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.

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.