• W Jack Rejeski, Edward H Ip, Anthony P Marsh, Qiang Zhang, and Michael E Miller.
• Department of Health and Exercise Science, Wake Forest University School of Medicine, Winston-Salem, NC 27109, USA. rejeski@wfu.edu
• Arch Phys Med Rehabil. 2008 Nov 1; 89 (11): 2102-7.

ObjectivesThis study employed relatively new statistical methods to understand how many states are needed to describe disability in older adults with knee pain, describe the relative probability of transitioning between states over time, and examine whether obesity influences the probability of transitioning between states.DesignProspective epidemiologic study of older adults with knee pain.SettingCommunity.ParticipantsThe participants, 245 women and 235 men, were 65 years or older, had chronic knee pain on most days, and had difficulty with at least 1 mobility-related activity caused by knee pain.InterventionsNot applicable.Main Outcome MeasureThe primary instrument, the Pepper Assessment Tool for Disability, evaluated self-reported difficulty with mobility, basic activities of daily living (ADLs), and instrumental activities of daily living (IADLs).ResultsThe Hidden Markov Model yielded 6 states reflecting changes in mobility, ADLs, and IADLs. There is evidence that loss in more demanding mobility-related activities such as stair climbing is an early sign for the onset of disability and that functional deficits in the lower extremities are critical to the early loss of ADLs. Overall the trend is for older adults to experience greater progression than regression and for obesity to be important in understanding severe states of disability.ConclusionsThese data provide a strong rationale for characterizing disability on a continuum and underscore the fluid nature of disability in older adults. As expected, lower-extremity function plays a key role in the disablement process; obesity is also particularly relevant to understanding severe states of disability.

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