Osteometry of the glenohumeral joint

Measurements made from radiographs of the shoulder are often used for evalu ation of the position of a shoulder prosthesis after surgery. The distances measured from a radiograph are subject to projection errors arising from p ositioning of the patient in front of the x-ray cassette and from the direc tion of the x-ray beam at the time of the exposure. The projection error wa s studied on radiographs of the glenohumeral joint in cadaver preparations. Measurements of the spatial relationship between the glenohumeral joint an d the scapula changed by 10% to 50% when the specimen was rotated by 20 deg rees around an axis through the glenohumeral joint. The values measured on radiographs of the proximal humerus changed by less than 10% when the humer us was rotated by 20 degrees (exorotation and endorotation). Proposals are made For specific measurements in evaluating the shoulder before and after a prosthesis is implanted.