Rotational alignment of the native knee joint using magnetic resonance imaging compared to current optimal angles in total knee replacement

Megan Boulton; Oday Al-Dadah

doi:10.1016/j.jor.2026.03.037

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76 (); 279-286

doi:

10.1016/j.jor.2026.03.037

Rotational alignment of the native knee joint using magnetic resonance imaging compared to current optimal angles in total knee replacement

Megan Boulton^a,, Oday Al-Dadah^b,c

a The Medical School, Newcastle University, Framlington Place, Newcastle-upon-Tyne, NE2 4HH, United Kingdom

b Department of Trauma and Orthopaedic Surgery, South Tyneside District Hospital, Harton Lane, South Shields, NE34 0PL, United Kingdom

c Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Framlington Place, Newcastle-upon-Tyne, NE2 4HH, United Kingdom

⁎Corresponding author: Megan Boulton. boulton.megan02@gmail.com

Received: 2026-3-20, Accepted: 2026-3-31, Published: 2026-4-1

The Authors

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

Abstract

Rotational malalignment is a key contributing factor to poor patient satisfaction following total knee replacement (TKR). Currently accepted target points may not be optimal for all patients. The aim of this study was to assess rotational alignment of native knee joints using magnetic resonance imaging (MRI).

The rotational alignment in native knee joints is different to current published optimal angles of rotation in TKR and different anthropological measurements affect this rotation.

Radiological cohort study evaluating MRI scans of native knee joints. A total of twelve rotational angle measurements of the distal femur and proximal tibia were analysed and compared with currently accepted values in TKR.

A total of 100 patients were evaluated. The posterior condylar angle (PCA) (mean 2.3°; range −3.1° to 5.8°) was significantly different to the conventional 3° used in TKR (p < 0.001), and was also significantly different between males (1.2°) and females (3.4°) (p < 0.001). There were also significant gender differences in the condylar twist angle (CTA) (p < 0.001) and the angle between Whiteside's line and the posterior condylar femoral line (PCFL) (p = 0.014). Height was inversely correlated with PCA (r = −0.46, p < 0.001), CTA (r = −0.37, p < 0.001) and the angle between Whiteside's line and PCFL (r = −0.32, p = 0.001). Conversely, height was directly correlated with the angle between the surgical transepicondylar axis (sTEA) and the posterior tibial condylar axis (PTCA) (r = 0.28, p = 0.005), and between the anatomical transepicondylar axis (aTEA) and the PTCA (r = 0.23, p = 0.024).

There were significant differences between rotational alignment of the native knee joint and the values considered optimal in TKR. Gender differences and significant correlations with anthropometric data highlight the need for a more tailored and individualised approach to rotational alignment in TKR.

Keywords

Rotational alignment

Native knee

Posterior condylar angle

Transepicondylar axis

Total knee replacement

Magnetic resonance imaging

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1 Introduction

Total knee replacements (TKR) are one of the most common orthopaedic procedures performed with over 85,000 primary TKRs performed each year in England and Wales.¹ Despite numerous advancements in the procedure, almost 20% of patients who undergo a TKR are not satisfied with the outcome, primarily due to ongoing pain and functional limitation.²^,³ Poor patient outcomes following TKR are multifactorial, however rotational malalignment has been identified as a key contributing factor.⁴ Errors in rotational alignment have been shown to increase the probability of developing complications such as femorotibial instability, subluxation, pain and limited function ^4–7.

Rotational alignment can be measured in terms of femoral rotation, tibial rotation and combined femoral and tibial rotation. There are a number of recognised axes to measure femoral rotation, including the surgical transepicondylar axis (sTEA), anatomical transepicondylar axis (aTEA),⁶^,⁷ Whiteside's line (anteroposterior (AP) axis),⁸ the posterior condylar femoral line (PCFL)⁶^,⁷^,⁹ and the more recently described anterior trochlear line (ATL) ^9–11. There are advantages and disadvantages to each of these axes, however the sTEA, which connects the most prominent point of the lateral epicondyle and the medial epicondyle sulcus,⁷ is widely accepted as the most reliable axis to measure femoral rotational alignment.¹²

In addition to femoral rotation, avoiding tibial rotational malalignment is also essential in optimising TKR function.¹³ However, unlike femoral rotation, there has been significantly less scrutiny into which anatomical landmarks should be used to establish the gold standard axis to measure tibial rotation.¹³^,¹⁴ Two anatomical landmarks which have been suggested are the Akagi line ⁶^,^14–16 and the Insall line.¹⁷^,¹⁸ Insall et al.¹⁷^,¹⁸ proposed using the medial 1/3 of the tibial tubercle as a suitable anatomic landmark and Akagi et al.¹⁴ suggested using an axis which is formed using the middle of the posterior cruciate ligament (PCL) and the medial border of the patellar tendon attachment. Despite the fact that these anatomic landmarks are considered to be reliable and accepted as appropriate reference points,¹⁹ many studies have shown uncertainty regarding the reproducibility of these axes due to variation in the location of the tibial tubercle.²⁰^,²¹

There are far fewer techniques established to measure the combined femoral and tibial rotation. One of the techniques is to use anatomical landmarks on both the tibia and femur.²² For example, the posterior tibial condylar axis (PTCA)²² is a described landmark on the tibia which can be used to measure rotation. The angle between the sTEA and the PTCA,²² the aTEA and the PTCA²³ and between the PCFL and the PTCA,¹⁶^,²² can be measured.

There are many suggested optimal degrees of rotational alignment. For example, it has been widely recognised that the sTEA should be 3° externally rotated to the PCFL⁴^,⁷^,²⁴^,²⁵ as a study by Anouchi et al.²⁶ found that internal rotation of the femoral component can lead to significant issues following TKR such as severe patellar maltracking. It has also been accepted that the relationship between Whiteside's line and the sTEA should be perpendicular,²⁵^,²⁷ and therefore leading to a 93° angle between the PCFL and Whiteside's line.²⁵

Despite extensive research into femoral rotation, there is significantly less focus on tibial rotation and less still for the combined rotational alignment.

The primary aim of this study was to assess rotational alignment of native knee joints using magnetic resonance imaging (MRI) and compare the values with those currently considered optimal in TKR. The secondary aim of this study was to compare the radiological measurements in the context of demographic variables and anthropometric measurements.

2 Materials and methods

This was a retrospective cohort study evaluating patients that attended a specialist knee clinic under the care of a consultant orthopaedic surgeon who specialises in knee surgery over a one-year period from May 2024 to May 2025. This study was registered with the Institution's Clinical Effectiveness Department (registration number CA11399).

The inclusion criteria for this study were patients who had an MRI scan of their native knee joint. Exclusion criteria consisted of patients with advanced arthritis (presence of osteophytes could alter angle measurements), presence of any form of prosthetics in the knee joint (i.e. TKR), acute trauma (i.e. fractures) or any form of recent knee surgery.

Patient demographic data was collated including age, gender, ethnicity, laterality, height, weight, body mass index (BMI), body surface area (BSA), waist circumference and waist/height ratio.

MRI images (with the knee in full extension) were obtained using a 1.5-T GE Healthcare SIGNA Artist MRI scanner. The MRI sequences were obtained as per standard knee protocols used by the radiology department which included sagittal, coronal, and axial proton density (PD) fat-saturated sequences alongside a sagittal T1-weighted sequence. The PD fat-saturated images on the axial view for all MRI scans were used to measure the angles of rotation for the purposes of data collection. The MRI scans were viewed on the Picture Archiving Communication System (PACS) (Centricity version 6, GE Healthcare, Chicago) by a single observer, trained by a consultant orthopaedic knee surgeon. Utilising the PACS measuring tools, a total of 12 anatomical measurements relating to the rotational alignment of the distal femur and the proximal tibia were collated. All the radiological measurements were analysed for an association with the patient demographic variables.

Femoral rotation was evaluated using 7 validated angle measurements which incorporated 5 reference axes. The 5 different reference axes are illustrated in Fig. 1 which include:1.Surgical transepicondylar axis (sTEA) which connects the most prominent part of the lateral epicondyle on the distal femur to the medial epicondyle sulcus.⁶^,⁷2.Anatomical transepicondylar axis (aTEA) which connects the most prominent point of the medial and lateral epicondyle.⁶^,⁷3.The posterior condylar femoral line (PCFL) which is an axis drawn tangent to the posterior femoral condyles.⁶^,⁷^,⁹4.Whiteside's line which is between the top of the intercondylar notch to the deepest point of the trochlear groove.⁸5.Anterior trochlear line (ATL) which is tangent to the anterior points of the most prominent parts of the medial and lateral anterior femoral condyles ^9–11.

Femoral rotation angle measurements on axial view MRI scan. (a) Posterior condylar angle between the sTEA and the PCFL. (b) Condylar twist angle between the aTEA and PCFL. (c) Angle between Whiteside's line and sTEA. (d) Angle between Whiteside's line and aTEA. (e) Angle between Whiteside's line and PCFL. (f) Angle between ATL and aTEA and angle between ATL and sTEA. sTEA: Surgical transepicondylar axis PCFL: Posterior condylar femoral line aTEA: Anatomical transepicondylar axis ATL: Anterior trochlear line.

From these axes, 7 angles were derived in order to measure the femoral rotation as illustrated in Fig. 1. The 7 angles are (Fig. 1a) the posterior condylar angle (PCA) between the sTEA and the PCFL,⁴^,⁷^,²⁴^,²⁵ (Fig. 1b) the condylar twist angle (CTA) between the aTEA and the PCFL, ⁹^,¹⁰^,^28–30 (Fig. 1c) the angle between Whiteside's line and the sTEA,²⁵^,²⁷ (Fig. 1d) the angle between Whiteside's line and the aTEA,²⁸ (Fig. 1e) the angle between Whiteside's line and the PCFL,⁸^,²⁵ (Fig. 1f) the angle between the ATL and the sTEA,¹⁰^,¹¹ and (Fig. 1f) the angle between the ATL and the aTEA.⁹^,³¹

Two validated angles were used to assess the tibial rotation as illustrated in Fig. 2. The first angle was formed between the Akagi line and the tibial anteroposterior (AP) axis ⁶^,^14–16. In order to find this angle, the sTEA was drawn (Fig. 2a) and projected onto the axial view slice in which the posterior cruciate ligament (PCL) is most visible. The line originating from the centre of the PCL and perpendicular to sTEA is the tibial AP axis (Fig. 2b). The tibial AP axis and the centre of the PCL was then projected to the axial view slice in which the patellar tendon in most visible. The Akagi line can then be drawn from the centre of the PCL to the medial border of the patellar tendon (Fig. 2c) and the angle between the Akagi line and the tibial AP axis can be determined. The Insall line connects the centre of the PCL to the medial third of the patellar tendon (Fig. 2c) and the angle between the Insall line and the tibial AP axis was measured.¹⁴

Tibial rotation angle measurements on axial view MRI scan. (a) sTEA (yellow line). (b) Projected sTEA onto the slice view where the PCL is most visible. Red line is the tibial AP axis which originated from the centre of the PCL and is perpendicular to sTEA. (c) Tibial AP axis projected onto view where patellar tendon is most visible. Akagi line (blue line) is from the projected centre of the PCL to the medial border of the patellar tendon. Insall line (green line) is from the projected centre of the PCL to the medial third of the patellar tendon (white line shows the division of the patellar tendon into thirds). sTEA: Surgical transepicondylar axis PCL: Posterior cruciate ligament.

The combined femoral and tibial rotation angle is a far less researched area as compared to both the femoral and tibial rotation angles individually. In order to ascertain the combined rotation, three different reference axes were employed as illustrated in Fig. 3. (Fig. 3a) the knee rotation angle which is between the PCFL on the distal femur and the posterior tibial condylar axis (PTCA), which is a line tangent to the posterior tibial condyles,¹⁶ (Fig. 3b) the angle between the sTEA and the PTCA³² and (Fig. 3c) the angle between the aTEA and the PTCA.²³

Combined tibial and femoral rotation angle measurements on axial view MRI scan. (a) Angle between PCFL and PTCA. (b) Angle between sTEA and PTCA. (c) Angle between aTEA and PTCA. PCFL: Posterior condylar femoral line PTCA: Posterior tibial condylar axis sTEA: Surgical transepicondylar axis aTEA: Anatomical transepicondylar axis.

3 Statistical analysis

All continuous data distributions were evaluated by plotted histograms with fitted curve lines, boxplots, normal Q-Q plots and the Kolmogorov-Smirnov test. All the radiological measurements displayed a normal distribution and were analysed using the appropriate parametric statistical tests. The one-sample student's t-test was used to compare continuous variables to published normative means (Table 2). If the published values were expressed as a range, the midpoint of that range was used for the analysis. The independent-sample students t-test was used for the between group analysis. Pearson product-moment correlation test was used for the correlation analysis. The level of statistical significance was set at p < 0.05. Statistical analysis was performed using SPSS for Windows version 29.0 (IBM Corp., Armonk, New York).

4 Results

A total of 100 patients were included in this study. The patient demographics are presented in Table 1. The mean age was 44 years (range of 12 to 83) with an even representation of gender, however, the majority of the patients were from a white ethnic background with only 3 patients being from a minority ethnic background. The mean height of the study cohort was 1.71m (range 1.52 to 1.93), mean weight was 88.8 kg (range 42.0 to 159.0) and the mean BMI was 30.2 kg/m² (range 16.2 to 46.3). The cohort had a good spread of patients with varying age and body habitus to allow for a meaningful comparison with the radiological measurements.

Table 1 Patient demographics.

	n = 100
Mean age (years) (±SD) [range]	44 (±20.7) [12 to 83]
Gender (Males: Females)	51 : 49
Ethnicity (White: Minority ethnic group)	97 : 3
Laterality (Left: Right)	40 : 60
Mean height (m) (±SD) [range]	1.71 (±0.1) [1.52 to 1.93]
Mean weight (kg) (±SD) [range]	88.8 (±22.5) [42.0 to 159.0]
Mean BMI (kg/m²) (±SD) [range]	30.2 (±6.3) [16.2 to 46.3]
Mean BSA (m²) (±SD) [range]	2.04 (±0.3) [1.36 to 2.91]
Mean waist circumference (cm) (±SD) [range]	97.9 (±14.6) [69.0 to 142.0]
Mean waist/height ratio (±SD) [range]	0.60 (±0.2) [0.43 to 1.52]

Table 2 Radiological Angle Measurements vs Published Normative Angles ^[reference^s].

	Mean (±SD) [range]	Published normative angles Midpoint [range]	p-value^a [95% CI]
Posterior condylar angle	2.3 (±1.7) [-3.1 to 5.8]	3⁴^,⁷^,²⁴^,²⁵ [−]	<0.001∗ [0.4 to 1.1]
Condylar twist angle	6.4 (±1.8) [0.8 to 11.1)	5.65 ⁹^,¹⁰^,^28–30 [4.4 to 6.9]	<0.001∗ [0.4 to 1.1]
Whiteside's line and sTEA	93.8 (±3.1) [85.5 to 100.4]	90²⁵^,²⁷ [−]	<0.001∗ [3.1 to 4.4]
Whiteside's line and aTEA	89.7 (±3.1) [82.7 to 97.1]	87.6 ²⁵^,^28–30^,³⁷ [86.1 to 89.0]	<0.001∗ [1.5 to 2.7]
Whiteside's line and PCFL	96.0 (±3.1) [89.3 to 103.0]	93²⁵ [−]	<0.001∗ [2.4 to 3.6]
ATL and sTEA	−5.7 (±3.0) [-13.7 to 2.4]	−7.1¹⁰^,¹¹ [-6.1 to −8.0]	<0.001∗ [0.8 to 2.0]
ATL and aTEA	−9.6 (±3.1) [-17.1 to 2.1]	−5.4⁹^,³¹ [-5.6 to −5.1]	<0.001∗ [3.5 to 4.8]
Akagi line and tibial AP axis	−2.0 (±3.2) [-6.6 to 8.4]	−0.85 ^14–16^,⁴⁰^,⁴¹ [-1.7 to 0]	<0.001∗ [0.5 to 1.8]
Insall line and tibial AP axis	7.3 (±3.8) [-6.1 to 18.3]	8.8¹⁴^,¹⁶^,⁴⁰ [7.5 to 10]	<0.001∗ [0.7 to 2.2]
Knee rotation angle	−3.9 (±5.0) [-13.4 to 8.4]	−4.6¹⁶ [−]	0.150 [-0.3 to 1.7]
sTEA and PTCA	−6.2 (±4.9) [-17.0 to 5.6]	−8.5³² [-6 to −11]	<0.001∗ [1.3 to 3.3]
aTEA and PTCA	−10.2 (±4.9) [-19.7 to 5.5]	−9.9²³ [−]	0.482 [-1.3 to 0.6]

a One-sample student's t-test.

Table 2 shows the data of each of the 12 radiological measurements and compares them to the normative published values from the existing literature for each angle. Of the femoral rotation angles, the mean PCA, CTA, angle between Whiteside's line and the sTEA and angle between Whiteside's line and the PCFL were all externally rotated measuring 2.3° ± 1.7°, 6.4° ± 1.8°, 93.8° ± 3.1° and 96.0° ± 3.1° respectively. However, each of these four angles ranged from internally rotated to externally rotated and it was only the CTA that was externally rotated in all 100 patients. In particular, the PCA ranged from 5.8° externally rotated to 3.1° internally rotated. Although the CTA measurement (6.4°) fell within the normal range (4.4° to 6.9°), it was significantly different to the midpoint of this range (5.65°, p < 0.001). All three measurements associated with Whiteside's line were significantly more externally rotated than the published normal range. The normal range for the angle between Whiteside's line and the aTEA was derived using the normal range for the CTA and the suggested optimal angle between Whiteside's line and the PCFL. The mean angle between Whiteside's line and the aTEA, angle between the ATL and the sTEA and angle between ATL and aTEA were all internally rotated, measuring 89.7° ± 3.1°, −5.7° ± 3.0° and −9.6° ± 3.1° respectively. The mean angle between the the ATL and the aTEA (–9.6°) was more internally rotated than the normal range for this angle (–5.6° to –5.1°). The disparity between this data is likely due to the fact that the studies from which the range was taken,^9,31 used a cohort of patients with severe osteoarthritis, however this was part of the exclusion criteria in the present study. All of the seven measured femoral rotation angles were significantly different from the midpoint of the published normative values. When measuring the Akagi line against the tibial AP axis, the mean angle was internally rotated (−2.0° ± 3.2°), whereas the mean angle between the Insall line and the tibial AP axis was externally rotated (7.3° ± 3.8°). Both of the measured tibial rotation angles were significantly different from the published normative value for these angles. All three of the mean combined femoral and tibial rotation angles were internally rotated. The mean angle between the sTEA and the PTCA was within the range of published values (although still significantly different from the midpoint of this range).

Table 3 demonstrates the correlation analysis between each of the radiological measurements with the patient demographic variables. None of the 12 rotational angles were significantly associated with age, however there was a statistically significant (p < 0.05) inverse correlation observed between the height of the patient and three of the femoral rotation measurements (PCA, CTA and angle between Whiteside's line and PCFL). Furthermore, two of the combined femoral and tibial rotation angles (sTEA and PTCA, and aTEA and PTCA) showed a significant direct correlation with height. All three of the combined femoral and tibial rotation angles demonstrated a significant direct correlation with weight, BMI and BSA of the patient cohort. Both the PCA and the angle between Whiteside's line and the PCFL showed a significant inverse correlation with BSA. The waist circumference was significantly (directly) correlated to two of the combined femoral and tibial rotational angles, whilst the waist/height ratio was only significantly (directly) correlated with one of the femoral rotation angles (angle between Whiteside's line and aTEA) but this was only of borderline statistical significance (p = 0.049).

Table 3 Correlation analysis.

	Age r (p-value^a) [95% CI]	Height r (p-value^a) [95% CI]	Weight r (p-value^a) [95% CI]	BMI r (p-value^a) [95% CI]	BSA r (p-value^a) [95% CI]	Waist circumference r (p-value^a) [95% CI]	Waist/height ratio r (p-value^a) [95% CI]
Posterior condylar angle	0.16 (0.103) [-0.03 to 0.35]	−0.46 (<0.001∗) [0.29 to 0.60]	−0.14 (0.152) [-0.33 to 0.05]	0.11 (0.289) [-0.09 to 0.30]	−0.21 (0.039∗) [0.01 to 0.39]	0.10 (0.595) [-0.25 to 0.42]	−0.05 (0.766) [-0.39 to 0.30]
Condylar twist angle	0.15 (0.131) [-0.05 to 0.34]	−0.37 (<0.001∗) [0.19 to 0.53]	−0.14 (0.166) [-0.33 to 0.06]	0.07 (0.490) [-0.13 to 0.26]	−0.19 (0.059) [-0.37 to 0.01]	0.08 (0.649) [-0.27 to 0.41]	−0.16 (0.373) [-0.48 to 0.19]
Whiteside's line and sTEA	0.05 (0.639) [-0.15 to 0.24]	−0.08 (0.427) [-0.27 to 0.12]	−0.09 (0.401) [-0.28 to 0.11]	−0.06 (0.547) [-0.25 to 0.14]	−0.09 (0.350) [-0.29 to 0.10]	0.03 (0.887) [-0.32 to 0.36]	0.26 (0.142) [-0.09 to 0.56]
Whiteside's line and aTEA	0.10 (0.335) [-0.10 to 0.29]	−0.09 (0.403) [-0.28 to 0.11]	−0.04 (0.723) [-0.23 to 0.16]	−0.00 (0.980) [-0.20 to 0.20]	−0.05 (0.614) [-0.25 to 0.15]	0.07 (0.698) [-0.28 to 0.40]	0.35 (0.049∗) [0.00 to 0.62]
Whiteside's line and PCFL	0.12 (0.225) [-0.08 to 0.31]	−0.32 (0.001∗) [0.14 to 0.49]	−0.17 (0.090) [-0.36 to 0.03]	−0.02 (0.871) [-0.21 to 0.18]	−0.21 (0.034∗) [0.02 to 0.39]	0.05 (0.783) [-0.29 to 0.38]	0.21 (0.253) [-0.15 to 0.51]
ATL and sTEA	0.11 (0.263) [-0.09 to 0.30]	−0.15 (0.143) [-0.33 to 0.05]	0.07 (0.493) [-0.13 to 0.26]	0.19 (0.063) [-0.01 to 0.37]	0.03 (0.751) [-0.17 to 0.23]	−0.21 (0.241) [-0.51 to 0.14]	−0.02 (0.897) [-0.36 to 0.32]
ATL and aTEA	0.06 (0.547) [-0.14 to 0.25]	−0.16 (0.124) [-0.34 to 0.04]	0.03 (0.775) [-0.17 to 0.22]	0.14 (0.168) [-0.06 to 0.33]	−0.01 (0.915) [-0.21 to 0.19]	−0.25 (0.160) [-0.54 to 0.10]	0.01 (0.946) [-0.33 to 0.35]
Akagi line and tibial AP axis	0.11 (0.291) [-0.09 to 0.30]	0.19 (0.060) [-0.01 to 0.37]	0.20 (0.050) [0.00 to 0.38]	0.10 (0.335) [-0.10 to 0.29]	0.20 (0.048∗) [0.00 to 0.38]	0.33 (0.054) [-0.01 to 0.60]	0.10 (0.599) [-0.26 to 0.42]
Insall line and tibial AP axis	0.07 (0.492) [-0.13 to 0.26]	0.08 (0.419) [-0.12 to 0.27]	0.17 (0.083) [-0.02 to 0.36]	0.14 (0.173) [-0.06 to 0.33]	0.16 (0.115) [-0.04 to 0.34]	0.30 (0.088) [-0.05 to 0.58]	−0.33 (0.059) [-0.61 to 0.01]
Knee rotation angle	0.12 (0.236) [-0.08 to 0.31]	0.15 (0.151) [-0.05 to 0.33]	0.30 (0.002∗) [0.11 to 0.47]	0.27 (0.007∗) [0.07 to 0.44]	0.29 (0.004∗) [0.10 to 0.46]	0.39 (0.022∗) [0.06 to 0.64]	0.12 (0.525) [-0.24 to 0.44]
sTEA and PTCA	0.05 (0.598) [-0.15 to 0.25]	0.28 (0.005∗) [0.09 to 0.45]	0.35 (<0.001∗) [0.17 to 0.52]	0.24 (0.015∗) [0.05 to 0.42]	0.36 (<0.001∗) [0.17 to 0.52]	0.36 (0.035∗) [0.03 to 0.62]	0.14 (0.455) [-0.22 to 0.46]
aTEA and PTCA	0.07 (0.467) [-0.13 to 0.27]	0.23 (0.024∗) [0.03 to 0.40]	0.32 (0.001∗) [0.13 to 0.49]	0.23 (0.020∗) [0.04 to 0.41]	0.32 (0.001∗) [0.13 to 0.48]	0.30 (0.082) [-0.04 to 0.58]	0.15 (0.410) [-0.21 to 0.47]

a Pearson's product moment correlation analysis.

The gender comparison analysis for each of the radiological measurements is presented in Table 4. This study found significant sex-based differences for three of the femoral rotation measurements. The mean PCA for females (3.4° ± 1.0°) was significantly higher (more externally rotated) as compared to males (1.2° ± 1.5°, p < 0.001). The mean CTA for females (7.4° ± 1.3°) was also significantly higher than that of males (5.5° ± 1.7°, p < 0.001). Finally, the mean angle between Whiteside's line and the PCFL was significantly higher for females (96.8° ± 3.2°) as compared to males (95.3° ± 2.8°, p = 0.014).

Table 4 Gender comparison analysis.

	Males (n = 51) Mean (±SD) [Range]	Females (n = 49) Mean (±SD) [Range]	p-value^a [95% CI]
Posterior condylar angle	1.2 (±1.5) [-3.1 to 3.4]	3.4 (±1.0) [0.3 to 5.8]	<0.001∗ [1.6 to 2.6]
Condylar twist angle	5.5 (±1.7) [0.8 to 8.9]	7.4 (±1.3) [3.7 to 11.1)	<0.001∗ [1.4 to 2.6]
Whiteside's line and sTEA	94.1 (±2.8) [88.0 to 100.4]	93.4 (±3.3) [85.5 to 100.4]	0.297 [-0.6 to 1.9]
Whiteside's line and aTEA	90.1 (±3.0) [84.8 to 97.1]	89.3 (±3.3) [82.7 to 96.2]	0.240 [-0.5 to 2.0]
Whiteside's line and PCFL	95.3 (±2.8) [90.2 to 102.6]	96.8 (±3.2) [89.3 to 103.0]	0.014∗ [0.3 to 2.7]
ATL and sTEA	−5.3 (±2.3) [-11.8 to −0.2]	−6.0 (±3.6) [-13.7 to 2.4]	0.252 [-0.5 to 1.9]
ATL and aTEA	−9.3 (±2.2) [-15.3 to −3.9]	−9.8 (±3.8) [-17.1 to 2.1]	0.485 [-0.8 to 1.7]
Akagi line and tibial AP axis	−2.0 (±3.6) [-6.6 to 8.4]	−2.0 (±2.8) [-5.9 to 4.8]	0.971 [-1.3 to 1.3]
Insall line and tibial AP axis	6.9 (±4.4) [-6.1 to 18.3]	7.8 (±3.0) [3.7 to 15.2]	0.251 [-2.4 to 0.6]
Knee rotation angle	−4.2 (±5.7) [-13.4 to 8.4]	−3.5 (±4.1) [-12.8 to 7.5]	0.462 [-2.7 to 1.2]
sTEA and PTCA	−5.6 (±5.4) [-15.1 to 5.6]	−6.9 (±4.3) [-17.0 to 3.6]	0.184 [-0.6 to 3.2]
aTEA and PTCA	−9.6 (±5.5) [-19.3 to 5.5]	−10.9 (±4.1) [-19.7 to −0.7]	0.203 [-0.7 to 3.2]

a Independent-sample student's t-test.

Table 5 demonstrates that there were no significant differences in terms of laterality between the left knee and the right knee among any of the rotational measurements, except for Whiteside's line and aTEA (p = 0.041), but this latter result might be attributed to a Type I statistical error.

Table 5 Laterality comparison analysis.

	Left knee (n = 40) Mean (±SD) [Range]	Right knee (n = 60) Mean (±SD) [Range]	p-value^a [95% CI]
Posterior condylar angle	2.1 (±1.9) [-3.1 to 5.8]	2.4 (±1.5) [-1.9 to 4.5]	0.292 [-1.0 to 0.3]
Condylar twist angle	6.5 (±2.2) [0.8 to 11.1]	6.4 (±1.5) [2.3 to 9.2]	0.814 [-0.7 to 0.8]
Whiteside's line and sTEA	93.3 (±2.9) [87.7 to 99.5]	94.1 (±3.2) [85.5 to 100.4]	0.203 [-2.0 to 0.4]
Whiteside's line and aTEA	88.9 (±2.7) [84.1 to 94.6]	90.2 (±3.3) [82.7 to 97.1]	0.041∗ [0.1 to 2.6]
Whiteside's line and PCFL	95.3 (±3.1) [90.2 to 102.6]	96.4 (±3.1) [89.3 to 103.0]	0.085 [-2.3 to 0.2]
ATL and sTEA	−5.8 (±2.7) [-13.1 to −0.4]	−5.6 (±3.2) [-13.7 to 2.4]	0.770 [-1.4 to 1.0]
ATL and aTEA	−10.0 (±2.5) [-17.1 to −4.8]	−9.3 (±3.5) [-16.6 to 2.1]	0.274 [-2.0 to 0.6]
Akagi line and tibial AP axis	−2.0 (±3.3) [-5.2 to 8.4]	−1.9 (±3.2) [-6.6 to 5.9]	0.941 [-1.4 to 1.3]
Insall line and tibial AP axis	7.5 (±4.0) [-6.1 to 18.3]	7.2 (±3.7) [-5.9 to 15.2]	0.678 [-1.2 to 1.9]
Knee rotation angle	−3.4 (±5.0) [-13.4 to 8.4]	−4.2 (±5.0) [-12.8 to 8.4]	0.396 [-1.2 to 2.9]
sTEA and PTCA	−5.6 (±4.7) [-14.3 to 5.6]	−6.6 (±5.0) [-17.0 to 5.1]	0.321 [-1.0 to 3.0]
aTEA and PTCA	−9.8 (±5.2) [-17.9 to 5.5]	−10.6 (±4.7) [-19.7 to 0.7]	0.419 [-1.2 to 2.8]

a Independent-sample student's t-test.

5 Discussion

This study has shown that rotational alignment of native knee joints has inter-individual variation. Body habitus is a key factor associated with the rotation of a native knee joint. In particular, height was significantly correlated to rotational alignment measurements. Another important finding of this study is that currently accepted “optimal” rotational alignment angles in the existing published literature cannot be applied to every patient, as one size does not fit all. This includes the PCA which ranged from −3.1° internal rotation to 5.8° external rotation, demonstrating that current guidelines, which suggest that the femoral prosthetic component in TKR should be 3° externally rotated to the PCFL for all patients,⁴^,⁷^,²⁴^,²⁵ is not suitable. Moreover, the measurements for 11 out of the total 12 radiological angles measured were significantly different from the published normative values which infers that the target points aimed for in TKR are significantly different to the rotational alignment in native knee joints. The significant findings of this study support the mantra that a more tailored and individualised approach to rotational alignment is required.

An important finding of the present study was the variation in range of femoral rotation angles observed which is consistent with previous studies.³³^,³⁴ Despite the CTA being externally rotated in all 100 patients in the present study cohort, the PCA ranged from 3.1° internally rotated to 5.8° externally rotated. Studies by Loures et al.³⁰ and Panicker et al.³⁵ support this conclusion as they found the PCA to range from −2.23° to 7.86° and −2.65° to 7.29° respectively. This supports the proposed philosophy that a more individualised approach to the chosen rotational alignment of the implanted prosthesis at the time of TKR surgery may better suit the final resting place within the knee joint and possibly reduce the risk of post-operative dissatisfaction rather than the current practice of one size fits all (i.e. 3° external rotation of the femoral component of the TKR).

Height was a key demographic variable which was significantly correlated with many of the rotational angles. This included a significant inverse correlation with three of the femoral rotation angles (PCA, CTA and the angle between Whiteside's line and the PCFL). This data shows that taller patients are more likely to have more internally rotated femoral rotation than what is considered normal in their native knee joint. However, two of the combined femoro-tibial rotation angles showed a significant direct correlation with height demonstrating a complex anatomical relationship between the height of patients and the rotational alignment of their native knee joint. A study by Cielinski et al.³⁶ contradicted the findings of the present study as they found a significant direct correlation between height and the PCA (in female patients only), unlike the results of the present study which found an inverse relationship.

Other anthropometric measures also had a notable influence on rotational alignment. Weight, BMI and BSA had a significant direct correlation with all three combined femoro-tibial rotation angles and, furthermore, waist circumference had a significant direct correlation with two of the combined femoro-tibial rotation angles. Conversely, there was a significant inverse correlation between BSA and the angle between Whiteside's line and the PCFL. Moreover, there was a significant direct correlation between waist/height ratio and the angle between Whiteside's line and the aTEA. This further highlights the intricacies of the relationship between body habitus with the different aspects of rotational alignment within the native knee joint.

There was a significant difference between males and females for three femoral rotation angles (PCA, CTA and the angle between Whiteside's line and PCFL), with the angles being more externally rotated in females. This aligns with a previous study by Aglietti et al.⁶ in which the PCA was also found to be more externally rotated in females. However, other studies contradict these findings. Jabalameli et al.²⁹ found the PCA to be internally rotated in females and a study by Cielinski et al.³⁶ found no significant correlation between gender and either the PCA or the CTA. The varying findings in each of these studies suggests that further research needs to be undertaken to evaluate gender-based differences in femoral rotation.

In contrast to gender and body habitus, there was no significant correlation between age or knee laterality and any of the 12 radiological measurements. This was also concluded in other studies, including Raju et al.³⁷ which found no significant difference between three of the femoral rotation angles (CTA, Whiteside's line and aTEA and Whiteside's line and PCFL) and age or laterality. Another study by Cielinski et al.³⁶ also found a high degree of symmetry of the PCA and the CTA between contralateral knees.

There are some limitations of this study to be acknowledged. The first being that although all patients with severe osteoarthritis were excluded, the study still included some patients with mild degenerative changes which could have influenced the measurement of the different rotational angles. This is due to the fact that it can cause structural changes to the joint such as joint space narrowing and osteophyte formation³⁸ (particularly at the posterior femoral condyles, intercondylar notch or tibial tubercle) which can obscure the clarity of the anatomical landmarks therefore altering the measured angles of rotation. Moreover, varying degrees of degeneration of the articular cartilage may have influenced the measurement of the angles. For example, the PCFL axis was measured at the level of the articular cartilage and therefore degradation of the articular cartilage covering the femoral condyles may alter the measured size of the angle. In general, radiological measurements on MRI scans can be inadvertently influenced by articular cartilage degradation. Another notable limitation was that 97% of the study cohort was comprised of patients from a white ethnic background with only 3% being from a minority ethnic group. Consequently, the present study was unable to assess whether ethnicity influences rotational alignment in a native knee joint.

A key strength of the present study is that most existing published studies only focus on one solitary component of rotation. However, the present study is one of the few to examine different angles in each femoral, tibial and combined femoral and tibial rotational alignment. Moreover, there are very few studies which compare angles of rotation between different patient demographic variables. Those studies that do, will only focus on one solitary variable such as gender³³^,³⁴ or ethnicity,³⁹ unlike this study which evaluates numerous variables to give a more comprehensive evaluation. There is also very limited research into the effect of body composition on rotational alignment with only one study comparing height and weight to femoral rotation.³⁶ However, the authors of these studies presented their findings cautiously, stating that further studies with a larger cohort need to be undertaken. The present study compares rotational alignment with a range of demographic variables including height and various body composition measurements.

Suggestions for future research includes larger scale studies with a more ethnically diverse population group to evaluate the influence of this demographic factor on rotational alignment. Furthermore, conducting in-vitro cadaveric studies where rotational alignment is radiologically evaluated and then a TKR prosthesis is implanted to match that of the pre-operative native knee joint, which is then subject to biomechanical analysis in a laboratory to assess the validity of this concept, in particular femoral components implanted in internal rotation. These results could then serve as a platform to conduct subsequent in-vivo clinical studies through randomised controlled trials comparing TKR surgery using the “currently accepted” target points of prosthesis rotational alignment with patients undergoing “tailored” rotational alignment target points based on their pre-operative native knee anatomy, and compare clinical outcomes, patient satisfaction and revision rates.

6 Conclusion

This study demonstrates that rotational alignment of the native knee joint was significantly influenced by various anthropometric variables and the gender of patients. At present, there are pre-defined prosthetic component rotation targets that are considered optimal for a TKR, however the findings of this study illustrate that a more personalised approach is needed for rotational alignment. Further research is required to investigate how a more tailored approach may positively impact clinical outcome and patient satisfaction following TKR and may reduce revision rates in the future.

Ethical approval

This radiological study was registered with the Institution's Clinical Effectiveness Department (registration number CA11399).

Author contributions

Megan Boulton: Methodology, Investigation, Validation, Writing - Original Draft, Visualization. Oday Al-Dadah: Conceptualization, Software, Formal Analysis, Resources, Data Curation, Writing – Review & Editing, Supervision, Project administration.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.

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Introduction

Materials and methods

Statistical analysis

Results

Discussion

Conclusion

Guardian/patient's consent

Ethical approval

Author contributions

Funding

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[1] Sutton P.M., Murray J.S., . The national joint registry 22 years on: what have we learned about knee replacements? Orthopaedics and trauma. . 2025;39(1):74-80.
[Google Scholar]

[2] Baker P.N., Meulen JHvd, Lewsey J., Gregg P.J., . The role of pain and function in determining patient satisfaction after total knee replacement. J Bone Joint Surg British. 2007;89-B(7):893-900.
[Google Scholar]

[3] Muertizha M., Cai X., Ji B., Aimaiti A., Cao L., . Factors contributing to 1-year dissatisfaction after total knee arthroplasty: a nomogram prediction model. J Orthop Surg Res. 2022;17(1):367.
[Google Scholar]

[4] Berger R.A., Crossett L.S., Jacobs J.J., Rubash H.E., . Malrotation causing patellofemoral complications after total knee arthroplasty. Clin Orthop Relat Res (356):144-153.
[Google Scholar]

[5] Romero J., Stähelin T., Binkert C., Pfirrmann C., Hodler J., Kessler O., . The clinical consequences of flexion gap asymmetry in total knee arthroplasty. J Arthroplast. 2007;22(2):235-240.
[Google Scholar]

[6] Aglietti P., Sensi L., Cuomo P., Ciardullo A., . Rotational position of femoral and tibial components in TKA using the femoral transepicondylar axis. Clin Orthop Relat Res. 2008;466(11):2751-2755.
[Google Scholar]

[7] Berger R.A., Rubash H.E., Seel M.J., Thompson W.H., Crossett L.S., . Determining the rotational alignment of the femoral component in total knee arthroplasty using the epicondylar axis. Clin Orthop Relat Res (286):40-47.
[Google Scholar]

[8] Whiteside L.A., Arima J., . The anteroposterior axis for femoral rotational alignment in valgus total knee arthroplasty. Clin Orthop Relat Res (321):168-172.
[Google Scholar]

[9] Morizane K., Takahashi T., Konishi F., Yamamoto H., . The anterior trochlear line as a reference for femoral component positioning in total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2011;19(12):2009-2015.
[Google Scholar]

[10] Ji H.M., Jin D.S., Han J., Choo H.S., Won Y.Y., . Comparison of alternate references for femoral rotation in female patients undergoing total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2016;24(8):2402-2406.
[Google Scholar]

[11] Won Y.-Y., Cui W.-Q., Baek M.-H., Yun T.-B., Han S.-H., . An additional reference axis for determining rotational alignment of the femoral component in total knee arthroplasty. J Arthroplast. 2007;22(7):1049-1053.
[Google Scholar]

[12] Jang E.S., Connors-Ehlert R., LiArno S., Geller J.A., Cooper H.J., Shah R.P., . Accuracy of reference axes for femoral component rotation in total knee arthroplasty: computed tomography-based study of 2,128 femora. J Bone Joint Surg Am. 2019;101(23)
[Google Scholar]

[13] Hofmann S., Tecame A., Victor J., Seitlinger G., Innocenti B., . Tibia rotational alignment in total knee arthroplasty: delphi consensus statements from European Knee Society (EKS) Arch Orthop Trauma Surg. 2025;145(1):221.
[Google Scholar]

[14] Akagi M., Oh M., Nonaka T., Tsujimoto H., Asano T., Hamanishi C., . An anteroposterior axis of the tibia for total knee arthroplasty. Clin Orthop Relat Res. 2004;420:213-219.
[Google Scholar]

[15] Akagi M., Mori S., Nishimura S., Nishimura A., Asano T., Hamanishi C., . Variability of extraarticular tibial rotation references for total knee arthroplasty. Clin Orthop Relat Res. 2005;436:172-176.
[Google Scholar]

[16] Zhang H., Cao C., Zhang H., Han S., . Determining the rotational alignment of the tibial component referring to the tibial tubercle during total knee arthroplasty: the tibial tubercle–trochlear groove can be an aid. J Orthop Surg Res. 2022;17(1):253.
[Google Scholar]

[17] Insall J.N., Binazzi R., Soudry M., Mestriner L.A., . Total knee arthroplasty. Clin Orthop Relat Res. 1985;192:13-22.
[Google Scholar]

[18] Thahir M., Naggar A., Hasanain S., et al . Rotational Alignment of Tibial Component in Total Knee Arthroplasty. 2025
[Google Scholar]

[19] Mitsuhashi S., Akamatsu Y., Kobayashi H., Kusayama Y., Kumagai K., Saito T., . Combined CT-based and image-free navigation systems in TKA reduces postoperative outliers of rotational alignment of the tibial component. Arch Orthop Trauma Surg. 2018;138(2):259-266.
[Google Scholar]

[20] Howell S.M., Chen J., Hull M.L., . Variability of the location of the tibial tubercle affects the rotational alignment of the tibial component in kinematically aligned total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2013;21(10):2288-2295.
[Google Scholar]

[21] Tao K., Cai M., Zhu Y., Lou L., Cai Z., . Aligning the tibial component with medial border of the tibial tubercle--is it always right? Knee. 2014;21(1):295-298.
[Google Scholar]

[22] Hernández-Hermoso J.A., Nescolarde L., Yañez-Siller F., Calle-García J., Garcia-Perdomo D., Pérez-Andres R., . Combined femoral and tibial component total knee arthroplasty device rotation measurement is reliable and predicts clinical outcome. J Orthop Traumatol. 2023;24(1):40.
[Google Scholar]

[23] Nam J.H., Koh Y.G., Kim P.S., Kim G., Kwak Y.H., Kang K.T., . Evaluation of tibial rotational axis in total knee arthroplasty using magnetic resonance imaging. Sci Rep. 2020;10(1)
[Google Scholar]

[24] Newman C.R., Walter W.L., Talbot S., . Femoral rotational asymmetry is a common anatomical variant. Clin Anat. 2018;31(4):551-559.
[Google Scholar]

[25] Twiggs J.G., Dickison D.M., Kolos E.C., et al . Patient variation limits use of fixed references for femoral rotation component alignment in total knee arthroplasty. J Arthroplast. 2018;33(1):67-74.
[Google Scholar]

[26] Anouchi Y.S., Whiteside L.A., Kaiser A.D., Milliano M.T., . The effects of axial rotational alignment of the femoral component on knee stability and patellar tracking in total knee arthroplasty demonstrated on autopsy specimens. Clin Orthop Relat Res (287):170-177.
[Google Scholar]

[27] Middleton F.R., Palmer S.H., . How accurate is Whiteside's line as a reference axis in total knee arthroplasty? Knee. 2007;14(3):204-207.
[Google Scholar]

[28] Atinga M., Loyal P., Oroko P., Chikophe I., Lutomia M., Baraza N., . Distal femur MRI rotational anatomy in a black African population: a pilot study. Ann Afr Surg. 2024;21:83-87.
[Google Scholar]

[29] Jabalameli M., Moradi A., Bagherifard A., Radi M., Mokhtari T., . Evaluation of distal femoral rotational alignment with spiral CT scan before total knee arthroplasty (A study in Iranian population) Arch Bone Jt Surg. 2016;4(2):122-127.
[Google Scholar]

[30] Loures F.B., Furtado Neto S., Pinto Rde L., et al . Rotational assessment of distal femur and its relevance in total knee arthroplasty: analysis by magnetic resonance imaging. Radiol Bras. 2015;48(5):282-286.
[Google Scholar]

[31] Nam J.H., Koh Y.G., Kim P.S., Kang K., Kang K.T., . The femoral trochlear anterior line is a better alternative intra-operative reference compared to femoral anterior tangent line for femoral rotation in both genders in total knee arthroplasty. J Exp Orthop. 2020;7(1):43.
[Google Scholar]

[32] Graw B.P., Harris A.H., Tripuraneni K.R., Giori N.J., . Rotational references for total knee arthroplasty tibial components change with level of resection. Clin Orthop Relat Res. 2010;468(10):2734-2738.
[Google Scholar]

[33] Cho B.W., Hong H.T., Koh Y.G., Choi J., Park K.K., Kang K.T., . Analysis of gender differences in the rotational alignment of the distal femur in kinematically aligned and mechanically aligned total knee arthroplasty. J Clin Med. 2021;10(16)
[Google Scholar]

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Rotational alignment of the native knee joint using magnetic resonance imaging compared to current optimal angles in total knee replacement

Abstract