The Ethnic and Geographical Distribution of Fabella: A Systematic Review and Meta-Analysis of 34,733 Knees

Abstract

Introduction: The primary studies demonstrated that fabellar prevalence (FP) varied with ethnic and geographical distribution. Osteoarthritis (OA) and age-related degeneration have a significant association with FP. The prevalence of OA worldwide was doubled with life expectancy. Increased life expectancy has increased exposure to OA and age-related degeneration which could be a possible reason for the rise of FP. The analysis was conducted to provide insight about FP in respect to geographical, ethnic, sex, and laterality distribution.

Methodology: Eighty-six studies were included which have data from 34,733 knee joints. Fifty radiological studies were consisting of 27,293 knees and 36 cadaveric studies had the data of 7,440 knees of dissected specimens, respectively. The prevalence, Odds, and rate ratios were calculated for aging, osteoarthritis, and ethnic variation. Results: The worldwide FP was 25% (95% CI, 0.22, 0.28). The prevalence of fabella was found to be higher in cadaveric studies (32%) than radiological studies (19%) with significant heterogeneity. The FP was 16-18% till 1950 which was doubled by 2020 (35%). The FP in OA knee was 51% which was thrice of baseline.

Keywords: age-related degeneration; knee joints; odds ratio; osteoarthritis; prevalence.

Figure 1. PRISMA flow diagram of the search strategy.

PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Figure 2. Forest plot computing the effective size of fabellar prevalence.

A: anatomical studies, R: radiographic studies based on X-ray, ROB: risk of bias, L: low, M: moderate, U: unknown, H: high. *Secondary reference.

Figure 3. Geographical distribution of fabella (mean fabellar prevalence) observed during 1875-2020.

Figure 4. (i) Fabellar degeneration and ossification flow diagram. (ii) Different grades of fabellar degeneration and ossification are shown in the lateral knee radiographs.

(A) Normal fabella: oval-shaped with anterior smooth surface articulating with the posterolateral condyle of the femur (arrow); (B) sclerosed fabella: subchondral sclerosis of anterior surface (arrow); (C) severe sclerosis of the fabella with osteophyte formation (arrow); (D) enlargement of fabella with marked osteophyte formation (arrow) [1]. Permitted under Creative Commons Attribution 4.0.