Segmental stem fracture of a cemented femoral prosthesis

We report an unusual case of segmental stem fracture in 4 places of a cemented femoral prosthesis in a 43-year-old man 4 years after total hip arthroplasty. To our knowledge, this is the first reported case of segmental stem fracture. Detailed analysis of the prosthesis was performed at an independent testing laboratory. Initiation of all the cracks occurred on the medial aspect on the stem where the manufacturer's identification lettering was present, and the fractures occurred sequentially along the stem from distal to proximal. Laser etching is likely to have caused the microstructural alterations found on the surface of the stem, which, in turn, predisposed to fatigue cracking. Proximal debonding of the cement-bone interface observed in prefracture radiographs suggests that cantilever-bending stresses represented the initial mode of failure.     

Effect of simulated metastatic lesions on the biomechanical behavior of the proximal femur

Pathologic fractures of femora in patients with metastatic cancer are associated with high morbidity and mortality. Prediction of impending fractures is based on unspecific clinical criteria or past clinician's experience, which leads to underestimation or overtreatment. The aim of this study was to investigate the effect of the site of metastatic lesions on biomechanical behavior of the proximal femur. Sixteen pairs of human femora were scanned with quantitative computed tomography (QCT) to asses bone mineral density. One femur of each pair remained intact while a defined lesion was reamed out in either the superolateral or inferomedial portion of the femoral neck of the contralateral femur. All femora were loaded in a mechanical test setup mimicking one‐legged stance and stiffness, failure load, and fracture location were determined. In the biomechanical experiments the superolateral lesion and the inferomedial lesion caused a stiffness reduction of 19% and 66%, respectively. The average failure load was 40% and 75% lower for specimens with the superolateral (4.53 ± 1.56 kN) and inferomedial (1.89 ± 1.73 kN) lesions, respectively, compared to intact specimens (7.66 ± 3.34 kN). Lesions in the femoral neck led to reduction in both stiffness and failure load of the proximal femur. Furthermore, the site of the lesion had a large effect on the magnitude of the reduction in biomechanical properties. The presented data emphasize the importance of differentiating between locations of the lesion in pathologic fracture prediction of the metastatic femur and underline the insufficient accuracy of current predictive guidelines. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2407–2414, 2017.

     

Effects of hip implant modular neck material and assembly method on fatigue life and distraction force

Hip implant neck fractures and adverse tissue reactions associated with fretting‐corrosion damage at modular interfaces are a major source of concern. Therefore, there is an urgent clinical need to develop accurate in vitro test procedures to better understand, predict and prevent in vivo implant failures. This study aimed to simulate in vivo fatigue fracture and distraction of modular necks in an in vitro setting, and to assess the effects of neck material (Ti6Al4V vs. CoCrMo) and assembly method (hand vs. impact) on the fatigue life and distraction of the necks. Fatigue tests were performed on the cementless PROFEMUR® Total Hip Modular Neck System under two different loads and number of cycles: 2.3 kN for 5 million cycles, and 7.0 kN for 1.3 million cycles. The developed in vitro simulation setup successfully reproduced in vivo modular neck fracture mode and location. Neck failure occurred at the neck–stem taper and the fracture ran from the distal lateral neck surface to the proximal medial entry point of the neck into the stem. None of the necks failed under the 2.3 kN load. However, all hand‐assembled Ti6Al4V necks failed under the 7.0 kN load. In contrast, none of the hand‐assembled CoCrMo necks and impact‐assembled necks (Ti6Al4V or CoCrMo) failed under this higher load. In conclusion, Ti6Al4V necks were more susceptible to fatigue failure than CoCrMo necks. In addition, impact assembly substantially improved the fatigue life of Ti6Al4V necks and also led to overall higher distraction forces for both neck materials. Overall, this study shows that the material and assembly method can affect the fatigue strength of modular necks. Finally, improper implant assembly during surgery may result in diminished modular neck survivability and increased failure rates. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2023–2030, 2017.

     

SPECT-CT评价股骨颈骨折后股骨头血供的变化

目的利用SPECT-CT观察不同分型股骨颈骨折后股骨头血供的变化和股骨头不同部位血供的分布情况。方法回顾性分析76例股骨颈骨折后股骨头的SPECT-CT检查资料,股骨颈骨折采用Garden分型,并将股骨头分为外上方（A）、外下方（B）和内下方（C）三个区域,分别计算患/健股骨头核素比值和三个区域与健侧股骨头核素计数比值,比较股骨颈不同类型骨折、同种骨折股骨头不同部位血供的变化。结果 GardenⅠ、Ⅱ、Ⅲ和Ⅳ型患/健比均值分别为：2.6、1.7、0.7和0.4（F=2.34,P〈0.05）。股骨头外上方、外下方和内下方与健侧股骨头的核素比分别为：（GardenⅠ型）1.9、3.2、2.4（F=3.85,P〈0.05）,（GardenⅡ型）1.3、2.3、1.6（F=4.56,P〈0.05）,（GardenⅢ型）0.3、0.9、0.5（F=3.47,P〈0.05）,（GardenⅣ型）0.1、0.6、0.3（F=2.73,P〈0.05）。结论股骨颈骨折移位程度越大,股骨头血供破坏越严重,尤其是股骨头的外上方部位血供下降程度最为明显。     

An Analysis of Reported Cases of Fracture of the Universal Exeter Femoral Stem Prosthesis

Background

Between 1991 and 2008, approximately 80 cases of fracture (neck or stem) have been reported. This study aimed at determining factors predisposing to implant fracture.

经口咽入路单节段固定治疗不稳定性寰椎骨折的研究进展

寰椎骨折是常见的颈椎骨折类型,由于上颈椎特殊的解剖结构,寰椎骨折通常为不稳定性骨折。以往的寰椎骨折治疗方法中,外固定往往带来低骨愈合率和远期颈痛,而颈枕融合与寰枢椎融合则牺牲了颈椎活动度。近年来,有学者经口咽入路到达寰椎前方,通过前路寰椎侧块螺钉及配套钢板同时完成骨折块的复位及固定,随访证明此术式保证骨性融合的同时最大程度地保留了颈椎活动度,还具有出血少、不剥离后路组织等优点,但存在术中脊髓与椎动脉的损伤及术后较高感染率等并发症,且对于其固定强度及手术的适应范围方面仍有待进一步研究证明。总之,经口咽入路单节段固定是治疗寰椎骨折的有效方法,给脊柱外科医师提供了新的思路。     

异型钢板内固定治疗桡骨远端不稳定骨折

目的:评价异型钢板治疗桡骨远端不稳定骨折的效果。方法:32例(32侧)术前X线片示远端不稳定骨折的患者经手术切开复位,以异型钢板内固定。结果:27例患者获得随访,平均随访时间18.3个月,根据术后X线片结果及改良Shea功能评估标准,23(85.2％)例功能良好,2例(7.4％)有内收功能受限伴腕关节疼痛。结论:切开复位异型钢板内固定是治疗桡骨远端不稳定骨折的有效方法。     

Medial migration of intramedullary hip fixation devices: a biomechanical analysis

Introduction Intramedullary nails for fixation of extracapsular hip fractures have gained popularity recently. Although clinically successful, they are not devoid of complications. An infrequently reported complication is the medial migration of the femoral neck element (FNE) of the implant into the pelvis. The purpose of this study was to create a biomechanical model simulating this effect based on a clinical case radiographic analysis. Methods Eight clinical cases of medial migration were available for radiographic analysis. Medial migration was quantified and the fractures were classified. A biomechanical model was built comprising two fixtures containing the nail and FNE respectively. A pivot between the two fixtures, representing a deficient femoral calcar, simulated an unstable fracture type. Two pivot points were used for each nail. The constructs were tested using sinusoidal loading (40–800 N at 2 Hz) and medial migration was assessed. Five different nail designs (TFN, PFN, PFN-a, Gamma-3 and IMHS) were tested (overall 75 tests). Results All the five implants demonstrated medial migration to a similar distance. The TFN required the highest number of cycles (3127 ± 2569) and the IMHS the lowest (58.8 ± 3.6) although this difference did not reach statistical significance (P = 0.07). Changing the pivot point for the medial calcar did not alter the results significantly. All eight clinical cases demonstrated an unstable intertrochanteric fracture pattern (AO/OTA 32A2). Conclusions Discrete biomechanical conditions are required to reproduce medial migration of the FNE in cephalomedullary devices.     

DXA-Based 3D Analysis of the Cortical and Trabecular Bone of Hip Fracture Postmenopausal Women: A Case-Control Study

Methods using statistical shape and appearance models have been proposed to analyze bone mineral density (BMD) in 3D from dual energy X-ray absorptiometry (DXA) scans. This paper presents a retrospective case-control study assessing the association of DXA-derived 3D measurements with osteoporotic hip fracture in postmenopausal women. Patients who experienced a hip fracture between 1 and 6 years from baseline and age-matched controls were included in this study. The 3D-SHAPER software (version 2.7, Galgo Medical, Barcelona, Spain) was used to derive 3D analysis from hip DXA scans at baseline. DXA and 3D measurements were compared between groups. Total hip areal BMD of hip fracture group as measured by DXA was 10.7% lower compared to control group. Differences in volumetric BMD (total hip) as measured by 3D-SHAPER were more pronounced in the trabecular compartment (−23.3%) than in the cortex (−8.2%). The area under the receiver operating curve was 0.742 for trabecular volumetric BMD, 0.706 for cortical volumetric BMD, and 0.712 for total hip areal BMD. Differences in the cortex were locally more pronounced at the medial aspect of the shaft, the lateral aspect of the greater trochanter, and the superolateral aspect of the neck. Marked differences in volumetric BMD were observed in the greater trochanter. This case-control study showed the association of DXA-derived 3D measurements with hip fracture. Analysis of large cohorts will be performed in future work to determine if DXA-derived 3D measurements could improve fracture risk prediction in clinical practice.     

The Medoff sliding plate and a standard sliding hip screw for unstable intertrochanteric fractures: A mechanical comparison in cadaver femurs

The Medoff sliding plate has a dual side capability along both the femoral shaft and neck to increase theoretically interfragmentary compression and load-sharing in hip fractures. We studied intertrochanteric fracture fixation in cadaveric bone to determine whether this device has a mechanical advantage over a standard sliding hip screw.

2-part and 4-part fractures were created in 12 cadaver femurs. The fractures were fixated and sequentially destabilized; bone and plate strains and fragment displacements were determined during testing, as a function of applied physiological loads before and after short-term cycling.

The Medoff sliding plate imposed a higher mean medial cortex strain than the sliding hip screw in all fracture models and at all loading levels, and the difference was statistically significant in the 2-part and in the unstable 4-part fracture models. The loading of the medial cortex region after cycling was approximately 50% higher in the Medoff samples than in the sliding hip screw samples. There were no significant differences in plate strains, fracture displacements or load to failure between the 2 devices.

These observations favor the dual sliding principle as regards providing fracture compression and load-sharing, which may explain low failure rates in clinical series of unstable intertrochanteric fractures, treated with the Medoff sliding plate.     

Fracture of hydroxyapatite coated prostheses: a report of two cases of stem failure in hip hemiarthroplasty

Hydroxyapatite (HA)-coated implants for hemiarthroplasty for fractures of the femoral neck offer the advantages of stable and permanent fixation. Since April 1994, we have treated 562 patients using the JRI Furlong HA-coated hemiarthroplasty system at the Worthing and Southlands Hospitals. Fracture of the fully-HA-coated stainless steel stem was seen in two patients. To our knowledge, this complication has not been reported in the literature. In both cases, the stem was well bonded distally and was loose proximally. The possible causes of stem fracture in these two cases could be related to stress shielding and the use of stainless steel implants. In addition, the junction between the wide proximal and narrow distal part might have served as a weak spot. We would advise surgeons to be aware of the complication of stem failure while using an HA-coated implant for hemiarthroplasty for femoral neck fracture in an active patient.     

Periprosthetic Femur Fractures After Total Hip Arthroplasty: Does the Mode of Failure Correlate With Classification?

BackgroundPeriprosthetic femur fracture is one of the most common indications for reoperation after total hip arthroplasty. Our objectives were to evaluate the incidence of reoperation after the surgical treatment of periprosthetic femur fractures and to compare the mechanisms of failure between fractures around a stable femoral component and those with an unstable femoral component.MethodsWe identified a consecutive series of 196 surgically treated periprosthetic fractures after total hip arthroplasty between 2008 and 2017. Mean age was 72 years (range, 29-96 years), and 108 (55%) were women. The femoral component was unstable in 127 cases (65%) and stable in the remaining 69 cases (35%). Mean follow-up was 2 years.ResultsThe 2-year cumulative probability of any reoperation was 19%. The most common indication for reoperation among the cases with a stable femoral component was nonunion, and the most common indication for reoperation among the cases with an unstable femoral component was infection. Fractures that originated at the distal aspect of the femoral component were associated with a high risk of nonunion (6 of 28 cases, P < .01) and reoperation (9 of 28 cases, P = .03).ConclusionSurgeons should take measures to mitigate the failure modes that are distinct based on fracture type. The high infection rate after surgical management of B₂ fracture suggests that additional antiseptic precautions may be warranted. For B₁ fractures, particularly those originating near the distal aspect of the femoral component, augmenting fixation with orthogonal plating, spanning the entire femur, or revising the stem in cases of poor proximal bone should be considered.     

Fracture of a ceramic liner in a total hip arthroplasty with a sandwich cup

Alumina ceramic-on-ceramic total hip arthroplasty (THA) has been widely used due to its advantages such as low wear, scratch resistance, wettable surface and relatively low biological reactivity of the wear particles. Nevertheless, this material in THA still persists to be one of the major concerns about the risk of fracture, due to its brittleness. Many authors have reported a fracture of the ceramic head but few reported a fracture of the ceramic acetabular insert. In order to reduce the rigidity of the ceramic-on-ceramic coupling and prevent an impingement between the rim of the ceramic liner and the metal neck of the femoral stem, a modular acetabular component with a sandwich insertion (alumina/polyethylene/titanium) was proposed. We report the fracture of the ceramic acetabular liner of such a ceramic sandwich cup due to a slightly retroverted position of the cup that causes an impingement between the femoral stem and the rim of the insert. The fracture occurred 3 years after the operation without trauma. At revision the entire cup was replaced using a polyethylene liner without inner ceramic liner.     

The diagnosis and treatment of deltoid ligament lesions in supination–external rotation ankle fractures: a review

The supination-external rotation or Weber B type fracture exists as a stable and an unstable type. The unstable type has a medial malleolus fracture or deltoid ligament lesion in addition to a fibular fracture. The consensus is the unstable type and best treated by open reduction and internal fixation. The diagnostic process for a medial ligament lesion has been well investigated but there is no consensus as to the best method of assessment. The number of deltoid ruptures as a result of an external rotation mechanism is higher than previously believed. The derivation of the injury mechanism could provide information of the likely ligamentous lesion in several fracture patterns. The use of the Lauge-Hansen classification system in the assessment of the initial X-ray images can be helpful in predicting the involvement of the deltoid ligament but the reliability in terms of sensitivity and specificity is unknown. Clinical examination, stress radiography, magnetic resonance imaging, arthroscopy, and ultrasonography have been used to investigate medial collateral integrity in cases of ankle fractures. None of these has shown to possess the combination of being cost-effective, reliable and easy to use; currently gravity stress radiography is favoured and, in cases of doubt, arthroscopy could be of value. There is a disagreement as to the benefit of repair by suture of the deltoid ligament in cases of an acute rupture in combination with a lateral malleolar fracture. There is no evidence found for suturing but exploration is thought to be beneficial in case of interposition of medial structures.     

Mixed-mode fracture toughness of the cobalt-chromium alloy/polymethylmethacrylate cement interface.

Mechanical debonding of the stem/cement interface has been implicated in the failure process of cemented femoral hip components. The nature of this failure process remains poorly understood due, in part, to limited understanding of how interfacial debonding occurs in response to a wide range of loading conditions. The purpose of this investigation was to determine the fracture toughness of the cobalt-chromium alloy/polymethylmethacrylate interface under mixed-mode loading conditions. The hypothesis was that the critical energy release rate was dependent on the phase angle of the crack tip and that the fracture response would be significantly different for a smooth compared with rough interface surface. A novel in-plane shear test fixture was developed with use of a combination of finite element and experimental fracture-mechanics tests. A wide range (-65-60 degrees) of phase angles was determined with the in-plane shear test and a clamped cantilever-beam test. Sixty experimental tests were performed for cobalt-chromium alloy bars with a plasma-sprayed coating or a precoat of polymethylmethacrylate over a satin-finished surface. For the specimens with the plasma-sprayed coating, critical energy release rates (500-700 J/m2) were not a function of the phase angle of the crack tip. In contrast, critical energy release rates (15-80 J/m2) were found to be strongly affected by the phase angle for the specimens precoated with polymethylmethacrylate. The critical energy release rate for specimens with the plasma-sprayed surface was significantly (p < 0.01) greater than for those precoated with polymethylmethacrylate. The critical energy release rate increased markedly with the phase angle of the crack tip for the specimens precoated with polymethylmethacrylate. The results suggest that the failure response of a stem with a plasma-sprayed surface may be insensitive to the loading angle of the crack tip, whereas a stem precoated with polymethylmethacrylate may be more likely to debond under tensile opening loading.     

Additional fixation of medial plate over the unstable lateral locked plating of distal femur fractures: A biomechanical study

IntroductionLateral locked plating is a standard treatment option for distal femur fractures. However, the unstable conditions after lateral locked plating are increasing. The objective of this study was to investigate the biomechanical strength of additional medial plate fixation over the unstable lateral locked plating of distal femur fractures.Materials and methodsA distal femur fracture model (AO/OTA 33-A3) was created with osteotomies in the composite femur. Three study groups consisting of 6 specimens each were created for single-side lateral locked plating with 6 distal locking screws (LP-6), single-side lateral locked plating with 4 distal locking screws (LP-4), and additional medial locked plating on LP-4 construct (DP-4). A compressive axial load (10 mm/min) was applied in the failure test. Mode of failure, load to failure, and ultimate displacement were documented.ResultsAll single-side lateral locked plating (LP-4 and LP-6) showed plate bending at the fracture gap, while none of the DP-4 showed plate bending at the fracture gap. Load to failure of DP-4 (mean 5522 N) was 17.1% greater than that of LP-6 (mean 4713.3 N, p < 0.05) and 29.2% greater than that of LP-4 (mean 4273.2 N, p < 0.05). Ultimate displacement of DP-4 (mean 5.6 mm) was significantly lower than that of LP-6 (mean 8.8 mm, p < 0.05) and LP-4 (mean 9.1 mm, p < 0.05).ConclusionsAdditional fixation of medial plate significantly increased the fracture stability in distal femur fractures fixed with the lateral locked plating. Especially in the clinical situations where sufficient stability cannot be provided at the distal segment, the medial plate may be considered as a useful biomechanical solution to obtain adequate stability for fracture healing.     

Fatigue fracture of a proximally modular, distally tapered fluted implant with diaphyseal fixation

We report and analyze the causes of a fracture in a proximally modular, distally tapered fluted MP stem in a 48-year-old woman (168 cm, 67 kg) with severe proximal bone deficiency. Evidence of fatigue failure with striations initiated laterally was observed in the laser etching of the tensile aspect of the prosthesis. However, metallurgical analysis suggested that laser engraving did not alter the microstructure of the stem. Stress due to the absence of proximal femoral bone support may have been sufficiently high to put this particular stem at risk for fatigue fracture. This important complication should be addressed when choosing this therapeutic option in cases with substantial proximal femoral bone loss. Strut allograft support should be recommended in such cases.     

不稳定肩胛颈骨折的手术治疗

目的 探讨不稳定肩胛颈骨折的手术治疗方法及疗效. 方法对2001年6月至2007年11月手术治疗且获得随访的13例不稳定肩胛颈骨折患者资料进行回顾性分析,其中男10例,女3例;左侧8例,右侧5例.单纯肩胛颈解剖颈骨折8例,肩胛颈骨折同时合并肩关节悬吊复合体损伤5例.手术采用肩关节后方入路,于因下肌与小测肌间隙进入,沿肩胛骨外缘到肩胛颈后方,复位固定肩胛颈骨折,同时固定合并的锁骨骨折、肩锁关节脱位及肩峰骨折.本组12例周定肩胛颈骨折的患者术前关节孟均向上倾斜,平均22.7°.采用Constant-Murley绝对值评分方法评价疗效. 结果 13例患者术后获平均45.1个月(10～90个月)随访.Constant-Mudey绝对值评分平均为81.2分(40～98分),平均前屈上举147.7°;优6例,良3例,可2例,差2例.术后12例固定肩胛颈骨折患者关节面向上倾斜平均为5.0°. 结论肩胛颈骨折的移位程度是影响预后的主要因素,采用肩关节后方入路复位固定移位的肩胛颈骨折可获得良好的临床效果.     

Wear and fracture of the acetabular cup in Charnley low-friction arthroplasty

Seven cases of progressive wear-out and fracture of the cemented high-density polyethylene cup in Charnley low-friction arthroplasty were identified in a group of 1,815 revisions of failed total hip arthroplasties. Normal function, rapid wear in the superolateral direction, and localized superolateral loss of bone-cement interface support with perfect medial cup fixation but, above all, asymptomatic nature of the problem until the moment of sudden failure were the characteristic features. The time to failure ranged from 11 to 20 years. Stem fixation remained unaffected. The findings suggest that the problem was wear-out without any changes that could have been attributed to the volume of high-density wear particles shed into the tissues.     

Incredible position of broken sliding dynamic hip screw implant in the medial of thigh

We report a case with implant failure after nailing of an unstable pertrochanteric fracture with dynamic hip screw. The patient presented with a medial sided thigh pain at 5 years after the surgery. Plain radiographs showed nonunion of the fracture with distant migration of assembled hip screw and side plate to the subcutaneous area of the inner thigh.