Eur J Orthop Surg Traumatol DOI 10.1007/s00590-014-1518-9

ORIGINAL ARTICLE

Towards a solution of the wires’ slippage problem of the Ilizarov external fixator C. Bairaktari • G. Athanassiou • E. Panagiotopoulos D. Deligianni



Received: 2 May 2014 / Accepted: 22 July 2014 Ó Springer-Verlag France 2014

Abstract Clinical experience has indicated that many complications during treatment with the Ilizarov method, and mainly tract infection, are related to decreased wire tension. The aim of this work was to evaluate biomechanically a novel wire tensioning and clamping system that will minimise or even diminish the reduction of the wire pretension during treatment. The proposed approach is based on threading of the wire end in a sufficient length. The wire pretension is applied by twisting a nut on the threaded part of the wires against the ring and is recorded by an incorporated force sensor. For biomechanical evaluation, the frame, consisting of a polyethylene bar, simulating the bone fragment, suspended on two rings, was subjected to a dynamic load of 0–800 N at a frequency of 0.5 Hz. After dynamic loading for 20 min, loss of the initial wire pretension for the novel clamping system ranged between 12 and 16 %. The average loss for conventionally clamped wires was 75 %. The advantages of the novel clamping system were the much greater ability to sustain the transverse load and the easy and effectual wire re-tensioning. Although wire slippage has been avoided with the novel system, wire material yield is still responsible for a pretension loss. Keywords Ilizarov external osteosynthesis  Threading  Force sensor  Wire pretension C. Bairaktari  G. Athanassiou  D. Deligianni (&) Laboratory of Biomechanics and Biomedical Engineering, Department of Mechanical Engineering and Aeronautics, University of Patras, 26500 Rion-Patras, Greece e-mail: [email protected] E. Panagiotopoulos Department of Orthopaedics, School of Medicine, University of Patras, 26500 Rion-Patras, Greece

Introduction The biology and modular system of external fixation developed by Ilizarov have revolutionised orthopaedic care. Nowadays, it is used globally in fracture healing, limb lengthening, in bone deformities correction, nonunion and bone defects and, increasingly, for the stabilisation of simple and complex fractures [1]. The major advantage of this procedure is that because the apparatus provides adequate support during bone union the patient remains active enhancing recovery. The Ilizarov method affords the asset of percutaneous fixation of the fracture without disturbing a precarious soft tissue envelope [2]. There is a general agreement that the pretensioning of the transosseous Kirschner wires is the most substantial aspect of the technique, which specifies the success of the method [2–4]. This criterion constitutes a whole field in the Ilizarov technique that affects the method in many ways. In the same time, wire tensioning demands specific operation and depends on several factors. Wire tensioning provides the apparatus with the requisite stability that leads to a successful treatment [2, 3, 5–7] as it is indissolubly associated with the internal stability of the treated segment which designates the fracture site motion [8, 9]. During treatment, the patient is encouraged to bear weight on the limb through normal activity. The resulting forces induce intermittent motion between bone fragments (interfragmentary motion), contributing beneficially in the process of bone healing [10]. Many scientists point the loss of the initial pretension of the wires as a main component of complications such us pain, delayed fracture healing and inflammation in the surrounding tissues, like pin tract infection that can decrease the stability of the pin–bone interface [6, 11, 12]. Thus, proper wire tensioning that would be maintained throughout the whole healing period brings about a suitable

123

Eur J Orthop Surg Traumatol

balance in the stability and flexibility of the frame [5, 6, 11]. However, wire tension is not maintained at its proper level during the whole treatment. Many scientists have studied the loss of wire tension that occurs immediately after removing the wire tensioner [13, 14] and during the loading of the frame [6, 13–16]. This loss is attributed by many scientists to the slippage of the wires through the clamps, since the existing clamping system of the frame is based on the fastening of the wires by frictional forces. Another reason responsible for this loss is the material yielding [17], as a result of bolt tightening in combination with the cyclic wire loading which causes plastic deformation of the wire at the clamp location [5, 9, 13–16]. However, a combination of the two above reasons (slippage, material yielding) could be culpable of the lost tension [10, 19]. Re-tensioning of the wires is possible, although difficult since the wire ends are bent during the surgery in order to avoid harms from their sharp ends. In other cases, wire retensioning cannot be performed due to complete lack of wrench access to the wire connection bolt and nut (i.e., all nearby holes are occupied). This situation dictates wire replacement, which is in fact a full-fledged adjustment procedure [11]. Our research focuses on the design and evaluation of a novel wire tensioning and clamping system that will minimise or even diminish the loss of pretension after clamping to the Ilizarov device rings and during the dynamic loading of the frame, sharing in the same time the capability of an easy and effectual re-tensioning of possible slack wires.

Materials and methods The wires used throughout this study were made from stainless steel 316, 370 mm in length and with a diameter of 2.0 mm. The external fixator was the original Ilizarov device (Smith and Nephew, Hellas S.A.). Description of the novel clamping system design Our fixator consisted of smooth and fine wires which were attached to 160 mm diameter rings. The basic principle of the novel system was the application of a firm, stable and unfaltering but simultaneously adjustable anchor system of the wires to the rings, instead of their anchoring only by friction forces through the bolt. For this purpose, one end of each wire was threaded in 20 mm length (with an outside diameter of 2.0 mm, and a pitch of 0.40 mm) and supplied with a M2.0 nut (Fig. 1). The other end was clamped to the corresponding ring with a custom-made stopper in such a way that no slippage was possible

123

(Fig. 2b). In this configuration, the wire pretension is achieved through the nut tightening torque applied according to the readings of a load cell. The nut is twisted against the side of the ring, which was configured in a suitable shaping (Fig. 2a). The threaded wires can be easily tensioned simultaneously, in contrast to the conventional clamping systems, preventing the corresponding rings from being distorted. Moreover, the wires can be easily re-tensioned in case of losing their pretension by nut twisting, regaining thus initial tension and providing increased stability. The determination of the wire thread characteristics and the thread strength were calculated in the ‘‘Appendix’’. Experimental set-up and measurements The standard Ilizarov frame (4 rings, 8 wires) is symmetrical with respect to the fracture site. Thus, we concentrated our measurements only on the upper 2 rings (4 wires) of the system. The experimental set-up (Fig. 3) consisted of a polyethylene bar with a diameter of 33 mm, which represented the bone fragment. The polyethylene bar was suspended on an Ilizarov frame that consisted of 2 stainless steel rings (diameter 160 mm) (Smith and Nephew, Hellas S.A.). Each ring supported two wires, at a crossing angle of 60° [20], with a diameter of 2.0 mm (Smith and Nephew, Hellas S.A.) that were drilled through the bar. The distance between the rings was 9.3 cm. The arrangement was assembled in order the polyethylene cylinder to be positioned in the centre of the frame for better stability of the apparatus [7]. For the attachment of the frame on the loading machine, we added a third ring with a bolted steel plate on the frame. Experiments were performed with two configurations. At the first configuration, the wires were fixed on the rings through the novel clamping system. The device was equipped with a force transducer (wire tension force sensor BB1, K&K group, Rostov on Don, Russia) that was able to monitor the forces in the wire (Fig. 4). The transducer was attached on one wire each time, for the continuous control of the wire tension before and during loading. The transducer had a rated capacity of 1,000 N, with 200 N overload. Tensioning of the wires was performed by screwing the threaded wire’s nut having, at the same time, the control of the imposed wire tension, in order to stop tensioning when the desired value was approached. During this procedure, the number of the nut turns which leaded to the desired wire tension was noted, in order to apply the same pretension at the rest of the wires which were not supplied with force transducers as mentioned above. Hence, pretension was monitored for one individual wire each time during the experiment. At the second configuration, slotted connection bolts where selected to hold all wires with frictional forces on the

Eur J Orthop Surg Traumatol Fig. 1 The proposed threadtype clamping and re-tensioning system. Left schematic drawing of the system on a part of the Ilizarov device ring. Retensioning is achieved by twisting the nut against the side of the ring. Right photograph of the assembled Ilizarov frame with the novel clamping replacing the bolted clamps

Fig. 3 Experimental set-up for dynamic load application

Fig. 2 Suitable shaping of the ring side for the attachment of the novel tensioning system (a) and the wire end, using a custom-made stop (b) on the circular frame of the Ilizarov device

ring, because of their slightly improved holding capacity in comparison with cannulated bolts [21]. The tightening bolt torque was 15 Nm [14] and was performed by a torque wrench with range 10–60 N m (M9256820). Tensioning of the wires was performed by the dynamometric wire tensioner that escorts the Ilizarov system. After fixing one end of each wire, the wire was pretensioned. When the desired amount of pretension was applied, the ‘‘free’’ end of the wire was attached to the ring using a slotted bolt. The wire pretension for the novel configuration ranged between 500 and 900 N approximately, according to the transducer’s reading. For the conventional configuration, 800–900 N wire pretension was applied, according to the scaling on the dynamometric tensioner (Smith and

Fig. 4 The clamping system was equipped with a custom-made force transducer that was able to monitor the wire tension during dynamic loading

Nephew, Hellas S.A.). Wires attached to the same ring were tensed simultaneously in order to distribute the tension to the wires evenly, and to prevent deformation of the rings.

123

Eur J Orthop Surg Traumatol

All experiments were done with this basic set-up. Each configuration was tested t times for each pretension level, and all tests were performed with the same bolts, nuts and Ilizarov rings. New wires were used for every test. To minimise the effect of possible material wear and plastic deformation, the tests with the various configurations were performed in random order. The complete frame was placed under a MTS 810 Material Test System machine and tested with a transverse (in respect to the wires) dynamic load of 0–800 N, for 600 cycles at a frequency of 0.5 Hz [14].

Fig. 6 A typical single wire stress versus time, after the application of pretension (A and B) until the moment of dynamic load application (C and D) for the two clamping systems 1000

Remaining wire tension, N

Fig. 5 Bone deflection for the two experimental configurations in different wire pretention values. Fix50–90: novel clamping system with 500–900 N of pretension. Slot 80: conventional clamping system with 800 N of pretension

900 800 700 600 500

conventional

400

new system

300 200 100 0 -100

Statistics The maximum axial displacements of the polyethylene bar of both configurations were analysed for statistical differences with ANOVA with Tukey HSD post hoc tests. The statistical analysis was performed with SPSS version 12.01 (SPSS Inc., Chicago, USA).

Results The axial displacement of the polyethylene bar, which represented the bone fragment, increased with decreasing pretension of the wire, as it was expected. Figure 5 displays the relationship between the wire pretension and the axial displacement of the polyethylene bar, at various pretension values. The results gave less axial displacement when the novel clamping system was used in comparison with the conventional system, at a similar pretension level. The mean maximum axial displacement of the polyethylene bar at pretension of 800 N with the novel clamping system was 4.90 mm (SD 0.20), whereas with the conventional system, it was 6.02 mm (SD 0.48). The maximum axial displacement between the two systems was significantly different. Figure 6 shows a typical graph of a single wire stress versus time after the application of the pretension (900 N)

123

0

100

200

300

400

500

600

Loading cycles

Fig. 7 Comparison of the two clamping systems in respect to the remaining wire tension during dynamic loading for 20 min

and the bolts tightening (a and b) until the moment of dynamic load application (c and d) for the two clamping systems. Every wire in all tests with the conventional clamping system showed a loss of pretension after tightening of the bolts to attach the wires to the rings. The average loss in pretension of the wires with the conventional clamping was about 15–30 % of the provided initial pretension. No pretension reduction was observed immediately after tightening the novel clamping system (Fig. 7). Wire pretension was reduced after 1,200 s of dynamic load application in both clamping systems. Moreover, rapid tension loss was observed in both systems reaching a steady state within \200 cycles applied. The tests performed with the conventional clamping system showed a further average pretension loss of 71.7 % at pretension levels of 900 N, resulting in total loss more than 85 %. Applying a dynamic load of 800 N on the novel system with 500–850 N pretension level, the total pretension loss was restricted to an average of 14.3 ± 1.55 % of the initial pretension, for all pretension levels (Table 1). In order to explain the loss of pretension in the novel system, stereoscopic images of the wire thread before and

Eur J Orthop Surg Traumatol Table 1 Average wire tension values measured at the 0th cycle and 600th cycle of dynamic loading

Type of fixator Conventional Novel

Pretension, N

Tension at 0th cycle, N (mean ± SD)

Tension at 600th cycle, N (mean ± SD)

Reduction, % of the tension at 0th cycle

800

600 ± 31.2

117 ± 35.2

80.5

900

748 ± 40.3

212 ± 7.4

71.7

500

496 ± 22.2

419 ± 33.1

15.6

600

609 ± 10.8

515 ± 24.1

15.8

700

738 ± 37.7

630 ± 27.6

14.6

800

793 ± 15.2

691 ± 22.4

12.9

900

864 ± 12.7

749 ± 19.7

12.4

Fig. 8 Plastic deformation of the wire at bending sites

after load application were taken. Close observation of the wire threads after disassembling showed that the threads of the wire were not deformed at all. However, permanent deformation was observed at the bends in the wires, i.e. adjacent to the polyethylene bar or over the ring (Fig. 8) at all pretension levels. This plastic deformation can explain the loss of pretension after the dynamic loading.

Discussion In the conventional clamping system, the fine wires of Ilizarov fixator are clamped on the rings of the apparatus by connection bolts that hold the wires through frictional forces. The wires lose their initial pretension, being the weak part of Ilizarov device. The causes of the loss of pretension are slippage [13–15, 22], material yield location [18, 23] or a combination of both [10, 16, 19]. Improvement in the design of wire fixators has been recognised to be necessary. In this context, our team proceeded in the design of a novel clamping system that would fix the wires onto the frame, alleviating the conventional disadvantages. The present study was part of a larger project aiming to design an integrated novel fixator of the wires on the rings of the Ilizarov device, in such a way that the wire pretension would be minimised or even diminished. Moreover,

any pretension loss will be detected, digitalised and transferred to the physician, providing the possibility for optimal tensile adjustment by the patient himself under real-time distant medical supervision. The proposed device, incorporating sensors and tele-support services, will be more expensive than the conventional one, but in this case, the cost will compensate for reduced hospital services that the device will provide. A number of wire tensioning systems are going to be designed and studied, with a capability of re-tensioning, in the simplest, most comfortable and most time efficient way. The proposed in this work clamping and tensioning system is a simple mechanical gripping device, complying with the above requirements. The new clamping implements two main improvements: The first is the easy and effectual wire re-tensioning by twisting the bolt against the ring, which elongates the wire in its initial direction. Currently, trying to re-tension the wire, by twisting the conventional slotted or cannulated bolt, results in an angular peripheral move of the wire, imposing possibly stresses on the bone at the pin entrance. The second improvement is its capacity to maintain a higher wire pretension. A number of efforts have been performed to prevent the loss of Ilizarov wire tension by optimising tightening torques [19, 21, 24, 25] or designing a ruffled wire–bolt interface [21]. This is the first study that has tried to

123

Eur J Orthop Surg Traumatol

diminish the loss of the tension through a novel clamping system of fine threaded wires. The proposed novel clamping system was tested mechanically by dynamic loading, and it was compared with the conventional one, used in the clinical practice. Slotted bolts were only examined, which tightened the wire edges with a torque of 15 N m. This torque was chosen following literature suggestions, showing that 10 N m [25] is too low to preserve the pretension [15] and torque above 18 N m causes shearing (or even failure [16]) of the bolts and creates mechanical deformation of the wires which results to disability of pretension maintenance [19]. The ideal initial wire pretension for the Ilizarov frame stability is not known. The exact amount of tensioning depends on many variables, like local frame construction (half rings vs. complete rings, offset vs. main ring wire), local bone condition (osteoporosis vs. normal bone), weight of the patient (small child vs. large adult) and functional wire loading (stabilization vs. dynamic loading). Ilizarov recommended wire tensions in the range 90–130 kg, for load bearing areas, dependent on the age and weight of the patient [11]. Through clinical experience, it has been proved that wire tension can range between 50 and 130 kg (490–1,274 N) and it is applied according the above variables. In this work, pretension up to 900 N was applied on all wires. This pretension value was chosen because, along with the vertically applied load, it represented the maximum load that the coarse (according to ISO Metric Coarse Pitch Series-AS1275-1985) thread of the Smith and Nephew stainless steel wires of 2.0 mm diameter could bear. In general, the novel clamping system showed a much greater ability to sustain the transverse load with smaller displacement of the polyethylene bar. The mean displacements measured in our experimental set-up for the conventional system were comparable to those found by other researchers [13, 16]. The displacements of the novel system were comparable to those found by the parametric analysis with finite elements by Hillard et al. [18], which were attributed to plastic deformation of the wires at bending sites, without slippage. However, the measured tension loss in our experiments was higher that the calculated by Hillard et al. [18], although these data represented larger ring diameter. This can be probably attributed to the material properties assigned to the wires in the finite element models. It has been found that a reduction of the imposed wire tension in the conventional clamping system starts already after tightening the wires to the ring and removal of the wire tensioning device [13, 15, 16, 18, 26]. Further considerable tension loss is measured during the weightbearing period [13, 15, 16, 18]. The reduction of pretension that occurs in the first stage, immediately after tightening

123

of the bolts and is probably due to wire slippage, was found in our experiments that was about 15–18 % of the imposed initial pretension. This value is lower than the findings of La Roussa et al. [14], Renard et al. [15], and Aquarius et al. [13], which were about 20, 22 and 24 %, respectively. The reason for the lower pretension loss, found in this study, was the lower initial pretension values used. It seems that, the friction forces which are intended for holding the fine wires tensioned are not adequate to keep them in place. Concerning the remaining wire tension after dynamic loading, although the novel clamping system proved to be considerably improved in comparison with the conventional one, a loss of tension was observed, originated probably from the plastic deformation of the wire at bending sites. Macroscopic and microscopic images showed that the deformed region is the areas where the wire bends over the ring. Moreover, at the contact area between the ring and the wire, the wire threads look flattened at the compressed side of the bending wire. Finite element analyses or analytical modelling of the conventional system, have found stresses, higher than yield point, in the wires close to the clamp sites resulting in material yielding [10, 17, 18, 23], leaving the wire segments between the clamps and the bone in the elastic behaviour zone. Our experimental work has verified these findings. The clamping system lends itself for further development. To minimise the degree of wire de-tensioning which occurs during function, a number of design optimisation procedures of the proposed clamping system will be considered: the diameter of the wires can be increased along the whole length of the wire or tapered wires can be constructed, with gradual increase of their diameter and the creation of the thread at the end of larger diameter. A further optimisation regarding the fixation of the clamping device on the ring in a way that occupies minimum number of ring holes will be performed. Different wire material with increased yield strength (e.g. 410 stainless, yield strength 965 MPa) can be used in order to avoid plastic deformation. Additionally, for further development of a novel clamping system, future work might implement destructive tests for pin breaking, as well as dynamic loading for longer time periods.

Conclusion Experimental evaluation led to the conclusion that the novel clamping and tensioning system constitutes an improved system in comparison with the conventional, providing a more accurate axial alignment of the wires during tightening, retaining the pretension during dynamic loading and allowing precise consecutive adjustment of each wire by the patient with the load sensors readings.

Eur J Orthop Surg Traumatol

The results showed that, although wire slippage through the clamps or wire squeezing at the clamping site have been avoided in the novel system, material yield is still responsible for system yield, as in the conventional one. Apparently, the wires with a diameter as small as 2.0 mm are probably not capable to treat lower limb conditions safely and undertake the corresponding patient weight, without having even a small pretension loss. Acknowledgments This work was financially supported by 7th Framework Programme, LEAD ERA Project, Call 2011: E-IlizaDevelopment of an e-health system in orthopedics. Conflict of interest

None.

Appendix The used wire thread was M2.0 and the corresponding dimensions (Fig. 9) were taken from the thread data chart (metric thread–coarse pitch): P = 0.40 mm; d2 = 1.740 mm; d3 = 1.509 mm; D1 = 1.567 mm; h3 = 0.245 mm; h1 = 0.217 mm; r = 0.058. The thread was pretensioned at a tension PPT = 880 N. After the application of the transverse dynamic load, each wire was loaded with an added load of DP = 100 N (value determined experimentally). Thus, the total maximum load for each wire was: PF ¼ PPT þ DP ¼ 880 N þ 100 N ¼ 980 N: The mean load applied on the thread was: Pm ¼

Pmin þ Pmax PPT PF ¼ þ ¼ 920N 2 2 2

and the alternating load was: Pr ¼

Pmax  Pmin DP ¼ 50N: ¼ 2 2

The corresponding applied stresses were:

Fig. 9 Configuration and dimensions of the metric thread

rm ¼

Pm Pm ¼ 2  ¼ 391:50 MPa; A3 pd2 4

rr ¼

Pr Pr ¼ ¼ 21:30 MPa, A3 pd22 =4

where d2 was the mean wire diameter d2 = 1.740 mm Using the Sodeberg criterion, the equivalent stress is given by the equation sy sy req ¼ rm þ rr  ð1Þ se N where sy, is the yield limit in shear strength and se, the yield limit in alternating shear strength. The wires used in our experiments were made of stainless steel 316L with sy = 520 MPa and se = 90 MPa. With the above values, Eq. (1) gives req = 514 MPa. Assuming a coefficient of safety N = 1, req = 514 MPa \ sy/N = 520 MPa and the Sodeberg criterion was satisfied.

References 1. Asaduzzaman M, Rahman QB, Aziz S et al (2010) Mandibular deformity correction by distraction osteogenesis. BSMMU J 3:103–106 2. Narayan B, Marsh DR (2003) (iv) The Ilizarov method in the treatment of fresh fractures. Curr Orthop 17:447–457 3. La Russa V, Skallerud B, Klaksvik J, Foss OA (2010) Wire tension versus wire frequency: an experimental Ilizarov frame study. J Biomech 43:2327–2331 4. Board TN, Yang L, Saleh M (2007) Why fine-wire fixators work: an analysis of pressure distribution at the wire–bone interface. J Biomech 40:20–25 5. Dong Y, Saleh M, Yang L (2005) Quantitative assessment of tension in wires of fine-wire external fixators. Med Eng Phys 27:63–66 6. Gessmann J, Jettkant B, Schildhauer TA, Seybold D (2011) Mechanical stress on tensioned wires at direct and indirect loading: a biomechanical study on the Ilizarov external fixator. Injury 42:1107–1111 7. Catagni MA, Guerreschi F, Lovisetti L (2011) Distraction osteogenesis for bone repair in the 21st century: lessons learned. Injury 42:580–586 8. Bronson DG, Samchukov ML, Birch JG et al (1998) Stability of external circular fixation: a multi-variable biomechanical analysis. Clin Biomech 13:441–448 9. Antoci V, Voor MJ, Antoci V Jr, Roberts CS (2007) Effect of wire tension on stiffness of tensioned fine wires in external fixation: a mechanical study. Am J Orthop 36:473–476 10. Watson MA, Mathias KJ, Maffulli N, Hukins DWL (2003) The effect of clamping a tensioned wire: implications for the Ilizarov external fixation system. Proc Inst Mech Eng H J Eng Med 217:91–98 11. Golyakhovsky V, Frankel VH (1993) Operative manual of Ilizarov techniques. Year Book Medical Pub, Chicago, pp 2–91 12. Parameswaran AD, Roberts CS, Seligson D, Voor M (2003) Pin tract infection with contemporary external fixation: how much of a problem? J Orthop Trauma 17:503–507 13. Aquarius R, van Kampen A, Verdonschot N (2007) Rapid pretension loss in the Ilizarov external fixator: an in vitro study. Acta Orthop 78:654–660

123

Eur J Orthop Surg Traumatol 14. La Roussa V, Skallerud B, Klaksvik J, Foss OA (2011) Reduction in wire tension caused by dynamic loading. An experimental Ilizarov frame study. J Biomech 44:1454–1458 15. Renard AJS, Schutte BG, Verdonschot N, van Kampen A (2005) The Ilizarov external fixator: what remains of the wire pretension after dynamic loading? Clin Biomech 20:1126–1130 16. Delprete C, Gola MM (1993) Mechanical performance of external fixators with wires for the treatment of bone fractures—Part II: wire tension and slippage. J Biomech Eng 115:37–42 17. Zhang G (2004) Avoiding the material nonlinearity in an external fixation device. Clin Biomech 19:746–750 18. Hillard PJ, Harrison AJ, Atkins RM (1998) The yielding of tensioned fine wires in the Ilizarov. Proc Inst Mech Eng H J Eng Med 212:37–47 19. Osei NA, Bradley BM, Culpan P et al (2006) Relationship between locking-bolt torque and load pretension in the Ilizarov frame. Injury 37:941–945 20. Spiegelberg B, Parratt T, Dheerendra SK et al (2010) Ilizarov principles of deformity correction. Ann R Coll Surg Engl 92:101–105

123

21. Gessmann J, Jettkant B, Konigshausen M et al (2012) Improved wire stiffness with modified connection bolts in Ilizarov external frames: a biomechanical study. Acta Bioeng Biomech 14:15–21 22. Aronson J, Harp JH (1992) Mechanical considerations in using tensioned wires in a transosseous external fixation system. Clin Orthop Rel Res 280:23–29 23. Zamani AR, Oyadiji SO (2008) Analytical modeling of Kirschner wires in Ilizarov circular external fixator using a tensile model. Proc Inst Mech Eng H: J Eng Med 222:967–976 24. Davidson AW, Mullins M, Goodier D, Barry M (2003) Ilizarov wire tensioning and holding methods: a biomechanical study. Injury 34:151–154 25. Mullins MM, Davidson AW, Goodier D, Barry M (2003) The biomechanics of wire fixation in the Ilizarov system. Injury 34:155–157 26. Gasser B, Boman B, Wyder D, Schneider E (1990) Stiffness characteristics of the circular Ilizarov device as opposed to conventional external fixators. J Biomech Eng 112:15–21

Towards a solution of the wires' slippage problem of the Ilizarov external fixator.

Clinical experience has indicated that many complications during treatment with the Ilizarov method, and mainly tract infection, are related to decrea...
867KB Sizes 0 Downloads 2 Views