Pathology Demonstrated:
- Fractures, lessions, and joint space abnormal ties are demonstrated.
Technical Factors:
- IR size- 18 x 24 cm (8 x 10 inches), lengthwise
- Grid or Bucky, >10 cm (70 +- 5 kV)
- Screen, tabletop, <10 cm (65 +- 5 kV)
- mAs 4
Shielding:
- Place lead shield over gonadal area.
Patient Position:
- This position may be taken as a horizontal beam lateral or in the lateral recumbent position.
Horizontal beam projection:
- This projection is ideal for the patient who is unable to flex the knee because of pain or trauma. Use a horizontal beam with IR placed beside knee. Place support under knee to avoid cutting off posterior soft tissue structure.
Lateral recumbent projection:
- This position is designed for patient who are able to flex the knee 20 to 30 degree. Take radiograph with patient in lateral recumbent position, affected side down; give pillow for head; provide support for knee of opposite limb placed behind knee being examined to prevent overrotation.
Part Position:
- Adjust rotation of body and leg until knee is in a true lateral position (femoral epicondyles directly superimposed and plane of patella perpendicular to plane of IR).
- Flex knee 20 to 30 degree for lateral recumbent projection (see note 1).
- Align and center leg and knee to CR and to midline of table or IR.
Central Ray:
- Angle CR 5 to 7-degree cephalad for lateral recumbent projection (see note 2)
- Direct CR to a point 1 inch (2.5 cm) distal to medial epicondyle.
- Minimum SID is 40 inches (100 cm)
Collimation:
- Collimate on both sides to skin margins, with full collimation at ends to IR borders to include maximum femur tibia and fibula.
Note 1: Additional flexion will tighten muscles and tendons that may obscure important diagnostic information in the joint space. The patella will be drawn into the intercondylar sulcus, also obscuring soft tissue detail from effusion and/or fat pad displacement. Additional flexion may result in fragment separation of patellar fractures, if present.
Note 2: Angle CR 7 to 10 degree on short patient with wide pelvis and only about 5 degree on tall, male patient with narrow pelvis for lateral recumbent projection.
Radiographic Criteria:
Structure Shown:
- The distal femur, proximal tibia and fibula, and patella are shown in lateral profile.
- Femoropatellar and knee joints should be open.
Position:
- Overrotation or underrotation can be determined by identifying the adductor tubercle on the medial condyle, if visible and by the amount of superimposition of fibular head by tibia. (Overrotation, less superimposition of fibular head; underrotation, more superimposition
- A true lateral position of the knee without rotation will demonstrate the posterior borders of the femoral condyles directly superimposed.
- The patella should be seen in profile with the femoropatellar joint space open.
Collimation and CR:
- The 5 to 10 degree cephalad angle of CR should result in direct superimposition of the distal borders of the condyles.
- The knee joint is in the center of the collimated field. The top and buttom are collimated minimally.
- All surrounding soft tissue structures should be included.
Exposure Criteria:
- Optimal exposure with no motion will visualize important soft tissue detail, including fat pads anterior to knee joint and sharp trabecular markings.
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Osteoarthritis (OA) is a common and disabling condition, with worldwide estimates suggesting that 500 million people are currently affected.1x[1]Hunter, D.J. Osteoarthritis in 2020 and beyond: a Lancet Commission. The Lancet. 2020; 396:
2 Abstract |
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Scopus (1326) Crossref Crossref Crossref Patient positioning during WLRs is an inducer of HKA measurement errors. The known factors are knee flexion and extension, foot rotation, hip rotation,
weight-bearing, and foot positioning.7x[7]Sanfridsson, J., Ryd, L., Svahn, G., Fridén, T., and Jonsson, K. Radiographic measurement of femorotibial rotation in weight-bearing: The influence of flexion and extension in the knee on the extensor mechanism and angles of the lower extremity in a healthy population. Acta Radiol.
2001; 42: 207–217 PubMed Crossref |
PubMed | Scopus (57) Crossref | PubMed |
Scopus (115) Crossref |
PubMed | Scopus (87) Crossref | PubMed |
Scopus (43) Crossref |
PubMed | Scopus (14) PubMed Crossref Crossref Crossref |
PubMed | Scopus (21) Crossref |
PubMed | Scopus (24) Crossref Crossref |
PubMed | Scopus (54) PubMed CrossrefIntroduction
Crossref | PubMed | Scopus (21)
| Google ScholarSee all References,18x[18]Maderbacher, G., Baier, C., Benditz, A., Wagner, F., Greimel, F., Grifka, J., and Keshmiri, A. Presence of rotational errors in long leg radiographs after total knee arthroplasty and impact on measured lower limb and component alignment. Int. Orthop. 2017; 41: 1553–1560Crossref | PubMed | Scopus (19)
| Google ScholarSee all References In addition to patient positioning, the height of the X-ray beam can also impact HKA accuracy.20x[20]Brage, M.E., Holmes, J.R., and Sangeorzan, B.J. The influence of x-ray orientation on the first metatarsocuneiform joint angle. Foot Ankle Int. 1994; 15: 495–497Crossref | PubMed | Scopus (32)
| Google ScholarSee all References Katsui et al reported error in malleolar angles could be up to 2.4° when the projection angle differed 10°.21x[21]Katsui, R. and Fujii, T. Change of the X-ray Beam Angle may Influence Ankle Image of Weight-bearing Anteroposterior View: Trial to Evaluate Ankle Joint on Standing Whole-leg Radiograph. Clin. Res. Foot Ankle. 2015; 04: 1–5Crossref
| Google ScholarSee all ReferencesThere is little evidence on the test-retest reproducibility of obtaining WLRs. Odenbring et al performed a test-retest study of the measured HKA on a very small scale including 8 lower limbs, with a mean difference of 1.3°.19x[19]Odenbring, S., Berggren, A.M., and Peil, L. Roentgenographic Assessment of the Hip-Knee-Ankle Axis in Medial Gonarthrosis. Clin. Orthop. 1993; : 195–196
PubMed
| Google ScholarSee all References Even this group made use of a meticulous method to determine the AP plane in every individual, by obtaining a lateral radiograph where the posterior aspects of the femoral condyles should be superimposed.19x[19]Odenbring, S., Berggren, A.M., and Peil, L. Roentgenographic Assessment of the Hip-Knee-Ankle Axis in Medial Gonarthrosis. Clin. Orthop. 1993; : 195–196PubMed
| Google ScholarSee all ReferencesInaccurate HKA measurements caused by the lack of standardization can result in misdiagnosis, inaccurate preoperative planning, and erroneous assessment of achieved surgical corrections. The radiographic technique should be consistent and accurate, with the desired accuracy of 0.45°, reported by Jones et al as the needed wedge accuracy to achieve target corrections in high tibial osteotomy.22x[22]Jones, L.D., Brown, C.P., Jackson, W., Monk, A.P., and Price, A.J. Assessing accuracy requirements in high tibial osteotomy: a theoretical, computer-based model using AP radiographs. Knee Surg. Sports Traumatol. Arthrosc. 2017; 25: 2952–2956
Crossref | PubMed | Scopus (7)
| Google ScholarSee all ReferencesTherefore, the purpose of the current study is to find the effects of leg rotation, knee flexion and different X-ray beam heights on the measured HKA. These results can be used to improve current guidelines for obtaining WLRs with improved accuracy and reproducibility of the measured HKA.
Material and methods
Solid foam sawbones (Sawbones Europe AB, Malmoe, Sweden) of a left leg including 1 femur, tibia, fibula, talus, calcaneus, and forefoot were used. The model had a mean femoral anteversion of 15° and tibiofibular torsion of
30°.23x[23]Bråten, M., Terjesen, T., and Rossvoll, I. Femoral anteversion in normal adults: Ultrasound measurements in 50 men and 50 women. Acta Orthop. 1992; 63: 29–32 Crossref | Scopus (112) PubMed Akagi line runs from the centre of the posterior cruciate ligament (PCL)
insertion to the medial border of the tuberosity. The femoral transepicondylar (TEA) is projected on the tibial surface.25x[25]Aglietti, P., Sensi, L., Cuomo, P., and Ciardullo, A. Rotational position of femoral and tibial components in TKA using the femoral transepicondylar axis. Clin. Orthop. 2008;
: 466 PubMed Measurement setup in the projection radiography room. This study used a Philips DigitalDiagnost v4.0, with a fixed X-ray beam height during acquisition where the source pivoted and aimed towards the upper, middle, and lower parts of the limb. The fixed distance between the detector plate and X-ray beam source was set to 265 cm. The X-ray settings were equal to the protocol for scanning patients with kV set at 81 and varying mAs. The radiographic system contained
a laser pointer (at the X-ray beam source) directed to the lead measurement tape indicating the X-ray beam height. First, a reference radiograph as shown in Fig. 3 was made with the sawbone model set to 5° varus, 0° leg rotation, and 0° knee flexion, with
X-ray beam height centred on the joint space. From this reference position, different combinations of leg-rotation (−10°, 5°, 0°, 5°,10°), knee flexion (0°, 5°,15°) and X-ray beam height (0 cm, 5 cm, 10 cm) were applied. Rotation of the leg was described as positive (external) and negative values (internal). Whole leg radiographs exported from PACS image viewer, with the sawbones in 5°
varus and 0° knee flexion. Left image illustrates the setup in AP (anteroposterior) direction and right illustrates the image in lateral view. HKAs were measured with one decimal place, using PACS IDS7 19.3 (Sectra AB, Linköping, Sweden) by annotating the metal spheres in the femoral head, tibial spine, and talus. Mechanical lateral distal femoral angle (mLDFA) is the lateral angle formed
between the mechanical axis line of the femur and the knee joint line of the femur in the frontal plane.5x[5]Paley, D. Normal Lower Limb Alignment and Joint Orientation. in: Princ. Deform. Correct.Springer Berlin Heidelberg, Germany, Berlin; 2002: 1–18 Crossref The first observer (CN)
rated the images twice randomly on independent moments with one week in between, to obtain intra-observer reliability. A second observer (WG) performed HKA measurements on all radiographs to obtain inter-observer reliability. The relationship between the measured HKA/mLDFA and knee flexion and/or leg rotation was determined using multivariable linear regression (SPSS version 25.0, Chicago, IL, USA). The
intra-observer reliability was tested for agreement using a two-way mixed Intraclass Correlation (ICC) for absolute agreement. A 2-way random ICC for absolute agreement was used to test the inter-rater agreement.Materials
Fig. 1
Fig. 2
Radiography system
Fig. 3
Angle measurement
Statistical analysis
Results
The HKA ICC for intra-observer reliability was perfect 1.000 (95% CI 0.999 - 1.000) and excellent for the mLDFA 0.993 (95% CI
0.986 -0.996). The HKA inter-rater reliability was nearly perfect with an ICC of 0.999 (95% CI 0.998 - 0.999).Intra- & inter-rater reliability
Effects of beam height, knee flexion and leg rotation
Multivariable linear regression analyses of leg rotation and knee-flexion on the measured HKA and mLDFA resulted in excellent significant correlations. Both knee flexion (within the range of 0° and 15°) and leg rotation (within the range of −15° and 10°) were linear related to the measured HKA and mLDFA (Figs. 4 and 5). Knee flexion and leg rotation had a significant interaction (P < .001), meaning that the effect of leg rotation is affected by the amount of knee flexion and vice versa. External leg rotation in combination with flexion caused the HKA and mLDFA to be overestimated with greater errors under higher flexion, while a slight flexion equalized the errors induced by rotation (HKA around 3° and mLDFA around 6° of knee flexion). Errors were biggest when there was 10° of leg rotation combined with 15° knee flexion, observed to be high as 2° for the measured HKA and 3° for the measured mLDFA. The HKA measurement error was 1° per 20° of leg rotation without flexion (P < .01). When 5° of flexion was added, the HKA measurement error was 0.8° per 20° rotation (P < .01). When the leg was in 15° flexion, the HKA measurement error became 4° per 20° rotation (P < .01) (Figs. 4 and 5). Leg rotation alone affected both the measured HKA and mLDFA significantly (P < .001).
Fig. 4
Scatterplot of the measured HKA (hip knee ankle angle) (on 5° varus model) for knee flexion angles and leg rotation angles. Each measurement was performed using three different X-ray beam heights, which are the different markers on the same leg rotation and knee flexion combinations. Multivariable linear regression analyses of leg rotation and knee-flexion on the measured HKA showed excellent significant correlations (P < .001). Leg rotation alone affected the measured HKA significantly (P < .001).
Fig. 5
Scatterplot of the measured mLDFA (mechanical lateral distal femoral angle) (on 90° mLDFA model) for knee flexion angles and leg rotation angles. Each measurement was performed using 3 different X-ray beam heights, which are the different markers on the same leg rotation and knee flexion combinations. Multivariable linear regression analyses of leg rotation and knee-flexion on the measured mLDFA showed excellent significant correlations (P < .001). Leg rotation alone affected the measured mLDFA significantly (P < .001).
X-ray beam height of 5 cm (P = .959) and 10 cm (P = .967) above the knee joint did not affect the measured HKA on a significant scale (Fig. 6). Also, X-ray beam height of 5 cm (P = .775) and 10 cm (P = .071) above the knee joint did not affect the measured mLDFA on a significant scale (Fig. 6).
Fig. 6
Boxplot of the effect of different X-ray Beam Heights on the HKA (hip knee ankle angle) and mLDFA (mechanical lateral distal femoral angle) measurements. All measurements were included in the boxplot (with different knee flexion and leg rotation angles). The horizontal black line displays the set 5° varus and 90° mLDFA angle of the model. X-ray beam height of 5 cm (P = .959) and 10 cm (P = .967) above knee joint did not influence the measured HKA on a significant scale. Also, X-ray beam height of 5 cm (P = 0.775) and 10 cm (P = .071) above knee joint did not influence the measured mLDFA on a significant scale.
Discussion
This study showed that leg rotation alone (without knee flexion) can lead to clinically relevant measurement errors when exceeding 9°. When 15° knee flexion was combined with 10° leg rotation the HKA measurement error became 2°, thereby grossly exceeding the desired osteotomy accuracy of 0.45° of wedge opening.22x[22]Jones, L.D., Brown, C.P., Jackson, W., Monk, A.P., and Price, A.J. Assessing accuracy requirements in high tibial osteotomy: a theoretical, computer-based model using AP radiographs. Knee Surg. Sports Traumatol. Arthrosc. 2017; 25: 2952–2956
Crossref | PubMed | Scopus (7)
| Google ScholarSee all References Different X-ray beam heights did not affect the measured HKA, regardless of flexion and rotation.Significant effects of leg rotation on the measured HKA were expected and our results correspond with previously published literature.8x[8]Brouwer, R.W., Jakma, T.S.C., Brouwer, K.H., and Verhaar, J.A.N. Pitfalls in determining knee alignment: a radographic cadaver study. J. Knee Surg. 2007; 20: 210–215
Crossref | PubMed | Scopus (57)
| Google ScholarSee all References,10x[10]Radtke, K., Becher, C., Noll, Y., and Ostermeier, S. Effect of limb rotation on radiographic alignment in total knee arthroplasties. Arch. Orthop. Trauma Surg. 2010; 130: 451–457Crossref | PubMed | Scopus (87)
| Google ScholarSee all References Radtke et al conducted a study using sawbones and found a similar effect of leg rotation, with 0.0558° measurement error as a result of 1° leg rotation, which is about the same as the 1° measurement error per 20° of leg rotation reported in our study.10x[10]Radtke, K., Becher, C., Noll, Y., and Ostermeier, S. Effect of limb rotation on radiographic alignment in total knee arthroplasties. Arch. Orthop. Trauma Surg. 2010; 130: 451–457Crossref | PubMed | Scopus (87)
| Google ScholarSee all References Brouwer et al conducted a comparative study investigating the relationship between leg rotation, knee flexion and their effects on the measured HKA. Knee flexion was manipulated to a cadaver leg with a transepicondylar rod to control leg rotation.8x[8]Brouwer, R.W., Jakma, T.S.C., Brouwer, K.H., and Verhaar, J.A.N. Pitfalls in determining knee alignment: a radographic cadaver study. J. Knee Surg. 2007; 20: 210–215Crossref | PubMed | Scopus (57)
| Google ScholarSee all References They concluded that the measured HKA is only significantly affected when leg rotation and knee-flexion are combined.8x[8]Brouwer, R.W., Jakma, T.S.C., Brouwer, K.H., and Verhaar, J.A.N. Pitfalls in determining knee alignment: a radographic cadaver study. J. Knee Surg. 2007; 20: 210–215Crossref | PubMed | Scopus (57)
| Google ScholarSee all References But our research showed that there are already clinically relevant effects of leg rotation even with full knee extension. Indeed, when knee flexion was combined with leg rotation the HKA measurement error turned out to be huge. The discrepancy in conclusions could be the result of different analyses performed by Brouwer et al and in this study. Brouwer et al only described the HKA in whole degrees while this study aimed to be precise on a 10th of a degree, which means that the desired osteotomy accuracy of 0.45° is achievable.8x[8]Brouwer, R.W., Jakma, T.S.C., Brouwer, K.H., and Verhaar, J.A.N. Pitfalls in determining knee alignment: a radographic cadaver study. J. Knee Surg. 2007; 20: 210–215Crossref | PubMed | Scopus (57)
| Google ScholarSee all References,22x[22]Jones, L.D., Brown, C.P., Jackson, W., Monk, A.P., and Price, A.J. Assessing accuracy requirements in high tibial osteotomy: a theoretical, computer-based model using AP radiographs. Knee Surg. Sports Traumatol. Arthrosc. 2017; 25: 2952–2956Crossref | PubMed | Scopus (7)
| Google ScholarSee all ReferencesBoth Radtke et al and Brouwer et al did not report the possible effect of different X-ray beam heights on the HKA measurement error.8x[8]Brouwer, R.W., Jakma, T.S.C., Brouwer, K.H., and Verhaar, J.A.N. Pitfalls in determining knee alignment: a radographic cadaver study. J. Knee Surg. 2007; 20: 210–215
Crossref | PubMed | Scopus (57)
| Google ScholarSee all References,10x[10]Radtke, K., Becher, C., Noll, Y., and Ostermeier, S. Effect of limb rotation on radiographic alignment in total knee arthroplasties. Arch. Orthop. Trauma Surg. 2010; 130: 451–457Crossref | PubMed | Scopus (87)
| Google ScholarSee all References This study investigated the possible effects of using different X-ray beam heights on the measured HKA, with no significant effects. Thus, the study revealed that in clinical care it is not necessary to standardize X-ray beam heights to obtain reliable and reproducible WLRs.Preoperative planning of lower limb osteotomy surgery requires insight into the mechanical medial proximal tibial angle (mMPTA) and the mechanical lateral distal femoral angle (mLDFA).5x[5]Paley, D. Normal Lower Limb Alignment and Joint Orientation. in: Princ. Deform. Correct.Springer Berlin Heidelberg, Germany, Berlin; 2002: 1–18
Crossref
| Google ScholarSee all References This study analysed the behavior of the mLDFA, and the results were comparable to the HKA measurement errors. The greatest mLDFA measurement errors occurred when the knee was flexed in 15° combined with 10° leg rotation, with approximately 3° discrepancy. Unfortunately, due to the hinge setup used in this study only the femur could tilt backwards in the sagittal plane and therefore mimic knee flexion. The tibia was fixed in the sagittal plane, leading to the exclusion of mMPTA measurements in knee flexion and leg rotation conditions. This study also included measurements performed on a 5° valgus stance. The same effect was observed in terms of the effect of knee flexion, leg rotation, and X-ray beam height on the measured HKA when the model was in 5° varus.Cooke and Sheehy proposed a WLR protocol with the purpose of eliminating leg rotation, at the same time accounting for torsional deformity of the tibia.14x[14]Cooke, T.D.V and Sled, E.A. Optimizing limb position for measuring knee anatomical axis alignment from standing knee radiographs. J. Rheumatol. 2009; 36: 472–477
Crossref | PubMed | Scopus (21)
| Google ScholarSee all References They proposed that practitioners align each leg using a rotating platform for each foot. Each platform would be fixed to a certain amount of rotation, determined by flexing the knee and observe the frontal plane while making sure that the flexion plane is in line with the X-ray beam.14x[14]Cooke, T.D.V and Sled, E.A. Optimizing limb position for measuring knee anatomical axis alignment from standing knee radiographs. J. Rheumatol. 2009; 36: 472–477Crossref | PubMed | Scopus (21)
| Google ScholarSee all References This protocol is very time-consuming and impractical, while this method heavily relies on the skillset of each practitioner.18x[18]Maderbacher, G., Baier, C., Benditz, A., Wagner, F., Greimel, F., Grifka, J., and Keshmiri, A. Presence of rotational errors in long leg radiographs after total knee arthroplasty and impact on measured lower limb and component alignment. Int. Orthop. 2017; 41: 1553–1560Crossref | PubMed | Scopus (19)
| Google ScholarSee all References The Paley and Herzenberg protocol is prone to non-reproducible radiographs, which relies on the skillset of different X-ray technicians to rotate the knee (using the patellae) the same way in clinical care.27x[27]Ahrend, M.-D., Finger, F., Grünwald, L., Keller, G., and Baumgartner, H. Improving the accuracy of patient positioning for long-leg radiographs using a Taylor Spatial Frame mounted rotation rod. Arch. Orthop. Trauma Surg. 2021; 141: 55–61Crossref | PubMed | Scopus (9)
| Google ScholarSee all References Also, patellar malalignment is quite common in arthritic knees, especially in cases of varus deformities.17x[17]Harrison, M.M., Cooke, T.D., Fisher, S.B., and Griffin, M.P. Patterns of knee arthrosis and patellar subluxation. Clin. Orthop. 1994; : 56–63PubMed
| Google ScholarSee all References The Paley and Herzenberg protocol is even more difficult in cases of total knee arthroplasties, with HKA measurement errors up to 3.5°.18x[18]Maderbacher, G., Baier, C., Benditz, A., Wagner, F., Greimel, F., Grifka, J., and Keshmiri, A. Presence of rotational errors in long leg radiographs after total knee arthroplasty and impact on measured lower limb and component alignment. Int. Orthop. 2017; 41: 1553–1560Crossref | PubMed | Scopus (19)
| Google ScholarSee all References This was probably caused by postoperative swelling and misleading surgical incisions, while technicians had difficulties to exactly centre the patella. Another important finding of this study is the overall average internal rotation of the lower limbs on WLRs, as the patella is located slightly lateral. Centring the patella as instructed in the Paley and Herzenberg protocol requires an internally rotated lower limb.18x[18]Maderbacher, G., Baier, C., Benditz, A., Wagner, F., Greimel, F., Grifka, J., and Keshmiri, A. Presence of rotational errors in long leg radiographs after total knee arthroplasty and impact on measured lower limb and component alignment. Int. Orthop. 2017; 41: 1553–1560Crossref | PubMed | Scopus (19)
| Google ScholarSee all ReferencesWLR acquisition guidelines should focus on eliminating leg rotation to minimize the possible effect of knee flexion and account for the mean tibial rotation. It should deliver reproducible radiographs while being quick and easy to perform by X-ray technicians with fixed positioning for the feet and leg rotation. First, there needs to be a consensus about which anatomical landmark is easy to define and useable for knee joint rotation assessments. A viable landmark to define proximal tibial rotation on CT scans is the Akagi line, which can represent the AP alignment of the knee-joint.28x[28]Saffarini, M., Nover, L., Tandogan, R., Becker, R., Moser, L.B., Hirschmann, M.T., and Indelli, P.F. The original Akagi line is the most reliable: a systematic review of landmarks for rotational alignment of the tibial component in TKA. Knee Surg. Sports Traumatol. Arthrosc. 2018; 27: 1018–1027
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| Google ScholarSee all References Unfortunately, this line is difficult to locate during physical examination. But the angle between the Akagi line and longitudinal axes of the feet in neutral stance is around 10°.24x[24]Turgut, A., Göktürk, E., Seber, S., Köse, N., Hazer, B., and Günal, I. Rotational profile of the lower extremity and foot progression angle: computerized tomographic examination of 50 male adults. Arch. Orthop. Trauma Surg. 2002; 120: 255–258Google ScholarSee all References,28x[28]Saffarini, M., Nover, L., Tandogan, R., Becker, R., Moser, L.B., Hirschmann, M.T., and Indelli, P.F. The original Akagi line is the most reliable: a systematic review of landmarks for rotational alignment of the tibial component in TKA. Knee Surg. Sports Traumatol. Arthrosc. 2018; 27: 1018–1027Crossref | PubMed | Scopus (38)
| Google ScholarSee all References, 29x[29]Chotanaphuti, T., Srisawasdi, R., Rattanaprichavej, P., and Laoruengthana, A. The rotational axis of the tibia and relationship to the tibial torsion in varus osteoarthritic knee. J. Med. Assoc. Thail. Chotmaihet Thangphaet. 2012; 95: 6–11PubMed
| Google ScholarSee all References-30x[30]Akagi, M., Mori, S., Nishimura, S., Nishimura, A., Asano, T., and Hamanishi, C. Variability of Extraarticular Tibial Rotation References for Total Knee Arthroplasty. Clin. Orthop. NA. 2005; : 172–176Crossref | Scopus (154)
| Google ScholarSee all References Aligning each knee straightforward using anatomical landmarks as the patella, malleoli, or condyles based on the X-ray technicians’ experience is very prone to inconsistencies and will result in measurement errors.14x[14]Cooke, T.D.V and Sled, E.A. Optimizing limb position for measuring knee anatomical axis alignment from standing knee radiographs. J. Rheumatol. 2009; 36: 472–477Crossref | PubMed | Scopus (21)
| Google ScholarSee all References,17x[17]Harrison, M.M., Cooke, T.D., Fisher, S.B., and Griffin, M.P. Patterns of knee arthrosis and patellar subluxation. Clin. Orthop. 1994; : 56–63PubMed
| Google ScholarSee all References,18x[18]Maderbacher, G., Baier, C., Benditz, A., Wagner, F., Greimel, F., Grifka, J., and Keshmiri, A. Presence of rotational errors in long leg radiographs after total knee arthroplasty and impact on measured lower limb and component alignment. Int. Orthop. 2017; 41: 1553–1560Crossref | PubMed | Scopus (19)
| Google ScholarSee all ReferencesThis report proposes a set of guidelines for reproducible WLR acquisition, based on the findings of this study (control leg rotation and knee flexion, with no effects of different X-ray beam heights) and what is already described in the literature. Patients should be positioned in maximum knee extension, which is more straightforward to apply by X-ray technicians compared to a certain knee flexion angle. The feet are pointed outwards with 10° of rotation and with 10 cm between the centre of their heels. The angle of 10° is situated between the longitudinal axes of the foot.24x[24]Turgut, A., Göktürk, E., Seber, S., Köse, N., Hazer, B., and Günal, I. Rotational profile of the lower extremity and foot progression angle: computerized tomographic examination of 50 male adults. Arch. Orthop. Trauma Surg. 2002; 120: 255–258Google ScholarSee all References,28x[28]Saffarini, M., Nover, L., Tandogan, R., Becker, R., Moser, L.B., Hirschmann, M.T., and Indelli, P.F. The original Akagi line is the most reliable: a systematic review of landmarks for rotational alignment of the tibial component in TKA. Knee Surg. Sports Traumatol. Arthrosc. 2018; 27: 1018–1027
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| Google ScholarSee all References-30x[30]Akagi, M., Mori, S., Nishimura, S., Nishimura, A., Asano, T., and Hamanishi, C. Variability of Extraarticular Tibial Rotation References for Total Knee Arthroplasty. Clin. Orthop. NA. 2005; : 172–176Crossref | Scopus (154)
| Google ScholarSee all References Practitioners thereby control the hip rotation, by placing the upper body in a straightforward position.7x[7]Sanfridsson, J., Ryd, L., Svahn, G., Fridén, T., and Jonsson, K. Radiographic measurement of femorotibial rotation in weight-bearing: The influence of flexion and extension in the knee on the extensor mechanism and angles of the lower extremity in a healthy population. Acta Radiol. 2001; 42: 207–217PubMed
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| Google ScholarSee all References The practitioners additionally instruct the patient to distribute the weight equally over both legs.9x[9]Specogna, A.V., Birmingham, T.B., Hunt, M.A., Jones, I.C., Jenkyn, T.R., Fowler, P.J., and Giffin, J.R. Radiographic measures of knee alignment in patients with varus gonarthrosis: Effect of weightbearing status and associations with dynamic joint load. Am. J. Sports Med. 2007; 35: 65–70Crossref | PubMed | Scopus (115)
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| Google ScholarSee all References Each WLR is made bilaterally and remarks about the acquisition should be annotated in the radiograph. These proposed guidelines were yet not tested in a clinical setting.Aligning the feet at 10° to define the AP alignment does not account for individual variances in tibiofibular torsion and femoral anteversion. However, the standard deviation of tibiofibular torsion and femoral anteversion within the population of both angles is below 9°, which means that approximately 68% of the patients show rotational variances below 9°23x[23]Bråten, M., Terjesen, T., and Rossvoll, I. Femoral anteversion in normal adults: Ultrasound measurements in 50 men and 50 women. Acta Orthop. 1992; 63: 29–32
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| Google ScholarSee all References,34x[34]S. Kawahara, T. Mawatari, G. Matsui, H. Mizu, Y. Akasaki, Malrotation of whole - leg radiograph less than 10 degrees does not influence preoperative planning in open - wedge high tibial osteotomy, (2020) 1–7.Google ScholarSee all References This rule of thumb is also substantiated by the results of Kawahara et al and Jud et al.31x[31]Jud, L., Trache, T., Tondelli, T., Fürnstahl, P., Fucentese, S.F., and Vlachopoulos, L. Rotation or flexion alters mechanical leg axis measurements comparably in patients with different coronal alignment. Knee Surg. Sports Traumatol. Arthrosc. 2019; Google ScholarSee all References,34x[34]S. Kawahara, T. Mawatari, G. Matsui, H. Mizu, Y. Akasaki, Malrotation of whole - leg radiograph less than 10 degrees does not influence preoperative planning in open - wedge high tibial osteotomy, (2020) 1–7.Google ScholarSee all References But with the proposed guidelines we aim at a more reproducible basis for obtaining WLRs. This benefits the postoperative assessment of realized lower limb osteotomies and future studies relying on reproducible WLRs.In cases with a suspicion of a large lower limb torsional deformity (tibia and/or femur), 3D imaging techniques in the work-up is advisable. Indications for rotational errors on an AP knee radiograph are no (or too much) tibia-fibular overlap and femoral condyle asymmetry.35x[35]Maderbacher, G., Schaumburger, J., Baier, C., Zeman, F., Springorum, H.-R., Dornia, C., Grifka, J., and Keshmiri, A. Predicting knee rotation by the projection overlap of the proximal fibula and tibia in long-leg radiographs. Knee Surg. Sports Traumatol. Arthrosc. 2014; 22: 2982–2988
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| Google ScholarSee all References When using the proposed protocol with fixed feet, the left and right knee should be presented in the same manner. In cases with differences between left and right, further analyses for possible rotational deformities should be conducted. Also, when there is a suspicion of hyperextension or fixed flexion deformity during physical examination, the WLR becomes unreliable.Our study has many limitations. First, our model could not represent the knee joint kinematics in terms of soft tissue compression and tension. During knee flexion, knee joint kinematics are complex due to muscle contractions and ligament tensions. Our sawbone model did not incorporate these parameters and the influence of weight-bearing. However, this study tried to mimic the knee-joint articulation by positioning the hinge points of the Ilizarov frame slightly above the knee-joint (on Blumensaat line).36x[36]in: M. Çakmak, C. Şen, L. Eralp, H.I. Balci, M. Civan (Eds.) Basic Techniques for Extremity Reconstruction. Springer International Publishing, Cham; 2018
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| Google ScholarSee all References Every position was checked with a frontal AP for varus alignment and a sagittal radiograph for flexion. Future research should also consider the role of hyperextension in lower limb alignment measurement errors. Second, leg rotation was simulated by rotating the whole sawbone model. In reality, the lower limb has multiple bones and joints which can cause or compensate for leg rotation. Both the ankle and femoral joint can rotate internally/externally. Third, this study did not include the mechanical tibia angle as described by Paley, due to model limitations.5x[5]Paley, D. Normal Lower Limb Alignment and Joint Orientation. in: Princ. Deform. Correct.Springer Berlin Heidelberg, Germany, Berlin; 2002: 1–18Crossref
| Google ScholarSee all References Future studies should investigate the reproducibility of positioning protocols, including the standard measurement protocol proposed by Paley. Fourth, our model did not include the patella, which is important in the WLR protocol of Paley.5x[5]Paley, D. Normal Lower Limb Alignment and Joint Orientation. in: Princ. Deform. Correct.Springer Berlin Heidelberg, Germany, Berlin; 2002: 1–18Crossref
| Google ScholarSee all References The exact influence of patella malalignment on lower limb geometry analyses could be interesting and a topic for future research.Conclusion
This study showed that leg rotation alone (without knee flexion) can lead to clinically relevant measurement errors when exceeding 9°. When there is 15° of knee flexion and 10° leg rotation the error becomes approximately 2°. Varying X-ray beam heights within a range of 10 cm does not affect the accuracy. Based on these findings, we propose guidelines for system setup and patient positioning during a WLR that is easy to apply and aims at minimizing errors when measuring the HKA.
Funding
This study received no funding.
Disclaimer
None
Declaration of competing interest
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Ethical approval & informed consent
As the study was performed using sawbones, ethical approval and informed consent was not needed.
Author contributions
WPG and HCN conducted this study, after developing the research question together with RJHC and NvE. KHS helped with the design of the study. WP and HC analysed the data and performed the statistics. HW and RJBS helped with the interpretation of the data. All authors contributed to the writing of the manuscript.