How Do Demographic, Surgical, Patient, and Cultural Factors Affect Pain Control After Unicompartmental Knee Arthroplasty? A Multivariable Regression Analysis.

Background: Controlling pain after unicompartmental knee arthroplasty (UKA) is essential for improving patient satisfaction, minimizing complications, and early rehabilitation. There is little literature available evaluating the effect of both treatment and patient characteristics on in-hospital pain after UKA. The purpose of this study was to examine the effect of patient and treatment characteristics on in-hospital pain after UKA. This study also evaluated the role of analgesic cocktail (traditional periarticular injection cocktail "[PAI]" vs cocktail including liposomal bupivacaine "[LBUP]").

Methods: The study sample included 442 consecutive UKA cases performed between December 2011 and August 2013. The primary outcome measures were the average Visual Analog Scale pain score and the percent of pain scores during hospitalization that were 0, that is, "no pain." Multivariable regression analyses were implemented to investigate associations between patient demographics and analgesic group with the outcomes. For the analgesic groups, the "PAI" group received injections of a cocktail including Marcaine, ketorolac, and morphine, the "LBUP" group received injections of LBUP.

Results: Postoperative pain was higher in females (P < .001) and younger patients (P = .002). The patient group treated with LBUP injection technique had similar overall average Visual Analog Scale pain scores to patients in the PAI group (P = .729); however, there was also a significant improvement in pain scores over time (as the study progressed) for patients in the LBUP group relative to the PAI group (P = .003), potentially indicating better outcomes with more experience with the injection technique. When compared individually by day, the LBUP group had lower pain scores from day 1 to 3 (P < .024).

Conclusion: The results showed that in patients undergoing UKA, postoperative pain was lower in males, older patients, patients with lower body mass index, and those treated with LBUP over the study period. Understanding these associations is necessary to effectively manage pain and encourage earlier ambulation and physiotherapy after UKA.