Static and dynamic compression regulate cartilage metabolism of PRoteoGlycan 4 (PRG4).

The boundary lubrication function of articular cartilage is mediated in part by molecules at the articular surface and in synovial fluid, encoded by Prg4. The objective of this study was to determine whether static and dynamic compression regulate PRG4 biosynthesis by cartilage explants. Articular cartilage disks were harvested to include the articular surface from immature bovines. Some disks were subjected to 24 h (day 1) of loading, followed by 72 h (days 2-4) of free-swelling culture to assess chondrocyte responses following unloading. Loading consisted of 6 or 100 kPa of static compression, with or without superimposed dynamic compression (10 or 300 kPa peak amplitude, 0.01 Hz). Other disks were cultured free-swelling as controls. PRG4 secretion into culture medium was inhibited by all compression protocols during day 1. Following unloading, cartilage previously subjected to dynamic compression to 300 kPa exhibited a rebound effect, secreting more PRG4 than did controls, while cartilage previously subjected to 100 kPa static loading secreted less PRG4. Immunohistochemistry revealed that all compression protocols also affected the number of cells expressing PRG4. The paradigm that mechanical stimuli regulate biosynthesis in cartilage appears operative not only for load bearing matrix constituents, but also for PRG4 molecules mediating lubrication.

Sensitivity of manual palpation in testing the neonatal hip.

Developmental dysplasia of the hip (DDH) is a term used to describe a group of disorders of the neonatal hip in which the head of the femur is unstable or incongruous in relation to the acetabulum. Early detection and treatment of the condition generally results in normal development, whereas late diagnosis has poor success. In Northern Ireland, despite all neonates being manually examined for hip disorders by a medical officer before hospital discharge, there is an unacceptable late diagnostic rate of almost 50% of all cases. To help reduce the number of late presentations, vibration arthrometry, a noninvasive form of screening for DDH, has been used to record hip vibration events during clinical testing. In a comparative study, 300 infants were examined by nurses and medical officers to establish the sensitivity of manual palpation to neonatal hip vibrations detected by the objective detection system. Experienced research nurses detected 86% of the signals; doctors in training detected less than 10%. This suggests that objective, noninvasive screening by vibration arthrometry would detect a higher proportion of vibration events in neonates during the early stages of DDH. More time should be invested in training medical officers and others involved in DDH screening.