Background: Severe postoperative pain following total knee arthroplasty [TKA] may cause patients agony and persistent
postsurgical pain [PPSP]. Periarticular injection [PAT] and femoral nerve block [FNB] are widely accepted as effective options for reducing postoperative pain and morphine consumption. Preemptive analgesia theoretically can has the ability to prevent sensitization of the nervous system and
consequent amplification of postoperative pain.

Objective: To explore whether the preemptive femoral nerve block [FNB] can provide additional pain relief for periarticular injection [PAT] after primary TKA.

Materials and Methods: The records of 112 patients, 53 who had received spinal anesthesia with periarticular injection (PAT group) and 59 who had received spinal anesthesia combined with preemptive femoral nerve block [FNB] and PAT (FNB + PAT group) were retrospective analyzed. All the data had been routinely recorded in a sequential fashion at our institution.

Results: Morphine consumption by the FNB + PAT group during the first 24 and 48 hours post operation were 7.13 and
11.61 mg, respectively, significantly lower than the 14.11 and 20.43 mg consumed by the PAT group (p = 0.001, and p = 0.01, respectively). The FNB + PAT group had lower pain scores in the first 24 hours, although that difference was not statistically significant. Tn terms of knee rehabilitation, the degrees of straight leg raise [SLR] in the FNB + PAT group was significantly higher in the first 24 hours, while, the degrees of knee flexion and extension lag [EL] were comparable between
the two groups.

Conclusion: Preemptive femoral nerve block [FNB] can reduce morphine consumption in the first 48 hours after total knee arthroplasty. Tn addition, the FNB tends to reduce the pain score and to facilitate knee rehabilitation on the first day after the index surgery.

Keywords: Total knee arthroplasty, Femoral nerve block, Periarticular injection, Preemptive analgesia