Erratum to: Difficult Cases in Robotic Arm-Assisted Total Knee Arthroplasty: A Case Series - Marchand, Robert C.; Khlopas, Anton; Sodhi, Nipun; Condrey, Caitlin; Piuzzi, Nicolas S.; Patel, Rickesh; Delanois, Ronald E.; Mont, Michael A. (The Journal of Knee Surgery, 2018)