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. 2024 Jun 27:16:120053.
doi: 10.52965/001c.120053. eCollection 2024.

Femorotibial angle on short knee radiographs fails to accurately predict the lower limb mechanical alignment. A systematic review and meta-analysis on different femorotibial angle definitions and short knee radiograph types

Giancarlo Giurazza  1   2 , Giovanni Perricone  1   2 , Edoardo Franceschetti  1   2 , Stefano Campi  1   2 , Pietro Gregori  1   2 , Biagio Zampogna  1   2   3 , Umberto Gabriele Cardile  1   2 , Giuseppe Francesco Papalia  1   2 , Rocco Papalia  1   2
Affiliations

Femorotibial angle on short knee radiographs fails to accurately predict the lower limb mechanical alignment. A systematic review and meta-analysis on different femorotibial angle definitions and short knee radiograph types

Giancarlo Giurazza et al. Orthop Rev (Pavia). .

Abstract

Introduction: Hip-knee-ankle angle (HKA) on Full Limb Radiographs (FLRs) is the gold standard for coronal knee alignment assessment. Despite the widespread utilization of the more convenient femorotibial angle (FTA) on either antero-posterior (AP) or postero-anterior (PA) short knee radiographs (SKRs), its definition and correlation with HKA remains controversial. This review is the first to systematically investigate FTA-HKA correlation and the effect of different FTA methods and SKRs.

Methods: Systematic literature search (Pubmed, Scopus, Cochrane Library) followed PRISMA guidelines, to evaluate studies examining the FTA-HKA correlation. Meta-analyses compared the 3 most common FTA methods, knee center determination method and SKR types.

Results: 17 studies (2597 patients, 3234 knees) were included. The strongest correlation with HKA (r = 0.78) was found for FTA Method 1 (angle formed by lines drawn from the midpoint of tibial spines to points 10 cm above and below the joint line). No significant differences were observed when grouping the FTA methods by knee center assessment (Group I, r = 0.78; Group II, r = 0.77). AP SKRs showed a trend towards stronger FTA-HKA correlation compared to PA SKRs, in both Method 1 (r = 0.79 vs 0.75) and Method 3 (r = 0.80 vs 0.66).

Conclusion: Irrespective of its definition or type of SKR used, FTA lacks reliable accuracy in predicting the HKA in most knees. FLRs should be used whenever precise estimation of the patient's alignment is necessary. Caution is warranted in interpreting studies investigating knee alignment or knee arthroplasty outcomes based on FTA.

Keywords: FTA-HKA correlation; Femorotibial angle (FTA); Full limb radiograph; Hip-Knee-Ankle angle (HKA); Short Knee Radiograph.

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Conflict of interest statement

The authors declare that they have not conflict of interest.

Figures

Figure 1.
Figure 1.. PRISMA 2020 flow diagram
Figure 2.
Figure 2.. FTA-HKA correlation of the 3 most commonly used FTA methods
Figure 3.
Figure 3.. FTA-HKA correlation based on the method used to determine the knee’s center: Group I, one reference point; Group II, one reference point for the proximal tibia e one for the distal femur
Figure 4.
Figure 4.. FTA-HKA correlation when using AP vs PA SKRs in Method 1 and Method 3
See this image and copyright information in PMC

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