The blockade of the femoral nerve (FNB) is the most common postoperative pain therapy after total knee replacement. Because of motor-driven weakness of the quadriceps muscle induced by femoral nerve block mobilization of Patients is difficult even dangerous (falls) and hospital stays are extended.

An alternative method could be an adductor canal block (ACB). Anatomical studies of the adductor canal demonstrated that the adductor canal contains the saphenous nerve, a pure sensory nerve for medial and anterior aspects of the knee and the tibia without any motor function.

This prospective, double-blinded, randomized study investigates the effect of FNB and ACB on quadriceps motor weakness and analgesia determined by Numeric Rating Scale (NRS).

We expect the ACB to be superior in muscle strength but equal in pain score. Both groups receive an additional anterior sciatic nerve block for complete sensory block of the operated knee

Inclusion Criteria:

• patients with knee replacement therapy and general anaesthesia
• informed consent
• preoperative "timed up and go" test performable

Exclusion Criteria:

• emergency patients
• BMI > 40 kg/m2
• American Society of Anaesthesiologists physical status (ASA) 4-5
• severe chronic obstructive pulmonary disease (COPD)
• rheumatic arthritis, diabetic Polyneuropathy, M. Parkinson
• nerve injury of lumbosacral plexus
• coagulopathy with bleeding tendency
• not capable of speaking or understanding german or english