Influence of the mental health status on a new measure of objective functional impairment in lumbar degenerative disc disease.

BACKGROUND CONTEXT: The Timed Up and Go (TUG) test has recently been proposed as a simple and standardized measure for objective functional impairment (OFI) in patients with lumbar degenerative disc disease (DDD).

PURPOSE: The study aimed to explore the relationship between a patient's mental health status and both patient-reported outcome measures (PROMs) and TUG test results.

STUDY DESIGN/SETTING: This is a prospective institutional review board-approved two-center study.

PATIENT SAMPLE: The sample was composed of 375 consecutive patients scheduled for lumbar spine surgery and a healthy cohort of 110 control subjects.

OUTCOME MEASURES: Patients and control subjects were assessed with the TUG test and a comprehensive panel of subjective PROMs of pain intensity (visual analog scale [VAS]), functional impairment (Roland-Morris Disability Index [RMDI]), Oswestry Disability Index [ODI]), as well as health-related quality of life (hrQoL; Euro-Qol [EQ]-5D).

METHODS: Standardized age- and sex-adjusted TUG test T-scores were calculated. The dependent variable was the short-form (SF)-12 mental component summary (MCS) quartiles, and the independent variables were the TUG T-scores and PROMs. Direct and adjusted analyses of covariance were performed to estimate the interaction between the SF-12 MCS quartiles and the independent variables.

RESULTS: In patients, there was a significant decrease in the subjective PROMs, notably the VAS back pain (p=.001) and VAS leg pain (p=.035), as well as significant increase in the RMDI (p<.001), ODI (p<.001), and the EQ-5D index (p<.001) with every increase in the quartile of the SF-12 MCS. There were no significant group differences of OFI as measured by the TUG T-scores across the SF-12 MCS quartiles (p=.462). In the healthy control group, a significant decrease in VAS leg pain (p=.028), RMDI (p=.013), and ODI (p<.001), as well as a significant increase in the EQ-5D index (p<.001), was seen across the SF-12 MCS quartiles, whereas TUG T-scores remained stable (p=.897).

CONCLUSIONS: There are significant influences of mental hrQoL on subjective measures of pain, functional impairment, and hrQoL that might lead to bias when evaluating patients with lumbar DDD who suffer from reduced mental hrQoL. The TUG test appears to be a stable instrument and especially helpful in the evaluation of patients with lumbar DDD and mental health problems.