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.     

Biomechanik der Verriegelungsmarknagelung bei Oberarmschaftfrakturen Vergleichsuntersuchungen zweier Marknagelsysteme und des Effekts der interfragmentären Kompression bei unaufgebohrtem Humerusnagel

In this biomechanical study the implanted Unreamed Humeral Nail (UHN) has been tested concerning bending and torsional stiffnesses. In literature other intramedullary implants have been criticized for insufficient rotatory stability especially in transverse and short oblique fractures of the humeral shaft. This study examined, whether the implanted UHN, as well as the UHN implanted with interfragmentary compression through a specific compression device, is able to augment torsional stiffness significantly. To evaluate bending and torsional stiffnesses, the UHN has been compared biomechanically to the Russell-Taylor humeral nail (RT) in paired mid-shaft osteotomized cadaveric humeri. Identic paired comparison has been performed with the UHN without and UHN with interfragmentary compression. In anterior-posterior, as well as medio-lateral direction stiffness under four-point-bending is significantly higher in stabilizing with the RT. Under torsional loading with moments of 4 Nm, 6 Nm and 8 Nm the UHN reached more than the double torsional stiffness. The RT, which is only dynamically interlocked, owns a high initial "play" between bolts and nail itself. Through additional interfragmentary compression stiffness of the UHN under four-point-bending in anterior-posterior, as well as medio-lateral direction augments significantly. Also under torsional loading with moments of 4 Nm, 6 Nm und 8 Nm torsional stiffness increases with interfragmentary compression significantly. In comparison to other biomechanical studies of different authorship it is clear, that this statically interlocked intramedullary nailing of the humeral shaft is superior to non-statically interlocked types of nailing concerning their stabilizing potency in torsion and serves especially for fracture types, which are critically under rotation, as transverse or short oblique humeral shaft fractures.     

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.     

低应力遮挡效应交锁髓内钉的研制与生物力学研究

目的 :研究新型股骨低应力遮挡交锁髓内钉治疗股骨干骨折的生物力学特性。方法 :将股骨干交锁髓内钉远端锁孔向近端分别扩大 1、 2、 3mm ,采用 4具成人男性尸体 8根股骨干标本制成横断骨折模型 ,分别打入 4种不同孔径髓内钉 ,进行骨折断端应力分析实验。结果 :远端锁孔直径 3mm的交锁髓内钉与实验中其它组相比较 ,应力遮挡率最小 ( 2 0 .6 0 %) (P <0 .0 5 ) ,在载荷—应变、载荷—位移、轴向强度及刚度上均占有明显优势 (P <0 .0 5 )。而 4种髓内钉在弯矩—应变、弯矩—桡度、扭矩—扭角关系中无明显差别。结论 :远端锁孔直径扩大 3mm的交锁髓内钉不但应力遮挡小 ,而且强度、刚度符合骨折内固定的生物力学要求 ,从而该实验为临床应用低应力遮挡交锁髓内钉提供了可靠理论依据。     

Locked Femoral Nailing

Locked intramedullary nailing has become the standard of care for most femoral fractures. Originally designed to prevent rotation and shortening in comminuted fractures of the midshaft, its application has been extended proximally and distally to nearly all femoral fractures from the lesser trochanter to the supracondylar area. Achieving a closed reduction and selecting the proper starting point in the piriformis region are crucial to a successful result. Following the proper surgical technique for the specific nail used is more important than nail material or design. Large-diameter reamed nails provide greater strength than unreamed nails. Static locking has been shown to yield nearly the same high union rates as dynamic locking and is now the accepted standard. Distal targeting of the interlocking screw remains the most difficult aspect of the surgical technique; most surgeons prefer freehand targeting with a sharp trocar. Second-generation (reconstruction) nails, with screws directed toward the femoral head, has extended the indications for locked nailing proximally to subtrochanteric fractures and combined femoral neck-shaft fractures.     

Biomechanics of femoral interlocking nails

Today there is a variety of different interlocking intramedullary nail designs available for the femur. We compared different nail types in the bone implant complex (BIC) of four unreamed solid nails and a slotted reamed nail with simulated comminuted mid shaft fractures to see if there are major differences in stiffness for axial load, bending and torsion. The fractures were simulated by a 2 cm defect osteotomy in paired human cadaver femora. Each bone was tested intact in a universal testing machine, osteotomy and osteosynthesis were performed, and the BIC was tested. Relative stiffness was calculated. In torque testing the unslotted solid nail showed significantly more stiffness (0.6-1.8 Nm/degrees) compared to the slotted nail (0.2 Nm/degrees). Compared to intact bone (6.9 Nm/degrees), both groups of nails were significantly less stiff (relative stiffness 2-20%). In axial load and bending testing the large diameter unreamed nail showed significantly higher stiffness (32-68%). This study shows that stiffness of bone implant complex in interlocking femoral nails is more dependent on nail profile than on the pressfit of nails in the medullary canal.     

Mechanical evaluation of six types of reconstruction following 25, 50, and 75% resection of the proximal femur

The structural stiffness and the stiffness of the osteotomy site after six types of reconstruction of the proximal femur were compared by testing in axial compression, mediolateral bending, and axial torsion in a canine model. An osteotomy was carried out for 25, 50, or 75% of the length of each femur, and the proximal portion was replaced by one of five allograft/endoprosthetic composites or a segmental replacement. The reconstructions included (a) a composite press-fit proximally and cemented distally, (b) a composite cemented proximally and distally, (c) a composite cemented proximally and fixed with two plates at the allograft-host bone interface, (d) a composite cemented proximally and secured distally with bicortical screws, (e) a composite secured proximally and distally with bicortical screws, and (f) a segmental prosthesis cemented into the distal femur. The results showed that the segmental reconstruction and the reconstruction with double-plate fixation and a cemented endoprosthesis were structurally stiffer and had greater stiffness of the osteotomy site than the other reconstructions. In comparison, reconstructions that involved cement alone or cement and press-fit techniques generally were more compliant than the others, both structurally and at the osteotomy site.     

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.     

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.     

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.     

Fatigue load of current tibial intramedullary nail designs: a simulated study

Comminuted tibial shaft fractures are traditionally treated with statically locked intramedullary nailing and protected weight bearing until fracture callous is evident. The purpose of this study was to demonstrate that a simulation of immediate full weight bearing following intramedullary nailing of these fractures does not result in implant failure.A comminuted fracture model was created using 2 pieces of polyvinyl chloride (PVC) pipe. Ten-millimeter-diameter tibial nails (Synthes, Paoli, Pennsylvania; Styker, Mahwah, New Jersey; Zimmer, Warsaw, Indiana; Smith & Nephew, Memphis, Tennessee) were inserted within the PVC pipe and secured proximally and distally with 2 or 3 locking bolts. The constructs were cycled in axial compression for 500,000 cycles or until implant failure. The tests were conducted using a modified staircase method (200 N per step), and the fatigue strength was identified for each of the tibial nail designs. When 2 interlocking bolts were placed proximally and distally, the fatigue strength was between 900 and 1100 N for the Stryker nail, 1100 and 1300 N for the Zimmer nail, 1200 and 1400 N for the Synthes nail, and 1400 and 1600 N for the Smith & Nephew nail. Adding a third interlocking bolt proximally and distally to the Smith & Nephew nail increased the fatigue strength by 13% to between 1700 and 1900 N. In all cases, implant failures occurred through the proximal or distal interlocking bolts.Biomechanical tests suggest that current tibial nail designs may permit immediate full weight bearing of comminuted tibial shaft fractures with minimal risk of implant failure. This may facilitate mobilization in the early postoperative period, especially in the multiply injured patient.     

Mechanical comparison of a distal femoral side plate and a retrograde intramedullary nail

OBJECTIVE: To compare quantitatively the axial and torsional stiffness of a retrograde intramedullary nail and a fixed angle screw side plate in treating a supracondylar femur fracture in osteopenic femora. To determine the modes of failure of an intramedullary nail and a side plate under axial loading. DESIGN: Matched pair cadaveric study. SETTING: Orthopaedic biomechanics laboratory. PATIENTS AND OTHER PARTICIPANTS: Eleven matched pairs of preserved human femora were selected. The cadaveric specimens were harvested from relatively elderly donors with an average age of 75.6 years, which represents the principal population at risk for poor fracture fixation. INTERVENTION: The eleven matched pairs were osteotomized to simulate segmental structural defects in the supracondylar region. One femur of each matched pair was fixed with an intramedullary nail, and the contralateral femur was fixed with a side plate. MAIN OUTCOME MEASURES: Axial and torsional stiffness values. Axial modes of failure. RESULTS: The intramedullary nail axial stiffness was 14 percent (p = 0.04) less and torsional stiffness was 17 percent (p = 0.05) less than that provided by the side plate. The axial failure of the intramedullary nail occurred distally, allowing the hardware to protrude into the articular space. The side plate also failed distally by displacing the condylar screw into a varus angulation. CONCLUSION: The mechanical advantages favor the use of the side plate if fixation stiffness is essential. The axial mode of failure occurs distally for both fixation devices.     

髓内扩张自锁钉治疗胫骨骨折的生物力学研究

目的对髓内扩张自锁钉(IESN)的生物力学性能进行实验研究,为临床应用提供理论依据。方法采用新鲜成人胫骨标本18根,制成中段斜行骨折模型;梅花针、交锁钉、IESN固定胫骨后进行抗屈伸、抗侧弯、抗短缩、抗扭转、抗疲劳方面的生物力学测试,评价IESN的内固定稳定性;同时比较三种内固定稳定程度的差异。结果IESN在抗侧弯、抗短缩、抗扭转、抗疲劳刚度方面明显强于梅花针(P<0.01),在抗屈伸方面与梅花针、交锁钉相当(P>0.05);在抗侧弯方面强于交锁钉(P>0.05);在抗扭转方面稍差于交锁钉(P>0.05);在抗短缩方面明显弱于交锁钉(P<0.01)。结论髓内扩张自锁钉具有良好的生物力学性能,有较强的固定作用和稳定性。     

Mechanical characterization of femoral interlocking intramedullary nailing systems

The most important mechanical characteristics of a nailing system are related to its stiffness (rigidity) and strength. This study evaluates the properties of three commercially available interlocking intramedullary nail systems using standardized test methods. An understanding of the mechanical properties along with the clinical data will assist the surgeon in choosing the optimum implant. Testing indicates that the bending strength and stiffness of the Grosse & Kempf, the AO/ASIF Universal, and the Russell-Taylor interlocking intramedullary nail designs are comparable. It is therefore not surprising that all of these nail systems have excellent clinical results. However, the nonslotted design is approximately 30 times more resistant to torsional loading than either the partially slotted design of the Grosse & Kempf nail or the fully slotted design of the AO/ASIF nail. The clinical relevance of the torsional values may not be known until a long-term comparison of the complication rates for these different systems is available. Analysis of screw design reveals a tradeoff in bending strength when compared to amount of bone purchase. The bending strength of fully threaded screws (allowing bicortical fixation) is less than that of partially threaded screws (allowing only unicortical fixation), which shows that for the implants tested, increased bone purchase requires a compromise in strength for similar sized screws.     

In vitro and In vivo study on the effect of autogenous cancellous bone and intramedullary polymethylmethacrylate on allograft construct strength

An in vitro study was performed to compare the effects of augmenting interlocking nails of one of two diameter (5 or 6 mm) with intramedullary polymethylmethacrylate. Subsequently, an in vivo study was performed to compare the effects of augmenting the interlocking nail with five combinations of intramedullary polymethylmethacrylate and autogenous cancellous bone applied to the periosteal surface or within the medullary canal. Dogs were killed 6 months after the procedure for biomechanical evaluation of the femora in axial compression, mediolateral and craniocaudal bending, and torsion. Results from the in vitrostudy at the proximal osteotomy indicated the 6-mm inteilocking nail with intramedullary polymethylmethacrylate had greater stiffness than the 5-mm interlocking nail without it (p < 0.05). At the distal osteotomy, regardless of the diameter of the interlocking nail, the addition of intramedullary polymethylmethacrylate increased stiffness (p < 0.05). Results from the in vivo study indicated greater global construct stiffness with an interlocking nail alone, an interlocking nail augmented with intramedullary polymethylmethacrylate and cancellous bone at the periosteal surface, and an interlocking nail augmented with cancellous bone within the medullary canal and at the periosteal surface (p < 0.05). At the osteotomy level, the interlocking nail augmented with intramedullary polymethylmethacrylate and cancellous bone at the periosteal surface had greater stiffness than did an interlocking nail alone or an interlocking nail augmented with either intramedullary polymethylmethacrylate. cancellous bone within the medullary canal, or cancellous bone at the periosteal surface (p < 0.05) but produced the same results as an interlocking nail augmented with cancellous bone within the medullary canal and at the periosteal surface. The results suggest that augmenting interlocking nail fixation with intramedullary polymethylmethacrylate by itself offers no advantage but that acombination of intramedullary polymethylmethacrylate and cancellous bone at the periosteal surface improves structural properties at 6 months.     

Five years' clinical experience with the unreamed humeral nail in the treatment of humeral shaft fractures

With the development of interlocking nail systems especially designed for the upper arm, standards for the operative treatment of humeral shaft fractures have appeared to change. The trumpet-like shape of the medullary cavity does not allow stable splinting with a nail alone, and therefore the bone--nail complex is commonly stabilized with interlocking bolts. Between June 1996 and June 2001, 51 fractures of the humeral shaft were treated operatively at the BG Unfallklinik Ludwigshafen with the unreamed humeral nail (UHN; Synthes). All nails were inserted by the retrograde technique. Ninety-five percent of the patients showed excellent or good shoulder function at follow-up examinations. For elbow function, 91.4% of the patients showed excellent or good results. Three out of four patients with poor elbow function had suffered from an additional injury to the brachial plexus; one patient developed heterotopic ossification. Intraoperative complications were: one iatrogenic lesion of the radial nerve, two intraoperative shaft fractures, one split at the insertion point, and one supracondylar fracture. As implants we used 7.5 mm nails in 36 cases and 6.7 mm nails in 15 cases. Among the 47 patients undergoing follow-up examinations, we found two cases of non-union. All patients were pain-free. Thirty-seven patients were very satisfied, six satisfied and four dissatisfied with the therapy. Decisive criteria for the use of a new implant are a high safety standard and simple reproducibility; these appear to be fulfilled by retrograde nailing of humeral fractures with the UHN. Interlocking nailing with the UHN enriches the range of therapeutic options for humeral shaft fractures.     

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.     

Influence of intramedullary nail diameter and locking mode on the stability of tibial shaft fracture fixation

Background  Fracture healing is affected by the type and the magnitude of movements at the fracture site. Mechanical conditions will be a function of the type of fracture management, the distance between the fracture fragments, and the loading of the fracture site. The hypothesis to be tested was that the use of a larger-diameter intramedullary nail, together with compressed interlocking, would enhance the primary stiffness and reduce fracture site movements, especially those engendered by shearing forces. Materials and methods  Six pairs of human tibiae were used to study the influence on fracture site stability of two different diameters (9 and 11 mm) of intramedullary nails, in tension/compression, torsional, four-point bending, and shear tests. The nails were used with two interlocking modes (static interlocking vs. dynamic compression). Results  With static interlocking, the 11-mm-diameter nail provided significantly (30–59%) greater reduction of fracture site movement, as compared with the 9-mm-diameter nail. Using an 11-mm-diameter nail, the stiffness of the bone-implant construct was enhanced by between 20 and 50%. Dynamic compression allowed the interfragmentary movements at the fracture site to be further reduced by up to 79% and the system stiffness to be increased by up to 80%. Conclusion  On biomechanical grounds, the largest possible nail diameter should be used, with minimal reaming, so as to minimize fracture site movement. Compression after meticulous reduction should be considered in axially stable fractures. Disclosures: Funding for this work was received from AIOD (Association Internationale pour l’Ostéosynthèse Dynamique). Geert von Oldenburg is an employee of Stryker Trauma.     

Fracture strain and stability with additional locking screws in intramedullary nailing: a biomechanical study

BACKGROUND: We studied the effect of additional locking screws on fracture strain and stability in tibial intramedullary nailing. METHODS: We drilled an additional diaphyseal locking hole into 8-mm solid tibial nails 185 mm from the proximal end of the nail, and locked it proximally and distally. An osteotomy was produced 4.5 cm distal to the additional hole, and the construct loaded axially, in flexion, extension, and torsion. The nails were also tested for their fatigue strength. RESULTS: With the additional locking screw, strain increased proximally during loading in neutral and flexion. Strain decreased on loading in extension. The extra locking screw decreased strain close to the osteotomy site in all loading positions. A significant reduction in angular motion at the osteotomy site occurred with the addition of the extra locking screw. The nails survived the fatigue test, although the stress increased around the additional locking hole CONCLUSIONS: Nails with additional locking options, by altering strain and motion at the fracture site, may have the clinical potential to affect fracture healing.     

A biomechanical comparison of the Surgical Implant Generation Network (SIGN) tibial nail with the standard hollow nail

Objective

In developing countries, tibial shaft fractures are frequently stabilised using Surgical Implant Generation Network (SIGN) nails. Despite widespread use throughout the world, little is known regarding their biomechanical properties. This study aimed to compare the mechanical stiffness of the SIGN tibial nail with a standard hollow tibial nail.

Methods

A fracture gap model was created to simulate a comminuted mid-shaft tibia fracture (AO/OTA42-C3) using synthetic composite bones. The constructs were stabilised with either a 9 mm solid SIGN nail or a 10 mm hollow Russell-Taylor nail. Both nail systems were interlocked proximally and distally. Following fixation, the specimens were loaded in axial, torsional, and cyclical axial modes to calculate construct stiffness and irreversible (plastic) deformation.

Results

The mean axial stiffness for the SIGN nail constructs was 47% higher than mean stiffness for the RT nail constructs (p < 0.001). The difference in torsional stiffness was not statistically significant. However, the SIGN group demonstrated 159% more irreversible deformation than the Russell-Taylor group (p = 0.006) for the loading parameters studied.

Conclusion

The SIGN tibial nail, despite its slightly smaller diameter, can provide similar construct stiffness and stability, when compared to a larger hollow nail for stabilisation of tibial shaft fractures.