The effect of locked distal screws in retrograde nailing of osteoporotic distal femur fractures: a laboratory study using cadaver femurs

OBJECTIVES: To examine the effects of locked distal screws in retrograde nails used in unstable osteopenic distal femur fractures. DESIGN: Biomechanical testing of paired human cadaveric femurs. INTERVENTION: Seven matched pairs of embalmed, moderately osteopenic cadaver femurs were instrumented with 12-mm intramedullary nails in a statically locked, retrograde fashion. One femur of each pair had locked distal screws and the other femur had unlocked distal screws. A 2.5-cm gap of bone was cut nine centimeters from the distal condyles to simulate an unstable fracture. The locked distal screw nails were compared to unlocked distal screw nails for collapse of the fracture gap, medial-lateral and anterior-posterior translation of the nail within the fracture site, and fracture angulation. The femurs were axially loaded, cycled, and then loaded to failure. MAIN OUTCOME MEASURES: Motion at the fracture site with axial cyclic loading and site of failure when loaded to failure. RESULTS: After cycling, both locked distal screw and unlocked distal screw nails demonstrated several millimeters medial and anterior translation within the fracture site and approximately 1 mm collapse of the fracture gap. Although no statistically significant differences were found, the locked distal screw nails had less anterior and medial translation, angulation, and collapse of the fracture gap after cycling. Loads to failure were similar for both locked distal screw and unlocked distal screw nails. It was noted that proximal femur failure occurred at the level of the proximal screw hole in the nail at the subtrochanteric level in 7 (4 locked distal screws and 3 unlocked distal screw groups) of the 14 samples. Four other samples failed through the intertrochanteric region (2 locked distal screw and 2 unlocked distal screw groups) and the remainder within the distal fragment by fracture of the femur along the medial cortex. CONCLUSIONS: Although most differences in fixation stability were not significant, the locked distal screw nails exhibited less fracture collapse and anterior and medial translation of the nail at the fracture site than the unlocked distal screw nails. The degree of varus angulation after cyclic loading was also less for the locked distal screw nails. The length of the nail chosen should avoid having proximal locking screws distal to the lesser trochanter, thus averting proximal femur stress risers and fractures.     

逆行交锁髓内钉治疗股骨远端骨折

目的 探讨逆行交锁髓内钉在治疗股骨远端骨折中的应用价值。方法 采用逆行交锁髓内钉对22例AO分型为A、C型新鲜股骨远端骨折病例行内固定。结果 所有病例均获随访，21例获牢固骨性愈合，未见畸形愈合、感染。1例发生主钉尾端处骨折，1例发生近端锁钉断裂。术后根据KSS评分体系，评价优14例，良6例，一般2例，优良率90．9％。结论 逆行交锁髓内钉适用于股骨远端骨折，具有高度的稳定性，操作简单，出血少，并发症少，功能恢复快。     

Anatomic considerations of locked humeral nailing

To investigate the risk of axillary nerve injury by the proximal locking screws in antegrade nailing of humeral fractures, the anatomy of the axillary nerve was examined in 20 fresh anatomic specimen humeri, which subsequently were nailed antegrade with specially designed humeral locked nails. The axillary nerve was found to be on average 45.6 mm below the tip of the greater tuberosity; it was jeopardized by insertion of the lower proximal locking screw in one of the 20 specimens. Short humeri, humeri with small heads, or too deeply inserted nails may increase the risk of nerve injury; likewise, a lower location and more horizontal direction of the locking screws and a greater curvature of the nail can heighten the risk. In addition to the examination of the axillary nerve, a geometric study of these anatomic specimen was performed and was aimed at improving retrograde nailing technique and thus treatment results. The humeral geometry indicated that for the best linearity in the sagittal plane, an entry portal incorporating the superior margin of the olecranon fossa would be recommended for the 14 humeri with a distal humeral offset less than 4 mm, whereas a supracondylar entry portal would be recommended for the six humeri with an offset larger than 4 mm. For best linearity in the coronal plane, the entry portal and nailing direction should be more lateral in humeri with a smaller humeral elbow angle.     

Biomechanical analysis of supracondylar femoral fractures fixed with modern retrograde intramedullary nails

OBJECTIVES: Several new retrograde supracondylar intramedullary nails have been developed to specifically address fractures of the distal femur. The nails appear clinically effective, but there are few biomechanical data documenting the stability of the fixation or the mechanical stiffness of the different designs. The goal of this study was to assess the torsional and bending stiffness of four designs of intramedullary nails developed for this application. METHODS: Four nail designs were tested in torsion and bending to determine system stiffness: Ace supracondylar, Richards "five hole" and "multi-hole" supracondylar, and Biomet retrograde. The nails were inserted into cadaveric femurs in which a one-centimeter distraction osteotomy had been created seven centimeters proximal to the condyles. The constructs were then tested on an Instron biaxial testing system. RESULTS: There were no statistically significant differences in bending stiffness among the groups of nails (range 0.79 to 1.18 newtons/meter; p > 0.1). However, the Ace nails (1.10 newtonmeters/degree) did exhibit a statistically lower torsional stiffness compared with the other nails (2.20 to 2.21 newton-meters/ degree; p < 0. 1). No differences were noted as a function of the number of locking holes. CONCLUSIONS: The bending stiffness of four currently available designs of retrograde intramedullary nails does not appear to be dependent on design variations. The torsional stiffness did vary among the four designs, but this was not determined by the number of fixation holes provided. It appears that a well-placed retrograde supracondylar nail of modern design should have sufficient stiffness to support the femur and provide stability during fracture healing.     

What is the risk of stress risers for interprosthetic fractures of the femur? A biomechanical analysis

Purpose

Due to increasing life expectancy we see a rising number of joint replacements. Along with the proximal prosthesis in the femur, more and more people have a second implant on the distal ipsilateral side. This might be a retrograde nail or a locking plate to treat distal femur fractures or a constrained knee prosthesis in the case of severe arthrosis. All these constructs can lead to fractures between the implants. The goal of this study was to evaluate the risk of stress risers for interprosthetic fractures of the femur.

Methods

Thirty human cadaveric femurs were divided into five groups: (1) femurs with a prosthesis on the proximal side only, (2) hip prosthesis on the proximal end and a distal femur nail, (3) femurs with both a hip prosthesis and a constrained knee prosthesis, (4) femurs with a hip prosthesis on the proximal side and a 4.5-mm distal femur locking plate; the locking plate was 230 mm in length, with ten holes in the shaft, and (5) femurs with a proximal hip prosthesis and a 4.5-mm distal femur locking plate; the locking plate was 342 mm in length, with 16 holes in the shaft.

Results

Femurs with a hip prosthesis and knee prosthesis showed significantly higher required fracture force compared to femurs with a hip prosthesis and a distal retrograde nail. Femurs with a distal locking plate of either length showed a higher required fracture force than those with the retrograde nail.

Conclusions

The highest risk for a fracture in the femur with an existing hip prosthesis comes with a retrograde nail. A distal locking plate for the treatment of supracondylar fractures leads to a higher required fracture force. The implantation of a constrained knee prosthesis that is not loosened on the ipsilateral side does not increase the risk for a fracture.     

Improved intramedullary nail interlocking in osteoporotic bone

OBJECTIVE: Intramedullary nail locking bolts often fail to gain purchase or cut out in osteoporotic bone. The biomechanical stability of a bladelike device that lowers intraosseous stress levels by distributing the load over a greater volume of bone was compared with conventional locking bolts in osteoporotic bone. METHODS: Standardized simulated comminuted supracondylar femoral fractures (segmental defect) in fresh-frozen paired osteoporotic (bone mineral density <200 milligrams per cubic centimeter) human cadaveric femurs were stabilized with a retrograde unreamed distal femoral nail and distally interlocked with conventional locking bolts or a bladelike device. The distal portions of the fixator-bone constructs were tested under axial load, and the stiffness and strength were compared (pairwise). RESULTS: Interlocking with a bladelike device was 41 percent stiffer (p = 0.01) and 20 percent stronger (p = 0.02) than that with conventional locking bolts. All posttesting radiographs showed compaction of the cancellous bone distal to the interlocking devices. Even after nail displacements of twelve millimeters, only a few locking bolts were plastically deformed and no bladelike device showed gross plastic deformation. CONCLUSION: This study showed the biomechanical benefits of increasing the bone-implant interface surface for improving the acute stiffness and strength of fracture fixation in osteoporotic cancellous bone. The fixator-bone construct withstood higher forces before failure in these fragile bones.     

Retrograde nailing of a femoral supracondyle

Because standard femoral supracondylar nails have certain disadvantages, they are often replaced by traditional femoral or tibial locked nails. The purpose of this study was to make a biomechanical comparison between both types of traditional locked nails to determine which technique was more suitable for treating unstable femoral supracondylar fractures. Fourteen left Sawbones femurs (Pacific Research Laboratories, Vashon, Washington) were osteotomized in the femoral supracondylar area. One centimeter of the medial cortex in the proximal fragment was obliquely removed to simulate an unstable fracture without shortening. Seven specimens were treated with traditional retrograde dynamic femoral locked nails, and the other 7 with traditional retrograde dynamic tibial locked nails. All specimens were tested with a servohydraulic materials testing machine to compare their relative stability. Static compression, dynamic cyclic compression, and static compression to failure were tested. An extensometer was used to measure the displacement of fragments. Displacement between the fragments increased following the increment in loads in both nails. The load-displacement curve was nearly linear up to 1000 N for both nails. The femoral nail had a greater stiffness compared with the tibial nail at 100 and 200 N (P=.02 and P=.04, respectively) in static compression and at 700 to 1000 N (P=.01 in each case) in dynamic cyclic compression, as well as larger loads in static compression to failure (8663 vs 7547 N, respectively; P<.001). Clinically, a traditional femoral locked nail may be more suitable to replace a standard femoral supracondylar nail in a retrograde fashion to treat an unstable femoral supracondylar fracture.     

远端锁钉数目对加锁髓内钉力学性能影响的研究

目的　测试远端锁钉数目对加锁髓内钉整体力学性能的影响。　方法　实验共选用国产 TAMZ钛合金制造 9mm胫骨加锁髓内钉 2 0根 ,将所有髓内钉随机分成单钉组 ,远端仅安装 1根锁钉 ;双钉组 ,远端安装 2根锁钉。各组再平均分成两小组 ,将髓内钉安装在自行设计的不锈钢模型中 ,利用万能力学实验机测试各组髓内钉的抗压缩和抗扭转力学特性。　结果　在压缩实验中单钉组平均最大压缩载荷为 1880 N,双钉组的平均最大载荷为 2 16 0 N,两组比较有统计学意义 (P<0 .0 5 ) ;在扭转实验中平均最大扭矩、扭角单钉组分别为 5 5 .5 Nm和 5 8.0°,双钉组分别为 5 5 .8Nm和 5 8.3°,两组无差异 (P>0 .0 5 )。　结论　单根锁钉的力学性质可满足临床要求。临床上安装髓内钉时 ,长管状骨近端或中 1/ 3较稳定的骨折 ,可在远端选择安装 1根锁钉 ;而远端 1/ 3骨折或者粉碎性、伴骨缺损的严重骨折 ,应在远端尽量安装 2根锁钉。     

Biomechanical characteristics of interlocking femoral nails in the treatment of complex femoral fractures

Interlocking intramedullary (IM) nails allow more comminuted and proximal or distal femoral fractures to be successfully treated than previously possible with routine IM nailing. Autopsy specimens were prepared to evaluate the effectiveness of different locking mechanisms on fracture site stability. Grosse-Kempf (GK) and Brooker-Wills (BW) IM nails were inserted in anatomic specimen femurs with transverse fractures and 1-, 2-, and 3-cm defects. The femurs were loaded in four-point bending, and bending stiffness was calculated. The femurs were also loaded in torsion, and the amount of slippage between the nail and bone (at 10 Nm of applied torque) was measured. The GK nail, fully interlocked, had the lowest amount of rotational slip, followed by the BW and the GK noninterlocked nail. Bending stiffness was not significantly different for these IM nails.     

Second generation intramedullary nailing of subtrochanteric femur fractures: a biomechanical study of fracture site motion

OBJECTIVES: To compare fracture site motion between different second-generation intramedullary nails used to fix subtrochanteric fractures of the proximal femur with and without femoral neck fractures. DESIGN: Nondestructive mechanical testing of four types of femoral intramedullary nails was undertaken to evaluate fracture site motion using a model that simulated single-leg and double-leg stance. METHODS: Three types of reconstruction nails (the Russell-Taylor Delta [Smith & Nephew, Memphis, TN], the Uniflex [Biomet, Warsaw, IN], Alta CFX [Howmedica-Osteonics, Rutherford, NJ]) and the Long Gamma nail (Howmedica-Osteonics, Rutherford, NJ), each measuring 11 x 380 mm, were inserted in fiberglass composite femurs. Four fracture patterns were studied (transverse subtrochanteric, subtrochanteric with posteromedial wedge comminution, subtrochanteric with one-centimeter gap, and a one-centimeter gap with a subcapital neck fracture). Single-and double-leg stance loading was simulated using a servohydraulic load frame (MTS, Eden Prairie, MN). Two-way analysis of variance and post hoc t tests were used to determine any statistically significant differences between groups. RESULTS: In single-leg stance there were significant differences in coronal plane rotation, shear, and axial translation across the subtrochanteric fracture site between the different nail types and the different fracture patterns (p < 0.001). In double-leg stance there were significant differences in coronal plane rotation and femoral head vertical motion between the different nail types and the different fracture patterns (p < 0.001), and there were significant differences in shear and axial translation between the different fracture patterns (p < 0.001) but not the different nail types (p > 0.05). CONCLUSIONS: For simple, well-reduced fractures the choice of implant is not critical. As fracture severity increased (comminution, gap, and combined neck fracture), the choice of implant, particularly with reference to proximal nail dimensions and implant materials, was a significant factor in reducing fracture site motion. Therefore, our laboratory data suggest that when subtrochanteric fractures are unstable (e.g., comminution, segmental bone loss) and early weight bearing is desirable, the choice of implant is critical and should be restricted to implants that allow minimal fracture site motion (Long Gamma and Russell-Taylor).     

Biomechanical evaluation of retrograde intramedullary stabilization for femoral fractures: the effect of fracture level

BACKGROUND: Retrograde stabilization of mid-diaphysis adolescent femur fractures has shown excellent biomechanical stability. However, it is unclear whether adequate stability is maintained for distal femur fractures using the retrograde approach compared with the clinically recommended antegrade approach. The purpose of this study was to evaluate the biomechanical stability of retrograde and antegrade nailing for mid-diaphyseal and distal diaphysis femoral fractures. METHODS: Twenty adolescent-sized synthetic femurs were randomly assigned to fracture location and surgical approach groups. Comminuted fractures were simulated at the mid-diaphysial level and 4 cm proximal to the distal physis. The retrograde approach used 2 c-shaped 3.5-mm titanium nails. The antegrade used c and s 3.5-mm nail configurations. Both techniques achieved maximum nail divergence at the level of the fracture. Biomechanical testing was conducted to determine differences in torsional range of motion (degrees)and failure load (N) at 5 mm. These data were analyzed with a 2-way analysis of variance (p < 0.05). RESULTS: In torsion, there were no differences related to surgical approach or fracture level. For axial compression to 5 mm, the antegrade approach required significantly greater force to achieve 5 mm of compression compared with the retrograde approach. The mid-diaphyseal fracture required significantly greater force to achieve 5 mm of compression compared with the distal diaphysis group. CONCLUSIONS: For maximum stabilization of a distal femur fracture, c- and s-shaped nails placed in the antegrade position is suggested. CLINICAL RELEVANCE: Surgical decision making regarding the use of either the antegrade or retrograde approach will be influenced by both the stability provided (antegrade) and the ease of insertion (retrograde).     

Biomechanical comparison of flexible stainless steel and titanium nails with external fixation using a femur fracture model

There are several options available for surgical stabilization of pediatric femoral shaft fractures. The purpose of this study was to compare the stability afforded by Ender stainless steel nails, titanium elastic nails, and one-plane unilateral external fixators for the fixation using a synthetic adolescent midshaft femur fracture model. The anterior-posterior (sagittal plane) bending, lateral (coronal plane) bending, torsional, and axial stiffness values were calculated using 6 different fixation configurations. These included pairs of 3.5-mm-diameter Ender nails with and without distal locking, 3.5- and 4.0-mm-diameter titanium elastic nails as well as single- and double-stacked monolateral external fixators. Eight synthetic femur models, 4 each with simulated transverse and comminuted fracture patterns, were sequentially tested for stability afforded by the various fracture fixation configurations. External fixation exhibited significantly greater control of anterior-posterior angulation compared with all flexible-nailing systems. Although Ender nails were slightly superior to titanium nails in control of sagittal plane angulation, this was not statistically significant. Compared with the external fixation constructs, all 4 flexible nail constructs demonstrated higher torsional stability. For prevention of axial shortening, all fixation methods were similar for the transverse fracture pattern, whereas external fixation was superior to flexible nails in the comminuted fracture model. No significant benefit was demonstrated with double stacking of external fixators. These findings may help guide clinicians choose the optimal fixation method for treatment of pediatric femoral shaft fractures.     

股骨髁上骨折的手术治疗

目的探讨提高股骨髁上骨折的手术治疗效果。方法(1)取6具人尸体新鲜股骨标本,制成有1cm骨缺损的股骨髁上骨折。采用逆行带锁髓内针和股骨髁支撑钢板两种内固定器材分别固定各骨折。对固定后的骨折进行应力测定,比较两种内固定物固定骨折的生物力学特性。用SPSS统计软件对结果进行分析。(2)对1995年8月到2000年12月收治的并可随访到的36例37肢体股骨髁上骨折(主要对其中的股骨髁支撑钢板16例16肢体,逆行带锁髓内针14例15肢体)进行临床随访分析,比较逆行带锁髓内针与股骨髁支撑钢板手术治疗股骨髁上骨折的临床结果。结果(1)生物力学性能用股骨髁支撑钢板固定的骨折的抗压缩强度值低于用逆行带锁髓内针固定。用股骨髁支撑钢板固定的骨折的抗弯曲的强度值高于用逆行带锁髓内针固定。( 2 )临床结果根据Neer膝关节功能评分标准,本组病例共有优秀26肢体,良好8肢体,可以1肢体,差2肢体。总体优良率91 9%。钢板类优良率94 7%,髓内针93 3%。膝关节屈伸活动范围平均110°。结论手术治疗股骨髁上骨折可获得良好的结果。逆行带锁髓内针和股骨髁支撑钢板固定在生物力学性能及临床应用方面各有优势。     

Initial results with the new tibial interlocking nail of the Orthopedic Study Group

The new AO universal tibia nail with interlocking possibility has several new features. The wall thickness has been increased from 1.0 to 1.2 mm. In order to give the stiffer nail smoother insertion properties and better cortical contact, the overall design has been altered with the help of computer calculation. Proximally there are 3 holes for locking purposes in the frontal plane, while distally we find two holes in the frontal and one in the sagittal plane to accommodate the locking bolts. The new nail has been applied in 17 clinical cases with overall good results. The indications were deliberately pushed to the extremes and even 5 open fractures were nailed after minimal remaining. There were 2 major perioperative complications: one proximal blow-out of the anterior cortex due to a wrong point of insertion and several other technical mistakes. The situation was salvaged with an external fixator. In an 85-year-old multiple injured lady with a 3-degree open tibia, the initial fixateur externe was replaced after 3 weeks by a 10 mm universal nail. Due to severe porosis and rather proximal extensive cortical comminution, the locking bolts and therefore the nail did not find a good hold in the tibia plateau. After uneventful healing of the soft tissues and additional splinting, the fracture, however, consolidated within 4 months. There were two superficial soft tissue infections early postoperatively, but no cases of osteitis. Healing of the fractures seems to progress without delay.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effectiveness of distally slotted proximal femoral nails on prevention of femur fractures during and after intertrochanteric femur fracture surgery

IntroductionIntra- and post-operative femoral shaft fractures related with nailing remain of concern. Although manufacturers have sought to solve the problem by providing distally slotted nails, it is not clear that these implants reduce fractures.We compare two distally slotted proximal femoral nails [trochanteric nail (TRON) and proximal femur intramedullary nail (PROFIN)].Patients and MethodsThe medical records of 195 hips treated with TRONs (distally slotted in four places in the sagittal and coronal planes) and 583 hips treated with PROFINs (distally slotted in two places in the coronal plane) in two institutes were retrospectively evaluated. The inclusion criteria were follow-up for at least 6 months; pertrochanteric fractures and age over 55 years.ResultsIn total, 161 hips in the TRON group and 512 hips in the PROFIN group were included. The mean follow-up time was 28.5 (range: 6–84) months in whole group. The demographic characteristics of the groups were similar. Only 2 intraoperative shaft and 3 proximal lateral cortex fracture was detected in PROFIN group, there wasn’t any postoperative fracture. Four proximal lateral cortex and 2 femur shaft fractures were detected in TRON group (one during operation and one at postoperative 8th month after a fall at pedestrian way).ConclusionsDistal cephalomedullary nail slotting prevented intra- and post-operative femoral fractures. A distal slot 50 mm in length may increase nail elasticity and reduce nail tip stress to a greater extent than a 30-mm slot. Distal slotting in both the sagittal and coronal planes afforded no advantage compared to coronal slotting only.Level of evidenceLevel III retrospective study     

Differences in biomechanical stability of femur fracture fixation when using titanium nails of increasing diameter

Purpose The purpose of this study was to compare the biomechanical stability generated when utilizing increasing sizes of titanium (Ti) flexible nails for fixation of simulated comminuted femur fractures. Methods Five synthetic adolescent-sized femur models were reamed to create a 9-mm canal. A 2-cm section was removed in the mid-diaphysis to simulate comminution. Each femur was first stabilized with bilateral, retrograde 3.0-mm titanium elastic nails. Femurs were tested in axial rotation and axial compression. The constructs were removed, and femurs were re-nailed with 3.5-mm nails. Identical testing was conducted. These nails were then removed, and femurs were re-nailed with 4.0-mm nails. This provided data on “canal fill” representing 67, 78 and 89% of the reamed canal diameter. Data for axial rotation (degrees) and failure load (N) required to produce 5 mm of fracture shortening were analyzed with a one-way ANOVA (P < 0.05) and a Tukey’s post-hoc test for multiple comparisons. Results For axial rotation, there were statistically significant improvements in rotational control for each increase in nail size. For axial stability, each increase in nail size resulted in increased axial failure loads to 5 mm, although these data were not statistically different. A specific comparison between 3.0- and 3.5-mm nails for compressive stability found significantly greater stability afforded by using 3.5-mm nails. Conclusions Data from this study demonstrate that increasing the amount of canal fill provides significant improvements in rotational control. The largest improvement was seen when increasing from 3.0- to 3.5-mm nails. While increasing the nail size from 3.5 to 4.0 mm again provided greater stability, larger nails may be more difficult to insert. Thus, increasing the nail size for femoral fracture fixation should be considered after measuring the diameter of the canal and evaluating the potential difficulty of insertion as well as specific demands of the fracture pattern.     

Femoral fracture at the proximal end of an intramedullary supracondylar nail: a case report

Retrograde intramedullary supracondylar nails have been added to the orthopedic armamentarium for treatment of distal femoral fractures. Major complications of this new technique have not been noted. We report a case of a femoral fracture at the proximal end of a retrograde intramedullary supracondylar nail. We hypothesize that this complication may be due to the proximal end of the nail acting as a stress riser, with the cortical holes drilled for the interlocking screws compounding this effect.     

股骨髓腔的解剖学测量及与股骨交锁髓内钉的匹配性研究

 目的 通过CT 扫描图像对股骨髓腔进行解剖学测量, 模拟分析髓腔与股骨交锁髓内钉的匹配性, 探讨髓内钉手术中远端锁钉置入困难的原因。方法 对30 个干燥股骨标本进行CT 横断面扫描, 每一个股骨按骨干全长均匀提取20 幅图像, 分别测量每幅图像中轴点及髓腔壁一周8 个点在X、Y 轴上的数据。用三维绘图软件画出髓腔、中轴线、髓内钉在三维空间上的形态, 重叠后进行比对。绘制髓腔中轴冠状面及矢状面的折线型数据图表, 与髓内钉数据结合, 模拟髓内钉插入髓腔, 观察髓内钉切出髓腔壁情况。结果 将股骨髓腔中轴线与髓内钉重叠后进行比对, 二者在冠状面上较一致, 在矢状面上髓腔弧度较髓内钉大。模拟髓内钉插入髓腔, 冠状面上有6 根髓内钉于股骨标本的中上段切出髓腔内侧或外侧壁, 切出率为20%(6/30), 矢状面上有13 根髓内钉从前缘切出, 切出率为43%(13/30)。结论 常规股骨交锁髓内钉与大多数股骨髓腔匹配, 但髓腔解剖结构有一定的变异性, 部分髓腔成角过大使髓内钉发生形变是引起髓内钉远端锁钉置入困难的主要原因。     

Effect of piriformis versus trochanteric starting point on fixation stability of short intramedullary reconstruction nails

Recently, a new, shorter IM nail using two 6 mm reconstruction screws for proximal fixation was introduced in two versions for femoral insertion: piriformis fossa (FAN) and greater trochanter (TAN). These nails were compared experimentally for their fixation stability, proximal load transmission, and failure strength in an unstable intertrochanteric fracture model in cadaveric femurs. Vertical and axial loads were first applied to the intact femurs. Fractures were created, subsequent fixation applied, and the femurs underwent a series of both vertical and axial loading tests. There was no significant difference in strain readings between the nails for either axial loading or cyclical loading. There was no statistically significant difference between the loads to failure for the trochanteric nails and the standard antegrade nails. The average ultimate loadfor the FAN and TAN nails were 3010 N and 2830 N respectively. These two nails performed very similarly throughout our testing.     

Using flexible nails to improve stabilization of proximal femur fractures in adolescents

Intramedullary fixation as a treatment for adolescent femur fractures has increased in popularity. We investigated the varus stability of 3 fixation techniques--the standard 2-nail configuration (2 retrograde nails), a 3-nail configuration (standard 2-nail configuration plus 1 antegrade nail), and a retrograde/antegrade 2-nail configuration--in synthetic femurs with 2 simulated fracture patterns (transverse, butterfly). A varus moment was applied to the specimens until 20 degrees of varus angulation was obtained. The varus angular stiffness of the construct defined varus stability. The 3-nail configuration had the most varus angular stiffness with both fracture patterns. The varus stability of the 3-nail configuration was statistically higher than that of the standard 2-nail configuration with the transverse fracture pattern only. Adding 1 antegrade nail to 2 retrograde nails significantly increased resistance to varus deformity of reduced proximal-third transverse femur fractures in the synthetic femur model.