Alignment evaluation using different distal reference points after total knee arthroplasty

Yoshinori Ishii; Hideo Noguchi; Junko Sato; Ikuko Takahashi; Hana Ishii; Ryo Ishii; Kei Ishii; Shin-ichi Toyabe

doi:10.1016/j.jor.2021.05.013

View/Download PDF

Buy Reprints

PDF

Translate this page into:

25 (); 186-190

doi:

10.1016/j.jor.2021.05.013

Alignment evaluation using different distal reference points after total knee arthroplasty

Yoshinori Ishii^a,, Hideo Noguchi^a, Junko Sato^a, Ikuko Takahashi^a, Hana Ishii^b, Ryo Ishii^c, Kei Ishii^d, Shin-ichi Toyabe^e

a Ishii Orthopaedic & Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan

b Kanazawa Medical University, School of Plastic Surgery, 1-1 Daigaku, Uchinada, Ishikawa, 920-0253, Japan

c Sado General Hospital, 161 Chikusa Sado, Niigata, 952-1209, Japan

d Iwate Prefectural Ninohe Hospital, 38 Horino, Ninohe, Iwate, 028-6193, Japan

e Niigata University Crisis Management Office, Niigata University Hospital, Niigata University Graduate School of Medical and Dental Sciences, 1 Asahimachi Dori Niigata, Niigata, 951-8520, Japan

∗Corresponding author: Yoshinori Ishii. ishii@sakitama.or.jp

Received: 2021-4-12, Accepted: 2021-5-6, Published: 2021-5-12

Professor P K Surendran Memorial Education Foundation

Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

To assess alignment for total knee arthroplasty, the center of the ankle has been used as the main reference point for the distal tibia; however, the true load-bearing mechanical axis should be determined as a line from the center of the femoral head to the lowest point of calcaneus. Thus, the purpose of this study was to compare the differences in alignment.

Patients with medial osteoarthritis who underwent primary total knee arthroplasty (Group A, center of ankle reference, or Group C, calcaneal contact reference) were recruited. We determined (1) the total number with calcaneal contact point lateral to the center of ankle and compared (2) percentage of displacement of the load-bearing axis at the level of the knee, (3) anatomical axis angle, (4) mechanical axis angle, and (5) tibial component angle.

The study included 94 patients (128 knees), with the calcaneal contact reference point located lateral relative to the center of the ankle in 88.3% (113/128 knees). Using calcaneal contact point references, displacement of the load-bearing axis at the knee was greater (p < 0.0001, 38.7% vs 34.0%), and angles demonstrated significantly valgus alignment (p < 0.0001, 5.6° vs. 4.8° for anatomical axis angle, −3.0° vs. −4.2° for mechanical axis angle, and 89.9° vs. 88.6°for tibial component angle).

Varus alignment measured by the ankle reference method might correspond to the neutral alignment by the amount of valgus alignment indicated by the calcaneal reference. Surgeons should take this into account when preoperative planning, performing intraoperative procedures, and during postoperative evaluation.

Keywords

Alignment study

Total knee arthroplasty

Load-bearing mechanical axis

Anatomical axis angle

Mechanical axis angle

Tibial component angle

Show Related Articles from PubMed

1 Introduction

In alignment evaluations after total knee arthroplasty (TKA), using X-rays of the full length of lower limbs, the center of the ankle joint has conventionally been used as the main reference point for the distal tibia. However, under load-bearing, the true mechanical axis of the lower limb should be taken as a line from the center of the femoral head to the lowest point of the calcaneus and not as the center of the tibial plafond¹; the load-bearing axis of the limb, theoretically, is from the ground to the pelvis (and includes the hindfoot, in particular the subtalar joint). Therefore, in recent years, several studies have evaluated and reported alignment using the hindfoot's contact point with the ground as a distal reference point.^1–4 In addition, in individuals with osteoarthritis and varus knee alignment, the calcaneal contact point tends to be located lateral to the center of the ankle, mainly to compensate for a valgus subtalar joint⁵^,⁶; surgeons should carefully examine any fixed or supple hindfoot deformities in patients with knee arthritis who are considering TKA.⁵^,⁶ Thus, it has been necessary to evaluate differences in both alignment methods. Comparative reports of alignment using ankle or calcaneal contact reference points were normal knee,²^,⁴ osteoarthritic knee,²^,⁴ and knee after unicompartmental knee arthroplasty,³ but their differences after TKA have not been adequately studied.

The purpose of this study was to compare radiographic indicators for defining axis alignment when the center of the ankle is used as the reference and when the calcaneal contact point is used as the reference. We hypothesized that axes defined using the calcaneal contact point with the ground would be lateral to those defined using the center of the ankle joint, and, as a result, the load-bearing axis of individuals would be located lateral to those in whom the ankle center reference was used, resulting in more valgus joint angles.

2 Materials and methods

Therefore, the patients who underwent primary TKA were recruited. Each alignment was measured with two methods that depended on distal tibial reference points (Group A, center of ankle reference, or Group C, calcaneal contact reference). Posterio-anterior full-length X-rays of the lower limb were used to define reference points and determine the mechanical load-bearing axis, the anatomical axis of the tibia, and the tibial component setting angle (TCA). The following were assessed: (1) number of knees with calcaneal contact point lateral to the center of the ankle, (2) percentage of displacement of the load-bearing axis from the medial tibial component of the implant at the level of the knee divided by the width of the tibial plateau (LBA%), (3) anatomical axis angle (AAA), (4) mechanical axis angle (MAA), (5) TCA.

All patients were given a description of the study protocol, and all provided informed consent. This research has been approved by the IRB of the authors’ affiliated institutions. The Hospital for Special Surgery score⁷ was used as a clinical score.

2.1

2.1 Definition of each index in full-length radiographical evaluation

Full-length load-bearing posterio-anterior computed radiography images of the lower limb were obtained including calcaneus following procedures described by Haraguchi et al.,¹ with the patella facing forward to minimize rotation. The X-ray guide is centered on the knee from a distance of 2 m. X-ray voltage and current are 200 mA and 85 kV, respectively. It is important to confirm on the radiograph that the patella is centered between the femoral condyles (Fig. 1). We measured the LBA%, AAA, MAA, TCA as defined below. To measure these indexes, the anatomical axis of the femur was drawn from the midpoint at the center of the femoral shaft (bisecting the proximal-to-distal length of the femur at the isthmus) to the midpoint 10 cm proximal to the joint line. The anatomical axis of the tibia was drawn from the center of the tibial component of the implant to the center of the ankle or calcaneal contact point to ground. The mechanical axis of the femur was defined by a line connecting the center of the femoral head and the center of the femoral component of the implant. The anatomical axis of the tibia was also used as the mechanical axis of the tibia (Fig. 2A).

Technique for the hip-to-calcaneus radiograph. Patient stands on a radiolucent platform, facing the long film cassette. For the lowest point of the calcaneus to be visualized on the radiograph, the cassette is slid into position with its lower edge passing the edge of the platform.

Definition of each axis and angle in full-length radiographical evaluation. This is an X-ray of the lower limb of an 83-year-old man with 6.0° and 2.0° anatomical and mechanical axis angles, evaluated with a calcaneal contact point reference (A) and 4.0° and 3.2°, respectively, with a center ankle reference (B).

The load-bearing axis, the mechanical axis of lower limb, was defined as a line connecting the center of the femoral head and the center of the ankle (talus) (axis A) or contact point of calcaneus to ground (axis C) (Fig. 3A). The LBA% at the knee was calculated by measuring the distance from the medial edge of the proximal tibia to the point where the mechanical axis intersected the proximal tibia (at the level of the tibial plateau), and then dividing that measurement by the entire width of the proximal tibia and multiplying the result by 100% (Fig. 3B). The LBA% at the ankle was calculated by measuring the distance from the medial edge of the talus to the point where the mechanical axis intersected the talus, and then dividing that measurement by the entire width of the talus and multiplying the result by 100%. The percentage value was negative when the axis intersected medial to the medial edge of the proximal tibia and was greater than 100% when it intersected more laterally than the lateral edge. Finally, the number of knees for which the calcaneal contact point was lateral to the center of the ankle was determined (Fig. 3C). The AAA—the angle between the anatomical axis of the tibia and the anatomical axis of the femur (Fig. 2A and B); the MAA—the angle between the mechanical axis of the femur and the mechanical axis of the tibia (Fig. 2A and B); and the TCA—the angle between a line parallel to the tibial plateau and the mechanical axis of the tibia (Fig. 3D) were determined. The letters A and C are used to denote ankle reference–derived and calcaneal contact point reference derived measures.

Load-bearing axis shown for the full leg (A), at the knee (B), and at the ankle (C) and Definition of tibial component angle (TCA) (D). (A,B,C) The gray line shows the load-bearing axis using a calcaneal contact point reference, and the dotted white line shows the axis defined using the ankle reference. (D) White line and dotted line show the TCA of calcaneal contact point (91.0°) and ankle center (89.0°) references, respectively.

2.2

2.2 Reproducibility

To examine the reproducibility of this method, two observers measured LBA% at the knee, AAA, MAA, and TCA twice, with a 1-month interval, using a subset of 20 X-rays. Intraobserver and interobserver reliabilities were evaluated with the intraclass correlation coefficient (ICC). ICCs of the intra- and interobserver reliability were >0.80 (range 0.86–0.98) for all measurements (Table 1). On the basis of the reliability observed above, measurements made by a single investigator were used in the analyses.

Table 1 Intraclass correlation coefficients for intra- and inter-observer reliability.

Variables	Ankle		Calcaneus
Variables	Intra-	Inter-	Intra-	Inter-
Weight-Bearing Axis knee（％）	0.98	0.95	0.98	0.91
Anatomical Axis Angle (°)	0.91	0.90	0.92	0.91
Mechanical Angle（°）	0.98	0.96	0.97	0.93
Tibial Component Angle（°）	0.93	0.90	0.86	0.86

2.3

2.3 Statistical analyses

Results of normality tests, such as the Q–Q plot, the Kolmogorov–Smirnov test, and the Shapiro–Wilk test, showed that all variables were normally distributed. Comparisons between the groups of continuous variables were analyzed using Student's t tests. Statistical analyses were performed using IBM SPSS Statistics version 23 (IBM Japan, Tokyo, Japan). Values are reported as mean ± standard deviation. For all tests, two-tailed p < 0.05 indicated statistical significance.

3 Results

We recruited 94 patients with medial osteoarthritis who underwent primary TKA (128 knees in total) with mechanical alignment procedure. Patients who were treated with revision arthroplasties, those who had previous tibial osteotomies, those who had suffered tibial or femoral shaft fractures, and those with rheumatoid arthritis were excluded. The clinical characteristics of the patients are summarized in Table 2. In 88.3% (113/128 knees), the reference point of calcaneus was lateral to the center of the ankle. The percentage of displacement of load-bearing axis at the level of the knee was 38.7 ± 19.0% and 34.0 ± 17.8% in Group C and A, respectively (p < 0.0001) (Table 3). Both AAA and MAA were approximately 1.2° more valgus in Group C than that in Group A (p < 0.0001) (5.6° ± 3.3° vs. 4.8° ± 3.1° for AAA, −3.0° ± 4.5° vs. −4.2° ± 4.7° for MAA, respectively) (Table 3), and TCA was approximately 1.3° more valgus in Group C than in Group A (89.9° ± 3.2° vs. 88.6° ± 3.3°, respectively; p < 0.0001) (Table 3).

Table 2 Patient characteristics.

Parameter	Patients
Patients	94
Male	15
Female	79
Knees	128
Male	18
Female	110
Age (years)	77 ± 8
Body height (cm)	151 ± 7
Body weight (kg)	61 ± 13
Body mass index (kg/m²)	27 ± 4
Median flexion (degrees)	112 ± 12
Median extension (degrees)	−1 ± 2
Hospital for Special Surgery Score [2]	92 ± 2
Follow-up period (months)	76 ± 67

Table 3 Results of radiographic indicators between two groups.

Variables	Ankle	Calcaneus	p
Load-bearing axis knee	34.0% ± 17.8%	38.7% ± 19.0%	<0.0001
Anatomical axis angle ^a	4.8° ± 3.1°	5.6° ± 3.3°	<0.0001
Mechanical axis angle ^a	−4.2° ± 4.7°	−3.0° ± 4.5°	<0.0001
Tibial component angle	88.6° ± 3.3°	89.9° ± 3.2°	<0.0001

a In line with current convention, the anatomical axis angle and mechanical axis angle are expressed as angular deviation from 180°, with negative values for varus alignment and positive values for valgus alignment (i.e., MAA-A = −3°in varus alignment).

4 Discussion

The important finding in this study was that 113 out of 128 knees (88.3%) had calcaneus contact points located lateral to the center of ankle. As a result, axes defined using a calcaneal contact point reference tended to be located lateral to those defined using a center of ankle reference. In addition, all angular parameters (AAA, MAA and TCA) showed a significantly valgus angle in Group C than they did in Group A. These results are supported by the findings of previous reports in normal controls,²^,⁴ osteoarthritic patients²^,⁴ and patients after unicompartmental knee arthroplasty.³

With regard to load-bearing axis (38.7% in Group C vs. 34.0% in Group A), in previous studies, 34% for healthy normal males⁸ and 29%⁹ for healthy normal females, have been reported. For TKA, the middle 1/3 of the width of tibial component,¹⁰ and center 1/2 of knee-joint width¹¹ were recommended for clinical good outcomes. In a recent report, after TKA using the ankle reference for the axis, a percentage of 34% from medial edge of knee joint in posterior cruciate ligament retaining designs and 42% in posterior cruciate ligament substituting designs were reported at a minimum of 1 year postoperatively with clinical good results.¹² These results are relatively consistent with our findings; both passing within the middle 1/3 of the width of tibial component. Therefore, it may be reasonable to assume that clinical outcomes previously reported using a center of the ankle reference10–12 are likely to be applicable to those using a calcaneal contact point reference as well, but future research to support this speculation is needed. Additionally, considering that the significant difference between the two methods in this study was small (less than 5%), a clinical implication when confirming the intraoperative alignment arises. Because of the difficulty of locating the calcaneal contact point during TKA surgery, when checking with a long rod between the femoral head and the midpoint of the easily palpable bilateral malleoli of the ankle joint as the distal reference, the rod should be slightly shifted laterally to simulate true load-bearing axis.

Correct overall limb alignment is a very important factor in the success of a TKA, as malalignment induces eccentric loading of the component and can lead to loosening. Therefore, there have been many clinical studies of the relationship between alignment and functional results of TKA. The desirable angles of MAA (commonly described as hip-knee-ankle angle), for good long-term clinical results, were defined as within ±3° from neutral alignment¹³^,¹⁴ and of AAA (femorotibial or tibiofemoral angle) were defined as 6° varus to 13° valgus.¹⁰^,¹⁵^,¹⁶ On the basis of this study, when assessing Group C, acceptable range and neutral limb alignment should be determined by taking the amount of valgus in relation to Group A into account. Furthermore, with regard to AAA, most studies were evaluated using standard X-rays not long X-rays. To date, reports from literature examining the correlation between standard and long leg X-rays after TKA are contradictory; using the ankle reference method, some¹⁷^,¹⁸ demonstrated high correlations, while others¹⁹^,²⁰ did not. Therefore, it is necessary to evaluate whether there are correlations between standard and long leg X-rays using the calcaneal contact reference.

Finally, regarding TCA, varus placement of tibial component has not been recommended owing to increased revision rates and wear of insert and subsidence of tibial tray.²¹^,²² Ritter et al.²¹ reported that failure was most likely to occur if the orientation of the tibial component was <90° relative to the tibial axis, in a large-series radiographic analysis of more than 6000 TKAs with a minimum follow-up of 2 years. Meanwhile, after the concept of kinematic alignment was introduced, there were reports that “a slight varus tibial placement in the kinematic alignment is allowed".²²^,²³ Despite selection of kinematic or mechanical alignment procedures, in the varus osteoarthritic knee, the calcaneal contact point tends to be located lateral to the center of the ankle, mainly to compensate for the valgus subtalar joint.⁵ Although it is necessary to verify how many degrees valgus, even in kinematic procedures, it is reasonable to assume that some degree of valgus alignment might also be induced. That is, in kinematic alignment, the slight varus tibial placement defined by the reference point of the ankle joint is likely to actually correspond to the neutral position by the valgus amount using the calcaneal reference. As a result, a slight varus tibial placement when using the ankle reference in the kinematic alignment could be allowed. The previous TCA evaluation after the kinematic procedure²²^,²³ should be re-evaluated using the calcaneal reference to examine the validity of this speculation.

Meanwhile, with regard to radiographic comparison of MAA and TCA in medial unicompartmental knee arthroplasty between ankle and calcaneal contact point references, a calcaneal contact point reference significantly decreased varus alignment by approximately 1° compared with those using an ankle reference3; this study also showed an approximately 1° difference between ankle and calcaneal reference with significant differences, although the clinical and biomechanical relevance was unclear. However, because less than 2° is a clinically acceptable variation in radiographic measurement,²⁴^,²⁵ we believe that the three desirable angles determined using an ankle reference after TKA were likely to be similar to those using a calcaneal contact point reference. Surgeons should pay special attention to excessive valgus placement in using the ankle-based evaluation and for excessive varus placement in using the calcaneus-based evaluation, because values of malalignment measured by one reference such as varus by calcaneus-based or valgus by ankle-based reference, would be worsened by those by using the other evaluation (varus by ankle-based and valgus by calcaneus-based). It is necessary to determine the alignment of the acceptable range of varus placement using the ankle reference and those of valgus placement using the calcaneus reference.

This paper has several limitations. First, because evaluations were two-dimensional, three-dimensional elements including torsion or bowing were not considered. We plan to perform three-dimensional evaluations with a three-dimensional analysis system yielding more accuracy, as has previously been reported with respect to load-bearing axis evaluated by ankle reference.12 Second, preoperative evaluation was not performed, and the changes between before and after TKA surgery were not examined. Clarifying these changes may help to predict postoperative alignment including knee and hindfoot alignment. Third, data from patients with medial osteoarthritis may not be generalizable to patients with lateral osteoarthritis, given that medial and lateral osteoarthritis have unique characteristics, including the compensatory reaction of the subtalar joint. Fourth, the follow-up period was not consistent. However, considering that load-bearing axis in the mediolateral directions of the coronal plane does not change significantly between 3 weeks and 1 year,¹² this did not seem to be critical. Despite these limitations, this study was the first study, to the authors' knowledge, that compared and evaluated postoperative lower limb alignment after TKA using two reference methods to determine alignment axis using long leg X-rays. This information is expected to be helpful for surgeons performing perioperative management in obtaining desirable alignment in TKA.

In conclusion, lower limb alignment using the calcaneus as a reference point for the theoretical load-bearing axis showed a slight valgus alignment compared with that derived from the ankle reference point. We should take this outcome into account in preoperative planning, intraoperative evaluation, and postoperative evaluation. In future, the evaluation of changes from pre-to postoperative alignment with three-dimensional analysis, including the sagittal plane, is required to obtain true desirable alignments in TKA.

Consent for publication

Not applicable.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Funding

None declared.

Authors’ contributions

YI contributed to the study conception and design, drafted the article, and ensured the accuracy of the data and analysis. HN, JS, and IT contributed to the study conception and design and to the analysis and interpretation of the data. HI, RI and KI contributed to the data collection. ST provided statistical expertise and contributed to ensuring the accuracy of the data and analysis. All authors approved the final manuscript.

Ethical review committee statement

The local institutional review board approved this study. All patients provided informed consent.

References

Haraguchi N., Ota K., Tsunoda N., Seike K., Kanetake Y., Tsutaya A., . Weight-bearing-line analysis in supramalleolar osteotomy for varus-type osteoarthritis of the ankle. J Bone Joint Surg Am. 2015;97(4):333-339.
[Google Scholar]
Kim S.G., Choi G.W., Kim H.K., Kim J.G., . Hip-to-calcaneus alignment differs from hip-to-talus alignment in patients with genu varum deformity. Knee Surg Sports Traumatol Arthrosc. 2021;29(3):975-981.
[Google Scholar]
Kuroda Y., Takayama K., Ishida K., et al . Radiographic comparison of the mechanical axis including calcaneus to the conventional mechanical axis in medial unicompartmental knee arthroplasty. J Knee Surg 2019 Dec 30
[Google Scholar]
Tanaka T., Takayama K., Hashimoto S., 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):1146-1152.
[Google Scholar]
Mullaji A., Shetty G.M., . Persistent hindfoot valgus causes lateral deviation of weightbearing axis after total knee arthroplasty. Clin Orthop Relat Res. 2011;469(4):1154-1160.
[Google Scholar]
Norton M., Callaghan J.J., Amendola A., 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):166-174.
[Google Scholar]
Alicea J., . Scoring systems and their validation for the arthritic knee. Surgery of the Knee. 2000;vol. 2:1507-1515.
[Google Scholar]
Minoda Y., Kobayashi A., Iwaki H., et al . Sagittal alignment of the lower extremity while standing in Japanese male. Arch Orthop Trauma Surg. 2008;128(4):435-442.
[Google Scholar]
Sugama R., Minoda Y., Kobayashi A., et al . Sagittal alignment of lower extremity while standing in female. Knee Surg Sports Traumatol Arthrosc. 2011;19(1):74-79.
[Google Scholar]
Ishii Y., Ohmori G., Bechtold J.E., Gustilo R.B., . Extramedullary versus Intramedullary guides for alignment of tibia in total knee arthroplasty. Clin Orthop Relat Res. 1995;318:167-175.
[Google Scholar]
Brys D.A., Lombardi A.V., Mallory T.H., Vaughn B.K., . A comparison of intramedullary and extramedullary alignment systems for tibial component placement in total knee arthroplasty. Clin Orthop Relat Res. 1991;263:175-179.
[Google Scholar]
Ishii Y., Noguchi H., Sato J., Ezawa N., Toyabe S.I., . Changes in the three-dimensional load-bearing axis after mobile-bearing TKA. Eur J Orthop Surg Traumatol. 2016;26(5):537-543.
[Google Scholar]
Howie D.F., Love G.J., Deakin A.H., Kinninmonth A.W., . Intraoperative deviation in limb alignment occurring at implantation in total knee arthroplasty. Knee. 2015;22(1):47-50.
[Google Scholar]
Kuroda Y., Takayama K., Hayashi S., et al . Varus deformity in the proximal tibia and immediate postoperative varus alignment result in varus progression in limb alignment in the long term after total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2020;28(10):3287-3293.
[Google Scholar]
Bargren J.H., Blaha J.D., Freeman M.A.R., . Alignment in total knee arthroplasty. Correlated biomechanical and clinical observations. Clin Orthop Relat Res. 1983;173:178-183.
[Google Scholar]
Jonsson B., Astrom J., . Alignment and long-term clinical results of a semiconstrained knee prosthesis. Clin Orthop Relat Res. 1988;226:124-128.
[Google Scholar]
Alzahrani M.M., Wood T.J., Somerville L.E., Howard J.L., Lanting B.A., Vasarhelyi E.M., . Correlation of short knee radiographs and full-length radiographs in patients undergoing total knee arthroplasty. J Am Acad Orthop Surg. 2019;27:e516-e521.
[Google Scholar]
Ishii Y., Ohmori G., Bechtold J.E., Sherman R.E., Gustilo R.B., . Accuracy of the short radiograph in the measurement of the tibiofemoral angle. Knee. 1995;2(2):81-84.
[Google Scholar]
Abu-Rajab R.B., Deakin A.H., Kandasami M., McGlynn J., Picard F., Kinninmonth A.W., . Hip-knee-ankle radiographs are more appropriate for assessment of postoperative mechanical alignment of total knee arthroplasties than standard AP knee radiographs. J Arthroplasty. 2015;30(4):695-700.
[Google Scholar]
Park A., Stambough J.B., Nunley R.M., Barrack R.L., Nam D., . The inadequacy of short knee radiographs in evaluating coronal alignment after total knee arthroplasty. J Arthroplasty. 2016;31(4):878-882.
[Google Scholar]
Ritter M.A., Davis K.E., Meding J.B., Pierson J.L., Berend M.E., Malinzak R.A., . The effect of alignment and BMI on failure of total knee replacement. J Bone Joint Surg Am. 2011;93(17):1588-1596.
[Google Scholar]
van Hamersveld K.T., Marang-van de Mheen P.J., Nelissen R.G.H.H., . The effect of coronal alignment on tibial component migration following total knee arthroplasty: a cohort study with long-term radiostereometric analysis results. J Bone Joint Surg Am. 2019;101(13):1203-1212.
[Google Scholar]
Howell S.M., Shelton T.J., Hull M.L., . Implant survival and function ten years after kinematically aligned total knee arthroplasty. J Arthroplasty. 2018;33(12):3678-3684.
[Google Scholar]
Krackow K.A., Pepe C.L., Galloway E.J., . A mathematical analysis of the effect of flexion and rotation on apparent varus/valgus alignment at the knee. Orthopedics. 1990;13(8):861-868.
[Google Scholar]
Laskin R.S., . Alignment of total knee components. Orthopedics. 1984;7(1):62-72.
[Google Scholar]