The association between component malalignment and post-operative pain following navigation-assisted total knee arthroplasty: results of a cohort/nested case-control study. 
Previous studies have noted an adverse relationship between implant malalignment during total knee arthroplasty (TKA) and post-operative pain.  Although some evidence exists indicating that computer-assisted surgical navigation for TKA can improve the accuracy of component alignment, its impact on clinical outcomes is currently unknown.  The dual goals of the present cohort/nested case-control study were to (1) compare self-reported responses to the Western Ontario-McMaster Osteoarthritis Index (WOMAC) questionnaire between computer-assisted TKA (123 patients) using the imageless PiGalileo navigation system and conventional TKA (207 patients) [cohort analysis], and (2) to investigate a potential association between malalignment and post-operative pain in 19 painful knees and 19 asymptomatic knees obtained from the cohort analysis using matched sampling [nested case-control study].  In the cohort analysis, a relevant but non-significant (P = 0.06) difference in the occurrence of chronic pain was observed between the navigated (12%) and conventional arms (20%).  Median post-operative WOMAC pain score was 100 (range, 50-100) in the conventional group and 100 (range, 65-100) in the navigated group.  However, the Mann-Whitney test revealed a significant difference in favor of the navigated group (P = 0.01).  In the nested case-control analysis, radiological outcomes and computer tomography (CT) measurements of femoral rotation were compared between the groups.  The CT rotation measurements yielded evidence of a relationship between post-operative pain and incorrect rotational alignment of the femoral component of more than 3 degrees (OR: 7; 95% CI: 1.2-42; P = .033).  In conclusion, there was no clinical benefit to computer-assisted navigation; however, a statistically significant relationship was observed between incorrect rotational alignment of the femoral component and symptoms of post-operative pain following TKA.