Objectives. External fixators are the traditional fixation method of choice for contaminated open fractures. However, patient acceptance is low due to the high profile and therefore physical burden of the constructs. An externalised locking compression plate is a low profile alternative. However, the biomechanical differences have not been assessed. The objective of this study was to evaluate the axial and torsional stiffness of the externalised titanium locking compression plate (ET-LCP), the externalised stainless steel locking compression plate (ESS-LCP) and the unilateral external fixator (UEF). Methods. A fracture gap model was created to simulate comminuted mid-shaft tibia fractures using synthetic composite bones. Fifteen constructs were stabilised with ET-LCP, ESS-LCP or UEF (five constructs each). The constructs were loaded under both axial and torsional directions to determine construct stiffness. Results. The mean axial stiffness was very similar for UEF (528 N/mm) and ESS-LCP (525 N/mm), while it was slightly lower for ET-LCP (469 N/mm). One-way analysis of variance (ANOVA) testing in all three groups demonstrated no significant difference (F(2,12) = 2.057, p = 0.171). There was a significant difference in mean torsional stiffness between the UEF (0.512 Nm/degree), the ESS-LCP (0.686 Nm/degree) and the ET-LCP (0.639 Nm/degree), as determined by one-way ANOVA (F(2,12) = 6.204, p = 0.014). A Tukey post hoc test revealed that the torsional stiffness of the ESS-LCP was statistically higher than that of the UEF by 0.174 Nm/degree (p = 0.013). No catastrophic failures were observed. Conclusion. Using the LCP as an external fixator may provide a viable and attractive alternative to the traditional UEF as its lower profile makes it more acceptable to patients, while not compromising on axial and torsional stiffness. Cite this article: B. F. H. Ang, J. Y. Chen, A. K. S. Yew, S. K. Chua, S. M. Chou, S. L. Chia, J. S. B. Koh, T. S. Howe. Externalised locking compression plate as an alternative to the unilateral external fixator: a biomechanical comparative study of axial and torsional stiffness. Bone Joint Res 2017;6:216–223. DOI: 10.1302/2046-3758.64.2000470

Background. Locking internal fixation through a relatively small surgical dissection presents an innovative technique for managing distal tibial extra-articular fractures. The aim of this study is to evaluate the biomechanical properties of one locking internal fixation plate used to treat these injuries. Method. An AO/OTA43-A3 fracture was created in synthetic composite tibiae. Locking internal fixation was achieved with an anatomically pre-contoured medial distal tibial locking plate. Comparisons were made between different screw configurations in holes proximal to the fracture and monocortical versus bicortical fixation. Axial stiffness was measured using a universal materials testing machine. Finite element analysis (FEA) was used to model the elastic deformation of the constructs. Outcome measures were axial stiffness under physiological loading conditions and compression load to failure. Results. A trend towards reduced mean axial stiffness from the bicortical to the monocortical fixation constructs was observed. The physical model demonstrated no difference in measured mean axial stiffness between constructs with all screw holes filled and constructs with 2 screws in the holes closest and furthest from the fracture site. There was a 19% reduction in mean measured axial stiffness between constructs with all holes filled and in constructs with 2 screws in adjacent holes furthest from the fracture site (p<0.05). FEA predicted increased plate deflection and reduced construct axial stiffness with increasing distance of screw placement from the osteotomy site. Conclusion. Axial stiffness of distal tibial extra-articular metaphyseal fractures stabilized by locking internal fixation is dependent upon the configuration of the screw in the plate

Open reduction and internal fixation of proximal humerus fractures with angular stable plates is, beside antegrade nailing of the humerus, a standard procedure. A retrograde nail has been developed to avoid penetrating the rotator cuff and to avoid opening the fracture side during osteosynthesis. The aim of our biomechanical study was to evaluate if retrograde nailing of proximal humerus fractures is as stable as locking plate osteosynthesis. The biomechanical properties of 2 implants were tested in 11 human fresh frozen cadaveric humeri pairs. The Retron Nail® and the Philos® plate were implanted after osteotomy. All specimens were suspected to axial and torque load for 1000 cycles in a servo pneumatic testing apparatus. The Philos® plate had greater torsion stiffness than the Retron® nail, but we found no significance. The Retron® nail had greater axial stiffness but our findings were not statistically significant. Our study showed, that there are no significant differences between a retrograde nail and locking plate osteosynthesis for proximal humerus fractures concerning axial and torsion deformities. Therefore the retrograde nail is a suitable alternative for fixation of proximal humerus fracture

Background. The inherently high stiffness of locked plate constructs is increasingly recognized as a potential cause of deficient healing observed in patients with periarticular locked plating systems. The objective of this study is to perform a biomechanical comparison of distal femur locked plating systems. Methods. Biomechanical study using bone substitutes in a distal femur fracture model (OTA/AO 33-A3). Four different locked plate fixation systems were compared (AxSOS, LCP, PERI-LOC, POLYAX). Eight bone implant constructs of each plating system were evaluated in a multiple testing model to examine static failure, stiffness under static and cyclic loading and cyclic fatigue. Results. The implant systems made of titanium alloy (POLYAX & LCP) supported smaller torsional stiffness values under static loads and smaller axial stiffness values under cyclic loads compared with the implant systems made of stainless steel (PERI-LOC & AxSOS). All bone implant constructs reached the cyclic failure criterion of 10 degrees displacement at the fracture area within the third load level (>50000 cycles) except for the LCP which failed earlier. Conclusion. The tested four different locked plating systems differ significantly in terms of stiffness and load to failure. Two of the clinical available systems differed almost 100% in stiffness values. And one system differed almost 100% in fatigue strength. For clinical use, this knowledge is essential for the practicing orthopaedic surgeon

In severe forearm injuries, the diagnosis of disruption of the interosseous membrane is frequently delayed and sometimes missed, giving difficulties in the salvage of forearm stability. We studied the structure and function of the interosseous membrane in 11 cadaver preparations, using mechanical and histological analysis. Seven of the specimens tested in uniaxial tension sustained a mid-substance tear of the central band of the membrane at a mean peak load of 1038 ± 308 N. The axial stiffness was 190 ± 44 N/mm with elongation to failure of 10.34 ± 2.46 mm. These results provide criteria for the evaluation of reconstructive methods. A preliminary clinical investigation of the use of ultrasound suggests that this may be of value in the screening of patients with complex fractures of the forearm, and for investigating the natural history of tears of the interosseous membrane

Introduction. Locking compression plate (LCP) fixation is an established method of treatment of distal third tibial fractures. No biomechanical data exists in the literature regarding their use. Additionally no data exists on the biomechanical advantage of locking screw fixation over non-locking screw fixation for these fractures. In this study the axial and torsional stiffness, axial load to failure and fatigue performance of a 3.5 mm LCP medial distal tibia Synthes plate was evaluated for the stabilisation of distal third tibial fractures. Additionally the performance of the plate in uni and bicortical locked mode as well as non-locked mode was evaluated. Methods. A standardized oblique fracture pattern was created in the tibial metaphysis of 3rd generation composite tibias, 40 mm from the distal end of the tibia (AO 43-A2.3). A 10mm fracture gap was used to model a comminuted metaphyseal fracture. A 3.5 mm medial distal tibia LCP was applied with bi or unicortical locking or bicortical non-locking screws to 5 tibias respectively. All the bio-mechanical tests were performed on a Bose 3510 Electroforce material testing machine. A ramp to load, loading profile was used to determine the static axial and torsional performance of the construct. Fatigue testing simulated a 6 week gradual weight bearing régime with the load increasing every two weeks by 400N until either 250,000 cycles were completed or the construct failed. Results. The non-locked plate demonstrated a significantly higher load to failure than both the bicortical and unicortical locked plates, 683N vs. 575N vs. 483N respectively(p<0.01). The non locked plate also demonstrated significantly higher mean axial stiffness than the bicortical locked plate and unicortical locked plate 632±13 N/mm, 337±12N/mm and 266±6 N/mm respectively (p <0.01). The non locked plate demonstrated the highest torsional stiffness followed by the bi and unicortical locking plates 1.16 ±.08 Nmm vs. 0.79 ± .06 Nmm vs.0.40 ± 0.02 Nmm respectively (p < 0.01). The non locked plate demonstrated higher endurance than the bi and unicortical locking plates over a 6 week simulated fatigue cycle with 1.75mm, 2.10mm and 2.3mm residual displacement at 1600N respectively (p < 0.01). Discussion. This is the first study that has examined the biomechanical properties of the LCP when used for distal third tibial fractures. A review of the literature suggests LCPs outperform dynamic compression plates in osteoporotic bone but demonstrates no clear biomechanical advantage in using a locking construct in non-osteoporotic bone. In our study the non locked construct outperformed the locked constructs in all parameters assessed. We conclude there is no advantage in using a locking construct for distal third tibial fractures in good quality bone

Aims

Postoperative malalignment of the femur is one of the main complications in distal femur fractures. Few papers have investigated the impact of intraoperative malalignment on postoperative function and bone healing outcomes. The aim of this study was to investigate how intraoperative fracture malalignment affects postoperative bone healing and functional outcomes.

We investigated a new intramedullary locking nail that allows the distal interlocking screws to be locked to the nail. We compared fixation using this new implant with fixation using either a conventional nail or a locking plate in a laboratory simulation of an osteoporotic fracture of the distal femur. A total of 15 human cadaver femora were used to simulate an AO 33-A3 fracture pattern. Paired specimens compared fixation using either a locking or non-locking retrograde nail, and using either a locking retrograde nail or a locking plate. The constructs underwent cyclical loading to simulate single-leg stance up to 125 000 cycles. Axial and torsional stiffness and displacement, cycles to failure and modes of failure were recorded for each specimen. When compared with locking plate constructs, locking nail constructs had significantly longer mean fatigue life (75 800 cycles (sd 33 900) vs 12 800 cycles (sd 6100); p = 0.007) and mean axial stiffness (220 N/mm (sd 80) vs 70 N/mm (sd 18); p = 0.005), but lower mean torsional stiffness (2.5 Nm/° (sd 0.9) vs 5.1 Nm/° (sd 1.5); p = 0.008). In addition, in the nail group the mode of failure was either cut-out of the distal screws or breakage of nails, and in the locking plate group breakage of the plate was always the mode of failure. Locking nail constructs had significantly longer mean fatigue life than non-locking nail constructs (78 900 cycles (sd 25 600) vs 52 400 cycles (sd 22 500); p = 0.04).

The new locking retrograde femoral nail showed better stiffness and fatigue life than locking plates, and superior fatigue life to non-locking nails, which may be advantageous in elderly patients.

Cite this article: Bone Joint J 2014;96-B:114–21.

We investigated the static and cyclical strength of parallel and angulated locking plate screws using rigid polyurethane foam (0.32 g/cm³) and bovine cancellous bone blocks. Custom-made stainless steel plates with two conically threaded screw holes with different angulations (parallel, 10° and 20° divergent) and 5 mm self-tapping locking screws underwent pull-out and cyclical pull and bending tests. The bovine cancellous blocks were only subjected to static pull-out testing. We also performed finite element analysis for the static pull-out test of the parallel and 20° configurations. In both the foam model and the bovine cancellous bone we found the significantly highest pull-out force for the parallel constructs. In the finite element analysis there was a 47% more damage in the 20° divergent constructs than in the parallel configuration. Under cyclical loading, the mean number of cycles to failure was significantly higher for the parallel group, followed by the 10° and 20° divergent configurations.

In our laboratory setting we clearly showed the biomechanical disadvantage of a diverging locking screw angle under static and cyclical loading.

Filling the empty holes in peri-articular locking plates may improve the fatigue strength of the fixation. The purpose of this in vitro study was to investigate the effect of plugging the unused holes on the fatigue life of peri-articular distal femoral plates used to fix a comminuted supracondylar fracture model.

A locking/compression plate was applied to 33 synthetic femurs and then a 6 cm metaphyseal defect was created (AO Type 33-A3). The specimens were then divided into three groups: unplugged, plugged with locking screw only and fully plugged holes. They were then tested using a stepwise or run-out fatigue protocol, each applying cyclic physiological multiaxial loads.

All specimens in the stepwise group failed at the 770 N load level. The mean number of cycles to failure for the stepwise specimen was 25 500 cycles (sd 1500), 28 800 cycles (sd 6300), and 26 400 cycles (sd 2300) cycles for the unplugged, screw only and fully plugged configurations, respectively (p = 0.16). The mean number of cycles to failure for the run-out specimens was 42 800 cycles (sd 10 700), 36 000 cycles (sd 7200), and 36 600 cycles (sd 10 000) for the unplugged, screw only and fully plugged configurations, respectively (p = 0.50). There were also no differences in axial or torsional stiffness between the constructs. The failures were through the screw holes at the level of comminution.

In conclusion, filling the empty combination locking/compression holes in peri-articular distal femur locking plates at the level of supracondylar comminution does not increase the fatigue life of the fixation in a comminuted supracondylar femoral fracture model (AO 33-A3) with a 6 cm gap.

Objectives

We aimed to further evaluate the biomechanical characteristics of two locking screws versus three standard bicortical screws in synthetic models of normal and osteoporotic bone.