# The Reliability of Measuring Muscle Cross‐Sectional Area in Children Undergoing Treatment for Musculoskeletal Sarcoma

## TL;DR

This study shows that MRI can reliably measure muscle area in children with bone cancer, helping track treatment effects.

## Contribution

The study establishes the reliability of MRI-based muscle cross-sectional area measurements in pediatric sarcoma patients.

## Key findings

- MRI measurements of muscle cross-sectional area showed excellent inter- and intra-rater reliability.
- Mid-femoral and mid-tibial muscle circumferences had the highest measurement precision.
- MDC values enable detection of clinically meaningful muscle changes over time.

## Abstract

Changes in musculoskeletal health and function are increasingly recognised as important long‐term consequences of treatment for malignant bone tumours in paediatric populations. Accurate and reliable assessment methods are critical for monitoring these changes during treatment. We aimed to determine the inter‐ and intra‐rater reliability of MRI‐based measurements of muscle cross‐sectional area in children undergoing treatment for paediatric musculoskeletal sarcoma.

We conducted a retrospective cohort study at a tertiary paediatric cancer centre. Eligible participants were aged 2–17 years and had undergone routine clinical MRI scans as part of their treatment for musculoskeletal sarcoma. Muscle cross‐sectional area was measured, focusing on key lower limb muscle/muscle groups. Three trained raters independently performed all measurements. Inter‐ and intra‐rater reliability were assessed using intraclass correlation coefficients (ICCs) with 95% confidence intervals (CIs). Measurement precision was evaluated using minimal detectable change (MDC) values, expressed as a percentage of mean muscle size.

Nineteen patients (mean age 11.6 ± 2.6 years; 11 female and 8 male) were included. Diagnoses included osteosarcoma (n = 12), Ewing sarcoma (n = 5), rhabdomyosarcoma (n = 1) and synovial sarcoma (n = 1). The most common tumour location was the distal femur (n = 9), followed by proximal tibia (n = 2), pelvis (n = 2), proximal fibula (n = 1), distal fibula (n = 1) and other sites (n = 4). Metastatic disease was present in seven patients, while 12 had localised disease. Once images affected by tumour were excluded, a minimum of 60 images of each muscle/muscle group were included for analysis.

Inter‐rater reliability was excellent for psoas (ICC = 0.97, 95% CI: 0.95–0.98), gracilis (ICC = 0.96, CI: 0.93–0.98), medial gastrocnemius (ICC = 0.91, CI: 0.86–0.94), mid‐femoral muscle circumference (ICC = 0.99, CI: 0.99–0.99) and mid‐tibial muscle circumference (ICC = 0.99, CI: 0.99–0.99). Good inter‐rater reliability was found for rectus femoris (ICC = 0.88, CI: 0.83–0.95) and biceps femoris (ICC = 0.83, CI: 0.75–0.89). Intra‐rater reliability was excellent across all muscles assessed (ICCs: 0.92–0.99).

MDC values indicated highest measurement precision for mid‐femoral muscle circumference (10.62%), mid‐tibial muscle circumference (11.69%) and psoas (18.26%), enabling detection of clinically meaningful changes over time.

This study demonstrates that MRI measurement of muscle cross‐sectional area in children with musculoskeletal sarcoma is a reliable tool. MDC values allow for identification of true muscle loss, supporting early intervention.