The infrapatellar branch of the saphenous nerve: an anatomic study.

OBJECTIVES: To describe the course of the infrapatellar branch of saphenous nerve (IPBSN) and define a risk zone in which the nerve would probably be located.

DESIGN AND MATERIALS: The course of the IPBSN was studied in twenty-eight cadaver specimens (fifteen male and thirteen female) chosen haphazardly. SETTING AND MAIN OUTCOME MEASUREMENTS: The adductor tubercle and the junction between the inferior pole of the patella and the medial (point A) and lateral (point B) borders of the patellar tendon were taken as reference points. The level of the joint line as well as the point of crossing of the IPBSN at the joint line were measured in relation to point A.

RESULTS: The IPBSN was located at 7.7 +/- 16.8 mm posterior to the adductor tubercle at the level of point A; at 0.8 +/- 20.5 mm anterior to the adductor tubercle at the level of joint line; and at 12.1 +/- 18.8 mm anterior to the adductor tubercle at 30 degrees from point A. The IPBSN crossed to the lateral border of the patellar tendon in 10 of the 28 specimens (36%). The vertical distance between point B and the nerve was 37.8 +/- 23.5 mm. Three zones are defined in relation to point A: a safe zone, a gray zone, and a risk zone. The limits of the safe zone could be represented by a curved line that crosses the following points: 31.0 mm medial to point A and at the same level; 17.2 mm from point A at the joint line; 13.2 mm infromedial to point A at an angle of 30 degrees; 9.6 mm at an angle of 60 degrees; and 5.8 mm inferior to point A.

CONCLUSION: Avoiding the risk zone in which the nerve would probably be located and performing a blind puncture or an arthrotomy within the safety zone may decrease the incidence of IPBSN injury.