Abstract: An infusion catheter adapter and cap assembly, the catheter adapter has a housing with an input, an output and a side port, normal to the housing axis, which has a cap. The cap is fixedly attached to the housing by a living hinge with a retaining knob. The retaining knob on the living hinge conjugates with a groove on the housing. The groove is formed as a transverse channel defined by two opposing locking fingers. The position of the retaining knob in the groove is further ensured by a recess on the knob which conjugates with a peak in the groove to center and lock the retaining knob in the groove.