Habitual hip joint activity level of the penned EMU (Dromaius novaehollandie).

Orthopaedic management of femoral head osteonecrosis remains problematic, partly because of inability to systematically compare treatments in an animal model whose natural history parallels the human in terms of progression to femoral head collapse. Recently, it was determined that collapse could be consistently achieved for cryogenically induced osteonecrosis in the emu. Toward delineating the comparative hip joint biomechanics of emus versus humans, for purposes of establishing the emu as a model for human femoral head osteonecrosis, habitual hip joint activity level was quantified for a group of seven healthy adult emus housed in an outdoor research pen typical of those used in emu farming operations. The daily number of steps taken, and the time spent with the hips loaded (standing, or squatting/sitting) versus unloaded (recumbent), were quantified from 24-hour videotape recordings, analyzed by four independent observers. The average number of steps taken per day was 9563, which extrapolates to 1.8 million hip loadings per year, a value that falls in the same general range as seen in normal adult humans. On average, the emus spent 4:05 hours per day idly standing, 2:12 hours squatting/sitting, and 10:44 hours recumbent; they underwent an average of 37 transitions per day between the respective posture/activity states.