View of our original intraoperative protractor (right, anteroposterior view; left, lateral view). The protractor is constructed with a 10-cm bar and a 20-cm bar. There is a projection at a point of intersection where the 10-cm bar is at the tibial tuberosity and the distal 20-cm bar is at the anterior tibial crest. The angle made by the two bars make is displayed on a scale at their intersection.
Mutsuzaki and Ikeda Sports Medicine, Arthroscopy, Rehabilitation, Therapy & Technology 2012 4:44 doi:10.1186/1758-2555-4-44