Background: Irrigation for treating septic joints in adults in the emergency department is possible but requires the development of novel systems that fit all body habitus. However, varying body habitus and age of patients may affect the amount of soft tissue surrounding the knee joint capsule. We examined whether the dimensions of the soft-tissue thickness at the superolateral approach of entry to the arthrocentesis site correlated with patient anthropometric data such as age, sex, height, weight, and body mass index (BMI, kg/m2).

Methods: Using the diagnosis code 844.2 (International Classification of Diseases, Ninth Revision), we reviewed findings of magnetic resonance imaging (MRI) of knees from 100 consecutive patients and gathered anthropometric data for each patient at the time of the MRI. We measured the soft-tissue thickness at the standard entry point for superolateral arthrocentesis.

Results: Soft-tissue thickness at the arthrocentesis site ranged from 5.5 mm to 38 mm and averaged 13.8 mm. Of the independent variables considered, BMI was the most closely correlated with joint-space size albeit poorly (R2 = 0.46). Every unit of increase in BMI correlated with a predicted average soft-tissue thickness increase of 0.61 mm.

Conclusions: The anthropometric data obtained from this study may help create a single, universal device for use in bedside joint irrigation. The correlation between BMI and soft-tissue thickness can guide future device designs.

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