Summary

Injured individuals activity level score is significantly different when evaluated by either MARS or its analogue part of HSS Pedi-FABS, with scores being lower in HSS Pedi-FABS.

Abstract

Background

The Marx Activity Rating Scale (MARS) and HSS Pedi-FABS (HSS-PF) are both validated Patient Reported Outcome Measures (PROMs) used to determine patient activity level. While MARS is based on a 4 items questionnaire and is used for all ages, HSS-PF was primarily validated in children and adolescents and is based on 8 items questionnaire, 4 of which are analogue to MARS with a different time frame for the measured activity: past year in MARS versus past month in HSS-PF.

Purpose

To determine whether the different time frames used in MARS and HSS-PF affects outcome scores, and if so, to determine whether age or injury status affect this difference.

Methods

The MARS and 4 analogous items on the HSS-PF were administered sequentially in random order to patients seen at two sports surgeons’ clinic for knee symptoms and scores were calculated (0-4 for each question and overall score of 0-16). Participant’s age was also recorded, along with time since injury (if applicable). Wilcoxon-Mann-Whitney tests were used to compare between scale’s scores. Spearman correlation was used to examine the level of association between scale’s scores. Tobit regression models were used to investigate the effect of age and injury status on the difference in scale’s overall score.

Results

88 out of 88 patients completed both questionnaires, of which 47% were aged 10-17 years old and were 53% aged 18-72 years old, 51% had a knee injury for which they came to clinic and 49% were healthy volunteers. There was a high correlation between MARS and HSS-PF scores in healthy individuals (Rho>0.5, p<0.001) with significantly higher scores on the MARS scale than the HSS-PF scale (mean difference of 1.74 in overall score, p<0.001). There was no correlation between scales in the injured individuals and injured participants score significantly higher on the MARS scale than the HSS-PF scale (mean difference of 7.5 in overall score, p<0.001). Tobit regression models showed that overall (for healthy and injured), a one year increase in age is associated with a 0.11 point decrease in the predicted difference between the scales (p=0.001) and that a knee injury is associated with a 4.59 times higher predicted difference value between the scales (p<0.001).

Conclusion

Healthy and injured individuals’ activity level is significantly different when evaluated by either MARS or its analogue part HSS-PF, with lower scores on the HSS-PF. This difference may stem from the timeframe differences of the two scales, since activity within the last month is more likely to be influenced by a recent injury or personal and seasonal factors than activity within the last year. Understating this difference can guide clinicians in using these scales appropriately when evaluating and comparing PROMs.