Value of IPACK block (interspace between the popliteal artery and the capsule of the posterior knee) with adductor canal block in total knee arthroplasty

INTRODUCTION

Acute postoperative pain after total knee arthroplasty (TKA) is so severe to the degree that necessitates proper analgesia which is one of the patients' human rights and prevents the drawbacks of pain on various body systems. Additionally, improper pain management leads to prolongation of hospital stay and rehabilitation period with the possibility of progression of acute pain to chronic one¹. About 60% of patients subjected to TKA had severe postoperative knee pain and about 30% of them experienced moderate pain. This high incidence of pain may push some patients to take the decision of not to be subjected to TKA^2,3.

Non-opioid analgesics alone are not enough to achieve the targeted pain relieve after this type of surgery and opioids alone, usually are not given in the optimal doses for fear of its side effects which include nausea,

 vomiting, respiratory depression and possibility of addiction³.

Multimodal analgesia is an ideal method for management of acute pain after TKA which may include preemptive analgesia, neuroaxial blockade, peripheral nerve block, and both narcotic and non-narcotic analgesics. One of the peripheral nerve blocks used for analgesia after TKA is adductor canal block (ACB) and this block may affect the vastus medialis muscle as its supplying nerve is one of the contents of the adductor canal. Another example of these nerve blocks is femoral nerve block (FNB) which may affect the motor function of quadriceps muscle^4,5. Also, both ACB and FNB may be associated with posterior knee pain that necessitates additional analgesics⁶. If sciatic nerve block is performed with femoral nerve block (FNB) for better analgesia, it may increase the risk of fall due to distal motor block⁷.

An interesting nerve block technique described by Sanjay K. Sinha, is an ultrasound-guided local anesthetic Infiltration between the Popliteal Artery and the Capsule of the Knee (IPACK) aiming at blockade of sciatic nerve terminal branches for analgesia after TKA without motor affection⁸.

The aim of this prospective study is to evaluate the efficiency of IPACK in combination with ACB in relieving postoperative pain after TKA, particularly posterior knee pain compared to ACB alone considering that this technique is relatively new and there are not much studies about evaluating this technique for this purpose.

The primary outcome measure was the visual analogue scale (VAS) for postoperative pain assessment. Secondary outcome measures included total morphine consumption during postoperative 48 hours, time to first rescue analgesia, and patient satisfaction.

PATIENTS AND METHODS

This prospec­tive double blinded randomized controlled study was conducted from September 2018 to March 2020 in Al-Azhar university hospitals. After obtaining the institutional approval and patients' informed consents, 60 patients enrolled in the study and randomly assigned by computer-generated random number tables to one of two equal groups: Group I (control group) received adductor canal block (ACB) while Group II (IPACK group) received ACB plus local anesthetic Infiltration between the Popliteal Artery and the Capsule of the Knee (IPACK block).

Patients involved in the study were ASA physical status I–III, 21-65 years old, and subjected to unilateral total knee arthroplasty (TKA). Exclusion criteria included patient refusal, neuromuscular disorders, allergy to local anesthetics, and contraindications to spinal anesthesia as coagulopathies and severe aortic stenosis.

Preoperative preparation had been performed for all patients including history, examinations, and investigations according to patient condition. In the preoperative holding area, a wide-pore IV cannula was inserted, and the patient was connected to standard monitors in the form of noninvasive arterial blood pressure, ECG, and pulse oximeter with measuring and recording of the baseline parameters. Ultrasound-guided ACB was performed for all patients in supine position under complete aseptic conditions. A high frequency (6-15MHz) linear probe of ultrasound machine (Sonosite Edge II) was positioned at the point midway between the anterior superior iliac spine and the upper pole of the patella. The adductor canal had been located as a hyperechoic structure beneath the sartorius muscle and after skin infiltration with 2ml of lidocaine 1%, a spinal needle 22G x 3.5 inches was advanced with the guidance of ultrasound in an in-plane technique and bupivacaine 0.5% 15ml was injected.

In Group II patients, IPACK block was performed after ACB while the patient was in supine position with slight knee flexion (figure 1). Under complete aseptic conditions, the probe was applied to the popliteal fossa for identification of popliteal artery and femur. Then, the probe was slid distally for revealing the two femoral condyles (figure 2) followed by proximal sliding of the probe until the humps of the femoral condyles disappeared and the flat metaphysis appeared. After skin infiltration with 2ml of 1% lidocaine, a spinal needle 22G x 3.5 inches was advanced from the lateral aspect and directed across the space between the popliteal artery and femur and once the needle reached the medial edge of the femur, nearly at the level of the popliteal artery, negative aspiration was confirmed and bupivacaine 0.5% 15ml was injected incrementally as the needle was withdrawn (figure 3).

Fig 1: (Photos A and B) Probe position for IPACK block and needle direction. (Note: Holding the probe and the needle, black dot for the puncture site).

Fig 2: Two femoral condyles and popliteal artery

Fig 3: (Photos A and B). (A) Needle position during IPACK, (B) Injection during needle withdrawal.

After ACB for Group I patients or ACB plus IPACK for Group II, the patient was shifted to the operating room with continuation of patient's monitoring. After infusion of 10ml/kg of lactated Ringer's solution within 15min, spinal anesthesia was given at the level of L3/4 while the patient was in the sitting position using a spinal needle 25G x 3.5 inches with injection of hyperbaric bupivacaine 0.5% 3ml under complete aseptic conditions. Intraoperative, heart rate, blood pressure, SpO₂, and respiratory rate were measured and recorded every 5 minutes. After surgery, the patient was observed in post anesthesia care unit and he was shifted to the ward.

Visual analogue scale (VAS) score was assessed at 2, 4, 8, 12, 16, 24, 32, 40 and 48hrs postoperative in the form of " horizontal line of 10-cm long with two ends one end was labelled as no pain 0 and the other end was labelled as worst pain 10". The patient was asked to put a mark at the point which described pain intensity the best. The length of the line to the patient’s mark is measured and recorded in centimeters. Total morphine consumption during postoperative 48hrs, time to first rescue analgesia, and patient satisfaction were recorded. Rescue analgesia in the form IV morphine 3mg was given if VAS ≥4. Perioperative complications were recorded and managed if occurred either opioid related as nausea and vomiting or related to the regional techniques used in the study as vascular injury and inadvertent intravascular injection of local anesthetic. Patient satisfaction with the analgesic regimen received was measured at the end of the assessment period using a scale from 0 to 10 where 0 meant extreme dissatisfaction while 10 meant extreme satisfaction. The patient was asked to circle 0 if no satisfaction and to circle any other number from 1 to 10 that best indicated the level of his satisfaction with pain management⁹.

Sample size calculation

Calculation of sample size was based on "MedCalc® version 12.3.0.0 program Ostend, Belgium"; statistical calculator based on 95% a confidence interval of 95% and power of the study 80% with α error 5%. According to a previous study done by Sankineani et al.¹⁰ showed that the Mean (SD) of VAS score at 8hr postoperative was decreased in patients received ACB plus IPACK (1.43 ± 0.64) compared with ACB alone (2.91 ± 0.64) with a p-value 

Statistical analysis

The analysis of data was performed by SPSS version 18 software package (SPSS Inc., Chicago, Ill., USA). Statistics were expressed in the form of mean ± standard deviation (SD), median with interquartile range (IQR-median) for non-parametric data, and quantitative data were expressed as frequencies and percentage. The results had been analyzed by t-test, Mann Whitney, and Fisher's exact test. P-value was considered significant if ≤0.05, nonsignificant if >0.05 is nonsignificant, and highly significant if <0.001.

RESULTS

As regards demographic data (age, sex, BMI, ASA, and duration of surgery), there were no statistically significant differences between the two groups (Table 1).

As regard to VAS, there were nonsignificant differences between both groups in the first 4 hours postoperative while at 8hr postoperative and up to 48hr postoperative, there were significant differences between both groups with less VAS scores in Group II (table 2).

Concerning total morphine consumption, it was less in Group II and the difference between both groups was statistically highly significant.Time to first rescue analgesia was shorter in Group I and the difference was highly significant. Patient satisfaction 48hr postoperative was higher in Group II than in Group I and the difference between both groups was highly significant (table 3).

No significant side effects related to opioid use had been recorded and no complications related to regional techniques used in this study. 

Table 1: Comparison between group I and group II according to demographic data (p-value >0.05 is nonsignificant).

Table 2: Comparison between groups as regards postoperative VAS score. Data are expressed as Median (Inter Quartile Range).

Table 3: Total morphine consumption, time to first rescue analgesia, and patient satisfaction. (p-value