Total knee arthroplasty (TKA) is a common surgery . However, a significant number of patients undergoing TKA develop unacceptable long-term postoperative pain despite unremarkable work-up . Persistent postsurgical pain (PPP) is defined as the discomfort that lasts for >3-months post-surgery . It is estimated that 10-43% of TKA patients develop PPP [4,5], with the highest quality studies reporting an incidence of ~20% . The primary aim of this retrospective study was to estimate the percentage of TKA patients who develop PPP.
- Material and Methods
After IRB approval, demographics, diagnosis/procedure codes, length of hospital stay, and NRS scores were obtained from HSS Registry. When possible, the registry collects NRS scores preoperatively and at 3, 6, and 12-months postoperatively. Intraoperative/postoperative data were collected via chart review. Inclusion criteria were primary unilateral or simultaneous bilateral TKA between 1/3/2011-4/13/2015. Exclusion criteria were missing demographics and/or NRS scores. The primary outcome was defined as NRS > 4 at a minimum of 3-months post-surgery. The risk of PPP was calculated as a percentage with a 95% Wilson score confidence interval. Multivariable logistic regression was used to estimate the association of patient demographics, diagnoses, length of hospital stay, and preoperative NRS with the odds of developing PPP. Exploratory, simple logistic regression was used to estimate the association between intraoperative and postoperative data and the odds of developing PPP.
A total of 5981 patients met inclusion criteria and 1172 patients had a preoperative NRS available; 578 patients also had at least one NRS available at a minimum of 3-months postoperatively. Patients, with (n=578) and without (n=594) postoperative NRS, were mostly similar with respect to baseline NRS, demographics, and comorbidities. However, patients with follow-up NRS had better ASA status, were less likely to use tobacco, were more likely to have bilateral TKA, and had slightly longer length of hospital stay. The risk of PPP after TKA was 31.3% (95% CI: 27.5, 35.0).
Multivariable regression revealed associations of baseline NRS and race with the odds of developing PPP. Every 2-point increase in baseline NRS was associated with 1.66 (95% CI: 1.37, 2.03) times the odds of developing PPP (p < 0.001). African-Americans had 1.82 (95% CI: 1.03, 3.22) times the odds of developing PPP compared to Caucasians (p = 0.040).
Exploratory, simple logistic regression analysis on the subgroup of patients with NRS at all time points (n=74) suggested that adductor canal saphenous nerve blocks are associated with 2.87 (95% CI: 1.00, 8.26) times the odds of developing PPP compared to femoral blocks (p = 0.049). Tourniquet duration may not be associated with the odds of developing PPP.
Our estimate of the risk of PPP in primary TKA patients was higher than what is typically reported in the literature (31.3% vs. ~20%, respectively). This discrepancy is likely attributable to follow-up bias; it is possible that patients with PPP were more likely to return for a follow-up visit and report NRS scores than those without PPP. Therefore, our estimate of the risk of PPP must be interpreted with caution.
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