Eleonora Croci (Basel / CH), Jeremy Genter (Winterthur / CH; Basel / CH), Dr. Corina Nüesch (Basel / CH), Prof. Dr. Daniel Baumgartner (Winterthur / CH), Prof. Annegret Mündermann (Basel / CH)
Abstract-Text (inkl. Referenzen und Bildunterschriften)
Question
Shoulders with rotator cuff (RC) tears undergo greater upward scapula rotation1, have greater shoulder muscle activity2 during 30° scaption than healthy shoulders, and such trends increase with loading but their relationship is unknown in healthy and pathological shoulders. This study aimed to examine the relationship between increases in shoulder kinematics and muscle activity with loading in shoulders with and without RC tears.
Methods
Fluoroscopy and electromyography (EMG) of 130 shoulders (43 healthy, 24 RC tendinopathy, 38 asymptomatic and 25 symptomatic RC tears) were acquired during 30° scaption with handheld weights (0, 2 and 4 kg). Shoulder kinematics (upward scapula rotation and superior glenohumeral (GH) translation) were measured during scaption.3 EMG of multiple shoulder muscles was normalised to the maximum voluntary isometric contraction and log transformed. A linear mixed model (kinematics, shoulder type) with random intercept and slope (IDs) was fitted to predict EMG. Slopes were examined for the shoulder types.
Results
Overall, significant slopes were found for almost all muscles with scapula rotation as a predictor in RC tears and healthy shoulders, with slopes higher in healthy shoulders and lower in symptomatic RC tears (Table 1, Fig 1). GH translation had only a few significant effects in pathological shoulders (Table 1).
Conclusions
In shoulders with healthy or torn RC, scapula rotation correlated not only with the activity of the upper trapezius but also of the other muscles, indicating that all contribute to shoulder motion. The little correlation with GH translation suggests that the shoulder remained stable. The higher levels of EMG and scapula rotation in shoulders with RC tears than healthy shoulders may contribute to secondary damage over time. Early detection of these increased parameters may be of clinical interest.
1Croci et al. Swiss Med Wkly 2023
2Croci et al. J Orthop Traumatol 2023
3Croci et al. Eur Radiol 2023