A method for assessing joint line shift post knee arthroplasty considering the preoperative joint space

BackgroundAccurate comparison of outcomes regarding various surgical options in knee arthroplasty can benefit from an improved method for joint line analysis that takes into account the preoperative joint space.MethodsThis article describes a new preoperative-based registration method that measures changes in the joint line by overlaying the 3D models of the bones with implants using preoperative CT along with preoperative and postoperative biplanar radiography. The method was tested on six cadaveric specimens for measuring alteration to the medial and lateral joint lines in extension and flexion.ResultsThe joint line shift, when measured using the new method, was in the range of − 0.2 to 1.3 mm on average (SD = 1.3 to 3.8 mm, for medial and lateral, in flexion and extension positions). This was significantly different (p ≤ 0.01) from the results of a previous postoperative-based registration method which did not account for the cartilage thickness in calculating alterations of the joint line (mean = 3.9 to 6.8 mm, SD = 1.2 to 4.3 mm).ConclusionThese results further highlight the importance of considering the preoperative joint space in analyzing the joint line, and demonstrate the utility of the newly introduced method for accurate assessment of changes in the joint line after arthroplasty.Clinical relevanceThe introduced method provides accurate means for investigating joint line alterations in relation to different surgical techniques and the subsequent biomechanical effects after knee arthroplasty