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"Tooth" sign in patellar degenerative disease.

In the total examination of the knee, degenerative changes and ossification in the quadriceps tendon easily recognized on the lateral roentgenogram may cause confusion in diagnosis when seen on the axial view. Vertical ridging of the osteophytes at the patellar insertion of the quadriceps tendon can resemble dentate structure ("tooth" sign). Two hundred and fifty examinations of the knee in different age groups were reviewed and several anatomical sections of the quadriceps-patella insertion were studied. The "tooth" sign represents the relief of severe osteophyte formation in the bundle of the quadriceps tendon at its insertion into the patella.