INTRODUCTION
The Patient-Reported Outcomes Measurement Information System (PROMIS) is a type of patient-reported outcome (PRO) that has become increasingly utilized to examine postoperative success among patients undergoing open lumbar discectomy or other elective procedures [
1,
2]. Spine surgeons utilize PROs to improve clinical practice [
3,
4]. PROMIS PF computer adaptive testing (CAT) is unique in that the survey modifies its questions based upon patient response, which may help with accurate data collection [
5,
6]. Although the terms PROMIS, PROMIS PF, and PROMIS PF CAT refer to different technical items, these terms are used interchangeably to refer to the PROMIS PF CAT score.
Questions that make PROMIS useful specifically for spine surgery are those contained in the physical function (PF) subsection. Such questions ask patients about their perceived ability to move, their relative strength, and their coordination when making movements [
6-
8]. There is limited research on the association of preoperative PROMIS PF scores with postoperative improvement in patients undergoing minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) [
2].
To evaluate outcomes in patients undergoing spine surgery, PROs such as the Oswestry Disability Index (ODI), visual analogue scale (VAS), and 12-Item Short Form Survey (SF-12) are often utilized [
2,
9]. During recovery from MIS TLIF, preoperative PROMIS scores (specifically the PF domain) have been associated with improved scores at 12 weeks and 6 months. PROMIS scores after MIS TLIF were also associated with the ODI, VAS, and SF-12, suggesting that PROMIS is likely a reliable measure after MIS TLIF [
2]. Part of the utility of PROMIS scoring is that, although it is periodically updated, scores from different versions can still be compared to each other [
10]. However, despite the fact that PROMIS can be used to monitor clinical outcomes, its utility in spine surgery has still not been fully elucidated [
11].
Previous studies have demonstrated that PROMIS scores may be associated with patient outcomes after MIS TLIF [
2]. However, spine surgeons are still determining the relationship between preoperative PROMIS scores, postoperative outcomes, and how the surgeon and patient can address these synergistically to create realistic postoperative expectations [
11]. The primary objective of the study is to examine preoperative PROMIS PF score, measured by PROMIS PF, and the change between pre- and postoperative PROMIS PF score at 6 weeks, 12 weeks, 6 months, 1 year, and 2 years following MIS TLIF.
DISCUSSION
PROs function to evaluate treatment success and are becoming increasingly referenced in orthopaedic spine surgery literature that is focused on the measurement of postsurgical PF improvement. While PROMIS scores have been studied and validated as one of many clinical diagnostics involved in evaluating postsurgical gains in PF after spine surgery, more recent studies have demonstrated preoperative PRO associations with postoperative outcomes [
11,
21]. In this study preoperative PROMIS scores were observed to be associated with postoperative PROMIS score improvement among patients that underwent primary, MIS TLIF procedures when improvement was assessed at 6 weeks, 12 weeks, and 6 months.
When compared to patients with higher preoperative PROMIS scores (≥ 35), those with lower preoperative PROMIS (< 35) scores demonstrated a larger mean difference of postoperative PROMIS scores. While a statistically significant difference in the PROMIS score improvement of PF was not seen at the 1-year postoperative evaluation, these findings nonetheless provide insight for clinicians to more accurately assist and counsel patients during pre- and postoperative evaluations. It is also important to understand that regardless of the differences within this study’s subgroups, linear regression demonstrated a tendency toward increased postoperative PROMIS scores with decreased absolute preoperative scores. Effective preoperative counseling might focus attention on the potential association with lower preoperative PROMIS scores for significant postoperative improvement up until the 6-month time period. It is also important to caution such patients that, despite the relative increased early postoperative improvement, the increase in function will likely still be comparable to that of other patients with a preoperative PROMIS score advantage (≥ 35) by the 1-year time point.
While others have investigated the significance of various subgroups of PROMIS PF score groups, our study uniquely investigates the NIH threshold score between “fair” and “poor” levels of PF. Patel et al. [
6] used 3 PROMIS PF subgroups (40–50, 30–39.9, and 20–29.9) which differs from our binary subgroup analysis of fair (≥ 35) and poor (< 35) PF cohorts. In addition, our study included patients with PROMIS PF scores that were greater than 50 while Patel et al. removed these patients.
Other investigators have also observed that, among MIS TLIF patients, PROMIS PF scores demonstrate statistically significant strong correlations with SF-12, ODI, and VAS-leg scores over the first 6 postoperative months [
22]. Furthermore, it has been demonstrated that PROMIS PF scores increase the most within the first 12 postoperative weeks and within the first 6 postoperative months. Further studies are required to investigate how PROMIS PF scores correlate with SF-12, ODI, VAS-back, and VAS-leg scores beyond 6 months.
While we did find a statistically significant difference among subgroups (those that had preoperative scores of ≥ 35 and < 35) in MCID achievement at 6 months, we found no statistically significant difference between either subgroup at any time point until 2 years. These findings indicate that the 35-point PROMIS PF score threshold may not necessarily be helpful in assessing whether or not patients are likely to achieve MCID based on their preoperative PROMIS PF score.
While the PROMIS system has numerous advantages, the system can be costly for any clinic. According to the PROMIS HealthMeasures publicly available fee documentation, having access to PROMIS can range from an annual $5,000 (United States dollar, USD) if starting a new study or $2,500 (USD) to continue a study [
23]. However, other costs such as server fees, tablets to administer the surveys and research assistants to analyze the data add additional costs. One recent study estimated the total cost of administration to be approximately $1,000 per month [
24]. Fees and other implicit costs are important to acknowledge as these could be significant hurdles for researchers to overcome. While baseline and operative variables were assessed for statistical significance, only 3 variables were observed to have statistically significant differences among the 2 subgroups (e.g., sex, obesity, length of hospital stay). Specifically for length of stay, the clinical significance of an 8-hour difference in the postoperative visit length is dependent on the surgical setting. For example, 8 hours may be the difference between a patient being admitted for greater than or less than 24 hours. In an ambulatory surgical setting, for example, remaining under the 24-hour surgical threshold has a meaningful clinical impact.
This study has several limitations, including additional variables that might be collected in future studies, its retrospective nature, its limited patient follow-up time period, and possible biases such as those related to selection. One variable that might have been useful to record in this study would have been bone mineral density (BMD). Having a record of patient BMD might have been useful to control for possible confounders. The authors of this study were not blinded while conducting the retrospective review, and given the recent increase of literature that investigates the associative nature of preoperative PROMIS scores in other fields [
11,
21], observer biases are plausible, i.e., researchers seeing a pattern they expected to see. Aligned with this, the relatively short follow-up time only permitted the observation of one statistically insignificant time point (e.g., at 1 year). Further follow-up time periods might be necessary in order to better elucidate whether this lack of statistical significance at 1 year is transient or sustained.
Particularly when investigating PROs, though a clinical setting portends numerous advantages in patient evaluation, sick patients are often regarded as more likely to return to clinic. This phenomenon can introduce selection biases, though it is unclear which patient group in this study might be most affected. Patients who had relatively low preoperative PROMIS scores (< 35), might be thought to follow-up with increased frequency based on their perceived low level of function. Contrarily, those who believe they are making less postoperative improvement in PF might also appear as more likely to return to clinic. Regardless of which patient group is more affected, selection bias remains a possible force at play in nearly any PROMIS score investigation because one patient group may have been more likely to return to clinic than another. An additional limitation is that we did not perform a multivariate analysis to evaluate a single dependent variable among our subgroups. While a multivariate regression is likely to be helpful in future studies, we were able to conduct this investigation with, bivariate regressions, t-tests, and chi-square tests. This allowed us to assess our 2 preoperative PROMIS PF subgroups to identify possible differences in postoperative PRO scores and score improvement.
Although our study did not specifically investigate the time required for patients to complete the PROMIS-PF survey, it is important for clinicians to be aware of this possible burden to patients. A previous investigation in a cohort of sports medicine patients by Kadri et al. [
25] determined that the time to complete the PROMIS-PF CAT questionnaire was 0.74 minutes. An additional limitation involves the subgroups based on the PROMIS-PF 35 cutoff [
13]. Further investigations should evaluate other possible clinically relevant PROMIS-PF subgroups that may be an indicator for postoperative outcomes.
Finally, PROMIS score evaluations require patients to follow-up, and further, they require follow-up at multiple time points. While the best attempts have been made to increase patient follow-up, this study observed a steady decline in the number of patients that continued to follow at each additional time interval. As mentioned earlier, selection bias can result from those who are more sick returning to follow-up more often. Conversely, loss to follow-up might also arise as a result of injured patients becoming less likely to return to clinic. Although numerous methods exist for assessing and altering a dataset that might be affected by selection biases [
26,
27], in this study we have noted the total number of patients at each timepoint, and we only used observations that pertained to a change in score when the same individual had followed up at both the initial (e.g., preoperative) and final (e.g., postoperative) time points.