a detailed balance approximation. The last term on the right-hand side accounts for energy stored in the form of dislocations.To illustrate the solutions of these equations of motion, we show in Fig. 2 just 2 of Samanta’s 32 stress–strain datasets, compared here with the TDT predictions. The agreement between theory and experiment shown here is reassuringly excellent. Ref. 16 has details about how the TDT equations were reformulated for numerical purposes and how parameter values were chosen for comparing their predictions with the experiments. In computing the curves shown in Fig. 2, we simplified the analysis by neglecting Eq. 6 for χ~ and simply solving Eq. 5 with χ~=χ~ss=0.23, consistent with our observation in ref. 3 that χ~→χ~ss very rapidly at high temperatures T. Our measured value of χ~ss is roughly consistent with our original guess that χ~ss∼0.25. The graphs in Fig. 2 are almost identical to those shown for wider ranges of temperatures and strain rates in the early TDT papers. They also illustrate the invariance of the onset slopes for non-prehardened copper discovered experimentally by Kocks and Mecking (14) and explained theoretically in refs. 3 and 7.Open in a separate windowFig. 2.Strain hardening curves for Cu: T=1,023 K, ϵ˙=1,800/s (upper blue) and T=1,173 K, ϵ˙=960/s (lower red). The data points are from ref. 15.We emphasize that these equations of motion are based entirely on fundamental principles—the laws of thermodynamics, energy conservation, and dimensional analysis. Specific phenomena such as hardening, grain-size effects, or yielding transitions play no role in deriving them. Those phenomena are predicted by the equations. The associated physical mechanisms are contained in the derivation of the double-exponential depinning formula, Eq. 2, and in the conversion factors κρ and ce f f in Eqs. 5 and 6. For example, the extreme stress sensitivity of the strain rate in Eq. 2 naturally explains the ρ and T dependences of yield stresses; the phenomenological concept of a “yield surface” is unnecessary. In a more specific way, the physically understandable grain-size dependence of the conversion factor κρ in Eq. 5 provides a simple explanation of Hall–Petch effects. Both of these predictions are discussed in ref. 7.One of the most remarkable aspects of these results is how many ingredients of conventional dislocation theories are completely absent in this elementary version of the theory. The TDT dislocations are simply lines. We do not ask whether they are edge dislocations or screw dislocations or whether they are excess dislocations or geometrically necessary ones. There are no partial dislocations. The crystals through which they move have no specific symmetries. Their motions are unaffected by crystalline orientations, slip planes, or stacking faults. They do not undergo cross-slip. They interact with each other only at the pinning junctions and not via long-ranged elastic forces.Apparently, we can go remarkably far with only this TDT caricature, but there must be limits. Finding and understanding those limits should be a high priority for new investigations. After we see what important physics is missing, we should be able to put realistic features back into the theory in fundamentally consistent ways and thereby understand what roles they play and how important those roles may be.This process of making the TDT more realistic should help us distinguish useful phenomenological concepts from those that are unrealistic. Our candidates for the “unrealistic” category include distinctions between “mobile” and “immobile” dislocations, distinctions between different “stages” of strain hardening, and the idea that large flow stresses at high strain rates can be explained by something called “phonon drag.” At present, we see no scientific basis for any of those conventional ideas, but surely we are mistaken in some cases. We expect to learn a great deal by finding clear counterexamples or missing ingredients in the TDT.Similarly, there must be many limits to the validity of our scaling analysis. Here is an already obvious one. We have pointed out that the assumption of constant χ~ss, and thus, constant ρss, must be changed at physically plausible, high strain rates. Already, in ref. 3, we showed how a simple strain rate dependence of χ~ss with a corresponding increase in ρss can explain the high stresses observed in strong-shock experiments. We thus found agreement between TDT and experiment over 15 decades of strain rate. This kind of analysis of high strain rates was also applied in ref. 8 to interpret molecular dynamics simulations of crystalline deformation (17). We consider those simulations to have been especially important in the development of the present theory.There are many other open issues, but most of them seem to be minor technicalities in comparison with a far more important question: what is the physics of brittle and ductile fracture in crystalline solids? Basic theoretical research in this area has been at a decades-long standstill comparable with that which has afflicted theories of strain hardening.Consider the following. We know that solids are stronger when they are colder; their yield stresses and flow stresses decrease with increasing temperature. This behavior is now predicted by the TDT as seen in Eq. 2 and its applications. However, we also know that solids become more brittle (i.e., they break more easily) at lower temperatures despite the fact that they are stronger. How can these properties be consistent with each other?This basic question has not been answered. So far as we know, it is seldom even asked in the solid mechanics literature. The conventional model used for studying brittle or ductile crack initiation is one in which dislocations are emitted from infinitely sharp crack tips and move out along well-defined slip planes (18, 19). These dislocations either move freely, supposedly implying brittle behavior, or become dense enough to shield the crack tip and somehow produce ductility and toughness. Agreement with experiment is modest at best. As stated in a recent experimental paper by Ast et al. (20), an “understanding of the controlling deformation mechanism is still lacking.” Finding a predictive theory of fracture toughness in crystalline solids should now be feasible and should be a high priority for materials theorists.     

Bilateral central acetabular fracture dislocation in a young patient due to seizure activity: a case report and review of the literature

Various musculoskeletal injuries are well known complications of epilepsy either because of direct trauma or because of unbalanced forceful muscle contraction. We report a case of non-traumatic bilateral central acetabular fracture dislocation due to seizure activity induced by neurocysticercosis of the brain, which was managed conservatively and obtained reasonable good outcome. This case highlights the importance of proper evaluation in young non-osteoporotic patients who have experienced an epileptic attack without any previous history. It is also imperative to mention that these patients should be thoroughly examined neurologically to find out the exact etiology and should be treated accordingly to prevent future seizure activity.