Abstract
Background: The range-of-motion of the Glenohumeral joint varies substantially between individuals and is dependent on humeral position. How variation in shape of the humerus and scapula affects shoulder axial range-of-motion at various positions has not been previously established. Hypothesis/Purpose: The aim of this study is to quantify variation in the shape of the Glenohumeral joint and investigate whether the scapula and humerus geometries affect axial rotational range of the Glenohumeral joint. Study Design: Cross-sectional study. Methods: The range of active and passive internal-external rotation of the Glenohumeral joint was quantified for 10 asymptomatic subjects using optical motion tracking at 60º, 90º and 120º humeral elevations in the Coronal, Scapular and Sagittal planes. Bone geometrical parameters were acquired from shoulder MRI scans and correlations between geometric parameters and maximum internal and external rotations were investigated. Three-dimensional subject-specific models of the humerus and scapula were used to identify collisions between bones at the end-of-range. Results: Maximum internal and external rotations of the Glenohumeral joint were correlated to geometrical parameters and were limited by bony collisions. Generally, the active axial rotational range was greater with increased articular cartilage and glenoid curvature; whilst a shorter acromion resulted in greater passive range. Greater internal rotation was correlated with a greater glenoid depth and curvature in the Scapular plane (r=0.76, p<0.01 at 60° elevation), a greater subacromial depth in the Coronal plane (r=0.74, p<0.01 at 90° elevation), and a greater articular cartilage curvature in the Sagittal plane (r=0.75, p<0.01 at 90° elevation). At higher humeral elevations, a greater subacromial depth and shorter acromion allowed a greater range-of-motion. Conclusion: The study strongly suggests that specific bony constraints restrict the maximum internal and external rotations achieved in active and passive glenohumeral movement. Clinical Relevance: This study identifies bony constraints which limit the range-of-motion of Glenohumeral joint. This information can be used to predict full range-of-motion and set patient specific rehabilitation targets for patients recovering from shoulder pathologies. It can improve positioning and choice of shoulder implants during pre-operative planning by considering points of collision which could limit range-of-motion.