Effective pain therapy, especially for direct postoperative pain reduction, has a significant influence on patient satisfaction and the spectrum of complications after implantation of a knee arthroplasty (TKA). A proven and effective principle is to perform regional anesthesia using an isolated and combined femoral and/or sciatic nerve block (FNB or SNB) with or without a permanent catheter. As an alternative procedure we investigated the local intraarticular infiltration therapy (LIA) avoiding the known risks of regional procedures in this study with a modified drug mixture. At present, the most effective pain management continues to be the subject of controversy.
The results of this work reflect the efficiency of this pain management with a lower consumption of analgesics, identical to reduced postoperative pain ratings and an improved ROM in the first postoperative days.
Further recent works has demonstrated a possible equivalent pain management using the LIA method, whereby the individual composition of substances such as adrenaline or different cortisone preparations still varied. Since LIA affects only the surgical area with moderate analgesia, there is limited interference to muscle strength of the lower limb and safety in short time follow up. Besides a low infection rate the procedure can be done by surgical team, no special skills are required to administer an injection into the periarticular tissues. Because the quadriceps strength is not inhibited, there is no motor paralysis caused. This means that the legs can be moved voluntarily from the early period after surgery, reducing the deep vein thrombosis associated with venous stasis.
In our study we compared this 2 routinely used methods that are both effective for postoperative pain relief in TKA. The large number of procedures for each pain management performed at one hospital by one high volume surgeon (LIA = 102 vs. FNB = 102) is methodologically advantageous. Concerning the outcome parameter pain intensity, pain killer consumption and postoperative range of motion, a slightly superiority of the local infiltration method over the singular femoral catheter is shown. Up to 72 h after surgery there was a significant reduction of the NRS score in the morning recorded values from the 1st − 7th postoperative day with advantage to the patient group with regional nerve blocks. With regard to opiate consumption, there is an increased consumption of painkillers in the patient group with FNB compared to the LIA patient population. The functional outcome parameter range of motion (ROM) also shows significantly better results for the 1st to 7th postoperative day after surgery, although a rapid approximation of the movement amounts is seen.
The present publication even tends to show an apparent superiority, however, this can only be expressed with reservations in the case of existing limitations of the study. These include the retrospective, non-randomized study design with consecutive influence on outcome parameters such as pain anamnesis, opiate consumption and functional postoperative rehabilitation. The two patient groups (LIA) vs. (FNB) received different additive pain medications pre- and postoperatively, so that a direct comparison of drug consumption can only be carried out to a limited extent. Previous studies also showed a positive effect on pain reduction by addressing the posterior capsule with a combined procedure of FNB and SNB, which could lead to a renewed reduction of pain medication. For regional reasons, only FNB was used. The preoperative consumption of painkillers could no longer be determined retrospectively as an influencing factor on the later consumption. Missing outcome parameters such as length of hospital stay, side effects and patient’s satisfaction with pain control are not documented and not subsequently evaluated.
Despite two current meta-analyses, the heterogeneity of the various, existing study designs makes it difficult to accurately assess the effectiveness of the intraarticular infiltration method. The definition of the outcome parameters differs in object and observed time span. Both, the application of painkillers by catheter or single shot or in combination with additive regional procedures and the composition of the intra-articular pain medications are various.
In their meta-analysis, Zhang et al. evaluate the results of 10 publications (RCT) that compare the efficacy of LIA with peripheral nerve blocks, primarily FNB . The outcome parameters are based on VAS (or NRS), total morphine consumption, ROM as well as length of hospital stay. The comparative analysis of the data showed a similar reduction of VAS after 24 h, 48 h and 72 h postoperatively with reduction of morphine consumption and improved range of motion without increase of the complication spectrum. The VAS was the primary outcome parameter. Five studies including 231–535 patients reported VAS scores for postoperative day 1 to day 3 showed no significant difference between both groups.
Fan et al. already showed similar results in a further meta-analysis (8 RCT), whereby 4 included publications were included in both meta-analyses . Again, the heterogeneity of the studies as well as the factors influenced by bias such as emotions, threshold of pain and sociocultural background were evaluated as decisive influences on the VAS (NRS).
On the other hand, Fan et al, in its previous meta-analysis, could show that NRS values for pain on rest were lower in the LIA group than in the group of regional methods applied. As to the NRS score with activity there was no significant difference between the two groups.
Toftdahl et al. could not detect any significant difference directly postoperatively between LIA and FNB analgesic patients at rest until the 2nd postoperative day (pod), but a better pain reduction in the first 24 h postoperatively after LIA, if the patient was already been treated in physiotherapy . Carli et al., however, showed significantly lower VAS values at rest in the LIA group and could not detect any difference between the two groups during physiotherapy. Affas et al. postulated significantly better pain management at rest and in physiotherapy in the group of patients who received articular infiltration therapy . In a recent study by Kurosaka et al., the LIA group showed superiority within the first 24 hours without differentiation between rest and stress .
The outcome parameter of morphine consumption is influenced by the fact that different opiates have been applied pre- and postoperatively. A comparison of the publications was approximated by the conversion into equivalent doses. Zhang et al. showed no difference between the two groups, whereby no time scheduling is shown. In contrast, Fan et al. describes lower morphine consumption in the LIA group compared to the patient group of the regional procedures on the 1st postoperative day with a low heterogeneity factor in its pooled data. In most studies, including our own, there is reduced opiate demand in the first 24 hours     . In contrast, Carli et al. showed in a double - blinded, randomized, controlled study that the group of FNBs were associated with a significantly reduced postoperative consumption of morphine and a trend to better analgesia compared with periarticular infiltration. The fact that in this study the FNB was only used in combination with a sciatic nerve block served as an explanation.
The comparison of both treatment strategies on the basis of the outcome parameter of postoperative functionality is again made difficult by the decisive differential definition of an acceptable function. Zhang et al. evaluated the passive ROM in 4 studies in 308 patients. There was no significant difference between the FNB and LIA group with regard to the knee ROM. Fan et al., also with reference to a high heterogeneity factor, also could not detect any significant difference in the range of motion after 3 months postoperatively. However, the study indicates earlier mobility and shorter hospital stays in the group of LIA patients  .
Our data indicate that the 2 analgesic regimens gave similar quality of pain relief and time of functional recovery during the directly postoperative time. Both, FNB and LIA resulted in low average pain intensity. A femoral nerve block is commonly administered to reduce the side effects and complications related to self-administered analgesia in patients who have had a TKA. Nevertheless diminished muscle control, nerve damage and local infection are recognized complications, ranging from 0.1% to 2.5% and 15% of femoral nerve blocks are unsuccessful. LIA offers the benefits of blocking pain influx at its origin and maximizing muscle control.
Both procedures are methods of analgesia that have an excellent effect for pain management after TKA, but the types, doses and methods of administration of the agents used have yet to be established. Despite existing meta-analyses including high-quality studies (prospective, blinded design), the sample size of all included studies is very small. With 101 patients per treatment branch for pain management, our study confirms the efficacy of intra-articular infiltration therapy as an attractive alternative treatment method without the risks of regional procedures.