Comparison of Perineural Catheter Depth for the Continuous Popliteal Nerve Block Using Ultrasound Guidance and Dermabond

• Change in Peripheral block score (PBS). [ Time Frame: 10, 20, and 30 minutes after intervention ] [ Designated as safety issue: No ]
  The extent of popliteal nerve blockade will be captured with four sensory groups (sural, superficial peroneal, tibial, and deep peroneal) and three motor groups (superficial peroneal, tibial, and deep peroneal). For each group, a score of 0, 1, or 2 will be assigned based on complete, partial, or no blockade, respectively. The peripheral block score (PBS) outcome variable will be based on the sum of these values and will range from 0 to 14.
  
  

• Pain score [ Time Frame: Arrival to PACU (Immediately after surgery, approximately 3-5 hours after intervention) ] [ Designated as safety issue: No ]
  The investigators will examine the difference in the pain scores (0-10 numeric rating scale) between the two groups.
  
  
• Analgesia failure rate [ Time Frame: Arrival to PACU (Immediately after surgery, approximately 3-5 hours after intervention) ] [ Designated as safety issue: No ]
  The investigators will examine the difference in analgesia failure rates in the PACU. Analgesia failure is defined as the failure of a rescue bolus (to treat patient pain).
  
  
• Catheter dislodgement rates [ Time Frame: Arrival to PACU (Immediately after surgery, approximately 3-5 hours after intervention) ] [ Designated as safety issue: No ]
  The investigators will examine the difference in the catheter dislodgement rates.
  
  
• Difference in total opioid usage [ Time Frame: Length of Stay In PACU (Approximately 5-7 hours after intervention) ] [ Designated as safety issue: No ]
  The investigators will examine the difference in the total opioid usage. We will compare medications separately and in total equivalent units (using an opioid conversion table).
  
  
• Degree of Doppler color agitation [ Time Frame: Immediately after intervention ] [ Designated as safety issue: No ]
  The investigators will examine the relationship between the degree of Doppler color agitation (evaluated at the time the catheter is placed) and block success (i.e., the outcome in the primary analysis). Degree of agitation color will be defined as the percentage of nerve covered during the color agitation.
  
  

Traditionally for the lower extremity, peripheral nerve catheters have been threaded greater than or equal to 5 centimeters past the tip of the Tuohy needle. The major rational for this practice is to reduce dislodgement. However, the greater the distance that a catheter is advanced, the greater the risk of contacting undesired structures, kinking, looping and knotting. For the continuous popliteal nerve block, the catheter is threaded perpendicular to the course of the nerve. This could result in the tip of the catheter being a significant distance from the targeted nerve which may lead to a decrease in the success rate or efficacy of the block.

Greater efficacy may be seen if the needle is closer to its target. This may be quantified by documenting a faster onset of motor and sensory changes and/or a lower catheter infusion rate required to maintain pain control. The study will investigate the difference in success rate between popliteal peripheral nerve catheters placed at 1 centimeter compared to 5 centimeters past the tip of a Tuohy needle.