https://orcid.org/0009-0000-1460-8154
Figures
Abstract
Background
In knee osteoarthritis, the subtalar joint undergoes valgus and varus contractions to compensate for deformities in the knee joint. In this cross-sectional study, we investigated the relationship between varus-type knee osteoarthritis severity and hindfoot alignment severity by concurrently assessing varus-type knee osteoarthritis severity and hindfoot alignment using radiographs in the long-leg weight-bearing anteroposterior view.
Patients and methods
A total of 114 patients with knee osteoarthritis graded Kellgren–Lawrence II or higher (128 knees) and 30 healthy controls (31 knees) underwent long-leg weight-bearing anteroposterior imaging for 1 year. Four angles were measured on radiographs in the long-leg weight-bearing anteroposterior view: the femorotibial angle; tibial calcaneal angle; tibial anterior surface angle; and talocrural joint angle between the tibial plafond and talar dome on weight-bearing. Group comparisons were conducted for each Kellgren–Lawrence classification, which was used to classify the severity of knee osteoarthritis at each measured angle. One-way analysis of variance was used to test the results.
Results
The mean tibial calcaneal angles were 9.7°, 11.3°, 8.8°, and 9.8° in controls and in patients with Kellgren–Lawrence grades II, III, and IV, respectively (p < 0.05). The mean femorotibial angles were 175.6°, 176.8°, 180.3°, and 186.2° in controls and in patients with Kellgren–Lawrence grades II, III, and IV, respectively (p < 0.05). On weight-bearing, the tibial anterior surface angle and the talocrural joint angle between the tibial plafond and talar dome varied according to severity level.
Conclusion
In varus-type knee osteoarthritis cases, defined in accordance with the Kellgren–Lawrence classification, hindfoot alignment leaned toward valgus. As the severity of knee osteoarthritis progressed, the valgus of the hindfoot alignment reduced. While future longitudinal analyses are necessary, these observations indicate both potential compensatory changes and their limitations in varus-type knee osteoarthritis.
Citation: Ozaki Y, Hara R, Okamura K, Kurokawa H, Inagaki Y, Ogawa M, et al. (2025) Correlation between varus-type knee osteoarthritis severity and hindfoot alignment: Analysis of radiographs in the long-leg weight-bearing anteroposterior view. PLoS One 20(6): e0324974. https://doi.org/10.1371/journal.pone.0324974
Editor: Xindie Zhou, The Affiliated Changzhou No 2 People's Hospital of Nanjing Medical University, CHINA
Received: May 9, 2024; Accepted: May 5, 2025; Published: June 3, 2025
Copyright: © 2025 Ozaki et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the manuscript.
Funding: The author(s) received no specific funding for this work.
Competing interests: The authors have declared that no competing interests exist.
Introduction
In knee osteoarthritis (KOA), the progression of joint destruction correlates with varus or valgus knee deformities [1,2]. Particularly, the subtalar joint in the hindfoot exhibits inverted valgus and varus characteristics with varus/valgus deformities in KOA [3]. Moreover, previous studies have reported that the proportion of unsatisfied patients after total knee arthroplasty for KOA ranged from 11% to 25% [4,5], with potential factors including changes in lower extremity joints beyond knee alignment correction. Preoperative and postoperative lower limb alignment may significantly affect patient outcomes. Postoperative valgus alignment (≥3°) leads to good clinical and functional outcomes, whereas varus alignment (≤−3°) is related to undesirable outcomes. Although osteoarthritis in the lower extremities does not necessarily affect lower extremity alignment alone, it is necessary to consider the relationship between KOA and associated changes in foot morphology when considering changes in lower extremity loading and alignment [6].
Previous reports of compensatory valgus and varus contraction of the subtalar joints with the varus and valgus of KOA have primarily utilized subtalar [7,8] or hip–calcaneus [9] radiography as the radiographic imaging method. However, in clinical settings, long-leg weight-bearing anteroposterior (LL-WB AP) radiography is commonly used to evaluate the effects of lower extremity alignment and loading [10–16]. The LL-WB radiograph is a more reliable method of assessing alignment than computer-assisted navigation, computer tomography, and hindfoot alignment radiography [17,18]. Although subtalar radiography is superior for hindfoot evaluation, LL-WB AP radiography has the advantage of simultaneous imaging and assessing the severity of the entire lower limb, from the hip to the hindfoot and knee joint, which was measured on radiographs in the LL-WB AP view in this study. To the best of our knowledge, no study has examined the association between the severity of KOA and changes in hindfoot alignment. Therefore, in this study, we aimed to determine the relationship between varus-type KOA deformity severity and alignment changes in the subtalar joint using radiographs in the LL-WB AP view.
Materials and methods
Study design, setting, and period
This retrospective case-control study included patients diagnosed with varus-type KOA who underwent LL-WB AP imaging at our department between January 2020 and December 2020. Data were accessed for research purposes between September 1, 2021 and December 31, 2023. The authors did not access personally identifiable participant information during or after data collection.
Study population and inclusion and exclusion criteria
Patients who underwent surgery on at least one of the hip, knee, or talocrural joints, as well as those who underwent imaging that was not valid for reading, were excluded. The control group comprised healthy limbs of patients with knee disorders, such as trauma, ligament injuries, pain, and soft tissue inflammation, whose radiographs were concurrently acquired in the LL-WB AP view. Both knees were evaluated for each patient.
The LL-WB AP view technique is shown in Fig 1. The patients were placed on the ground under a bipedal standing load. The X-ray tube position was set at a distance of 2 m from the patella according to the patellar elevation. Radiographs were captured from the fourth lumbar vertebra to the lower end of the calcaneus [19]. Digital radiographs were used for reading in all cases. One LL-WB AP imaging was performed per patient between January 2020 and December 2020.
Imaging: Fourth lumbar vertebrae to the lower end of the calcaneus; Middle point of imaging: Patella.
Measures
Four angles were measured to evaluate lower limb alignment. First, the femorotibial angle (FTA) was defined as the lateral angle of the femur and tibia diaphyseal lines. This measurement was conducted using the midpoint of the transverse diameter located 10 cm from the center of the femoral and tibial epiphyses, respectively (Fig 2a). Second, the tibial calcaneal angle (TCA) was defined as the angle between the tibial axis and the line connecting the calcaneal contour contact point, which is tangential to the line perpendicular to the tibial axis and center of the tibial canal. The calcaneal contour was defined as the easily discernible cortical bone contour line of the calcaneus in the LL-WB AP view (Fig 2b). The third angle, known as the tibial anterior surface angle (TAS), was measured as the medial angle between the tibial axis and tibial canopy in the frontal view of the talocrural joint (Fig 2c). Finally, the angle between the tibial plafond and talar dome during weight-bearing (TTW) was determined. This angle was defined as the positive angle for varus deformation of the talocrural joint (Fig 2d).
We defined each angle as above, using the Kellgren–Lawrence (K–L) classification and four measured angles, and analyzed the differences between each group for each severity of varus-type KOA at each measured angle.
Two experienced orthopedic surgeons participated in a reliability test regarding the reliability of the assessment when reading the radiographs. Each orthopedic surgeon used randomly selected radiographs and measured the four angles according to established definitions.
When the intra- and inter-examiner reliabilities were examined, the intraclass correlation coefficients for reliability were as follows: FTA, 0.99 for intra-rater and 0.99 for inter-rater; TCA, 0.97 for intra-rater and 0.97 for inter-rater; TAS, 0.71 for intra-rater and 0.86 for inter-rater; and TTW, 0.99 for intra-rater and 0.95 for inter-rater.
Varus-type KOA severity was classified using the K–L classification [20], whereas ankle osteoarthritis severity was assessed using the Takakura–Tanaka (T–T) classification [21,22].
Distinguishing between K–L grade 0 and I KOA based solely on radiographs was challenging. This resulted in the index group being split into three groups: KL grade II, III, and IV.
Compliance with ethical standards
All procedures performed in the study involving human participants were reviewed and approved by the Nara Medical University Ethics Committee and adhered to the ethical standards of the institution where the study was conducted (Approval No. 3094), the 1964 Declaration of Helsinki, and subsequent amendments or equivalent. Consent was obtained from patients through an open-written opt-out method.
Statistical analyses
One-way analysis of variance (ANOVA) was performed to assess the significance of the differences between the grade and control groups in the K–L classification across the four measured angles. Additionally, ANOVA was used to assess differences between the stage and control groups in the T–T classification at the TCA. Post-hoc analysis was performed using the Bonferroni test for multiple comparisons. The level of significance was set at p < 0.05. All statistical analyses were performed using IBM SPSS software (version 28; Armonk, NY, USA).
Results
Participant selection
From January and December 2020, 200 patients with varus-type KOA (216 knees) underwent LL-WB AP imaging. After excluding cases wherein surgery involved more than one joint in the lower limbs, those wherein interpretation of bone contour shadows was difficult when reading radiographs, and those with insufficiently captured radiographs, the study cohort comprised 114 patients (128 knees).
Baseline participant characteristics
The distribution of K–L classification within the study cohort was as follows: 35 knees from 28 patients classified as grade II, 55 knees from 52 patients classified as grade III, and 38 knees from 34 patients classified as grade IV. The control group consisted of 31 knees from 30 patients (Table 1).
KOA severity
The FTA, TCA, TAS, and TTW for each grade group of the K–L classification and control groups are presented in Table 2. Significant differences were observed in the FTA and TCA among the four groups (p < 0.05) (Fig 3a, b). Specifically, the mean TCAs were 9.7° for controls, 11.3° for those with grade II, 8.8° for those with grade III, and 9.8° for those with grade IV, with a significant difference observed when comparing those with grade II and those with grade III (p = 0.026). No significant difference was observed in the TAS and TTW among the four groups (p = 0.94 and p = 0.17, respectively) (Fig 3c, d).
(a) Femorotibial angle (p < 0.05); (b) tibial calcaneal angle (p < 0.05); (c) tibial anterior surface angle (p = 0.94); (d) talar dome during weight-bearing (p = 0.17).
KOA and ankle OA severity
Across all severities of varus-type KOA, ankle osteoarthritis was found to be in its early stages in approximately half of the cases, whereas all talocrural joints in the control group were categorized as stage 0 (Table 3).
Discussion
This study compared the severity of each varus-type KOA grade with lower limb and hindfoot alignment. Our findings revealed a correlation between the severity of varus-type KOA and FTA, consistent with those of previous reports [1,23,24]. Notably, this study contributes to the literature by investigating the association between varus-type KOA severity and hindfoot alignment. Although previous studies have examined knee and hindfoot alignment, such as in the study by Norton et al. [3], in this work, we examined the association between the severity of varus-type KOA [20] and hindfoot alignment. To assess varus/valgus deformities, we used TAS to confirm the presence and extent of varus/valgus deformities in the talar canal [25,26] and TTW to confirm the presence and extent of varus/valgus deformities in the anterior view of the talofemoral joint [27] in varus-type KOA. To observe hindfoot alignment, we defined the TCA and measured it to determine hindfoot valgus with respect to the tibial axis. As it is possible to identify the contour of the calcaneus in the LL-WB AP view, we decided to measure calcaneal alignment using the contour. Our findings revealed that the hindfoot may compensate for varus-type KOA by changing hindfoot alignment.
In this study, we did not observe a correlation between the TCA and the severity of varus-type KOA. This finding could be attributed to several factors. First, as more than half of the patients in this study had early-stage ankle osteoarthritis (T-T stage 0, 1, 2), the influence of the TAS and TTW on the TCA might have been minimal. Moreover, the varus/valgus of the subtalar joint might have affected the change in the TCA. Although a positive correlation between knee joint valgus/varus and hindfoot varus/valgus has been reported in KOA using radiographs in the LL-WB AP view [3], no study to date has reported on changes in hindfoot varus/valgus based on KOA severity as per the K–L classification. The present study showed a positive correlation up to grade II of K-L classification of varus-type knee OA and no positive correlation at grade III. The reason may be the limitation or failure of the compensatory function of the hindfoot between grades II and III.
As indicated by the TCA, the observed reduction in medial load, particularly in cases classified as below K–L grade II, may be attributed to the alterations in the TCA shown in our study results. One conservative treatment for KOA is the use of plantar plates. Interestingly, previous reports have shown that lateral wedge insoles with arch support improved knee instability [28] and significantly improved pain and physical function [29]. Particularly, the use of lateral wedge insoles reportedly improves the load values on the medial meniscus and the difference between unloaded and loaded load values, especially in individuals with early varus-type KOA (K–L classification grade II or lower) [30]. A previous report [31] revealed that the lateral wedge plantar plate is effective in verticalizing the load axis from the hip joint to the calcaneus owing to the valgus of the calcaneus at the subtalar joint.
This study had some limitations. First, the calcaneal loading site was not validated in three dimensions. In the present study, we assessed both the knee joint and hindfoot solely from the frontal view of radiographs in the LL-WB AP view. It may be challenging to evaluate the effectiveness of conservative treatment for all severities of knee osteoarthritis using only the two-dimensional evaluation of radiography. We acknowledge the necessity of conducting further research to perform a three-dimensional morphological evaluation of the hindfoot joint surface and identify the point of passage of the lower limb-loading axis. Second, as this was a cross-sectional study, it was not possible to demonstrate a causal relationship. Future longitudinal studies are warranted to address this limitation and elucidate any causal relationships between varus-type KOA severity and hindfoot alignment changes over time.
Conclusion
In our evaluation using radiographs in the LL-WB AP view, we observed ectropion of the hindfoot in K–L classification grade II, with a subsequent reduction in hindfoot ectropion noted in varus-type KOA grade III cases. These results suggest the potential for alignment correction in the hindfoot and highlight its limitations in the progression of varus-type KOA.
Acknowledgments
The authors would like to thank Dr. Yuuki Nishimura for his assistance in the research and validation of the measurements.
References
- 1. Brouwer GM, van Tol AW, Bergink AP, Belo JN, Bernsen RMD, Reijman M, et al. Association between valgus and varus alignment and the development and progression of radiographic osteoarthritis of the knee. Arthritis Rheum. 2007;56(4):1204–11. pmid:17393449
- 2. Sharma L, Song J, Dunlop D, Felson D, Lewis CE, Segal N, et al. Varus and valgus alignment and incident and progressive knee osteoarthritis. Ann Rheum Dis. 2010;69(11):1940–5. pmid:20511608
- 3. Norton AA, Callaghan JJ, Amendola A, Phisitkul P, Wongsak S, Liu SS, et al. Correlation of knee and hindfoot deformities in advanced knee OA: compensatory hindfoot alignment and where it occurs. Clin Orthop Relat Res. 2015;473(1):166–74. pmid:25024033
- 4. Kim C-W, Gwak H-C, Kim J-H, Lee C-R, Kim J-G, Oh M, et al. Radiologic factors affecting ankle pain before and after total knee arthroplasty for the varus osteoarthritic knee. J Foot Ankle Surg. 2018;57(5):865–9. pmid:29779992
- 5. Lee JH, Jeong BO. Radiologic changes of ankle joint after total knee arthroplasty. Foot Ankle Int. 2012;33(12):1087–92. pmid:23199858
- 6. Zheng T, Liu D, Chu Z, Luo Y, Lu Q, Zhang B, et al. Effect of lower limb alignment on outcome after lateral unicompartmental knee arthroplasty: a retrospective study. BMC Musculoskelet Disord. 2024;25(1):82. pmid:38245762
- 7. Tanaka Y, Takakura Y, Fujii T, Kumai T, Sugimoto K. Hindfoot alignment of hallux valgus evaluated by a weightbearing subtalar x-ray view. Foot Ankle Int. 1999;20(10):640–5. pmid:10540995
- 8. Neri T, Barthelemy R, Tourné Y. Radiologic analysis of hindfoot alignment: comparison of Méary, long axial, and hindfoot alignment views. Orthop Traumatol Surg Res. 2017;103(8):1211–6. pmid:28965994
- 9. Tanaka T, Takayama K, Hashimoto S, Kanzaki N, Hayashi S, Kuroda R, et al. Radiographic analysis of the lower limbs using the hip-calcaneus line in healthy individuals and in patients with varus knee osteoarthritis. Knee. 2017;24(5):1146–52. pmid:28800855
- 10. Chang CB, Choi J-Y, Koh IJ, Seo ES, Seong SC, Kim TK. What should be considered in using standard knee radiographs to estimate mechanical alignment of the knee?. Osteoarthritis Cartilage. 2010;18(4):530–8. pmid:20060951
- 11. Issa SN, Dunlop D, Chang A, Song J, Prasad PV, Guermazi A, et al. Full-limb and knee radiography assessments of varus-valgus alignment and their relationship to osteoarthritis disease features by magnetic resonance imaging. Arthritis Rheum. 2007;57(3):398–406. pmid:17394225
- 12. Jawhar A, Wasnik S, Scharf H-P, Roehl H. Fibula head is a useful landmark to predict the location of posterior cruciate ligament footprint prior to total knee arthroplasty. Int Orthop. 2014;38(2):267–72. pmid:24045910
- 13. Paley D, Herzenberg JE, Tetsworth K, McKie J, Bhave A. Deformity planning for frontal and sagittal plane corrective osteotomies. Orthopedic Clinics of North America. 1994;25(3):425–65.
- 14. Lonner JH, Laird MT, Stuchin SA. Effect of rotation and knee flexion on radiographic alignment in total knee arthroplasties. Clin Orthop Relat Res. 1996;(331):102–6. pmid:8895625
- 15. Rauh MA, Boyle J, Mihalko WM, Phillips MJ, Bayers-Thering M, Krackow KA. Reliability of measuring long-standing lower extremity radiographs. Orthopedics. 2007;30(4):299–303. pmid:17424694
- 16. Swanson KE, Stocks GW, Warren PD, Hazel MR, Janssen HF. Does axial limb rotation affect the alignment measurements in deformed limbs?. Clin Orthop Relat Res. 2000;(371):246–52. pmid:10693572
- 17. Babazadeh S, Dowsey MM, Bingham RJ, Ek ET, Stoney JD, Choong PFM. The long leg radiograph is a reliable method of assessing alignment when compared to computer-assisted navigation and computer tomography. Knee. 2013;20(4):242–9. pmid:22892197
- 18. Reilingh ML, Beimers L, Tuijthof GJM, Stufkens SAS, Maas M, van Dijk CN. Measuring hindfoot alignment radiographically: the long axial view is more reliable than the hindfoot alignment view. Skeletal Radiol. 2010;39(11):1103–8. pmid:20062985
- 19.
Paley D, Herzenberg J. Radiographic assessment of lower limb deformities. In: Principles of deformity correction. Vol 3. Berlin, Heidelberg, New York: Springer; 2005. p. 31–60.
- 20. Kellgren JH, Lawrence JS. Radiological assessment of osteo-arthrosis. Ann Rheum Dis. 1957;16(4):494–502. pmid:13498604
- 21. Takakura Y, Tanaka Y, Kumai T, Tamai S. Low tibial osteotomy for osteoarthritis of the ankle. Results of a new operation in 18 patients. J Bone Joint Sur British. 1995;77(1):50–4.
- 22. Tanaka Y, Takakura Y, Hayashi K, Taniguchi A, Kumai T, Sugimoto K. Low tibial osteotomy for varus-type osteoarthritis of the ankle. J Bone Joint Surg Br. 2006;88(7):909–13. pmid:16798994
- 23. Felson DT, Cooke TDV, Niu J, Goggins J, Choi J, Yu J, et al. Can anatomic alignment measured from a knee radiograph substitute for mechanical alignment from full limb films?. Osteoarthritis Cartilage. 2009;17(11):1448–52. pmid:19505430
- 24. Duryea J, Neumann G, Niu J, Totterman S, Tamez J, Dabrowski C, et al. Comparison of radiographic joint space width with magnetic resonance imaging cartilage morphometry: analysis of longitudinal data from the osteoarthritis initiative. Arthritis Care Res (Hoboken). 2010;62(7):932–7. pmid:20589702
- 25. Harada S, Teramoto T, Takaki M, Asahara T, Katoh N, Takenaka N, et al. Radiological assessments and clinical results of intra-articular osteotomy for traumatic osteoarthritis of the ankle. Injury. 2021;52(11):3516–27. pmid:34462118
- 26. Burssens A, Susdorf R, Krähenbühl N, Peterhans U, Ruiz R, Barg A, et al. Supramalleolar osteotomy for ankle varus deformity alters subtalar joint alignment. Foot Ankle Int. 2022;43(9):1194–203. pmid:35786021
- 27. Kurokawa H, Taniguchi A, Miyamoto T, Tanaka Y. The relationship between the distal tibial fibular syndesmosis and the varus deformity in patients with varus ankle osteoarthritis. Foot Ankle Orthop. 2021;6(4):24730114211041111. pmid:35097473
- 28. Jindasakchai P, Angthong C, Panyarachun P, Rajbhandari P, Rungrattanawilai N. Therapeutic significance of insoles in patients with knee osteoarthritis. Eur Rev Med Pharmacol Sci. 2023;27(11):5023–30. pmid:37318476
- 29. Zafar AQ, Zamani R, Akrami M. The effectiveness of foot orthoses in the treatment of medial knee osteoarthritis: a systematic review. Gait Posture. 2020;76:238–51. pmid:31874456
- 30. Ishii Y, Ishikawa M, Hayashi S, Kanemitsu M, Omoto T, Kurumadani H, et al. The correlation between osteoarthritis stage and the effect of the lateral wedge insole for 3 months on medial meniscus extrusion in the knee joint. Knee. 2021;28:110–6. pmid:33333466
- 31. Yasuda K, Sasaki T. The mechanics of treatment of the osteoarthritic knee with a wedged insole. Clin Orthopaed Relat Res. 1987;215(NA):162–171.