Discussion:
Current literature review demonstrates no case reports describing
documenting distal deltoid tendon rupture from the deltoid tuberosity.
This case vignette is the first to describe such injury of humeral site
deltoid tendon rupture and describes successful surgical repair. In
contrast to our distal deltoid tear, there have been multiple reports on
proximal deltoid origin site detachment from the acromion and distal
clavicle [4-6]. The mechanism of injury described by prior research
for this rare injury includes seatbelt-induced injury after a motor
vehicle accident, cricket bowling maneuver, and pull-up exercises
[4-6].
Our patient was performing barbell shoulder shrugs with 450 pounds when
he experienced acute posterior left shoulder pain during the eccentric
phase of the exercise. Andersen and colleagues evaluated the shoulder
girdle muscle activity using surface electromyography in a cohort of
middle-aged females [7]. The level of muscle activation was measured
as a percentage of maximal voluntary static contraction. Activation of
the posterior portion of the deltoid muscle was found to be
significantly higher during exercises that involved a forward incline of
the body including reverse flys (102 +/- 9%), One hand rows (83 +/-
6%) and shoulder shrugs (71 +/- 5%). Comparing this to our study
participant, he described a slight forward flexion at his waist in order
to bring the barbell out from rubbing on his thighs during the shrug
exercise. This suggests an increase force vector directed through the
posterior deltoid fibers, which may have contributed to the tendon
rupture. There are some limitations of direct comparison between our
patient and the reported data. The shrugs exercise performed by
Andersen’s female patients utilized dumbbells to the side rather than a
barbell.
A recent study analyzing the anatomy of the deltoid muscle tendons
examined eight cadaver specimens with an average age of 76 years of age
identifying the deltoid origins and end tendons insertion sites. The
final model from the study consisted of an end tendon consisting of a
continuous succession of bipennate end tendon blades centrally
interspaced by unipennate tendon parts, creating a natural segmentation.
They identified an average of 2.9 +/- 0.8 end tendon blades inserting
posteriorly at the lateral humerus [8]. This is consistent with our
intraoperative findings and successful fixation of two bipennate
posterior end tendons. There is currently no research on the clinical
significance of individual end tendon ruptures.
Treatment of isolated proximal deltoid tears has generated controversy
due to limited data on the subject and the diversity of patients
currently reported on. Support for surgical fixation in healthy active
individuals in based on case report data that demonstrated satisfactory
results following operative treatment [5-7]. Following operative
fixation patients regained functional deltoid strength and experienced
painless range of motion after completing post-operative physical
therapy. Support for nonoperative therapy with a supervised
rehabilitation program stems from a case report on a partial deltoid
detachment from the posterolateral acromion in a healthy 31 year old
cricket player. Nonoperative treatment including Indomethacin treatment
and physical therapy resulted in a return of function in 8 weeks.
However, the patient’s MRI was complicated by areas of myositis
ossificans and heterotropic calcification present at the posterolateral
acromion [4].
This case is unique due to the posterior deltoid tendon rupture, with
confirmed tendon retraction on magnetic resonance imaging; additionally
the patient had physical deformity with associated weakness and pain
affecting his occupation. Operative management was successful and
allowed him to return to work with similar pre-injury strength, range of
motion and functional capacity within four months of surgery