Normative Values for Femoral Length, Tibial Length, and the Femorotibial Ratio in Adults Using Standing Full-Length Radiography

Round 1

Reviewer 1 Report

This paper details the use of radiography to measure limb length to give population averages which would be of use in limb reconstruction surgery. Overall the paper is concise, well-written and the conclusions well supported by the data and analysis

The only minor comment I have is that key to accurate measurement of limb length with radiography is to minimise parallax effects. Please include more details on how the scanning radiography system works and how the parallax effect is minimised, and if possible give an indication of the measurement error arising from this effect - is this at a similar level to the pixel size? Also what was the pixel size of the radiographs?

Author Response

Many thanks for your comments.

I have amended 2.2 and 2.3 to provide greater detail regarding consistent image capture and parallax concerns. The 'weak link' in the chain when making PACS measurements on radiographs is the monitor used, and I have added relevant information here.

Reviewer 2 Report

The article is interesting, But needs to address the following questions.

1. The sample size is predominantly male, Can the author include female scan data.
2. If they have omitted the female data, the reasons needs to be described.
3.  Did the author check if this model works on models pre and post surgical cases.

Author Response

Thank you for your comments.

1. Yes, there is a preponderance of male data, which reflects the gender distribution of patients who underwent lower limb alignment films at my hospital.
2. Women have not been deliberately omitted.
3. No, I have simply presented details of the normal range and relationship of lower limb lengths. I have not examined any cases of limb length discrepancy

Reviewer 3 Report

Thank you very much for your hard work in performing this very interesting study. 

Your study will have clinical significance as the first study to measure leg length.

I have made some comments below.

Introduction
Please explain in detail the necessity of leg length(femoral length, tibial length, and the  femoro-tibial ratio) measurement in the manuscript.

Results

Please fill out the table and present it in the manuscript.

Discussion

Please recapitulate the clinical value and strengths of this study and present it in the manuscript.

Author Response

Thank you for your comments.

I have amended the introduction and first two paragraphs of the discussion to provide further emphasis on the clinical relevance of the results presented here.

My apologies, I am unable to find the Results table you refer to.

Reviewer 4 Report

In this interesting, paper Stuart Aitken from Maine General Medical Center in Augusta, USA, reports the normative values for lower limb length by using the standing full-length radiographs of 753 patients (61% male) by employing PACS-software based length measurement method (PACS; Picture Archiving and Communication System; IntelliSpace Enterprise Version 4, The Netherlands). Lower limb length, femoral length, tibial length and the femorotibial ratio were measured in 1077 limbs, and the study found a moderately strong inverse linear relationship between tibial length and the corresponding femorotibial ratio, with excellent inter-observer reliability of the PACS method (ICC of 0.99). The study presents the normal range of values for lower limb length in adults and is the first to identify a linear relationship between tibial length and the femorotibial ratio. The experimental approaches are sound and state of the art and the PACS-based length measurement method used in this study might be used in future for post-traumatic cases. This is a well designed study including adequate number of subjects to do statistical analysis. For comparability to future studies and other reports, the authors should provide a comprehensive table summarizing all the major patient characteristics and also the COSONSORT form for patient inclusion/exclusion under point 2.1 Patients. The authors included 753 patients, but only 1077 lower limbs were analysed, why were the other limbs not suitable for measurement? What were the exact criteria for inclusion/exclusion of patients or limbs? From the 753 patients 459 (63%) were male, but the authors made no gender dependent correlations in their analysis. Do they see any differences in their ratios when they divide their patients gender dependent?

Author Response

Thank you for your helpful comments.

I have included a Table detailing the participants and inclusion / exclusion data.

Additionally, I have included more detail about gender as it relates to the femorotibial ratio. I did not find a difference between the sexes when looking at 'long tibiae' and 'short tibiae'. It seems that the ratio is associated with patient height (or more accurately 'lower limb length') than it is with gender.