An Exact Localization of Adductor Canal and Its Clinical Significance: A Cadaveric Study.

BACKGROUND AND OBJECTIVES: Adductor canal block is a regional anesthetic block procedure commonly employed for knee surgeries. This study aims at locating the adductor canal precisely which will be of great use for the surgeons operating on knee.
MATERIALS AND METHODS: Forty cadaveric lower limbs fixed with formalin were utilized for the study. The length of the lower limb from anterior superior iliac spine to the base of patella is measured, and the midpoint between the two is marked. Adductor canal is dissected and the distance between proximal foramen and the midpoint of thigh, the length of the adductor canal, and the distance between the distal foramen and the base of the patella are measured.
RESULTS: The mean value of the adductor canal is about 10.5 cm. The average distance from anterior superior iliac spine to proximal foramen is 25 cm. The average distance from base of patella to distal foramen is 8.5 cm. In 36 (90%) lower limbs, the proximal foramen is 3 cm distal to the midpoint of the thigh. INTERPRETATION AND
CONCLUSION: This study suggests that a point more than 3 cm below the midpoint of thigh will be the ideal location for the approach of adductor canal block.

INTRODUCTION

Adductor canal block is an effective and commonly performed peripheral nerve block for knee[1] and foot[2] surgeries. Van der Wal et al.[3] first described the adductor canal block using surface landmarks, whereas Manickam et al.[4] performed the adductor canal block for knee surgeries under ultrasound guidance. It is also commonly utilized for postoperative pain analgesia following total knee arthroplasty.[5] Adductor canal block provides excellent pain control and shortens the time of stay in hospital. It preserves quadriceps muscle strength,[6] improved mobility,[7] and reduced risk of fall[8] following total knee arthroplasty.

Adductor canal is also called as Hunter's canal. It is a conical musculoaponeurotic tunnel located in the mid-thigh extending from the apex of femoral triangle (Scarpa's triangle) to the hiatus magnus which is the opening in the adductor magnus.[9] It is triangular in cross-section being bounded anteriorly by medial vastus proximoposteriorly by adductor longus and distoposteriorly by adductor magnus and bridged medially by vaso adductor membrane.[10] Medially, the adductor canal is overlapped by the sartorius muscle and so also called subsartorial canal [Figure 1]. The femoral vein and the femoral artery with its descending genicular and saphenous branches are the vascular content passes beyond the adductor hiatus on their way to the popliteal fossa to continue as popliteal vessels.[11] Nerve to vastus medialis which is motor to medial vastus and also sensory to anterior and medial aspect of knee and saphenous nerve which is a purely sensory nerve are the two important nerves in the adductor canal. While ultrasound-guided location of adductor canal has been studied extensively, cadaveric study of adductor canal is reported minimally in the literature, and hence, this study has been taken to focus on exact localization of adductor canal.

Figure 1

Adductor canal overlapped by Sartorius medially

MATERIALS AND METHODS

A cadaveric study was performed at the Department of Anatomy, Sri Ramachandra Medical College, Sri Ramachandra Institute of Higher Education and Research, Porur, Chennai. The study materials include 40 (30 males and 10 females) formalin-fixed cadaveric lower limbs. The length of the thigh is measured between two points, one at the anterior superior iliac spine and other at the base of the patella. The midpoint between the two is marked [Figure 2]. The front of the thigh is dissected, and boundaries of femoral triangle formed laterally by medial border of sartorius muscle and medially by medial border of adductor longus and the inguinal ligament forming the base are identified. The apex of the femoral triangle formed by the meeting point of medial and lateral boundary is considered as the proximal foramen of adductor canal, and the aponeurotic opening in the adductor magnus is the distal foramen in the posterior aspect of the thigh [Figure 3]. The distance between the proximal and distal foramina gives the length of the adductor canal [Figure 4]. The distance between anterior superior iliac spine and the proximal foramen, the distance between base of patella and the distal foramen, and the distance between the proximal foramen and the midpoint of the thigh are measured.

Figure 2

Midpoint between the anterior superior iliac spine and the base of the patella

Figure 3

Diagrammatic representation of femoral triangle boundaries

Figure 4

Length of the adductor canal

RESULTS

The average length of the thigh is about 44.2 cm in males and 42 cm in females. The average length of the adductor canal is about 10.5 cm in males and 8.5 cm in females. In 36 (90%) lower limbs, the proximal foramen is caudal to the mid-thigh. In four lower limbs (10%) the proximal foramen in cephalad to the mid-thigh. The average distance of anterior superior iliac spine to the proximal foramen is 25 cm in men and 24 cm in women. The average distance of distal foramen to the base of the patella is about 9 cm in males and 9.5 cm in females.

DISCUSSION

In the present study, the average value of the length of the thigh from anterior superior iliac spine and the base of the patella is about 44.2 cm and 42 cm in males and females, respectively, and the midpoint of thigh is about 22.1 cm and 21 cm from anterior superior iliac spine. Wong et al.[12] with the guidance of ultrasound measured the length of the thigh from anterior superior iliac spine to the base of the patella as 45.7 cm. In our study, we found that the proximal foramen of the adductor canal is at a distance of about 25 cm and 24 cm from the anterior superior iliac spine in males and females, respectively. Wong et al.[12] in their ultrasound study of adductor canal found the proximal foramen at a distance of 27.4 cm from anterior superior iliac spine. Tubbs et al.[10] in their cadaveric study found the proximal foramen of adductor canal at a distance of 28 cm from the anterior superior iliac spine.

The average length of the adductor canal in the present study is about 10.5 cm and 8.5 cm in males and females, respectively. The average length of the adductor canal according to Wong et al. is about 11.5 cm. In 90% of specimens, we found that the proximal foramen is caudal to the midpoint of the thigh at a mean distance of 4.5 cm (range: 3–10 cm). Anagnostopoulou et al.,[13] in their cadaveric study described that in 23% the proximal foramen was cranial to the midpoint of the thigh and in the remaining 77% of cadavers, it is caudal to the midpoint at a mean distance of 6.5 cm (range: 1.8–10.0 cm). Ultrasonographically, the proximal foramen is found to be at a mean distance of about 4.6 cm (range: 2.3–7.0 cm) according to Wong et al. In this study, we found that the distance between the distal foramen and the base of the patella is about 9 cm and 9.5 cm in males and females, respectively.

CONCLUSION

The present study confirms with the previous cadaveric and radiological studies that the proximal foramen of adductor canal is consistently well below the midpoint of the thigh. The present study suggests that a distance of about 3 cm below the midpoint of the thigh will be the ideal site for adductor canal block.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.