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Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty
THEKNE-02901; No of Pages 8 The Knee xxx (xxxx) xxx
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The Knee
Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty Andreas Kappel a,b,⁎, Jacob Fyhring Mortensen c, Poul Torben Nielsen a, Anders Odgaard c, Mogens Laursen a,b a b c
Orthopaedic Research Unit, Aalborg University Hospital, Aalborg, Denmark Department of Clinical Medicine, Aalborg University, Aalborg, Denmark Department of Orthopedic Surgery, Copenhagen University Hospital Herlev-Gentofte, Hellerup, Denmark
a r t i c l e
i n f o
Article history: Received 30 May 2019 Received in revised form 4 August 2019 Accepted 19 September 2019 Available online xxxx Keywords: Total knee arthroplasty Soft tissue Laxity Stress radiography Reliability Agreement
a b s t r a c t Background: Stress radiography is used in the valuation of soft tissue laxity following total knee arthroplasty (TKA). However, reliability and agreement is largely unknown. Methods: In this prospective reliability study, we included 15 participants with prior TKA. Standardized coronal stress radiographs were obtained in both extension and flexion and with both varus and valgus stress. All radiographs were repeated (test–retest). In extension the Telos stress device was used, and flexion radiographs were obtained using the epicondylar-view. Three independent raters measured angulation between femoral and tibial component from all radiographs. Reliability was assessed by intra-class correlation coefficient (ICC) and agreement visualized with Bland–Altman plots and by mean difference and limits of agreement (LOA). Results: Stress radiography in extension showed excellent reliability with ICC = 0.96 (0.95– 0.98) and LOA of ±1.2°. Stress radiography at 80–90° of flexion showed good to excellent reliability when measuring medial laxity with ICC = 0.94 (0.89–0.97) and LOA of ±1.7°; however, when measuring lateral laxity the reliability was only moderate to good with ICC = 0.70 (0.51–0.84) and LOA of ±6.3°. Conclusion: Stress radiography is clinically applicable and the methods described in this study provide excellent reliability for measurement of laxity in extension. The reliability of measurements in flexion is good to excellent when measuring medial laxity but only moderate to good when measuring lateral laxity. © 2019 Elsevier B.V. All rights reserved.
1. Introduction Radiographs are routinely used after knee replacement to obtain documentation of positioning and sizing of implants, and radiographic investigations are fundamental in the examination of patients with poorly functioning implants [1]. The functional outcome of knee arthroplasty is dependent on soft tissue balancing, where poor outcomes may be caused by the knee being too loose or too tight [2,3]. Radiographic techniques may provide good means of quantifying knee laxity and its importance for functional outcome, but the performance of the functional radiographic techniques is largely unknown. Stress radiography using the Telos stress device (TSD) (Telos GmbH, Hungen – Obbornhofen, Deutschland) can be used to assess ligament laxity and joint space width in both native [4] and total knee arthroplasty (TKA) knees [5,6]. The reliability of this method, in the assessment of coronal laxity in extension following TKA, has not been reported previously. Different methods of
⁎ Corresponding author. E-mail address: [email protected]. (A. Kappel).
https://doi.org/10.1016/j.knee.2019.09.013 0968-0160/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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obtaining coronal stress radiography in flexion have been described and one method using manual traction and fluoroscopy has been found to be reliable [7]. However, this method may not be applicable in general due to the exposure of radiation to the examiner. The methods used in recent publications [8,9] do not use fluoroscopy and have not yet been statistically validated. Stress radiographic measurement of laxity in flexion has been associated with patient-reported outcomes [8,9]. Standardized and reliable methods to quantify soft tissue laxity, which can be implemented in clinical practice and clinical research, are required in the evaluation of surgical results following TKA. The objective of this study was to examine reliability and agreement of coronal stress radiographs in extension using the TSD and in flexion using the epicondylar view (EV) by comparison of repeated stress-radiographs (test–retest). 2. Materials and methods The north Denmark regional committee on health research ethics (N-20180028) and the Danish data protection agency (200858-0028/2018-79) approved the study. 2.1. Participants Fifteen participants with prior TKA were recruited from the outpatient clinic during May 2018. Patients participating could only participate with one knee. 2.2. Inclusion and exclusion criteria Inclusion criteria were posterior cruciate retaining TKA and follow-up of at least 12 months. Exclusion criteria were pain upon physical examination, extension deficit above five degrees and flexion below 100°. A body mass index (BMI) limit of 35 kg/m2 was set to decrease the uncertainty that might follow from excessive subcutaneous tissue. 2.3. Stress radiographs 2.3.1. Extension Coronal stress radiographs in extension were obtained with use of the TSD. Procedure followed the method described earlier [5,6], and followed the manufactures guidelines, with application of 150 N varus or valgus stress at the level of the joint-line, while observing the patella facing forwards. During the examination, the knee was resting on a pillow, securing a flexion of approximately 10°. 2.3.2. Flexion The procedure for obtaining stress radiographs in flexion using the EV followed the methods described by Oh et al. [9] and Tsukiyama et al. [8]. The participant was placed sitting on the radiographic table with the lower leg hanging free resulting in a knee angulation of 80–90°. The X-ray beam was directed from posterior to anterior in an upward angulation of 15° towards the centre of the jointline, the distance between the X-ray tube and the cassette was set at 150 cm (Figure 1(a)). Coronal stress was applied in a horizontal direction, and resulted in either varus or valgus stress. Traction was applied just above the ankle joint with a force of 50 N (Figure 1(b)). A supplementary video describing this method can be found online at: https://video.rn.dk/stress-radiographic. Radiographs were recorded in varus- and valgus-stress in both extension and flexion, and all radiographs were repeated (test– retest). Before the repeated radiographs the participants had a break and a short walk. Three dedicated radiographers were responsible for all radiographs in the study. Radiation exposure to the participants was minimized by narrowing the field of expose and by using low-dose radiographs to allow visualization of implants but not soft tissues. 2.4. Radiologic evaluation Following maximal enlargement of the area between the femoral and tibial components, joint opening angle between these was measured. The tibial line was marked from the most lateral and distal corner of the tibial tray to the most medial and distal corner of the tray, and the femoral line connected the most distal medial and lateral parts of the femoral condyles. Angulation between these two lines, the joint opening angle, was read to one decimal place (Figure 2(a)–(e)). Three raters independently measured all radiographs two times with an interim period of two weeks. Radiographs were blinded and presented in different randomized sequences. Rater 1 was a resident and PhD student within orthopedics, Rater 2 was a consultant orthopedic surgeon specializing in hip surgery, and Rater 3 was a consultant orthopedic surgeon specializing in knee surgery. Raters 2 and 3 were very familiar with digital measurement in the PACS viewer, but only Rater 3 had expertise in measurement of knee implants. 2.5. Statistical analysis Power calculation was carried out with respect to test–retest reliability using Bonett's method [10]. A sample size of 12 cases was calculated, 15 cases were included to allow for dropout. Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
A. Kappel et al. / The Knee xxx (xxxx) xxx
a) Epicondylar View radiographs sagittal view
b) Epicondylar View radiographs coronal view
Figure 1. Epicondylar view radiographs: (a) sagittal view; (b) coronal view.
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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a) Measurement points for joint opening angle
b)Telos valgus stress
c)Telos varus stress
d) Epicondylar View valgus stress
e)Epicondylar View varus stress
Figure 2. (a) Measurement points for joint opening angle. (b) Telos valgus stress. (c) Telos varus stress. (d) Epicondylar view valgus stress. (e) Epicondylar view varus stress.
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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Table 1 Participant characteristics. Age at surgery BMI Follow up Sex Side Implant
65.9 ± 9.1 (42.9–75.4) years 28.2 ± 3.2 (22–33.2) kg/m2 5.3 ± 0.7 (3.3–6.4) years 5 female, 10 male 6 right, 9 left 14 Vanguard CR, 1 NexGen CR
BMI, body mass index.
Intra-class correlation coefficient (ICC) was used to assess reliability between raters and between the repeated-stress radiographs. ICC was interpreted according to Koo et al. [11], where ICCs below 0.5 are indicative of poor reliability, values between 0.5 and 0.75 indicate moderate reliability, values between 0.75 and 0.9 indicate good reliability, and values greater than 0.90 indicate excellent reliability. Agreement between raters and between the repeated stress radiographs was visualized using Bland–Altman plots, and assessed by the systematic error and the 95% limits of agreement (LOA). LOA predicts the maximal variation in 95% of the repeated measurements [12–14]. Except for the results for intra-rater reliability, all results were based on the mean values of the individual raters two measurements from the same radiograph. This method, using the mean of two or even three measurements, is reported in five of the studies [5,6,8,15,16] cited in Table 2 and not specified in the remaining three of the eight studies [9,17,18]. All analyses were conducted in STATA 15 (StataCorp LLC).
3. Results All participants and raters completed the protocol. Patient characteristics are listed in Table 1.
3.1. Mean results of laxity Mean results of laxity showed that knees were tighter medially than laterally in both extension and flexion; range of laxity was especially large for lateral laxity in flexion; current results and results from previous studies are listed in Table 2.
3.2. Intra- and inter-rater reliability Excellent correlation was demonstrated for both intra- and inter-rater measurement from the radiographs (Table 3). Both experience in using the PACS viewer software, and experience in measuring knee implants improved the results, LOAs ranged from ±0.4° to ±1.7° (Table 3). Bland–Altman plots (Figures 3, 4) illustrate this.
Table 2 Mean results from current and previous studies. Extension (Telos)
Current study Tsukiyama et al. Knee 2017 Nakahara et al. KSSTA 2015 Yoshihara et al. KSSTA 2015 Oh et al. Arch Orthop Trauma Surg 2015 Kobayashi et al. J Arthroplasty 2012 Seon et al. Int Orthop 2007 Matsuda et al. Clin Orthop 2004 Ishii et al. J Orthop Sci 2003
Flexion (Epicondylar view)
Medial laxity
Lateral laxity
Medial laxity
Lateral laxity
n = 15 n = 50
4.0 ± 2.5° (0.5–9.5°) 4.0 ± 2.4° (0–9.0°)
4.6 ± 2.3° (0.7–10.6°) 4.0 ± 2.5° (0–10.0°)
3.8 ± 2.5° (0.5–10.7°) 3.9 ± 2.6° (0–10.0°)
8.0 ± 4.1° (1.7–17.3°) 6.2 ± 4.4° (0–22.3°)
n = 15
5.0 ± 1.6° (1.5–9.0°)
5.9 ± 2.7° (1.0–12.7°)
n = 49
3 ± 2° (0–7°)
5 ± 3° (0–11°)
4 ± 3° (0–9°)
6 ± 4° (0–20°)
n = 61
4.1 ± 2.1° (0.4–12.6°)
4.7 ± 2.4° (0.4–12.1°)
n = 41
3.4 ± 1.4°
6.2 ± 2.5°
n = 42
3.5 ± 1.4° (1.1–6.8°)
4.4 ± 1.4 (0.8–9.3°)
n = 30
4.0 ± 1.7°
3.5 ± 1.0°
n = 53
4.8 ± 2.1°
4.5 ± 2.8°
Mean laxity ± standard deviation (range).
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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Table 3 Intra- and inter-rater reliability and agreement. All
Intra-rater
ICC (95% CI) LOA Systematic error
Inter-Rater
1 vs. 1
2 vs. 2
3 vs. 3
1 vs. 2
1 vs. 3
2 vs. 3
0.97 (0.96–0.98) ± 1.7° −0.01°
0.98 (0.97–0.98) ± 1.3° 0.14°
1.0 (1.0–1.0) ± 0.4° −004°
0.98 (0.97–0.98) ± 1.4° 0.14°
0.98 (0.97–0.99) ± 1.3° 0.11°
0.99 0(0.99–1.0) ± 0.7° −0.03°
CI, confidence interval; ICC, intra-class correlation coefficient; LOA, limit of agreement.
Figure 3. Intra-rater agreement.
Figure 4. Intra-rater agreement.
3.3. Test–retest reliability When analyzing all three raters' mean measurements for the repeated stress-radiographs, good to excellent correlation was found for all TSD stress radiographs and for EV medial laxity (Table 4). However, only moderate to good correlation was found for EV on lateral laxity. When examining the Bland–Altman plots (Figures 5, 6), these findings are illustrated. Figure 6 shows how all three raters found more than four degrees of difference between test–retest epicondylar view lateral laxity stress radiographs for three of the participants. Systematic error and LOAs are listed in Table 4. When using the mean of two measurements from the same rater, very minor differences between the raters are found and the individual raters' results are very close to the mean results (Tables 4, 5). However, the two more experienced raters produced consistently narrower LOA than Rater 1 (Table 5).
Table 4 Agreement and reliability between repeated stress radiographs. Telos and epicondylar
ICC (95% CI) LOA Systematic error
Telos
Epicondylar view
Medial + lateral laxity
Medial + lateral laxity
Medial laxity
Lateral laxity
Medial + lateral laxity
Medial laxity
Lateral laxity
0.87 (0.83–0.90) ±3.4° 0.06°
0.96 (0.95–0.98) ±1.2° −0.13°
0.97 (0.94–0.98) ±1.3° −0.14°
0.96 (0.93–0.98) ±1.3° −0.12°
0.83 (0.75–0.88) ±4.7° 0.24°
0.94 (0.89–0.97) ±1.7° −0.19°
0.70 (0.51–0.82) ±6.3° 0.67°
CI, confidence interval; ICC, intra-class correlation coefficient; LOA, limit of agreement.
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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Figure 5. Test–retest, Telos stress radiographs.
Difference between measurements -5 -4 -3 -2 -1 0 1 2 3 4 5
EV lateral laxity
0
2
4
6
8 10 12 Mean of measurements
observed average agreement
14
16
18
95% limits of agreement
Figure 6. Test–retest, epicondylar view stress radiographs.
4. Discussion When comparing results of laxity measurements using TSD and EV stress radiography, this study and previous reports using the same methodology are consistent (Table 2). This could indicate that the methods and results are reproducible both between clinics and between minor variations in the methods used. Intra- and inter-rater agreement between repeated measurements of joint opening angle from the same radiograph following TKA has been reported previously [15,16,18,19]. Excellent correlation has been obtained both when measuring electronically and on film. However, LOAs in this study show that routine and experience might influence the results (Tables 3 and 5). Two previous studies reporting reproducibility or reliability of stress radiography in flexion have been identified. Stähelin et al. [7] described a method of obtaining stress radiographs at 80° of flexion. Two different observers, one orthopedic surgeon one radiologist, obtained varus- and valgus-stress radiographs using fluoroscopy and by applying a manual force of 50 N, measured with a spring load, to the knee. Twelve participants each had one TKA examined by both observers (test–retest). ICC was reported to be 0.93 (95% confidence interval 0.84–0.97) and the systematic error between the two measurement was 0.5° and LOA was ±3.1°. When comparing our results in flexion, using the EV, to the results obtained by Stähelin et al., our results seem slightly inferior (Table 4). It might be that the use of fluoroscopy facilitates optimal radiographic projections. However, Stähelin et al.
Table 5 Agreement and reliability between repeated stress radiographs, results for individual raters.
Rater 1
Rater 2
Rater 3
ICC (95% CI) LOA ICC (95% CI) LOA ICC (95% CI) LOA
Telos and epicondylar
Telos
Medial + lateral laxity
Medial + lateral laxity
Medial laxity
Lateral laxity
Epicondylar view Medial + lateral laxity
Medial laxity
Lateral laxity
0.85 (0.76–0.91) ±3.8° 0.88 (0.80–0.93) ±3.3° 0.88 (0.81–0.93) ±3.3°
0.96 (0.92–0.98) ±1.4° 0.97 (0.93–0.98) ±1.3° 0.97 (0.93–0.98) ±1.2°
0.96 (0.88–0.99) ±1.5° 0.97 (0.92–0.99) ±1.3° 0.97 (0.91–0.99) ±1.3°
0.96 (0.89–0.99) ±1.3° 0.96 (0.89–0.99) ±1.3° 0.97 (0.92–0.99) ±1.2°
0.81 (0.63–0.90) ±5.2° 0.84 (0.69–0.92) ±4.6° 0.85 (0.70–0.92) ±4.5°
0.94 (0.82–0.98) ±1.9° 0.95 (0.87–0.98) ±1.5° 0.93 (0.82–0.98) ±1.7°
0.66 (0.24–0.87) ±7.2° 0.73 (0.37–0.90) ±6.2° 0.74 (0.400–0.91) ±6.0°
CI, confidence interval; ICC, intra-class correlation coefficient; LOA, limit of agreement.
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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did not analyze medial and lateral laxity separately, and our results for medial laxity display a reduced LOA compared to the results obtained by Stähelin et al. Kuster et al. [20] reported on manual stress radiographs at 30° of flexion repeated by two examiners. Four participants with bilateral TKA had both legs examined in varus- and valgus-stress and the 16 repeated measurements were compared between observers, the results were reported to differ by less than one degree for each set of measurements. Because these results were not analyzed statistically, comparison with our results is troublesome. The interval of soft tissue laxity that facilitates optimal function and pain relief, and the minimal clinical important differences of laxity following TKA are largely unknown. In previous publications, EV stress radiographs have been shown to correlate with patient-reported outcomes and superior outcome is found in knees with limited medial laxity [5,6]. We believe that the LOA for TSD and EV medial stress radiographs that is below two degrees for all raters is acceptable for both clinical and research purposes (Table 5). However, the reliability for EV lateral laxity stress radiography was only moderate to good and the LOA was approximately five times larger than for the Telos radiographs and four times larger than for the epicondylar view medial laxity, which limits the use of this method. A large range of lateral laxity has been demonstrated in this and in earlier publications (Table 2), and it might be that this larger laxity introduced increased risk of rotational variation between the repeated radiographs. However, it is unclear whether the use of fluoroscopy assisted stress radiography can improve the reliability when measuring lateral laxity in flexion. Participants in this study and in the above-mentioned studies do not suffer from significant knee pain, it is unclear to which extent knee pain and muscle contraction might influence the results and reproducibility of stress radiography. 5. Conclusion Stress radiography is a reliable and clinically applicable method of assessing coronal laxity following TKA; the methods might be of benefit for both clinical and research purposes. Acknowledgements The authors thank the radiological staff and the project nurses for their contribution to the work. The Augustinus Foundation, grant number 18-1215, funded the study. The funding agency had no role in planning of study design, the interpretation of the data or the decision to submit the manuscript for publication. Declaration of competing interest The authors declare that they have no conflict of interest. References [1] Gromov K, Korchi M, Thomsen MG, Husted H, Troelsen A. What is the optimal alignment of the tibial and femoral components in knee arthroplasty? Acta Orthop 2014;85:480–7. [2] Wilson CJ, Theodoulou A, Damarell RA, Krishnan J. Knee instability as the primary cause of failure following Total Knee Arthroplasty (TKA): a systematic review on the patient, surgical and implant characteristics of revised TKA patients. Knee 2017;24:1271–81. [3] Kappel A, Laursen M, Nielsen PT, Odgaard A. Relationship between outcome scores and knee laxity following total knee arthroplasty: a systematic review. Acta Orthop 2019 Feb;90(1):46–52. [4] Koppens D, Sørensen OG, Munk S, Rytter S, Kärk S, Larsen A, et al. The lateral joint space width can be measured reliably with Telos valgus stress radiography in medial knee osteoarthritis. Skeletal Radiol 2019 Jul;48(7):1069–77. [5] Ishii Y, Matsuda Y, Ishii R, Sakata S, Omori G. Coronal laxity in extension in vivo after total knee arthroplasty. J Orthop Sci 2003;8:538–42. [6] Matsuda Y, Ishii Y. In vivo laxity of low contact stress mobile-bearing prostheses. Clin Orthop Relat Res 2004:138–43. [7] Stähelin T, Kessler O, Pfirrmann C, Jacob HAC, Romero J. Fluoroscopically assisted stress radiography for varus-valgus stability assessment in flexion after total knee arthroplasty. J Arthroplasty 2003;18:513–5. [8] Tsukiyama H, Kuriyama S, Kobayashi M, Nakamura S, Furu M, Ito H, et al. Medial rather than lateral knee instability correlates with inferior patient satisfaction and knee function after total knee arthroplasty. Knee 2017;24:1478–84. [9] Oh C-S, Song E-K, Seon JK, Ahn YS. The effect of flexion balance on functional outcomes in cruciate-retaining total knee arthroplasty. Arch Orthop Trauma Surg 2015:401–6. [10] Bonett DG. Sample size requirements for estimating intraclass correlations with desired precision. Stat Med 2002 May 15;21(9):1331–5. [11] Koo TK, Li MY. A guideline for selecting and reporting intraclass correlation coefficients for reliability research. 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[17] Seon JK, Song EK, Yoon TR, Bae BH, Park SJ, Cho SG. In vivo stability of total knee arthroplasty using a navigation system. Int Orthop 2007;31:45–8. [18] Kobayashi T, Suzuki M, Sasho T, Nakagawa K, Tsuneizumi Y, Takahashi K. Lateral laxity in flexion increases the postoperative flexion angle in cruciate-retaining total knee arthroplasty. J Arthroplasty 2012;27:260–5. [19] Hatayama K, Terauchi M, Saito K, Higuchi H. Does residual varus alignment cause increasing varus laxity at a minimum of five years after total knee arthroplasty? J Arthroplasty 2017;32:1808–13. [20] Kuster MS, Bitschnau B, Votruba T. Influence of collateral ligament laxity on patient satisfaction after total knee arthroplasty: a comparative bilateral study. Arch Orthop Trauma Surg 2004;124:415–7.
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
Contents lists available at ScienceDirect
The Knee
Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty Andreas Kappel a,b,⁎, Jacob Fyhring Mortensen c, Poul Torben Nielsen a, Anders Odgaard c, Mogens Laursen a,b a b c
Orthopaedic Research Unit, Aalborg University Hospital, Aalborg, Denmark Department of Clinical Medicine, Aalborg University, Aalborg, Denmark Department of Orthopedic Surgery, Copenhagen University Hospital Herlev-Gentofte, Hellerup, Denmark
a r t i c l e
i n f o
Article history: Received 30 May 2019 Received in revised form 4 August 2019 Accepted 19 September 2019 Available online xxxx Keywords: Total knee arthroplasty Soft tissue Laxity Stress radiography Reliability Agreement
a b s t r a c t Background: Stress radiography is used in the valuation of soft tissue laxity following total knee arthroplasty (TKA). However, reliability and agreement is largely unknown. Methods: In this prospective reliability study, we included 15 participants with prior TKA. Standardized coronal stress radiographs were obtained in both extension and flexion and with both varus and valgus stress. All radiographs were repeated (test–retest). In extension the Telos stress device was used, and flexion radiographs were obtained using the epicondylar-view. Three independent raters measured angulation between femoral and tibial component from all radiographs. Reliability was assessed by intra-class correlation coefficient (ICC) and agreement visualized with Bland–Altman plots and by mean difference and limits of agreement (LOA). Results: Stress radiography in extension showed excellent reliability with ICC = 0.96 (0.95– 0.98) and LOA of ±1.2°. Stress radiography at 80–90° of flexion showed good to excellent reliability when measuring medial laxity with ICC = 0.94 (0.89–0.97) and LOA of ±1.7°; however, when measuring lateral laxity the reliability was only moderate to good with ICC = 0.70 (0.51–0.84) and LOA of ±6.3°. Conclusion: Stress radiography is clinically applicable and the methods described in this study provide excellent reliability for measurement of laxity in extension. The reliability of measurements in flexion is good to excellent when measuring medial laxity but only moderate to good when measuring lateral laxity. © 2019 Elsevier B.V. All rights reserved.
1. Introduction Radiographs are routinely used after knee replacement to obtain documentation of positioning and sizing of implants, and radiographic investigations are fundamental in the examination of patients with poorly functioning implants [1]. The functional outcome of knee arthroplasty is dependent on soft tissue balancing, where poor outcomes may be caused by the knee being too loose or too tight [2,3]. Radiographic techniques may provide good means of quantifying knee laxity and its importance for functional outcome, but the performance of the functional radiographic techniques is largely unknown. Stress radiography using the Telos stress device (TSD) (Telos GmbH, Hungen – Obbornhofen, Deutschland) can be used to assess ligament laxity and joint space width in both native [4] and total knee arthroplasty (TKA) knees [5,6]. The reliability of this method, in the assessment of coronal laxity in extension following TKA, has not been reported previously. Different methods of
⁎ Corresponding author. E-mail address: [email protected]. (A. Kappel).
https://doi.org/10.1016/j.knee.2019.09.013 0968-0160/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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obtaining coronal stress radiography in flexion have been described and one method using manual traction and fluoroscopy has been found to be reliable [7]. However, this method may not be applicable in general due to the exposure of radiation to the examiner. The methods used in recent publications [8,9] do not use fluoroscopy and have not yet been statistically validated. Stress radiographic measurement of laxity in flexion has been associated with patient-reported outcomes [8,9]. Standardized and reliable methods to quantify soft tissue laxity, which can be implemented in clinical practice and clinical research, are required in the evaluation of surgical results following TKA. The objective of this study was to examine reliability and agreement of coronal stress radiographs in extension using the TSD and in flexion using the epicondylar view (EV) by comparison of repeated stress-radiographs (test–retest). 2. Materials and methods The north Denmark regional committee on health research ethics (N-20180028) and the Danish data protection agency (200858-0028/2018-79) approved the study. 2.1. Participants Fifteen participants with prior TKA were recruited from the outpatient clinic during May 2018. Patients participating could only participate with one knee. 2.2. Inclusion and exclusion criteria Inclusion criteria were posterior cruciate retaining TKA and follow-up of at least 12 months. Exclusion criteria were pain upon physical examination, extension deficit above five degrees and flexion below 100°. A body mass index (BMI) limit of 35 kg/m2 was set to decrease the uncertainty that might follow from excessive subcutaneous tissue. 2.3. Stress radiographs 2.3.1. Extension Coronal stress radiographs in extension were obtained with use of the TSD. Procedure followed the method described earlier [5,6], and followed the manufactures guidelines, with application of 150 N varus or valgus stress at the level of the joint-line, while observing the patella facing forwards. During the examination, the knee was resting on a pillow, securing a flexion of approximately 10°. 2.3.2. Flexion The procedure for obtaining stress radiographs in flexion using the EV followed the methods described by Oh et al. [9] and Tsukiyama et al. [8]. The participant was placed sitting on the radiographic table with the lower leg hanging free resulting in a knee angulation of 80–90°. The X-ray beam was directed from posterior to anterior in an upward angulation of 15° towards the centre of the jointline, the distance between the X-ray tube and the cassette was set at 150 cm (Figure 1(a)). Coronal stress was applied in a horizontal direction, and resulted in either varus or valgus stress. Traction was applied just above the ankle joint with a force of 50 N (Figure 1(b)). A supplementary video describing this method can be found online at: https://video.rn.dk/stress-radiographic. Radiographs were recorded in varus- and valgus-stress in both extension and flexion, and all radiographs were repeated (test– retest). Before the repeated radiographs the participants had a break and a short walk. Three dedicated radiographers were responsible for all radiographs in the study. Radiation exposure to the participants was minimized by narrowing the field of expose and by using low-dose radiographs to allow visualization of implants but not soft tissues. 2.4. Radiologic evaluation Following maximal enlargement of the area between the femoral and tibial components, joint opening angle between these was measured. The tibial line was marked from the most lateral and distal corner of the tibial tray to the most medial and distal corner of the tray, and the femoral line connected the most distal medial and lateral parts of the femoral condyles. Angulation between these two lines, the joint opening angle, was read to one decimal place (Figure 2(a)–(e)). Three raters independently measured all radiographs two times with an interim period of two weeks. Radiographs were blinded and presented in different randomized sequences. Rater 1 was a resident and PhD student within orthopedics, Rater 2 was a consultant orthopedic surgeon specializing in hip surgery, and Rater 3 was a consultant orthopedic surgeon specializing in knee surgery. Raters 2 and 3 were very familiar with digital measurement in the PACS viewer, but only Rater 3 had expertise in measurement of knee implants. 2.5. Statistical analysis Power calculation was carried out with respect to test–retest reliability using Bonett's method [10]. A sample size of 12 cases was calculated, 15 cases were included to allow for dropout. Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
A. Kappel et al. / The Knee xxx (xxxx) xxx
a) Epicondylar View radiographs sagittal view
b) Epicondylar View radiographs coronal view
Figure 1. Epicondylar view radiographs: (a) sagittal view; (b) coronal view.
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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a) Measurement points for joint opening angle
b)Telos valgus stress
c)Telos varus stress
d) Epicondylar View valgus stress
e)Epicondylar View varus stress
Figure 2. (a) Measurement points for joint opening angle. (b) Telos valgus stress. (c) Telos varus stress. (d) Epicondylar view valgus stress. (e) Epicondylar view varus stress.
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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Table 1 Participant characteristics. Age at surgery BMI Follow up Sex Side Implant
65.9 ± 9.1 (42.9–75.4) years 28.2 ± 3.2 (22–33.2) kg/m2 5.3 ± 0.7 (3.3–6.4) years 5 female, 10 male 6 right, 9 left 14 Vanguard CR, 1 NexGen CR
BMI, body mass index.
Intra-class correlation coefficient (ICC) was used to assess reliability between raters and between the repeated-stress radiographs. ICC was interpreted according to Koo et al. [11], where ICCs below 0.5 are indicative of poor reliability, values between 0.5 and 0.75 indicate moderate reliability, values between 0.75 and 0.9 indicate good reliability, and values greater than 0.90 indicate excellent reliability. Agreement between raters and between the repeated stress radiographs was visualized using Bland–Altman plots, and assessed by the systematic error and the 95% limits of agreement (LOA). LOA predicts the maximal variation in 95% of the repeated measurements [12–14]. Except for the results for intra-rater reliability, all results were based on the mean values of the individual raters two measurements from the same radiograph. This method, using the mean of two or even three measurements, is reported in five of the studies [5,6,8,15,16] cited in Table 2 and not specified in the remaining three of the eight studies [9,17,18]. All analyses were conducted in STATA 15 (StataCorp LLC).
3. Results All participants and raters completed the protocol. Patient characteristics are listed in Table 1.
3.1. Mean results of laxity Mean results of laxity showed that knees were tighter medially than laterally in both extension and flexion; range of laxity was especially large for lateral laxity in flexion; current results and results from previous studies are listed in Table 2.
3.2. Intra- and inter-rater reliability Excellent correlation was demonstrated for both intra- and inter-rater measurement from the radiographs (Table 3). Both experience in using the PACS viewer software, and experience in measuring knee implants improved the results, LOAs ranged from ±0.4° to ±1.7° (Table 3). Bland–Altman plots (Figures 3, 4) illustrate this.
Table 2 Mean results from current and previous studies. Extension (Telos)
Current study Tsukiyama et al. Knee 2017 Nakahara et al. KSSTA 2015 Yoshihara et al. KSSTA 2015 Oh et al. Arch Orthop Trauma Surg 2015 Kobayashi et al. J Arthroplasty 2012 Seon et al. Int Orthop 2007 Matsuda et al. Clin Orthop 2004 Ishii et al. J Orthop Sci 2003
Flexion (Epicondylar view)
Medial laxity
Lateral laxity
Medial laxity
Lateral laxity
n = 15 n = 50
4.0 ± 2.5° (0.5–9.5°) 4.0 ± 2.4° (0–9.0°)
4.6 ± 2.3° (0.7–10.6°) 4.0 ± 2.5° (0–10.0°)
3.8 ± 2.5° (0.5–10.7°) 3.9 ± 2.6° (0–10.0°)
8.0 ± 4.1° (1.7–17.3°) 6.2 ± 4.4° (0–22.3°)
n = 15
5.0 ± 1.6° (1.5–9.0°)
5.9 ± 2.7° (1.0–12.7°)
n = 49
3 ± 2° (0–7°)
5 ± 3° (0–11°)
4 ± 3° (0–9°)
6 ± 4° (0–20°)
n = 61
4.1 ± 2.1° (0.4–12.6°)
4.7 ± 2.4° (0.4–12.1°)
n = 41
3.4 ± 1.4°
6.2 ± 2.5°
n = 42
3.5 ± 1.4° (1.1–6.8°)
4.4 ± 1.4 (0.8–9.3°)
n = 30
4.0 ± 1.7°
3.5 ± 1.0°
n = 53
4.8 ± 2.1°
4.5 ± 2.8°
Mean laxity ± standard deviation (range).
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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Table 3 Intra- and inter-rater reliability and agreement. All
Intra-rater
ICC (95% CI) LOA Systematic error
Inter-Rater
1 vs. 1
2 vs. 2
3 vs. 3
1 vs. 2
1 vs. 3
2 vs. 3
0.97 (0.96–0.98) ± 1.7° −0.01°
0.98 (0.97–0.98) ± 1.3° 0.14°
1.0 (1.0–1.0) ± 0.4° −004°
0.98 (0.97–0.98) ± 1.4° 0.14°
0.98 (0.97–0.99) ± 1.3° 0.11°
0.99 0(0.99–1.0) ± 0.7° −0.03°
CI, confidence interval; ICC, intra-class correlation coefficient; LOA, limit of agreement.
Figure 3. Intra-rater agreement.
Figure 4. Intra-rater agreement.
3.3. Test–retest reliability When analyzing all three raters' mean measurements for the repeated stress-radiographs, good to excellent correlation was found for all TSD stress radiographs and for EV medial laxity (Table 4). However, only moderate to good correlation was found for EV on lateral laxity. When examining the Bland–Altman plots (Figures 5, 6), these findings are illustrated. Figure 6 shows how all three raters found more than four degrees of difference between test–retest epicondylar view lateral laxity stress radiographs for three of the participants. Systematic error and LOAs are listed in Table 4. When using the mean of two measurements from the same rater, very minor differences between the raters are found and the individual raters' results are very close to the mean results (Tables 4, 5). However, the two more experienced raters produced consistently narrower LOA than Rater 1 (Table 5).
Table 4 Agreement and reliability between repeated stress radiographs. Telos and epicondylar
ICC (95% CI) LOA Systematic error
Telos
Epicondylar view
Medial + lateral laxity
Medial + lateral laxity
Medial laxity
Lateral laxity
Medial + lateral laxity
Medial laxity
Lateral laxity
0.87 (0.83–0.90) ±3.4° 0.06°
0.96 (0.95–0.98) ±1.2° −0.13°
0.97 (0.94–0.98) ±1.3° −0.14°
0.96 (0.93–0.98) ±1.3° −0.12°
0.83 (0.75–0.88) ±4.7° 0.24°
0.94 (0.89–0.97) ±1.7° −0.19°
0.70 (0.51–0.82) ±6.3° 0.67°
CI, confidence interval; ICC, intra-class correlation coefficient; LOA, limit of agreement.
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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Figure 5. Test–retest, Telos stress radiographs.
Difference between measurements -5 -4 -3 -2 -1 0 1 2 3 4 5
EV lateral laxity
0
2
4
6
8 10 12 Mean of measurements
observed average agreement
14
16
18
95% limits of agreement
Figure 6. Test–retest, epicondylar view stress radiographs.
4. Discussion When comparing results of laxity measurements using TSD and EV stress radiography, this study and previous reports using the same methodology are consistent (Table 2). This could indicate that the methods and results are reproducible both between clinics and between minor variations in the methods used. Intra- and inter-rater agreement between repeated measurements of joint opening angle from the same radiograph following TKA has been reported previously [15,16,18,19]. Excellent correlation has been obtained both when measuring electronically and on film. However, LOAs in this study show that routine and experience might influence the results (Tables 3 and 5). Two previous studies reporting reproducibility or reliability of stress radiography in flexion have been identified. Stähelin et al. [7] described a method of obtaining stress radiographs at 80° of flexion. Two different observers, one orthopedic surgeon one radiologist, obtained varus- and valgus-stress radiographs using fluoroscopy and by applying a manual force of 50 N, measured with a spring load, to the knee. Twelve participants each had one TKA examined by both observers (test–retest). ICC was reported to be 0.93 (95% confidence interval 0.84–0.97) and the systematic error between the two measurement was 0.5° and LOA was ±3.1°. When comparing our results in flexion, using the EV, to the results obtained by Stähelin et al., our results seem slightly inferior (Table 4). It might be that the use of fluoroscopy facilitates optimal radiographic projections. However, Stähelin et al.
Table 5 Agreement and reliability between repeated stress radiographs, results for individual raters.
Rater 1
Rater 2
Rater 3
ICC (95% CI) LOA ICC (95% CI) LOA ICC (95% CI) LOA
Telos and epicondylar
Telos
Medial + lateral laxity
Medial + lateral laxity
Medial laxity
Lateral laxity
Epicondylar view Medial + lateral laxity
Medial laxity
Lateral laxity
0.85 (0.76–0.91) ±3.8° 0.88 (0.80–0.93) ±3.3° 0.88 (0.81–0.93) ±3.3°
0.96 (0.92–0.98) ±1.4° 0.97 (0.93–0.98) ±1.3° 0.97 (0.93–0.98) ±1.2°
0.96 (0.88–0.99) ±1.5° 0.97 (0.92–0.99) ±1.3° 0.97 (0.91–0.99) ±1.3°
0.96 (0.89–0.99) ±1.3° 0.96 (0.89–0.99) ±1.3° 0.97 (0.92–0.99) ±1.2°
0.81 (0.63–0.90) ±5.2° 0.84 (0.69–0.92) ±4.6° 0.85 (0.70–0.92) ±4.5°
0.94 (0.82–0.98) ±1.9° 0.95 (0.87–0.98) ±1.5° 0.93 (0.82–0.98) ±1.7°
0.66 (0.24–0.87) ±7.2° 0.73 (0.37–0.90) ±6.2° 0.74 (0.400–0.91) ±6.0°
CI, confidence interval; ICC, intra-class correlation coefficient; LOA, limit of agreement.
Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013
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did not analyze medial and lateral laxity separately, and our results for medial laxity display a reduced LOA compared to the results obtained by Stähelin et al. Kuster et al. [20] reported on manual stress radiographs at 30° of flexion repeated by two examiners. Four participants with bilateral TKA had both legs examined in varus- and valgus-stress and the 16 repeated measurements were compared between observers, the results were reported to differ by less than one degree for each set of measurements. Because these results were not analyzed statistically, comparison with our results is troublesome. The interval of soft tissue laxity that facilitates optimal function and pain relief, and the minimal clinical important differences of laxity following TKA are largely unknown. In previous publications, EV stress radiographs have been shown to correlate with patient-reported outcomes and superior outcome is found in knees with limited medial laxity [5,6]. We believe that the LOA for TSD and EV medial stress radiographs that is below two degrees for all raters is acceptable for both clinical and research purposes (Table 5). However, the reliability for EV lateral laxity stress radiography was only moderate to good and the LOA was approximately five times larger than for the Telos radiographs and four times larger than for the epicondylar view medial laxity, which limits the use of this method. A large range of lateral laxity has been demonstrated in this and in earlier publications (Table 2), and it might be that this larger laxity introduced increased risk of rotational variation between the repeated radiographs. However, it is unclear whether the use of fluoroscopy assisted stress radiography can improve the reliability when measuring lateral laxity in flexion. Participants in this study and in the above-mentioned studies do not suffer from significant knee pain, it is unclear to which extent knee pain and muscle contraction might influence the results and reproducibility of stress radiography. 5. Conclusion Stress radiography is a reliable and clinically applicable method of assessing coronal laxity following TKA; the methods might be of benefit for both clinical and research purposes. Acknowledgements The authors thank the radiological staff and the project nurses for their contribution to the work. The Augustinus Foundation, grant number 18-1215, funded the study. The funding agency had no role in planning of study design, the interpretation of the data or the decision to submit the manuscript for publication. Declaration of competing interest The authors declare that they have no conflict of interest. References [1] Gromov K, Korchi M, Thomsen MG, Husted H, Troelsen A. 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Please cite this article as: A. Kappel, J.F. Mortensen, P.T. Nielsen, et al., Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty, The Knee, https://doi.org/10.1016/j.knee.2019.09.013