1. Background:
Arthrosis is a degenerative disease that damages the cartilage, bone and synovial membrane of the joint, and that is accompanied by pain and inability for physical activity. Total knee arthroplasty (TKA) is a surgical procedure that consists of replacing the injured or degenerated joint surfaces with an artificial joint (prosthesis). This surgery aims to eliminate pain, restore joint mobility and improve the quality of life of affected patients.
In Spain, more than 45 million ATRs are performed annually, with a prevalence of 33.7% in people older than 70 years1. This type of orthopedic and traumatological surgery has severe postoperative pain in 60% of patients and moderate in 30% 2.
The painful peak is between the 3rd and 6th postoperative hours, decreasing between 24 and 36 hours, becoming low intensity after the third day. It is a pain that increases with continuous passive mobilization during rehabilitation3.
An effective analgesic control not only guarantees the comfort of the patient, but allows an early ambulation and initiation of physiotherapy, thus accelerating recovery and reducing hospital stay, thus reducing the risk of postoperative complications such as thromboembolic disease or nosocomial infections4,5.
Years ago, the therapeutic plan of choice for postoperative pain in ATR consisted of the administration of opioid analgesics via parenteral, through bolus or PCA systems. However, the use of parenteral opioids is associated with the appearance of adverse effects such as nausea, vomiting, pruritus, gastrointestinal alterations and excessive sedation, which can negatively interfere with the comfort and well-being of the patient, delaying the start of rehabilitation. These undesirable effects have justified the use of locoregional techniques, which have developed a remarkable evolution in recent years and have provided a new alternative in the treatment of acute postoperative pain.
Each of the analgesic techniques used has characteristics and limitations that make them more suitable in one type of patient and not in others, so that the more techniques we know and use correctly, the greater the range of analgesic possibilities that we can offer to our patients. If we also take into account that patients undergoing this type of intervention are elderly patients and usually with associated comorbidities, we will understand the importance of choosing an optimal analgesic technique that offers good pain control with the benefits that this entails.
The current approach to postoperative pain in major knee surgery is based on a multimodal analgesia model, which consists of the association of different analgesic techniques that act at different levels of the pain pathways. The current recommendations are the association of acetaminophen / NSAID + regional technique (epidural or peripheral nerve blocks), relieving the use of opiates as rescue analgesia or in situations in which locoregional techniques are contraindicated, refused by the patient or not its realization was possible5. 
The current recommendations in clinical practice guidelines consider that postoperative pain is controlled when the patient has an EVA ≤3 at rest and an EVA value ≤4 during movement6.
The aim of our study was to compare the efficacy and safety of different analgesic regional techniques for the control of DAP such as femoral block (FB), femoral block combined with posterior sciatic block (FCB), and epidural block. (EB) after ATR surgery.

2. Material and methods
A prospective observational study was conducted in which 30 patients undergoing TKA from June 2016 to May 2017 were included. In all patients, the anesthetic technique used in the operating room was an intradural anesthesia with 0.5% hyperbaric bupivacaine between 11 and 13 mg + fentaline 10 -20 mcg.
After the surgical intervention and once the anesthetic motor block was recovered, the epidural infusion was started through the placed catheter or the peripheral nerve block was performed by neurostimulation and echoguiding. For this, 3 groups of patients were divided to compare the different postoperative analgesic techniques to be performed, such as the femoral block (FB), the femoral block combined with posterior sciatic block (FCB), and the epidural block (EB):
•	Group 1: Femoral block (FB) by means of a single puncture in the immediate postoperative period with Bupivacaine 0.375% 20 ml
•	Group 2: Femoral + sciatic block (FCB) by means of single punctures in the immediate postoperative period with Bupivacaine 0.375% 20 ml
•	Group 3: Epidural block (EB) with continuous infusion after surgery with 0.125% Levobupivacaine + 2 mcg / ml Fentanyl at a rate between 3 and 5 ml / h
Demographic data such as sex, age and weight were recorded, pain assessment was also recorded according to the EVA scale at 8, 12 and 24 postoperative hours, the need for rescue analgesia with opiates and the side effects of the technique was assessed. The common analgesic regimen consisted of dexketoprofen (50 mg / 12 h iv) and paracetamol (1 g / 6 h iv), during the first 72 h. If the pain assessment was equal to or greater than 3 on the visual analogue scale (VAS, from 0 to 10), morphine 0.05-0.1 mg / kg iv was administered.

3. Results:
3 groups of patients were divided. In the first (N1 = 10) a femoral block (BF) was performed, in the second (N2 = 10) a femoral + sciatic block (BFC) was performed, and in the third (N3 = 10) an epidural block (BE ) once the absence of motor block has been checked.
At 8 o'clock
• Group 1 (FB): EVA 1-3 was 89.8%, EVA 4-7 of 10.1% and EVA> 7 is 0.1%
• Group 2 (FCB): EVA was 1-3 in 91.6%, EVA 4-7 in 8.2% and EVA> 7 in 0.2%
• Group 3 (EB): EVA 1-3 was 72.6%, EVA 4-7 of 26.8% and EVA> 7 is 0.6%

At 12 o'clock:
• Group 1 (FB): EVA 1-3 was 87.3%, EVA 4-7 of 12.3% and EVA> 7 is 0.4%
• Group 2 (FCB): EVA was 1-3 in 88.1%, EVA 4-7 in 11.9% and EVA> 7 in 0%
• Group 3 (EB): EVA 1-3 was 62.3%, EVA 4-7 of 37.7% and EVA> 7 is 0%

At 24 hours:
• Group 1 (FB): EVA 1-3 was 86.8%, EVA 4-7 of 12.7% and EVA> 7 is 0.5%
• Group 2 (FCB): EVA was 1-3 in 87.9%, EVA 4-7 in 11.8% and EVA> 7 in 0.3%
• Group 3 (EB): EVA 1-3 was 68.5%, EVA 4-7 of 31.3% and EVA> 7 is 0.2%
The average morphine consumption in the postoperative period was significantly lower in the BFC group compared to the other two. In addition, the BE group presented a higher incidence of complications such as nausea, vomiting, pruritus or the appearance of acute urinary retentions.
4. Discussion:
The postoperative analgesia after total knee arthroplasty has been and continues to be a topic of continuous debate, questioning which is the technique of choice in most cases. There is still no consensus based on the evidence on the management of postoperative pain. The ideal analgesic technique in the postoperative period of total knee arthroplasty would be one that provides an important control of pain, with minimal side effects, with the least possible impact on motor function in order to facilitate early postoperative mobilization, optimal rehabilitation and get early hospital discharge or fast-track. The beneficial effect of regional anesthesia such as epidural analgesia and peripheral blocks against intravenous analgesia, in terms of quality of analgesia, consumption of morphine and related side effects, has been demonstrated. 
Until a few years ago, epidural analgesia was considered the gold standard or analgesic technique of reference with very good efficacy and acceptance. In fact, some studies suggest the superiority of epidural analgesia in the control of pain with respect to the continuous blockage of the femoral nerve. The drawback of this technique is the possible secondary effects derived from the sympathetic blockade that it produces, such as arterial hypotension, urine retention, with the possibility of sometimes requiring urinary catheterization that could even become a cause of postoperative morbidity and prolong by both the hospitalization, the less frequent but serious neurological complications, and those derived from the motor blockade that could hinder the patient's early mobilization. 
Peripheral nerve blocks are an equally effective alternative in terms of the quality of analgesia provided in the postoperative period with the advantage of producing fewer side effects. In our study, the association of a sciatic block to the femoral block is related to a lower painful intensity and lower opioid consumption in the postoperative period of TKA compared to the isolated femoral block, since this leaves the posterior part of the knee uncovered. In addition, these regional blockades, in turn, have fewer adverse events and are less severe than the epidural block group.
In view of these results, it is inevitable to consider the possibility of associating a sciatic block with BF to optimize the analgesia and obtain better results. 
There are several studies in the literature comparing the analgesic efficacy of single FB versus FB associated with sciatic nerve block. Santiveri et al.7, in 2009, conducted a non-randomized observational study with a sample of 1,550 patients divided into three groups based on the analgesic technique: single FB, FCB and EB.
This study showed that pain intensity was lower in the group of patients with FB associated with sciatic block with respect to the FB group. However, a more recent meta-analysis, carried out by Paul et al.8 in 2010, determined that the three techniques were equivalent in analgesic terms at 24h and 48h, both at rest and in movement, finding no statistically significant differences. Therefore, and despite the theoretical hypothesis, there is not enough scientific evidence to affirm that the association of FB to sciatic blockade provides greater analgesia compared to the other blocks compared. 
In addition, our study has certain limitations, highlighting the small number of samples analyzed. Therefore, new studies would be necessary to expand the sample size in order to generalize the hypotheses reached and be confirmed with a clinical trial.

02 / Comparison of femoral block (FB), femoral + sciatic block by posterior route (FCB) and epidural block (EB) in the control of acute postoperative pain after knee arthroplasty