Update in Pediatric Regional Anesthesia

Regional Anesthesia for Pediatric Knee Surgery

By Loren Babirak, MD; Elizabeth O’Brien, MD; Wallis Muhly, MD
Department of Anesthesiology and Critical Care
The Children’s Hospital of Philadelphia
Perelman School of Medicine
University of Pennsylvania,
Philadelphia, Pennsylvania

Knee pain and injury are responsible for nearly one-fourth of musculoskeletal complaints across all age groups.1 While knee issues are less frequent in young children, the incidence increases in adolescents and young adults who can present with a variety of congenital, developmentally acquired, and traumatic etiologies. Congenital lesions, such as patellofemoral dysfunction as seen in healthy patients and patients with cerebral palsy, or flexion/extension contractures associated with  arthrogryposis and pterygium syndrome, are often surgically treated in late childhood, prior to epiphyseal plate closure.1-4 Many of these patients have multi-level joint involvement and may be facing corrective procedures at the hip and ankle, in addition to the knee. Surgical repairs can include tendon lengthening, ligament transfers, and distal femoral extension osteotomies. Patients with congenital knee deformities may be at higher risk of needing subsequent procedures and postoperative pain management may be challenging.5 Acquired or traumatic knee injuries, such as anterior cruciate ligament (ACL) tears, tibial eminence fractures, and meniscal tears are becoming more common as sports participation increases nationally.7 These injuries, especially ACL tear, should be surgically managed in a timely manner even in skeletally immature patients, as delaying surgical fixation has been shown to lead to chronic joint instability, premature osteoarthritis and decreased functional status.8 Further, these procedures are more commonly being performed in an outpatient setting, making adequate pain control a priority.9 Regional anesthesia, either in the form of a single-injection peripheral nerve block (PNB) or continuous peripheral nerve block (CPNB) with an indwelling catheter, is an attractive adjunct for perioperative multimodal analgesia, and should be considered for this vulnerable patient population.5,6

An understanding of knee innervation is key to safely performing an effective regional anesthetic for surgery.10-12,15 Regional analgesia for knee surgery involves blocking the femoral and sciatic nerves or their corresponding terminal branches.8-10,13,15  The innervation of the knee originates from the lumbosacral plexus, which is formed from the ventral rami of all five lumbar nerves and the first, second, and third sacral nerves. The plexus is located between the anterior and posterior masses of the psoas major muscle in line with the intervertebral foramina. The branches of the lumbar plexus include iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral and obturator nerves while the sacral plexus gives rise to the sciatic nerve. The femoral nerve innervates the dermatomes over the anterior thigh and knee as well as the femur. The nerve runs between the psoas major and the iliacus muscle deep to the fascia iliaca at the level of the inguinal ligament. At the level of the inguinal ligament, the femoral nerve is typically located lateral to the femoral artery. It then divides into anterior and posterior divisions before branching as it descends the thigh.10 Two of its terminal branches, the saphenous nerve and nerve to the vastus medialis, provide sensory innervation to the anteromedial knee.11 The obturator nerve provides sensory and motor innervation of the thigh, and it may contribute sensory articular branches to the knee. It is formed by the anterior divisions of the second, third, and fourth lumbar nerves in the psoas major muscle. While the femoral nerve emerges lateral to psoas major, the obturator emerges medial to it. At the level of the inguinal ligament, the obturator nerve is separated from the femoral nerve by several fascial compartments. The lateral femoral cutaneous (LFC) nerve provides sensory innervation to the skin of the lateral aspects of the thigh and knee. It is formed by ventral rami of the second and third lumbar nerves. The LFC nerve penetrates the inguinal ligament about one centimeter from the anterior superior iliac spine and proceeds down the thigh.10 The ventral rami of fourth and fifth lumbar nerves and the first, second, and third sacral nerves form the sciatic nerve. The sciatic nerve innervates the posterior thigh and knee. The sciatic nerve exits the pelvis through the greater sciatic notch, lateral and posterior to the lesser trochanter of the femur on the posterior aspect of the adductor magnus and deep to the biceps femoris muscle. The sciatic nerve divides into the tibial nerve and common peroneal nerve near the popliteal fossa.10,16 Variations in the nerve anatomy of the knee during pediatric development have been demonstrated by computed topographic studies, which may have implications in regional blockade.16

Strategies and Outcomes
Femoral Approach to Regional Anesthesia
PNB for knee surgery in pediatric patients has been shown to be safe and effective.13-15 In a 2014 retrospective review of 376 children aged 7-18 years old undergoing arthroscopic knee surgery, investigators compared patients managed with a single-injection femoral PNB and patients managed with intraarticular local anesthetic injection placed by the surgeon. They found that patients managed with a femoral PNB had lower postoperative pain scores, decreased postoperative opioid requirements, and a lower rate of hospital admission in a subset of patients presenting with ACL reconstruction.13 Similarly, a 2018 single-center prospective observational study reported outcomes for 47 children aged 13-18 years who received a single-injection femoral PNB with or without a single-injection sciatic PNB for ACL reconstruction or meniscus repair only. Both surgical populations reported low median pain scores with no readmissions or pain related complications up to 72 hours after surgery.14

In children, single-injection blocks are more commonly utilized compared to continuous catheter techniques.17 However, CPNB with indwelling catheters allow for provision of pain control for procedures that require analgesia for longer than 12-24
hours.6,9,17  Femoral CPNB with an indwelling catheter has been shown to provide effective postoperative analgesia following pediatric knee surgery.6,17,18 Femoral CPNB with indwelling catheter can be more technically challenging to place, and has secondary failure rates as high as 10-15%.19, 20 One strategy proposed to mitigate this failure rate is the use of stimulating catheters that allow for continued stimulation during catheter placement to ensure adequate perineural position, as opposed to a blind catheter insertion after successful needle placement. This strategy has been studied in numerous prospective, retrospective, and randomized-control trials with consistent results showing similar rates of efficacy demonstrated by visual analog scores and morphine-equivalent consumption in both catheter types, without clear benefit of stimulating catheters over non-stimulating varieties.20-25 To date, there have not been robust studies in the pediatric population comparing stimulating to non-stimulating catheters, but it is likely that with the rise in ultrasound proficiency which allows for visual confirmation of local anesthetic deposition and catheter placement, the difference in success is less dependent on catheter type.

Motor Function Concerns
In addition to providing analgesia, PNB can lead to impaired motor function postoperatively. Specific to knee surgery, blockade of the femoral nerve leads to quadricep weakness, which may necessitate passive physiotherapy in the early recovery period.14 This may not be acceptable if the surgeon prioritizes early active physiotherapy with early ambulation.  Additionally, there have been reports suggesting that the presence and type of perioperative femoral blockade (PNB or CPNB) may have lasting impacts on patient recovery.25-29 In a retrospective chart review, investigators reported that adolescents undergoing  ACL reconstruction who received a femoral PNB had significantly diminished isokinetic strength and were four-times less likely to return to sport activities at six months when compared to patients managed without PNB.27  In another retrospective study, investigators compared single-injection femoral PNB to CPNB in pediatric patients undergoing ACL reconstruction.  The authors found that patients managed with femoral CPNB had more asymmetric limb weakness at six months compared to the single-injection group.29

Alternative Techniques for Knee Analgesia
Given the concerns about the impact of femoral PNB on quadricep strength and functional recovery, some have advocated for regional approaches that minimize perioperative motor weakness.30 The adductor canal block (ACB) has emerged as an alternative to the femoral nerve block for knee surgeries including ACL reconstructions.30-35 The ACB is performed in the mid-thigh and targets a purely sensory branch of the femoral nerve branch, the saphenous nerve, and well as a branch of the obturator nerve, the nerve of the vastus medialis.32 The ACB has been shown to improve pain at rest and reduce opioid consumption for up to 24 hours postoperatively in adults undergoing ambulatory ACL reconstruction.31-33 Additionally, the ACB has been shown to be non-inferior to the femoral PNB following ACL reconstruction with respect to pain scorers at rest, intraoperative opioid requirements, and time to first analgesic request postoperatively in adults.32 However, there is controversy about the degree to which the ACB preserves quadriceps strength. Some studies report quadricep strength preservation with ACB compared to femoral PNB in ACL reconstruction in adults.32,33 Yet, other studies have demonstrated no statistical difference in quadricep strength between adult patients with ACB versus femoral PNB in the immediate postoperative period up and to six months post-surgery.31,34 Further investigation of quadricep preservation with ACB versus femoral PNB in pediatric patients undergoing ACL reconstruction is needed. 

Another emerging approach for regional analgesia for knee surgery involves infiltration of local anesthetic between the popliteal artery and the capsule of the posterior knee or “IPACK” block. The IPACK block provides motor-sparing analgesia to the posterior portion of the knee, and includes coverage of the articular branches of the obturator, tibial, and common peroneal nerves.36-38 Utilizing ultrasound guidance, the block targets the space between the popliteal artery and the femoral condyle and is commonly placed from the medial aspect of the knee with the patient in a supine position.36-39 The IPACK block has been used as an alternative to the sciatic nerve block, in combination with the femoral nerve block or adductor canal block, as an effective adjunct in total knee arthroplasty (TKA) and in ACL reconstruction.38-40 A recent case series showed positive results of the IPACK block to augment femoral CPNB in adolescents, suggesting this may be a useful technique for pediatric patients, though more data is needed to confirm this definitively.39

PNB is a valuable component of a multimodal analgesic regimen and it has been shown to be a safe and effective strategy for children. Knowledge of the regional anesthesia techniques for knee surgery is relevant to the anesthesiologist routinely involved in the care of children given the growing incidence of knee injuries related to sports activities7-9 as well as the move toward outpatient surgery for knee arthroscopy in children.9 More pediatric clinical trials are needed to better understand the value of CPNB techniques compared to single-injection PNB and the importance of motor-sparing regional techniques on acute recovery and return of functional status.


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