The authors report a study conducted on 107 CT scans taken between January and December 2001 in 76 patients affected with femoropatellar pain, that did not benefit from physiotherapy. It is the purpose of this study to present a new CT scan parameter denominated torsion angle of the patellar tendon (TAPT) and to define an algorithm of treatment for this complex pathology based on the changes revealed by CT scan according to the Lyonese protocol. CT scan based on the Lyonese protocol provides an explanation of the symptoms and the objectivity via traditional parameters in 59.63% of patients. Thanks to the introduction of this new parameter (TAPT), which allows us to reveal the presence of an extrarotation of the proximal metaphysis of the tibia, the percentage of sensitivity with CT scan has been increased to 83.92%.