Popliteal Plexus Block for Total Knee Arthroplasty

The Effect of the Popliteal Plexus Block on Postoperative Pain After Total Knee Arthroplasty - a Randomized, Controlled, Double-blinded Study

Methodological problems/problems in the study design (competing pain and a placebo effect). No serious adverse events or other safety issues

This study aims to assess the analgesic effect of the popliteal plexus block as a supplement to a femoral triangle block in patients undergoing total knee arthroplasty

A femoral triangle block (FTB) effectively anesthetizes the anterior group of nerves innervating the knee (infrapatellar branch of the saphenous nerve, the medial femoral cutaneous nerve and the terminal branch of the medial vastus muscle nerve). However, the posterior group of nerves innervating the knee joint is not covered with an FTB, and therefore most patients complain of significant, opioid-requiring pain despite a successful FTB. The posterior group consists of the popliteal plexus, which is derived from the tibial nerve and the posterior branch of the obturator nerve. The popliteal plexus is located in the popliteal fossa, where it entwines the popliteal artery and vein. Recent cadaver studies have suggested that an injection into the distal part of the adductor canal will spread to the popliteal fossa (PubMed Identifier (ID): 28937534; PubMed ID: 27442773). This study aims to assess the analgesic effect of the popliteal plexus block (PPB) as a supplement to a femoral triangle block (FTB) after total knee arthroplasty (TKA). In the study all patients will receive an FTB with 10 ml bupivacaine-epinephrine (0.5%-1:200,000) with the addition of 0.5 ml Dexamethasone (4 mg/ml). All patients are postoperatively observed for the development of significant pain (NRS > 3) in the primary observation period (POP) defined as: a 3-hour observation period starting at the return of completely normal cutaneous sensation (lateral thigh and lateral side of the lower leg) after spinal anesthesia. If the patient reports pain (NRS > 3) in the POP, the patient will be randomized to the study treatment - a PPB with 10 ml bupivacaine-epinephrine or 10 ml saline.

Arthroplasty, Replacement, Knee, Anesthetics, Local, Pain, Postoperative, Nerve Block, Bupivacaine, Epinephrine

Success of the PPB is defined as the proportion of patients with significant postoperative pain (NRS > 3) after FTB, who drop in pain score to NRS ≤ 3 after PPB and maintain NRS ≤ 3 without any opioids until 60 minutes after PPB

The onset time is defined as the time from withdrawal of the block needle and until the patient reports NRS ≤ 3. The maximal onset time is defined as 60 minutes

The pain scores after PPB are evaluated every 5 minutes until 15 minutes after PPB and hereafter every 15 minutes until 60 minutes after PPB

Performed as a pinprick test on the lateral aspect of the lower leg. Sensation to pinprick is graded on a 3-point scale: 0 = no sensation, 1 = reduced sensation and 2 = normal sensation to pinprick compared to the contralateral side

The effect of PPB on isometric muscle strength of the he dorso- and plantar flexors of the ankle joint

Dorsal and plantar flexion of the foot is measured as the maximum voluntary isometric contraction (MVIC). During the test, a handheld dynamometer is kept immobile and the patient is asked to push against the dynamometer with maximal force and maintain this maximal pressure for 5 seconds. The MVIC is measured three times, separated by a 30-second pause, and the highest of the three MVIC values is registered

Subjects receiving PPB: From after PPB placement and up until 4 hours after PPB. Subjects not receiving PPB: From the end of the primary observation period (POP) and up until 4 hours after the end of the POP

Subjects receiving PPB: From 4 hours after PPB placement and up until 24 hours after PPB. Subjects not receiving PPB: From 4 hours after the end of the POP and up until 24 hours after the end of the POP

Pain scores (Numerical Rating Scale, NRS, 0-10 where 0 is "no pain" and 10 is "worst pain imaginable"

For subjects receiving a PPB, pain scores will be performed 2, 4 and 24 hours after PPB. For subjects not receiving a PPB, final pain scores will be made at the 24 hrs follow-up visit

Subjects with NRS > 3: when significant pain is reported during the POP; 15 and 60 min after PPB; at any increase in NRS score at any time during the 60 min after PPB; 2, 4 and 24 hrs after PPB. For subjects with NRS ≤ 3: at the 24 hrs follow-up visit

The number of patients experiencing NRS > 3 as a proportion of all patients with femoral triangle block (FTB)

All patients receive an FTB and are observed postoperatively for the development of NRS > 3 during the primary observation period (POP) defined as: A 3-hour observation period starting at the return of normal cutaneous sensation after spinal anesthesia

Inclusion Criteria: Male or female at least 50 years of age at screening Scheduled to undergo primary total knee arthroplasty in spinal anesthesia Normal sensory function at the lateral part of the thigh and lower leg American Society of Anesthesiologists (ASA) physical status 1, 2, or 3 Able to provide informed consent Exclusion Criteria: Unable to cooperate and follow the study protocol Communication problems Allergic towards any medical product administered in the study Diabetes requiring medical treatment Pregnancy (a pregnancy test will be conducted on all women of childbearing potential prior to inclusion in the study. A positive test result will result in exclusion from the study) Preoperative opioid treatment (dosed > once daily)

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