Fig. 3
Catheter position categories in the sonographic image. a- perineural intrafascial position: catheter tip is located within the paraneural sheath indicated by saline bolus spread. b- 1st degree dislocation, also called perineural extrafascial: catheter tip is located outside the paraneural sheath but still close to the nerve. Saline bolus (red frame line) moisture the fascial paraneural sheath (yellow frame line) but run away into surrounding tissue. This category is also recorded as dislocated for evaluation since efficacy is decreased. c- 2nd degree dislocation, catheter tip is outside the paraneural sheath without proximity to the nerve. Saline bolus spreads diffuse within the biceps femoris muscle. White arrow- catheter, * preferred correct position