1 Introduction

A picture archiving and communication system (PACS) is a means wherein the images are acquired, displayed, transmitted, and stored digitally. It is a computerized way of replacing a traditional hard copy radiological film.^1,2 With the increasing use of PACS in the medical field, the use of hard copy radiological films has been gradually going down.

In a total knee replacement, to produce an acceptable result, extensive pre-operative planning is very important. Also, correct alignment of the implant which can be measured using post-operative radiographs is an important predictor of implant durability and patient satisfaction.^3,4 The scanogram is the gold standard that is used for the measurements related to the alignment of the knee. However, there is evidence suggesting the standard anterior-posterior (ap) entire leg view is better in assessing the alignment.⁵ In most hospitals, these measurements are done using PACS. There is a wide usage of PACS now in most centers, and with advances like the Trauma-CAD integrated with the PACS, it is relatively easy to determine the alignment of the knee.² But not every center is equipped with this expensive software, especially in economically weaker countries.

There have been many medical applications that help in the diagnosis, treatment, and medical education, on various mobile/IPAD platforms. Most of them, however, have not been tested and reviewed for accuracy.^6,7 Bone Ninja is an application on iPad (Apple Inc.) on the IOS platform, developed for patient/physician education by Rubin Institute for Advanced Orthopedics as a teaching tool for deformity corrections around the knee. But this application could also be used for measuring preoperative and postoperative alignment parameters in total knee arthroplasty without the need for expensive software. It is cheap and could be used by an individual user.

Though the application has been commonly used by orthopedic surgeons for many years, there is only one study evaluating the accuracy of measurement of alignment parameters for patients undergoing TKR through bone ninja application and comparing it with PACS⁸ but this may be biased as the study was done by the founder institute itself. Therefore, the principal objective of this study is to determine the reliability and consistency of Bone Ninja application in measuring the preoperative and postoperative alignment in patients undergoing a total knee arthroplasty and compare it with the PACS.

2 Methods

This retrospective cross-sectional study was done using preoperative and postoperative leg-length radiographs of 50 consecutive patients (50 knees) who underwent unilateral total knee arthroplasty in our hospital between January 2019 and December 2019. For the study, the institutional ethical committee provided approval. Only those patients who had both preoperative and postoperative leg length radiographs were included. Three voluntary participants (Two orthopedists and a radiologist) independently measured the intended preoperative and postoperative measurements.

For all measurements, the following points were used: Femoral head center, as determined by the observer center of hip, knee center, as determined by the midpoint of tibial spine, and ankle center as determined by the midpoint of inner edges of malleoli. A line running from the center of the ankle to the center of the femoral head is the mechanical axis of the lower limb. Anatomically, the mechanical axis of a femur is defined by the line connecting the center of the knee with the femoral head center, and that of a tibia by connecting the knee center with the ankle center.

The preoperative parameters measured include a) Lateral distal femoral angle (LDFA), b) Tibiofemoral angle (TFA), and c) Medial proximal tibial angle (MPTA) (Fig. 1). The tibiofemoral angle is calculated by the angle between the mechanical axis of the tibia and the mechanical axis of the femur on the leg length radiographs. Lateral distal femoral angle (LDFA) is the angle between the distal femoral articular surface and the femoral mechanical axis. Medial Proximal Tibia Angle (MPTA) is the angle between the line joining the articular surface of the proximal tibia and the mechanical axis of the tibia. The postoperative alignment parameters measured include a) Tibial alignment angle (TAA), b) Tibiofemoral angle (TFA), and c) Femoral alignment angle (FAA) (Fig. 2). Angle between anatomical and mechanical axes of tibia is referred to as tibial alignment angle whereas Angle between anatomical and mechanical axes of femur is referred to as the femur alignment angle in postoperative leg length radiographs.

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Fig. 1 Illustrative example of preoperative measurements a) LDFA, b) MPTA, c) TFA done using BONE NINJA application.

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Fig. 2 Illustrative example of postoperative measurements a) FAA, b) TFA, c) TAA done using BONE NINJA application.

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All the radiographs were deidentified and assigned sequential numbers. All the measurements were measured using Picture Archiving and Communication Systems (PACS) and the sequence was shuffled using randomization software and repeat measurements were done again in 6 weeks. The sequence shuffled again, and measurements were repeated at 6 weeks intervals using bone ninja application. The radiographs were downloaded in JPEG format (666 × 977 pixels) and the bone ninja application was used on the IPAD platform (IPAD OS version 12/13) for the measurement. Each participant doing the calculation was given instructions on how to use and demonstrated how to do the calculation both on PACS and bone ninja application and were made to calculate the above measurements for at least 15 patients not included in the study under supervision before doing the actual calculation. Institutional computers were used for measurements using PACS and the IPAD 6th generation was used for measurements using the bone ninja application.

Incorporating all the data into an electronic spreadsheet, the analysis was performed using SPSS software v.23 (IBM Corp., Armonk, NY) and Microsoft Office 2007 (Microsoft Corporation, Redmond, WA). We calculated the intraobserver and interobserver correlation coefficients in both the PACS and Bone Ninja with associated 95% confidence intervals to gauge the precisions of the ICCs. Based on a Cohen kappa value, we estimated agreement to be poor, fair, moderate, substantial and good if the values are >0.2, 0.21–0.40, 0.41–0.60, as 0.61–0.80, >0.80 respectively.

3 Results

Preoperative measurements like TFA, LDFA, and MPTA showed highly correlated intraobserver correlation coefficients. Cohen kappa value for TFA, LDFA and MPTA were 0.97, 0.88 and 0.91 respectively for PACS and 0.96, 0.84 and 0.94 for BNA. This demonstrates that there is an excellent intraobserver correlation, therefore measurements made by any participant in BNA are as accurate as that done by PACS. Postoperative measurements like TAA, FAA, and TFA showed highly correlated intraobserver correlation coefficients. Cohen kappa value for TAA, FAA, and TFA were 0.96, 0.95 and 0.85 respectively for PACS and 0.94, 0.96 \and 0.83 for BNA. This demonstrates that there is an excellent intraobserver correlation, therefore measurements made by any participant in BNA are as accurate as that done by PACS (Table 1).

Preoperative measurements like TFA, LDFA, and MPTA showed highly correlated interobserver correlation coefficients. Cohen kappa value for TFA, LDFA and MPTA were 0.96, 0.98 and 0.94 respectively for PACS and 0.88, 0.85 and 0.90 for BNA. The cohen kappa values of BNA were slightly lesser compared to PACS but it was still a good agreement between the participants. Similarly for postoperative measurements, Cohen kappa value for TAA, FAA, and TFA were 0.99, 0.91 and 0.96 respectively for PACS and 0.92, 0.82 and 0.83 for BNA. The cohen kappa values of BNA were slightly lesser compared to PACS but it was still a good agreement between the participants (Table 2).

4 Discussion

The use of technology in the field of orthopedics is increasing day by day. Picture archiving and communication system (PACS) is being utilized regularly by orthopedic surgeons for templating, angular and linear measurements. In the last 2 or 3 decades, PACS has ushered a revolution in the practice of orthopedic surgery. It increases efficiency by streamlining operations throughout the healthcare delivery process. It also allows rapid and efficient communication between orthopedic surgeons and radiologists. With the implementation of the PACS throughout the hospital, diagnoses are made faster and healthcare is delivered more efficiently.⁹ PACS remains the gold standard for image distribution. With updates like Trauma–Cad, PACS remains the workhorse for templating pre-operative and post-operative angular and linear measurements. The accuracy and sensitivity of these measurements as compared to traditional methods based on hard radiographs and pencil tracings have been validated in previous studies.^9,10

Even though PACS has many benefits, it also has a few drawbacks. One of these is the economic burden it puts on the healthcare system. Financial inputs are needed not only for the computers but also for the IT technicians involved in their maintenance. This setup may not be possible for small-sized private hospital setups. Moreover, orthopedists who do independent private clinics may not have access to PACS at all. The essence of PACS is making radiological imaging universally accessible. Making images accessible on smartphones would, therefore, be a step in the right direction. PACS is a hospital-based system and cannot be accessed on smartphones. Applications such as Bone Ninja are being increasingly used by orthopedic surgeons worldwide.

Whitaker et al. compared linear measurements such as leg length, as well as angular measurements like the medial proximal tibial angle (MPTA), and the lateral distal femoral angle (LDFA) of 24 patients (48 limbs) measured using bone ninja application with PACS.¹¹ They observed excellent consistency and reliability of measurements by PACS with excellent inter and intraobserver reliability. But this was the study by the founding institute and may be subjected to bias. Therefore, it was important to check reliability and consistency by independent study. In this study, we have compared the reliability and reproducibility of preoperative angular measurements such as TFA, LDFA, MTPA, and postoperative angular measurements such as TAA, FAA, and TFA in patients undergoing total knee replacement obtained using Bone Ninja application with PACS.

The accuracy of the Bone ninja application has also been compared to PACS in its usage of deformity surgeries. When compared with PACS, Hong et al. Investigated whether the Bone Ninja application was a reliable method for learning the reverse planning method (RPM) for implantable intramedullary (IM) limb-lengthening devices. They concluded, Bone Ninja had similar accuracy in measuring deformity angles and RPM can be applied to IM limb lengthening and deformity correction surgery using bone ninja rather than paper or pencil cutouts.¹² Similarly, Kaul et al. used Bone Ninja for preoperative assessment of 22 patients undergoing high tibial osteotomy. They found no statistical difference in the patient-reported outcomes in these patients as compared to those patients where a preoperative assessment was done based on traditional paper tracing methods.¹³

This study is only the second study comparing the reliability of Bone Ninja to PACS in measuring preoperative and postoperative alignment parameters relating to total knee arthroplasty. This study, therefore, adds to the very limited evidence available on the subject. However, further studies with larger cohorts and patient-reported outcomes are needed to further validate Bone Ninja is a useful and efficient tool in comparison to PACS. The limitation of the study is that accuracy of the linear measurements is not assessed. More studies are needed to validate the reliability of bone ninja for linear measurement. Another limitation of this study is it is a cross-sectional study. The outcome of the surgical procedure following the use of Bone Ninja has not been compared to the patients that underwent surgery after PACS-based surgical planning.

Bone ninja application is a cheaper, user-friendly device that can be used for accurate preoperative planning in total knee arthroplasty and deformity corrective surgeries. The main advantage is that its available on a mobile/IPAD platform and can be used by the individual user even in the comfort of home. This mainly helps the small-scale hospitals where PACS may be available or not affordable. Moreover, it can be used as an excellent educational tool to demonstrate preoperative planning in various workshops and conferences. But it has its drawbacks. Currently, the Bone Ninja application requires manual image transfer from the existing PACS, or any computer system used. This is cumbersome and time-consuming and makes the use of this application limited. This drawback needs to be overcome by the creation of software updates based on existing PACS that can allow automated image sharing and the use of measurement tools for devices such as smartphones and iPads. This might require modifications to images to make them easily transferable without excessive data consumption. Further, there are issues such as data protection. The sharing of images with all health care providers inside a hospital on PACS is generally based on end-user authorization. This needs to be incorporated into the development of applications for mobile use. Another challenge is if the images could not be downloaded or transferred, authors have limited experience of using app by clicking of picture using mobile of Xray film or from the computer screen. Without overcoming these challenges, the use of such applications will remain low.

The use of PACS remains the gold standard for templating, preoperative measurements, and planning. The use of applications such as Bone Ninja instead of PACS may not be recommended in larger hospitals. The current evidence available about the reliability of applications such as Bone Ninja is scarce. More studies with many participants are needed to further validate the findings. The authors recommend that more studies are needed with long-term follow-up to assess the outcome of various orthopedic procedures where applications such as Bone Ninja have been used for templating and planning.

5 Conclusions

PACS remains the gold standard, but bone ninja application is a reliable alternative for preoperative and postoperative alignment measures in total knee arthroplasty where PACS is not available.

Ethical approval

“Institutional Ethical Committee Approval” is taken (no. VIEC/2019/APP/124).

Funding/sponsorship

“This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors”.

CRediT authorship contribution statement

Nuthan Jagadeesh: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration. Ankur Kariya: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Writing – review & editing, Supervision. Srinath Pammi: Methodology, Investigation, Writing – original draft, Writing – review & editing. Vishwanath M. Shivalingappa: Visualization, Supervision, Project administration, Investigation, Data curation, Writing – review & editing. Chethana Ramakrishna: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Project administration, Investigation, Data curation, Writing – review & editing.