Biomechanik von Femurverriegelungsmarknägeln im Knochen-Implantat-Verbund

Today there is a variety of different interlocking intramedullary nail designs available for the femureach designed with a different approach to achieve stability for fracture fixation. We compared different nail types in the bone-implant complex (BIC) of four unreamed solid nails and a slotted, reamed nail to see if there are major differences in stiffness for axial load, bending and torsion. We simulated comminuted mid-shaft fractures by a 2 cm defect osteotomy in paired human cadaver femora. Each bone was tested intact in a Universal testing machine. The results were recorded, osteotomy and osteosynthesis were performed, and the BIC was tested. Relative stiffness was calculated for each individual bone. ForP-values less than 0.01 (‘least significance difference test’) the difference between groups was considered to be significant. In torque testing the unslotted solid nails showed significantly more stiffness (0.6–1.8 Nm/^o) compared to the slotted nail (0.2 Nm/^p). Compared to intact bone (6.9 Nm/^o), both groups of nails were significantly less stiff (relative stiffness 2–20%). In axial load and bending testing, the largediameter unreamed nail showed greater higher stiffness (32–68%). This study shows that stiffness of the BIC in interlocking femoral nails is more dependent on nail profile than on the press-fit of nails in the medullary canal. For torque stiffness the absence of a slot is of special importance. According to our study, all of the unslotted nails tested give adequate stability for fracture fixation.     

Biomechanical comparison of slotted and nonslotted interlocking nails in distal femoral shaft fractures

The torsional and compressive biomechanical characteristics of slotted and nonslotted interlocking nails in distal femoral shaft fractures were evaluated. Slotted (Grosse-Kempf) and nonslotted (Russell-Taylor) locked nail systems were implanted in anatomic specimen femora, which were then tested in torsion and axial compression. For torsional studies, each femur was transversely sectioned distal to the isthmus; for axial loading, a distal 3-cm section of bone was removed. The mean peak torsional stiffness of the femora fixed with nonslotted nails was 0.955 Nm per degree, which was significantly greater than that (0.300 Nm per degree) for the femora fixed with the slotted nails. However, when loaded to failure in compression, the nonslotted nail group failed at a mean load of 2490 N compared with 3050 N for the group fixed with the slotted devices. These results could be due in part to the lesser rigidity of the slotted nail, which may have facilitated greater load sharing with bone and increased resistance to compression failure.     

Bending and torsional stiffness in cadaver humeri fixed with a self-locking expandable or interlocking nail system: a mechanical study

OBJECTIVES: This study was designed to gain data about a new expandable, noninterlocked intramedullary nail's capacity to stabilize unstable transverse humeral shaft fractures without the need for interlocking, thus making nail implantation simpler and to prove our goal hypothesis: that in a midshaft osteotomy of the humeral shaft the expandable humeral nail will show the same bending and torsional stiffness as an interlocked humeral nail, when implanted correctly according to the manufacturer's instructions. DESIGN: Pair randomization. SETTING: Mechanical laboratory testing. PARTICIPANTS: Eight pairs of freshly harvested cadaveric humeri. INTERVENTIONS: Fracture model was a midshaft transverse osteotomy, gapped to 3 mm. Each humerus pair received an expandable humeral nail (Fixion) or an interlocked humerus nail (Synthes) through a retrograde approach. The humeri were fixed in polymethylmethacrylate cylinders and tested in a servo-pneumatic material-testing machine. MAIN OUTCOME MEASUREMENTS: Torsional stiffness and bending stiffness of the nail-bone-construction. RESULTS: Expandable nails (interlocked nails) showed a lateral bending stiffness of 0.73 +/- 0.14 (0.63 +/- 0.1) KN/mm (P = 0.026) and a frontal bending stiffness of 0.67 +/- 0.18 (0.58 +/- 0.09) KN/mm (P = 0.084). Torsional stiffness values were 0.13 +/- 0.19 (0.43 +/- 0.09 Nm/degrees) (P = 0.012). Lower torsional stiffness in the expandable nail group was observed in humeri with a funnel shaped proximal intramedullary canal. CONCLUSIONS: The nail systems showed similar characteristics for frontal bending (P = 0.084), but not for lateral bending (P = 0.026). For lateral bending, the Fixion nail showed significantly more stiffness than the UHN nail (P = 0.026). There was significantly lower torsional stiffness with expandable nails compared with interlocked nails. Clinical correlation would suggest that in rotationally unstable fractures (A2 and A3 diaphyseal fractures), interlocked nails would provide increased stability over expandable nails.     

Biomechanical comparison of bending and torsional properties in retrograde intramedullary nailing of humeral shaft fractures.

OBJECTIVE: To establish whether the bending and torsional stiffness of an implanted nail are influenced by nail design and nail-bolt interface, this study compared two implanted retrograde nail systems: the AO/ASIF unreamed humeral nail (UHN) and the Russell-Taylor (RT) nail. DESIGN: Pair randomization. SETTING: Mechanical laboratory testing. SPECIMENS: Twelve pairs of freshly harvested cadaveric humeri. METHODS: Transverse fractures were simulated with a standardized midshaft osteotomy and a three-millimeter gap. Both nails were proximally and distally interlocked. The RT nail has a single interlock at its base and tip. The UHN has double interlocking both proximally and distally. The screw hole design of the RT nail features slots, whereas the UHN has round screw holes. MAIN OUTCOME MEASURES: Anteroposterior and mediolateral bending stiffness and torsional stiffness. RESULTS: The RT nail showed higher bending stiffness in anteroposterior and mediolateral bending. Large differences were seen in the torsional characteristics: for the first 30 degrees, the RT nail showed a much lower resistance against torsion than the UHN. Analysis of variance of stiffness at four, six, and eight newton-meters showed statistical significance (p < 0.0001). Torsional stiffness, defined as the slope of a straight line approximated to between 75 and 100 percent of the maximum torque, was very similar in both nails. CONCLUSION: The torsional differences between the two nail systems are attributable to the nail-bolt interface of the RT nail. This dynamic system allows a clinically relevant degree of movement. The greater resistance to rotatory forces of the UHN is explained by the fact that the interlocking at its tip and base creates a static rather than a dynamic system.     

Biomechanical evaluation of retrograde docking nailing to a total hip arthroplasty stem in a periprosthetic femur fracture model

IntroductionSlotted nails allow a connection to a total hip arthroplasty (THA) stem and act as intramedullary load carrier. This study compares construct stiffness, cycles to failure and failure load between a retrograde slotted femur nail construct docked to a THA stem and a lateral locking plate in a human periprosthetic femur fracture model.Materials and methodsIn seven pairs of fresh-frozen human anatomic femora with cemented THA, a transverse osteotomy was set simulating a Vancouver type B1 fracture. The femora were instrumented pairwise with either a retrograde slotted nail coupled to the prosthesis stem, or a locking plate plus a locking attachment plate. Four-point mediolateral bending, torsional and axial bending construct stiffness was investigated via non-destructive tests. Cyclic testing under progressively increasing physiologic loading was performed at 2 Hz until catastrophic construct failure.ResultsMediolateral bending stiffness did not differ significantly between the two groups (P=0.17) but exhibited a biphasic profile with significantly increased stiffness in both groups (P<0.01). Nail constructs provided a significantly lower torsional stiffness (0.49 ± 0.66 Nm/°) than plate constructs (1.70 ± 0.86 Nm/°), P=0.03. Axial bending stiffness did not differ significantly between the groups (Nail: 605 ± 511 N/mm; Plate: 381 ± 428 N/mm), P=0.61. Cycles to failure and failure load were significantly higher for the plate constructs (25’700 ± 8’341; 3’070 ± 1334 N) compared with the nail constructs (20’729 ± 7’949; 2’573 ± 1295 N), P=0.04.ConclusionThe docking nail construct provides an intramedullary fixation with connection to the prosthesis stem; however, it is biomechanically weaker in stable fractures compared to the plate construct.     

A biomechanical study on flexible intramedullary nails used to treat pediatric femoral fractures

Flexible intramedullary nails have been indicated to treat femoral fractures in pediatric patients. The purpose of this study was to examine the stability of simulated transverse fractures after retrograde intramedullary flexible nail fixation. Various nail diameter combinations were tested using composite femurs in bending, torsion, and a combined axial/bending test where a vertical compressive force was applied to the femoral head. The cross-sectional percent area fill of the nails within the femurs was also determined. In 4 point bending, the greatest repair stiffness was 12% of the intact stiffness. In torsion, the greatest stiffness was 1% of the intact stiffness for either internal or external rotation. The greatest repair stiffness was 80% of the intact stiffness for a compressive load applied to the femoral head. Nail combinations with single nail diameters greater than 40% of the mid-shaft canal width, as measured from an AP radiograph, prevented the fracture from being reduced and left a posterior gap. Flexible intramedullary nails may be of value in the treatment of pediatric femoral fractures, but care must be taken to insert nails that are correctly sized for the canal and to protect the healing fracture from high torsional and bending loads.     

Are Inflatable Nails an Alternative to Interlocked Nails in Tibial Fractures?

Recently developed inflatable nails avoid reaming and interlocking screws in tibial fractures and reflect a new principle for stabilization of long bone fractures. We asked if the bending stiffness, rotational rigidity, or play (looseness of rotation) differed between an inflatable versus large-diameter reamed interlocked nails, and whether the maximal torque to failure of the two bone-implant constructs differed. In a cadaveric model, we compared the biomechanical properties with those of an interlocked nail in eight pairs of fractured tibial bones. Bending stiffness, rotational rigidity, play (looseness in rotation), and torsional strength within 20° rotation were investigated using a biaxial servohydraulic testing system. For all biomechanical variables, we found a large interindividual variance between the pairs attributable to bone quality (osteoporosis) for both fixation methods. The inflatable nail had a higher bending stiffness, with a mean difference of 58 N/mm, and a lower torsional strength, with a mean difference of 13.5 Nm, compared with the locked nail. During torsional testing we noted slippage between the inflatable nail and bone. We observed no differences in play or rotational rigidity. Given the lower torsional strength we recommend caution with weightbearing until there are signs of fracture consolidation. Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. Each author certifies that his or her institution has approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.     

Should insertion of intramedullary nails for tibial fractures be with or without reaming? A prospective, randomized study with 3.8 years' follow-up

OBJECTIVE: To determine if any differences exist in healing and complications between reamed and unreamed nailing in patients with tibial shaft fractures. DESIGN: Prospective, randomized. SETTING: Level 1 trauma center. PATIENTS: Forty-five patients with displaced closed and open Gustilo type I-IIIA fractures of the central two thirds of the tibia. INTERVENTION: Stabilization of tibial fractures either with a slotted, stainless steel reamed nail or a solid, titanium unreamed nail. MAIN OUTCOME MEASUREMENTS: Nonunions, time to fracture healing, and rate of malunions. RESULTS: The average time to fracture healing was 16.7 weeks in the reamed group and 25.7 weeks in the unreamed group. The difference was statistically significant (P = 0.004). There were three nonunions, all in the unreamed nail group. Two of these fractures healed after dynamization by removing static interlocking screws. The third nonunion did not heal despite exchange reamed nailing 2 years after the primary surgery and dynamization with a fibular osteotomy after an additional 1 year. There were two malunions in the reamed group and four malunions in the unreamed group. There were no differences for all other outcome measurements. CONCLUSION: Unreamed nailing in patients with tibial shaft fractures may be associated with higher rates of secondary operations and malunions compared with reamed nailing. The time to fracture healing was significantly longer with unreamed nails.     

Biomechanical performance of locked intramedullary nail systems in comminuted femoral shaft fractures

The biomechanical properties of commercially available locked nail systems designed for use in comminuted femoral shaft fractures were compared and evaluated. Ender nails as well as three forms of interlocking nails, Brooker-Wills (B-W), Klenm-Schellman (K-S), and Grosse-Kempf (G-K), were implanted in cadaver femora. The femora were tested in torsion, bending, and axial loading to failure. Two fracture models were tested--a 3 cm subtrochanteric defect and an 8 cm midshaft defect. Results of the testing revealed the three interlocking nails to be comparable to each other and superior to Ender nails in bending and torsion. However, the distally bolted locked nails (K-S, G-K) resisted significantly higher loads than either the distally bladed locked nail (B-W) or Ender nails when tested to failure by axial loading.     

Biomechanical comparison of methods of fixation of a midshaft osteotomy of the humerus

Using paired humeri with a midshaft osteotomy, the biomechanical stiffness of four intramedullary internal fixation devices were compared with each other, a dynamic compression plate, and with the intact bone. In posterior and lateral bending and in torsion, flexible intramedullary pin fixed humeri (Enders and Hackethal) performed similarly and were less stiff than intact specimens were. Interlocking intermedullary nail constructs (Russell-Taylor and Seidel) also tested similarly to each other, and were stiffer than the flexible pins in all bending tests. Compared with the intact humerus, interlocking nails were stiffer in torsion, but in bending they more closely simulated the stiffness of the bone.     

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.     

Biomechanical analysis of peri‑implant fractures in short versus long cephalomedullary implants following pertrochanteric fracture consolidation

IntroductionPertrochanteric femur fracture fixation with use of cephalomedullary nails (CMN) has become increasingly popular in recent past. Known complications after fracture consolidation include peri‑implant fractures following the use of both short and long nails, with fracture lines around the tip of the nail or through the interlocking screw holes, resulting in secondary midshaft or supracondylar femur fractures, respectively. Limited research exists to help the surgeon decide on the use of short versus long nails, while both have their benefits. The aim of this biomechanical study is to investigate in direct comparison one of the newest generations short and long CMNs in a human anatomical model, in terms of construct stability and generation of secondary fracture pattern following pertrochanteric fracture consolidation.MethodsEight intact human anatomical femur pairs were assigned to two groups of eight specimens each for nailing using short or long CMNs. Each specimen was first biomechanically preloaded at 1 Hz over 2000 cycles in superimposed synchronous axial compression to 1800 N and internal rotation to 11.5 Nm. Following, internal rotation to failure was applied over an arc of 90° within one second under 700 N axial load. Torsional stiffness as well as torque at failure, angle at failure, and energy to failure were evaluated. Fracture patterns were analyzed.ResultsOutcomes in the study groups with short and long nails were 9.7 ± 2.4 Nm/° and 10.2 ± 2.9 Nm/° for torsional stiffness, 119.8 ± 37.2 Nm and 128±46.7 Nm for torque at failure, 13.5 ± 3.5° and 13.4 ± 2.6° for angle at failure, and 887.5 ± 416.9 Nm° and 928.3 ± 461.0 Nm° for energy to failure, respectively, with no significant differences between them, p ≥ 0.17. Fractures through the distal locking screw holes occurred in 5 and 6 femora instrumented with short and long nails, respectively. Fractures through the lateral entry site of the head element were detected in 3 specimens within each group. For short nails, fractures through the distal shaft region, not interfacing with the implant, were detected in 3 specimens.ConclusionFrom a biomechanical perspective, the risk of secondary peri‑implant fracture after intramedullary fixation of pertrochanteric fractures is similar when using short or long CMN. Moreover, for both nail versions the fracture pattern does not unexceptionally involve the distal locking screw hole.     

Computational comparison of reamed versus unreamed intramedullary tibial nails.

We compared, via a computational model, the biomechanical performance of reamed versus unreamed intramedullary tibial nails to treat fractures in three different locations: proximal, mid-diaphyseal, and distal. Two finite element models were analyzed for the two nail types and the three kinds of fractures. Several biomechanical variables were determined: interfragmentary strains in the fracture site, von Mises stresses in nails and bolts, and strain distributions in the tibia and fibula. Although good mechanical stabilization was achieved in all the simulated fractures, the best results were obtained in the proximal fracture for the unreamed nail and in the mid-diaphyseal and distal fractures for the reamed nail. The interlocking bolts, in general, were subjected to higher stresses in the unreamed tibial nail than in the reamed one; thus the former stabilization technique is more likely to fail due to fatigue.     

Mechanics of intramedullary nails for femoral fractures

Biomechanical studies were carried out to assess the function and performance of intramedullary (IM) nails for femoral fractures. An appropriately sized femoral IM nail with a radius of curvature of about 109 cm would most closely match the anterior bow of most human femora. A number of parameters can interact to result in bursting of the femur during insertion of the nail. These include mismatch in curvature of the nail and femur, high stiffness in bending, and poor location of the starting hole. An anatomic starting position for the IM nail is just medial to the greater trochanter and anterior to the pyriformis recess. Moving anterior to the midline of the femur significantly increases the potential for bursting the femur during insertion of the nail. Other factors can decrease the force of insertion of the IM nail in the femur. These include overreaming, shortening the axial length of the fracture component, and use of a nail of lower bending rigidity. IM-nail-fixed femoral shaft fractures with locking bolts can be expected to have about 75% the rigidity of the intact femur in bending and can support about 400% of normal body weight (= 70 kg). Slotted IM nail/femur constructs have only about 3% the rigidity of the intact femur in torsion, while an unslotted (closed) section implant produces constructs with about 50% the rigidity. The distal locking bolts increase the torsional rigidity and maximum axial load capacity of the construct, and reduce the potential for shortening and the residual deformation upon release of a torsional load. Two distal bolts reduce the toggle of the nail in the femoral shaft.(ABSTRACT TRUNCATED AT 250 WORDS)     

Two-part surgical neck fractures of the proximal part of the humerus. A biomechanical evaluation of two fixation techniques

BACKGROUND: Successful internal fixation of fractures of the surgical neck of the humerus can be difficult to achieve because of osteopenia of the proximal aspect of the humerus. The purpose of this study was to compare the biomechanical stability of a proximal humeral intramedullary nail and a locking plate for the treatment of a comminuted two-part fracture of the surgical neck in a human cadaver model. METHODS: Twenty-four cadaveric humeri were instrumented with use of either a titanium proximal humeral nail (PHN) or a 3.5-mm locking compression plate for the proximal part of the humerus (LCP-PH). The specimens were matched by bone mineral density and were separated into four experimental groups with six humeri in each: PHN bending, LCP-PH bending, PHN torsion, or LCP-PH torsion. Comminuted fractures of the surgical neck were simulated by excising a 10-mm wedge of bone. Bending specimens were cyclically loaded from 0 to 7.5 Nm of varus bending moment at the fracture site. Torsion specimens were cyclically loaded to +/-2 Nm of axial torque. The mean and maximum displacement in bending, mean and maximum angular rotation in torsion, and stiffness of the bone-implant constructs were compared. RESULTS: In bending, the LCP-PH group demonstrated significantly less mean displacement of the distal fragment than did the PHN group over 5000 cycles (p = 0.002). In torsion, the LCP-PH group demonstrated significantly less mean angular rotation than did the PHN group over 5000 cycles (p = 0.04). A significant number of specimens in the PHN group failed prior to reaching 5000 cycles (p = 0.04). The LCP-PH implant created a significantly stiffer bone-implant construct than did the PHN implant (p = 0.007). CONCLUSIONS: The LCP proximal humeral plate demonstrated superior biomechanical characteristics compared with the proximal humeral nail when tested cyclically in both cantilevered varus bending and torsion. The rate of early failure of the proximal humeral nail could reflect the high moment transmitted to the locking proximal screw-bone interface in this implant. CLINICAL RELEVANCE: The high failure rate in torsion of the proximal humeral nail-bone construct is concerning, and, with relatively osteoporotic bone and early motion, the results could be poor.     

Proximal humeral fractures: how stiff should an implant be? A comparative mechanical study with new implants in human specimens

BACKGROUND: The objective of this study was to determine the in vitro characteristics of the clinically used and newly developed implants for the stabilization of proximal humeral fractures under static and cyclic loading. The goal was to optimize implant stiffness for fracture stabilization even in weak bone stock. METHODS: In a laboratory study using 35 fresh human humeri, the specimens were randomized into 5 groups, which included the clinically used humerus T-plate (HTP), the cross-screw osteosynthesis (CSO), the unreamed proximal humerus nail with spiral blade (UHN), the recently developed Synclaw Proximal Humerus Nail (Synclaw PHN) and the angle-stable Locking Compression Plate Proximal Humerus (LCP-PH). The implant stiffness was determined for three clinically relevant load cases: axial compression, torsion and varus bending. In addition, a cyclic varus-bending test was performed to determine the implant properties under cyclic loading. RESULTS: In contrast to a rather elastic and minimally invasive implant(LCP-PH), the conventionally designed ones (Synclaw PHN, CSO, HTP, UHN) showed rather high stiffness values under static loading. In cyclic loading, a strong decrease in stiffness ( p<0.05) was found for the rigid implants HTP and UHN. In comparison with the other implants, only the elastic implant (LCP-PH) showed a significantly lower load reduction in a weak bone stock (17+/-6.2%). CONCLUSION: The high initial stiffness of rigid implants led to an early loosening and failure of the implant-bone interface under cyclic loading. Implants with low stiffness and elastic characteristics, however, appear to minimize the peak stresses at the bone-implant interface, making them particularly suitable for fracture fixation in osteoporotic bone.     

非扩髓带锁髓内钉治疗粉碎性胫腓骨骨折

目的 总结非扩髓带锁髓内钉治疗粉碎性胫腓骨骨干骨折的临床经验、方法使用非扩髓带锁髓内钉治疗粉碎性胫腓骨骨干骨折47例,其中闭合性骨折36例,开放性骨折11例。结果患行5个月内骨折完全愈合,膝关节、踝关节功能均正常。2例开放性多段骨折患者,术后患肢红肿热痛经切开引流和应用抗生素,感染得到控制。结论 非扩髓带锁髓内钉能有效地稳定胫腓骨粉碎性骨折,减少骨折局部血运的破坏,有利于骨折的愈合。     

A biomechanical comparison of the antegrade inserted universal femoral nail with the retrograde inserted universal tibial nail for use in femoral shaft fractures

Femoral shaft fractures with and without bony contact were simulated in cadaver specimens fixed with one of two different types of intramedullary locked nail systems; conventional antegrade nail fixation of the femur with the universal AO femoral nail or retrograde insertion in the femur with the universal tibial nail (a smaller diameter slotted nail) were utilized. Mechanical testing simulated one leg stance, and resultant deformation was measured in bending, torsion, and shortening. In stable fractures, fracture stability was similar to both devices, while in unstable fractures, the larger femoral nail was more stable. Furthermore, the simulation of single leg stance led to a coupled deformation of varus bending, axial shortening, and external rotation, which was dependent on bone geometry.     

Slotted versus non-slotted locked intramedullary nailing for femoral shaft fractures

Summary Experimentally, two slotted nails, the Grosse-Kempf nail and the AO/ASIF universal femoral nail, were compared to the non-slotted Grosse-Kempf nail and control bone using a cadaver femoral osteotomy. The stiffnesses and strengths of the osteotomies fixed with slotted nails in 10–30° torsion were 6–8% and the values of non-slotted nails 40% of control bone. The maximal moments were 14–18% and 48%, respectively. In the clinical range of torsion, the implant-bone construct never failed or was deformed. Clinically, 46 femoral shaft fractures were randomized to treatment with Grosse-Kempf nails, 24 with slotted nails and 22 with non-slotted nails. Four complications in the slotted nail group and three in the non-slotted nail group were considered to be independent of the choice of nail and did not affect the end result. Three splinterings of the distal fragment, one resulting in a change of the osteosynthesis implant to a condylar plate, were considered to result from the high stiffness of the non-slotted nail. Osteosynthesis of femoral shaft fractures using slotted nails has not resulted in healing disturbances, which could be accounted for by the high torsional elasticity of the nail; there seems to be no indication for high-stiffness nails in femoral fractures.     

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.