The Role of Intra-Operative Intracapsular Blocks in Post-Operative Pain Management Following Total Knee Arthroplasty

Research Summary

Purpose of Study This prospective, randomized, blinded controlled trial will be conducted to evaluate post-operative pain control and physical therapy outcomes in primary total knee arthroplasty (TKA) with the use of spinal analgesia and intra-operative posterior capsular injections of ropivicaine 0.5% in conjunction with a continuous femoral nerve catheter.

We believe the results of this study will show an improvement in pain control and physical therapy outcomes compared to traditional methods of analgesia in post-op total knee arthroplasty. To the best of our knowledge, there are no studies in the literature using this combination of femoral nerve analgesia and posterior capsular injection.

Certainly regional anesthesia methods such as femoral nerve blocks used alone or in conjunction with sciatic nerve blocks have improved patient pain outcome measures in total knee arthroplasty. Several studies have shown a beneficial effect of intra-articular analgesia after capsular closure. We believe our study design will combine the beneficial effects of the aforementioned methods, and ultimately improve patient pain, therapy effort, and safety through less narcotic use.

Our goal is to share these results in a peer-reviewed journal, and at national orthopaedic or anesthesia meetings. The data collected will ideally improve care and safety in the post-operative total knee arthroplasty patient.

Background and Significance Post-operative pain control in total knee arthroplasty is an area of great study in the orthopaedic surgery and anesthesia literature. The use of spinal/epidural alone or in combination with regional anesthesia is well studied in the recent literature. These techniques have significantly improved patient pain management, physical/occupational therapy outcomes, and shortened time to discharge.

Additionally, intra-articular injection of local anesthetic after capsular closure has been studied recently. Several studies have demonstrated a beneficial effect of intra-articular local anesthetic on pain outcome measures (6, 8, 9, 10, 15). Although other studies have reported more equivocal results. The impact of capsular analgesia has on post-operative pain is intriguing. Decreased afferent pain perception by the capsular nerves from local anesthetic may improve outcomes, especially in sensory distributions where regional anesthesia is inadequate or not performed.

Much study has centered on regional anesthesia, specifically the use of single shot or continuous femoral nerve blockade (4, 5, 11, 14, 16). Such studies have demonstrated a statistically significant decrease in total narcotic use, sedation scores, and visual analog pain scores. Femoral nerve blockade is now an accepted method of post-op pain control in the total knee arthroplasty patient.

Further investigation has centered on the addition of sciatic nerve blockade to femoral nerve block (1-3, 7, 12, 13). Several studies demonstrate a further improvement in pain outcomes compared to isolated femoral nerve anesthesia. Sciatic nerve blocks can slow physical therapy efforts secondary to a dense motor blockade. Equivocal results have been reported in other studies due to this motor block, however, the sensory component appears to provide improved pain outcome measures.

Femoral nerve blockade is a well-accepted modality for analgesia in total knee arthroplasty. However, femoral nerve block alone does not provide adequate anesthesia to the posterior aspect of the knee. We believe that intra-operative injection of ropivicaine 0.5% into the posterior capsule will provide analgesia analogous to the sensory component of a sciatic nerve block, while eliminating the limiting effects of the motor blockade. The combination of femoral nerve block and intra-operative posterior capsular injection will ideally yield improved pain management and physical therapy efforts above a baseline femoral nerve block.

Design and procedures This is a prospective double-blinded, randomized trial consisting of two study groups: posterior capsular saline injection (control), and the experimental posterior capsular ropivicaine 0.5% injection group. All patients will receive spinal anesthesia and a continuous femoral nerve block. Each group will include 45 patients (n = 90 patients).

All patients will have an elective primary total knee arthroplasty performed. No revision or bilateral cases will be included. Exclusion criteria will include patients with a known allergy to ropivicaine or fentanyl, a known history of narcotic abuse or chronic pain, a known diagnosis of peripheral neuropathy or complex regional pain syndrome, or a significant impediment to physical therapy participation.

Following the informed consent process, patients will receive a continuous femoral nerve block via catheter placed by experienced regional anesthesiologists at our institution. Each patient will also receive spinal anesthesia for intra-operative pain control. A standard midline skin incision with medial para-patellar arthrotomy will be performed followed by implantation of either a Next Gen (Zimmer/Warsaw, IN), or Natural Knee II (Zimmer, Warsaw, IN), or Posterior Femoral Component (PFC) Sigma (DePuy, Warsaw, IN) system. Prior to surgery, patients will be randomized to the saline or ropivicaine groups. Both groups will receive their respective injection prior to implantation of the components.

The posterior capsule of the knee will be divided in to four quadrants, each receiving a saline or ropivicaine injection per randomization. Safety measures will include standard pre-injection aspiration to check for vascular blush and intra-operative Doppler ultrasound to identify vascular structures in the posterior knee. Additionally, the anesthesiologist will not be blinded, as he/she will be responsible for assuring the appropriate medication is used, and will be closely monitoring for cardiac arrhythmias in the unlikely event that an intravascular injection occurs. Post-operatively, a standard bulky dressing will be applied. All patients will be weight bearing as tolerated post-operative day 1. A fentanyl PCA will be initiated in the PACU, and will be continued until post-operative day 2. Dosing will be calculated based on lean body mass. Continuous femoral nerve blockade will continue until post-operative day 2 as well.

Outcomes will include total PCA narcotic use, visual analog pain scale with a diagram to localize pain, and Ramsey sedation scores. This data will be collected at the following intervals: in the PACU, 4, 8, 12, and 24 hours post-operatively. We will also measure post-operative day 1 knee range of motion, total ambulation distance, and time to straight leg raise. A standard, Institutional Review Board (IRB) approved, data collection sheet will be utilized.

We hypothesize that total post-operative narcotic use, visual analog pain scores, and Ramsey sedation scores will be significantly lower in the study group (posterior capsular ropivicaine 0.5% injection). Additionally, we anticipate the knee range of motion, total ambulation distance, and time to straight leg raise to be significantly improved as well.