Biomechanical trade-offs after superior capsular reconstruction and tendon transfers for massive irreparable posterosuperior rotator cuff tears: a combined musculoskeletal–finite element analysis

Massive irreparable posterosuperior rotator cuff tears can disrupt the glenohumeral force couple and increase abnormal cartilage loading. Superior capsular reconstruction (SCR), latissimus dorsi transfer (LDT), and lower trapezius transfer (LTT) are commonly used joint-preserving procedures, but their local biomechanical differences remain unclear. This study compared their effects on glenoid cartilage stress and peri-anchor bone stress using a combined musculoskeletal–finite element (MSK–FE) workflow. Subject-specific musculoskeletal and finite element shoulder models were developed from computed tomography data of a single subject. Five models were established: Healthy, irreparable rotator cuff tear (IRCT), SCR, LDT, and LTT. Muscle forces and skeletal kinematics calculated by the musculoskeletal model were transferred to the finite element models. Simulated conditions included 0°, 30°, 60°, and 90° pure abduction; 60° abduction with 20° internal rotation; and 60° abduction with a 10-N vertical hand load. The primary and secondary outcomes were peak glenoid cartilage and peri-anchor bone von Mises stress, respectively. The IRCT model showed higher glenoid cartilage stress than the Healthy model under all conditions. SCR showed greater reductions in cartilage stress at middle-to-high abduction angles, decreasing to 1.45 MPa at 90° abduction. Under 60° abduction with 20° internal rotation, the resultant glenohumeral shear force was 290.9 N in the IRCT model, compared with 104.7 N and 99.7 N in the LDT and LTT models, respectively; this was accompanied by lower cartilage stress in both tendon transfer models, with the lowest value observed in the LDT model. Under 60° abduction with a 10-N hand load, the IRCT model reached the highest cartilage stress of 7.04 MPa, whereas all reconstruction models reduced cartilage stress. Peri-anchor bone stress was higher in the SCR model under most abduction and loading conditions, with a maximum of 45.32 MPa during 10-N loading. Within this single-subject computational model, SCR, LDT, and LTT showed distinct condition-dependent biomechanical effects. SCR was associated with lower glenoid cartilage stress under high-abduction and loading conditions but higher peri-anchor bone stress. LDT and LTT were associated with lower resultant glenohumeral shear force and cartilage stress under the selected rotation-related high-shear condition. These findings should be considered hypothesis-generating and interpreted within the context of a single-subject computational analysis.