Biomechanical contributions of upper cervical ligamentous structures in Type II odontoid fractures

Fractures of the odontoid present frequently in spinal trauma, and Type II odontoid fractures, occurring at the junction of the odontoid process and C2 vertebrae, represent the bulk of all traumatic odontoid fractures. It is currently unclear what soft-tissue stabilizers contribute to upper cervical motion in the setting of a Type II odontoid fracture, and evaluation of how concomitant injury contributes to cervical stability may inform surgical decision-making as well as allow for the creation of future, accurate, biomechanical models of the upper cervical spine. The objective of the current study was to determine the contribution of soft-tissue stabilizers in the upper cervical spine following a Type II odontoid fracture. Eight cadaveric C0-C2 specimens were evaluated using a robotic testing system with motion tracking. The unilateral facet capsule (UFC) and anterior longitudinal ligament (ALL) were serially resected to determine their biomechanical role following odontoid fracture. Range of motion (ROM) and moment at the end of intact specimen replay were the primary outcomes. We determined that fracture of the odontoid significantly increases motion and decreases resistance to intact motion for flexion–extension (FE), axial rotation (AR), and lateral bending (LB). Injury to the UFC increased AR by 3.2° and FE by 3.2°. ALL resection did not significantly increase ROM or decrease end-point moment. The UFC was determined to contribute to 19% of intact flexion resistance and 24% of intact AR resistance. Overall, we determined that Type II fracture of the odontoid is a significant biomechanical destabilizer and that concurrent injury to the UFC further increases upper cervical ROM and decreases resistance to motion in a cadaveric model of traumatic Type II odontoid fractures.     

Biomechanical Comparison of Different Stabilization Constructs for Unstable Posterior Wall Fractures of Acetabulum. A Cadaveric Study

Purpose

Operative treatment of unstable posterior wall fractures of acetabulum has been widely recommended. This laboratory study was undertaken to evaluate static fixation strength of three common fixation constructs: interfragmentary screws alone, in combination with conventional reconstruction plate, or locking reconstruction plate.

Methods

Six formalin-preserved cadaveric pelvises were used for this investigation. A posterior wall fracture was created along an arc of 40–90 degree about the acetabular rim. Three groups of different fixation constructs (two interfragmentary screws alone; two interfragmentary screws and a conventional reconstruction plate; two interfragmentary screws and a locking reconstruction) were compared. Pelvises were axial loaded with six cycles of 1500 N. Dislocation of superior and inferior fracture site was analysed with a multidirectional ultrasonic measuring system. Results: No statistically significant difference was found at each of the superior and inferior fracture sites between the three types of fixation. In each group, the vector dislocation at superior fracture site was significantly larger than inferior one.

Conclusions

All those three described fixation constructs can provide sufficient stability for posterior acetabular fractures and allow early mobilization under experimental conditions. Higher posterior acetabular fracture line, transecting the weight-bearing surface, may indicate a substantial increase in instability, and need more stable pattern of fixation.     

俯卧位后外侧入路联合内侧切口治疗三踝骨折35 例的临床疗效评价

目的:探讨在俯卧体位下采用后外侧入路联合内侧切口治疗三踝骨折方法的临床疗效及安全性。方法:选择2014年1月~2015年1月在我院治疗并由同一治疗组医生采用俯卧体位下治疗的三踝骨折患者35例,治疗外踝骨折时将钢板置于腓骨后侧或外侧,使用钢板或螺钉对后踝骨折进行固定,2枚拉力螺钉固定内踝。观察术后切口及骨折愈合、踝关节功能恢复情况。术后定期随访,采用AOFAS踝-后足评分标准对踝关节功能进行评价。结果:手术时长50~142 min,平均90 min,1例患者内侧切口出现局部红肿,抬高患肢及定期换药后局部红肿好转,未出现明显切口感染征象。2例病人术后出现足背部麻木,分别在术后6周、9周时消失。随访时间6~18月,平均随访15个月。术后3月X线显示所有病人骨折线模糊,骨痂生长良好,按美国足踝外科协会踝-后足评分系统评分:优28例,良5例,可2例,优良率94.29%。结论:在俯卧体位下采用后外侧切口治疗三踝骨折可一次性复位、固定后踝和外踝骨折,联合内侧切口可在一个体位下完成三踝骨折的手术,缩短手术时间,对软组织破坏少,骨折可获得解剖复位,术后踝关节功能恢复佳,可降低因反复翻身而污染术野的概率。     

胸腰椎爆裂性骨折的治疗新进展

胸腰椎爆裂骨折是常见的脊柱损伤性疾病之一,其发病率、致残率较高是由胸腰段脊柱的解剖学特点所决定。国内外有多种脊柱骨折的分类,临床中使用较多的有AO分类及Denis分类,脊柱载荷分享分类现多用于评价患者是否适合于后路手术,而不能应用于评估手术指征。目前国内外胸腰椎爆裂性骨折的治疗尚无统一定式,大多数学者倾向于积极的手术治疗,其中尤以后路手术治疗为主,后路手术多采取短节段椎弓根定内固定加植骨治疗。近些年又出现了经后路270°或360°椎管减压,重建脊柱的三柱稳定性。前路及前后路联合手术都有其各自的适应症。保守治疗多采取卧床休息、体位复位、外固定支具法及功能康复等。本文总结了近年来关于胸腰椎爆裂骨折的最新治疗进展。     

Fracture mechanics of the femoral neck in a composite bone model: Effects of platen geometry

Load applicator (platen) geometry used for axial load to failure testing of the femoral neck varies between studies and the biomechanical consequences are unknown. The purpose of this study was to determine if load application with a flat versus a conical platen results in differing fracture mechanics. Femurs were aligned in 25° of adduction and an axial compressive force was applied to the femoral heads at a rate of 6 mm/min until failure. Load application with the conical platen resulted in an average ultimate failure load, stiffness, and energy to failure of 9067 N, 4033 N/mm, and 12.12 J, respectively. Load application with the flat platen resulted in a significant (p<0.05) reduction in ultimate failure load (7620 N) and stiffness (2924 N/mm). Energy to failure (12.30 J) was not significantly different (p=0.893). Different fracture patterns were observed for the two platens and the conical platen produced fractures more similar to clinical observations. Use of a flat platen underestimates the strength and stiffness of the femoral neck and inaccurately predicts the associated fracture pattern. These findings must be considered when interpreting the results of prior biomechanical studies on femoral neck fracture and for the development of future femoral neck fracture models.     

齿状突骨折手术方式的选择及治疗效果分析

目的:通过回顾性分析齿状突骨折不同术式的疗效,从而指导后期临床治疗。方法:回顾分析齿状突骨折26例,对比观察前、后路手术时间、出血量、平均住院时间及术后疼痛数字评分、颈椎功能障碍指数评分(NDI)等指标。结果:前路齿状突螺钉内固定手术时间105.7±35.3 min、出血量62.1±18.5 mL、平均住院时间7.0±1.9天、疼痛数字评分3.6±1.7分、NDI 24.3%±11.7%,后路寰枢椎融合手术时间148.2±36.2 min、出血量338.4±143.3 mL、平均住院时间11.2±2.1天、疼痛数字评分5.1±1.4分、NDI33.6%±13.4%。结论:前路齿状突螺钉内固定术具有手术时间短、出血少、平均住院时间短、疼痛数字评分低、对颈椎活动功能影响小等优势,而后路寰枢椎融合术具有手术适应范围广、手术操作难度小等优势,而其对颈椎活动功能影响较大。     

Quantitative evaluation of facet deflection,stiffness, strain and failure load during simulated cervical spine trauma

Traumatic cervical facet dislocation (CFD) is often associated with devastating spinal cord injury. Facet fractures commonly occur during CFD, yet quantitative measures of facet deflection, strain, stiffness and failure load have not been reported. The aim of this study was to determine the mechanical response of the subaxial cervical facets when loaded in directions thought to be associated with traumatic bilateral CFD – anterior shear and flexion. Thirty-one functional spinal units (6 × C2/3, C3/4, C4/5, and C6/7, 7 × C5/6) were dissected from fourteen human cadaver cervical spines (mean donor age 69 years, range 48–92; eight male). Loading was applied to the inferior facets of the inferior vertebra to simulate the in vivo inter-facet loading experienced during supraphysiologic anterior shear and flexion motion. Specimens were subjected to three cycles of sub-failure loading (10–100 N, 1 mm/s) in each direction, before being failed in a randomly assigned direction (10 mm/s). Facet deflection, surface strains, stiffness, and failure load were measured. Linear mixed-effects models (α = 0.05; random effect of cadaver) accounted for variations in specimen geometry and bone density. Specimen-specific parameters were significantly associated with most outcome measures. Facet stiffness and failure load were significantly greater in the simulated flexion loading direction, and deflection and surface strains were higher in anterior shear at the non-destructive analysis point (47 N applied load). The sub-failure strains and stiffness responses differed between the upper and lower subaxial cervical regions. Failure occurred through the facet tip during anterior shear loading, while failure through the pedicles was most common in flexion.     

Experimental model of tibial plateau fracture for biomechanical testing

Although adequate reduction and stable fixation have been recognized to be the prime goals in the treatment of displaced tibial plateau fractures, the optimal fixation technique remains controversial. The lack of a reliable model and a standard methodology contribute to this situation. The purpose of this study is to develop an experimental model of a tibial plateau fracture and a testing methodology that reproduces the failure mode commonly seen in the clinical setting. Using solid-foam and composite Sawbones tibiae, three different models of bi-condylar tibial plateau fracture (solid-foam, reinforced solid-foam and composite), six specimens for each model, were created and stabilized with double plating. The specimens were subjected to cyclic axial compression with increasing maximum load until failure. A femoral component of a total knee replacement of similar size and shape to the synthetic tibial surface was used as a load applicator. The experiment was repeated on six specimens of human cadaver tibiae. Among the Sawbones specimens, only the reinforced solid-foam model was found to produce a consistent failure mode (collapse in the medial plateau) comparable to that reported clinically in the literature. This mode of failure was also confirmed by the cadaver experiments. The failure load of the reinforced solid-foam model ranged from 4150 to 4260 N with a mean +/- SD of 4201 +/- 44 N and a coefficient of variance of 0.01, whereas for the cadaver model the failure load ranged from 1675 to 6096 N with a mean +/- SD of 3768 +/- 1482 N and a coefficient of variance of 0.39. We recommend the reinforced-foam model for future mechanical tests to compare different fixation methods for tibial plateau fractures.     

胫骨螺旋形骨折合并后踝骨折与单纯踝关节骨折的区别

目的:比较后踝骨折两种不同类型的临床区别,为后踝骨折的临床诊治提供借鉴参考依据。方法:选取2010年1月-2013年1月我院收治的成人胫腓骨骨干骨折和单纯踝关节骨折患者3578例为研究对象,对两种骨折患者的后踝骨折发生率、后踝骨折合并外踝骨折的发生率等进行比较分析。结果:(1)TAF患者的后踝骨折发生率高于单纯踝关节骨折患者的后踝骨折发生率,差异具有统计学意义(P0.05);(2)TSPMF患者的外踝骨折发生率低于单纯后踝关节骨折的外踝骨折发生率,差异具有统计学意义(P0.05)。结论:胫骨螺旋形骨折与单纯踝关节骨折存在一定程度的差异,临床实践中应针对两种骨折的临床特点实施有针对性的治疗方案。     

Off-axis loads cause failure of the distal radius at lower magnitudes than axial loads: a finite element analysis

Distal radius (Colles') fractures are a common fall-related injury in older adults and frequently result in long-term pain and reduced ability to perform activities of daily living. Because the occurrence of a fracture during a fall depends on both the strength of the bone and upon the kinematics and kinetics of the impact itself, we sought to understand how changes in bone mineral density (BMD) and loading direction affect the fracture strength and fracture initiation location in the distal radius. A three-dimensional finite element model of the radius, scaphoid, and lunate was used to examine changes of +/-2% and +/-4% BMD, and both axial and physiologically relevant off-axis loads on the radius. Changes in BMD resulted in similar percent changes in fracture strength. However, modifying the applied load to include dorsal and lateral components (assuming a dorsal view of the wrist, rather than an anatomic view) resulted in a 47% decrease in fracture strength (axial failure load: 2752N, off-axis: 1448N). Loading direction also influenced the fracture initiation site. Axially loaded radii failed on the medial surface immediately proximal to the styloid process. In contrast, off-axis loads, containing dorsal and lateral components, caused failure on the dorsal-lateral surface. Because the radius appears to be very sensitive to loading direction, the results suggest that much of the variability in fracture strength seen in cadaver studies may be attributed to varying boundary conditions. The results further suggest that interventions focused on reducing the incidence of Colles' fractures when falls onto the upper extremities are unavoidable may benefit from increasing the extent to which the radius is loaded along its axis.     

The sphenozygomatic suture as a key site for osteosynthesis of the orbitozygomatic complex in panfacial fractures: a biomechanical study in human cadavers based on clinical practice

The aims of this study were to determine the forces required for fracturing the intact orbitozygomatic complex and to evaluate the strength of the orbitozygomatic complex-fixation, especially with regard to the sphenozygomatic suture as a fixation point. In severe midfacial and panfacial fractures, the sphenozygomatic suture is routinely used in the authors' practice as a key site for fixation of the orbitozygomatic complex, thus establishing a stable outer frame as a basis for subsequent reconstruction. However, this has never been formally described, nor has it been biomechanically tested. Eight human cadaver heads were subjected to forces applied in a standard fashion to the orbitozygomatic complex on both sides (n = 16) using a servohydraulic testing machine. The force required to break the intact orbitozygomatic complex was measured on both sides. Subsequently, fracture patterns were noted and each orbitozygomatic complex (n = 16) was assigned to one of four groups: four-point fixation (zygomatic arch, frontozygomatic suture, infraorbital rim, zygomaticomaxillary buttress) using a 1.3/2.0-mm titanium system (group 1) and a 2.0-mm bioresorbable system (group 3); or three-point fixation (zygomatic arch, frontozygomatic suture, sphenozygomatic suture) using 1.3/2.0-mm titanium system (group 2) and a 2.0-mm bioresorbable system (group 4). Forces for failure of the constructs were measured. The force for failure of the intact orbitozygomatic complex was 1826 +/- 852 N. The mean force required for failure of the reconstructed orbitozygomatic complex was 504 +/- 178 N for group 1, 620 +/- 304 N for group 2, 93 +/- 22 N for group 3, and 133 +/- 31 N for group 4. The titanium constructs provided 27.7 percent (four-point fixation) and 31.7 percent (three-point fixation) of the intact breaking strength of the orbitozygomatic complex, which was significantly higher (p < 0.05) compared with 5.4 percent (four-point fixation) and 7.7 percent (four-point fixation) for the bioresorbable system. Plate bending (91 percent) was the primary cause for failure in the titanium plating system, whereas plate and screw breakage (57 percent) was responsible for failure of the resorbable system. The fixation of the sphenozygomatic suture was a key site in the fixation of the orbitozygomatic complex, which could be demonstrated with superior results in the three-point fixation group compared with the four-point fixation group. The bioresorbable system showed the lowest values in this cadaver study. Further experimental and clinical studies might determine whether the bioresorbable materials are sufficient for the treatment of complex fractures of the orbitozygomatic complex.     

Effectiveness of pedicle screw inclusion at the fracture level in short-segment fixation constructs for the treatment of thoracolumbar burst fractures: a computational biomechanics analysis

When treating thoracolumbar burst fractures (BF), short-segment posterior fixation (SSPF) represents a less invasive alternative to the traditional long-segment posterior fixation (LSPF) approach. However, hardware failure and loss of sagittal alignment have been reported in patients treated with SSPF. Including pedicle screws at the fracture level in SSPF constructs has been proposed to improve stiffness and reliability of the construct. Accordingly, the biomechanical performance of the proposed construct was compared to LSPF via a computational analysis. Pedicle screws at fracture level improved the performance of the short-segment construct. However, LSPF still represent a biomechanically superior option for treating thoracolumbar BF.     

人体颈椎松质骨显微结构和力学性能的区域性差异研究

目的:探讨人体脊柱松质骨骨骼显微结构和力学性能的区域性差异,为松质骨三维结构采样部位的选取提供参考。方法:显微CT扫描6块颈6椎体标本获得三维图像,依据椎体内解剖位置的不同,将松质骨划分为6个位置组:外侧、内侧、腹侧、背侧、头侧和尾侧。利用显微结构参数骨体积分数(Bone volume to tissue volume,BV/TV)、骨表面积和骨体积的比值(Bone surface to bone volume,BS/BV)、骨小梁数量(Trabecular number,Tb.N)、骨小梁厚度(Trabecular thickness,Tb.Th)、骨小梁分离度(Trabecular separation,Tb.Sp)和个体化骨小梁分割方法(Individual trabeculae segmentation,ITS)分析6个位置组内松质骨显微结构,并利用有限元分析,获得6个位置组内松质骨的力学性能参数表观弹性模量和表观剪切模量。分别两两对比外侧和内侧,腹侧和背侧,头侧和尾侧松质骨的显微结构参数(BV/TV、BS/BV、Tb.N、Tb.Th、Tb.Sp和个体化骨小梁分割得到的参数)和力学性能参数(表观弹性模量和表观剪切模量)。结果:头侧和尾侧的主要显微结构参数BV/TV、Tb.Th、Tb.N等和表观弹性模量均存在显著差异(P0.05)。腹侧和背侧、内侧和外侧的主要显微结构参数BV/TV、Tb.Th、Tb.N等无显著差异。外侧和内侧的表观弹性模量在非主方向即内外方向和腹背放上上存在显著差异(P0.05),在主方向即头尾上无显著差异。结论:在实验中采集椎体松质骨样本以及临床上利用高分辨率CT分析椎体松质骨结构时,感兴趣区域要同时涵盖头侧和尾侧。     

Pure orbital blowout fracture: new concepts and importance of medial orbital blowout fracture.

Pure orbital blowout fracture first occurs at the weakest point of the orbital wall. Although the medial orbital wall theoretically should be involved more frequently than the orbital floor, the orbital floor has been reported as the most common site of pure orbital blowout fractures. A total of 82 orbits in 76 patients with pure orbital blowout fracture were evaluated with computed tomographic scans taken on all patients with any suspicious clinical evidence, including nasal fracture. Isolated medial wall fracture was most common (55 percent), followed by medial and inferior wall fracture (27 percent). The most common facial fracture associated with medial wall fracture was nasal fracture (51 percent), not inferior wall fracture (33 percent). This finding suggests that the force causing nasal fracture is an important causative factor of pure medial wall fracture as the buckling force from the medial orbital rim. Of patients with medial wall fractures, 25 percent had diplopia and 40 percent had enophthalmos. On plain radiographs, diagnostic signs were found in 79 percent of medial wall fractures and in 95 percent of inferior wall fractures. On computed tomographic scans, late enophthalmos was expected in 76 percent of medial wall fractures. Therefore, the medial orbital blowout fracture may be an important cause of late enophthalmos, because it has a high incidence of occurrence, a low diagnostic rate, and a high severity of defect. Among the causes of limitation of ocular motility, muscle traction of the connective septa and direct muscle injury were found frequently, but true incarceration of the muscle was extremely rare in all fractures. The medial and inferior orbital walls are clearly demarcated by the bony buttress, which is an important structure supporting these orbital walls. Its buttress was closely correlated with the fracture of these orbital walls. Most orbital blowout fractures without collapse of the bony buttress had a trapdoor fracture with or without small fragments of punched-out fracture.     

Fracture management of civilian gunshot wounds to the hand

Civilian gunshot wounds to the hand are typically caused by low-velocity weapons, which create a localized pattern of soft-tissue and bone injury that usually allows for early definitive treatment. A retrospective chart review of 72 patients treated for 98 gunshot wound fractures at an urban level I trauma center was conducted to evaluate the results of limited debridement and early definitive fracture fixation of urban gunshot wound fractures of the hand. The incidence of hand fractures, means of fracture fixation, number of operations, occurrence of infection, and level of patient compliance were determined. Twenty-nine fractures were managed definitively with reduction and splinting in the emergency department or intensive care unit. Sixty-eight fractures were treated surgically, at a mean of 2 days after injury. Eleven patients required more than one operation. The overall infection rate was 8 percent and was not influenced by the fracture fixation method. All infections were superficial and resolved with antibiotics alone. Thirty-nine percent of patients were lost to follow-up after hospital discharge and 85 percent of patients were lost to follow-up before documented fracture healing. Twenty-six percent of patients were lost to follow-up with a removable fixation device in place. Limited debridement and early definitive fracture fixation are associated with low rates of complications for typical civilian handgun wound fractures. Cases with extensive injury or contamination do require a staged approach to treatment. Poor patient compliance in the urban trauma setting should be expected and may affect the management plan.     

Dislocated intra-articular fracture of the base of the fifth metacarpal: a clinical study of 23 patients

Twenty-three patients with dislocated intrarticular fractures of the base of the fifth metacarpal were treated during the last 3 years in our department. This fracture characteristically occurs in young, active males, and the most frequent mechanism of this injury is axial force striking the metacarpal head, mostly in fist fights. In 8 patients, the fracture was caused by direct force hitting the base of the fifth metacarpal. Four certain fracture patterns are described. Operative treatment by open reduction and fixation with two Kirschner wires generally gave good results.     

中西医结合内固定治疗股骨远端骨折30例临床研究

目的探讨DCS内固定配合中医药对30例股骨远端骨折的治疗效果。方法按AO分类：A型14例,B型6例,C型10例,经股骨下段前外侧切口入路整复骨折,并用DCS固定骨折配合中药内服外敷,术后早期进行康复训练。结果经1年随访,骨折愈合,平均愈合时间6个月,关节功能优良率85.71%,其中C型骨折1例术后出现膝内翻。结论DCS内固定配合中医药是治疗股骨远端骨折是较理想的方法。可早期进行康复训练。     

前环经皮Infix固定联合后路固定治疗垂直不稳定骨盆骨折的效果

目的:探讨前环经皮内固定架(Infix)固定联合后路固定治疗垂直不稳定骨盆骨折的效果。方法:采用回顾性方法,选择本院2013年8月到2018年2月诊治的垂直不稳定骨盆骨折患者61例患者,根据手术方法的不同分为观察组31例与对照组30例,对照组给予钢板内固定治疗,观察组给予前环经皮Infix固定联合后路固定,记录与观察两组预后。结果:所有患者都完成手术,无术中严重并发症发生,观察组的切口长度、术中出血量与骨折愈合时间显著少于对照组(P0.05),两组手术时间与术中透视次数对比差异无统计学意义(P0.05)。观察组术后1个月的钉道感染、神经损伤、静脉血栓、切口感染发生率低于对照组(6.5%vs.33.3%, P0.05)。观察组与对照组术后3个月的Majeed评分优良率分别为93.5%和73.3%,骨折复位优良率分别为96.8%和73.3%,观察组高于对照组(P0.05)。结论:前环经皮Infix固定联合后路骶髂关节螺钉固定治疗垂直不稳定骨盆骨折能减少创伤,促进骨折愈合,减少术后并发症的发生,提高骨盆复位质量与骨盆功能。     

An efficient and accurate prediction of the stability of percutaneous fixation of acetabular fractures with finite element simulation

Posterior wall fracture is one of the most common fracture types of the acetabulum and a conventional approach is to perform open reduction and internal fixation with a plate and screws. Percutaneous screw fixations, on the other hand, have recently gained attention due to their benefits such as less exposure and minimization of blood loss. However their biomechanical stability, especially in terms interfragmentary movement, has not been investigated thoroughly. The aims of this study are twofold: (1) to measure the interfragmentary movements in the conventional open approach with plate fixations and the percutaneous screw fixations in the acetabular fractures and compare them; and (2) to develop and validate a fast and efficient way of predicting the interfragmentary movement in percutaneous fixation of posterior wall fractures of the acetabulum using a 3D finite element (FE) model of the pelvis. Our results indicate that in single fragment fractures of the posterior wall of the acetabulum, plate fixations give superior stability to screw fixations. However screw fixations also give reasonable stability as the average gap between fragment and the bone remained less than 1 mm when the maximum load was applied. Our finite element model predicted the stability of screw fixation with good accuracy. Moreover, when the screw positions were optimized, the stability predicted by our FE model was comparable to the stability obtained by plate fixations. Our study has shown that FE modeling can be useful in examining biomechanical stability of osteosynthesis and can potentially be used in surgical planning of osteosynthesis.     

During sideways falls proximal femur fractures initiate in the superolateral cortex: Evidence from high-speed video of simulated fractures

Results of recent imaging studies and theoretical models suggest that the superior femoral neck is a location of local weakness due to an age-related thinning of the cortex, and thus the site of hip fracture initiation. The purpose of this study was to experimentally determine the spatial and temporal characteristics of the macroscopic failure process during a simulated hip fracture that would occur as a result of a sideways fall. Twelve fresh frozen human cadaveric femora were used in this study. The femora were fractured in an apparatus designed to simulate a fall on the greater trochanter. Image sequences of the surface events related to the fractures were captured using two high-speed video cameras at 9111 Hz. The videos were analyzed with respect to time and load to determine the location and sequence of these events occurring in the proximal femur. The mean failure load was 4032 N (SD 370 N). The first surface events were identified in the superior femoral neck in eleven of the twelve specimens. Nine of these specimens fractured in a clear two-step process that initiated with a failure in the superior femoral neck, followed by a failure in the inferior femoral neck. This cadaveric model of hip fracture empirically confirms hypotheses that suggested that hip fractures initiate with a failure in the superior femoral neck where stresses are primarily compressive during a sideways fall impact, followed by a failure in the inferior neck where stresses are primarily tensile. Our results confirm the superolateral neck of the femur as an important region of interest for future hip fracture screening, prevention and treatment research.