Rebound pain after peripheral nerve blocks reduces the benefits of regional anesthesia and increases opioid consumption. This rebound pain most likely results from suboptimal pain management, as patients receiving a peripheral nerve block are typically not given scheduled opioid doses. Oral Patient Controlled Analgesia (PCA) consists of an oral morphine prescription that allows patients to self-administer doses based on their pain score.

This study will compare patients undergoing elective orthopaedic surgery under general anaesthesia or sedation with a peripheral nerve block, receiving oral morphine PCA either with or without additional scheduled oral morphine doses.

This study contains two parts, one for the upper limb and one for the lower limb. Each part will be published independently.

This registration concerns the lower limb cohort.

Patients from each cohort (upper limb and lower limb) will be randomized into two groups of 25 patients each, for a total enrollment plan of 50 patients per cohort. After written informed consent, patients will be allocated to one of the two groups according to a computer-generated randomization list.

In the control group, morphine will be administered exclusively on demand via oral PCA,based on pain intensity assessed using a numeric rating scale (VAS > 4). For oral PCA, one10 mg morphine tablet is placed on the patient's bedside table by the nursing staff. When the patients experience pain, they may take the tablet autonomously and subsequently inform the nurse, who then prepares and places a new tablet at bedside for the next potential pain episode. No scheduled or prophylactic opioid administration will be provided in this group. The maximal allowed dose through oral PCA will be 6 tablets (10mg each) per 24-hour period.

In the intervention group, morphine will be administered at predefined regular intervals, starting immediately in the postoperative period in addition to the availability of oral PCA morphine as mentioned above. Scheduled doses of 20mg slow-release oral morphine will be given at fixed 12 hour intervals. Patients will therefore receive regular morphine to ensure continuous baseline analgesia while still having access to an additional tablet via oral PCA in case of breakthrough pain, following the same nursing procedure as in the control group.

In both groups, standardized multimodal analgesia will be provided

The primary objective of this study is to assess and compare the highest pain score within the first 24 postoperative hours between the two groups using the Visual Analog Scale (VAS). The secondary objective is to assess the effect of the intervention on postoperative pain and analgesic outcomes, including morphine consumption, pain scores, need for additional nerve blocks, incidence of chronic pain, duration of analgesia, postoperative side effects, complications, and hospital length of stay.

Inclusion Criteria:

• Patients scheduled for elective orthopaedic surgery on the upper limb
• Patients scheduled for elective orthopaedic surgery on the lower limb.
• Score ASA I-III; Patients aged over 18 years; Signed informed consent.
• Surgery under general anaesthesia or under sedation

Exclusion Criteria:

• Refusal or inability to understand the informed consent
• Allergy to any of the following medications: ropivacaine, paracetamol, ibuprofen, ketorolac, morphine,sufentanil, ondansetron, or dexamethasone
• Patients with long term opioid treatment
• Bleeding diathesis
• Neurological disorders of the operated limb
• Known renal insufficiency (eGFR <30 mL/min)
• Known hepatic insufficiency (Child-Pugh class B or C);
• Pregnant or breastfeeding women;
• Alcohol dependence syndrome;
• Patients under spinal anaesthesia;
• Patients undergoing amputation procedures