Is conventional knee radiograph reliable enough to assess the anatomical knee alignment and total knee prosthesis position in Indian population?

Suryamanikanta Balabadra; Ratnakar Vecham; Maryada Venkateshwar Reddy; Adarsh Annapareddy; M. Mahendra Kumar; A. V. Gurava Reddy

doi:10.4103/jotr.jotr_59_21

ORIGINAL ARTICLE

Year : 2022 | Volume : 14 | Issue : 1 | Page : 42-45

Is conventional knee radiograph reliable enough to assess the anatomical knee alignment and total knee prosthesis position in Indian population?

Suryamanikanta Balabadra¹, Ratnakar Vecham¹, Maryada Venkateshwar Reddy¹, Adarsh Annapareddy¹, M. Mahendra Kumar², A. V. Gurava Reddy³
¹ Department of Orthopedics, Sunshine Hospitals, Secunderabad, Telangana, India
² Department of Radiology, Sunshine Hospitals, Secunderabad, Telangana, India
³ Department of Radiology and Imaging, Sunshine Hospitals, Secunderabad, Telangana, India

Date of Submission	24-Jun-2021
Date of Acceptance	25-Dec-2021
Date of Web Publication	15-Jun-2022

Correspondence Address:
Dr. Ratnakar Vecham
Department of Orthopedics, Sunshine Hospitals, Secunderabad, Telangana
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jotr.jotr_59_21

Abstract

Background: The success and survivorship of primary total knee replacement mainly depend on the postoperative alignment and implant position. Long-leg radiograph (LLR) is considered gold standard in assessing knee alignment postoperatively. Studies have reported that bowing of the femoral shaft in the coronal plane is prevalent in Asian population, which is not fully visualized on a conventional knee radiograph (CKR) and may affect the assessment of coronal alignment. However, postoperatively, CKR is easy to perform and has several advantages if it provides similar precision. Purpose: The purpose was to evaluate the validity of CKR in assessing the anatomical knee alignment and prosthesis position as compared with the LLR in Indian population. Materials and Methods: One hundred knees in 83 patients were subjected to CKR and LLR during postoperative follow-up at 6 weeks. Three parameters were evaluated to assess the coronal alignment and the component positions - femoral component angle (FCA), tibial component angle (TCA), and tibiofemoral angle (TFA). Results: There was an excellent correlation between the TCA as measured from the long and CKRs (r = 0.884, P = 0.01). There was a high positive correlation between the FCA (r = 0.703, P = 0.01) and TFA (r = 0.754, P = 0.01) as measured from the long radiographs and the conventional radiographs. Regression analysis defined these relationships to be linear. Conclusion: CKR could be an appropriate alternative for the LLR in evaluating the postoperative knee alignment and total knee prosthesis position despite the fact that there is excessive femoral bowing in Indian population.

Keywords: Conventional knee radiograph, coronal alignment posttotal knee arthroplasty, femur component angle, long-leg radiograph, tibial component angle, tibiofemoral angle

How to cite this article:
Balabadra S, Vecham R, Reddy MV, Annapareddy A, Kumar MM, Reddy AV. Is conventional knee radiograph reliable enough to assess the anatomical knee alignment and total knee prosthesis position in Indian population?. J Orthop Traumatol Rehabil 2022;14:42-5

How to cite this URL:
Balabadra S, Vecham R, Reddy MV, Annapareddy A, Kumar MM, Reddy AV. Is conventional knee radiograph reliable enough to assess the anatomical knee alignment and total knee prosthesis position in Indian population?. J Orthop Traumatol Rehabil [serial online] 2022 [cited 2022 Jun 26];14:42-5. Available from: https://www.jotr.in/text.asp?2022/14/1/42/347367

Introduction

Total knee arthroplasty (TKA) has become a common surgical procedure worldwide. The long-term outcome of primary total knee replacement mainly depends on the postoperative alignment. Furthermore, the survivorship of the implant depends on the postoperative coronal alignment and implant position.^{[1],[2],[3],[4]} Although long-leg radiograph (LLR) is considered to be the gold standard to assess coronal alignment.^[5],[6] Selecting the most efficient radiograph, with the best precision, in economically constrained settings is necessary. Previous studies in literature report that the bowing of the femoral shaft in the coronal plane affects lower limb alignment and is prevalent in Asian population, and the same femoral bowing is reflected in postoperative coronal alignment.^[7],[8],[9] Femoral bowing is better visualized on a LLR.^[10] However, LLR is not always used because of limited accessibility, greater exposure to radiation, more sophisticated techniques required, and higher cost. Conventional knee radiograph (CKR) is a cheaper and readily available alternative with less radiation exposure.^[11],[12] Therefore, using CKR to measure the anatomical knee alignment and prosthesis position in the coronal plane may offer some advantages over LLR if it provides similar precision. The purpose of the present study was to evaluate the validity of CKR in assessing the anatomical knee alignment and prosthesis position as compared with the LLR in Indian population. We hypothesized that LLR would be more accurate than a CKR to assess prosthesis position and knee alignment, considering the prevalence of femoral bowing.

Materials and Methods

Approval from the Institutional Ethics committee was obtained. The current study prospectively evaluated 100 knees in 83 patients who underwent primary TKA with posterior stabilized prosthesis (Maxx Implant) between July 2018 and September 2018. Subjects were excluded if they had flexion contracture or recurvatum >10°, those with extra-articular deformity, and those who underwent previous lower extremity surgery other than total knee replacement. All the 100 knees were subjected to CKR and LLR during postoperative follow-up at 6 weeks. Patients were positioned at standard distance of 180 cm from the radiographic tube in a bipedal stance with both patellae facing forward to prevent rotational error. For the CKR, cassette size of 35 cm × 43 cm was used. The center of the film was focused on the lower part of the patella. Radiographs were performed using 50–120 mAs and 80–120 kVp, depending on the patient's body mass, and the digital radiographs were electronically transferred to a picture archiving and communication system (PACS). The 3 feet LLRs were taken using three cassettes each of size 35 cm × 43 cm stacked one above the other in a customized chamber. Anteroposterior view of the knee including hip and ankle was taken, and the three images were merged using FLFS software in AGFA DX-G machine to obtain LLR. Outcome measures: three parameters were evaluated to assess the coronal alignment and the component positions - femoral component angle (FCA), tibial component angle (TCA), and tibiofemoral angle (TFA). The angles were measured digitally using tool devices in PACS as described by Tammachote et al.^[13] FCA is the medial angle between the anatomical femoral axis and the articular surface of femoral component [Figure 1] and [Figure 2], on conventional and long leg radiograph respectively], whereas TCA is the medial angle between the anatomical tibial axis and the base plate of the tibial component [Figure 1] and [Figure 2], on conventional and long leg radiograph respectively]. TFA is defined as the angle between the anatomical axis of the femur and the anatomical axis of the tibia on the medial side [Figure 3] and [Figure 4], on conventional and long leg radiograph respectively]. Femoral axis on conventional radiograph is a line that connects the center of medial and lateral condyles of femoral component with the center of the femoral shaft 15 cm above the joint line [Figure 1] and [Figure 3] , whereas on long radiograph, it is a line that connects the center of the femoral shaft 1 cm below the lesser trochanter and 10 cm above the joint line [Figure 2] and [Figure 4]. Tibial axis on long radiograph is a line that connects the center of tibial component and the center of the talus, whereas on conventional radiograph, it is the line that connects the center of tibial component and the center of the tibial shaft 15 cm below the joint line.

Figure 1: Femoral component angle (FCA) and tibial component angle (tca) measurement on conventional knee radiograph

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Figure 2: Femoral component angle (FCA) and tibial component angle (tca) measurement on long leg radiograph

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Figure 3: Tibio-femoral angle (TFA) measurement on conventional knee radiograph

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Figure 4: Tibio-femoral angle (TFA) measurement on long leg radiograph

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Statistical analysis

Data were entered in a Microsoft Excel Sheet, and the SPSS Statistics 24 software (IBM Corp. Released 2016. IBM SPSS Statistics for Windows, Version 24.0. Armonk, NY: IBM Corp.) was used for statistical analysis. Data were analyzed using Pearson's correlation coefficient (r) values and simple linear regression. Descriptive statistics such as mean, standard deviation, and 95% confidence intervals (CIs) were assessed. Differences between the measured values were analyzed by paired t-test. Intra-rater and inter-rater reliabilities were first evaluated in 25 randomly selected LLR, and 25 randomly selected CKR using intraclass correlation coefficients (ICCs). Blinded measurements by two observers (ICC model 2, 1) and repeated measurements by one observer with a 2 weeks interval (ICC model 1, 1) were performed. Intra-rater and inter-rater reliabilities exceeded 0.8 for all measurements except one and were regarded as good to excellent [Table 1]. Because these results indicated that measurements were highly reliable, measurements taken by a single observer were used in the analyses.

Table 1: Intra-rater and inter-rater correlation coefficients

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Results

A total of 100 knee radiographs in 83 patients (61 women and 22 men) were evaluated. Seventeen patients had bilateral TKA. The mean age at the time of TKA was 62.15 years. The alignment characteristics of each measurement are shown in [Table 2]. The CKR measurements resulted in a mean increment of 0.74 (95% CI, 0.20–1.28; P = 0.007) for TCA, 1.58 (95% [CI], 1.08–2.09; P = 0.000) for FCA, and 1.98 (95% 1 CI, 1.23–2.73; P = 0.000) for TFA compared to LLR [Table 3]. There was an excellent correlation between the TCA as measured from the long and CKRs (r = 0.884, P = 0.01). Regression analysis defined this relationship to be linear. TCA angles measured from the conventional radiographs accounted for r² = 0.782% of the total variability in TCA measured from the long radiographs. There was a high positive correlation between the FCA (r = 0.703, P = 0.01) and TFA (r = 0.754, P = 0.01) as measured from the long radiographs and the conventional radiographs. Regression analysis defined these relationships to be linear. The FCA and TFA measured from the conventional radiograph accounted for r² = 0.495% and r² = 0.568%, respectively, of the total variability in angles measured from long radiograph.

Table 2: Alignment characteristics of the cohort

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Table 3: Mean differences and t-test results

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Discussion

Adequate assessment of the postoperative coronal alignment of the lower extremity is important to find the success of TKA. In addition, longevity of TKA in large part depends on the ability to achieve proper alignment because numerous studies in the current literature have shown that malalignment of a TKA adequately increases contact stresses through the implant and can be one of the factors leading to failure.^[14],[15] Full-length radiograph is considered gold standard to assess the mechanical alignment, but in the existing literature, there are reports of both long and conventional radiographs being used in assessing the alignment.^{[5],[16],[17]} Radiographic features of the femur and tibia in the coronal plane have implications on measurement of alignment. Studies have reported variations in femoral bowing between ethnicities.^[18],[19] Many Asian studies found excessive lateral femoral bowing in knees with advanced osteoarthritis.^[7],[8],[10] Femoral bowing is better visualized on LLRs. However, long radiographs are not readily accessible and are costly. The study evaluates the effectiveness of CKRs as compared with that of LLRs in the assessment of postoperative limb alignment and total knee prosthesis position in Indian population.

Skyttä et al.^[20] conducted a similar study and reported TFA had an excellent correlation, whereas FCA and TCA had good correlations between the long and regular knee radiographs. However, the measurements were taken manually using goniometer. Our study aimed at minimizing the error by measuring precisely using digital films. In our study, TCA angle showed excellent correlation, whereas FCA and TFA showed a high correlation between the conventional and LLRs which suggest that alignment of components and tibiofemoral angle can be reliably measured on CKRs. In the current study, the mean TCAs, FCAs, and TFAs measured from conventional radiographs slightly overestimated valgus alignment by 0.74°, 1.58°, and 1.98°, respectively. The valgus overestimation in the CKR could be due to a shorter distance above the joint line where it meets the lateral bowing of the femur.^[21]

Kim et al. in their study concluded that surgeons should aim at overall anatomical knee coronal alignment at an angle of 3°–7.5° valgus; femoral component alignment, 2°–8° valgus; and tibial coronal alignment, 90°, to improve the survival of total knee prosthesis.^[22] Another study by Fang et al. has proposed that alignment between 2.4° and 7.2° of valgus is acceptable, and they have the best survival rates.^[4] Even though CKRs in this study have slightly overestimated valgus alignment, the mean values of the alignment characteristics fell within the acceptable range. Therefore, clinical outcomes and survivorship of implants may not vary. However, in cases with excessive femoral or tibial bowing and in those with conflicting clinical and radiological findings, full-length radiograph in at least one follow-up is advisable.

Limitations of the study

The study has looked only at the coronal alignment, but it is important to understand that alignment concerns are three dimensional. Second, rotation of the limb when obtaining the radiograph can have an effect on the value of the measured angles. However, all of our radiographs were obtained under a single-institutional protocol, and this approach has minimized this potential limitation.

Conclusion

CKR could be an appropriate alternative for the LLR in evaluating the postoperative knee alignment and total knee prosthesis position despite the fact that there is excessive femoral bowing in Indian population.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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