Hallux surgery is known to be extremely painful. Standard pain therapy is treatment with NSAID and opioid painkillers. Patients are frequently not-satisfied with this. Some institutions use a nerve block (single shot or catheter technic) of the ischiadic nerve. But this procedure is invasive, has a potential risk of nerve lesion, and is not accepted by all surgeons. A single shot nerve block of the posterior tibial nerve is less invasive and could be superior compared to standard pain treatment. A great variability of nerve supply of the foot is well described. There are some hints that the posterior tibial nerve supplies the first metatarsal bone and the first metatarsal joint. A nerve block could reduce postoperative pain in hallux surgery. To assess the effectiveness of this investigated measure, the requested morphine dose of a PCA pump will be used to verify the effectiveness of the tibial nerve block.

The overall purpose is to evaluate the effectiveness of tibial nerve block for postoperative pain relief after hallux surgery. The primary objective is to assess the morphine requirement in the first 24 hours after surgery. Secondary objectives are maximum pain scores and sleeping quality in the postoperative period. Patient's satisfaction with the pain therapy and approximately nerve block duration will be asked in the final interview.

Primary study endpoint is a 50% reduction of morphine requirement with a 60% standard deviation within 24 hours after surgery. Power is 80%, the level of significance is set at 5% (p < 0,05).

Secondary endpoints are sleeping quality and maximum pain scores (maximum VAS) measured by means of postoperative questionnaire.

Inclusion Criteria:

• Age over 18 years
• Elective Hallux valgus surgery ("Magerl" operation technique)

Exclusion Criteria:

• Patient refusal, pregnancy
• Regular medication with opioids
• Drug abuse
• Contraindication for regional anesthesia
• Known allergy against one of the study drugs
• Polyneuropathia, or any other neurodegenerative disorders