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Objective—To quantify geometric, inertial, and histomorphometric properties at the mid-diaphyseal level of left and right metacarpal bones (MCB) of racing Greyhounds. Sample Population—MCB from 7 racing Greyhounds euthanatized for reasons unrelated to MCB abnormalities. Procedures—Mid-diaphyseal transverse sections of left and right MCB were stained with H&E or microradiographed. Images of stained sections were digitized, and cross-sectional area, cortical area, and maximum and minimum area moments of inertia of each bone were determined. Histomorphometric data (osteonal density, osteonal birefringence, and endosteal new lamellar bone thickness) were collected in 4 quadrants (dorsal, palmar, lateral, medial). Values were compared between limbs and among bones and quadrants. Results—Cross-sectional area, cortical area, and maximum and minimum moments of inertia of left MCB-IV and -V were significantly greater, compared with contralateral bones. Overall osteonal densities in the dorsal quadrants of left MCB were greater, compared with lateral and medial quadrants. Also, percentage of birefringent osteons was significantly greater in the dorsal quadrant of left MCB-III, -IV, and -V, compared with the palmar quadrant. Thickness of new endosteal lamellar bone was not significantly influenced by limb, bone, or quadrant. Conclusions and Clinical Relevance—Increased cortical thickness and geometric properties of left MCB-IV and -V of Greyhounds, together with altered turnover and orientation of osteons in the dorsal quadrants of left MCB, are site-specific adaptive responses associated with asymmetric cyclic loading as a result of racing on circular tracks. Site-specific adaptive remodeling may be important in the etiopathogenesis of fatigue fractures in racing Greyhounds. (Am J Vet Res 2001;62:787–793)

The large-scale use of titanium and its alloys for orthopaedic applications began in the early 1970s in England (clinical use of the first low-stress implant application such as heart-valve parts made of pure titanium actually dates back to the mid 1950s). Due to an increasing number of clinical reports of fatigue fractures of the cast stem as well as proximal bone resorption due to the excessively stiff CoCr stems, interest in the more elastic and higher-strength titanium alloys grew rapidly in Europe and North America in the second half of the 1970s. Corrosion and bio-compatibility tests have proved the excellent compatibility of titanium and its alloys with the body, showing that they can be recommended as materials for endoprostheses intended to remain permanently inside the human body [6,45,134, 156].

Fatigue fractures of the femoral neck are potentially disabling injuries if the diagnosis is missed or delayed and proper treatment is not provided. Previously considered primarily an injury of military personnel, femoral-neck fatigue fractures are becoming increasingly more common among nonmilitary athletes. The pathogenesis of this condition is multifactorial. Ultimately, fracture is thought to be caused by repetitive submaximal stresses that occur with a frequency that exceeds the adaptive ability of the bone. The clinical hallmark of a femoral-neck fatigue fracture in an impact-loading athlete is nonspecific, activity-related hip pain that is relieved by rest. Plain radiographs obtained initially are often negative. Radionuclide imaging is useful but not specific. Magnetic resonance imaging has demonstrated better specificity, sensitivity, and accuracy than are available with other modalities in the diagnosis of this injury. Treatment of compression-side injuries is generally conservative. Treatment of tension-side injuries remains controversial. The authors recommend aggressive treatment of tension-side injuries to prevent the potentially catastrophic sequelae of displacement, which include osteonecrosis, malunion, and coxarthrosis.

Background: One major problem with the use of small-diameter nails in the treatment of tibial fractures is the high rate of fatigue fractures of the locking screws. The objective of this study was to correlate such parameters as diameter of locking screws, influence of notch effect, and material with fatigue strength and fatigue limit. Methods: In a biomechanical study, the mechanical properties of 11 different locking screws and screw designs to be used in solid tibial nails were tested under typical fatigue conditions. Results: The results showed that an increase in the screw's diameter significantly increased the fatigue strength of the tested locking screws and prototypes (p < 0.0005). A 20% increase of diameter improved fatigue strength by 25 to 70%. Absence of thread at the location where the screw contacts the nail's aperture (where the main load is transmitted to the screw and where the screw, therefore, usually tends to break) may double the fatigue strength and fatigue limit by avoiding the negative notch effect of the screw's thread. It was further significant that titanium alloys had a higher fatigue strength compared with stainless steel alloys (p < 0.001). However, the fatigue strength of titanium implants is massively reduced by minimal damage to the surface. Conclusion: Optimizing the core diameter of the locking screws at the aperture of the solid tibial nail by using screws without a continuous thread generates a fatigue strength two to three times higher compared with screws with a continuous thread. Increasing fatigue strength of locking screws might decrease malunion in fractures stabilized by small-diameter nails.

We lengthened 9 tibial segments over a nail to reduce the time in the external fixator in 5 patients with constitutional shortness. The median lengthening was 7 (5.5-7.3) cm and the external Ilizarov frame was removed after median 99 (63-125) days. In spite of a short time in the external fixator, consolidation was slow, with a median lengthening index of 4.4 (2.4-6.1) months/cm. The procedure resulted in 3 fatigue fractures of the intramedullary nail or interlocking screws that needed revision and bone grafting. In 1 patient, a deep intramedullary infection occurred. After the experience of these major complications we have returned to the traditional callotasis lengthening method described by Ilizarov.

The interdisciplinary approach to the management of MS patients includes the services of both physical and occupational therapy. These professions complement one another in their concerted effort to mobilize the patient, thereby minimizing the symptoms of progressive weakness, fatigue, and spasticity. The ambulant patient is far less likely to develop complications of inactivity such as contractures, decubitus ulcers, venous thrombosis, or osteoporosis (with its associated fatigue fractures), as well as bowel or bladder complications.

Introduction Isthmic spondylolysis (ISP) in the lower lumbar spine is commonly seen in athletes involved in sports with repetitive spinal motions. Some morphometric features in the lumbar spine are considered to be associated with ISP. The exact mechanism responsible for ISP, however, is still obscure. This study aims to test the hypothesis that the shape of the neural arch in the lumbar spine in SP is associated with certain morphometric characteristics. Methods Using a Microscribe three-dimensional apparatus (Immersion Co. San Jose, CA) the transverse facet angles, articular facet dimensions (length, width and depth) and all interfacet distances in the lumbar spine (L1–L5) were measured. One hundred and twenty male skeletons with normal lumbar spines and 115 with bilateral SP at L5 were selected from the Hamann-Todd Human (HTH) Osteological collection housed at the Cleveland Museum of Natural History (Cleveland, OH). ANOVA was carried out to examine the differences between spondylolytic and normal spines. Results From L3 to L5, the transverse angle of the right inferior facets (and left inferior facet of L5) is greater in SP, indicating a more frontally oriented facet. In SP, all lumbar articular facets are flatter than in the norm. L4 in SP is a key vertebra as it's neural arch combines major morphometric characteristics: (a) significantly greater interfacet widths; (b) significantly shorter inter-facet heights; (c) significantly shorter and narrower articular facets; and (d) the inferior inter-facet width is of similar size to the superior interfacet width of the vertebra below (L5). Conclusions Individuals with L4 "ISP morphological characteristics" such as smaller, flatter and more frontally oriented facets and increased interfacet width, whose spine is exposed to over-load or involved in repetitive movements such as athletes are at greater risk to develop fatigue fractures in the shape of isthmic lysis at L5.

Objective. The objective of this paper is to describe fatigue fractures in the supramalleolar area of the tibia. The spectrum of imaging findings in 14 cases is presented, with emphasis on plain film radiographic findings. Design and patients. Fourteen patients with fatigue fractures in the supramalleolar area of the distal tibia were seen in a 6-year period. The 13 men and 1 woman had an age range from 14 to 64 years (mean 30 years). These patients had no underlying conditions that would predispose them to fractures. Sequential plain film radiographs and other special imaging studies (technetium-99m scans and computed tomography) were retrospectively reviewed. Results and conclusions. Initial plain film radiographs showed a horizontal linear band of increased density in only 2 cases, a subtle cortical bulge in 5 cases, a focal ”graying” of the cortex in 2 cases, a single layer periosteal reaction in 1 case, and no abnormality in the final 4 cases. Technetium-99m scans were done in 11 cases and showed focal areas of increased uptake in all 11. These areas of increased uptake were vertically orientated in 10. One patient had computed tomography showing cortical thickening around a linear lu-cency. The spectrum of imaging findings is similar to that seen in fatigue fractures in more common locations. Supramalleolar fatigue fractures should be suspected in patients who have pain in the distal tibia even when initial plain film radiographs are normal. When initial radiographs are normal, technetium-99m scans can confirm the diagnosis.

Three cases of patellar fatigue fracture are reviewed. Two fractures presented with acute displacement and were initially thought to represent pathological fractures. Histological appearances in one case, and the clinical course in another, subsequently indicated that these were fatigue fractures. A third patient developed a chronic undisplaced fracture and followed the typical clinical course of fatigue fractures at other sites. The importance of recognizing patellar fatigue fractures and of differentiating spontaneously displaced fatigue fractures from pathological fractures is emphasized.

The stem described here [1] was proposed by the author and produced in 1968, in cooperation with Otto Frei, engineer with Sulzer Brothers Ltd., Winterthur, Switzerland (Fig. 1). It consists of three straight and three curved stems, at first made from CoCrMo cast alloy but since 1973 from CoCrMo hot forged alloy. Fatigue fractures, which were a problem with earlier cast alloy stems, have occurred only twice in more than 100 000 forged stems. The first ball heads for the rotation cylinder were made of polyester.

Introduction In elderly patients with reduced bone quality, insufficiency fractures of the OS sacrum are relatively common and are typically associated with intense, debilitating pain. The objective of our study was to determine the practicability of cement augmentation using a balloon catheter via individual approaches taking into consideration the complex anatomy of the sacrum and the course of the fracture, as well as the postinterventional determination of leakages and representation of the outcome pain. Material and Methods In 30 patients with severe osteoporosis (23 women with an average age of 72.4 years, seven men with an average age of 68.7 years), a sacral fracture was detected by CT and MRT. This fracture was unilateral in 17 women and bilateral in the other patients. In order to achieve a cement distribution longitudinally in relation to the fracture, the balloon catheter was inserted into the OS sacrum via a hollow needle either from caudal to cranial, from dorsal to ventral or from lateral transiliac to medial. The balloon catheter was then inflated and deflated 1–3 times along the fracture in the respective direction, and the hollow space created was then filled with PMMA cement using a low-pressure procedure. A conventional radiograph in two planes and a control CT were then performed. Pain intensity was determined pre-intervention, on the second day post-intervention and 6 and 12 months post-intervention, using a visual analogue scale. Results The balloon sacroplasty was performed successfully from a technical point of view in all patients. The radiographic and CT control showed sufficient cement distribution in the sacrum along the course of the fracture, whereby leakage could be ruled out. According to the visual analogue scale, the mean value for pain was 8.8 pre-intervention, there was a significant reduction in pain on the second postoperative day, with an average value of 2.7 (p Discussion Approaches that take into account the anatomy of the OS sacrum and the course of the sacral fracture enable reliable augmentation with an optimum amount of cement. This makes balloon sacroplasty an effective treatment that has few complications for rapid and significant pain relief in patients with a sacral fracture. Competing interests None.

A 24-year-old female gymnast had a 3-month history of bilateral forearm pain. A Tc-99m MDP bone scan demonstrated focally increased activity in the radial shafts on blood pool and delayed images, characteristic of fatigue fractures. Fatigue fractures commonly occur in the lower extremities. Upper extremity fatigue fractures, in contrast, are uncommon and usually involve the humerus or ulna. Fatigue fracture of the radial shaft from gymnastic exercise has not been previously reported.

Fatigue fractures may be confused with malignant bone lesions on radiography and hence are periodically referred for further imaging assessment with computed tomography (CT) and magnetic resonance imaging (MRI). The appearances on MRI are characteristic although not pathognomonic. Typical findings include: intramedullary bands of low signal intensity, continuous at some point with the cortex, indicative of a fracture line; intramedullary areas of high signal on both T2-weighted and short-tau inversion recovery (STIR) images representing marrow oedema or haemorrhage, together with evidence of periosteal oedema. We present seven cases of fatigue fractures of the long bones of the lower limb and discuss the MRI findings and compare CT and MRI in imaging these lesions.

Isolated first rib fractures are uncommon. They are usually associated with severe blunt trauma, although other mechanisms have been suggested, these being (a) indirect trauma, (b) sudden contraction of the neck muscles, and (c) stress or fatigue fractures attributable to repeated pull of muscles. Two cases are reported of stress fracture of the first rib, who presented to the accident and emergency department.

The use of nitinol stents in the superficial femoral artery (SFA) is becoming commonplace. The SFA is a tortuous biomechanical environment that has challenged the durability of these devices. A thorough understanding of the biomechanical loading environment is necessary to design and evaluate new stents. This paper reports recent methods for use of bench testing as a tool to predict fatigue fracture of stents for complex multimode duty cycles.

We have reported three cases of fatigue fracture of the ulna in male pitchers of fast-pitch softball. To elucidate the etiology of injury, we first selected three healthy male and three healthy female pitchers from a well- trained college team and analyzed their forearm move ment by high-speed cinematography. This showed slight flexion of the elbow joints during wind-up motion, dorsal flexion of the hand joints upon releasing the ball, and extreme pronation of the forearms during the fol low-through. We then took 8 mm CT scanning sections of the forearms. Using these images, we investigated shapes and areas of cross-sections of the ulna and its cortical and cancellous bones from the elbow to the hand joints. Our results reveal that the shapes of the sections are significantly different from circles at around the center of the ulna, and the cross-sectional areas are smaller in the middle one-third of the ulna than in other parts. These observations imply that fatigue frac tures of the ulna in pitchers of fast-pitch softball must be torsionally induced, tending to occur at the middle one-third of the bone.

Fatigue fractures usually involve the lower extremities after unaccustomed or inappropriate exercise. Although unusual in the upper extremity, symptomatic fatigue fractures of the ulna have been described in tennis players, volleyball players, weight lifters, and softball pitchers. The mechanism is

While fatigue fractures are common in military practice they are much less so in civilian practice and thus tend to be overlooked. Fractures occur most commonly in the distal second and third metatarsal shafts and within the calcaneum, but occur in almost any other bone of the foot. Any suspicious history of repetitive stress or sudden change in activity, athletic or otherwise, associated with swelling and point tenderness warrants further investigation by bone scintigraphy. Attention is drawn to the importance of understanding the basic biomechanical function of the foot and how it may affect the development of fatigue fractures. A distinction is drawn between the distal fractures of the second and third metatarsal shafts and those occurring in the proximal shafts of any of the metatarsals which have a different aetiology. Following conventional management in a plaster cast, it is suggested that any biomechanical anomaly which is present is compensated appropriately with an orthotic insole.

Autografts, because they are histocompatible, are the standard by which other bone grafts are judged. There is, however, increased morbidity for the patient from which large autografts, of limited supply in any case, must be obtained. In contrast, allografts are readily obtainable in large quantities and are used routinely in procedures for major limb salvage, trauma involving bone loss, and joint reconstruction. They have achieved sufficient success to warrant continued use, although a high incidence of nonunions, fatigue fractures, and occasional premature graft resorption suggest they are often poorly incorporated [3]. Of the two allograft materials, cancellous and cortical bone, the former shows a faster and more complete incorporation when donor and recipient are immuno- and histocompatible, as shown by Goldberg et al. [5]. Yet, they also display a higher incidence of histoincompatibility and cannot provide the immediate structural support required in some long bone procedures. Accordingly, cortical allografts with improved incorporability are viable alternatives to both autografts and cancellous allografts. The achievement of such improvement is enhanced with an understanding of cortical allograft incorporation in general and creeping substitution in particular. Because of the central role of neovascularization in all forms of healing, including that characteristic of graft incorporation, a study of neovascularization in cortical allografts was undertaken using the rabbit tibia implanted with an allograft-bearing bone chamber as its model. The goal of the subproject reported here was to test the hypothesis that the model yields data consistent with that of other cortical allograft models. An additional goal was to obtain the data in the form of quantitative measurements.

The fatigue life of 40CrNiMoA (AISI4340) steel with different microstructures under ultrasonic fatigue loading (f = 20 KHz, R = –1) and its influencing factors were studied by the ultrasonic fatigue test. The results showed that the ultrasonic fatigue life of the specimen was markedly increased by surface treatment, and the ultrasonic fatigue life with the microstructures characterised by both strength and toughness was longer. The specimens' fatigue fractures were analysed by a scanning electron microscope. The results showed that crack initiation took place at the defect of the material surface at the ultrasonic fatigue loading and the crack propagated towards the inside. The fracture had both the features of cleavage and that of quasi-cleavage. The different microstructures of 40CrNiMoA steel have two different types of S–N curve: a continuously decreasing curve and a stepwise curve. The specimens continued to fail over 107 stress cycles.

Fatigue fractures involving the sacrum are extremely rare, and to our knowledge no occurrence of such a fracture in a child has been reported in the English-language literature. These fractures may mimic primary bone tumours or infection, and it is important to make an accurate diagnosis so that unnecessary biopsy can be avoided. We report a fatigue fracture of the sacrum in an 11-year-old child following prolonged aerobic exercise.

Three cases of patellar fatigue fracture are reviewed. Two fractures presented with acute displacement and were initially thought to represent pathological fractures. Histological appearances in one case, and the clinical course in another, subsequently indicated that these were fatigue fractures. A third patient developed a chronic undisplaced fracture and followed the typical clinical course of fatigue fractures at other sites. The importance of recognizing patellar fatigue fractures and of differentiating spontaneously displaced fatigue fractures from pathological fractures is emphasized.

The clinical mechanical failures of small diameter intramedullary interlocking nails were evaluated to determine the relationship of failure modes to the type or location of tibial fractures. Methods were developed to duplicate failure modes in vitro in standardized tests to simulate the clinical situations. Where standard test methods were inadequate, new methods were developed to provide quantifiable, reliable methods of evaluating potential clinical performance. The modes and rates of mechanical failure in the clinical series were consistent among participating centers: (1) In diaphyseal fractures with secondary trauma, the intramedullary nail bent at the fracture site where the working length was unsupported; (2) failures that occurred several weeks after nailing were the result of fatigue fractures of the locking screws, usually at the distal end; and (3) nail and screw failures occurred most commonly in proximal and distal tibial fractures. The strength of the 8- and 9-mm sizes of Synthes and Russell-Taylor nails were comparable.

Overdentures were consecutively inserted in 92 severely resorbed maxillae and followed for 1 year. The dentures were supported by a total of 430 implants. Of these, 69 (16%) became loose and were removed during the follow-up period. The mobile implants caused 7 complete failures of the overdenture treatment. Postinsertion maintenance was more extensive for the overdentures than for fixed prostheses supported by implants. Problems arose in relation to the mucosa around the implants, and there were also fatigue fractures of the acrylic resin and the retentive clips. Fewer speech problems were reported in the overdenture group when compared to those with fixed prostheses.

SUMMARY Over a 6-year period a total of 23 greyhounds and 10 dogs of other breeds were presented with metacarpal and metatarsal fractures. While in other breeds trauma was the usual cause, in greyhounds the injuries were stress or fatigue fractures. In the greyhounds the fractures occurred mainly in young dogs and were often comminuted. Fifteen cases involved the fifth metacarpal bone of the left foreleg. The fractures were managed by either external immobilisation (8 cases) or internal fixation, mainly with lag screws (14 cases). Of 16 dogs which recovered sufficiently to be trialled, 6 were retired due to poor performance, 2 suffered further fractures and 4 raced in less than 10 races each. Four dogs entered in more than 10 races each and won 23 of a total of 109 starts.

Summary Today, in this age of technology, vibration caused by machinery is an almost universal hazard. Vibration transferred from a machine to the human body may cause discomfort, a reduction of performance, and even injury. Vibratory manual tools may cause damage to the circulatory system of the upper extremities (Raynaud's syndrome), to the peripheral nerves (peripheral neuropathy), and to the bones and joints (aseptic necrosis, fatigue fractures, degenerative joint disease). Vehicles and machines causing floor vibration cause degenerative disc disease of the lumbar spine. The pathogenesis of vibration injuries is still not completely clear and there is no effective treatment. Some of the abnormalities are irreversible and may cause permanent decrease of working ability, and even unemployment.

Der Gultigkeits- und Anwendungsbereich der linear-elastischen und der elastisch-plastischen Risbruchmechanik wird nach praktikablen quantitativen Kriterien abgegrenzt. Erstere ist beim Niederspannungssprodbruch in relativ sprodem Werkstoff anwendbar, letztere beim Sprod- und Verformungsbruch in Zaherem Werkstoff bei hoherer Spannung. Die eigentliche kontinuumsmechanische Bruchbedingung ist dabei noch nicht erfast. Die linear-elastische Risbruchmechanik ist bei Ermudungsbruchen weitgehend anwendbar, wobei das Zusammenwirken niedriger und hoher Lastwechsel zu berucksichtigen ist. Die risbruchmechanische Sprod- und Ermudungsbruchprufung wird den herkommlichen Verfahren gegenubergestellt. Fracture Mechanics Range of Validity and Application. The range of validity and application of the linear-elastic and elasto-plastic fracture mechanics is determined according to practicable quantitative criteria. The former is applicable to the low stress brittle fracture in brittle materials, the latter is applicable to the higher stress brittle and tear fracture in tougher materials. The real continuum mechanics fracture criterium is not yet determined. The linear-elastic fracture mechanics is widely applicable to fatigue fractures. Taking into account the interaction and sequence effect of low and high load amplitudes is necessary. The fracture mechanics approach to brittle and fatigue fracture is compared with traditional testing techniques.

— Fracture surfaces of both service and laboratory fatigue fractures frequently show dark tongue-shaped marks. In fatigue tests on 7075–T6 specimens such tongues were produced by high peak loads. Measurements indicated that a tongue is not formed during a single burst of crack extension but is the result of a number of successive pop-ins requiring an increasing load. Therefore tongue formation is a quasi-stable phenomenon. The tunnelling fracture in the centre of plate thickness is accompanied by unfailed ligaments at the plate surfaces which reduce the stress intensity at the crack tip. The effect of different material conditions and loading direction on tongue forming was studied. A new model was developed to describe the growth of a tongue. The model was in good agreement with the various test results. The analysis of the problem has some relevance to validity requirements for K1c. A formula pertaining to tongues proposed by Forsyth was slightly modified and found to be approximately correct for the present results.

Experimental tests demonstrate that there is a sharp drop in resistance to fatigue fracture when the grain size is increased from 75 to 150 micrometers. This is at least a partial explanation for fatigue fractures of the stems of total hip-joint prostheses reported in the literature. It is also shown that plastic strains associated with fatigue stressing increase with increasing grain size so that loosening of the bone cement embedment may also be part of the premature failure process.

A retrospective review of 206 consecutive thoracic and lumbar fusions revealed a variety of surgical procedures performed for instability and malalignment after severe trauma. Stabilization procedures included insertion of 103 Harrington distraction and 15 Harrington compression rods, 84 Weiss spings, six Luque rods, and 10 miscellaneous plates and wires as single or multiple devices in combination with anterior and/or posterior fusions. Complications of surgical fusion included nine unhooked rods, six fatigue fractures of rods and springs, five overdistractions of vertebrae, four cases of severe kyphosis, and two failures of reduction. A meaningful postoperative radiologic evaluation can be accomplished only when indications for surgical techniques, their radiologic appearance, and possible complications are known.

1. The relief of the fatigue fracture can be connected with crack growth rate, and the effect of the corrosive action of the medium on the latter can be established. 2. Cathodic protection with magnesium neutralizes anodic dissolution of the material at the crack tip in the case of a low crack growth rate. The form of the fracture surface in this case is the same as in air. 3. The fractures of steel 14Kh17N2 are more ductile than those of steel 20Kh13, which can be attributed to the difference in their structures (ferrite-martensite and bainite, respectively). This explains the fact that the CGR is somewhat lower in steel 14Kh17N2 than in steel 20Kh13.

1. The resistance to thermal fatigue of heat-resistant, cast nickel alloy ZhS6U, directionally solidified, was determined. 2. It was shown that at Δe>1%, the fatigue life of specimens with a longitudinal orientation of grains is 1.5–2 times greater than that of specimens with a transverse orientation of grains. The difference is manifest principally in the case of loading in cycles with holding of the specimen at maximum temperature. The difference in the behavior of material with coarse acicular and fine acicular macrostructure is less substantial. 3. A description was given of the characteristic features of the macrostructure and microstructure of thermal fatigue fractures distinguishing them from mechanical fatigue fractures.

A survey is given of the mechanical failures of the femoral component of Charnley and Charnley-Muller type total hip prostheses. Fractographic analysis reveals that all the prostheses have broken by metal fatigue. A review of the clinical data has been combined with a metallurgical and a mechanical study in order to assess the reasons of the mechanical failures. The following conclusions have been reached. The prosthesis should be inserted in varus position with regard to the axis of the intramedullary canal, and the prosthesis should be made of an alloy with appreciably higher yield stress and fatigue strength than the alloys of the investigated broken Charnley and Charnley-Muller type prostheses.

Es wird uber makro- und mikrofraktographische Strukturen an reinem Epoxidharz sowie an GFK und CFK nach Schwingbeanspruchung berichtet. In Epoxidharz treten Schwingungsstreifen und Bruchbahnen, ahnlich wie an Metallen auf. Der Abstand der Schwingungsstreifen betragt 0,70 bis 150 mm und nimmt in Bruchfortschrittsrichtung kontinuierlich zu. Die Gewaltbruche in reinem Harz zeigen neben Wallner-Linien und Lanzettenstruktur durchwegs Bruchhyperbeln. Delaminationsbruchflachen von GFK weisen fur den faserverstarkten Verbundwerkstoff charakteristische Schwingungsstreifen auf, deren Morphologie sich von den Schwingungsstreifen an reinem Harz unterscheidet. Damit ist es erstmals gelungen, an faserverstarkten Verbundwerkstoffen mit einem Fasergehalt von 70 Vol.% Schwingungsstreifen zu finden. Letztere sind am Ort der Fasern besonders ausgepragt und durften nur bei genugend hoher, ortlicher Spannungsintensitat entstehen. Des weiteren konnten die Betrage der ortlichen Schal- und Schubspannungskomponenten, aus denen sich die bruchwirksame Spannung zusammensetzt, fur die Bildung von Schwingungsstreifen mitverantwortlich sein. Die Ausbildung der Schwingungsstreifen last auf die bruchwirksame, ortliche Spannungsverteilung und den ortlichen Risfortschritt im faserverstarkten Kunststoff schliesen. Die Gewaltbruchflachen von GFK und CFK weisen Bruchhyperbeln auf. Damit ist ein weiteres Unterscheidungsmerkmal zu den Schwingbruchflachen gegeben. Structures of Fatigue Fractures in Fibre-Reinforced Plastics The report deals with macrofractographic and microfractographic structures in non-reinforced epoxide resins as well as in glass-fibre reinforced plastics and carbon-fibre reinforced plastics after fatigue stresses. Epoxide resins show fatigue striations and fracture lines similar to those in metals. The distance between the fatigue striations amounts to between 0.70 and 150 mm and increases continuously in the direction of fracture propagation. The instantaneous fractures in non-reinforced resin show parabolic cusps besides Wallner-lines and lance-shaped structures. Surfaces of delamination fractures of glass-fibre reinforced plastics show fatigue striations which are characteristic for fibre-reinforced composites, but their morphology differs from the fatigue striations in non-reinforced resin. This was the first time that fatigue striations could be discovered in fibre-reinforced composites of a fibre content of 70 per cent by volume. These fatigue striations are strongly marked at the positions of the fibres and will probably arise only in case of a sufficiently high local stress intensity. Moreover, the amounts of the local slicing and shearing stress components, of which is composed the stress causing the fracture, could be partly responsible for the formation of fatigue striations. The formation of the fatigue striations allows to draw conclusions with respect to the fracture-causing local stress distribution and the local crack propagation in fibre-reinforced plastics. The surfaces of instantaneous fractures in glass-fibre reinforced plastics and carbon-fibre reinforced plastics show parabolic cusps. This is another distinguishing characteristic as compared with the surfaces of fatigue fractures.

Forty-four adult male mongrel dogs were used to compare segmental cortical freeze-dried allogeneic bone grafts with fresh autogenous, freeze-dried autogenous, and fresh allogeneic segmental cortical grafts. Group I consisted of bilateral fresh autografts as external controls; Group II, a fresh autograft on one side for internal control and a freeze-dried autogenous graft on the other side to evaluate the effect of freeze-drying on repair; Group III, a fresh autograft on one side and a fresh allograft on the other side to measure the differences between autogenous and allogeneic grafts; and Group IV, a fresh autograft on one side and a freeze-dried allogeneic graft on the other to see if freeze-drying altered the repair of allogeneic grafts. The grafts were analyzed qualitatively over a six-month period by the use of interval roentgenograms to determine the times of graft-host union and the incidence of fatigue fractures. Six months after operation, the repair processes in the four groups were compared quantitatively with respect to biological repair and physical strength using torsional stress-testing, tetracycline labeling, and microradiography. The results indicate both qualitatively and quantitatively that: (1) fresh bilateral segmental cortical autografts show reproducible characteristics, so that the canine fibula furnishes a satisfactory model (Group I); (2) freeze-drying does not inhibit the repair process per se (Group II); (3) fresh allografts are rejected in varying degrees of intensity (Group III); and (4) freeze-drying does not protect cortical allogeneic grafts from such rejection (Group IV).

Fatigue tests were performed upon a coarse-grain-size nickel in an attempt to obtain faceted fractures, such as occur in many nickel-based superalloys. Well-developed facets occurred in a small minority of grains during high cycle fatigue. It is believed that the restricted faceting in nickel is a consequence more of good inherent fatigue resistance, rather than of high stacking fault energy. Thus, stresses well above the yield stress are necessary to produce fatigue failures. The corollary is that faceted fractures are indications of poor fatigue properties.