Knee Morphometry in Asian and Western Populations: A Systematic Review and Meta-Analysis of Anterior Cruciate Ligament-Related Parameters.

Abstract

Importance: Intercondylar notch dimensions, anterior cruciate ligament (ACL) width, and posterior tibial slope (PTS) are recognized as important anatomical factors associated with ACL injury risk, and anatomical reference values for these parameters are derived predominantly from Western cohorts. Individual studies suggest that ACL-related knee morphology may vary across populations, but whether such differences are consistent between Asian and Western populations across commonly assessed magnetic resonance imaging (MRI)-measured parameters remains uncertain.

Aim: To determine whether MRI-measured knee morphology differs between geographically defined Asian and Western adult populations with radiologically intact ACLs across six prespecified parameters: femoral notch volume (FNV), notch width (NW), notch width index (NWI), medial tibial slope (MTS), lateral tibial slope (LTS), and ACL width.

Methods: This systematic review and meta-analysis was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 statement and prospectively registered with the International Prospective Register of Systematic Reviews (PROSPERO) [CRD420261403854]. Four electronic databases were searched from inception to 11 June 2026 for MRI studies reporting eligible morphometric outcomes in adults with radiologically intact ACLs. Studies were classified as Asian or Western by country of cohort recruitment, reflecting geographic origin rather than verified individual ethnicity. Single-arm random-effects meta-analyses using restricted maximum likelihood estimation were pooled separately by cohort and compared using the Q test for subgroup differences. Meta-regression evaluated geographic cohort, measurement technique, mean age and sex composition as potential sources of between-study variation. Statistical significance was defined as two-sided p < 0.05.

Results: Thirty-one studies (2,463 knees; 15 Asian, 16 Western) were included. No statistically significant between-cohort differences were identified for FNV (7.26 versus 7.64 cm³, p = 0.78), NW (20.13 versus 19.86 mm, p = 0.77), NWI (0.28 versus 0.24, p = 0.45), MTS (5.66° versus 6.04°, p = 0.67) or LTS (5.73° versus 6.24°, p = 0.53). ACL width also did not differ statistically significantly (5.20 versus 7.62 mm, p = 0.08). Heterogeneity, quantified using the I² statistic, was substantial across all outcomes (I² = 75-100%) and prediction intervals were wide and overlapping between cohorts. Geographic cohort was not a statistically significant moderator of any outcome (p = 0.09-0.82). Measurement technique was associated with LTS (p = 0.03), explaining 44% of the between-study variance (R²), but with no other outcome (p = 0.28-0.89), whereas study-level sex composition was associated with NW (regression coefficient [β] = 6.48 mm, p = 0.02), FNV (β = 5.34 cm³, p = 0.04) and mean cohort age was associated with both MTS (β = 0.11°/year, p = 0.02) and LTS (β = 0.11°/year, p < 0.01). Within Asian cohorts, males had statistically significantly greater FNV than females (7.65 versus 5.66 cm³, p < 0.01).

Conclusion: MRI measures of femoral notch morphology, PTS, and ACL width did not differ statistically significantly between Asian and Western populations with radiologically intact ACLs (p = 0.08-0.78). Given the substantial heterogeneity and wide prediction intervals, these findings indicate an absence of detectable differences in the available literature rather than anatomical equivalence between populations, and clinically important differences cannot be excluded. Clinically, geographic origin alone should therefore not be considered a surrogate for individual knee morphology when assessing ACL-related anatomical risk or planning reconstruction. Although study-level sex composition, mean age and measurement technique may contribute to variation in the measured parameters, these associations should be interpreted cautiously given the ecological nature of the analysis.

Level of evidence: Level IV (systematic review and meta-analysis of Level III-IV observational studies).