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Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture
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JINJ-6451; No. of Pages 9 Injury, Int. J. Care Injured xxx (2015) xxx–xxx
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Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture Igor Bumcˇi a,*, Tomislav Vlahovic´ b,1, Filip Juric´ a, Mirko Zˇganjer a, Gordana Milicˇic´ a, Hinko Wolf c, Anko Antabak d a
Children’s Hospital Zagreb, Croatia Paediatric Surgeon, Croatia University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, Croatia d Department of Surgery, University Hospital Centre Zagreb, Croatia b c
A R T I C L E I N F O
A B S T R A C T
Keywords: Child Fracture Ankle Osteosynthesis
Background: Paediatric ankle fractures comprise approximately 4% of all paediatric fractures and 30% of all epiphyseal fractures. Integrity of the ankle ‘‘mortise’’, which consists of tibial and fibular malleoli, is significant for stability and function of the ankle joint. Tibial malleolar fractures are classified as SH III or SH IV intra-articular fractures and, in cases where the fragments are displaced, anatomic reposition and fixation is mandatory. Methods: Type SH III–IV fractures of the tibial malleolus are usually treated with open reduction and fixation with cannulated screws that are parallel to the physis. Two K-wires are used for temporary stabilisation of fragments during reduction. A third ‘‘guide wire’’ for the screw is then placed parallel with the physis. Considering the rules of mechanics, it is assumed that the two temporary pins with the additional third pin placed parallel to the physis create a strong triangle and thus provide strong fracture fixation. To prove this hypothesis, an experiment was conducted on the artificial models of the lower end of the tibia from the company ‘‘Sawbones’’. Each model had been sawn in a way that imitates the fracture of medial malleoli and then reattached with 1.8 mm pins in various combinations. Prepared models were then tested for tensile and pressure forces. Results: The least stable model was that in which the fractured pieces were attached with only two parallel pins. The most stable model comprised three pins, where two crossed pins were inserted in the opposite compact bone and the third pin was inserted through the epiphysis parallel with and below the growth plate. Conclusion: A potential method of choice for fixation of tibial malleolar fractures comprises three Kwires, where two crossed pins are placed in the opposite compact bone and one is parallel with the growth plate. The benefits associated with this method include shorter operating times and avoidance of a second operation for screw removal. ß 2015 Elsevier Ltd. All rights reserved.
Introduction Distal tibial and fibular physeal fractures comprise 25–38% of all fractures of the physis and are the second most common physeal fractures [1,2]. Only 4% of all ankle fractures affect the physis [2]. The individuals most affected are children aged between 8 and 15 years [3]. Tibial malleolar fractures are classified as SH III and SH IV fractures, which are caused by injury that
* Corresponding author at: Department of Paediatric Surgery, Children’s Hospital Zagreb, Klaic´eva 16, Zagreb, Croatia. Tel.: +385 1 4600178; fax: +385 1 4600016. E-mail address: [email protected] (I. Bumcˇi). 1 Retired.
involves supination and inversion of the foot, as described by Dias and Tachdjian [4]. Medial tibial malleolar fractures are intraarticular fractures that require anatomical repositioning of fracture fragments. Failure to achieve anatomical repositioning often causes arthrosis of the joint in later years because of articular incongruity [5]. Growth arrest and deformity may occur after such fractures due to injury to the growth zone, particularly if fracture fragments are treated roughly and the reposition is not anatomical [6]. The risk of growth arrest is dependent on the age of the child: a young child will have a higher risk of growth arrest than an older child in whom the physis is soon to be closed. In rare cases, treatment of tibial malleolar fractures can be achieved by closed reduction, but this is possible only if fracture displacement is minor. In cases where anatomic reduction cannot be obtained by
http://dx.doi.org/10.1016/j.injury.2015.10.043 0020–1383/ß 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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closed methods, open reduction with internal fixation should be performed [7]. During open reduction, usually to obtain anatomical position of a fragment, two K-wires are used for temporary fixation until one or two cannulated screws are placed in the epiphysis and metaphysis parallel with the growth plate. In smaller children there is barely enough space between the physis and the articular surface of the bone to place a screw. The use of screws that are too big or are placed too close to the growth plate may cause damage to this structure. Using only Kwires minimises the risk of damage to the growth plate [7]. Three K-wires, two pins for fragment stabilisation and a third guide wire for the positioning of the screw are used in open reduction. This study assessed the stability of fragments that are fixated with only K-wires and considered various combinations of K-wires to establish the most stable combination. Materials and methods An artificial tibial bone model from ‘‘Sawbones’’ (Sawbones Europe ABß, Malmo¨, Sweden) was used in this study. This model is usually used in AO training exercises. The bone model is made of composite material with very similar mechanical characteristics to those of real bone [8]. Various combinations of constructions of Kwires were compared and the stability of the osteosynthesis was assessed.
Five models of osteosynthesis with K-wires were designed. Each bone was cut to imitate medial malleolus fracture: the cut was between the upper and medial articular surface of the tibial malleolus with an angle of 58 in the coronal plane. An electric drill was used to induce 1.8 mm thick K-wires at the same angle. In model A, two parallel K-wires were induced diagonally from the tip of the malleolus to the opposite compact bone (Fig. 1). In model B, two crossed K-wires were induced from the tip of the malleolus to the opposite compact bone. The solid angle between the wires was 278, and the angle in the lateral direction was 618 (Fig. 2). In model C, one K-wire was induced from the tip of the malleolus diagonally to the opposite compact bone and the other K-wire was induced laterally through the malleolus and epiphysis beneath and parallel with the growth plate. The solid angle between the wires was 278 in the coronal plane and 488 in the laterolateral (LL) plane (Fig. 3). In model D, two parallel K-wires were induced diagonally from the tip of the malleolus to the opposite compact bone and the third wire was induced laterally through the malleolus and epiphysis parallel with the growth plane (Fig. 4). In model E, two crossed K-wires were induced diagonally through the malleolus in the opposite compact bone and the third wire was induced laterally through the malleolus and epiphysis parallel with the growth plane. The solid angle between the
Fig. 1. Model A – two parallel k-wires are pined thru the malleolus into opposite corticalis.
Fig. 2. Model B – two crossed k-wires are pined thru the malleolus into opposite corticalis.
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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Fig. 3. Model C – one k-wire is pinned in the opposite corticalis parallel with growth plate and the other from the tip of the malleolus.
Fig. 4. Model D – two k-wires are pinned parallely from the tip of the malleolus to the opposite corticalis and one k-wire is pinned from the medial side of malleolus parallel with growth plate into opposite corticallis.
crossed wires was 258. Angles between the crossed wire and the third wire in lateral projection were 448 (Fig. 5). Solid angles between K-wires were measured with a protractor Type 45 Hoffmann Gruppe, which enables the measurement of angles to an accuracy of one minute.
The medial malleolus is under forces of pressure and tension during standing and walking. In the standing position, the pressure force is transferred through the ends of the ankle mortise on the talus, calcaneous and further on the foot bone forcing ends of the mortise to spread out and up. In contrast, contraction of the lateral
Fig. 5. Model E – two k-wires are crossed pinned from the tip of the malleolus into opposite cortiallis and one k-wire is pinned from the medial side of malleolus parallel with growth plate into opposite corticallis.
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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ankle muscle group (movement of pronation and eversion) strains the deltoid ligament, which is attached on the tibial malleolus below the growth plate, and the tightening of this ligament causes the malleolus to move down and in [8]. The current experiment was set up to imitate those forces so all models are tested on forces of tension and pressure. In the experiment to measure pressure forces (Fig. 6), the force was acting on the middle point of the inner side of the malleolus at an angle of 458 to the longitudinal axis. The model of the bone was secured by two U bolts on a mount. The pressure force was created using a screw mechanism by manually turning the screw thread spindle through the female screw, which was secured on the metal plate. The force was measured with a force sensor, which was connected to an eight-channel universal measuring amplifier. Catman Ver 4.2 original software was used to collect data on force strength during the load and relief of the model. Authoritative data for the assessment of stability of osteosynthesis is the fracture gap that holds after unloading the model. In the current study, fracture gap was measured with a digital microscope during the pressure load and after unloading. In the model for measuring tension forces (Fig. 7), the bone was secured on a metal plate in the same way as in the pressure force experiment, with the exception of a wood chock placed beneath the distal bone part to disable movement in the direction of force. The tension force was established with a screw mechanism that was attached to the fractured part with a hook and wire. Force was measured with a dynamometer. Fracture gap was measured with a
digital microscope and the movement sensor was placed perpendicularly to the fracture surface. Stability of osteosynthesis with K-wires in each model was determined by assessing the fracture gap between the tibial malleolus and the tibia. A digital microscope was used to measure the initial fracture gap, the fracture gap during the maximum torque and the fracture gap after the load. Pressure was initially set at 50 N, and the load was increased by 50 N after each measurement. The maximum and permanent widening of the gap was determined. Maximum widening of the fracture gap is equal to the difference between the maximal and initial fracture gap. Permanent widening is equal to the difference between the residual and initial fracture gap. Measurement was stopped if permanent widening was greater than 2 mm. Results Pressure stability results Tables 1a–1e show the results of osteosynthesis stability for models A to E at pressure load. Increase of fracture width on peak pressure load is shown for each of the models on Graph 1A. On Graph 1B, the results of fracture widening after load are shown for each model. As shown on the graphs, the strongest model of osteosynthesis was model E, which comprised two crossed K-wires pinned in the opposite compact bone and one pinned
Fig. 6. Pressure measurement apparatus.
Fig. 7. Tension measurement apparatus.
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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JINJ-6451; No. of Pages 9 I. Bumcˇi et al. / Injury, Int. J. Care Injured xxx (2015) xxx–xxx Table 1a The impact of pressure force on model A. Initial width of fracture gap: 0.263 mm. Peak load N
58.38 95.52 146.16 194.34 256.56
Fracture gap
Widening of a fracture
At load mm
After load mm
At load mm
After load mm
0.355 0.395 0.593 1.203 2.763
0.290 0.368 0.566 1.040 2.329
0.092 0.132 0.330 0.940 2.500
0.027 0.105 0.303 0.777 2.066
Table 1b The impact of pressure force on model B. Initial width of fracture gap: 0 mm. Peak load N
52.74 110.88 151.80 204.36 241.92 291.60 349.98 394.98
Fracture gap
Widening of a fracture
At load mm
After load mm
At load mm
After load mm
0.092 0.276 0.329 0.542 0.881 1.479 2.226 4.577
0.053 0.053 0.053 0.118 0.263 0.842 1.285 3.306
0.092 0.276 0.329 0.542 0.881 1.479 2.226 4.577
0.053 0.053 0.053 0.118 0.263 0.842 1.285 3.306
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through the epiphysis. The next strongest model was B, followed by D and C, and the weakest was model A. The stability of osteosynthesis was assessed using information about the widening of the fracture gap after the load (Graph 1B). In this case, model E was by far the most stable model. During pressure testing on model E, the hook broke at a force of 610 N with the gap widening of 1.07 mm. Tension stability results Tables 2a–2e show the osteosynthesis stability results at different tension forces. The increase in fracture gap depending on the amount of tension force is shown in Graph 2A. As shown in this graph, the strongest model was E followed by models D, B, A and C. Table 3 shows a summary of gap widening after tension and pressure force and, therefore, is more relevant in assessing the stability of osteosynthesis. Model E was the most stable model. This model held the force of 369 N (which is equal to a force of 37.62 kg) for tension and a force more than 610 N (which is equal to a pressure of 62 kg) for pressure load. The next most stable model was D, followed by models B, C and A.
Table 2a The impact of tension force on model A. Initial width of fracture gap: 0 mm. Table 1c The impact of pressure force on model C. Initial width of fracture gap: 0.342 mm. Peak load N
56.58 97.68 152.88 198.24 265.12
Fracture gap
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.658 1.013 1.631 2.249 4.141
0.421 0.539 0.921 1.340 2.542
0.316 0.671 1.289 1.907 3.799
0.079 0.197 0.579 0.998 2.200
Table 1d The impact of pressure force on model D. Initial width of fracture gap: 0.830 mm. Peak load N
Fracture gap At load mm
54.6 99.66 156.84 192 242.22 308.54
0.911 0.977 1.098 1.365 1.994 3.452
Widening of a fracture After load mm 0.830 0.870 0.990 1.191 1.593 2.985
Peak load N 0.080 0.147 0.268 0.535 1.164 2.622
55.2 96.72 152.52 198.36 240 299.16 334.14 390.78
Fracture gap
47.22 98.34 153.12 219.54 242.28 300.54 316.86
0.000 0.040 0.160 0.361 0.763 2.155
Fracture gap
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.469 0.784 1.215 1.633 2.328 2.966 5.263
0.135 0.148 0.308 0.404 0.883 1.017 3.052
0.469 0.784 1.215 1.633 2.328 2.966 5.263
0.135 0.148 0.308 0.404 0.883 1.017 3.052
Remark: Because of loosening of the model it was not possible to achieve the planned force of 350 N.
Table 2b The impact of tension force on model B. Initial width of fracture gap: 0.892 mm. Peak load N
At load mm
Table 1e The impact of pressure force on model E. Initial width of fracture gap: 0.364. Peak load N
Peak load N
62.04 104.04 151.08 210.42 249.3 302.64 349.38
Fracture gap
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
1.435 1.731 2.150 2.837 3.153 4.063 5.169
0.977 1.069 1.171 1.383 1.666 2.135 3.002
0.543 0.839 1.258 1.945 2.261 3.171 4.277
0.085 0.177 0.279 0.491 0.774 1.243 2.110
Table 2c The impact of tension force on model C. Initial width of fracture gap: 0 mm.
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.396 0.462 0.623 0.827 1.074 1.542 2.168 3.036
0.364 0.368 0.420 0.520 0.778 1.200 1.776 2.726
0.032 0.098 0.259 0.463 0.710 1.178 1.804 2.672
0.000 0.004 0.056 0.156 0.414 0.836 1.412 2.362
Peak load N
57.96 102.36 171 200.22 251.34 316.26 364.08
Fracture gap
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.678 0.945 1.437 2.029 2.629 3.757 5.898
0.135 0.229 0.242 0.312 0.665 1.605 3.717
0.678 0.945 1.437 2.029 2.629 3.757 5.898
0.135 0.229 0.242 0.312 0.665 1.605 3.717
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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Table 2d The impact of tension force on model D. Initial width of fracture gap: 0.790 mm. Peak load N
Fracture gap
55.44 96.84 144.96 201.54 254.76 290.04 348.96 411.54 447.12
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.991 1.178 1.619 2.315 2.851 3.266 3.962 4.725 5.702
0.803 0.816 0.977 1.124 1.633 1.673 2.128 2.423 3.493
0.201 0.388 0.829 1.525 2.061 2.476 3.172 3.935 4.912
0.013 0.026 0.187 0.334 0.843 0.883 1.338 1.633 2.703
Table 2e The impact of tension force on model E. Initial width of fracture gap: 0 mm. Peak load N
Fracture gap
54.48 98.52 146.94 209.64 264.18 303.24 358.02 399.54 451.86 488.58 553.96 612.78
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.522 0.790 1.004 1.365 1.499 1.713 2.075 2.423 2.891 3.105 3.172 3.359
0.000 0.000 0.000 0.094 0.174 0.321 0.455 0.509 0.736 0.776 0.790 1.071
0.522 0.790 1.004 1.365 1.499 1.713 2.075 2.423 2.891 3.105 3.172 3.359
0.000 0.000 0.000 0.094 0.174 0.321 0.455 0.509 0.736 0.776 0.790 1.071
Remark: At a force of 692 N, the hook was damaged and the experiment was terminated.
Discussion Widening of the fracture gap after osteosynthesis with K-wires is a very complicated process from a biomechanical point of view. This widening is partly the result of K-wire bending and partly because of fracture fragments slipping on the K-wire. All the forces that are transferred from the fracture fragment on the K-wire can be disassembled on components: the vertical component and that parallel with the K-wire. The vertical component is responsible for bending the wire, and the parallel component is responsible for fragment sliding along the wire. Bending of the wire causes it to be elastically deformed (the wire returns to its original state after the force load); however, it can also be plastically deformed (the wire does not return to its original state after the force load). The parallel component of the force is trying to move the fragment along the wire. When the force is greater than the friction, the fragment
Table 3 Maximum force needed for constant fracture gap of 2 mm.
1. 2. 3. 4. 5.
Model
Pressure force (N)
Model
E B D A C
369 366 301 253 246
E D B C A
Tension force (N) a
424 343 325 308
a Constant fracture gap of 1.07 mm was accomplished at force of 610 N. Due to damage of the hook, the experiment was terminated.
slides along the wire. If the K-wires are crossed, the situation is a bit more complicated. Crossed K-wires are associated with greater resistance for fragment sliding along the wires, so sliding is only possible if the wires are deformed. If these deformations are elastic, the wires will be trying to return to their original state after the force has ceased and the fracture fragment will be placed back. If the vertical force on the wire is greater than the parallel force, the wire will deform plastically and the spread of the gap will be constant. The relationship between these abovementioned mechanisms of fracture gap widening depends on the type of load (amount, direction and position of force) and the type of osteosynthesis (number and position of K-wires). The maximum pressure needed for constant gap widening of 2 mm on each model is shown in Table 3. The data show that models E and B are equally stable and they are followed by models D, A and C. Models A, B and C have two K-wires. Model C is the weakest model: in this model, the wire is placed laterally through the epiphysis and is parallel with the growth plate and this creates less sliding resistance than if the wire had been placed diagonally through the tip of the malleolus to the opposite compact bone. This explains why model A, which has two parallel wires from the tip of the malleolus to the opposite compact bone, is stronger than model C. Model B is the strongest model with two wires. The wires in model B are crossed and placed in the opposite compact bone and make a solid angle of 268, which creates more resistance for fragment sliding. Model D is similar to model A, but has one additional wire laterally through the malleolus and epiphysis and parallel with the growth plate; this feature means that model D is more stable than model A, but it is still weaker than model B. The resistance provided by the third wire in model D (as seen also in model C) is weak and does not contribute significantly to the overall stability of the osteosynthesis. Models E and B are similarly constructed and are the strongest models. Both these models have two crossed wires pinned in the opposite compact bone and model E has an additional third wire placed laterally through the malleolus and epiphysis parallel with the growth plate. This third wire does not contribute much to the stability of the model (as seen with model D versus model A). As shown in Graph 1B, model B is even stronger than model E for lower force load. This is because of the greater solid angle between wires 1 and 2 on model B (angle (1, 2) = 278) compared with in model E (angle (1, 2) = 258). Graph 2B shows the influence of tension forces on the models. The strongest model is again model E. Model D is well behind model E, but is still about 25% stronger than models B, C and A, which are quite uniform. Tension force on the models is in the direction of the tibial axis. A major improvement in stability (in contrast to models A, B and C) was achieved by inducing the third wire to pass perpendicularly to the direction of the tension force. Taking into account the action of both forces (pressure and tension) on the model and the force direction (tension acting in the direction of the tibial axis, and pressure acting at 458 on the tibial axis), the most stable model is model E. Models B and D have similar characteristics. Model B is stronger on pressure load whereas model D is more stable on tension forces. Models A and C are the weakest. The results of this study indicate that the greater the solid angle between the two wires, the more stable is the model on pressure load, and the addition of a third wire positioned perpendicularly to the direction of tension force increases the stability on tension. The tibial malleolus is under influence of both forces: pressure in around 458 of the direction on the tibial axis and tension in the direction of the tibial axis. Fracture of the medial malleolus is usually treated by open reduction and fixation with cannulated screws. There are three wires that secure the fracture during temporary fragment fixation and placement of the cannulated
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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Graph 1. Fracture widening under and after compression load.
screw. Reviewing the models in this study, particularly model E, which has proven to be the strongest model, osteosynthesis with three K-wires is sufficient for holding fractured fragments and could be used as a method of treatment for medial tibial malleolus
fracture. Additional cast immobilisation is still mandatory because of the instability of K-pin osteosynthesis. A further benefit of treatment with K-wires is the avoidance of a second operation for screw removal.
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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Graph 2. Fracture widening under and after tension load.
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Conflict of interest The authors of manuscript have no affiliations with or involvement in any organisation or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript. References [1] Hynes D, O’Brien T. Growth disturbance lines after injury of the distal tibial physis. J Bone Joint Surg Br 1988;70:231–3. [2] Mizuta T, Benson WM, Foster BK, Paterson DC, Morris LL. Statistical analysis of the incidence of physeal injuries. J Pediatr Orthop 1987;7:518–23.
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[3] Mann DC, Rajmaira S. Distribution of physeal and nonphyseal fractures in 2650 long-bone fractures in children aged 0–16 years. J Pediatr Orthop 1990;10:713–6. [4] Dias LS, Tachdjian MO. Physeal injuries of the ankle in children: classification. Clin Orthop Relat Res 1978;136:230–3. [5] Marsh JS, Daigneault JP. Ankle injuries in pediatric population. Curr Opin Pediatr 2000;12:52–60. [6] Kling T. Fractures of the ankle and foot. In: Drennan J, editor. The child’s foot and ankle. New York: Raven; 1992. [7] Bright RW. Physeal injuries. In: Rockwood A, Wilkens E, King E, editors. Fractures in children. Philadelphia: JB Lippincott; 1991. p. 87–170. [8] Grant JA, Bishop NE, Gotzen N, Sprecher C, Honl M, Morlock MM. Artificial composite bone as a model of human trabecular bone: the implant–bone interface. J Biomech 2007;40:1158–64.
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Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture Igor Bumcˇi a,*, Tomislav Vlahovic´ b,1, Filip Juric´ a, Mirko Zˇganjer a, Gordana Milicˇic´ a, Hinko Wolf c, Anko Antabak d a
Children’s Hospital Zagreb, Croatia Paediatric Surgeon, Croatia University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, Croatia d Department of Surgery, University Hospital Centre Zagreb, Croatia b c
A R T I C L E I N F O
A B S T R A C T
Keywords: Child Fracture Ankle Osteosynthesis
Background: Paediatric ankle fractures comprise approximately 4% of all paediatric fractures and 30% of all epiphyseal fractures. Integrity of the ankle ‘‘mortise’’, which consists of tibial and fibular malleoli, is significant for stability and function of the ankle joint. Tibial malleolar fractures are classified as SH III or SH IV intra-articular fractures and, in cases where the fragments are displaced, anatomic reposition and fixation is mandatory. Methods: Type SH III–IV fractures of the tibial malleolus are usually treated with open reduction and fixation with cannulated screws that are parallel to the physis. Two K-wires are used for temporary stabilisation of fragments during reduction. A third ‘‘guide wire’’ for the screw is then placed parallel with the physis. Considering the rules of mechanics, it is assumed that the two temporary pins with the additional third pin placed parallel to the physis create a strong triangle and thus provide strong fracture fixation. To prove this hypothesis, an experiment was conducted on the artificial models of the lower end of the tibia from the company ‘‘Sawbones’’. Each model had been sawn in a way that imitates the fracture of medial malleoli and then reattached with 1.8 mm pins in various combinations. Prepared models were then tested for tensile and pressure forces. Results: The least stable model was that in which the fractured pieces were attached with only two parallel pins. The most stable model comprised three pins, where two crossed pins were inserted in the opposite compact bone and the third pin was inserted through the epiphysis parallel with and below the growth plate. Conclusion: A potential method of choice for fixation of tibial malleolar fractures comprises three Kwires, where two crossed pins are placed in the opposite compact bone and one is parallel with the growth plate. The benefits associated with this method include shorter operating times and avoidance of a second operation for screw removal. ß 2015 Elsevier Ltd. All rights reserved.
Introduction Distal tibial and fibular physeal fractures comprise 25–38% of all fractures of the physis and are the second most common physeal fractures [1,2]. Only 4% of all ankle fractures affect the physis [2]. The individuals most affected are children aged between 8 and 15 years [3]. Tibial malleolar fractures are classified as SH III and SH IV fractures, which are caused by injury that
* Corresponding author at: Department of Paediatric Surgery, Children’s Hospital Zagreb, Klaic´eva 16, Zagreb, Croatia. Tel.: +385 1 4600178; fax: +385 1 4600016. E-mail address: [email protected] (I. Bumcˇi). 1 Retired.
involves supination and inversion of the foot, as described by Dias and Tachdjian [4]. Medial tibial malleolar fractures are intraarticular fractures that require anatomical repositioning of fracture fragments. Failure to achieve anatomical repositioning often causes arthrosis of the joint in later years because of articular incongruity [5]. Growth arrest and deformity may occur after such fractures due to injury to the growth zone, particularly if fracture fragments are treated roughly and the reposition is not anatomical [6]. The risk of growth arrest is dependent on the age of the child: a young child will have a higher risk of growth arrest than an older child in whom the physis is soon to be closed. In rare cases, treatment of tibial malleolar fractures can be achieved by closed reduction, but this is possible only if fracture displacement is minor. In cases where anatomic reduction cannot be obtained by
http://dx.doi.org/10.1016/j.injury.2015.10.043 0020–1383/ß 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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closed methods, open reduction with internal fixation should be performed [7]. During open reduction, usually to obtain anatomical position of a fragment, two K-wires are used for temporary fixation until one or two cannulated screws are placed in the epiphysis and metaphysis parallel with the growth plate. In smaller children there is barely enough space between the physis and the articular surface of the bone to place a screw. The use of screws that are too big or are placed too close to the growth plate may cause damage to this structure. Using only Kwires minimises the risk of damage to the growth plate [7]. Three K-wires, two pins for fragment stabilisation and a third guide wire for the positioning of the screw are used in open reduction. This study assessed the stability of fragments that are fixated with only K-wires and considered various combinations of K-wires to establish the most stable combination. Materials and methods An artificial tibial bone model from ‘‘Sawbones’’ (Sawbones Europe ABß, Malmo¨, Sweden) was used in this study. This model is usually used in AO training exercises. The bone model is made of composite material with very similar mechanical characteristics to those of real bone [8]. Various combinations of constructions of Kwires were compared and the stability of the osteosynthesis was assessed.
Five models of osteosynthesis with K-wires were designed. Each bone was cut to imitate medial malleolus fracture: the cut was between the upper and medial articular surface of the tibial malleolus with an angle of 58 in the coronal plane. An electric drill was used to induce 1.8 mm thick K-wires at the same angle. In model A, two parallel K-wires were induced diagonally from the tip of the malleolus to the opposite compact bone (Fig. 1). In model B, two crossed K-wires were induced from the tip of the malleolus to the opposite compact bone. The solid angle between the wires was 278, and the angle in the lateral direction was 618 (Fig. 2). In model C, one K-wire was induced from the tip of the malleolus diagonally to the opposite compact bone and the other K-wire was induced laterally through the malleolus and epiphysis beneath and parallel with the growth plate. The solid angle between the wires was 278 in the coronal plane and 488 in the laterolateral (LL) plane (Fig. 3). In model D, two parallel K-wires were induced diagonally from the tip of the malleolus to the opposite compact bone and the third wire was induced laterally through the malleolus and epiphysis parallel with the growth plane (Fig. 4). In model E, two crossed K-wires were induced diagonally through the malleolus in the opposite compact bone and the third wire was induced laterally through the malleolus and epiphysis parallel with the growth plane. The solid angle between the
Fig. 1. Model A – two parallel k-wires are pined thru the malleolus into opposite corticalis.
Fig. 2. Model B – two crossed k-wires are pined thru the malleolus into opposite corticalis.
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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Fig. 3. Model C – one k-wire is pinned in the opposite corticalis parallel with growth plate and the other from the tip of the malleolus.
Fig. 4. Model D – two k-wires are pinned parallely from the tip of the malleolus to the opposite corticalis and one k-wire is pinned from the medial side of malleolus parallel with growth plate into opposite corticallis.
crossed wires was 258. Angles between the crossed wire and the third wire in lateral projection were 448 (Fig. 5). Solid angles between K-wires were measured with a protractor Type 45 Hoffmann Gruppe, which enables the measurement of angles to an accuracy of one minute.
The medial malleolus is under forces of pressure and tension during standing and walking. In the standing position, the pressure force is transferred through the ends of the ankle mortise on the talus, calcaneous and further on the foot bone forcing ends of the mortise to spread out and up. In contrast, contraction of the lateral
Fig. 5. Model E – two k-wires are crossed pinned from the tip of the malleolus into opposite cortiallis and one k-wire is pinned from the medial side of malleolus parallel with growth plate into opposite corticallis.
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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ankle muscle group (movement of pronation and eversion) strains the deltoid ligament, which is attached on the tibial malleolus below the growth plate, and the tightening of this ligament causes the malleolus to move down and in [8]. The current experiment was set up to imitate those forces so all models are tested on forces of tension and pressure. In the experiment to measure pressure forces (Fig. 6), the force was acting on the middle point of the inner side of the malleolus at an angle of 458 to the longitudinal axis. The model of the bone was secured by two U bolts on a mount. The pressure force was created using a screw mechanism by manually turning the screw thread spindle through the female screw, which was secured on the metal plate. The force was measured with a force sensor, which was connected to an eight-channel universal measuring amplifier. Catman Ver 4.2 original software was used to collect data on force strength during the load and relief of the model. Authoritative data for the assessment of stability of osteosynthesis is the fracture gap that holds after unloading the model. In the current study, fracture gap was measured with a digital microscope during the pressure load and after unloading. In the model for measuring tension forces (Fig. 7), the bone was secured on a metal plate in the same way as in the pressure force experiment, with the exception of a wood chock placed beneath the distal bone part to disable movement in the direction of force. The tension force was established with a screw mechanism that was attached to the fractured part with a hook and wire. Force was measured with a dynamometer. Fracture gap was measured with a
digital microscope and the movement sensor was placed perpendicularly to the fracture surface. Stability of osteosynthesis with K-wires in each model was determined by assessing the fracture gap between the tibial malleolus and the tibia. A digital microscope was used to measure the initial fracture gap, the fracture gap during the maximum torque and the fracture gap after the load. Pressure was initially set at 50 N, and the load was increased by 50 N after each measurement. The maximum and permanent widening of the gap was determined. Maximum widening of the fracture gap is equal to the difference between the maximal and initial fracture gap. Permanent widening is equal to the difference between the residual and initial fracture gap. Measurement was stopped if permanent widening was greater than 2 mm. Results Pressure stability results Tables 1a–1e show the results of osteosynthesis stability for models A to E at pressure load. Increase of fracture width on peak pressure load is shown for each of the models on Graph 1A. On Graph 1B, the results of fracture widening after load are shown for each model. As shown on the graphs, the strongest model of osteosynthesis was model E, which comprised two crossed K-wires pinned in the opposite compact bone and one pinned
Fig. 6. Pressure measurement apparatus.
Fig. 7. Tension measurement apparatus.
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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JINJ-6451; No. of Pages 9 I. Bumcˇi et al. / Injury, Int. J. Care Injured xxx (2015) xxx–xxx Table 1a The impact of pressure force on model A. Initial width of fracture gap: 0.263 mm. Peak load N
58.38 95.52 146.16 194.34 256.56
Fracture gap
Widening of a fracture
At load mm
After load mm
At load mm
After load mm
0.355 0.395 0.593 1.203 2.763
0.290 0.368 0.566 1.040 2.329
0.092 0.132 0.330 0.940 2.500
0.027 0.105 0.303 0.777 2.066
Table 1b The impact of pressure force on model B. Initial width of fracture gap: 0 mm. Peak load N
52.74 110.88 151.80 204.36 241.92 291.60 349.98 394.98
Fracture gap
Widening of a fracture
At load mm
After load mm
At load mm
After load mm
0.092 0.276 0.329 0.542 0.881 1.479 2.226 4.577
0.053 0.053 0.053 0.118 0.263 0.842 1.285 3.306
0.092 0.276 0.329 0.542 0.881 1.479 2.226 4.577
0.053 0.053 0.053 0.118 0.263 0.842 1.285 3.306
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through the epiphysis. The next strongest model was B, followed by D and C, and the weakest was model A. The stability of osteosynthesis was assessed using information about the widening of the fracture gap after the load (Graph 1B). In this case, model E was by far the most stable model. During pressure testing on model E, the hook broke at a force of 610 N with the gap widening of 1.07 mm. Tension stability results Tables 2a–2e show the osteosynthesis stability results at different tension forces. The increase in fracture gap depending on the amount of tension force is shown in Graph 2A. As shown in this graph, the strongest model was E followed by models D, B, A and C. Table 3 shows a summary of gap widening after tension and pressure force and, therefore, is more relevant in assessing the stability of osteosynthesis. Model E was the most stable model. This model held the force of 369 N (which is equal to a force of 37.62 kg) for tension and a force more than 610 N (which is equal to a pressure of 62 kg) for pressure load. The next most stable model was D, followed by models B, C and A.
Table 2a The impact of tension force on model A. Initial width of fracture gap: 0 mm. Table 1c The impact of pressure force on model C. Initial width of fracture gap: 0.342 mm. Peak load N
56.58 97.68 152.88 198.24 265.12
Fracture gap
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.658 1.013 1.631 2.249 4.141
0.421 0.539 0.921 1.340 2.542
0.316 0.671 1.289 1.907 3.799
0.079 0.197 0.579 0.998 2.200
Table 1d The impact of pressure force on model D. Initial width of fracture gap: 0.830 mm. Peak load N
Fracture gap At load mm
54.6 99.66 156.84 192 242.22 308.54
0.911 0.977 1.098 1.365 1.994 3.452
Widening of a fracture After load mm 0.830 0.870 0.990 1.191 1.593 2.985
Peak load N 0.080 0.147 0.268 0.535 1.164 2.622
55.2 96.72 152.52 198.36 240 299.16 334.14 390.78
Fracture gap
47.22 98.34 153.12 219.54 242.28 300.54 316.86
0.000 0.040 0.160 0.361 0.763 2.155
Fracture gap
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.469 0.784 1.215 1.633 2.328 2.966 5.263
0.135 0.148 0.308 0.404 0.883 1.017 3.052
0.469 0.784 1.215 1.633 2.328 2.966 5.263
0.135 0.148 0.308 0.404 0.883 1.017 3.052
Remark: Because of loosening of the model it was not possible to achieve the planned force of 350 N.
Table 2b The impact of tension force on model B. Initial width of fracture gap: 0.892 mm. Peak load N
At load mm
Table 1e The impact of pressure force on model E. Initial width of fracture gap: 0.364. Peak load N
Peak load N
62.04 104.04 151.08 210.42 249.3 302.64 349.38
Fracture gap
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
1.435 1.731 2.150 2.837 3.153 4.063 5.169
0.977 1.069 1.171 1.383 1.666 2.135 3.002
0.543 0.839 1.258 1.945 2.261 3.171 4.277
0.085 0.177 0.279 0.491 0.774 1.243 2.110
Table 2c The impact of tension force on model C. Initial width of fracture gap: 0 mm.
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.396 0.462 0.623 0.827 1.074 1.542 2.168 3.036
0.364 0.368 0.420 0.520 0.778 1.200 1.776 2.726
0.032 0.098 0.259 0.463 0.710 1.178 1.804 2.672
0.000 0.004 0.056 0.156 0.414 0.836 1.412 2.362
Peak load N
57.96 102.36 171 200.22 251.34 316.26 364.08
Fracture gap
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.678 0.945 1.437 2.029 2.629 3.757 5.898
0.135 0.229 0.242 0.312 0.665 1.605 3.717
0.678 0.945 1.437 2.029 2.629 3.757 5.898
0.135 0.229 0.242 0.312 0.665 1.605 3.717
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Table 2d The impact of tension force on model D. Initial width of fracture gap: 0.790 mm. Peak load N
Fracture gap
55.44 96.84 144.96 201.54 254.76 290.04 348.96 411.54 447.12
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.991 1.178 1.619 2.315 2.851 3.266 3.962 4.725 5.702
0.803 0.816 0.977 1.124 1.633 1.673 2.128 2.423 3.493
0.201 0.388 0.829 1.525 2.061 2.476 3.172 3.935 4.912
0.013 0.026 0.187 0.334 0.843 0.883 1.338 1.633 2.703
Table 2e The impact of tension force on model E. Initial width of fracture gap: 0 mm. Peak load N
Fracture gap
54.48 98.52 146.94 209.64 264.18 303.24 358.02 399.54 451.86 488.58 553.96 612.78
Widening of a fracture
At load mm
After load mm
Peak load N
At load mm
0.522 0.790 1.004 1.365 1.499 1.713 2.075 2.423 2.891 3.105 3.172 3.359
0.000 0.000 0.000 0.094 0.174 0.321 0.455 0.509 0.736 0.776 0.790 1.071
0.522 0.790 1.004 1.365 1.499 1.713 2.075 2.423 2.891 3.105 3.172 3.359
0.000 0.000 0.000 0.094 0.174 0.321 0.455 0.509 0.736 0.776 0.790 1.071
Remark: At a force of 692 N, the hook was damaged and the experiment was terminated.
Discussion Widening of the fracture gap after osteosynthesis with K-wires is a very complicated process from a biomechanical point of view. This widening is partly the result of K-wire bending and partly because of fracture fragments slipping on the K-wire. All the forces that are transferred from the fracture fragment on the K-wire can be disassembled on components: the vertical component and that parallel with the K-wire. The vertical component is responsible for bending the wire, and the parallel component is responsible for fragment sliding along the wire. Bending of the wire causes it to be elastically deformed (the wire returns to its original state after the force load); however, it can also be plastically deformed (the wire does not return to its original state after the force load). The parallel component of the force is trying to move the fragment along the wire. When the force is greater than the friction, the fragment
Table 3 Maximum force needed for constant fracture gap of 2 mm.
1. 2. 3. 4. 5.
Model
Pressure force (N)
Model
E B D A C
369 366 301 253 246
E D B C A
Tension force (N) a
424 343 325 308
a Constant fracture gap of 1.07 mm was accomplished at force of 610 N. Due to damage of the hook, the experiment was terminated.
slides along the wire. If the K-wires are crossed, the situation is a bit more complicated. Crossed K-wires are associated with greater resistance for fragment sliding along the wires, so sliding is only possible if the wires are deformed. If these deformations are elastic, the wires will be trying to return to their original state after the force has ceased and the fracture fragment will be placed back. If the vertical force on the wire is greater than the parallel force, the wire will deform plastically and the spread of the gap will be constant. The relationship between these abovementioned mechanisms of fracture gap widening depends on the type of load (amount, direction and position of force) and the type of osteosynthesis (number and position of K-wires). The maximum pressure needed for constant gap widening of 2 mm on each model is shown in Table 3. The data show that models E and B are equally stable and they are followed by models D, A and C. Models A, B and C have two K-wires. Model C is the weakest model: in this model, the wire is placed laterally through the epiphysis and is parallel with the growth plate and this creates less sliding resistance than if the wire had been placed diagonally through the tip of the malleolus to the opposite compact bone. This explains why model A, which has two parallel wires from the tip of the malleolus to the opposite compact bone, is stronger than model C. Model B is the strongest model with two wires. The wires in model B are crossed and placed in the opposite compact bone and make a solid angle of 268, which creates more resistance for fragment sliding. Model D is similar to model A, but has one additional wire laterally through the malleolus and epiphysis and parallel with the growth plate; this feature means that model D is more stable than model A, but it is still weaker than model B. The resistance provided by the third wire in model D (as seen also in model C) is weak and does not contribute significantly to the overall stability of the osteosynthesis. Models E and B are similarly constructed and are the strongest models. Both these models have two crossed wires pinned in the opposite compact bone and model E has an additional third wire placed laterally through the malleolus and epiphysis parallel with the growth plate. This third wire does not contribute much to the stability of the model (as seen with model D versus model A). As shown in Graph 1B, model B is even stronger than model E for lower force load. This is because of the greater solid angle between wires 1 and 2 on model B (angle (1, 2) = 278) compared with in model E (angle (1, 2) = 258). Graph 2B shows the influence of tension forces on the models. The strongest model is again model E. Model D is well behind model E, but is still about 25% stronger than models B, C and A, which are quite uniform. Tension force on the models is in the direction of the tibial axis. A major improvement in stability (in contrast to models A, B and C) was achieved by inducing the third wire to pass perpendicularly to the direction of the tension force. Taking into account the action of both forces (pressure and tension) on the model and the force direction (tension acting in the direction of the tibial axis, and pressure acting at 458 on the tibial axis), the most stable model is model E. Models B and D have similar characteristics. Model B is stronger on pressure load whereas model D is more stable on tension forces. Models A and C are the weakest. The results of this study indicate that the greater the solid angle between the two wires, the more stable is the model on pressure load, and the addition of a third wire positioned perpendicularly to the direction of tension force increases the stability on tension. The tibial malleolus is under influence of both forces: pressure in around 458 of the direction on the tibial axis and tension in the direction of the tibial axis. Fracture of the medial malleolus is usually treated by open reduction and fixation with cannulated screws. There are three wires that secure the fracture during temporary fragment fixation and placement of the cannulated
Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043
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Graph 1. Fracture widening under and after compression load.
screw. Reviewing the models in this study, particularly model E, which has proven to be the strongest model, osteosynthesis with three K-wires is sufficient for holding fractured fragments and could be used as a method of treatment for medial tibial malleolus
fracture. Additional cast immobilisation is still mandatory because of the instability of K-pin osteosynthesis. A further benefit of treatment with K-wires is the avoidance of a second operation for screw removal.
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Graph 2. Fracture widening under and after tension load.
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Conflict of interest The authors of manuscript have no affiliations with or involvement in any organisation or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript. References [1] Hynes D, O’Brien T. Growth disturbance lines after injury of the distal tibial physis. J Bone Joint Surg Br 1988;70:231–3. [2] Mizuta T, Benson WM, Foster BK, Paterson DC, Morris LL. Statistical analysis of the incidence of physeal injuries. J Pediatr Orthop 1987;7:518–23.
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Please cite this article in press as: Bumcˇi I, et al. Evaluation of stability of osteosynthesis with K-wires on an artificial model of tibial malleolus fracture. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.10.043