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Results and biomechanical consideration of treatment of congenital lower limb shortening and deformity using the Ilizarov method

Morasiewicz P., Morasiewicz L., Stępniewski M., Orzechowski W., Morasiewicz M., Pawik Ł., Wrzosek Z., Dragan S.

Acta of Bioengineering and Biomechanics

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2014

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Vol. 16, no. 1

133--140

EN

One of the applications of the Ilizarov apparatus is the correction of congenital shortening and deformities. Ilizarov external fixator produces biomechanical structure with surrounding tissue, which is the reason why very important is correct stability of fixator. Large distraction in the case of high value of lengthening, and large deformity corection result in shear stresses that occur additionally in the regenerate, which can potentially lead to damage of the regenerating nutritive microcirculation of bone tissue and bone fragment displacements. Our objective was to assess the results of the Ilizarov method in the treatment of congenital shortening taking into account treatment strategy and the size of the axis of lengthening and correction. Our research problems include presenting the effects of biomechanics of musculoskeletal deformations on treatment results, presenting complications and their treatment. Between 1989 and 2009, 62 patients underwent surgery to correct congenital lower limb deficiencies at our Clinic; 33 patients were followed-up. In total, there were 70 surgeries (2.12/patient). Axial correction was performed in 26 patients (78.79%). Average age at the start of the treatment was 15.58 years. Mean follow-up was 8.58 years. Mean lengthening per surgery was 3.17 cm with the lengthening index of 50.7 day/cm. Results were very good for 23 patients, good for 7 patients, satisfactory for 3 patients. Complications appeared in 24 patients, problems occurred in 74.42% of the cases, obstacles in 4.65% of cases, and true complications in 20.93% of the cases. The best results were achieved in the treatment of patients with two-stage and two-segment lengthening with a total elongation of less than 7 cm, and without correction of the axis. Congenital shortening of the lower limb should be treated comprehensively because the shortening applies to all segments, and disturbs biomechanics of all lower limb. In the case of axial correction and large amount of elongation high soft tissue forces counteract the distraction forces. Hybrid construction may help to shorten treatment time, increase fixator stability and decrease rate of complications. We suggest use of hybrid Ilizarov fixator, especially when large elongation and axis corection are planned.

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Pedobarographic evaluation of body weight distribution on the lower limbs and balance after derotation corticotomies using the Ilizarov method

Morasiewicz P., Dragan S

Acta of Bioengineering and Biomechanics

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2013

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Vol. 15, no. 2

91--96

EN

Distortion of the axis and shortening of the limbs result in multiple musculoskeletal pathologies. Rotation disorders should also be included among the disorders of the axis of the lower limb. In the case of rotational distortion, only derotation osteotomy can effectively correct torsion-associated deformations. Rotational distortion correction is accompanied by translational displacement and torsion, which results in more complex biomechanics. Using the pedobarographic platform, it is possible to evaluate static and dynamic posture and gait, percentage of body weight distribution on the lower limbs, and balance. Physiological gait and distribution of weight on the lower extremities are symmetrical. Balance is one of the determinants of proper biomechanics of the musculoskeletal system. An important aspect of treatment evaluation is pedobarographic assessment of balance and body weight distribution on the lower extremities ratio. The aim of this work was to evaluate the pedobarographic assessment of body weight distribution on the lower limbs and balance in patients with derotation corticotomies using the Ilizarov method. The study examined a group of 56 patients, who underwent derotation corticotomy using the Illizarov method between 1996 and 2012 at the Clinic of Orthopaedics and Traumatology of the Musculoskeletal System in Wrocław. The control group consisted of 54 patients, who were treated with correctional derotation-free corticotomy using the Ilizarov. Distribution of body weight on the lower limbs and balance were assessed with the pedobarographic platform. Following derotation corticotomy, the amount of body weight placed on the operated limb by subjects from the study group averaged 47.81%, 52.19% in the case of the healthy limb. These differences were not statistically significant. The difference between the average percentage of body weight placed on the diseased and healthy limb in the study group and the controls were not found to be statistically significant. There were no statistical differences in the average length of the gravity line or in the average surface area of the center of gravity position between the study and control groups. Balanced distribution of body weight on the lower limbs was achieved following derotation corticotomies using the Ilizarov method. Derotation corticotomies performed with the Ilizarov method allow for achieving normalization of body weight distribution on the lower limbs and balance, with values similar to those resulting from Ilizarov method derotation-free osteotomy.

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The impact of the type of derotation mechanism on the stiffness of the Ilizarov fixator

Morasiewicz P., Filipiak J., Konietzko M., Dragan Sz.

Acta of Bioengineering and Biomechanics

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2012

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Vol. 14, no. 1

67-73

EN

One of the applications of the Ilizarov apparatus is the correction of rotational deformities. There are several types of designs commonly used for derotation. Different types of derotators have different mechanical properties, which affect the stability of the entire Ilizarov apparatus. The aim of this study was to determine the stiffness of the Ilizarov fixator depending on the type of derotation mechanism. We analyse three types of derotators: the type Z, the type H, and the cubicoid derotator. The tests were conducted on physical models in which the fixator analysed was fitted to polyethylene pipe segments. The reference fixator was the Ilizarov apparatus in the configuration adapted for thigh lengthening. The pipe segments intersected at a point corresponding to the osteotomy site of the distal thigh. The fixator was assembled with one proximal arch fixed with two Schanz screws, a proximal ring fixed with two Kirschner wires (K-wires), a middle free ring, and a distal ring fixed with three K-wires. There were three different types of derotation mechanisms installed between the proximal and middle rings. We determined the axial stiffness kA and the transverse stiffnesses of the compared fixators in two planes: frontal kM-L and sagittal kA-P. The results of the research lead to two basic conclusions. Firstly, the use of any of the derotators analysed has no negative impact on the stiffness of the Ilizarov apparatus. Secondly, similar stiffness values of the fixators with different derotation mechanisms suggest their equal applicability and the choice between them can be made based on practical considerations. In the case of axial stiffness, the differences do not exceed 7.5%. The highest value of stiffness kA was obtained for the type H derotator, while the lowest value was obtained for the type Z derotator. There is a greater difference in the case of transverse stiffness in the sagittal plane, which only concerns the fixator with the type Z derotators. The stiffness coefficient kA-P for that fixator is lower by approximately 19% compared to the reference fixator.

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Improved wire stiffness with modified connection bolts in Ilizarov external frames: a biomechanical study

Gessmann J., Jettkant B., Königshausen M., Schildhauer T.A., Seybold D.

Acta of Bioengineering and Biomechanics

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2012

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Vol. 14, no. 4

15-21

EN

Frame stability in Ilizarov external fixators is mainly dependent on the tension of the transosseous wires, which are clamped to the ring by connection bolts. It was the purpose of this biomechanical study to investigate the holding capacity of a modified bolt design featuring a ruffled wire-bolt interface (TrueLokTM0 and its influence on wire stiffness in comparison with that of classic bolts featuring a smooth, unruffled wire-bolt interface. Six different ring and bolt configurations were tested using a simplified model consisting of a single ring and wire. The holding capacity at two different tightening torques (10 and 14 Nm) of classic cannulated bolts (CB) and slotted bolts (SB) was determined on Ilizarov and Taylor Spatial Frame (TSFTM) rings, whereas the modified TrueLokTM CBs and SBs were used with the TrueLokTM rings. The wire stiffness was calculated via a regression analysis of the load-displacement graphs. The modified TrueLokTM bolts demonstrated significantly better slippage resistance than the classic bolts in all configurations and wire stiffness was significantly higher in the TrueLokTM frame set-ups. After maximum loading, all of the wires showed plastic deformation, including constant wire deflection and dent marks at the clamped wire ends. In conclusion, the decrease in wire stiffness can be explained mainly as a result of wire slippage, but plastic deformation and material yielding also contribute. The relatively simple modification made by roughening the wire-bolt interface results in improved holding capacity and wire stiffness. A frame that contains these modified TrueLokTM bolts should provide improved mechanical stiffness.

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Assessment of the effect of hybrid implant systems in the Ilizarov fixator on the stability of fragments of the femur subjected to elongation

Filipiak J., Morasiewicz L.

Acta of Bioengineering and Biomechanics

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2001

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Vol. 3, nr 1

15-24

EN

Possible ways of improving the stability of the fragments of the femur under elongation by introducing hybrid implant systems (the Kirschner wires and the Schanz screws) into the Ilizarov fixator structure were explored. Laboratory studies were conducted on physical models with the fixator mounted on a pipe section modelling the femur shaft. Ten modifications of the Ilizarov fixator were developed and tested. The designs differed in the kind and configuration of implants. The effect of the developed Ilizarov fixator designs was examined by comparing the coefficients of axial, transversal and torsional rigidity of the structures. The research results clearly show that the Ilizarov fixator's rigidity (particularly transversal rigidity) coefficients can be considerably increased by replacing the Kirschner wires with the Schanz screws or using hybrid systems of these implants. As a result, the stability of the femur fragments improves and so does the quality of the regenerated bone, which makes it possible to reduce the treatment time to a minimum.