The ideal pain management for knee surgery should provide excellent analgesia while minimizing opioid consumption and allowing early mobilization and rehabilitation.

The use of the continuous technique in ACB allows the delivery of a larger quantity of local anaesthetic into the adductor canal than in the single-shot technique.

The usual approach for ultrasound-guided ACB catheter insertion is through short-axis in-plane approach in which the ultrasound transducer is applied horizontally over the femoral artery and saphenous nerve. In this approach, the catheter is inserted through a 90-degree angulation with the nerve which might make the catheter insertion difficult.

In the new oblique position, the catheter will be inserted in a less than 90-degree angulation. This study speculates that decreasing the angle of catheter insertion will make catheter insertion easier and faster.

Inclusion Criteria:

• adult patients more than 18 years
• ASA I-III
• scheduled for unilateral knee surgery under spinal anesthesia with an adductor canal perineural catheter planned for postoperative pain control

Exclusion Criteria:

• Patient who had an allergy to any drug used in the study
• Patients with neuropathy of any etiology in the affected extremity, hepatic or renal failure.
• pregnant females
• Patients who are unable to communicate with the investigators and hospital staff