Is the Marx Activity Scale Reliable in Patients Younger Than 18 Years?

BACKGROUND There is no baseline activity scale yet validated in pediatric patients. The Marx and Tegner scales have been validated in adult patients only. The Tegner scale involves questions not pertinent to children, such as their work activity. The Marx scale is simple, and all its questions can be related to athletic activities. HYPOTHESIS The Marx scale is reliable for use in a pediatric population. STUDY DESIGN Cohort study. LEVEL OF EVIDENCE Level 2. METHODS Patients younger than 18 years were given the Marx activity scale in clinic and again 3 weeks later. The patients were divided into 3 groups, of at least 50 patients each, based on presenting diagnosis: knee injury, lower extremity (non-knee) injury, and upper extremity injury. Test-retest reliability was determined for the overall scores and the individual questions. Differences in scores were also compared based on age (<14 vs ≥14 years). RESULTS A total of 162 patients (mean age, 14.4 years; range, 8-17 years) were included. The Marx scale had a high intraclass correlation coefficient (ICC) overall as well as for each of its 4 questions. Both older and younger patients had ICCs >0.80, though the older group generally had higher scores. The mean score was 13.55 (out of 16), and 50.6% scored the maximum; only 1.9% scored the minimum. Mean scores for the knee, lower extremity, and upper extremity groups were 13.71 (SD, 3.70), 13.22 (SD, 4.18), and 13.68 (SD, 3.33), respectively (P > 0.05). There also was no difference in total score based on age (P = 0.88). CONCLUSION The Marx activity scale is reliable in patients younger than 18 years with injuries to the knee and lower extremities, though the scale was less reliable in patients younger than 14 years. There is a significant ceiling effect present, which limits its overall usefulness. CLINICAL RELEVANCE Although there is no other current substitute, the Marx activity scale is not an ideal measurement of younger patients' baseline activity levels.