[Practical application of phonoarthrography in the diagnosis of knee joint disease (author's transl)]

Analysis of knee joint sound signals for non-invasive diagnosis of cartilage pathology

The need for a safe, objective, noninvasive tool for the early detection, localization, and quantification of both hyaline articular cartilage and meniscal pathology in the knee is discussed, and the possible use of joint sounds for this purpose is examined. A historical survey of joint sound analysis is given, and the authors' own research is described. The analysis of the knee joint sounds, using time-domain signal plots and three-dimensional spectral plots, supported the authors' assumptions regarding the nature of various degrees of chondromalacia and meniscal lesions, and the associated sounds. Quantitative features such as energy, frequency peaks, duration of signal components, and bandwidths can be easily computed from the data. Further subclassification, however, would require more accurate quantification or parametric representation of signal features, which should be possible by modeling techniques such as linear prediction.

Automatic de-noising of knee-joint vibration signals using adaptive time-frequency representations

A novel de-noising method for improving the signal-to-noise ratio of knee-joint vibration signals (also known as vibro-arthrographic (VAG) signals) is proposed. The de-noising methods considered are based on signal decomposition techniques, such as wavelets, wavelet packets and the matching pursuit (MP) method. Performance evaluation with synthetic signals simulated with the characteristics expected of VAG signals indicates good de-noising results with the MP method. Statistical pattern classification of non-stationary signal features extracted from time-frequency distributions of 37 (19 normal and 18 abnormal) MP method-de-noised VAG signals shows a sensitivity of 83.3%, a specificity of 84.2% and an overall accuracy of 83.8%.

Analysis of knee vibration signals using linear prediction

Clinical methods used at present for the diagnosis of cartilage pathology in the knee are invasive in nature, and carry some risks. There exists a need for the development of a safe, objective, noninvasive method for early detection, localization, and quantification of cartilage pathology in the knee. This paper investigates the possibility of developing such a method based on an analysis of vibrations produced by joint surfaces rubbing against one another during normal movement. In particular, the method of modeling by linear prediction is used for adaptive segmentation and parameterization of knee vibration signals. Dominant poles are extracted from the model system function for each segment based on their energy contributions and bandwidths. These dominant poles represent the dominant features of the signal segments in the spectral domain. Two-dimensional feature vectors are then constructed using the first dominant pole and the ratio of power in the 40-120 Hz band to the total power of the segment. The potential use of this method to distinguish between vibrations produced by normal volunteers and patients known to have cartilage pathology (chondromalacia) is discussed.

Optical measurements of physiological patellofemoral crepitus

An optical method to measure directly small displacements of the patella has been developed. Light from a helium-neon laser was reflected from a plane mirror taped to the skin over the patella to a glass plate which generated a set of fringes by interference of light reflected from the front and rear surfaces of the plate. The movement of the fringe system was detected using a photodiode. The optical measurements of displacement were compared with those deduced from an accelerometer attached to the same joint. The method was found to be capable of detecting patellar displacements in the range from 20 microns to 180 microns.

Vibration arthrometry. A preview

Throughout the ages, physicians have listened to sounds and felt vibrations from human joints in their attempts to diagnose pathology. They have used a wide vocabulary to describe these phenomena, but technology has been slow to provide recording and analytic equipment. Lately, accelerometers have been used with considerable success in a new noninvasive method now known as vibration arthrometry (formerly "arthrography"). The technique has been used in early detection of congenital dislocation of the hip and also in diagnosis of meniscal pathology. More recently, patellar vibration has been used to assess the mechanical properties of articular cartilage. Vibration arthrometry has also yielded new information on a possible damage mechanism associated with shock vibration that arises during cavitation of synovial fluid. Joint vibrations are therefore useful aids to diagnosis and may even be etiologic in orthopedic disease.