Effect of external loads and cyclic loading on normal patellofemoral joint signals

Pain over the anterior portion of the knee joint is a common clinical complaint. A condition known as 'chondromalacia patella' (softening of the cartilage under the patella), which frequently causes anterior knee pain is difficult to diagnose monitor. Vibrations detected by a contract transducer over the patellofemoral joint may be useful inn the assessment of chondromalacia patella. This paper utilized this technique known as vibroarthrography (VAG), to study two potential sources of variability of the normal patellofemoral joint signal. The effect of increased muscular force on the VAG signal was measured by externally loading the joint. The effect of load history (cyclic loading) on the VAG signal was determined by comparing signals before, during and after application of weights under similar cyclic loading conditions. Results indicated that external loading of the patellofemoral joint caused only minor signal variation. Cyclic loading of the joint, on the other hand, was determined to be major source of variability of the normal patellofemoral joint signal, which must be controlled in future VAG tests.