Distinct Cognitive Trajectories in the First Year After Hip Fracture.

OBJECTIVES

Change in cognitive functioning is often observed after hip fracture. Different patterns, with both improvement and decline, are expected, depending on premorbid cognitive functioning and events that occur during hospitalization. These patterns are unknown and important for older hip fracture patients with different levels of premorbid cognitive functioning.

DESIGN, SETTING, PARTICIPANTS, MEASUREMENTS: We conducted a secondary analysis of a multi-center randomized controlled trial. 302 consecutive patients aged 65-102 years old, admitted for hip fracture surgery, were enrolled. The Mini Mental State Examination (MMSE) was obtained at hospital admission, at discharge, and at 3 and 12 months after discharge. Cognitive trajectories were identified with Group Based Trajectory Modelling, using the repeated MMSE measurements as outcome variable. To illustrate the specific characteristics of this relative novel methodological approach, it was contrasted with results obtained from linear mixed effects modeling.

RESULTS

146 (48.3%) patients had premorbid cognitive impairment and 85 patients (28.1%) experienced delirium during admission. Three distinct cognitive trajectories were identified and labeled based on different MMSE course over time: improvement (57.9%), stable (28.1%), and rapid decline (13.9%), with an annual MMSE change of 1.7, 0.8, and -3.5 points respectively. With mixed effects modeling an overall annual increase of 0.7 MMSE points was estimated for the group as a whole.

CONCLUSION

Three distinct cognitive trajectories were identified in a population of older hip fracture patients. These trajectory groups can be used as a starting point to inform patients and caregivers on the possible prognosis after hip fracture. Group based trajectory modelling is a useful technique when the purpose is to describe patterns of change within a population and a variety of trajectories are expected to exist.