Keywords
scapula/anatomy & histology - scapula/surgery - shoulder
Introduction
The incidence of scapula fractures has increased in orthopedic practice and it is
usually associated with trauma of great energy, affecting mainly young adults (35–45
years old) victims of car accidents or falls from great heights.[1]
[2]
[3] The indications for surgical treatment of glenoid neck fractures are: when they
are deviated with a translation greater than one centimeter or when the glenopolar
angle is less than 20° (normal 30∘–45∘).[4] The objective of the surgery is to restore the length, alignment, and rotation of
the scapula, leading to the improvement of the functional results.[5]
Extended scapular approaches provide excellent posterior visualization, useful accessing
of the body, spine, and neck of the glenoid.[6] The posterior approach described by Judet, which implies the extensive dissection
of the infraspinatus muscle, has been widely used in the treatment of scapular fractures
but is being replaced by less invasive variations due to the high morbidity and risk
of neurovascular lesions.[5]
In the posterior approach, it is important to identify and protect the suprascapular
nerve (SN), which emanates from the spinoglenoid notch to innervate the infraspinatus
muscle in its fossa (traction on this nerve can cause weakness of the rotator cuff
and should be avoided).[6]
Despite the variations, the less invasive approaches usually use the interval between
the infraspinatus muscle (SN) and the teres minor muscle (axillary nerve—AN) to access
the lateral angle of the scapula. With abduction of the shoulder at 60° to 90°, access
is facilitated due to the superior detachment of the fibers from the posterior deltoid;
however, an excessive abduction can strain the AN and put it at risk during access
and bring it closer to the surgical field.[7]
[8]
[9]
[10]
The objective of this study is to evaluate the mean distance and proximity of the
AN and SN to the infraglenoid tubercle (IT) in order to quantify a safety zone so
as to assist the surgeon during surgical access to the scapular neck and body.
Methods
The cadaver study was performed at the Verification of Death Service, from the dissection
of a total sample of 13 shoulders from 13 corpses, random laterality, in order to
identify the periscapular neurovascular structures (AN and SN) and obtain measurements
of their distances to the IT. Only one dissection per corpse was authorized.
The definition of the IT as a bony landmark was determined by its fixed position in
relation to the bone structures and by being the topography in which the SN becomes
directly visible in the surgical path under discussion.
The approach developed was a modified version of Judet's, which proved to be an excellent
option for the fixation of scapular fractures, since it provides optimal exposure
without injuring the scapular musculature as it does not involve disengagement of
its fibers.[5] Each cadaver was positioned in lateral decubitus according to the side to be operated,
with the ipsilateral upper limb held initially along the body. An L-shaped incision
was made on the skin and subcutaneous tissue, beginning at the lateral border of the
acromion to the superomedial angle of the scapula, then curved towards the lower angle,
over the medial margin. An exposure plan was developed between the more subcutaneous
skin flap and the scapular musculature. For the exposure of the structures, we opted
for disinsertion, and for the folding of the posterior portion of the deltoid muscle
([Fig. 1A]). The interval between the infraspinatus and the teres minor muscles was developed
so that we could demarcate, with a pin, a fixed and immutable reference point: the
inferior tubercle of the glenoid— easily palpable at that location ([Fig. 1B]).
Fig. 1 L-shaped incision on the medial border of the scapula and subcutaneous flap exposing
the musculature (A); folding of the posterior portion of the deltoid muscle and divulsion
of the interval between infraspinatus and teres major muscle (B).
Through careful dissection of the anterior region of the infraspinatus and teres minor
muscles, their respective nerves were identified: suprascapular and axillary branch,
and then demarcated with pins at the point of their penetration into the belly of
each muscle ([Fig. 2A] e [2B]).
Fig. 2 Pin marking on the infraglenoid tubercle in the intermuscular spacing and on the
most distal portion of the axillary nerve branch to the teres minor muscle (A); marking
the suprascapular nerve over its most distal dissected portion (B).
Measurements were made using a universal caliper between the defined static reference
point— the IT—and the pins placed at the most distal points of each nerve. The distances
were determined in millimeters: IT to SN and IT to AN.
In addition to the specific data of the measurements, the data of the corpses studied
were collected: gender, age, weight, height.
Exclusion criteria: specimens showing signs of injury or previous shoulder surgeries
or previous diseases of the shoulder girdle.
Results
The parameters were evaluated in 13 shoulders of 13 fresh cadavers. Among these, eight
were male and five were female. The mean age was 70.1 years old (from 48–98).
The mean weight of the studied corpses was 61.5 kg, while the mean height was 1.64
m, ranging from 1.52 to 1.75 m. The mean distance from the IT to the AN was 23.8 mm,
ranging from 17 to 28 mm, and the standard deviation (SD) was 7.6 mm. The mean distance
from the IT to the SN was 33.2 mm, ranging from 17 to 43 mm. The SD was 23.8 mm, ranging
from 17 to 32 mm.
Discussion
With the increased incidence of scapular fractures due to high energy trauma, it is
natural that there is also an increase in the severity of these fractures and, thus,
the probability of surgical treatment.
Barbieri et al[11] reported good results in 106 patients with conservatively treated scapula fractures
and suggest that surgical cases are the minority because this is, among other causes,
a difficult approach and with risks of muscular injuries.
Even with the development of new access techniques, as seen in the works of Jerosch
et al,[8] Wirth et al,[9] and Pizanis et al,[12] who reported a low incidence of complications, the surgical approach of the scapula
may jeopardize some neurovascular structures, such as the AN and the SN, with injuries
occurring in up to 2 to 3% of cases in the postoperative period. Excessive traction
of these nerves by detachment of tissues during access may cause weakening of the
rotator cuff.[6]
Jerosch et al developed a posterior subdeltoid access and revealed a mean distance
of 21.98 mm up to the AN but they did not establish in their work the reference points
used.[8]
Longo et al[13] cited a 6% rate of SN injury during surgeries for shoulder instability and noted
that the course of this nerve is altered in cases of rupture of the rotator cuff.
During their study, the distance between the posterior border of the glenoid and the
SN was measured in the spinoglenoid notch with mean values of 12 mm in internal rotation
and 19 mm in external rotation of the shoulder.
Wirth et al[9] studied posterior access through division of the deltoid muscle and advised caution
(during dissection) with the SN, which may be located about 15 mm medial to the edge
of the posterior glenoid. Ball et al,[14] in a study of the anatomy of the posterior branch of the AN have described that
the branch to the teres minor muscle arises immediately at the inferior border of
the glenoid next to the origin of the long head of the triceps and measures about
11 to 25 mm (mean of 18 mm) until it enters the muscle.
We considered that, in the Ball study, the origin of the branch of the AN for the
teres minor muscle is the same of the parameter we used for the measurement, which
is the IT. Thus, in comparison to our study, we reached slightly higher values with
a mean of 23.8 mm for the distance between the IT and the AN.
Shaffer et al,[15] during electroneuromyographic assessment of the SN during posterior access with
horizontal division of the infraspinatus muscle, obtained a mean value of 22.5 mm
distance between the posterior border of the glenoid to the nearest branch that crossed
that muscular division. This measurement has the parameters very close to those of
our study referring to the same nerve, but presents values considerably lower than
those found in ours, whose mean value was 33.2 mm for the distance between the IT
to the SN, probably due to the difference in bone parameter and muscle division had
been randomized in the Shaffer study.
It is important to emphasize that in our study the mean age of the patients was 70.1
years and the mean weight of 60.5 kg. This reflects the profile of the elderly specimens
studied at a Verification of Death Service, with hypotrophic muscle characteristics
expected for the studied age group, and their possible influence on the distances
between established parameters. We assume that in younger and more active individuals,
the values may be relatively higher due to a greater muscular trophism. However, due
to the small number of specimens studied, we are unable to prove such an assertion.
Conclusion
The surgical approach for the treatment of glenoid neck fractures is considered safe
through the interval between the infraspinatus and teres minor muscles; however, much
attention and caution should be exercised during muscle spacing due to the short distance
between the fracture site and the location of the SN and AN, thus avoiding major postoperative
complications.
