Copyright © 2009 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
William J. Robertson, MD, and Bertram Zarins, MD*,
Massachusetts General Hospital, Boston, Massachusetts
Posted April 2009
The finding that young individuals who participate in vigorous
physical activities and sports sustain more traumatic shoulder dislocations
than their less-active counterparts is not surprising or new. Several
epidemiological studies have shown an increased incidence of shoulder
instability in young active individuals as compared with an older and more
sedentary group1-3. The study by Owens et al. utilized a powerful
database to determine the incidence of first-time shoulder dislocations among
active-duty military personnel.
Owens et al. made use of data from the database of the
United States Department of Defense to determine the incidence of shoulder
dislocation in the four branches of the U.S. Armed Forces over a nine-year
period. With use of the total number of U.S. soldiers on active duty as the denominator,
the overall incidence of shoulder dislocations was calculated. Multivariate
analysis was also performed to determine the impact of several factors (sex,
race, branch of military service, rank, and age) on the incidence of first-time
dislocation. They found an overall incidence rate of 1.69 dislocations per 1000
person-years. The authors concluded that male sex, white race, and an age of
twenty-nine years or less were significant independent risk factors for injury.
This overall incidence falls between that previously
reported for general populations in the United States2 and Europe1 (0.08 and 0.17 per 1000 person-years, respectively) and that reported for
military cadets at the U.S. Military Academy4 (4.35 per 1000
person-years). The findings in the current paper by Owens et al. seem somewhat
intuitive considering that their study population participated in high-risk
activities yet represented a more stratified age group than the age group represented
in the population of military cadets.
Men were twice as likely as women to sustain a traumatic
shoulder dislocation. This finding is in contrast to a similar study performed
by the same author at the United States Military Academy4, where the
rates between sexes were similar. Another study1 in an urban
population over a five-year period found that 53% of 216 shoulder dislocations
were in men. In addition, whites had a slightly higher shoulder dislocation
rate than blacks or other races, and younger service members sustained more
shoulder dislocations than older service members did.
Owens et al. acknowledge that a main limitation to this
study is the lack of information regarding the activity being performed at the
time of dislocation. Other factors, such as anatomic variability between groups,
may also play a role. Churchill et al.5 studied the glenoid anatomy
of 172 paired cadaveric shoulders. The sample consisted of fifty black men, fifty
white men, fifty black women, and twenty-two white women, with an age range of twenty
to thirty years at the time of death. While those authors found no difference
in glenoid size between blacks and whites, the average glenoid version was
significantly different between races (p = 0.000014). Men and women of the same
race had similar degrees of retroversion, but differences existed for both
sexes between races.
Owens et al. concluded that shoulder dislocation is endemic
in military personnel. This might be an overstatement, since young athletic
cohorts are the population at risk to sustain this injury. Detailed information
regarding the mechanism of injury would have provided valuable information to
the reader and perhaps to the U.S. Military Academy for use in formulating
their training practices. Developing strategies to prevent shoulder dislocation
on the basis of the known data is still a long way away.
*The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.
References
1. Krøner K, Lind T, Jensen J. The epidemiology of shoulder dislocations. Arch Orthop Trauma Surg. 1989;108:288-90.
2. Simonet WT, Melton LJ 3rd, Cofield RH, Ilstrup DM. Incidence of anterior shoulder dislocation in Olmsted County, Minnesota. Clin Orthop Relat Res. 1984;186:186-91.
3. Yeap JS, Lee DJ, Fazir M, Borhan TA, Kareem BA. The epidemiology of shoulder dislocations in Malaysia. Med J Malaysia. 2004;59 Suppl F:19-23.
4. Owens BD, Duffey ML, Nelson BJ, DeBerardino TM, Taylor DC, Mountcastle SB. The incidence and characteristics of shoulder instability at the United States Military Academy. Am J Sports Med. 2007;35:1168-73.
5. Churchill RS, Brems JJ, Kotschi H. Glenoid size, inclination, and version: an anatomic study. J Shoulder Elbow Surg. 2001;10:327-32.
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