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2025 ISAKOS Biennial Congress ePoster

Local Soft Tissue Thickness in Unicompartimental Knee Arthroplasty: Strong Inter-Parameter Correlation, Moderate Correlation with BMI, and no Impact on Implant Positioning

Lorenz Pichler, MD, Vienna AUSTRIA
Moses Kamal Dieter El Kayali, MD, Berlin GERMANY
Rosa Berndt, MD, Berlin, Berlin GERMANY
Carsten Perka, MD, PhD, Berlin GERMANY
Clemens Gwinner, MD, Berlin GERMANY
Danko Dan Milinkovic, MD, Berlin GERMANY
Charité - University Medicine Berlin, Berlin, Berlin, GERMANY

FDA Status Cleared

Summary

The local soft tissue thickness of the lower limb only moderately correlates with BMI and has no impact on implant positioning in patients undergoing unicompartmental knee arthroplasty.

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Abstract

Background

Several parameters for measuring the local soft tissue thickness (LSTT) of the lower limb exist. However, their inter-parameter correlations, correlations with patient body mass index (BMI), and impact on implant positioning in unicompartmental knee arthroplasty (UKA) remain unclear.

Purpose

To report on the inter-parameter correlations, correlations with BMI, and the impact of LSTT on implant positioning in patients undergoing UKA.

Methods

Demographic data and postoperative radiographs of 93 patients undergoing conventional unilateral medial UKA using the Oxford Partial Knee System were analyzed. LSTT was measured on radiographs using three established parameters: pretibial subcutaneous fat (PSF), knee adipose index (KAI), and ankle adipose index (AAI). Parameters of implant positioning were measured on radiographs according to the surgical technique guidelines of the implant manufacturer, including femoral valgus/varus angle (FVVA), femoral flexion/extension angle (FFEA), tibial varus/valgus angle (TVVA), and tibial flexion/extension angle (TFEA). The percentage of cases within the respective range (FVVA, FFEA & TVVA) and within ±3 degrees of the target value (TFEA) recommended by the surgical technique guidelines was reported. The Pearson correlation coefficient (CC) was calculated between LSTT parameters, LSTT parameters and BMI, and LSTT parameters and implant positioning parameters.

Results

At an average BMI of 28.41 (SD, 4.91), patients exhibited a mean PSF of 12.40 mm (SD, 5.81), a KAI of 1.68 (SD, 0.24), and an AAI of 1.19 (SD, 0.12). Parameters of LSTT were strongly correlated with each other (PSF/KAI 0.70; PSF/AAI 0.61; KAI/AAI 0.64) but only moderately correlated with BMI (PSF 0.46; KAI 0.45; AAI 0.36). The recommended implant position was achieved in 89.2% (FVVA), 77.4% (FFEA), 66.7% (TVVA), and 77.4% (TFEA) of cases. Parameters of LSTT showed no to very weak correlations (< 0.4) with the parameters of implant positioning measured on radiographs.

Conclusion