Stefanie Hoffmann

Biomechanical comparison of locked plate osteosynthesis, reamed and unreamed nailing in conventional interlocking technique, and unreamed angle stable nailing in distal tibia fractures.

INTRODUCTION The treatment of distal tibia shaft fractures is still problematic because of the thin soft tissue envelope and less stable osteosynthesis. Therefore, nonunions are often seen in this region. When reamed nailing is performed, construct stiffness can be increased and fracture gap movement can be reduced, but in open fractures the question whether reamed nailing is before unreamed nailing is still uncertain. Therefore, unreamed nails with angle stable interlocking options were produced with the idea to improve the biomechanical properties of unreamed nails. This study compared reamed and unreamed nailing either with angle stable or conventional interlocking to plate osteosynthesis. The hypothesis was that angular stability in unreamed nailing will increase the construct stiffness and reduce the fracture gap movement. METHODS In this study, four groups of five artificial tibiae were treated with different osteosynthesis techniques. Group 1 was treated with a reamed nailing technique, group 2 with a distally angle stable locked nail in an unreamed technique, group 3 with an unreamed nail in a conventional locking technique, and group 4 with a locked medial plate system. After osteotomy of the intersection of the distal 4/5 to 5/5 of the tibia, stiffness of the implant-bone construct and micromovement of the fragments were measured. In addition, the range of motion at the mechanical zero under torsional load was calculated. RESULTS Biomechanical tests showed that the stiffness of the reamed nail constructs was significantly higher than the compared implants. The unreamed conventionally locked nail and unreamed distally angular stable locked nails were less stiff than the larger sized reamed nail, but the implant-bone construct showed higher stiffness values than the locked plate osteosynthesis. Regarding stiffness of the two unreamed groups, no significant differences were found. The interfragmentary movement in axial and torsional force exhibited the highest range of motion for locked plating, while the reamed nail significantly exhibited the least. The range of motion at the mechanical zero under torsional load was the lowest for the unreamed and angle stable locked nail. CONCLUSIONS Under biomechanical considerations, the treatment of distal tibia fractures using the reamed nailing technique is before unreamed nailing, but distal angle stable interlocking of the nail may also be a satisfactory method.

Biomechanical evaluation of interlocking lag screw design in intramedullary nailing of unstable pertrochanteric fractures.

Objectives: Intramedullary nails with special lag screw designs may provide improved mechanical performance and alleviate clinical problems. We hypothesize that the proximal design of trochanteric nails affects mechanical performance. Methods: Ten pairs of human cadaveric femora were implanted with 2 different short intramedullary nails without (Gamma3) and with an interlocking lag screw (Intertan). An unstable, multifragmentary, pertrochanteric fracture was created. Bones were tested in a cyclic testing protocol with increasing loads until failure simulating 1 leg stance. Stiffness, failure load, cycles to failure, and fracture gap movements were measured. Results: Initially stiffness of the interlocking lag screw nail was almost 40% larger (P = 0.005) compared with the noninterlocking nail. During the test, the difference in stiffness gradually decreased. Failure load (13%, P = 0.02) and cycles to failure (18%, P = 0.02) were larger for the interlocking nail construct. Rotation and varus collapse of the head were initially up to 84% lower (P = 0.013) for the interlocking technique. During the test, the rate of rotational instability gradually increased for both techniques. Conclusions: The interlocking lag screw design reduced movement of the femoral head and relative movement between fracture fragments. Beyond that the trapezoidal nail design of the Intertan reduced toggling within the trochanteric area and prolonged survival. Although this study showed a decrease in the retention of stability over time, failure did not occur until the equivalent of 2–3 months of reduced physical activity in which healing may have occurred under normal clinical conditions.

Auxiliary locking plate improves fracture stability and healing in intertrochanteric fractures fixated by intramedullary nail.

BACKGROUND Intertrochanteric fractures present a significant management challenge due to their low inherent stability. The objective of this study was to determine whether an auxiliary locking plate decreases interfragmentary motions and improves fracture healing in intertrochanteric fractures treated by intramedullary nail. METHODS Biomechanical tests and a clinical retrospective study in intertrochanteric to subtrochanteric nonunions were performed. Six synthetic femurs were osteotomized intertrochanterically and fixated with a long gamma nail and an additional locking compression plate. Mechanical tests were conducted that simulated the hip joint force during gait cycle. Following the initial test, the locking compression plate (LCP) was removed from each specimen and the test was repeated. Interfragmentary motions, strains on implants and osteosynthesis stiffness were determined. For the clinical part of the study, 13 intertrochanteric to subtrochanteric nonunions were treated with revisional long gamma nail and additional locking compression plate. Complications and time to union were determined. FINDINGS Biomechanically, interfragmentary rotation was 48% smaller (P=0.047) and interfragmentary shear movement was 42% smaller (P=0.007) with locking compression plate. Strains on the nail decreased by 20-27% (P<0.027) and the osteosynthesis stiffness increased by 23% (P=0.005) with locking compression plate. Clinically, fracture healing was achieved in eleven out of 13 patients after 9.0months (range 4 to 22months). INTERPRETATION The findings of our study indicate that auxiliary locked plating considerably improves biomechanical performance and results in successful healing of unstable intertrochanteric to subtrochanteric femur fractures.

Effect of angular stability and other locking parameters on the mechanical performance of intramedullary nails

Abstract To extend the indications of intramedullary nails for distal or proximal fractures, nails with angle stable locking options have been developed. Studies on the mechanical efficacy of these systems have been inconsistent likely due to confounding variables such as number, geometry, or orientation of the screws, as well as differences in the loading mode. Therefore, the aim of this study was to quantify the effect of angular stability on the mechanical performance of intramedullary nails. The results could then be compared with the effects of various locking screw parameters and loading modes. A generic model was developed consisting of artificial bone material and titanium intramedullary nail that provided the option to systematically modify the locking screw configuration. Using a base configuration, the following parameters were varied: number of screws, distance and orientation between screws, blocking of screws, and simulation of freehand locking. Tension/compression, torsional, and bending loads were applied. Stiffness and clearance around the zero loading point were determined. Angular stability had no effect on stiffness but completely blocked axial clearance (p=0.003). Simulation of freehand locking reduced clearance for all loading modes by at least 70% (p<0.003). The greatest increases in torsional and bending stiffness were obtained by increasing the number of locking screws (up to 80%, p<0.001) and by increasing the distance between them (up to 70%, p<0.001). In conclusion, our results demonstrate that the mechanical performance of IM nailing can be affected by various locking parameters of which angular stability is only one. While angular stability clearly reduces clearance of the screw within the nail, mechanical stiffness depends more on the number of screws and their relative distance. Thus, optimal mechanical performance in IM nailing could potentially be obtained by combining angular stability with optimal arrangement of locking screws.