Clavicle hook plates are an effective plate fixation alternative for distal clavicle
fractures and severe acromioclavicular joint dislocations. However, post-operative
complications associated with the subacromial portion of the hook include acromial
osteolysis and subacromial impingement. We examine and quantify the three-dimensional
position of the subacromial portion of the hook plate relative to surrounding acromial
and subacromial structures in a series of cadaveric shoulders to determine if hook
positioning predisposes the shoulder to these noted post-operative complications.
Fifteen cadaveric shoulders (seven males, eight females) were implanted with 15- or
18-mm hook plates. Dimensions of the acromion and hook plate were digitised and reconstructed
into a three-dimensional model to measure acromion dimensions and distances of the
subacromial hook relative to surrounding acromial and subacromial structures.
Inter-specimen dimensions of the acromion were highly variable. Mean acromion width
and thickness were greater in males than in females (p=0.01). The posterior orientation
of the subacromial hook varied widely (mean posterior implantation angle=32.5+/-20
degrees, range 0-67 degrees). The hook pierced the subacromial bursa in 13/15 specimens,
made contact with the belly of the supraspinatus muscle in 9/15 specimens, and had
focal contact at the hook tip with the undersurface of the acromion in 9/15 specimens.
The wide range of acromial dimensions leads to a high degree of variability in the
positioning of the subacromial hook. The observed frequency of hook contact with surrounding
subacromial structures in a static shoulder confirms that the position of the hook
portion of the implant can predispose anatomic structures to the post-operative complications
of subacromial impingement and bony erosion.
Copyright 2009 Elsevier Ltd. All rights reserved.