DOI: 10.1097/AAP.0b013e31819a273e
,
,
PMID: 19282716
Issn Print: 1098-7339
Publication Date: 2009/03/01
Facebook
Twitter
LinkedIn
Email
 |
Checking for direct PDF access through Ovid | |
Excerpt
It is with great interest that we read the excellent letter to the editor by Drs. Krombach and Gray1 describing the use of ultrasound guidance for saphenous nerve block near the adductor canal. In their correspondence, they point out that "the saphenous nerve can often be imaged (as it pierces the vastoadductor membrane)…. In some subjects, a descending branch of the femoral artery can be identified with power Doppler adjacent to the saphenous nerve." They also recommend that "by use of an in-plane approach, 5 to 10 mL of local anesthetic can be placed adjacent to the saphenous nerve in the vastoadductor membrane deep to the sartorius muscle." Although we fully agree with their observations that the injection of a local anesthetic deep to the sartorius muscle results in reliable and successful block, in our experience, a practitioner with novice-level ultrasound-guidance skills sometimes finds it challenging to confidently identify, at this level, either the sartorius muscle or, more important, the small descending branch of the femoral artery (ie, saphenous branch of the descending genicular artery).
The saphenous nerve is the terminal branch of the femoral nerve. It leaves the femoral nerve proximally in the femoral triangle (Scarpa triangle), descends within the adductor canal, and courses beneath the sartorius muscle with the femoral artery (beginning lateral to the vessel at first and then crossing to the medial side superior to the artery just proximal of the lower end of the adductor magnus muscle). Further distally, the femoral artery departs away from the sartorius muscle, traveling deep to continue as the popliteal artery at the adductor hiatus. At this location, the saphenous nerve continues its course under the sartorius muscle, traveling adjacent to the saphenous branch of the descending genicular artery. In fact, such a transsartorial approach has been described as one of the most effective ways to block the saphenous nerve in a blind fashion.2,3 Based on the anatomic course of the saphenous nerve, we suggest that this nerve can also be blocked slightly more proximally in the thigh when using ultrasound guidance, where it is situated in close proximity to the femoral artery and deep to the sartorius muscle. This approach is very similar to that recommended by Drs. Krombach and Gray, yet uses the slightly more proximally located larger femoral artery as the main landmark, in addition to the clearly delineated sartorius muscle, rather than relying on an oftentimes homogeneous (in our opinion) muscle mass and smaller artery. At this transsartorial perifemoral level, the sartorius muscle can easily be identified as being a superficial roof to the relatively large landmark of the femoral artery before the artery travels deep and becomes the popliteal artery via the adductor hiatus (Fig. 1).
To perform a transsartorial perifemoral approach for a saphenous nerve block, one can use a high-frequency linear ultrasound transducer (eg, L38, MicroMaxx; SonoSite, Bothell, Wash) by placing the probe transversely to the longitudinal axis of the extremity at the midthigh, approximately 10 to 12 cm proximal and 3 to 4 cm medial to the midpoint of the patella. The femoral artery can be identified here with certainty by power Doppler; this in turn confirms the identity of the overlying sartorius muscle. The probe is then used to scan distally until it captures the point just before where the femoral artery becomes the popliteal artery. At this location, the saphenous nerve can be blocked by inserting the needle deep to the sartorius muscle and depositing local anesthetic medial to the artery (Fig. 2).
