Background: Glenohumeral instability associated with a large osseous defect of the glenoid can be treated with bone graft to restore the glenoid concavity. The shape and positioning of the graft is critical: a graft that encroaches on the extrapolated glenoid curvature can prevent the head from seating completely in the glenoid, whereas a graft that is too far from the curvature does not restore the glenoid concavity. The purpose of the present study was to investigate how the intrinsic stability that is provided by the glenoid is affected by (1) a standardized anteroinferior glenoid defect and (2) different configurations of anteroinferior glenoid bone graft.
Methods: The anteroinferior stability provided by the glenoid was quantitated by measuring the balance stability angle in that direction. The balance stability angle is the maximal angle that the direction of the net humeral joint-reaction force can make with the glenoid centerline before dislocation takes place. The anteroinferior stability was assessed in each of four fresh-frozen, grossly normal cadaveric glenoids in (1) the unaltered state, (2) after the creation of a standardized defect of a magnitude that has been reported by other investigators to be sufficient to require a bone graft, and (3) after each step of a series of bone-grafting procedures involving grafts of varying height and contour.
Results: The anteroinferior glenoid defect significantly diminished the anteroinferior stability by almost 50% (p = 0.006). Bone-grafting significantly increased the stability provided by the glenoid. The increase in stability as compared with that of the glenoid with the standardized defect was particularly marked for contoured graft heights of 6 and 8 mm, for which the increases were 150% (p = 0.0001) and 229% (p < 0.00025), respectively. Contouring of the graft minimized the potential for unwanted contact between the ball and the graft.
Conclusions: Anteroinferior shoulder instability caused by an osseous defect in the glenoid can be corrected with bone-grafting. The effectiveness of the graft in restoring the lost stability is related both to its height and to the extent to which it is contoured as long as the graft is not so prominent that it forces the ball posteriorly from the center of the glenoid.
1 Departments of Orthopaedics and Sports Medicine (W.H.M. Jr., M.W., F.A.M. III) and Medicine (C.H.), University of Washington Medical Center, Box 356500 (W.H.M. Jr., M.W., F.A.M. III) and Box 356420 (C.H.), 1959 N.E. Pacific Street, Seattle, WA 98195. E-mail address for F.A. Matsen III: email@example.com
2 Department of Orthopedic Surgery, Akita University School of Medicine, Hondo 1-1-1, Akita 010-8543, Japan
3 Akron General Medical Center, 224 West Exchange Street, Suite 440, Akron, OH 44302