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