Analysis of the Transepicondylar Angle in the Indian Population: A Single-Centre Study Using CUVIS Robot and Computed Tomography Scan Data

Introduction

Total knee replacement (TKR) is one of the most common orthopaedic procedures performed worldwide. The success of TKR largely depends on precise implant positioning, particularly the rotational alignment of the femoral component.¹ In this context, the transepicondylar axis (TEA)—the line connecting the medial and lateral epicondyles of the femur—serves as a critical reference. Proper alignment along this axis ensures balanced flexion gaps and optimal patellofemoral tracking, which are vital for long-term joint stability and function.²

In most surgical protocols, the posterior condylar axis (PCA) and TEA are used interchangeably or in combination to determine femoral rotation.³ However, studies suggest considerable variability between these axes depending on individual anatomy and ethnicity. The angle between TEA and PCA, referred to as the posterior condylar angle (PCA) value,, plays an essential role in identifying rotational mismatches that could lead to complications such as pain, stiffness, patellar maltracking, or even early prosthetic failure.⁴

Previous anatomical studies in Western populations have reported the average PCA value (i.e., TEA-PCA difference) to range from 3.5° to 5°.5 For instance, Dennis et al. (2001)6 and Whiteside et al. (2003)⁷ emphasised the importance of using TEA over PCA for consistent alignment in femoral component positioning due to its reproducibility. However, Asian and Indian populations, owing to genetic and functional anatomical differences such as habitual squatting and cross-legged sitting, exhibit different morphometric characteristics. Indian studies have reported lower PCA values (~4.67°), suggesting a more externally rotated distal femur compared to Western populations.⁸

Such ethnic differences are often overlooked in the design of TKR instrumentation and surgical planning, which predominantly rely on datasets derived from Caucasian morphologies. A few magnetic resonance imaging (MRI)-based morphometric studies in India (Gupta et al., 20151 ) have indicated the necessity of ethnicity-specific implant design and preoperative planning using computed tomography (CT) or MRI data to account for these variations. Furthermore, the introduction of robotic-assisted systems (like CUVIS, MAKO, and ROSA) has enhanced the ability to accurately measure such parameters, thereby personalising TKR planning.⁵

This study contributes to the growing body of evidence advocating for population-specific references in TKR. It leverages CT-based data and robotic precision to analyse TEA in the Indian population—data which may be pivotal in optimising rotational alignment, minimising intraoperative guesswork, and improving long-term clinical outcomes.

Methods

This retrospective study analysed 200 patients who underwent preoperative CT scans as part of robotic TKR planning at a single centre. The TEA was measured using the CUVIS robotic system, ensuring accuracy and consistency in angle measurement. Data were categorised and analysed for statistical variation.

Statistical analysis included mean, standard deviation, range, and interquartile range (IQR). The distribution and variation of TEA values were illustrated using data visualisation tools such as histograms and box plots, presented in Figure 1 and Figure 2, respectively.

Results

• Mean TEA: 1.83° (±1.13°)

• Range: 0.00° to 5.80°

• 5th percentile: 0.90°

• Median: 1.80°

  
  

• 75th percentile: 2.60°

• No significant correlation was observed between TEA and patient age