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LETTER TO THE EDITOR
Year : 2018  |  Volume : 4  |  Issue : 1  |  Page : 60-62

Respond to the letter to the editor about the article “analysis of strut-to-bone lengthening ratio for hexapod frames using mathematical modeling”


Center for Excellence in Limb Lengthening and Reconstruction, Texas Scottish Rite Hospital for Children, Dallas, TX, USA

Date of Web Publication3-May-2018

Correspondence Address:
Dr. Alexander Cherkashin
Texas Scottish Rite Hospital for Children, 2222 Welborn Street, Dallas, TX 75219
USA
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jllr.jllr_8_18

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How to cite this article:
Cherkashin A. Respond to the letter to the editor about the article “analysis of strut-to-bone lengthening ratio for hexapod frames using mathematical modeling”. J Limb Lengthen Reconstr 2018;4:60-2

How to cite this URL:
Cherkashin A. Respond to the letter to the editor about the article “analysis of strut-to-bone lengthening ratio for hexapod frames using mathematical modeling”. J Limb Lengthen Reconstr [serial online] 2018 [cited 2018 Dec 18];4:60-2. Available from: http://www.jlimblengthrecon.org/text.asp?2018/4/1/60/231790

We are delighted that the article draws so much attention and concern from the surgeons using hexapod frames for deformity correction and lengthening. Discrepancy between the amount of strut length and bone length increase though quite obvious was never mentioned in the literature before. I was also rather amazed to find that most of the surgeons were not aware of such a difference.

We absolutely agree with Dr Lovisetti's corrections of the geometrical explanation of the phenomenon. Obviously he is much more skilled in geometry than we are. When we made illustration for the article, we traded geometrical precision for the visual appearance. And while the mistake was made, it actually resulted in an underestimation of the discrepancy between amount of the bone length increase and the strut lengthening.

However, when making calculations for the frame height increase per 1 mm strut length increase [Table 1] in the article: Vol. 3, Issue 1, p. 47], we did not use the geometrical calculations. Instead, all of the numbers were calculated by the TSF software (Smith and Nephew, Inc. Memphis, Tennessee) using chronic mode. All allowable neutral strut lengths (from 75 to 311 mm) were entered on the Strut Settings page of the software with 1 mm increment. For each strut length, initial and final frame heights were calculated by the software. Therefore, results of the real discrepancy are recognized and presented by the software. In addition, we validated all the measurements by building the real frames and measuring the discrepancy between strut lengthening and frame height increase.
Table 1: Frame height increase per 1 mm strut length increase for each particular neutral frame height as calculated by the TSF software

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Since the article was published, there is more awareness about this problem and also there are newer hexapods on the market, which allow <1 mm increment of strut length adjustment. Ability to go with smaller increment will allow performing bone lengthening more gradually and closer to the original Ilizarov protocol. There is also the need for more studies to evaluate how gradually deformity correction in hexapod frames is affected by the strut-to-bone lengthening ratio.

We appreciate Dr. Lovisetti's interest in the problem and are very thankful for the correction. Hopefully, this will farther elevate awareness of the problem and development of different approaches to avoid possible complications.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.





 
 
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