Mechanical properties of muscles around shoulder in breast cancer patients: Intra- and inter-reliability and symmetry using MyotonPRO

Abstract

Treatment related shoulder dysfunction and anterior chest wall stiffness is common in breast cancer patients. Objective information of muscle properties can be useful for evaluating these problems and the effect of intervention. Recently MyotonPRO has been used to measure muscle properties such as stiffness, tone and elasticity. Our study aimed to assess mechanical properties and symmetry of muscles around shoulder and to investigate the inter- and intra-rater reliability of parameters measured by MyotonPRO in breast cancer patients. Twenty-two breast cancer patients who underwent mastectomy were studied. Frequency (tone, Hz), Stiffness (N/m) and Decrement (elasticity) were measured in both Pectoralis major (PM), Sternocleidomastoid (SMC) and Upper trapezius (UT). Rater 1 measured two sets with a time interval of 30 minutes in order to confirm intra-rater reliability. Rater 2 measured one set at the time interval. After the each measurement, the markings are completely erased so as to not influence the subsequent testing session. A paired t -test was used to compare muscle properties between affected side and unaffected side. Reliability was assessed using intra-class correlation coefficients (ICCs) and Bland and Altman analysis. Intra-rater reliability was excellent (ICC > 0.75, 0.85–0.98) in all parameters for two sets of repeated measurements from the PM, SCM and UT in affected and unaffected upper limb in breast cancer patients. Inter-rater reliability was fair to excellent in all parameters except the unaffected PM elasticity (ICC = 0.34). Significant differences in all parameters were observed in the affected side PM and the unaffected side PM. In both SCM and UT, there was no significant difference between all the parameters. Our findings indicate that MyotonPRO is a feasible tool to quantify PM stiffness and tone in breast cancer patients. Studies assessing the changes in PM muscle properties caused by pathology or treatments are needed.