Physiological patellofemoral crepitus in knee joint disorders.

Vibration waves produced by the knee joint during extension-flexion may be recorded by vibration arthrometry. When the speed of this motion is less than 5 degrees per second, the vibration produced by the patella is referred to as physiological patellofemoral crepitus (PPC), which reflects the integrity of articular cartilage. PPC signals were recorded before a scheduled arthroscopic examination or operations in 17 patients whose patellofemoral joint cartilage was found subsequently to be normal, and in 25 patients (36 knee joints) who underwent arthroscopic debridement, osteotomy, or total knee replacement due to degenerative osteoarthritis. The PPC signals of five normal adults (10 knees) without any knee problems were also recorded as a control group. The root mean square (RMS) values of the PPC signals of the control group, the group with knee injuries, and the osteoarthritic patients were 0.69, 0.17, and 0.04 m/sec2, respectively. Differences among these groups were statistically significant (P<0.001). When the time domain pattern and RMS value of the preoperative PPC signals were studied and compared with the corresponding pathological findings in joint cartilage, as noted in the surgical findings, three types of PPC signals of the osteoarthritic knees could be identified. Each indicated pathological changes of a different extent. When the 53 PPC signals were reviewed according to these criteria, the accuracy, sensitivity, and specificity of the diagnosis of osteoarthritic change of the patellofemoral joint by vibration arthrometry were found to be 94.3%, 97.2%, and 88.2%, respectively. Based on these results, the detection of PPC by vibration arthrometry may be considered a reliable and non-invasive diagnostic procedure for the evaluation of the patellofemoral joint cartilage integrity.