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. 2024 Feb 26;19(2):e0297634. doi: 10.1371/journal.pone.0297634

Femoral anterior condyle height decreases as the distal anteroposterior size increases in total knee arthroplasty: A comparative study

Bo Yang 1,2,¤,#, Fu-zhen Yuan 1,#, Hai-jun Wang 1, Xi Gong 1, Yan-hai Chang 2,*, Jia-Kuo Yu 1,3,*
Editor: Gennaro Pipino4
PMCID: PMC10896507  PMID: 38408088

Abstract

Purpose

The anterior flange height of the current femoral component increases with an increasing distal femoral anteroposterior dimension. During total knee arthroplasty (TKA), we have observed that a large femur may have a thinner anterior condyle, whereas a small femur may have a thicker anterior condyle. The first purpose of this study was to examine whether the femoral anterior condyle height decreases as the distal femoral anteroposterior size increases and whether gender differences exist in anterior condyle height.

Methods

A total of 1218 knees undergoing TKA intraoperative and computed tomography scans from 303 healthy knees were used to measure the anterior lateral condylar height (ALCH), anterior medial condylar height (AMCH), and the lateral anteroposterior (LAP) and medial anteroposterior (MAP) dimensions of distal femurs. The LAP and MAP measurements were used for adjustments to determine whether gender differences exist in anterior condyle heights. Linear regression analysis was performed to determine correlations between ALCH and LAP or between AMCH and MAP.

Results

There were significant differences between males and females in ALCH in both the CT and TKA groups and AMCH in the CT group (all P<0.01). After adjusting for LAP and MAP, there were significant gender differences in the lateral and medial condylar heights in both groups (P<0.01). There were significant negative correlations between ALCH and LAP values and between AMCH and MAP values in both CT and TKA measurements, with the LAP and MAP values increasing as ALCH and AMCH decreased.

Conclusions

The results demonstrate that femoral anterior condylar height decreased with increasing anteroposterior dimension in both the medial and lateral condyle. In addition, this study also showed that anterior condylar heights are highly variable, with gender differences. The data may provide an important reference for designing femoral anterior flange thickness to precisely match the natural anterior condylar anatomy.

Introduction

Although total knee arthroplasty (TKA) is successfully used to treat advanced osteoarthritis of the knee [1], patellofemoral complications are still a main cause of dissatisfaction with the outcome after TKA [2, 3]. In addition to surgical technique (implant positioning, soft-tissue balancing, etc.), patellofemoral component design (patellar component design, femoral component design, etc.) affects the patellofemoral biomechanics associated with these complications [4, 5]. Many studies have focused on the patellofemoral anatomic morphology for properly designing knee components [6, 7]. The anterior flange thickness of the femoral component strongly influences the biomechanics of the patellofemoral joint [8]. If the anterior flange thickness of the femoral component is larger than the resected anterior condyle, there is a risk of overstuffing, anterior knee pain, and limiting the postoperative knee range of motion; if it is smaller than the resected anterior condyle, there is a risk of decreased quadriceps moment arm, resulting in a functional disadvantage [6, 9].

One of the design details considered to be important is restoration of the natural anterior condylar height. Several studies have reported that the anterior condylar height positively correlates with the length of the femur or femoral size [10, 11]. Traditionally, the anterior flange thickness of currently used femoral components increases as the component size increases [12]. However, while performing TKA, we have observed that a large femur may have a thinner anterior condyle, and a small femur may have a thicker anterior condyle. This raises questions about whether the anterior condylar height increase as the femoral size increases and whether the anterior flange currently used in femoral components mismatch the natural anterior condyle anatomy.

The anteroposterior (AP) dimension was used to select an implant of appropriate size during TKA. No study has yet analyzed the relationship between anterior condyle height and distal femoral AP size. The aim of the present study was to examine the relationship between anterior condyle height and distal femoral AP size to provide data for designing size-matched anterior flanges for femoral components. We hypothesize that femoral anterior condyle height decreases as the distal femoral AP size increases.

Materials and methods

This study was approved by the institutional review board of Peking University Third Hospital. Prior to the start of the study, all participants provided informed verbal consent.

Method for intraoperative measurement

Between August 2011 and September 2015, a total of 1218 knees in 222 male and 996 female primary OA patients undergoing TKA were evaluated in this study. The mean patient age was 67.3 ± 7.8 years for males and 65.6 ± 6.9 years for females. Patients were excluded if they had a history of femur fracture or congenital anomaly or if the bone loss or degradation was so serious that augmentation was required or if the knee had a varus or valgus deformity of >15°. All TKA procedures were performed by the senior surgeon (Yu). The NexGen knee prosthesis system (Zimmer, Warsaw, IN, USA) was used for all patients.

Intramedullary femoral alignment was used to make a 10 mm distal femoral resection at 5–7° valgus to the anatomic axis. The femoral external rotation 3°relative to the posterior condylar axis or paralleling the transepicondylar axis or perpendicular to Whitesides’ line for the distal femoral cut. Anterior referencing instrumentation was used to cut the anterior condyle. The anterior condylar heights were measured intraoperatively only for patients whose anterior condylar cut line flushed with the anterior cortical surface of the distal femoral shaft (Fig 1A). Patients whose anterior condylar cut lines were above or below the anterior cortical surface were excluded. All visible osteophytes were removed before measurements were taken, and all measurements were taken twice: once by the surgeon and the second by his assistant to reduce random error. The anterior lateral condylar height (ALCH) and anterior medial condylar height (AMCH) are the maximum thickness of the cut-down at the anterior lateral and medial condyle, respectively. The femoral lateral anterior-posterior (LAP) and medial anterior-posterior (MAP) dimensions were defined as the distance between the lowest lateral and medial condyle, respectively, and the anterior condyle cut surface (Fig 1B).

Fig 1. Diagram of cuts and measurements in the distal femur.

Fig 1

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(a) Anterior condylar cut line, which is flush with the anterior cortical surface of the distal femoral shaft; (b) Measurements of the distal femur. ALCH: anterior lateral condylar height; AMCH: anterior medial condylar height; LAP: lateral anterior-posterior; MAP: medial anterior-posterior.

Measurement on computed tomography

Between August 2011 and December 2012, a total of 152 Chinese males and 151 females were recruited at the time of computed tomography (CT) of the knee after anterior or posterior cruciate ligament reconstruction. The mean age was 32.0 ± 10.9 years for males and 27.9 ± 7.2 years for females. Subjects were excluded if they had a history of femoral fracture or congenital anomaly, if they had diseases that could affect the normal formation of the knee joint, or if the knee had a varus or valgus deformity greater than 10°.

A CT scan of each knee was performed using a helical CT scanner (120 kVp, 200 mA, Somatom Sensation 16, Siemens Healthcare, Germany). The patient was placed supine with the knee in a full extended position on the scanner with the patella facing towards the ceiling. The scanning procedure acquired 1-mm CT slices (image size, 512 × 512 pixels). All CT images were burned into discs. The images of the knees were segmented using a region-growing method to construct 3D bony models. To simulate TKA anterior condyle cuts and measure the femoral condyle geometry, a line connecting the medial sulcus of the medial epicondyle and the lateral epicondylar prominence was defined as the surgical transepicondylar axis (STEA) created on each knee model. An orthogonal coordinate system was then established at the lateral end point of the STEA on the surface model. The X-axis was defined as the STEA; the Y-axis was defined as a line parallel with the femur mechanical axis, which is 6° valgus with the anatomical axis (the line along the femoral shaft) in the coronal plane (Fig 2A); and the Z-axis was vertical to the X- and Y-axes, passing through the lateral end point of the STEA (Fig 2B). An anterior condyle flush cut along the anterior femur cortex surface, parallel to the femoral shaft and without anterior femoral notching, was performed on each femur (Fig 2A).

Fig 2. The anterior femoral condyle cut and measurements.

Fig 2

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(a) The anterior femoral condyle cut viewed in the coronal plane. (b) The anterior femoral condyle cut and measurements viewed in the transverse plane.

The ALCH and AMCH were defined as the maximum thicknesses of the anterior cut at the lateral and medial condyles, respectively. The femoral LAP and MAP dimensions were defined as the distance between the lowest lateral and medial condyle, respectively, and the anterior condyle cut surface (Fig 2B).

Statistical analysis

SPSS software 18.0 (SPSS, Chicago, IL) was used for statistical analysis. Dimensions were summarized as means and standard deviations. A Kolmogorov-Smirnov test for normality was performed, and the data were found to be normally distributed. Comparative means between males and females were obtained using the independent t-test. The adjusted P-values were determined by logistic regression. The AMCH was adjusted using the MAP dimension, and ALCH was adjusted using the LAP dimension to determine whether there were gender differences in the anterior condylar height. Linear regression analysis was used to determine correlations for the ALCH and LAP, AMCH and MAP dimensions. The differences were considered significant when P<0.05.

Results

Anterior lateral and medial condylar heights

The mean ALCH of males was significantly larger than females in both the CT and TKA groups (P<0.01). The mean ALCH was 7.7 ± 1.9 mm for males and 6.6 ± 1.7 mm for females in the CT group, and 8.4 ± 2.7 mm for males and 7.5 ± 2.3 mm for females in the TKA group. After adjusting for the LAP dimension, there were significant gender differences in the ALCH in both the CT and TKA groups (P<0.01; Table 1).

Table 1. Anterior lateral condylar dimensions (mm).

Male Female P-value Adjusted for LAP
CT group 7.73 ± 1.92 6.60 ± 1.65 <0.01 <0.01
TKA group 8.36 ± 2.71 7.46 ± 2.34 <0.01 <0.01
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Values are mean ± standard deviation. LAP: lateral anterior-posterior.

The mean AMCH in males was 3.5 ± 1.9 mm in the CT groups, which is significantly larger than the mean in females (2.7 ± 1.6 mm; P<0.01). The mean AMCH was 4.4 ± 2.4 mm for males and 4.3 ± 2.6 mm for females in the TKA group, showing no significant gender difference (P = 0.418). After adjusting for the MAP dimension, there was a significant gender difference in the AMCH in both the CT and TKA groups (P<0.01; Table 2).

Table 2. Anterior medial condylar dimensions (mm).

Male Female P-value Adjusted for MAP
CT group 3.53 ± 1.94 2.66 ± 1.57 <0.01 <0.01
TKA group 4.44 ± 2.42 4.29± 2.56 0.418 <0.01
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Values are mean ± standard deviation. MAP: medial anterior-posterior

In addition, the dimensions of the anterior condylar height were highly variable, regardless of gender. The range of ALCH was 2.2–13.1 mm for males and 0.5–10.9 mm for females in the CT group, and 1–15.5 mm for males and 1.5–15.5 mm for females in the TKA group. The range for AMCH was 0–8.6 mm for males and 0–7.3 mm for females in the CT group, and 0–13 mm for males and 0–15 for females in the TKA group.

Correlations between ALCH and the LAP dimension

There were significant negative correlations between the ALCH and LAP dimensions in both the CT and TKA groups, with the LAP dimension increasing as ALCH decreased regardless of gender. The line for males is above the line for females, indicating that males generally have a larger ALCH than females for a given MAP dimension (Fig 3).

Fig 3. The ALCH against the LAP dimensions in males and females.

Fig 3

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ALCH decreased as the LAP measurement increased. (a) CT group. (b) TKA group.

Correlations between AMCH and the MAP dimension

There were significant negative correlations between AMCH and the MAP dimension in both the CT and TKA groups, with the MAP dimension increasing as AMCH decreased regardless of gender. The line for males is above the line for females, indicating that males generally have a larger AMCH than females for a given MAP dimension (Fig 4).

Fig 4. The AMCH against the MAP dimensions in males and females.

Fig 4

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AMCH decreased as the MAP measurement increased. (a) CT. (b) TKA.

Discussion

The most important finding in this study was that anterior femoral condyle heights decreased with increasing AP dimensions in both the medial and lateral condyle, which contradicts the current femoral component design in which the anterior flange height increases with increasing AP dimensions.

The anterior condylar height is one of the major anatomical differences taken into consideration when designing femoral components. Many studies have reported the anterior condylar anatomy using different methods. Gillespie et al measured 1207 skeletal cadaver femora (547 males and 660 females) and found that the anterior condyle height is related to the length of the femur, with a mean increase in the ALCH of 0.03 mm or AMCH of 0.02 mm for every 1 mm increase in the femoral length [11]. Fehring et al studied 212 knees in magnetic resonance (MR) images and reported that the average ALCH and AMCH was positive with medial-lateral (ML) size of the femur [6]. These values corroborate the findings of Li et al, who also reported that the thickness of the ALCH and AMCH was positive with ML size of the femur [10]. According to the above results, anterior flange heights in femoral components currently increase with increasing component size.

It has been widely accepted that restoration of native patellofemoral joint thickness at the time of TKA is important. Increasing patellar bone or anterior condyle thickness during TKA may cause patellofemoral joint overstuffing, which may lead to decreased flexion and possibly pain after TKA [9,13]. Bracey et al evaluated the effect of patellar thickness on knee flexion and patellar kinematics and found that knee flexion decreased an average 1.2° with each additional 2 mm of patellar thickness. In addition, kinematic tracking data showed a significantly greater lateral shift and tilt of the patella with the +8 mm prostheses [14]. Oishi et al examined varying amounts of patellofemoral build up in a cadaver model and reported that a 2 mm or 4 mm increase in patellar button thickness resulted in a significant increase in shear force at flexion angles greater than 40°, which may lead to early failure of the implant due to loosening or increased wear [15]. In a cadaveric knee study, Mihalko et al reported a 4 mm anterior buildup on the femur that resulted in an approximately 4° loss of passive knee flexion [16]. Kawahara intraoperatively measured patellofemoral contact forces using three different femoral components in deep knee flexion and found that an increase in the AP dimensions of the femoral component significantly increased the patellofemoral contact forces at 120°, 130°, and 140° of flexion compared with the standard component [12].

Our data indicate that anterior femoral condyle height decreased with increasing AP dimensions in both the medial and lateral condyle (see Figs 3 and 4). One can infer from our data that the replacement of a knee with a small anterior condyle (large femur) with an implant with a thicker anterior flange can cause overstuffing, and the replacement of a knee with a large anterior condyle (small femur) with an implant with a thinner anterior flange can cause understuffing when using contemporary TKA components. Thus, to better fit the anterior femoral condyles, the small femoral implant should have a thicker anterior flange, and the large femoral implant should have a thinner anterior flange. Theoretically, the design of femoral components should more closely approximate the thickness of the original resected anterior condyle. Patellofemoral component design influences the patellofemoral kinematics [4, 17], which may ultimately contribute to some of the patellofemoral problems observed after TKA, such as pain or loss of motion and extensor mechanism deficiency [6, 18, 19]. Whether modification of the prosthetic anterior condyle would change the kinematics at the patellofemoral joint and offer a clinical advantage requires further study.

Most recent studies have focused on the gender differences in anterior condylar height. Poilvache et al measured the anterior condyle height of 46 males and 54 females after making the anterior cut and reported an average 1.4 mm lower ALCH and 1.6 mm lower AMCH for females compared with males [20]. Lonne et al intraoperatively studied the distal femurs of 100 males and 100 females and made similar observations; they reported an average difference between males and females of 1.48 mm anterolaterally and 0.76 mm anteromedially [21]. Other researchers recognized that gender differences were the result of a smaller femur in females. These data were direct, absolute measurements uncorrected for the size of the distal femur or patient height. Fehring et al measured the anterior condylar heights of males and females on MR images and found a significant difference in AMCH but no difference in ALCH [6]. A recent study using 3D anatomic knee models reported that the difference between the sexes with regard to anterior condylar anatomy averaged 1.1 mm anterolaterally and 0.9 mm anteromedially [10]. However, the gender differences were no longer significant after adjusting for ML femoral size. Our data showed significant gender difference in ALCH and AMCH on CT, but only ALCH in the TKA group. In further analysis to eliminate the effect of femoral size, we found that the AMCH and ALCH of female knees were smaller than the size in corresponding male knees after adjusting for MAP and LAP measurements. We found significant gender differences in the lateral and medial anterior condylar heights in both the CT and TKA groups. Based on a large number of knees measured intraoperatively and on CT, we conclude that gender differences exist with respect to anterior condylar height. The discrepancy between the results from our study and other studies can be explained by anatomic variations among ethnicities and using different methods. Several studies have demonstrated ethnic differences in the shape and size of the knee [22, 23].

Our study has several advantages. First, the present study used a large sample size, giving it the power to verify significant features in anterior condylar anatomy. Second, the data in this study, measured in TKA patients after making the bone cut, accurately reflects the real clinical situation. Furthermore, via a virtual TKA procedure that simulated an anterior condyle cut on 3D CT knee models, we were able to obtain consistent results, strengthening the intraoperative measurement. A limitation was that all of the subjects recruited in the present study were from the Chinese population. Therefore, the subjects in the current study only represent a subgroup of the Chinese population, and other ethnic populations should be studied to verify our results.

Conclusion

This study demonstrated that anterior femoral condylar height decreased with increasing AP dimensions in the medial and lateral condyle, which contradicts the present design in which the anterior flange increases with increasing AP dimensions. This study also showed that anterior condylar heights are highly variable, with gender differences. The data may provide an important reference for designing femoral anterior flange thickness to precisely match the natural trochlear anatomy.

Supporting information

S1 File. Support data.

(ZIP)

pone.0297634.s001.zip (4.2MB, zip)

Data Availability

All relevant data are within the manuscript and its Supporting Information files.

Funding Statement

We declare that this study was approved by institute review board of author’ hospital (No: IRB00006761-2011073). This research was funded by Instrument Research Project of the National Natural Science Foundation (No. 81327001), which took part in study design, data collection and analysis, preparation and decision to publish the manuscript; Science and Technology Program of Shaanxi Province (No.2022SF-049), which took part in preparation and revised the manuscript; Capital’s Funds for Health Improvement and Research (No.2022-1-4091) and National Natural Science Foundation-Beijing Natural Science Foundation Regional Innovation Union Development Fund (No.U22A20283).

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Decision Letter 0

Gennaro Pipino

26 May 2023

PONE-D-23-04989Femoral anterior condyle height decreased as the distal anteroposterior size increasing: contrary to the current designed femoral componentPLOS ONE

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Upon re-submitting your revised manuscript, please upload your study’s minimal underlying data set as either Supporting Information files or to a stable, public repository and include the relevant URLs, DOIs, or accession numbers within your revised cover letter. For a list of acceptable repositories, please see http://journals.plos.org/plosone/s/data-availability#loc-recommended-repositories. Any potentially identifying patient information must be fully anonymized.

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Additional Editor Comments:

As you know, the manuscript has a strong title and theme. Which sets the stage for a true revolution of the modern concept of knee prosthesis.

In general, as you can read from the following reports of the reviewers, it emerged that in order to suggest a new prosthetic design, more knowledge on many aspects is needed.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Partly

Reviewer #3: Partly

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: 1. GENERAL COMMENTS

Manuscript topic is current and of interest.

The sample of patients completed the survey was satisfactory.

The English language is ok.

The study contains some anatomical features. Although there are some limitations, I would accept it for publication because it presents some interesting things related to total knee arthroplasty.

2. INTRODUCTION

The introduction provide the necessary background.

The purpose is clear.

3. METHODS (Material, patients and methods)

The design of the study is acceptable.

4. RESULTS

ok

4. DISCUSSION

The discussion is ok, although you should state that there are many designs that take into account the dimensions of the femur and that with the newest techniques like robotics the surgeon can calculate the amount of the bone that is necessary to be cut and adjust it to the specific implant design to be used in each patient.

6. CONCLUSION

ok

7. ABSTRACT

ok

8. TITLE

The title is ok.

9. REFERENCES

ok

10. TABLES

ok

Reviewer #2: Dear authors, i had the opportunity of reviewing your work, and i hope that my comments help strengthening your manuscript. You disclosed that you received no funds, however, later on you acknowledge your funding agency, please correct accordingly.

TITLE: please indicate in the title that this was a comparative study.

ABSTRACT: please made it clear that the measurements were clinical in the TKA cases and radiographic in the CT scans

INTRODUCTION:-references 10,11 in line 82 are old, please update

-lines 85 to 87: seems out of context, please correct or remove

-please rephrase the aim of the study and report it into primary objective and secondary objectives, as the authors through the methods and results reported on may differences not only the assessment of the anterior condylar height.

METHODS: - why the data was collected a long time ago (till 2015), it is almost 8 years, where major changes were made in the design of the implants, furthermore, as long as this was a historical group, why the authors did not report any data regarding the development of PFJ complications which is the main concerned point with their study.

-the authors reported using one implant for all of their cases, i was wondering why they did not report a comparison between the sizes of the femoral component anterior flange and compare it against their population. Furthermore, as long as they already know the femoral component sizes placed in each patient, they could have tested theses sizes against the measured resected anterior femoral cut.

-The authors did not report any inclusion or exclusion criteria, did they include all forms and magnitudes of deformities? patients with different pathologies such as RA, or patients with posttraumatic OA where the anatomy could be distorted?

-What was the exact technique for performing the TKA especially the rotation which could affect the anterior femoral condyles cut thickness?

RESULTS:

-the authors concentrated their comparisons on the gender differences, supposing that the CT group were a normal group, why the authors did not compare both groups to detect if there was a disturbance according to the pathological process leading to performing TKA.

-Could the differences between bone cuts thickness between males and females be attributed to the fact that the male skeleton is larger than the female skeleton?

-the authors stated that "the dimensions of the anterior condylar height were highly variable, regardless of

gender.", how could this be solved by changing the implants design? could a custom made implant for each patient becomes the solution?

DISCUSSION:

-Please indicate some possible solutions in view of your results.

Reviewer #3: Thank you for giving me the opportunity to review this manuscript. The authors describe differences in the dimensions regarding distal femur morphology of patients undergoing TKA and participants with "healthy" knees

Although I believe the manuscript would have some interest for the reader, I believe it is not ready for publication in the current form since there are significant methodological and language issues which cannot be ignored.

General comment:

I've never read or heard the term "condyle" regarding the anterior part of the distal femur. Usually the terms "anterior cortex" etc. are used.

Major issues:

There are many grammatical errors throughout the whole manuscript, which in some parts makes the reading/understanding of the text almost impossible. There is an urgent need for editing by a native speaker. Otherwise I do not see a chance for publication.

According to the findings of this study. There must be a high rate of patients with anterior overstuffing which should be visible in an impairment of clinical function or patient reported outcome measurements. It should be considered to include clinical data. Additionally, overstuffing should be measurable in postop. radiological evaluation. It should also be considered to include post-TKA CT and correlate the restoration of the anterior cortex by the anterior flange.

Methods:

Why do the authors compare healthy and degenerate knees? The implications of the study will mainly influence patients undergoing TKA. Additionally, patients undergoing ACL-reconstruction do not necessarily have a "healthy" knee anatomy.

The authors need to deliver more details on the intraoperative evaluations:

It is hard to define "flush" when it comes to the anterior cut of the distal femur. What was the exact definition in your study?

Were varus and valgus deformity included?

How much external rotation was used for the distal femoral cut?

Results:

Can the authors explain the different results from CT and intraop.?

Line 180 and following: I cannot find the calculations for the correlations between ALCH and LAP and AMCH and MAP respectively. Correlations should be calculated (e.g. Spearman) to display whether these findings show a significance. The method should then also be named in the M+M section.

Discussion:

Line 197-206: The authors report on studies which show results in contradiction to their findings and which support the rationale of contemporary TKA designs --> the bigger the femoral component size the bigger the anterior flange. However, the authors do not elucidate why these differences in their study are explainable.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

**********

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PLoS One. 2024 Feb 26;19(2):e0297634. doi: 10.1371/journal.pone.0297634.r002

Author response to Decision Letter 0

24 Aug 2023

Dear Editors and Reviewers:

Thank you very much for your letter and for the reviewers’ careful reading and constructive comments concerning our manuscript entitled “Femoral anterior condyle height decreased as the distal anteroposterior size increasing: contrary to the current designed femoral component” (Manuscript # PONE-D-23-04989). According to editor and reviewers' comments and suggestions, we have revised the manuscript point by point.

We would like to resubmit the revised manuscript to PLOS ONE, and hope it is acceptable for publication in the journal. The detailed changes were tracked in red in the revised manuscript and listed in the following:

Looking forward to hearing from you soon.

Best wishes!

For editors:

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Answer: Thank you for your good comments. We have edited the manuscript according to PLOS ONE's style requirements.

2. Thank you for stating the following in the Acknowledgments Section of your manuscript:

"This research was funded by Instrument Research Project of the National Natural Science Foundation (No. 81327001). Science and Technology Program of Shaanxi Province (No.2022SF-049)."

We note that you have provided additional information within the Acknowledgements Section that is not currently declared in your Funding Statement. Please note that funding information should not appear in the Acknowledgments section or other areas of your manuscript. We will only publish funding information present in the Funding Statement section of the online submission form.

Please remove any funding-related text from the manuscript and let us know how you would like to update your Funding Statement. Currently, your Funding Statement reads as follows: "The author(s) received no specific funding for this work."

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Answer: Thank you for your careful reading and suggestions, we have changed funding-related text in revised manuscript and cover letter.

3. We note that the grant information you provided in the ‘Funding Information’ and ‘Financial Disclosure’ sections do not match.

When you resubmit, please ensure that you provide the correct grant numbers for the awards you received for your study in the ‘Funding Information’ section.

Answer: Thank you very much, we have corrected grant numbers in the ‘Funding Information’ section.

4. Thank you for stating the following financial disclosure:

"The author(s) received no specific funding for this work."

At this time, please address the following queries:

a) Please clarify the sources of funding (financial or material support) for your study. List the grants or organizations that supported your study, including funding received from your institution.

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c) If any authors received a salary from any of your funders, please state which authors and which funders.

d) If you did not receive any funding for this study, please state: “The authors received no specific funding for this work.”

Please include your amended statements within your cover letter; we will change the online submission form on your behalf.

Answer: Thank you, we have changed funding-related text in revised manuscript and cover letter.

5. In your Data Availability statement, you have not specified where the minimal data set underlying the results described in your manuscript can be found. PLOS defines a study's minimal data set as the underlying data used to reach the conclusions drawn in the manuscript and any additional data required to replicate the reported study findings in their entirety. All PLOS journals require that the minimal data set be made fully available. For more information about our data policy, please see http://journals.plos.org/plosone/s/data-availability.

Upon re-submitting your revised manuscript, please upload your study’s minimal underlying data set as either Supporting Information files or to a stable, public repository and include the relevant URLs, DOIs, or accession numbers within your revised cover letter. For a list of acceptable repositories, please see http://journals.plos.org/plosone/s/data-availability#loc-recommended-repositories. Any potentially identifying patient information must be fully anonymized.

Important: If there are ethical or legal restrictions to sharing your data publicly, please explain these restrictions in detail. Please see our guidelines for more information on what we consider unacceptable restrictions to publicly sharing data: http://journals.plos.org/plosone/s/data-availability#loc-unacceptable-data-access-restrictions. Note that it is not acceptable for the authors to be the sole named individuals responsible for ensuring data access.

We will update your Data Availability statement to reflect the information you provide in your cover letter.

Answer: Thank you very much, we have provide the related figures and table in supporting information. But we can not provide detailed information for our data. Because we are applying for a patent and designing mew femoral prosthesis according to the data now. thank you.

6. We note that you have stated that you will provide repository information for your data at acceptance. Should your manuscript be accepted for publication, we will hold it until you provide the relevant accession numbers or DOIs necessary to access your data. If you wish to make changes to your Data Availability statement, please describe these changes in your cover letter and we will update your Data Availability statement to reflect the information you provide

Answer: Thank you for your kindly remind us that we can not provide repository information for our data after acceptance. Because of we are applying for a patent and designing mew femoral prosthesis according to the data now. we have described it online and in the cover letter.

7. PLOS requires an ORCID iD for the corresponding author in Editorial Manager on papers submitted after December 6th, 2016. Please ensure that you have an ORCID iD and that it is validated in Editorial Manager. To do this, go to ‘Update my Information’ (in the upper left-hand corner of the main menu), and click on the Fetch/Validate link next to the ORCID field. This will take you to the ORCID site and allow you to create a new iD or authenticate a pre-existing iD in Editorial Manager. Please see the following video for instructions on linking an ORCID iD to your Editorial Manager account: https://www.youtube.com/watch?v=_xcclfuvtxQ.

Answer: Thank you，I have registered a new ORCID iD.

8. Please include captions for your Supporting Information files at the end of your manuscript, and update any in-text citations to match accordingly. Please see our Supporting Information guidelines for more information: http://journals.plos.org/plosone/s/supporting-information.

Answer: Thank you very much.

Additional Editor Comments:

As you know, the manuscript has a strong title and theme. Which sets the stage for a true revolution of the modern concept of knee prosthesis.

In general, as you can read from the following reports of the reviewers, it emerged that in order to suggest a new prosthetic design, more knowledge on many aspects is needed.

Answer: Thank you very much. We have revised the manuscript point by point as fellows according to reviewers’ comments.

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Partly

Reviewer #3: Partly

Answer: Thank you for your comments. We have amended the whole manuscript carefully in the revised manuscript.

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

Answer: Thank you for your comments. We have amended the problems of statistical analysis in the revised manuscript.

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

Answer: Thank you very much.

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

Answer: Thank you very much. Our manuscript had been edited for English-language problems by Paul Kretchmer, Managing Director, San Francisco Edit.

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Answer: Thanks. We have answered the questions above.

Reviewer #1:

1.GENERAL COMMENTS

Manuscript topic is current and of interest.

The sample of patients completed the survey was satisfactory.

The English language is ok.

The study contains some anatomical features. Although there are some limitations, I would accept it for publication because it presents some interesting things related to total knee arthroplasty.

Answer: Thank you very much for your good praise.

2. INTRODUCTION

The introduction provide the necessary background.

The purpose is clear.

Answer: Thank you for your comments.

3. METHODS (Material, patients and methods)

The design of the study is acceptable.

Answer: Thank you.

4. RESULTS

ok

Answer: Thanks.

5. DISCUSSION

The discussion is ok, although you should state that there are many designs that take into account the dimensions of the femur and that with the newest techniques like robotics the surgeon can calculate the amount of the bone that is necessary to be cut and adjust it to the specific implant design to be used in each patient.

Answer: Thank you for your comments.

6. CONCLUSION

ok

Answer: Thanks again.

7. ABSTRACT

ok

Answer: Thank you.

8. TITLE

The title is ok.

Answer: Thanks.

9. REFERENCES

ok

Answer: Thank you very much.

10. TABLES

ok

Answer: Thank you again.

Reviewer #2:

Dear authors, i had the opportunity of reviewing your work, and i hope that my comments help strengthening your manuscript. You disclosed that you received no funds, however, later on you acknowledge your funding agency, please correct accordingly.

Answer: Thank you for your careful reading and suggestions, we have changed funding-related text in revised files.

TITLE: please indicate in the title that this was a comparative study.

Answer: Thank you. We have revised the title as “Femoral anterior condyle height decreases as the distal anteroposterior size increases in total knee arthroplasty: A comparative study ” in revised manuscript(line 5-6).

ABSTRACT: please made it clear that the measurements were clinical in the TKA cases and radiographic in the CT scans.

Answer: Thank you, we have described the measurements were undergoing TKA intraoperative and computed tomography scans in revised manuscript (line 45-46).

INTRODUCTION:

-references 10,11 in line 82 are old, please update

Answer: Thank you for your suggestion, we have updated the references 10,11 in revised manuscript(line 297-299).

10. Li P, Tsai TY, Li JS, Wang S, Zhang Y, Kwon YM, et al. Gender analysis of the anterior femoral condyle geometry of the knee. Knee. 2014; 21(2): 529-533.

11. Gillespie RJ, Levine A, Fitzgerald SJ, Kolaczko J, DeMaio M, Marcus RE, et al. Gender differences in the anatomy of the distal femur. J Bone Joint Surg Br. 2011; 93(3):357-63.

lines 85 to 87: seems out of context, please correct or remove

Answer: Thank you for your suggestion, we have corrected these sentences in the revised manuscript(line 82-85).

please rephrase the aim of the study and report it into primary objective and secondary objectives, as the authors through the methods and results reported on may differences not only the assessment of the anterior condylar height.

Answer: Thank you for your good suggestion. We have added secondary objectives that whether gender differences exist in anterior condyle height in the revised manuscript(line43-44).

METHODS: - why the data was collected a long time ago (till 2015), it is almost 8 years, where major changes were made in the design of the implants, furthermore, as long as this was a historical group, why the authors did not report any data regarding the development of PFJ complications which is the main concerned point with their study.

Answer: This study mainly clarified the anatomy features we found that the femoral anterior condyle height decreases with the increase of the distal femur dimension, which is different from the prosthesis currently used (femoral anterior flange increases with the prosthesis size increased). During that period, we didn't publish a paper because we applied for a patent and designed mew femoral prosthesis according to the data. In clinic, some patients have PFJ-related complications after TKA, including prosthesis overfilling, which is partly due to that the anterior flange thickness of prosthesis is greater than that of anterior condyle resection thickness. I hope I can answer your question. Thank you.

-the authors reported using one implant for all of their cases, i was wondering why they did not report a comparison between the sizes of the femoral component anterior flange and compare it against their population. Furthermore, as long as they already know the femoral component sizes placed in each patient, they could have tested theses sizes against the measured resected anterior femoral cut.

Answer: Thanks, the question you raised is very good, and we have neglected this aspect. Later, we will collect relevant data and make a summary. This paper mainly wants to explain the anatomy features we found that the femoral anterior condyle height decreases with the increase of the distal femur dimension, which is different from the prosthesis currently used (femoral anterior flange increases with the prosthesis size increased).

-The authors did not report any inclusion or exclusion criteria, did they include all forms and magnitudes of deformities? patients with different pathologies such as RA, or patients with posttraumatic OA where the anatomy could be distorted?

Answer: Thank you. The criteria for inclusion and exclusion of cases are very important. We choose primary OA subjects for this study. Patients were excluded if they had a history of femur fracture or congenital anomaly or if the bone loss or degradation was so serious that augmentation was required or if the knee had a varus or valgus deformity of >15°. We have described it in the revised manuscript(line 95-99).

What was the exact technique for performing the TKA especially the rotation which could affect the anterior femoral condyles cut thickness?

Answer: Generally, The femoral external rotation 3°relative to the posterior condylar axis for the distal femoral cut, or paralleling the transepicondylar axis or perpendicular to Whitesides’ line to ensure the flexion gap balance. We have described it in the revised manuscript(line 102-104).

RESULTS:

The authors concentrated their comparisons on the gender differences, supposing that the CT group were a normal group, why the authors did not compare both groups to detect if there was a disturbance according to the pathological process leading to performing TKA.

Answer: Thank you, it is a good question. The pathology of TKA patients may have some influences on the anatomy of knee joint. The cartilage of TKA patients was partly worn or even disappeared completely, and there was no cartilage exit in CT image. In addition, the present study mainly to elucidate the anatomical features that anterior condyle height decreased as the increase of the distal femur. CT images and TKA intraoperative measurements verify the results for each other.

Could the differences between bone cuts thickness between males and females be attributed to the fact that the male skeleton is larger than the female skeleton?

Answer: Many literatures have previously reported that gender differences of knee anatomy were the result of a smaller skeleton in females. Femoral anterior condylar cuts thickness between males and females partly attributed to the fact that the male skeleton is larger than the female skeleton. In addition, we found significant gender differences of anterior condylar resection thickness.

The authors stated that "the dimensions of the anterior condylar height were highly variable, regardless of gender.", how could this be solved by changing the implants design? could a custom made implant for each patient becomes the solution?

Answer: Our results showed that there is a negative correlation between the femoral anterior condyle height and the distal femur size. But the individual is highly variable. Custom-made prostheses are the best solution, and many researchers and companies are now working on personalized design and 3D printing. our research group also has been working in this area, and we believe it can be realized in the near future.

DISCUSSION:

-Please indicate some possible solutions in view of your results.

Answer: Thanks, according to our results, in order to better fit the femoral anterior condyles, when designed femoral prosthesis, the large femoral implant should have a thinner anterior flange, and the small femoral implant should have a thicker anterior flange. Theoretically, femoral components designed like this should more closely approximate the thickness of the original resected anterior condyle.

Reviewer #3: Thank you for giving me the opportunity to review this manuscript. The authors describe differences in the dimensions regarding distal femur morphology of patients undergoing TKA and participants with "healthy" knees.

Although I believe the manuscript would have some interest for the reader, I believe it is not ready for publication in the current form since there are significant methodological and language issues which cannot be ignored.

Answer: Thank you very much. We have edited the language issues of whole manuscript by a native speaker.

General comment:

I've never read or heard the term "condyle" regarding the anterior part of the distal femur. Usually the terms "anterior cortex" etc. are used.

Answer: Thank you for your question. The term "condyle" regarding the anterior part of the distal femur usually used the terms "anterior cortex" etc. But some authors use it too, such as:

Fehring TK, Odum SM, Hughes J, Springer BD, Beaver WB Jr. Differences between the sexes in the anatomy of the anterior condyle of the knee. J Bone Joint Surg Am. 2009; 91-A: 2335-2341.

Ishitani K, Ito T, Hatada R, Kuriyama S, Nakamura S, Ito H, Matsuda S. High and varied anterior condyle of the distal femur is associated with limited flexion in varus knee osteoarthritis. Cartilage. 2021;13(1suppl):1487S-1493S.

If you don't think it's appropriate, later we will change it. Thanks again.

Major issues:

There are many grammatical errors throughout the whole manuscript, which in some parts makes the reading/understanding of the text almost impossible. There is an urgent need for editing by a native speaker. Otherwise I do not see a chance for publication.

Answer: Thank you for your comments. Our manuscript had been edited for English-language problems by a native speaker, Paul Kretchmer, Managing Director, San Francisco Edit.

According to the findings of this study. There must be a high rate of patients with anterior overstuffing which should be visible in an impairment of clinical function or patient reported outcome measurements. It should be considered to include clinical data. Additionally, overstuffing should be measurable in postop. radiological evaluation. It should also be considered to include post-TKA CT and correlate the restoration of the anterior cortex by the anterior flange.

Answer: Thanks, the question you raised is very good. According to our results, there must be a high rate of patients with anterior overstuffing in bigger knee or understuffing in smaller knee, which finally results in function impairment in clinical, such as anterior knee pain, limiting postoperative knee range of motion, etc. These could be evaluated by radiological method after TKA. However, the mainly purpose in this paper was to clarity the anatomy features that femoral anterior condyle height decreases as the femoral AP size increases. The clinical and radiological evaluation requires further study. Later, we will collect relevant clinical and radiological data, and make a summary. I hope I can answer your question. Thank you again.

Methods: Why do the authors compare healthy and degenerate knees? The implications of the study will mainly influence patients undergoing TKA. Additionally, patients undergoing ACL-reconstruction do not necessarily have a "healthy" knee anatomy.

Answer: Thank you very much, it is a good question. The present study mainly to elucidate the anatomical features of femoral anterior condyle height decreased as femoral AP size increases. CT images and TKA intraoperative measurements verify the results for each other. In addition, we selected ACL reconstruction patients with normal knee anatomy, we have described it in revised manuscript(line 123-125).

The authors need to deliver more details on the intraoperative evaluations: It is hard to define "flush" when it comes to the anterior cut of the distal femur. What was the exact definition in your study?

Answer: Thank you very much. Anterior referencing instrumentation was used to cut the anterior condyle. The anterior condylar heights were measured intraoperatively only for patients whose anterior condylar cut line flushed with the anterior cortical surface of the distal femoral shaft. We Illustrate it with a legend (fig 1a) in revised manuscript (line 102-107).

Answer:

Were varus and valgus deformity included?

Answer: Thank you. The criteria for inclusion and exclusion of cases are very important. Patients were excluded if they had a history of femur fracture or congenital anomaly or if the bone loss or degradation was so serious that augmentation was required or if the knee had a varus or valgus deformity of >15°. We have described it in the revised manuscript (line 95-99).

How much external rotation was used for the distal femoral cut?

Answer: Thank you. Generally, The femoral external rotation 3°relative to the posterior condylar axis for the distal femoral cut, or paralleling the transepicondylar axis or perpendicular to Whitesides’ line to ensure the flexion gap balance. We have described it in the revised manuscript (line 102-105).

Results:

Can the authors explain the different results from CT and intraop.?

Answer: Thank you, it is a good question. The pathology of TKA patients have some influences on the anatomy of knee. The cartilage thickness of TKA cases was partly worn or even disappeared completely, and there was no cartilage exit in CT image. So we didn't compare their differences. In addition, the present study mainly to elucidate the anatomical features of femoral anterior condyle height decreased as femoral AP size increases. CT images and TKA intraoperative measurements verify the results for each other.

Line 180 and following: I cannot find the calculations for the correlations between ALCH and LAP and AMCH and MAP respectively. Correlations should be calculated (e.g. Spearman) to display whether these findings show a significance. The method should then also be named in the M+M section.

Answer: Thank you, we apply linear regression analysis to determine correlations between ALCH and LAP, AMCH and MAP dimensions. We have described it in the revised manuscript (line 154-155).

Discussion:

Line 197-206: The authors report on studies which show results in contradiction to their findings and which support the rationale of contemporary TKA designs --> the bigger the femoral component size the bigger the anterior flange. However, the authors do not elucidate why these differences in their study are explainable.

Answer:

Some studies have reported that the anterior condylar height have a positive correlation with the length of the femur or femoral ML size. There has not been a study that analyzed the relationship between anterior condyle height and distal femoral AP size. Our study found that the femoral anterior condyle height decreased with the distal femur size increase, which contrary to the prosthesis currently used. This is the anatomical feature of femoral anterior condyle that we found.

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Attachment

Submitted filename: Response to Reviewers.docx

pone.0297634.s002.docx (34.7KB, docx)

Decision Letter 1

Gennaro Pipino

10 Jan 2024

Femoral anterior condyle height decreases as the distal anteroposterior size increases in total knee arthroplasty: A comparative study

PONE-D-23-04989R1

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Reviewer #2: Partly

Reviewer #4: Yes

**********

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Reviewer #2: I Don't Know

Reviewer #4: Yes

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Reviewer #2: No

Reviewer #4: Yes

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Reviewer #1: Yes: KONSTANTINOS G. MAKRIDIS

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Reviewer #4: No

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Acceptance letter

Gennaro Pipino

16 Feb 2024

PONE-D-23-04989R1

PLOS ONE

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    pone.0297634.s002.docx (34.7KB, docx)

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