Definition of a Global Coordinate System in the Foot for the Surgical Planning of Forefoot Corrections

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors worked in the Definition of a Global Coordinate System in the Foot. The research is interesting; however the manuscript needs some modifications.

 The authors say that the facies superior of the trochlea tali was manually drawn and the question is what kind of parameter were used to draw the trochlea tali

 The authors should provide a picture of the splint used o create a constant plantigrade foot and neutral 106 ankle position across patients.

 Finally the authors should provide information about softwares that may be used to generate the 3D foot model.

Author Response

Comments to the Author

The authors worked in the Definition of a Global Coordinate System in the Foot. The research is interesting; however the manuscript needs some modifications.

We want to thank the reviewer for the review work.

1. The authors say that the facies superior of the trochlea tali was manually drawn and the question is what kind of parameter were used to draw the trochlea tali

The facies superior of the trochlea tali was manually drawn using the Wave Brush Mark tool with a brush diameter of 6 mm in 3-Matics. We added the protocol for the construction of the coordinate systems in 3-Matic to the Supplementary Materials. (Protocol S1 line 123 and Protocol S2 line 125)

2. The authors should provide a picture of the splint used o create a constant plantigrade foot and neutral 106 ankle position across patients.

We agree with the reviewer. Therefore, we added a picture of the splint used to create a constant plantigrade foot and neutral ankle position across patients. (Figure 1 line 145)

3. Finally the authors should provide information about softwares that may be used to generate the 3D foot model.

This study generates the 3D foot model using Materialise’s Interactive Medical Image Control System 21.0 (Mimics v21.0, Materialise NV, Leuven, Belgium). Other software tools that may be used to generate the 3D foot model are 3D Slicer (https://www.slicer.org) and ITK-SNAP (http://www.itksnap.org/pmwiki/pmwiki.php). However, because the authors have no expertise with these software tools and the purpose of this study is not to generate a 3D foot model, the were not included in this paper.

Reviewer 2 Report

Comments and Suggestions for Authors

The development of a global coordinate system for forefoot correction planning is valuable. The emphasis on the repeatability and clinical relevance of CS1 and CS2 is noteworthy. The perfect repeatability of the automated CS2 is significant. This study offers an important contribution to forefoot osteotomy planning.
The manuscript is well written. The english language is well written. The methodology is perfectly followed. Figures are high quality. References are new and up to date. 

I suggest accepting this article as it is.

Author Response

Comments to the Author

The development of a global coordinate system for forefoot correction planning is valuable. The emphasis on the repeatability and clinical relevance of CS1 and CS2 is noteworthy. The perfect repeatability of the automated CS2 is significant. This study offers an important contribution to forefoot osteotomy planning.

The manuscript is well written. The english language is well written. The methodology is perfectly followed. Figures are high quality. References are new and up to date.

I suggest accepting this article as it is.

We want to thank the reviewer for his/her kind words and acknowledgement of the added value of our work.

Reviewer 3 Report

Comments and Suggestions for Authors Thanks to the authors for having presented such an interesting original article about “The definition of a Global CoordinationSystem in the foot for frefoot surgeries”. It is a well written manuscript that deals with a very comon pathology in the field of foot and ankle surgery. I believe that no revisions are necessary and it is suitable for publication even if major two weak points are present: - the necessity to perform a CT scan for patient with minor pathologies that are usuelly addressed with standard x-rays, with consequently more radiation exposure for the patient and more costs that appeared not justified - the weight-bearing is only simulated with te methods described and this bias could affect the results  Despite these points, it is a preiminary study that can followed but further studies, useful to make this technology more available

Author Response

Comments to the Author

Thanks to the authors for having presented such an interesting original article about “The definition of a Global CoordinationSystem in the foot for frefoot surgeries”. It is a well written manuscript that deals with a very comon pathology in the field of foot and ankle surgery. I believe that no revisions are necessary and it is suitable for publication even if major two weak points are present: - the necessity to perform a CT scan for patient with minor pathologies that are usuelly addressed with standard x-rays, with consequently more radiation exposure for the patient and more costs that appeared not justified - the weight-bearing is only simulated with te methods described and this bias could affect the results  Despite these points, it is a preiminary study that can followed but further studies, useful to make this technology more available

We want to thank the reviewer for this comment.

We agree with the two limitations as indicated by the reviewer. That is why we added in our discussion section the following:

- Fourthly, a limitation is the necessity of acquiring a CT scan for patients with minor pathologies. The availability of CT scanners can also differ from hospital to hospital or country to country. Although this is outside the scope of this study, quite some initiatives have been set up to transfer data from 2D radiographic images to a 3D digital model [31,32]. This might be a future solution to avoid the need for a CT scan for patients with minor pathologies. (Line 392-397)

- Thirdly, the weight-bearing condition is not taken into account in this study. Weight-bearing CT scanners (WBCTs) enables imaging of the foot to be done in the natural weight-bearing position. Weight-bearing widens the forefoot when the medial ray moves through the tarsometatarsal joint [25-28]. WBCT has the advantage of reduced radiation exposure [29,30] and it improves the evaluation of forefoot deformities [14,26,27]. However, the patients in this study could not stand in the CT scanner during image acquisition. The splint (Figure 1) provided the greatest possible replication of stance on a flat surface, maintaining a constant plantigrade foot and neutral ankle position across patients. It is believed that the use of this splint results in automatically selected points on the same level as in the weight-bearing situation, leading to a similar normal vector. Consequently, weight-bearing is believed to have little to no effect on the constructed coordinate system and its virtual images. Nevertheless, it is recommended to use WBCT for the evaluation of forefoot deformities when this is available in the hospital. (Line 377-392)

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Authors:

I want to congratulate with You for Your paper. Anyway, in my opinion, some revision is needed. There are major points that need to be addressed:

- First and second paragraphs of introduction can be united and shorten. 

- recurrence of deformity and nonunion are only some of the complication; more important (and a coordinate system could be of help for this) is subsequent metatarsalgia (to the 1st ray or transfer metatarsalgia to the lesser rays)

- line 89: among requirements there is "not include bones in the forefoot as they might be deformed." but for automatic CS the head of the 5th metatarsal bone and the 1st metatarsal/sesamoids complex are taken into account

- weight bearing is not taken into account; weight bearing (for foot&ankle bipodal WB X-rays are indicated) plays a major role in the alignement of the foot/forefoot; a splint cannot play the same role.

- CT scan can be seen as a too invasive methods to plan forefoot surgery;

- these CS take into account the talus, assuming the talus and the midfoot are normally aligned, which sometimes is not

- there is no clinical example of applicability of the present method; how can the usual measurements (useful to evaluate the foot pre-op, intra-op and post-op) be calculated with this method? how can the HV angle, the intermetatarsal angle, the Maestro line be calculated and expressed?

- being a "biomechanic" study, the computed algorithm should be offer as supplementary materials, and tables with CT parameters should be added

- a power analysis demonstrating that 9 cases are sufficient should be added

Comments on the Quality of English Language

minor revision is required

Author Response

Comments to the Author

Dear Authors:

I want to congratulate with You for Your paper. Anyway, in my opinion, some revision is needed. There are major points that need to be addressed:

We want to thank the reviewer for the review work.

1. First and second paragraphs of introduction can be united and shorten.

We agree with the reviewer. The first and second paragraphs of the introduction are now united and shortened. We changed this in: Surgical reconstruction of forefoot deformities is the most common and a frequently challenging pathologic condition that a foot and ankle surgeon treats [1]. In particular, forefoot corrective osteotomies to improve the alignment are difficult procedures and can lead to a variety of complications (i.e., metatarsalgia, recurrence of the deformity, and nonunion) [2-4]. Hallux valgus can typically be diagnosed through physical examination and standard weight-bearing lateral and anteroposterior (AP) radiographic two-dimensional (2D) images of the foot [5]. However, due to the rotational, multiplanar nature of hallux valgus, it is difficult to describe and quantify hallux valgus accurately and reliably on standard radiographic 2D images [6,7]. This can lead to unintentional corrections in untargeted planes during surgery [8]. Preoperative planning in three-dimensions (3D) might assist in successfully managing forefoot deformities. As the primary objective of 3D preoperative planning is to effectively correct the deformity, reduce postoperative morbidity and maintain normal foot biomechanics [4,9]. Computed tomography (CT) makes it possible to quantify the absolute and relative position and orientation of the bones in the foot and contributes to advanced knowledge of the multiplanar nature of hallux valgus. This might assist with the preoperative planning of hallux valgus corrections and may overcome the errors induced by 2D analysis [10,11]. (Line 25-41)

2. recurrence of deformity and nonunion are only some of the complication; more important (and a coordinate system could be of help for this) is subsequent metatarsalgia (to the 1^st ray or transfer metatarsalgia to the lesser rays)

We agree with the reviewer. We changed this line in: In particular, forefoot corrective osteotomies to improve the alignment are difficult procedures and can lead to a variety of complications (i.e., metatarsalgia, recurrence of the deformity, and nonunion). (Line 26-29)

3. line 89: among requirements there is “not include bones in the forefoot as they might be deformed.” But for automatic CS the head of the 5^th metatarsal bone and the 1^st metatarsal/sesamoids complex are taken into account

We understand the confusion. We cannot fit objects into the bones in the forefoot for the construction of the coordinate system since their shape and orientation vary. We changed this line in: not include the shape and orientation of the bones in the forefoot by fitting an object since these bones might be deformed. (Line 119-120)

4. weight bearing is not taken into account; weight bearing (for foot&ankle bipodal WB X-rays are indicated) plays a major role in the alignement of the foot/forefoot; a splint cannot play the same role.

We are aware that weight bearing plays a major role in foot/forefoot alignment, as it widens the forefoot when the medial ray moves through the tarsometatarsal joint. A splint cannot play the same role as a weight-bearing CT scan. However, it is believed that the splint results in automatically selected points on the same level as with weight-bearing. This will lead to a similar normal vector. Consequently, weight-bearing is believed to have little to no effect on the constructed coordinate system. We changed this section in: Thirdly, the weight-bearing condition is not taken into account in this study. Weight-bearing CT scanners (WBCTs) enables imaging of the foot to be done in the natural weight-bearing position. Weight-bearing widens the forefoot when the medial ray moves through the tarsometatarsal joint [25-28]. WBCT has the advantage of reduced radiation exposure [29,30] and it improves the evaluation of forefoot deformities [14,26,27]. However, the patients in this study could not stand in the CT scanner during image acquisition. The splint (Figure 1) provided the greatest possible replication of stance on a flat surface, maintaining a constant plantigrade foot and neutral ankle position across patients. It is believed that the use of this splint results in automatically selected points on the same level as in the weight-bearing situation, leading to a similar normal vector. Consequently, weight-bearing is believed to have little to no effect on the constructed coordinate system and its virtual images. Nevertheless, it is recommended to use WBCT for the evaluation of forefoot deformities when this is available in the hospital. (Line 377-392)

5. CT scan can be seen as a too invasive methods to plan forefoot surgery;

We agree with the reviewer. That is why we added in our discussion section the following:

Fourthly, a limitation is the necessity of acquiring a CT scan for patients with minor pathologies. The availability of CT scanners can also differ from hospital to hospital or country to country. Although this is outside the scope of this study, quite some initiatives have been set up to transfer data from 2D radiographic images to a 3D digital model [31,32]. This might be a future solution to avoid the need for a CT scan for patients with minor pathologies. (Line 392-397)

6. these CS take into account the talus, assuming the talus and the midfoot are normally aligned, which sometimes is not

We agree with the reviewer. That is why we changed in our discussion section the following:

First, talus deformities may result in different orientations of its inertia axes, affecting the coordinate system. In addition, talus and midfoot malalignment may lead to a different y-axis orientation relative to the forefoot. Since forefoot deformities were the focus of this study, the morphology of the hindfoot and the alignment of the talus and mid-foot were assumed to be more or less normal. (Line: 398-403)

7. there is no clinical example of applicability of the present method; how can the usual measurements (useful to evaluate the foot pre-op, intra-op and post-op) be calculated with this method? How can the HV angle, the intermetatarsal angle, the Maestro line be calculated and expressed?

This study represents the preliminary step towards preoperative 3D planning of forefoot corrections (constructing the coordinate system). Clinical examples of applicability of the present method are therefore not the focus of this study. However, added in our discussion section the following: Currently, radiographic 2D measurements are necessary for the clinical interpretation of hallux valgus (e.g., the hallux valgus angle (HVA) and intermetatarsal angle (IMA)). With the proposed coordinate system, it becomes possible to derive clinically relevant measurements from the 3D foot model by projecting them onto the virtual views of the coordinate system. For example, the longitudinal inertia axes of the first metatarsal and the proximal phalanx can be automatically generated and projected on the virtual AP view of the coordinate system to measure the HVA. Similarly, the longitudinal inertia axes of the first and second metatarsals can be automatically generated and projected on the virtual AP view of the coordinate system to measure the IMA. (Line 418-426)

8. being a “biomechanic” study, the computed algorithm should be offer as supplementary materials, and tables with CT parameters should be added

We agree with the reviewer. However, this study does not use an algorithm. Therefore, we added the protocol for the construction of the coordinate systems in 3-Matic to the Supplementary Materials (Protocol S1 line 123 and Protocol S2 line 125). For the CT parameters, we added Table 2 in the report (Line 144).

9. a power analysis demonstrating that 9 cases are sufficient should be added

Thank you for addressing this item. However, we feel in this stage that no power analysis was to be made a priori as we were exploring the feasibility of generating a coordinate system that could meet all set criteria. Finally, as we show that the final coordinate system can be generated fully automatically, for which adding more similar patients would not add to the strength of this paper.

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Authors: I am fine with the present version of the paper. congrats!, and best regards.