Knee Torsion Varies by Ethnicity: Why It Matters for Joint Replacements
"New research highlights the importance of considering ethnic differences in distal femoral torsion for better knee replacement outcomes."
Total knee arthroplasty (TKA) aims to relieve pain and restore function in individuals with severe knee joint damage. Achieving optimal alignment of the femoral component is critical for long-term implant survival and functional outcomes. Proper alignment directly influences the biomechanics of the knee, affecting both stability and patellar tracking.
Key to femoral component positioning is understanding distal femoral torsion (DFT), the angle between the posterior condylar axis (PCA) and the transepicondylar axis (TEA). The TEA, encompassing the anatomical and surgical epicondylar axes, serves as a reference point. While the surgical TEA guides prosthesis rotation, the anatomical TEA is more reliably measured through imaging. Understanding the nuances between these measurements is vital for precise TKA.
While individual variation in DFT is well-documented, the potential influence of ethnicity has been largely unexplored. A recent study comparing the 3D morphology of the distal femur between Caucasian and Asian populations revealed distinct differences, prompting further investigation into DFT variations between these groups. This research aims to address that gap, analyzing DFT values in non-arthritic knees across different ethnicities, ages, sexes, and sides of the body.
Measurement Variability
A study of radiographic distal femoral torsion measurements found satisfactory reproducibility for aPCA, but not for sPCA. It also reported marked inter-individual variability in aPCA, which tended to increase when the knee was in valgus. These findings underscore measurement limitations; the source does not provide population statistics on torsion by ethnicity or its overall impact.
Established Surgical Approaches
Orthobullets describes the standard medial parapatellar, midvastus, and subvastus approaches for total knee arthroplasty (TKA), noting that no midterm or long-term functional outcome differences have been shown among them. For complex primary or revision TKA, it lists approaches such as the medial parapatellar incision, quadriceps snip, and V-Y turndown. A separate chapter notes that some knee incisions and approaches originated in open meniscectomy and reconstructive procedures before arthroscopy and are now mainly of historical value.
Distal Femoral Torsion (DFT): What the Study Revealed
A comprehensive study was conducted using computed tomography (CT) scans of distal femurs from 515 patients. The study group comprised 259 Asian patients (from China) and 256 Caucasian patients (from France). Exclusion criteria ensured that all patients had healthy knees without any signs of osteoarthritis or bone pathologies. Researchers carefully measured the anatomical distal femoral torsion (TEFD) and analyzed its relationship with ethnicity, age, sex, and laterality.
- Significant Ethnic Variation: Asians exhibited a significantly greater mean TEFD (6.4°) compared to Caucasians (5.5°). This difference highlights the need to consider ethnicity in preoperative planning.
- No Impact from Age, Sex, or Laterality: The study found no significant correlation between TEFD and factors like age, sex, or whether it was the left or right knee.
- Reliable Measurements: The measurement techniques employed demonstrated low inter- and intra-observer variability, ensuring the reliability and accuracy of the results.
Robotics and Contemporary TKA Research
A study published April 1, 2024, evaluated femoral implant rotational positioning using the ROSA Knee® robotic system, with the stated hypothesis that its rotational accuracy would be comparable to navigation. The provided source summary does not report the study's findings, so it does not establish whether that hypothesis was supported. A 2025 Cureus review describes TKA as the gold-standard operation for end-stage knee osteoarthritis and covers procedure history, implant choices, perioperative guidelines, and technologies. A separate review examined 2023 TKA and unicompartmental knee arthroplasty research published in KSSTA, identifying research themes, advancements, and global contributions.
Limits of Rotational Alignment Evidence
A study of distal femoral rotation in an Iranian population cautions that relying on a single technique to determine rotational characteristics may not be reasonable, even among people of the same ethnicity. A systematic review found insufficient evidence to state a clear cutoff for revising malrotated TKA components. Research on distal femur morphology in healthy Turkish individuals notes that osteoarthritic knees may produce different results. A European knee society Delphi consensus likewise says that evidence has not conclusively linked pre- and intraoperative rotational findings to clinical outcomes and calls for further high-level studies to identify appropriate individual femoral rotation.
Sources Do Not Support a Comparison
The listed sources do not provide a supported comparison of knee torsion, ethnicity, or joint-replacement outcomes. One source concerns postpancreatectomy hemorrhage and reports that 35 patients developed it; it does not address knee surgery. The other is a 2026 guide to alternatives to knee replacement, including gel injections, physical therapy, PRP, bracing, and emerging treatments said to potentially delay or avoid TKR. These sources therefore cannot establish how torsion-informed replacement compares with alternatives.
Personalized Approaches: The Future of Knee Replacements
This research underscores the importance of recognizing ethnic variations in knee anatomy for optimizing outcomes in total knee arthroplasty. By considering these differences and employing precise measurement techniques, surgeons can better personalize procedures, potentially reducing complications and improving patient satisfaction. Preoperative CT or MRI scans are valuable tools for accurately assessing TEFD and guiding the rotational alignment of the femoral component. Further research is needed to explore the clinical implications of these findings and develop tailored surgical approaches that account for ethnic-specific anatomical variations.
Alignment Depends on the Case
A magnetic resonance imaging analysis reports that most TKA instruments use the femoral posterior condylar line to guide implant positioning, with three-degree external rotation in the axial plane. It describes that reference as appropriate for neutral or varus knee alignment, but not ideal in valgus deformity. A separate report describes a retrospective cohort of 382 patients treated by one surgeon from 2022 to 2023 with robotic-assisted TKA using a functional-alignment strategy for end-stage varus knee osteoarthritis; the provided summary states the study aim but not its outcomes. Another report describes TKA combined with tibial derotation osteotomy and tibial tuberosity transfer in ten patients (twelve knees) with advanced osteoarthritis, excessive external tibial torsion, and chronic patellar subluxation.
Complex Cases and Complications
The Orthopedic Surgery Case Reports Journal publishes open-access case reports and case series on complex TKA, including severe deformities, revision procedures, bone loss, ligament instability, and advanced surgical strategies. Another case-report source states that TKA relieves pain and restores mobility for hundreds of thousands of patients annually, while some recipients experience rare complications that standard preoperative counseling may barely mention and postoperative surveillance may miss. A 2025 systematic review set out to evaluate complications, reinterventions, revisions, and conversions to TKA after knee rotational osteotomies used to correct lower-limb rotational malalignment in patients with anterior knee pain and/or patellofemoral instability; the supplied summary does not give its results.