Elsevier

Injury

Volume 41, Issue 6, June 2010, Pages 613-619
Injury

Subacromial morphometric assessment of the clavicle hook plate

https://doi.org/10.1016/j.injury.2009.12.012Get rights and content

Abstract

Background

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.

Materials and methods

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.

Results

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°, range 0–67°). 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.

Conclusions

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.

Section snippets

Materials and methods

Ethical approval to undertake this study was obtained from our institutional ethics board (Protocol #: 2007-037) and the University of Toronto (Protocol #: 22238). We evaluated 16 fresh frozen cadaveric shoulder specimens with the upper torso intact (eight male, eight female, mean age 74.8 ± 20.2 years). Specimens with external signs of shoulder surgery or disruptions to the sternoclavicular or the acromioclavicular joint were excluded. During the process of clavicle hook implantation and

Results

Sixteen shoulder specimens (eight male and eight female) were implanted with clavicle hook plates. After initial dissection, one specimen was excluded due to the presence of large osteophytes on the head of the humerus and the glenoid fossa. As a result, 15 specimens (n = 15; seven male and eight female) met all inclusion criteria and were subject to digital and statistical analyses. All seven male specimens received an 18-mm implant. Four female specimens received 15-mm implants; the remaining

Discussion

The results of our study indicate a high degree of inter-specimen variability in both the morphological dimensions of the acromion and the position of the subacromial hook, relative to specific points on the acromion. Our observation of sex differences in acromion width (male (M) = 45.3 ± 4.6 mm, female (F) = 36.7 ± 5.9 mm) and thickness (M = 6.1 mm, F = 4.4 mm) is consistent with the findings of Nicholson et al. on over 400 scapulae (M = 48.5 mm, 7.7 mm; F = 40.6 mm, 6.7 mm, respectively).34 We noted the mean

Conclusions

Our results suggest that the unique anatomy of each patient, and the lack of standard acromion dimensions, impact the location and position of the subacromial hook when a clavicle hook plate is used. 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.

Conflict of interest

None of the authors, their immediate families, or any research foundation with which they are affiliated received financial payments or other benefits from any commercial entity related to the subject of this article.

Funding source

Funding of this study was provided through an unrestricted research grant from Synthes® (Canada) Ltd. Synthes® reviewed the attached article prior to its submission to this journal. However, Synthes® at no time participated in the data collection, data analysis or preparation of the article.

Acknowledgements

We would like to thank William Wood in the Division of Anatomy and John Geary, M.Sc. PT, for their technical services. We would also like to thank Synthes® (Canada) Ltd. for providing an unrestricted research grant and the clavicle hook plates used in this study.

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