Measurement of patellar tracking: assessment and analysis of the literature.

Patellar tracking is defined as the motion of the patella relative to the femur or femoral groove on knee flexion and extension. Abnormalities of tracking (maltracking) are thought to relate to many disorders of the patellofemoral joint and may be defined easily or may be extremely difficult to observe. Accurate measurement of patellar tracking, and definition of normal tracking, have not been achieved yet in experimental conditions or in clinical conditions. Such information would be valuable in the diagnosis and treatment of patellofemoral disorders. In the current report, the literature is reviewed critically with an emphasis on methodology and results. The reporting of patellar tracking is affected significantly by basic definitions of coordinate systems and reference points. The method of muscle loading, range, and direction of knee motion, use of static or dynamic measurement techniques, and tibial rotation also will affect the results obtained. The accuracy of the equipment used is important as differences in tracking may be small. Comparison between existing studies is difficult because of differences in methodology. There is general agreement that the patella translates medially in early knee flexion and then translates laterally. Regarding patellar tilt, results are less consistent, especially in vivo and the results for patellar rotation are highly variable.