Continuous Infusion of a Local Anesthetic for Pain Relief Following Total Knee Arthroplasty Surgery

1Frank M. Ivey, MD, 1Robert E. Cox Jr., BS & 2Tatsuo Uchida, MS

1Division of Sports Medicine, Department of Orthopaedics and Rehabilitation, The University of Texas Medical Branch, Galveston, TX

2Division of Epidemiology and Biostatistics, The University of Texas Medical Branch, Galveston, TX

Background

The pain resulting from total knee arthroplasty surgery is often excruciating for patients. Adequate pain control improves satisfaction, alleviates anxiety, and hastens rehabilitation and discharge from the hospital. Locally administered pain medications may reduce the need for systemic narcotics that sedate the patient, depressing respiratory and cardiac function, which may complicate rehabilitation.

Though continuous infusion of a local anesthetic—bupivacaine (marcaine)—with a pain control infusion pump (PCIP) has been successfully used for pain relief after numerous surgical procedures, it has not been studied after total knee arthroplasty. The purpose of this study is to determine if this treatment method is effective in reducing post-operative pain following total knee arthroplasty.

Experimental Design and Methods

This is an ongoing randomized, prospective, double-blind study comparing the effects of intraarticular marcaine versus placebo (saline) on post-operative pain management. The study is approved by the Institutional Review Board of the authors’ institution. Three pain-assessment variables are analyzed for the 48-hour period after surgery: a pain visual analog scale (VAS), taken at 0, 12, 24, 36, and 48 hours; the amount of morphine administered by the patient controlled analgesia (PCA) pump, measured at 12, 24, 36, and 48 hours; and the number of attempts at morphine administration, measured at 12, 24, 36, and 48 hours.

Eligible patients are at least 18 years old, are not taking pre-operative narcotic pain medication, and are undergoing unilateral primary total knee arthroplasty. All patients are enrolled following thorough discussion of the study and after signing an informed consent.

Patients are recruited from the surgical schedule of the primary investigator at the University of Texas Medical Branch (UTMB). The prosthesis is posterior cruciate substituting, and all components are cemented. A midline incision with a median parapatellar approach is used. Navigation is not employed. At the end of surgery, with the patient still under general anesthesia, two plastic catheters are inserted percutaneously

into the knee joint for continuous infusion of a local anesthetic (0.5% marcaine) or saline. The catheters are attached to the PCIP unit. The patient’s pain is assessed using a pain visual analog scale at the 0 time point. After this, the PCIP is started with a bolus of 10cc and then reset to infuse continuously at 4cc per hour for 48 hours. A patient-controlled analgesia (PCA) pump is initiated at this time as well; this device, the standard of care for all total-knee-arthroplasty patients, records the amount of morphine administered per hour and the number of administration attempts per hour. Both indices are collected for 48 hours. The PCIP is removed and the study concluded after collection of the data from the 48-hour time point.

We hypothesize that patients in the experimental group will require less systemic pain medication administered through the PCA pump to achieve similar pain relief.

Results

The collected data in the study indicate the following: Twenty-eight patients were female (68.2%) and 13 were male (31.7%). Twenty-four patients were Caucasian (58.5%), nine were Hispanic (21.9%), and eight (19.5%) were African American. Patient ages ranged from 46 to 85 years with a median age of 66; average age was 65.8 years. The average age of patients receiving marcaine was 63.3 years, and the average for patients receiving placebo was 68.3 years.

A total of 21 patients received marcaine (51.2%) and 20 received the placebo (48.7%). VAS scores for pain reveal that, for both groups, measurements peak at hour 0 and then decline considerably (by at least two points) by hour 12; however, between hours 24, 36, and 48, for both groups, scores decrease slightly or remain steady, but do not exhibit the larger decrease seen between hours 0 and 12.

The number of attempts for morphine delivery between the groups showed its strongest difference at hour 12 (mean 43.9 attempts for the marcaine group and 61.1 for placebo group); however, after hour 12 there was little difference between the groups.

The amount of actual morphine delivered between the two groups was similar at all measuring points (range: 18.3-26.0 for marcaine and 19.7-29.7 for placebo).

Conclusion

These results suggest little difference between the use of the PCIP containing marcaine and the use of morphine only for the management of pain following total knee arthroplasty.