Two-year validation and minimal clinically important difference of the Veterans RAND 12 Item Health Survey Physical Component Score in patients undergoing minimally invasive transforaminal lumbar interbody fusion

Abstract

OBJECTIVE The Physical Component Score of the Veterans RAND 12 Item Health Survey (VR-12 PCS) has been assessed for use at short-term and intermediate-term time points for lumbar fusion populations. This study assesses the long-term validity and establishes minimal clinically important difference (MCID) values of VR-12 PCS in patients undergoing minimally invasive transforaminal lumbar interbody fusion (MIS TLIF). METHODS A surgical registry was retrospectively reviewed for primary, elective, single-level MIS TLIF procedures with posterior instrumentation. Patients missing preoperative and 2-year postoperative VR-12 PCS survey data were excluded. VR-12 PCS, SF-12 Health Survey Physical Component Summary (SF-12 PCS), Patient-Reported Outcomes Measurement Information System Physical Function (PROMIS PF), and Oswestry Disability Index (ODI) patient-reported outcome measures (PROMs) were recorded preoperatively and postoperatively. Responsiveness of the VR-12 measure was assessed in two ways. First, the mean postoperative PROM scores were compared with preoperative baseline values using a paired Student t-test. Second, MCID values were calculated using both distribution-based and anchor-based methods and used to assess improvement in VR-12 score at the 2-year time point. Discriminant validity of the VR-12 was assessed using cross-sectional and longitudinal anchors. Convergent validity of the VR-12 measure was assessed using Pearson’s correlation coefficient and partial time-independent correlation. Floor and ceiling effects were assessed. RESULTS A total of 74 patients who underwent MIS TLIF were included. The VR-12 PCS demonstrated significant improvements at all time points from 12 weeks to 2 years (p < 0.001 for all). VR-12 PCSs were significantly different for patients classified using cross-sectional anchors (p < 0.001) and longitudinal anchors (p ≤ 0.005). Calculated MCID values ranged from 4.1 to 8.5, and 4.1 was selected as the optimal MCID, which 87.8% of patients achieved. Strong, significant correlations of the VR-12 PCS with SF-12 PCS and PROMIS PF were demonstrated at all time points (p < 0.001 for all). No significant floor or ceiling effects were detected. CONCLUSIONS The VR-12 PCS demonstrated excellent responsiveness, discriminant and convergent validity, and no significant floor or ceiling effects up to 2 years after MIS TLIF. Therefore, VR-12 PCS may serve as a valid measure of long-term physical function.