Bone Ninja application is reliable alternative to PACS in measuring preoperative and postoperative alignment parameters of total knee arthroplasty.

A picture archiving and communication system (PACS) is a means wherein the images are acquired, displayed, transmitted, and stored digitally. Bone Ninja is an application on iPad (Apple Inc.) on the IOS platform, developed as a teaching tool for deformity corrections around the knee. The principal objective of this study is to determine the reliability and consistency of Bone Ninja application in measuring the preoperative and postoperative alignment in patients undergoing a total knee arthroplasty and compare it with the PACS. This retrospective cross-sectional study was done using preoperative and postoperative leg-length radiographs of 50 consecutive patients (50 knees) who underwent unilateral total knee arthroplasty. Using Bone Ninja application and PACS, preoperative Lateral Distal Femoral Angle (LDFA), Tibiofemoral Angle (TFA), Medial Proximal Tibial Angle (MPTA) and postoperative Tibial alignment angle (TAA), Tibiofemoral angle (TFA), Femoral alignment angle (FAA) were measured independently by three doctors (two orthopedists and one radiologist). The measurements were repeated after an interval to determine intra and interobserver reliability. Both preoperative (TFA, LDFA, MPTA) and postoperative measurements (TFA, TAA, FAA) showed highly correlated intraobserver and interobserver correlation coefficients. Cohen kappa values for all the measurements were greater than 0.80 but the values were higher for PACS compared to Bone Ninja application. PACS remains the gold standard, but bone ninja application is a reliable alternative for preoperative and postoperative alignment measures in total knee arthroplasty where PACS is not available.