Fatigue fracture of the interlocking nail in the treatment of fractures of the distal part of the femoral shaft

The clinical and mechanical factors predisposing to a fatigue fracture of an interlocking nail were studied in seven patients who were treated for a fracture of the distal part of the femur. In all patients, the fracture of the femur was five centimeters or less from the more proximal of the two distal screw-holes. Finite-element analysis revealed that the stress on the nail exceeded its fatigue endurance limit and that the femur had to regain 50 per cent of its original stiffness through healing to accommodate weight-bearing without the risk of fatigue failure of the nail. The risk of fatigue failure may be minimized by using nails that have a larger diameter and by avoiding early weight-bearing.     

Noninvasive fatigue fracture model of the rat ulna.

Fatigue damage occurs in response to repeated cyclic loading and has been observed in situ in cortical bone of humans and other animals. When microcracks accumulate and coalesce, failure ensues and is referred to as fatigue fracture. Experimental study of fatigue fracture healing is inherently difficult due to the lack of noninvasive models. In this study, we hypothesized that repeated cyclic loading of the rat ulna results in a fatigue fracture. The aim of the study was to develop a noninvasive long bone fatigue fracture model that induces failure through accumulation and coalescence of microdamage and replicates the morphology of a clinical fracture. Using modified end-load bending, right ulnae of adult Sprague-Dawley rats were cyclically loaded in vivo to fatigue failure based on increased bone compliance, which reflects changes in bone stiffness due to microdamage. Preterminal tracer studies with 0.8% Procion Red solution were conducted according to protocols described previously to evaluate perfusion of the vasculature as well as the lacunocanalicular system at different time points during healing. Eighteen of the 20 animals loaded sustained a fatigue fracture of the medial ulna, i.e. through the compressive cortex. In all cases, the fracture was closed and non-displaced. No disruption to the periosteum or intramedullary vasculature was observed. The loading regime did not produce soft tissue trauma; in addition, no haematoma was observed in association with application of load. Healing proceeded via proliferative woven bone formation, followed by consolidation within 42 days postfracture. In sum, a noninvasive long bone fatigue fracture model was developed that lends itself for the study of internal remodeling of periosteal woven bone during fracture healing and has obvious applications for the study of fatigue fracture etiology.     

Fatigue fracture of the distal femur arising in the elderly

Fatigue fractures most frequently involve the tibia and metatarsal bones in the young. We report a very unusual case of fatigue fracture in the distal femur of a 62-year-old man. The differential diagnosis was a pathological fracture due to a metastatic bone tumor. The diagnosis of fatigue fracture was based on the fact that the patient walked every day for a long time, together with the following radiological features: no definite cortical destruction, a radiolucent area surrounded by sclerosis on CT, no extraskeletal mass, and sharp linear low signal intensities in the center of the lesion on MR images. Rest and restricted walking improved his symptoms and fracture healing. Fatigue fracture should be ruled out even in the elderly, especially those who engage in sports activities for long periods.     

Osteon pullout in the equine third metacarpal bone: effects of ex vivo fatigue.

An important concept in bone mechanics is that osteons influence mechanical properties in several ways, including contributing to toughness and fatigue strength by debonding from the interstitial matrix so as to "bridge" developing cracks. Observations of "pulled out" osteons on fracture surfaces are thought to be indicative of such behavior. We tested the hypothesis that osteon pullout varies with mode of loading (fatigue vs. monotonic), cortical region, elastic modulus, and fatigue life. Mid-diaphseal beams from the dorsal, medial, and lateral regions of the equine third metacarpal bone were fractured in four point bending by monotonic loading to failure under deflection control, with or without 10(5) cycles of previous fatigue loading producing 5000 microstrain (15-20% of the expected failure strain) on the first cycle; or sinusoidal fatigue loading to failure, under load or deflection control, with the initial cycle producing 10,000 microstrain (30-40% of the expected failure strain). Using scanning electron microscopy, percent fracture surface area exhibiting osteon pullout (%OP.Ar) was measured. Monotonically loaded specimens and the compression side of fatigue fracture surfaces exhibited no osteon pullout. In load-controlled fatigue, pullout was present on the tension side of fracture surfaces, was regionally dependent (occurring to a greater amount dorsally), and was correlated negatively with elastic modulus and positively with fatigue life. Regional variation in %OP.Ar was also significant for the pooled (load and deflection controlled) fatigue specimens. %OP.Ar was nearly significantly greater in deflection controlled fatigue specimens than in load-controlled specimens (p=0.059). The data suggest that tensile fatigue loading of cortical bone eventually introduces damage that results in osteonal debonding and pullout, which is also associated with increased fatigue life via mechanisms that are not yet clear.     

Fracture and fatigue properties of acrylic bone cement: the effects of mixing method, sterilization treatment, and molecular weight

The purpose of this study was to characterize the relative and combined effects of sterilization, molecular weight, and mixing method on the fracture and fatigue performance of acrylic bone cement. Palacos R brand bone cement powder was sterilized using ethylene oxide gas (EtO) or gamma irradiation. Nonsterile material was used as a control. Molecular weights of the bone-cement powders and cured cements were measured using gel permeation chromatography. Hand and vacuum mixing were employed to mold single edge-notched bend specimens for fracture toughness testing. Molded dog-bone specimens were used for fatigue tests. Electron microscopy was used to study fracture mechanisms. Analysis of variance and Student t-tests were used to compare fracture and fatigue performance between sterilization and mixing groups. Our results indicate that vacuum mixing improved significantly the fracture and fatigue resistance (P<.05, P<.07) over hand mixing in radiation-sterilized and EtO-sterilized groups. In vacuum-mixed cement, the degradation in molecular weight resulting from gamma irradiation decreased fracture resistance significantly when compared with EtO sterilization and control (P<.05). A corresponding decrease in fatigue resistance was observed in the cement that was degraded severely by a radiation dose of 10 MRad (P<.05). In contrast, EtO sterilization did not result in a significantly different fracture resistance when compared with unsterilized controls for vacuum-mixed cement (P>.1). For hand-mixed cement, fracture and fatigue resistance appeared to be independent of sterilization method. This independence is believed to be the result of higher porosity that compromised the mechanical properties and obscures any effect of sterilization. Our results indicate that a combination of nonionizing sterilization and vacuum mixing resulted in the best mechanical performance and is most likely to contribute to enhanced longevity in vivo.     

Displaced fatigue fractures of the femoral shaft

For this study, all displaced fatigue fractures of the femoral shaft treated during a 20-year period at a national military hospital were analyzed. Ten previously healthy male recruits sustained displaced femoral shaft fatigue fractures, the incidence being 1.5 per 100,000 person-years in military service. The median age of the patients was 19 years (range, 18-20 years). None had any previous fatigue fractures. The median body mass index was normal. Before the fracture displacement, nine recruits experienced thigh or knee pain for 1 to 6 weeks. Six of the 10 fractures were located in the distal third of the diaphysis. Only one fracture occurred in the proximal third. Six fractures showed a noncomminuted, oblique, or oblique-transverse configuration. Five fractures were treated using an intramedullary nail, four fractures with a dynamic compression plate, and one with a dynamic condylar screw-plate. The bone at the site of fracture proved to be abnormally brittle. In six patients this resulted in additional comminution intraoperatively. Two reoperations were necessary to exchange a nail and a screw because of technical faults. The median time to solid bony union was 3.5 months (range, 3-5 months). The recruits returned to light duty military service 6 weeks postoperatively, on the average. Two were exempted from military service for 2 years. Displacement is a rare, highly undesirable consequence of fatigue osteopathy of the femoral shaft among young recruits during basic military training. Preventive methods should focus on early, effective detection of developing fatigue fractures to avoid a displaced fracture, with subsequent prolonged morbidity and possible complications. Gentle handling of the bone during the fracture fixation procedure is imperative because of the extraordinary brittleness of the fracture fragments.     

Displaced femoral neck fatigue fractures in military recruits

BACKGROUND: Displaced fatigue fractures of the femoral neck are uncommon, but they can lead to substantial patient morbidity. This study was performed to examine the incidence, long-term consequences, radiographic findings, risk factors, and complications associated with this fracture. METHODS: Between 1975 and 1994, twenty-one military recruits sustained a displaced fatigue fracture of the femoral neck. Nineteen patients were followed for an average of eighteen years. Data regarding the population at risk, hospital records, initial and follow-up radiographs, and physical findings were analyzed. The impact of instructions from the Finnish Defense Forces, Department of Medical Services, provided in 1986 for prevention of femoral neck fatigue fractures was assessed. RESULTS: At our institution, the incidence of displaced fatigue fractures of the femoral neck was 5.3/100,000 service years from 1975 to 1986, prior to the introduction of the prevention regimen in 1986, and it was 2.3/100,000 service years (95% confidence interval, 0.11 to 1.31) from 1987 to 1994. The rate of Garden type-IV fractures decreased from 3.8 to 0/100,000 service years (95% confidence interval, 0 to 0.66) between the first and second time-periods. The detection of nondisplaced symptomatic fatigue fractures of the femoral neck increased from 15.5 to 53.2/100,000 service years (95% confidence interval, 2.27 to 5.21) between the two time-periods. Eighteen of the nineteen patients had had prodromal symptoms prior to the fracture displacement. Following fracture treatment, six patients had delayed union or nonunion of the fracture. Osteonecrosis of the femoral head developed in six patients and was significantly associated (p = 0.001) with shortening of the femoral neck. Severe osteoarthritis developed in eight patients. CONCLUSIONS: A displaced fatigue fracture of the femoral neck leads to long-term morbidity in a high percentage of patients. Most patients have prodromal symptoms, which provide an opportunity to prevent fracture displacement. Our results indicate that, in a military setting, an educational program can diminish the incidence of fatigue fracture displacement by increasing the awareness of these fractures and their prodromal symptoms and by facilitating diagnosis in the early stages before displacement occurs. LEVEL OF EVIDENCE: Therapeutic Level III.     

Early fatigue failures of cemented, forged, cobalt-chromium femoral stems at the neck-shoulder junction

Femoral component fracture is a rare but well-documented complication after total hip arthroplasty. Historically, most stem fractures have occurred at the middle third of the implant, where proximal stem loosening and solid distal stem fixation result in cantilever bending and eventual fatigue failure. In contrast, we report 2 early fatigue failures of well-positioned, well-fixed, cemented, forged, cobalt-chromium femoral components at the neck-shoulder junction. A contributing factor to the implant failures was heavy laser etching in a region of the implant subjected to high stresses, leading to decreased fatigue resistance and subsequent fracture.     

The effect of gamma radiation sterilization on the fatigue crack propagation resistance of human cortical bone

BACKGROUND: Clinical evidence has suggested that the rate of fracture in allografts sterilized with gamma radiation may be higher than that in controls. Gamma radiation sterilization has been shown to affect the post-yield properties of bone but not the elastic modulus. Since most allograft fractures occur with subcritical loads during activities of daily living, it may be that the fatigue properties of irradiated allografts are diminished. In this study, the fatigue crack propagation behavior of cortical bone sterilized with gamma radiation was compared with that of gender and age-matched controls. We hypothesized that gamma radiation significantly reduces the resistance of cortical bone to fatigue crack growth. METHODS: Specimens for fatigue crack propagation testing were machined from four pairs of fresh-frozen human femora obtained from four individuals (a younger male, younger female, older male, and older female donor). Half of the specimens were sterilized with 31.7 kGy of gamma radiation. The specimens were cyclically loaded to failure in a servohydraulic testing system, and crack growth was monitored. The cyclic stress intensity factor and the fatigue crack growth rate were calculated to examine the kinetics of fatigue crack growth. Following testing, the damage zone around the fracture plane was analyzed histologically. RESULTS: The morphology and kinetics of crack growth in irradiated specimens differed from the control data. Overall, the irradiated bone was significantly less resistant to fatigue crack growth than was control tissue (p < 0.05). There was less microdamage associated with fracture in the irradiated specimens than in the control specimens, with the exception of the bone from the older female donor. CONCLUSIONS: Gamma radiation sterilization significantly reduces the fatigue crack propagation resistance of cortical bone. Irradiated specimens also demonstrate a smaller amount of microdamage along the fracture plane. These findings may be due to ultrastructural alterations in the collagen matrix caused by radiation. CLINICAL RELEVANCE: This study suggests that, despite having pre-yield mechanical properties that are similar to those of nonirradiated bone, gamma-radiation-sterilized allograft may be more predisposed to fracture even under the subcritical loads that occur during the activities of daily living.     

应力性骨折影像诊断

目的应力性骨折,由于缺乏正确认识常造成误诊,本文重点强调影像诊断的价值。方法回顾性总结了1977～2000年间的应力性骨折64例,男性27例,女性37例。64例均进行X线检查,28例不典型者随后行ECT、MRI、CT检查。结果将应力性骨折分为疲劳性和衰竭性应力骨折两大类,其中疲劳性应力骨折12例占18.7%,衰竭性应力骨折52例占81.3%。36例为单纯平片诊断,28例平片结合ECT、MRI、CT诊断。疲劳性应力骨折以青少年胫骨常见;衰竭性应力骨折以老年妇女的胸、腰椎为多发区域。结论应力性骨折通常根据临床和X线平片即可明确诊断,疑难病例或早期诊断应结合ECT、MRI和CT扫描作出诊断。     

Subchondral fatigue fracture of the femoral head in military recruits

BACKGROUND: Subchondral stress fracture of the femoral head is a rare condition that usually occurs as an insufficiency fracture in people with poor bone quality. We evaluated the clinical characteristics of subchondral fatigue fractures of the femoral head that occurred in young, healthy military recruits. METHODS: Between January 1998 and November 2001, seven subchondral fatigue fractures of the femoral head were treated in five patients. The characteristics of this condition were ascertained by assessing the clinical course as well as radiographs, bone scintigrams, and magnetic resonance images. RESULTS: All patients were male military recruits in their early twenties in whom pain had developed within five months after recruitment. Definite abnormal findings were observed on the initial radiographs of four hips in three patients, and the femoral head was markedly collapsed in two of these four hips. Bone scintigrams were made of five hips in four patients, and all of them showed increased radionuclide uptake in the femoral head. In all affected hips, magnetic resonance images demonstrated a localized or diffuse bone-marrow-edema pattern in the femoral head and/or neck. A subchondral fracture line (a magnetic resonance crescent sign) was identified in all hips. In the patients who did not have collapse of the femoral head, the pain decreased gradually and disappeared completely within six months, with correspondingly improved findings on sequential magnetic resonance images. The patients with femoral head collapse were treated with total hip arthroplasty or an iliac bone strut graft. CONCLUSIONS: When a military recruit or an athlete reports hip pain, a diagnosis of subchondral fatigue fracture of the femoral head should be considered.     

Nonunion of Stress Fracture of Femoral Neck in a Child Managed with Valgus Osteotomy

Stress fracture of the femoral neck is very rare in children with an open upper femoral physis. There are only a few cases reported in the literature with most of these fatigue fractures of femoral neck managed conservatively. Some fractures require internal fixation either for displacement or for nonunion. A 7-year-old girl with a fatigue fracture of the femoral neck is presented, which resulted in coxa vara and functional disability. She was managed with valgus osteotomy and internal fixation using a dynamic hip screw. This resulted in union of the fracture site with good functional outcome.     

Leaflet fracture in Edwards-Duromedics bileaflet valves

Two cases of leaflet fracture in the Edwards-Duromedics valve at 36 and 38 months after implantation are reported. Both patients were immediately reoperated on and recovered well. In one valve an older housing fracture with partial tissue ingrowth was noted beside a recent transverse leaflet fracture. In the other valve the leaflet was fractured near the pivot mechanism. All larger embolized parts were detected in the iliac artery region by computed tomographic scan and were subsequently removed. Problems in diagnosis and the importance of immediate reoperation, even without exact diagnosis, are discussed. Technical evaluation of the valve revealed crack growth and arrest, giving evidence of fatigue fracture. Scanning electron microscopic examination revealed several areas of pitting and erosion. Although the exact cause of mechanical disruption remains speculative, pyrolytic carbon seems to have the characteristic of fatigue fracture as well as erosion damage. A connection between the two might exist.     

Fatigue subcapital fracture of the femur after the removal of the hip plate in transtrochanteric rotational osteotomy

We report two cases of fatigue subcapital fracture of the femur after the removal of the hip plate used for fixation in transtrochanteric rotational osteotomy for osteonecrosis. Two patients, a 42-year-old man and a 43-year-old man, underwent transtrochanteric rotational osteotomy, and bony union was achieved in both patients. However, fatigue subcapital fracture of the femur occurred in both patients 15 months after the removal of the hip plate. Transtrochanteric rotational osteotomy greatly changes the trabecular bone structure in the proximal femur, thus affecting the strength of the femoral neck. Therefore, for the trabecular bone to be remodeled and for the proximal femur to achieve sufficient strength, a sufficient period is necessary after complete bony union has occurred in the transtrochanteric lesion, before removal of the plate. Received: March 29, 2001 / Accepted: August 26, 2001     

腰椎疲劳骨折后松质骨力学性质的变化

目的　了解人体腰椎疲劳骨折后椎体松质骨力学性质的变化。方法　取正常和疲劳实验后的腰椎标本从中取出松质骨制成 1.2 cm× 1.0 cm× 1.0 cm长方体 ,标本进行压力载荷实验 ,然后进行力学计算和分析。结果　疲劳骨折后松质骨标本的极限压力强度和弹性模量均低于正常标本 ,标本破坏时的应变大于 0 .8%比正常标本大。结论　腰椎疲劳骨折时松质骨力学性质改变较大。     

A case of repeated faulty operation of bilateral fracture of the femoral diaphysis causing bilateral fatigue fracture of the femoral neck]

Bilateral diaphyseal fracture of the femur on different occasions, repeated faulty use of medullary nails and postoperative therapy followed by bilateral fatigue fracture of the femoral neck. Author thought the case because of its lesson worthy of publication.     

Understanding Bone Strength Is Not Enough

Increases in fracture risk beyond what are expected from bone mineral density (BMD) are often attributed to poor “bone quality,” such as impaired bone tissue strength. Recent studies, however, have highlighted the importance of tissue material properties other than strength, such as fracture toughness. Here we review the concepts behind failure properties other than strength and the physical mechanisms through which they cause mechanical failure: strength describes failure from a single overload; fracture toughness describes failure from a modest load combined with a preexisting flaw or damage; and fatigue strength describes failure from thousands to millions of cycles of small loads. In bone, these distinct failure mechanisms appear to be more common in some clinical fractures than others. For example, wrist fractures are usually the result of a single overload, the failure mechanism dominated by bone strength, whereas spinal fractures are rarely the result of a single overload, implicating multiple loading cycles and increased importance of fatigue strength. The combination of tissue material properties and failure mechanisms that lead to fracture represent distinct mechanistic pathways, analogous to molecular pathways used to describe cell signaling. Understanding these distinct mechanistic pathways is necessary because some characteristics of bone tissue can increase fracture risk by impairing fracture toughness or fatigue strength without impairing bone tissue strength. Additionally, mechanistic pathways to failure associated with fracture toughness and fatigue involve multiple loading events over time, raising the possibility that a developing fracture could be detected and interrupted before overt failure of a bone. Over the past two decades there have been substantial advancements in fracture prevention by understanding bone strength and fractures caused by a single load, but if we are to improve fracture risk prevention beyond what is possible now, we must consider material properties other than strength. © 2017 American Society for Bone and Mineral Research.     

Fracture and fatigue properties of acrylic bone cement

The purpose of this study was to characterize the relative and combined effects of sterilization, molecular weight, and mixing method on the fracture and fatigue performance of acrylic bone cement. Palacos® R brand bone cement powder was sterilized using ethylene oxide gas (EtO) or gamma irradiation. Nonsterile material was used as a control. Molecular weights of the bone-cement powders and cured cements were measured using gel permeation chromatography. Hand and vacuum mixing were employed to mold single edge-notched bend specimens for fracture toughness testing. Molded dog-bone specimens were used for fatigue tests. Electron microscopy was used to study fracture mechanisms. Analysis of variance and Student t-tests were used to compare fracture and fatigue performance between sterilization and mixing groups. Our results indicate that vacuum mixing improved significantly the fracture and fatigue resistance (P < .05, P < .07) over hand mixing in radiation-sterilized and EtO-sterilized groups. In vacuum-mixed cement, the degradation in molecular weight resulting from gamma irradiation decreased fracture resistance significantly when compared with EtO sterilization and control (P < .05). A corresponding decrease in fatigue resistance was observed in the cement that was degraded severely by a radiation dose of 10 MRad (P < .05). In contrast, EtO sterilization did not result in a significantly different fracture resistance when compared with unsterilized controls for vacuum-mixed cement (P > .1). For hand-mixed cement, fracture and fatigue resistance appeared to be independent of sterilization method. This independence is believed to be the result of higher porosity that compromised the mechanical properties and obscures any effect of sterilization. Our results indicate that a combination of nonionizing sterilization and vacuum mixing resulted in the best mechanical performance and is most likely to contribute to enhanced longevity in vivo.     

Osteochondral Fracture of the Fourth Metatarsal Head Treated by Open Reduction and Internal Fixation

Fracture of the metatarsal head is uncommon, and reports of isolated osteochondral fracture of the metatarsal head are rare. Because of the distal location of the fracture, it is difficult to achieve and maintain reduction, and potential complications include avascular necrosis and subchondral fatigue fracture. The authors present a case of an osteochondral fracture in a 40-year-old man, which was treated by open reduction and internal fixation with a single twist-off screw, with good results 12 months postoperatively.